Albert's Series: Basic stuff, but serious.
I. Short and simple Math notes:
A few simple words on Nuclear weapons.Date: 17/11/2017
Remark: Almost ready. Please refresh the page to view any updates.
Photo: WikiMedia commons.
"Trinity", the very first nuclear explosion (test), on July 16, 1945, in a desert, New Mexico (USA).
The photo shows the explosion just 0.016 sec (16 ms) after detonation.
The explosion was estimated to be of a magnitude of 15 - 22 KiloTon. In the figure, the diameter of the
ball is about 210 m at that point in time.
The device was "pure fission", mainly based on Pu, using the "implosion" technique.
It was in fact a small device, compared to the "hundreds of KiloTon", or "MegaTon", classes of weapons.
Only a smaller percentage of the total amount of fissable material, actually fissioned at the "Trinity" test.
It is known fact, that with Fatman (the third nuclear explosion ever), from the about 6 kg Pu,
only about 1 kg actually fissioned.
This is a very simple note on nuclear devices, viewed from a rather "wide" angle, so I believe.
1. Quick and simple overview of Nuclear weapons.I personally like to talk on "generations" of nuclear weapons, as will be shown
as of chapter 2 below.
I think it helps to understand slightly better, where something like a neutron bomb must be placed.
However, many folks catagerorize nuclear weapons (somewhat generalized) in the following "types"
as shown directly below. Therefore, it is important to start showing this generalized listing first:
1.1 Generalized classification of types:
In a nutshell:
-The nuclei of heavy fissile isotopes such as 239Pu, after a neutron capture, may break up, or fission,
into two lighter isotopes. In this process, a large amount of energy is released, as well as other neutrons
(2 or 3) are released.
If almost all nuclei of all atoms of, say, 5 kg of 239Pu or 235U, do that (more or less) at
"almost" the same time (fast sequence of generations of chainreactions), an extremely fast and enormous powerful
The very first nuclear weapons worked solely by that principle. These are "pure fission" weapons.
-The nuclei of very light isotopes, such as Deuterium or Tritium, may "melt", or fusion, into a somewhat more
heavier isotope like a Helium nucleus. Also, in this process, are large amount of energy is released.
Thus, if a relatively large amount of such isotopes all "melt", or fusion, more or less at the same time,
an extremely fast and enormous powerful detonation follows.
For fusion to start, a high pressure and Temperature is needed. That's why this process is often started by
using a "pure fission" stage (actually a fission bomb).
1.2 Types of delivery:Having nuclear weapons is one thing. How to "deliver" them, is another.
Larger nuclear nations potentially have, generally speaking, the following options:
=> Tactical weapons / methodology:
Often shorter distances are involved, like with using Jets, or using smaller, shorter-range rockets.
The methodology can also be associated with battle fronts, and local area's.
=> Strategic weapons / methodology:
Often larger distances are involved, using:
-Large ICBM's (Intercontinental Ballistic Missiles), which might be launched from stationary silo's,
or from specialized heavy trucks.
It's not uncommon that their range is well over 10000 km, have a max speed of around mach 24, and reach
their targets within 30 min.
- SLBM's (Submarine Launched Ballistic Missiles), which in principle can be fired from "anywhere".
Having a medium- to long range, will type these rockets too.
- Strategic bombers: long-range bomber planes.
Most large nuclear capable nations use such a "triade" of deterrence, or are striving to realize it.
1.3 Why is Energy output of a nuclear device so high?
"Chemical energy" versus "Nuclear energy".In just a few words...:
It's certainly not easy to describe chemical energy, or for that matter, describe nuclear energy.
Many factors play a role here.
For example, when studying molecules, one need to take into account many terms like
potential energies, vibrational and rotational energies etc..
However, I can focus on a few important components, thanks to the simple atom model of Rutherford / Bohr.
It can help to see why nuclear processes may yield more energy.
When considering just some "atom" of a certain element, we can describe the energy levels of the electrons,
(in the "outer shells"), and compare it to the binding energies of the protons/neutrons inside the nucleus.
Please realize that the simple atom model of Rutherford/Bohr is not fully consistent with Quantum Mechanics (QM),
or not even with classical theories. For example, "well-defined" positions of electrons are not consistent with QM.
However, the "shells" correspond nicely with an abstract representation of the discrete "energy levels",
which makes the model indeed rather usable.
Captured in "energy levels", some typical energies for an electron to change shells, or to get free, sits in the
order of tens of eV, or hundreds of eV, to a maximum of some thousends of eV etc...
This is an important component of "capturing"/"visualizing" chemical energy.
Note: the "electronVolt" (eV) is a convienient and standard energy measure to describe energies in the
in the atomic domain, or elementary particles.
Typical binding energies of protons/neutrons in the atomic nucleus, sits in the ranges of many MeV (mega eV).
This is an important component of "capturing" nuclear energy.
This maybe a nice pointer that typical nuclear processes (per Atom), are much more "energetic" than
So, typically, certain nuclear processes deliver a factor of several thousends more energy, compared
to chemical energy output "per atom".
It's very instructive to take a look at the figure below.
Fig. 1: Average binding energy per nucleon (proton or neutron), against the mass number (the elements)
Source: My own Jip Janneke figure, as an approximation of experimental graphs from Physics.
So, a socalled "fissile" heavy isotope as 235U, may split up (after capture of a single neutron),
in two medium weight isotopes (like Ba).
If you look at the figure, the energy difference per nucleon (proton or neutron) is in the order of a couple of MeV.
So, if one whole 235U atomic nucleus splits up (while containing 235 protons/neutrons), the whole
energy difference then is in the order of 200 MeV (per atomic nucleus).
So, if you would have 1 kg of fissile Uranium or Plutonium, and you would manage (in some way) that all
nuclei splits in more or less the same time, you have an equivalent of many thousends of explosive power
compared to 1kg of the best chemically based bombs.
Some fissile heavy isotopes like 235U or 239Pu, have the chacteristic that when
a certain "mass/concentration/geometry" is reached, together with an initial flux of neutrons, will participate
in very fast generations of chainreactions of fission.
The story above is actually way too simple, and a more thourough explanation will follow in chapter 3.
1.4 Some principal "explosive" materials in nuclear devices.239Pu (Plutonium), 235U (Uranium):
For "pure fission", most often the heavy isotopes 239Pu (Plutonium), or 235U (Uranium) is used.
Those "fissile" isotopes have the property to be able to absorb a (slow or fast) neutron, then to break up
into medium weight isotopes (like Ba), while releasing a large amount of energy, and a few fast neutrons too.
Under the right circumstances, it's possible that a supercritical amount displays the fact of fast chainreactions,
meaning that in an uncontrolled way, one fission "ignites" other fissions (due to the released neutrons of the former fission),
faster and faster (almost exponentially).
The most abundand isotope of Uranium, that is 238U, does not display (in the sense discussed above),
the fact of fast sequences of chainreactions.
However, it can still fission (break-up) like the isotopes described above do.
Even fully depleted 238U may fission.
238U can even play an important part in the energy output of a nuclear device.
Suppose you have an outer spherical, or cilindrical "tamper" (casing) of 238U, surrounding
a nuclear device. At detonation, a large flux of high energetic neutrons bombard the tamper, resulting
in a considerable amount of fission of 238U, and thus a relatively large contribution
in the total energy output is realized.
The fact that common 238U may contribute in a nuclear device, might have surprised you!
An outer shell of 238U may also be used to scatter neutrons back, or reflect X rays back
to a secondary stage. It may also be used to provide structural support, or a combination of
all of the properties above.
Tritium 3H, and Deuterium 2H:
Very light elements might "melt" into (e.g.) Helium, where energy is released at such event.
This is "fusion" (somewhat the opposite of fission).
The most common fusion partners are the Hydrogen isotopes Tritium and Deuterium.
Since Tritium has a "half-live" of about 12 years, in practice, often some compound containing Lithium-Deuteride
is used, which can extremely rapid release Tritium (by nuclear reaction), thereby avoiding the problem
of the natural decay of tritium.
Deuterium - Deuterium:
In principle Deuterium - Deuterium fusion can be used, however, the initially required Temperature
is higher, and this is why it is not used in Thermonuclear devices.
2. A few words on Generations of Nuclear weapons.
2.1 The 1st, the 2nd and 3rd generations.
2.1.1. The 1st and 2nd generations.Although some idea's on nuclear bombs already existed, early in the former century (e.g. H.G Wells, 1914),
it all became much more serious shortly before the start of WWII (around '39 of the former century).
As we all know, the first "pure fission" weapons (A-bomb) were developed in '44/'45, and two of them
were actually really dropped on two Japanese cities. Due to immense respect of the victims, I dare not say anything
about the "socalled" neccessity as to why they were really used, but it resulted in an absolute, complete total horror.
Then, in the early '50's. the first "thermonuclear" devices were tested.
In a way, you might call the thermonuclear device, a multi-stage weapon.
The thermonuclear class are "multi-stage" weapons, and very often just "two-stage" devices.
The primary stage then, uses pure "fission", like for example with a implosion technique Pu weapon.
The secondary stage is charcterized with materials which can "fuse", like Tritium with Deuterium, or a compound
as "Litium6 Deuteride", or another suitable substance.
The processes behind "fission" and "fusion" will be explained later (chapter 3).
When the primary stage detonates, within µ seconds, the energy and radiation is so intense, that it will sufficiently heat up
the secondary stage, where primarily "fusion" takes place.
So, this weapon might also be typed as a "fission-fusion" weapon.
In certain cases, the stages, or the entire weapon, might be enclosed by a fissionable 238U, which will
fission too (due to an intense neutron flux), when the secondary stage is detonating.
However, today, a true "pure" fusion weapon does not exist yet. There is always (up to now) a first "fission component".
Some people call the devices above, the "first"- and "second" generation.
Today, the "thermonuclear" device (in all sorts and shapes) is the most abundant type of weapon.
They can be used in tactical situations (the accent here is "local regions"), or strategic deployments
(the accent here is on long distance, like in rather large ICBM rockets, or long range bombers).
A popular name for the "thermonuclear" device, is the "Hydrogen bomb" (referring to the fusion stage, using
Since the very early designs, during the '50s and '60s, downsizing of both fission and fission/fusion weapons
was realized. Using neutron reflecting materials, optimizing geometry, increase in efficiency, made that possible.
2.1.2. The 3rd generation.In time, knowledge grew on how to utilize neutron absorbers and enhancers inside the device,
and refinenments in stages.
From the early '60's, up to the '70's, '80's, the "ERB" weapons were in development. ERB is short for
"Enhanced Radiation, Reduced Blast". Sometimes they are also called "ERW", or Enhanced Radiation Weapons.
A popular variant is the "neutron bomb", where indeed the primary weapon function is radiation,
accompanied with a lower "blast" (but there will always be a rather significant blast).
In principle, it's a thermonuclear device, but the architecture is optimized to let neutrons escape the weapon,
instead to use neutron reflectors to bounce fast neutrons back, which would enhance efficiency of the "blast".
Some people call such devices (like the ERW weapons), nuclear weapons of the "third" generation.
Also, in this same generation, some really strange (or rather insane) variants were proposed.
For example, the "Cobalt bomb", would use a thermonuclear device as it's core, and a very large quantity
of Cobalt surrounding it, producing (on detonation) a radioactive Cobalt isotope, that potentially
could cover (fall-out) on a whole continent, or even a large part of Earth (depending on the amount of Cobalt).
It's an absurt scenario, ofcourse, but I am sure that some "deep studies" were indeed performed.
2.2 The 4th generation.These are not a reality yet. However, science is rather unstoppable. Also, when sufficient funds are provided,
and/or facilities are provided, then this generation may come into existence.
Although a very clear definition of the 4th generation is still missing, it's obvious that it must
be different from all that we have seen above.
The fourth generation is arguably essentially about furher downsizing. There are multiple roads here.
Most folks think that "pure" fusion (without the fission stage) might form the basis for the 4th generation.
Increadably, since "pure fusion" is often seen as the coming archetype for 4th generation,
then the true payload then, might be very small, maybe even "pellet" size.
However, the "driver" that makes fusion possible, might still have quite considerable dimensions.
Ofcourse, the above statement at this point, is still fully hypothetical.
Various technical studies have been performed, rather recently, and are still ongoing.
Once chapter 3 is done, we have knowledge about the principles of fission and fusion,
and we can return, more prepared, to the specifics of a pure fusion weapon.
3. The basic principles of fission and fusion.
3.1 Some principles first.
3.1.1. The Atom number.The number of protons in the nucleus of an atom, is called the "atomic number". However, apart from Hydrogen (H), there
will always be a certain number of (neutral) neutrons as well. Since protons are charged positively, you might say that the
classical Electromagnetic force will immediately drive them apart. However, at short distances,
the strong nuclear (attractive) force between protons and neutrons, "rules".
Ofcourse, today physicists know of a (theoretical) deeper structure (quarks, gluons), but that does not play
a role in this simple note. As a part in the "standard model", quarks are seen as the constituents of
protons and neutrons. They play an important role in Quantum Chromodynamics (QCD).
So, a nucleus of a certain atom (or certain "element"), contains protons and neutrons. The number of neutrons may vary slightly,
resulting in socalled isotopes of that element.
For example, the element Cobald is often written as: 2759Co, meaning that the atom number is "27"
(which is the number of protons), while the total of protons and neutrons is "59" (the mass number).
So, in the upper example, the number of protons is 27, and the number of neutrons is (59-27).
As another example, one isotope of Uranium might we written as 92238U.
The "type" of atom (like Cobalt), is determined by the number of protons. Or stated in an equivalent way:
The atom number (number of protons) defines the sort of "element", like Hydrogen (H), Helium (He), Carbon (C), Iron (Fe) etc...
The total mass of the atom, is determined almost fully by the nucleus (all protons+neutrons).
So, in general, if we consider element "X", then it might be notated as ZNX, where
"Z" represents the "atom number" (the element actually) which is equivalent to the number of protons,
and "N" represents the "mass number", which is equivalent to the number of protons and neutrons together.
When considering a certain element, "N" might vary slightly, resulting in the various isotopes
of that particular element.
The nuclear force is extremely strong. However, it only operates in the range of femto meters,
which is very small indeed.
The classical Electric force (between the positively charged protons), is also large, and,
according to the classical ElectricDynamical theory, only diminishes by 1/r2.
So, protons at the "rim" of the nucleus would experience a large repulsive force. In a simple model,
the neutrons and protons are sort of "mixed" throughout the nucleus, so, thanks to the presence of
neutrons nearby those protons, the attractive nuclear force still holds the nucleus together.
Indeed, Jip and Janneke language, but that will be better formulated later on.
3.1.2 Electronshells in the Atom. Quantumnumbers and Atomic theory.Atomic physics, enables to familiar ourselves to "quantum numbers" and orbitals,
which define the state of an electron "around" the nucleus.
The theory is not too hard, and later on we will reckognize some of those features in nuclear theory,
since the "shell model" of the nucleus is important in nuclear physics too.
Let's take a look at the electrons "moving around" the nucleus in "certain orbits". Actually, such a picture
is wrong. However, everybody knows this classical picture of a number of electrons "moving around" the nucleus.
In figure 2 below, this is depicted by illustration "1".
Fig. 2: Some illustrations of electrons around the nucleus of an Atom.
Source: My own Jip Janneke figure.
Even according to classical theory, such an electron would quickly spiral towards the nucleus
while emitting radiation.
Quantum Mechanics (QM) delivers us a reasonable model which explains the stability of the electron shells.
Near the end of the 1800's and the early 1900's, some amazing experiments were performed.
While the "classical" theories (electrodynamics, classical mechanics), made a clear distincion between particles
and "waves", some experiments pointed towards a more dualistic character of entities.
For example, particles that were beamed through a "double slit", created an interference pattern,
a phenomenon of which it was formerly thougth, that it could only be produced by "waves" like electromagnetic radiation.
As another example, the photoelectric effect showed that light, at certain circumstances, behaved like particles,
like transferring momentum to a real particle (such as an electron).
So, at certain observations, particles could behave like waves, and the other way around, what was traditionally seen
as waves, could behave like a particle.
Especially in the early days of QM, a theory called "wave mechanics" was often used to decribe quantum systems
like a particle. Intuitively, a wave like description of a particle, also means a certain distribution
of that particle in space, instead of talking purely of a "classical point particle".
Around 1924, 'De Broglie' showed, that there exists a "relation" between momentum (p) and wavelength ( λ),
in a "universal" way. In fact, it's a rather simple equation (if you see it), but with rather large consequences. It's this:
p = ℎ / λwhere h is Planck's constant. Now, "momentum", at that time, was considered to be a true 'particle-like' property,
while 'wavelength' was understood to be a typical 'wave-like' property, which for example stuff like
light and radio waves have.
So, what description would fit an electron around a nucleus better? One thing which you might propose
is a "standing wave", as depicted in (2) in figure 2 above.
In such a case, we do not have a moving point particle, which would quickly moves towards the nucleus, anymore.
In such a case, you might say that the "orbital" must obey the condition 2πr = nλ
where λ is the wavelength of the electron, and n is a discrete number, and 2πr is the
circumference of the "orbit".
Ok, in this case you would have neatly placed "n" wavelengths along the orbit: hence a standing wave.
Note that in such description, you have imposed a sort of "quantization", by requiring that 2πr = nλ.
The QM description, however, is somewhat more elaborate.
Often, for the wavefunction of the particle, a notation like Ψ(r,t) is used.
It should attend you to the fact that (unmeasured/unobserved), it is distributed in space,
since we can vary "r" (the position), and that might produce regions of higher probabilities of finding the particle,
and regions of lower probabilities (just as you might expect from a wave-packet).
To search for the states of electron, you might consider the general atom, having Z protons, thereby
having a Ze positive total charge.
However, a study of the Hydrogen atom (1 proton, 1 electron), is good enough for discussing
quantum states and orbitals of the electron.
As Schrodinger found, the energy relation (equation) for Ψ(r,t) (or Ψ(r), leaving out "time"
for a moment) is:
This equation is not so special since it essentially says Etotal = Ekinetic energy + Epotential energy
Not ready yet.
3.1.3. Radioactive decay (natural radioactivity).This subsection is not really neccessary (as I realize myself now), but I leave it anyway.
The advantage is that we get a quick intro in some nuclear "equations".
The "notations" used is in typical "Albert style", so, it really could be better and neater...
If you are new to this all, you better "google" on nuclear equations, and see how it is properly done.
There are several types of "spontaneous" radioactive processes, or you may also say "natural radioactivity".
(Not all are listed here (!))
Example: β decay.
It's possible that in a nucleus, a neutron "flips" into a proton, and thereby emitting a fast electron (e-),
and a "anti-neutrino" (-υ) as well.
It can actually happen with a "free" neutron too.
Ofcourse, "flips" is not an explanation. Particle physicists have a theory that fundamentally describes that process.
In this note, we do not have to go into depth, because it requires a discussion of the "weak" force, the W bosons, and quark types.
A reasonable explanation is this:
The strong force between nucleons (protons/neutrons) acts mostly and attrctively, between nearest neighbours.
At the same time the ElectroMagnetic coulomb repulsion, acts between all protons. So, that's a tendency
to drive them apart.
In such a sense, the presence of neutrons then acts as the glue which hold the particles in the nucleus together.
However, there is a limit to such usefullness of the number of neutrons.
Or in other words (semi-classical): The neutrons acts to screen the protons from each other, making the nucleus stable.
You might say that for effective screening there needs to be a little more neutrons than protons.
As said above, the socalled weak force is responsible for β decay.
However, the resulting proton (from the neutron) must be able to find a free quantum state (Pauli exclusion principle).
The higher the neutron/proton ratio, the more "chance", of having a free state for the "resulting" proton,
and the more chance on β decay.
In β decay, we have:
n -> p + e- + -υ
where "n" is the neutron, "p" is the proton, e- is the electron, and -υ- denotes the anti-neutrino.
If it happens in the nucleus of atom X (or atom of element X), we would have:
ZA X -> (Z+1)A Y + e- + -υ
Since a neutron was "changed" into a proton, we thus have an atom of element "Y".
Above is an example of β- decay (there also exists the β+ decay).
Thus in real example, we may have:
53131 I -> 54131 Xe + e- + -υ
Example: Alpha decay.
A relatively "unstable" nucleus, may even emit an α particle, which is essentially a He (Helium) nucleus (24He).
Or stated in other words: α particle decay is the phenomenon whereby an unstable nuclei goes into a stable state,
by emitting an α particle.
92238U -> 90234Th + 24He
Here, an Uranium isotope decays into Thorium, and an α particle is emitted.
Interestingly, a classical potential barrier would not allow that. However, Quantum Mechanical "tunneling"
through barriers, is possible. So, there exists a "means" to go from unstable to stable.
Alpha decay, is often followed by the emission of a high-energy γ photon, since the result nucleus, is often
still in an exited state.
3.2 A short description of Fission.Quite some isotopes of elements, are "unstable". Sometimes, an nucleus can "break up" into two (sometimes 3, 4)
roughly "equally heavy" elements, while also producing radiation, and/or particles of some kind, and energy.
This is often called "fission".
It is generally more often observed with isotopes with higher masses (the "A" number of ZA X).
Since those two parts are more stable than the original, it seems rather logical that energy gets released.
But there must be more than that.
In fact, a full (complete) explanation is not deviced yet, but very good "pointers" go around.
It's even not very obvious to cleary define "stable" and "unstable" elements.
For example, if about half of a certain amount of an isotope of an element, decays in 107 years,
then it is not so very stable, but also not so increadably unstable as well.
But for another isotope, it might be something like 5 years, then we may say that's quite unstable.
A detailed examination of decay requires isobaric spin, other quantum numbers, possibly shell theories, flavours etc..
That's not neccessary for us to do so.
Increadably, for my purpose, we can come away with a few pointers, and one is just the binding energy.
3.2.1. Binding Energy:In semi-classical language:
The mass of a nucleus is always less, than the sum of all of the individual masses of the protons and neutrons.
The mass difference corresponds to an energy E = Δmc2, which is ofcourse one of Einstein's
famous relations. This mass difference is also often called the mass defect.
When protons and neutrons comes close, and react together in making bonds, to form a nucleus, in that process energy is released,
which then (sort of) will "sit" in the "binding energy".
One can talk of the binding energy of an individual particle (proton/neutron), or consider the total binding energy.
As an example of such individual value, you might think of a number like 8 MeV.
In some articles, "binding energy" is characterize as negative energy, which *might* be a bit of an unfortunate term.
It's probably better to say, that if the "binding energy" increases, the particles are "deeper in the well",
thereby making their bonds stronger.
So, if an nucleus has a high binding energy, in general, it's more stable.
In the latter part of first halve of the former century (say 1935), nuclear physicist already did enormously much
experimental work, and many hypothesis were proposed. Gradually, great theories were deviced.
It's pretty useless to give here a fairly accurate equation of calculating the Binding Energy.
However, I think it's a great illustration. It's a formula from around that time (Weizsacker's formula).
It's from around 1935:
EB = av A - as A2/3 - ac Z2 / A1/3 - aA (A-Z)2/ A + δ(A,Z)
There are several terms, like an Area component, a Coulomb component etc..
The formula is partly theoretical (thus created by theory) and empirical (values from measurements).
Except for the very light elements, it works.
The figure below, shows the binding energy (per nucleon, that is, proton or neutron) along all elements.
Note that the figure rises very sharply, then has a maximum for in the "neighboorhoud" of Iron (Fe), and when
the massnumber increases, the slope is pointed downwards.
Ofcourse, pure Hydrogen (11H), only has one proton, so, the binding energy does not really apply here.
Then, for the next light elements, the slope is very steep.
Fig. 3: Average binding energy per nucleon, against the mass number (the elements)
Source: Wikimedia commons.
It also means this: Suppose some heavy Uranium isotope, breaks up into two smaller parts (e.g. 140Ba and 93Kr),
then from figure 3, you can find the difference in binding energies, from Uranium, and the two fragments.
Remember that the figure above, illustrates the binding energy per nucleon.
Taking all nucleons together, we may have an energy release of something in the order of 200MeV.
3.2.2. Fission of some specific heavy isotopes, and chain reactionsSome heavy isotopes may undergo fission, only after capuring a fast neutron like 238U, while other
isotopes may undergo fission after capuring a slow, or "thermal" neutron, like 235U.
This behaviour is found to be related to the number of neutrons in that nucleus, and whether the total is an even
or odd number.
In general, low-energy (thermal) neutrons are able to cause fission only in those isotopes of Uranium and Plutonium
where the nuclei contain odd numbers of neutrons (that is: 233U, 235U, and 239Pu).
Thermal neutronsSome heavy isotopes are rather "succeptible" to thermal neutrons.
A thermal neutron is considered to be a relatively "slow" moving particle. If a rather potential unstable nucleus
like 235U, caputures that neutron, we have a very short phase of 236U.
There are several models, like the "shell" model, or the "liquid droplet" model, which might give us
a high level understanding of the nucleus and structure.
Using the "liquid droplet" (Gamov, 1930), it's rather easy to understand the fission of such large isotope.
That 236U nucleus is immediately in an excited state, and starts to oscillate, and the moment a small "neck"
begins to form, the short-range "(nuclear) strong force" will lose from the electric Coulomb force,
which will tear the two parts apart. Hence, we have fission.
What's rather disturbing, is that this sole nucleus, undergoing fission, will produce not only the the two new nuclei,
(e.g. 140Ba and 93Kr), but also 3 neutrons.
However, the neutrons produced at the fission path in figure 3, are, with a high probability, highly-energetic,
or fast neutrons.
Suppose you have a densily packed piece of optimized heavy isotope(s), then fission of one nucleus,
will possibly "ignite" other 235U nuclei, which may undergo fission, which will produce neutrons,
which will ignite still other nuclei etc.. etc.. Such process will go extremely rapidly.
In effect, you may have a chain reaction.
In the early days of A-bombs (pure fission weapons), scientists tried to find an architecture, which would
create the best environment to produce such a fast chain reaction. In the early days, it was often an puzzle
whether fast-, or thermal neutrons, and the use of moderators, would provide the best results.
Fig. 4: Simple illustration of one possible fission path of 235U
Source: my own "Jip en Janneke" figure.
By the way, there are multiple decay paths from 235U. That is, other fragments than 140Ba and 93Kr, may form.
The nuclear equation for the fission depicted in figure 4, is:
01n + 92235U -> 56141Ba + 3296Kr + 301n + 200 MeV
Fast neutronsWhen fission occurs only after capuring a slow thermal neutron (<10keV), or fast neutrons (>1MeV),
the isotope is called a "fissile" isotope, like 235U.
But when only fast neutrons (>1MeV) will produce fission, the isotope is called "fissionable",
A better way to characterize fissile isotopes, is to say that their decay process (fission) may "ignite" other
nuclei to do the same, since the fast neutrons may be captured by those other nuclei.
So, they may split up too, while they again emit fast neutrons (most often 3 neutrons)
This is also often called "chain-reaction".
When the mass and concentration is high enough, extremely fast successions of chains may occur.
The decay chains of 238U is rather complex, involving many steps. Many "by-products" can
form, and 238U may for example start to emit an Helium nuclues and form Th:
92238U -> 90234Th + 24He
Here, an Uranium isotope decays into Thorium, and an α particle is emitted.
It may also capture a thermal neutron and transmutates into 239Pu. This latter one is
beneficial in a Nuclear Reactor for energy production.
238U is the most abundant isotope of uranium found in nature, something around 99%.
It has a very high half-life, which explains why we still find it in Nature.
It almost cannot perform chain reactions, since it has a large chance to scatter neutrons,
and in particular give rise for inelastic collisions. However, high-energetic decays can occur.
Although the "fissile" isotopes 235U and 239Pu are important in pure fission weapons,
or the first stage of a thermonuclear weapon, even 238U may play a role in nuclear weapons.
While 238U does not exhibit chain reactions, it may fission under a very high neutron flux.
So, in boosted- or real thermonuclear weapons, even depleted 238U may be may be used
to contribute in the total energy output. This fact may surprise you, since 238U is rather common.
3.2.3. More on fissionable, and fissile, elements.- A "fissile" element (isotope of an element) can undergo fission with a higher probability,
if it captures a (slow) thermal neutron. But they can undergo fission too with capturing a fast neutron.
This sort of isotopes might cascade in fast chainreactions, depending on e.g. density, amount, geometry..
-The term "fissionable" is slightly different from above. A fissionable isotope can undergo fission
when it captures a high energy neutron (> 1MeV).
But this sort of isotopes will not cascade in fast chainreactions.
Thus: All fissile nuclides are fissionable, but only some fissionable nuclides are also fissile.
Important is to remember:
-238U will only undergo fission using fast neutrons, thereby it is "fissionable",
but not "fissile".
-235U and 239Pu will undergo fission having slow, and fast neutrons,
although the "cross-section" for slow neutrons is much higher.
And what's important here, is that the non-fissile isotopes often display scattering,
thereby preventing (in itself) a chain reaction. But they can fission.
A more consistent way to distinguish between fissile and fisionable isotopes, is the fact
that "fissile nuclei" may participate in chain reactions, while fissionable isotopes
generally don't do that, for example, because the neutron scattering is too high.
A special thing in Nuclear reactors is, that 238U can transmutate into 239Pu,
which is quite common in Reactors.
A relevant portion of the energy then comes from the fission of 239Pu.
In most reactions, two lighter elements are the result of the fission, while typically also neutrons are produced.
Those two lighter elements are in the range of mass number 90 (plus/minus a few) and 140 (plus/minus a few).
If after capturing the slow neutron, the probability of fission is "high", then indeed the term "fissile" is used,
and a chain rection may result if the nuclei of that isotope are close.
Especially fissile isotopes are 233U, 235U, 239Pu, 240Pu and 241Pu.
The isotopes 235U and 239Pu, are the main "succeptible" isotopes in fission chains.
You might expect those as main candidates for nuclear weapons. True, but many multi-stage weapons use fusion in some
middle stage, produce many fast neutrons, where a substance like the fissionable 238 comes into play.
Nuclear technology is wide and deep. This is also true for Nuclear Reactors in civil live.
Some types of Reactor plants, may even be used to "breed" fissile material.
Thus it indeed may be troublesome, if an unstable nation (but who am I to judge that), has
a nuclear plant, or wants one.
For any nation in possesion of Nuclear plants, it must hold that strict inspections are absolutely mandatory.
With respect to nuclear energy in civil live, many folks are "pro" and many are "contra".
If you would like to know my opinion: I myself do not like, or want, nuclear energy at all, with an exception:
Having facilities for producing certain isotopes for medicine, is absolutely critical.
Even for just this fact: you cannot or may not "ban" nuclear facilities completely, since production for
medical purposes is extremely important.
3.2.4. Critical mass.If one have "fissile" material (see above), and a efficient means for starting neutron showers,
a self-sustained chain reaction could really possible, if certain conditions are met.
The term "critical mass" is often heard in this context.
It's not an absolute figure, since densely packing, appliances for neutron showers, temperature,
geometry, the purity of fissile material etc.. has a strong influence on what the "critical mass" is,
in a certain situation or device.
For example, you might have a certain amount of fissile material, but for several reasons,
the chain reactions are not self-sustained.
Maybe your material is not pure enough, not dense enough, too little material, no neutron reflectors etc..
It might be better to read "critical mass" as "density/geometry/amount/neutron-initiater".
The very first pure fission bombs, used a spherical design, where at an outer sphere
at many wellchosen places, fissile material was located. Behind it, convential high explosives
was stores which would shoot with an extreme speed those fissile fragments as "a front" to the centre, where also
and amount of fissile material was present. Precisely at the core, it's likely that some neutron initiator
(for creating a high flux of neutrons) was present too.
This setup, created a situation that, just before detonation, the "critical mass" was met, and a
The setup described above, is often characterized as the "implosion method".
So, it's important to understand, that critical mass, is not simply the "amount" of fissile material.
By the way, in the first pure fission devices, it is known that the "efficiency" of actual fission,
was rather low. Meaning that a certain amount (a certain percentage) of fissile material remained intact.
3.3 A short description of Fusion.
3.3.1. General principles.Figure 1 remains illustrative, also for this section too.
If you "go" to the left, from the most heavy isotopes, to "medium weight", then you can see a significant
difference in "binding energy" per nucleon.
Likewise, if you go from the lightest isotopes, and stop somewhat before Iron (Fe), then you again can see
a significant difference in "binding energy" too.
Although quite a few lighter elements might be thought to be candidates for fusion, it has turned out that Nature
favours the Hydrogen (H) isotopes, Deuterium (12H) and Tritium (13H).
A simple explanation is that the H isotopes only have one proton, thereby making the repulsive Coulomb force
weaker compared to the elements with more protons.
Once the individual nuclei are very close, the strong attractive "nuclear force" starts to become in effect.
Here too, the masses of the individual constituents are larger, than that of the resulting element.
In other words, the mass of the combination will be less than the sum of the masses of the individual nuclei.
Again, this mass defect is equivalent to "energy", and Einstein's famous equation works here too: E = Δmc2.
Below, the famous, and often used "Deuterium Tritium" fusion reaction, is shown:
12H + 13H -> 24He + 01n + 17.59 MeV
You can see that the result is a Helium nucleus, plus a neutron, and 17.59 MeV.
Quite a few other fusion events (and corresponding equations) are possible.
Here is the "Deuterium Deuterium" fusion reaction:
12H + 12H -> 13H + 11H + 4.03 MeV
To start fusion, the individual particles needs to get very close, in order that the "nuclear force" starts
to get working. The "range" of this force, is very small.
It simply means that the velocity, or Energy, of the individual particles must be high, or, in other words,
the Temperature must be very high. In Thermonuclear devices, the first stage of the weapon is "fission" which produces
an enormous pressure, radiation, and Temperature, which is the trigger to get fusion working.
The processes might be a tiny bit more complex. Sometimes the weak force may "turn" a proton into a neutron,
or the other way around. Althoug such an event may not generally happen "often", it can result in another
sequence of "end products".
It can be fun to do a websearch of the fusion chain inside the core of the Sun.
If you like that, you can even compare young stars, and heavy stars which enter
the final stages of their life.
For example, for a Red Giant, at a certain stage, the Temperature can get high enough for more
heavier elements to start to "fuse".
3.3.2. Crossections, Detection, scattering, and production neutrons.Crossections, and Detection:
A neutron has no electrical charge, and this fact makes it somewhat more difficult to detect.
Other forms of radiations, like the well-known α (Helium nucleus)-, β (electrons)-,
and γ (high energy photons) radiation, have well known interactions with other matter.
For neutrons, it makes certainly sense to talk about "cross section". It also makes sense to talk
about the wavelength of a neutron (shorter or longer, depending on it's speed or energy).
One way to detect neutrons, is that some nucleus "captures" it, and consequently this nucleus
may decay into another element, thereby also emitting α, β, or γ radiation, which is more easy to detect.
Some elements have a "large" cross section for capturing thermal (slow) neutrons, like 10B (Boron).
Fast neutrons are then first often slowed down (by some material), and next are detected by some method like above.
Many sorts of detectors go around.
As it turns out, different elements have different crossections for reacting on neutrons with different "speeds",
which makes it even possible to generate "spectra" of neutron energies.
It's good to remember that "cross section" is a sort of relative measure, of how well a certain nucleus
is able to "capture" a neutron.
Scattering of neutrons:
According to Quantum Mechanics, to elementary particles, a wave-length may be asscociated,
which is related to it's energy (or impuls). The famous de Broglie relation describes that.
In this sense, when neutrons of a certain energy approach some material, then at some point,
this material looks a lot like a "grid" (or lattice) on which we can almost use classical wave theory
to calculate the amount (spectra) of "scattering" of those neutrons.
In some specific setups, the neutrons may penetrate very deep, but in other specific setups
(meaning the speed of neutrons, and the material used), many of such a neutron flux, may scatter (bounce)
to some very specific directions.
This feature can also be used in some thermonuclear devices. It "helps" to intensify neutron "showers".
Often, in nuclear weapons, some "neutron initiator/neutron multiplier" was used to produce the very first "neutron shower".
This can also be in the form of a "neutron source", producing a constant rate of neutrons.
Both methods can be in such a setup, that just before the intended detonation, a conventional explosion
presses U or Pu fragments with a high speed towards a pit, inside where also this intended neutron generator
is present. The high pressure then activates this neutron initiator.
As another solution, it's also possible that a small potential fusion mechanism (Deuterium-Tritium)
is at the centre, which can generate (fast) neutrons.
It can also be true that an external "neutron initiator" is present, in the form of a small accelerator,
which accelerates Deuterium- and/or Tritium ions, and let them slam on a similar target. This creates the fusion
process needed to generate neutrons.
Today these devices are even smaller than hand-held devices.
4. The basic principles of the pure fission- and thermonuclear devices.A nuclear device, "runs" on fast neutrons.
Although the "crosssection" of 235U, or 239Pu, is very high with slow neutrons,
they can react on fast neutrons as well (they are fissile).
It's very instructive to see a chart with the value of the cross-sections, against neutron energy.
Thermal or slow neutrons will not efficiently generate the "fission cascades" in een large volume,
in an short enough period of time. But fast neutrons can.
The main types of implementations of nuclear devices, are:
-1. A pure fission weapon. It obviously uses "fission" only. The "fuel" might be 239Pu
or 235U, or a combination of both (and sometimes even also small amounts of other fissile isotopes).
-2. A "boosted" fission weapon. A pure fission weapon can be boosted by layers of Tritium and Deuterium,
or a central region with those H isotopes (or compounds which will quickly transform in Tritium and Deuterium).
This class is often not considered to fall into the real "thermonuclear" multi-stage weapons.
-3. Thermonuclear weapons are multi-stage weapons (often two stage), with a primary fission stage,
and a secondary stage which most often combines fission and fusion.
section 4.1 shortly discusses the "pure fission" and "boosted fission" devices.
Section 4.2 provide some crude examples of the true "Thermo nuclear" class.
Section 4.4 is concerned about the very first pure fission weapons, but with a strong accent on
the history of development too.
A nuclear bomb will not explode in the traditional way. No, the outer casing of the bomb "dis-integrates",
since in an extremely short time, radiation, and other manifestations of energy, is released.
One important feature of any nuclear device is "timing". In case of pure fission, a sufficiently amount of
cascade fissions (chains) need to have taken place, before the structure gives away.
Otherwise, the chance of a socalled "fizzle" is a reality, which we may describe as a yield of
very low intensity compared to what could have been reached.
Since fission is also a part of the boosted weapon, or even the Thermonuclear class, the same
principle holds here too.
4.1 The pure fission weapon and the boosted fission weapon.
Fig. 5: Simple illustration of a pure fission- and boosted fission weapons.
Source: my own Jip and Janneke figure. Very crude figures indeed. Some layers are "over" dimensioned for clarity.
The first image in figure 5 shows a pure fission device, using the "implosion" technique.
In '45 (and later), other geometries were also used (like the gun-barrel, or gun-type geometry).
Most often, the setup displayed above, is implemented by most Nations.
Indeed, the figure suggests that this setup uses the implosion principle. The curled outer "shell" is supposed
to represent conventional high explosives, carefully arranged, in order that the Pu or U shell (the reddish ring),
quickly and uniformly compresses and hit the inner pit, with the maximum speed possible, in such setup.
Indeed, in less than microseconds (μ seconds) a supercritical environment exists, which almost immediately therafter,
will pass through a large number of generations of fissions.
In the compressed object, the mean free path of a fast neutron is short, and the probability that it gets
absorbed by another Pu or U nucleus is relatively high.
In the setup, it's rather difficult to obtain a high efficiency of 'total' fission.
In the literature, the figures varies somewhat, but often only 20% of full fission is reached, before
the bomb structure totally gives away (disintegrates).
Critical mass (needed to start fast chains of generations of fission), is a relative number.
It depends on the amount, density, geometry, and other factors, but certainly also on how efficient neutrons
can interact with the nuclei.
Usually, relatively small amounts of Tritium and Deuterium can be used to "boost" the fission net result.
It's not really targeted to increase the energy output directly, but to increase the total efficiency of fission.
A major goal is downsizing of the nuclear device, and reduce the need for larger quantities of Pu or U,
and reduces the need for very strong structural supports.
The setup displayed in image 2, is rather similar to image 1, except for the addition of Tritium/Deuterium,
most often located in the central core of the device.
The process starts as already described in the subsection above, However, at the time only a relatively smaller
part of fission occured, the conditions are met for a limited fusion process. This sets off an intense neutronflux
radially outward, increasing the chance of fission of individual nuclei, in cooperation with the chains which
would already occur anyway.
The net-result is a very efficient fission process, greatly improving the energy output, compared to
the original setup displayed in image 1.
4.2 The Thermonuclear class (H bomb).Please take a short look at figure 6 below.
Modern bombs often start with a pure fission "trigger" (the primary stage), which in itself is a large powerfull
It might be an implosion type of device, where conventional explosives, generate a carefully designed wavefront
which pushes sub-critical pieces of Pu (or U) towards a centre. Immediately a supercritical object exists, and
if an neutron initiator creates a neutron flux, a cascaded fission starts (chainreaction), timed in μ seconds.
After a number of generations of chains, the energy release in X- and γ rays, is already so enormous,
that the temperature must be expressed in millions of degrees Celcius (or Kelvin), enough for fusion to start.
The device still did not exploded, since a little more time is needed.
Meanwhile, still in μ seconds, the foam turns into plasma, and neutrons bombards the secondary stage.
The secondary stage reacts in the most violent way and fission and fusion takes place.
A more scientific explanation will go into the details that the second stage ignites due to a
"radiation initiated" implosion of the second stage.
Next, the bomb fully disintegrates. Next, a short intense light flash is visible, as observed from large distances,
mainly due to interaction of X- and γ rays in the environment. Immediately followed by an energy "ball", which as you
have seen with the Trinity test (figure at the start of this note), easily expands to hundreds of meters in size,
in just a few miliseconds.
If an outer layer (or tamper) of 238U exists, than we can think of it as if a "third stage"
is present. The enourmous neutronflux of fast neutrons, will fission a very relevant percentage of that
238U material, which significantly adds to the total energy release of the device.
Most often however, a third stage is percieved as another secondary stage, physically present in the device.
This way, you can repeat (to a certain limit) the secondary stages in the bomb.
In the following two sub sections, two examples of Thermonuclear weapons, will be touched upon.
Some more architectures exists (or have existed), but I believe that two examples will suffice to provide
a general idea of the architecture of such weapons.
Where below 239Pu is shown in the figures and text, might in some other implementations
be replaced by 235U.
4.2.1 Spherical setup of a multi-stage Thermonuclear weapon.
Fig. 6: Simple illustration of a multi-stage Thermonuclear weapon.
Source: my own Jip and Janneke figure.
Ofcourse, true usable (workable) details, really only exists in classified literature.
Well, at least that's what I hope is true.
Suppose, just hypothetically: If someone would found true clear workable details in some accessible document,
like e.g., on the internet, then that would be Treason at the maximum level, by the perpetrator.
Figure 6 is not detailed at all.
It is true, that the primary stage often is a pure fission component.
However, it could also contain a fusion substage (container with Lithium(6) Deuteride, or Tritium/Deuterium).
In this case, the primary is often called a "boosted" primary.
Figure 6 suggests that the primary stage uses the implosion principle. The blue outer "shell" is supposed
to represent conventional high explosives, carefully arranged, in order that the Pu or U shell (the reddish ring),
quickly and uniformly compresses and hit the inner pit, with the maximum speed possible, in such setup.
Indeed, in less than microseconds (μ seconds) a supercritical environment exists, which almost immediately therafter,
will pass through a large number of generations of fissions.
From former sections, you might remember the "critical mass". It's not just an amount of mass.
Using neutron reflectors, like shells of Berrilium, you can increase the efficiency of fission, that is,
more generations of chains in a shorter amount of time. Indeed, part of the neutronflux that would otherwise
have escaped, now bounce back.
The compounds used, and the geometry of the primary stage (like having neutron reflectors), greatly influence
the needed mass to have an extremely fast and intense fission rate, and thus how fast energy (heat),
and radiation is produced.
Without those elements, the downsizing of modern weapons, and the yield, would not have been possible.
Note that with this elementary description of the Primary stage, there is no further need to describe
the pure fission weapon any further.
In figure 6, both the Primary- and Secondary stages, are spherical. However, for many real-world designs,
the secondary is cilindrical. For our purpose, it's not so important, since in this note we only want
to describe the primary processes.
For the overall "shape" and geometry of the setup, the casing where the primary- and secondary are mounted in,
is supposed to reflect much of the X- and γ radiation, towards the secondary.
This is represented in figure 6, by the "peanut-shape" of the inner casing.
High pressure, -energy, -temperature, and bombardment by fast neutrons from the primary, will ultimately
setof the secondary. There are many practical considerations, on how exactly, the secondary will go of.
One consideration, is on how to maximize the heat-transfer "rate" to the fusion fuel.
Another consideration is, how to make sure the Secondary undergoes a fast implosion as well.
In figure 6, The secondary is enclosed by 235U, with a similar "pit".
Just having a 238U tamper, is possible too.
This "pit" functions as a "spark plug". But this one may be absent too.
A global mechanism to offset the secondary, is that primary detonation first generates so much X radiation
so that the secondary compresses at very high velocity. If a fission spark plug is present, then this one
should give the last "push" to ignite the fusion. If a spark plug is absent, then superfast series of
shockwaves should converge at the centre of the Tritium/Deuterium compound, driving the Temperature
to the needed condition for fusion to start.
Once the fusion starts, again enourmous heat, radiation, and fast neutrons are generated.
Any 238U tamper, that is, a surrounding of a single stage, or even the entire weapon,
will undergo fission as well, strongly adding to the total energy release of the device.
There are ofcourse many details, which are not explained in this "Jip and Janneke" text.
- For example, if you look at the Primary, what would be the advantage of using such hollow shell design?
It seems obvious, that it's more easy to compress such a setup with an enormous velocity.
- As another example: the use and geometry of 238U tampers, is very complex.
Only the people who were involved in the extensive testing periods, that is, mainly the '50's
and '60's of the former century (USA, USSR), have gained an enormous knowledge on how to develop
effective thermonuclear weapons.
For having extremely large detonations (many Megatons), one would need a relatively large Primary stage too.
However, very large fission primaries are elaborous, quite heavy, and even dangerous due to the large amount
of sub-critical "parts" of fissile material. Often, it is limited to a max. of hunderds of kilotons
of explosive power.
For large detonations, a large Secondary is needed, and often even a Tertiary Stage.
4.2.2 Cilindrical setup of a multi-stage Thermonuclear weapon.The example shown here, is also called the (older) "Teller-Ulam Configuration".
Fig. 7: Simple illustration of the older "Teller-Ulam" weapon.
Source: my own Jip and Janneke figure.
Again, we might have a pure fission primary stage.
The main principle of such primary already has been discussed above.
The second stage too, is supposed to implode violently.
Heat, also contributed by foam, and most certainly of the energy due to the X rays, and
enormous pressure from the primary, will implode the secondary stage, where the Pu sub-critical parts
are compressed into a supercritical object.
This gives rise to an immediate fission chain, which generates the temperature needed
to support fusion.
Here too, the timeline must be measured in μ seconds.
It's possible that an 238U tamper (outer shell) surrounds the main device.
This enhances structural support at the very first stages of fission/fusion, and later
contributes to the total energy output since a relevant fraction will fission too.
4.3 Other considerations
4.3.1 FizzleIf you consider a pure fission weapon, or even a thermonuclear wapon, then having a bad design,
might end up in a fizzle.
Let's take a look at a pure fission weapon.
Then a fizzle is essentially a device where a very low amount of fissile material actually fissioned.
In nuclear weapons, timing is very important, as well as how you have arrange the conventional
high-explosives, in order to compress the sub-critical parts. If that arrangement is not good enough,
then compression to a supercritical object may only partially take place, to a result that the enormous
pressure will detonate the bomb, before any significant amount of fission took place.
One keypoint is namely, (if using an implosion type of trigger), that the demands on the placement
of the conventional explosives is very high, and it must be very precise, in order to make sure
that a very uniform wavefront compresses the 235U or 239Pu materials.
So, you may view a fizzle as a failed detonation, where at most only a very small part of the fissile material
actually fissioned, resulting in a very limited detonation, and indeed, a very dirty one.
Implementing a fission weapon often uses the "implosion type" of design.
However, the "gun-type" of design, where a sub-critical part of fissile material
was shot (like bullet) to another sub-critical part, was used as well.
4.3.2 The "Dirty" Bomb.Discussing regular nuclear weapons, the terms "dirty" and "clean" are also used (or mis-used).
For example, having the smallest possible primary stage (using fission, which will always produce
radioactive byproducts), but a larger fusion component, might ultimately produce a lot of energy/heat
and neutrons, but a relatively lower amount of radioactive fall-out.
However, in public discusions, a dirty bomb has a different meaning.
It often refers to a conventional charge, with some potporrie of medium- to high radio active materials.
It ofcourse has nothing to do with a nuclear detonation: this conventional explosion then will simply throw that
radioactive stuff over a larger area, hurting many people.
It's extremely unlikely that terrorists are able to produce a real nuclear weapon.
But a "Dirty Bomb" seems not so hard to create.
I am sure that lots of Governmental agencies are studying this topic.
At least, I really hope so.
In the very unlikely event that they were not, then they should immediately do so.
4.4 Short description of the very first pure fission weapons.Let's turn our attention on the history of the development of the very first few fission weapons.
This section is absolutely ultra-thin, and only mentions some highlights.
It only covers, roughly, the period 1940 - 1950.
4.4.1 USA.Then this must be about "Little Boy" and "Fat Man", and ofcourse "Trinity" (the very first nuclear explosion,
executed as a test). Fat Man was very similar (but slightly improved) to the device used in the Trinity test.
- Both Trinity, and Fat Man, used the "implosion" principle, similar as to the "primary stage" of
a multi-stage weapon as we have seen above.
- In contrast, Little Boy used the socalled "gun barrel" or "gun type" technique.
The gun-barrel type, used as subcritical rod, which was (conventionally) fired into another subcrital rod,
which was slightly wider and hollow. The idea is thus that when the parts "merged", a supercritical object exist,
which, with help of a neutron-generator (if still needed), went through extremely fast generations of fissions.
However, there were serious issues when using Pu, originally thought to be the fuel for "Slim Man",
the predecessor of Little Boy. Indeed, the impurities of 240U in 239U,
fed the fear of "pre-detionation" into a fizzle (see section 3.1.2).
It's indeed so that "spontaneous fission" of 240U, might enhance the chance of a fizzle.
Ultimately, with Little Boy (the follow-up of Slim Man), 235U was used.
Contrary, the implosion principle could use Pu, since a highly delicated implosion "lens" of
carefully placed conventional explosives in an outer shell, would make it possible that subcritical parts
would be highly symmetrical compressed, and thus would make the needed time to form such a dense supercritical
object much smaller compared to the gun-barrel design. The chance on a fizzle is smaller.
Little Boy and Fat Man, were actually used on two Japanese cities, respectively on Hiroshima and Nagasaki,
in august 1945.
Fat Man might be viewed (as the predecessor to) the Mark III weapon, which was in service until 1949, and
that one was followed up by an improved (but largely similar) version in 1949, the Mark IV.
The Mark IV was absolutely more fault-proof, and used much longer lasting electronics, and also used
a removable composite pit (centre core), using Pu and U.
Then in august 1949, the Sovjet Union peformed it's first nuclear test, RDS-1, in Kazakhstan.
It was a pure fission bomb, most certainly based on the Fat Man, or the Mark III, design.
From then on, developments and testing (on both sides: USA, USSR) went faster and faster.
Let's take a super-quick look on the history of development of the very first weapons.
In the late '30's of the former century, is was discovered that fission of heavy isotopes
could produces large amounts of energy.
As you may remember of sections 2.1.1., 2.2.1 and 2.2.2, the energy release is much higher
per atom compared to pure chemical processes. By some physicists, it was realized that this
might be utilized in some weapon of some sort.
Then ofcourse, in '39/'40, WWII broke out. Still, many brilliant physicists were in Germany.
Fear existed among some insiders in the Allied forces, that Nazi Germany was underway developing
a nuclear weapon.
In a response, in the US, the socalled "Manhattan Project" started in '42, which ultimately resulted
in the Trinity test, and the bombs Little Boy and Fat Man in 1945.
Those three devices were by no means "rugged" and "time-proof". It is known that with Fat Man, some parts
of the electronics only lasted for a couple of days, and there were problems with the core pit too,
just to name a few issues. It simply meant that once fully assembled, then either use it, or
disassemble some critical parts.
The follow-up, the Mark IV (1949) finally was rugged, and preservation was relatively OK.
4.4.2 Sovjet Union.Interestingly, the Sovjets did not lagged behind that much, in pure "theory", that is.
Here too, in the late '30's, ideas were discussed among physicists to employ nuclear fission into usable weapons.
Only when through intelligence, the Russians learned about the Manhatten Project, and after several
notifications by Sovjet physicists to Stalin, finally the Russians slowly started their own project.
Historians do not doubt that several ocurrences of serious Russian intelligence took place
during the period '42 - '45, and even direct handsout of intel by some subjects (e.g. Fuchs)
that occurred, likely lowered the learning path of the Russians at that time.
But it was only after it became clear that nuclear weapons really were employed by the US in '45,
the Sovjets were fully triggered to go ahead at full speed, and build them themselves.
As already said above, in august 1949, the Sovjet Union peformed it's first succesful nuclear test.
4.4.3 Great Britain.Great Britain was aware too, of the potential of fission of suitable heavy isotopes.
They first fired up their own project (somewhere around 1940), but then in 1943, it more or less
was integrated into the Manhatten project.
It must be said that the British were the very first to actually fire up a project.
So, the British collected quite some relevant information. Short after WWII, there were
"certain reasons" as to why the British decided to get the weapon themselves.
You might expect some "help" or involvement from the USA.
However, it seems that the USA was rather reluctant to provide support in any way, in that phase.
Only historians (or politicians) can provide you solid details of why this was so at first.
Already as of '46, '47 this relaxed somewhat. However still no direct, active support from the US.
Since the British were now very determined to aquire the weapon, support facilities in the UK
were setup, and lots of detailed information was already in their hands anyway.
Their first test of a Pu based pure fission device, was performed in early october, 1952.
So, as of 1952, three nuclear capable states existed: USA, USSR, and Great Britain.
4.4.4 Other nations.-In februari 1960, France performed their first test of a fission bomb as well, thereby aquiring
the status of a nuclear capable state.
- In october 1964, China followed with their first pure fission device, based on the
well-known implosion principle.
- Still later, some other nations joined the "club", like India and Pakistan.
4.4.5 Other remarks.What was not mentioned in this subsection, that even before the "pure fission" bomb became
a reality, already physicists theorized about utilizing fusion as the main principle
for nuclear weapons.
The first test of a two-staged Thermonuclear device, was the US build bomb "Ivy Mike",
in November 1952.
In the decades that followed, we saw an avalance of nuclear tests, with at least 500
atmosperic tests, and nummerous other tests underground.
You do not need to be Einstein to understand that all those tests implied a huge exposure
to radioctive nuclides, to humanity and the environment.
Many reports exists, governmental, or from research facilities, or other expert reviews,
confirming this huge exposure.
Various studies have linked such exposure to life-threatening diseases.
But even without studies and reports, this is rather evident ofcourse.
5. Overview Nuclear capabilities per Nation.It's no more than understandable that you may have strong reservations to all mentioned below.
Here, a simple and short overview will be presented on the present Nuclear capabilities of:
UK, France, China, Russia, USA, India, Pakistan, and an attempt is made to say something useful on NK.
Israel will be left out from the discussion.
Once, treaties had some value. However, in the present day climate, I am sorry to say
that any agreement between the US and the Russian Federation, is gliding downhill.
Formally/Legally, they still seem to stand. But rather recent statements from leaders made it quite clear
that we cannot expect too much any more from words on paper documents.
Have violations then been observed? Officially, "no", but some sources point out that
it's actually a fact. Sources can be even so mundane as the "New York Times" newspaper, and others.
They speak of, for example, recent violations of the "Intermediate-Range Nuclear Forces Treaty".
Other examples exist too. Providing mis-information is about the worst thing to do on a website,
but as I see it, no one actually knows the exact current positions anymore.
My personal view is, that the uncertainty will only increase in time.
Maybe you do not believe in such violations.
It's really not too hard to find out about these matters yourself !
By the way, I do not suggest that any article about such violations, represents the truth.
5.1 Unclearity about counts of devices.In general, treaties specify (among other things), the number of devices, and the count of "delivery systems"
which can transport, or fire them.
For the nuclear devices themselves, it's rather evident that they may have the status of:
-In various stages of development.
-In final stages of development, nearing the operational status.
-Variable explosive power, which hold for some special devices.
-The exact known mountpoint (in grenade, payload of rocket, torpedo, bomb).
-Part of a cluster of devices (like mirv of an ICBM).
-Set aside as Candidate for dismantling.
-Somewhere in the chain of development, operational/stockpiled, candidate for dismantling, dismantled.
-Dismantled, or in progress of dismantling, to make them fully unusable.
-Dismantled, or in progress of dismantling, but never to make them fully unusable.
-Originated from a friendly nation, but stored (operational/stockpiled) at this particular Nation.
This does not neccessarily obscure the counts of nuclear devices, but it certainly makes it harder
to exactly distinguish the "Operationals/Stockpiled" from all the rest of the devices.
This would hold for Nations which agreed to some treaty of some sort.
The obscurity actually really exists for Nations which did not adhere to any treaty at all.
You might agree that it is not possible, on a Global scale, to accurately specify the number
of nuclear devices. Likewise, it is not possible to accurately specify the the number of
"Operationals/Stockpiled" number of devices.
An estimate is the best we can do.
5.2 Main current nuclear weapons of France.
5.2.1. Current overview main nuclear systems:It seems reasonable to assume that France has about 350 nuclear devices "Operational/Stockpiled".
-The majority is meant for use in SLBM's on submarines.
These can be considered to be strategic weapons.
-The best estimation I could find is a figure of about at least 50 reserved for Air-Surface missiles,
most notably to be mounted on the Rafale, and still too for the Mirage.
These can be considered to be tactical weapons.
-Unknown how many are "somewhere" in the chain of development, up to Candidate for dismantling.
The French government, on several occasions, declared that a number of 300 devices would fit
their policy of deterrence.
5.2.2. Tactical nuclear weapons:Most notably the ASMP, and ASMP-A cruise missiles, fired from Rafale, Mirage, and comparable planes.
Highly likely to be distributed among the Airforce and Air-Naval services (Navy).
Range: about 500 - 600 km.
Speed: about max Mach 3.
Warhead: thermonuclear warhead, probably 150 kT - 300 kT
Specifics: ability to cruise at low altitude.
Delivery: fired from Rafale, some Mirage types.
5.2.3. Strategic nuclear weapons:Most notably the new Triomphant class of nuclear submarines, equipped with SLBM's (16).
Four of those vessels are in operation, as of 2010, with no plans for others.
SLBM: M51 (or M51.2:), French design, and development:
Range: probably max 8000 km.
Speed: probably max Mach 25 in decent.
Warheads: likely to be 6 in MIRV configuration, per rocket.
Thermonuclear warhead, probably 100 kT. For the M51.2: 150 kT.
5.3 Main current nuclear weapons of Great Britain (UK).
5.3.1. Current overview main nuclear systems:-The British Government does not have an open policy on it's own nuclear arsenal, in terms of
numbers, and sizes of nuclear devices.
An often heard number (in magazines, wiki's etc..) is "about 200" devices, of which we may assume
that they are reserved for the Trident II D-5 missiles in the Vanguard-class submarines.
-Also, the British Government, in principle, still allows US nuclear weapons to be stored on British soil.
Formally, the nuclear deterrence is solely build on 4 modern SLBM based Vanguard-class submarines.
Those entered service in the period 1993 - 1999.
A programme for the successor of the Vanguard class is accepted.
In 2016 the Britsh decided to start to build a fleet of 4 new "Dreadnought-class" submarines,
likely to be operational somewhere around 2028 - 2030.
Presently, there seems to be a lack of nuclear tactical capabilities. But the strategic component
is very strong, based on the 4 SLBM based Vanguard-class submarines.
However, it's possible that Vanguard-class submarines may carry (when needed), medium range missiles,
or other better optimized delivery systems for shorter ranges, instead of Tridents.
It's simply not disclosed information. It's dangerous here, to slip into speculations.
5.3.2. Tactical nuclear weapons:Formally, it seems to be none. And formally, it is declared to be none.
This used to be very different in the past. For example, around the end of the '80s, the UK had around
250 tactical weapons, of which most of them were WE-177 bombs that could be dropped from e.g. Tornado jets.
A smaller number of other types of bombs (most designed to be delivered by plane), were around too.
It's said that all of them were decommisioned.
It's possible that Vanguard-class submarines may also carry better optimized delivery systems for shorter ranges,
instead of using Trident SLBM's.
Also, it's possible that still Tridents can be given a "sub-strategic", or "near-tactical role",
if the British wishes to do so. For me personally, it's a bit hard to see how a MIRV based
long-range missile, can be put in a tactical short-range role. I can be very wrong here.
Furher, I could speculate about many alternatives, but it's not allowed to do so.
5.3.3. Strategic nuclear weapons:Excusively by the Trident II (D-5) missiles in the 4 Vanguard-class submarines.
Tubes: 16 launchtubes. 16 Trident missiles. It's reported that generally a "partial fill" is in place (likely 8).
warheads: up to 8 in MIRV configuration. Thermonuclear. Standard as 100 kT. Selectable between various kT output.
Range: US Trident II D-5 about 12000 km.
Max speed: around Mach 24.
Pool: The Royal Navy shares their missiles from a shared pool with the U.S. Navy.
5.4 Main current nuclear weapons of China (People's Republic of China).China possesses an extremely large conventional military force.
It's almost impossible to provide a comprehensive overview of those forces.
Considering the nuclear capabilities of China, is certainly an enormous chalange too.
Just to name a few obstacles:
of China having "only" about 250 -300 active warheads.
5.4.1. Current overview of the main (more or less modern) nuclear systems:In the public literature, China is often portrayed as a much smaller nuclear nation, compared
to the USA and the Russian Federation.
Most of the professional literature speaks of about "only" about 250 - 300 nuclear warheads in total.
I somewhat doubt the numbers, and I am curious in how much of the older warheads have been decommisioned,
or have been re-used, or simply stored as spares.
Also, as you will see with the Dongfeng missiles: the exact numbers are probably not known,
meaning that counts of operational warheads is very difficult.
To be blunt: Personally I believe the number of warheads is higher than 250 - 300,
but that's not the official standpoint of Qualified institutions (Western Intelligence, Military).
Another way to look at matters is to see how much "weapon grade" fissile materials is available.
After consulting several sites, there seems to be a consensus of about:
18 ± 4 ton Higly Enriched Uranium (weapon grade).
1.8 ± 0.5 ton weapon grade Plutonium.
There seems to be quite some capacity for additional nuclear devices.
In recent years, China discovered several new locations on it's territory with Uranium ore,
where some are promising enough to setup mining. The most important motivation to do this,
is the projected rather large expansion in nuclear energy for the years to come.
It is likely that with newer MIRV based ICBM's, like the new DongFeng-41, will seriously increase
the number of active warheads.
The most important weapon systems maybe described by the:
5.4.2. Strategic- and Tactical nuclear weapons:
18.104.22.168. Short-range-, medium-range-, and longrange Missiles:=> 22.214.171.124.1. The Dongfeng "DF" series (or NATO classifier CSS- series) of Missiles:
This constitutes a rather wide series of types of short-range, medium-range, and long-range missiles,
where some of the latter really qualify as ICBM's.
As you will see below, not from all types, the exact numbers are known.
Also, different sources publishes slightly different specs, at least as of the DF-26.
The following types are known to exist:
Older types, Dongfeng 3 (CSS-2), Dongfeng 4 (CSS-3), Dongfeng 5 (CSS-4), Dongfeng 11 (CSS-7)
Dongfeng 12 (CSS-X-15), Dongfeng 15 (CSS-6), Dongfeng 16 (CSS-11), Dongfeng 21 (CSS-5), Dongfeng 25
Dongfeng 26, Dongfeng 31 (CSS-10), Dongfeng 41 (CSS-X-10)
The listing of missiles is quite long, but some of the more interresting missiles were, or are:
Medium-range. In operation 1974-2014, modified during that period, but now probably phased out.
Range: about max 3000 km
Probably 10 mobile launchers
warhead: probably 100 kT
Medium range. DF-21A in operation since 1996. Probably several dozens in operation.
Several dozens of Mobile launchers.
Range: about max 2000 km.
Warhead: Often quoted to be 300 kT.
Medium range. DF-21C in operation since 2006. Number in operation: unknown.
Range: about max 1500 km.
Unknown number of Mobile launchers.
Warhead: Reported to be intended for conventional warhead. However, believed to have a nuclear warhead.
Accuracy (CEF): very high, tens of meters.
Other similar subtypes: DF-21D. High accuracy (CEF). Max range > 2000 km. Number in operation: unknown.
DF-26 and DF-26B
Viewed as the successor of the DF-21.
Medium/Long range, or "intermediate-range". In operation since 2014. Number in operation: probably 16.
Range: probably max 4000 km, which is medium-range, or "intermediate-range".
Number of Mobile launchers: likely to be 16.
Warhead: Nuclear warhead. Possibly MIRV. No confirmed kT specifications.
Accuracy (CEF): very high, tens of meters.
Long range MIRV capable missile. In operation, probably, since 2009.
Range DF-31A: probably max 11000-12000 km.
Number of Mobile launchers: likely to be over 30.
Warhead: 1 MT, or in MIRV > 3x300 kT (?)
Accuracy (CEF): very high. Probably with detection evasion capabilities.
State of the Art Long range MIRV capable missile. In operation, or near end of Testing phase.
Range DF-41: probably max 14000 km.
Number of Mobile launchers: unknown.
Warhead: in MIRV probably up to 10x300 kT (?) Some sources publish 12 warheads in MIRV.
Accuracy (CEF): very high. Probably with detection evasion capabilities.
Remark: One of the most deadly ICBM's today.
=> 126.96.36.199.2. JL-1 / JL-2 SLBM Missiles:
The JL-1 is an older type of missile, roughly comparable to the DF-21.
The JL-2 is a modified version of the DF-31, especialy adapted to be operated as SLBM's
The JL-3 seems to be in development, probably for a SLBM role too.
It is believed that about 48 JL-2's have been produced.
The specs should be further largely comparable to the DF-31 series.
188.8.131.52 Strategic SLBM submarines:Quite some conventional submarines were, or still are, in use with the Chinese Navy.
However, here we focus on submarines with nuclear SLBM capabilities.
One sub operational as of 1983. It's the oldest of the ballistic SLBM submarines.
It uses 12 JL-1 SLBM's with a short/medium range. The one Xia class sub, uses 12 launch tubes.
Some reports say that it has a relatively "loud" footprint.
Developed between 1999 and 2010, there are currently 4 Jin-class subs in service.
It seems that 2 more were planned, but this might be superseeded by the newer 096 series.
It uses 12 JL-2 SLBM's with medium- to large range.
Most articles mention a max range 0f 4000 km. However, if the JL-2 is really a modified
DF-31, a substantial larger range seems appropriate, as well as a high accuracy.
The projected Tang 096 class:
Probably already in development. It's likely that it will use 24 lauching tubes.
It seems unknown at this stage which missiles will be implemented.
It also seems that this class will pretty soon represent an enormous firepower.
184.108.40.206 Strategic/tactical bombers:Russian planes which might have a tactical role:
China purchased from Russia, the outstanding Sukhoi 35 fighter, which many defence specialists
compare to the F22 and F35. However, a nuclear tactical role is probably not the first
role in mind, you would assign to the Su-35. Although it's payload is enormous.
But China also bought (during the 2000s), the Su-30 fighter/bomber (multirole fighter),
likely to be in the form of around 76 Su-30MKK and around 24 Su-30MK2.
A nuclear tactical role fits the Su-30 well. It's not known (by me) in howfar such role actually
have been assigned to those Su-30's.
So no clarity (from me) on the nuclear roles of those Su machines.
But in principle: yes, it's possible for the Su-30.
China's "own" developed planes which might have a tactical role:
There exists a rather wide J-xx range of planes, which can be attributed all well-know
roles, like fighters, multi-role, or specific bombers.
Some are capable of a nuclear tactical role. I'am still sorting this out.
Then ofcourse we have the long-range Xian H-6 bomber. This is a large plane, with
a max range of about 6000 km, depending on the subtype.
Indeed, quite some variants were build. It's original design was based on the Russian Tu-16.
A range of older versions, as well as quite recent versions exist. It's believed that near
120 bombers are in service.
Defence specialists often say that a primary role is Air-to-Vessel (ships) attack.
Strange thing is, that quite recently a number of such planes patroled near the costs of Japan.
It certainly has short/medium range nuclear capabilities, like obviously using nuclear gravity bombs,
and, using cruise missiles.
I still need to inventory the different sorts of cruise missiles.
Sofar about China. New information will be placed in this section.
It amazes me, that a large expansion of nuclear capabilties is going on, like the Dongfeng-41,
and the new projected Tang 096 class of SLMB submarines (24 tubes, probably with the new JL-3).
I think we can "forget" the many "wiki's" stating that the number of warheads sits in the range
of 250-300. That period has definitely be gone. That my opinion anyway.
Suggestion: if you do not know the Dongfeng-41, I suggest you do a further websearch on this missile.
5.5 Main current nuclear weapons of Russia.
5.6 Main current nuclear weapons of the USA.
5.7 Main current nuclear weapons of India.
5.8 Main current nuclear weapons of Pakistan.
5.9 An attempt to say something on the capabilities of NK.