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A few simple words on Nuclear weapons.

Date: 24/07/2017
Version: 1.3
Remark: Not ready yet. Did some minor corrections too. 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 small (and very simple) note on the various architectures, as well as current implementations on
various carriers (like ICBM's, or for example the small B61 tactical weapon etc..), as in use by nuclear
capable nations. This means that Chapter 5 is a major part of this note.
That chapter is a short review of operational weapons per nation, and (as much as is possible),
what new devices and carriers they are planning or are working on.
It's almost beyond comprehension, if you see what is actually is operational, right now.

Let me also immediately make clear that I do not want nuclear weapons at all. They must go away, and all research,
which I personally believe is ongoing and very extensive, should be stopped.

Warning: About such research: not all folks (scientists, politicians, military) might share such a view,
or are possibly even not much aware of it (like many politicians might be).

Furthermore, I think we are approaching (or are already in) a rather dangerous time, and even management/control
of those weapons, seem to slip away. You may believe that, or maybe you don't. But you might agree, that the leaders
of the Superpowers (USA, Russia, China) are not exactly Einsteins.
Also, some other countries are almost desperately climbing the nuclear ladder (like, e.g., India).
Some have not even signed any relevant treaty.

Anti-nuclear nations and politicians can protest ofcourse, but other means might be at their disposal too.

For example, very stringent control on production of light elements (e.g. deuterium, tritium, berrilium, etc..),
and very hard import/export restrictions, might be a nice punch.

I'am not saying that all sorts of restrictions are not in place already, but there might be material
which deserves much more attention.
Who knows? Maybe we get some good ideas somewhere, to temper the nuclear business.

As another problem, nuclear devices, also age. You can stockpile several thousends of them,
but important questions arise, such as: how long are they reliable?, or, how to handle retired stuff?
Since 1945, weapon technology changed tremendously ofcourse. However, if you read the accounts from the assembly
of the first few of Pu or Pu/U bombs, you can see how fast several interfaces and "components" deteriorated at that time.
Even today, this may be a sort of "hidden" problem too. In chapter 6, I will try to say something useful on this too.

All in all, I would say that this note is no more than a very simple attempt to bring some clarity
for folks, who are not familiar with those subjects at all.

1. Quick overview on "generations" of Nuclear weapons.

1.1 The 1st, the 2nd and 3rd generations.

1.1.1. 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.

In the thermonuclear class, quite some variants exists, like e.g. the socalled "fusion-boosted fission" weapon,
and other morphologies. In this note, I collect them all together into one class
If we take a look at the "fusion-boosted fission" weapon, it's main principle is actually fission, but
lighter elements (like tritium) are embedded in the architecture, to produce neutrons, and thereby greatly enhancing
the efficiency of fission.
So, some folks would still characterize it as a fission weapon.

Multi-Staged thermonuclear weapons fits the thermonuclear class better, since the fusion role is certainly prominent.

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).

The thermonuclear class has made "downsizing" possible, that is the physical dimensions, resulting in much
smaller devices, compared to the first generation of "pure fission" devices.

But it even holds for modern (almost) pure fission devices.
Especially using "tritium" in "smart" appliances, can generate neutron showers, thereby significantly
enhancing chain-reactions.

1.1.2. 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).

Some people call such devices (like the ERW weapons), nuclear weapons of the "third" generation.

In this same generation, other variants were present too, like one focused on Blast, and reduced radiation (RRR).

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.

1.2 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 downsizing. There are multiple roads here.

1.2.1. "Pure" fusion.

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 large dimensions.
Ofcourse, the above statement at this point, is still fully hypothetical.

Warning: Again a warning. Many physicists will tell you that "pure fusion" is still a long, long, road to go.

Yes, that might be true. I insert those "warnings" at various places.

Indeed, "pure fusion" for large-scale energy production is still a long road to go. But small scale fusion, is demonstrated
in many (even) small scale devices, like for example very small accelerators.
Some accelerator-based neutron generators use beams of deuterium and/or tritium ions and some sort of hydride targets
which also contain these isotopes. Here, the fusion process is active, often with the purpose of generating neutrons.
Believe it or not, some have the physical dimensions of a hand-held device.
These have applications in medicine, engineering and the like, but are ofcourse not even slightly related
to the 4th generation.

But it's important to know that small scale fusion processes, are really quite commonplace.

Research is done over many decades now. "Pure" fusion as the method for a 4th generation bomb, might
make sense if it (for example) really contributes in significant downsizing.
Due to so much research, some folks believe it may ultimately contribute to the construction of the 4th generation bomb.
You might think of the "Nuclear Non-Proliferation Treaty" that can counteract it, but that does not cover a country's own
domestic research, or research in general.

An interesting question may be, what the state is of current treaties, and how effective they are.
As I will try to show a little later, current treaties seem to be a bit of a dissapointment.

Although the principles of "fission" and "fusion" have not been explained yet, usually, for a
"pure" fission device, one need a total amount of fissable material near (or more) the socalled critical mass.
However, many factors determine the needed amount of critical mass to ultimately obtain a chain reaction.
Some factors are tampers, neutron reflectors, or the construction of the bomb to withstand extremely high
pressure/temperature in the pre-phase before explosion, or indeed to use light elements that will produce
a "neutron shower" in order to help the chain reaction.

For "pure" fusion, such a requirement of critical mass is much less stringent.
However, to "start" fusion, an extreme temperature is needed.

One hurdle to solve here, is how to "trigger" the fusion process (for a considerable mass), without the need for fission.

Even if the appearance of "The 4th generation" is only remotely likely, I would say that the public
on a Global scale, should demand a full and immediate stop on further development of nuclear weapons.
As I see it, current treaties do not cover this at all.
Also, as I see it, the public interest seems to be extremely low (as contrary to the '70's and '80's).

In the next chapter, I like to say something more on the fundamental principles behind fission and fusion,
and architectures. In chapter 5, some real world examples of carriers and devices (per nation) will be shown.

Some articles:

If you like to see more on classifications and types of architectures, here is a nice Cornell (arxiv) article:

Fourth Generation Nuclear Weapons: Military effectiveness and collateral effects (arxiv)

If you like to see some thoughts on using nano-technology in 4th generation nuclear weapons, then you might like:

Nanotechnology and Fourth Generation Nuclear Weapons (cern.ch)

You might find the upper articles a bit coloured, so to speak, but I think they are still good for a reasonable "impression".


The search for fusion (for generating energy) was very hot in the '80's.
Enormous machines were build. Big money and effort was spend. However, the results remained
a bit dissapointing. Fusion worked, but not long enough, and the net gain was ultimately too low.
So, the fusion projects more or less collapsed.

Later, a new kick off was started, as an international project: ITER.

Still later, one article appeared, with some warnings on nuclear proliferation. The overall atmosphere of that article,
somehow fits in my note. You might take a look at that article here.
Again, some criticism is needed here too.

2. The basic principles of fission and fusion.

2.1 Some principles first....

2.1.1. "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, or thousends of eV etc...
This is an important component of "capturing" chemical energy.

Typical binding energies of protons/neutrons in the 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
chemical processes.

What we have seen above, is certainly not good enough. But for my purpose, it is sufficient.

2.1.2. 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 force "rules".

Ofcourse, today physicists know of a deeper structure (quarks, gluons), but that does not play a role in this simple note.

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 (protons+neutrons).

2.1.3. 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.

For example:

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.

2.2 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.

2.2.1. 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. 1: Average binding energy per nucleon, against the mass number (the elements)

Source: Wikimedia commons (free).

It also means this: Suppose some heavy Uranium isotope, breaks up into two smaller parts (e.g. 140Ba and 93Kr),
then from figure 1, 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.

2.2.2. Fission of some specific heavy isotopes, and chain reactions

Some 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 neutrons

Some 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 1, 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. 2: 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 1, is:

01n + 92235U -> 56141Ba + 3296Kr + 301n + 200 MeV

Fast neutrons

When fission occurs only after capuring a slow thermal neutron (<10keV), the isotope is called
a "fissile" isotope, like 235U.

But when only fast neutrons (>1MeV) will produce fission, the isotope is called "fissionable",
like 238U.
For about the latter definition, some descriptions include both "fast"- and "thermal" neutrons.

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.

2.2.3. 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.

-The term "fissionable" is slightly different from above. A fissionable isotope can undergo fission
when it captures a high energy neutron (> 1MeV), or (formally) also by a thermal neutron.
So, here "fast" and "slow" neutrons may activate fission. However, many descriptions talk about
"fast" neutrons only. That can be somewhat confusing. But formally, both "fast" and "slow" fall
in the definition.

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.

However, 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 Reactors:

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.

2.2.4. 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
detonation followed.
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.

2.3 A short description of Fusion.

2.3.1. 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".

2.3.2. 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".

Neutron shower:

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.

3. 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.

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.

Please take a short look at figure 3 below.

Modern bombs start with a pure fission "trigger" (the primary stage), which in itself is a large powerfull
device, ofcourse.
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.

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.

3.1 Example setup of a multi-stage Thermonuclear, weapon.

Fig. 3: Simple illustration of a multi-stage Thermonuclear weapon.

Source: my own Jip and Janneke figure.

Let's discuss the various stages:

3.2 Example setup of a the first pure fission weapon.

4. A few words on past and existing Treaties, and agreements.

This will be an extremely short section. Actually, it will be no more than just a few words.
I hope it's any good, or informative.

However, the material itself, is huge. It can easily form the basis for be a post-doctoral study, to categorize
historical facts, all relevant proposals, and do research and analyze where exactly things went right and wrong.

There existed many proposed and partially executed, treaties between the USA and Russia.
There were (and still are) also many UN initiated proposals, for example the recent "Ban on nuclar Arms",
where the Chinese president reacted (sort of) positively on, but 4 other nuclear nations refrained from.

There are almost too many proposals to list, unless one has a specialized site for that specific subject.
Just a few more examples: "New Strategic Arms Reduction Treaty", "Limited Test-Ban Treaty", "INF",
or the SEANWFZ treaty (which aims on a nuclear free South East Asia), etc.. etc..

One agreement is very well-know, almost reckognized by all countries, and that is the "Nuclear Nonproliferation Treaty" (NPT)
which focusses primarily on stopping the spread of nuclear weapons, and generally promotes nuclear disarmament.


-Treaties on resources, imports/exports etc..
Treaties do not only focus on arms control. There are classes that focusses on imports/exports of fissile materials,
most notably, the fissile isotopes of U and Pu.

That's why stringent imports/exports limitations of light elements, needed for nuclear weapons (deuterium, tritium),
might be a good initiative too.
I seem to miss that in major agreements, but I might be wrong here.

-Authorative Agencies:
For example the "IAEA". It's an organization striving for peaceful use of nuclear energy, and for
cooperation among nations. Most countries are member of this organization.

-Lastly, agreements on nuclear plants, and parts thereof, fall under several unilateral regulations, which however
some nations do not subscribe to.

Bilateral treaties: USA - Russia

Historically, and up to early 2016 or so, treaties were proposed, followed up by others, between Russia and the US.
In the literature, or on the Net, many details can be found on for example SALT, START, START II, new START, INF.
The historical information is rather gigantic !

One if the first steps was probably the signing of the "Partial Test Ban Treaty", by Kennedy and Khrushchov in 1963.

Many proposals followed, and some were signed, and some later not prolonged, or simply one party withdrew.

As you might agree, a well balanced treaty, prevents an enormous waste of money, and enhances security
on both sides, or in better words, enhances security for the whole Planet.

After the break-down of the Sovjet Union, the early '90's were a relatively calm and stable time, a good climate for detente.

It's important not to present "coloured" information, but both sides did quite irritating stuff, say, from
the late '90's, up to this very day.
So, I will completely leave out to describe any fact of, what I called, "quite irritating stuff".
I hope you understand what I mean here. Again: It's important not to present "coloured" information.

A real shock (to some) happened early Februari, 2017. President Trump announced that current nuclear agreements
are a bad deal for the US, and his nation must get back to be "on top of the pack".

True, I don't know exactly the motivation to express such a statement, but I am quite sure
that anything that was still good, went over the cliff at that point.

But even worse, there were little, or almost "0" public reactions from Western or European politicians.

This whole business simply means a new impetus on research and development.
This is a practical example of my statements at the very beginning of his note.

Note: However, the fact that Pres. Putin, and Pres. Trump, on their very first meeting (7/7/2017),
(at the G20 top Hamburg/Germany), spoke each other for well over 2 hours, is rather encouraging.
Those two top leaders obviously had something talk about. As we all know, communication is paramount.

As another recent event (May-July 2017): China seems to be rather upset on the fact that the US
currently placed/places the Thaad system (anti-ballistic missile rockets) in South Korea.
It's just an event. However, since Thaad aimes specifically on ballistic rockets, the Chinese might
be triggered to develop a "response" strategy. Again, it's just an event.

One may continue to sum up, similar events of various degrees of being potentially dangerous.

However, one cannot focus solely on the current position of the US administration.

-It's quite clear that Russia has rebuild rather massively it's conventional capabilities, as well
has redesigned (and is redesigning) it's nuclear capabilities (e.g. new types of SLBM's and ICBM's).
Ofcourse, the budgets between the US and Russia differ greatly, so everthing is rather relative here.

- To a lesser degree, but still very serious, China recently has developed a few large types of ICMB's,
and put them in operation, most notably the "Dongfeng" DF-41.
Also conventionally, quite a few thing changed, like new frigates, and new SAM systems (like the S400).

Bilateral treaties: between other countries

They exist to a certain extend, but it's too complicated to say anything usefull in this short note.
An example may be several implementations of the "The 123 Agreement", for example, between the US and India.
These are geared towards nuclear plants, and other material in general.

India, Pakistan:

Both states are quite "outside" major treaties.
Especially India invests rather major in new conventional weapons, and is quite active
in developing ICBM type of delivery systems (instead of their jet based tactical delivery).

France, Great Britain:

France signed the major nonproliferation treaties and international export regulations.
Although part of NATO, the country is for nuclear weapons self sustained, and it declared a
complete independent nuclear policy.

Great Britain developed (in cooperation with the USA), it's own nuclear weapons.
For SSBM's, they have US Trident class missiles.
It also signed the major nonproliferation treaties and international export regulations.

Danger of downsizing:

Intuitively, very large nuclear "bombs" should be feared most, like the Russian AH602 (50 Megaton),
or the largest of the wide American B series.
Most of the large bombs are "retired". Ofcourse, today, there still exists a whole range
of many kilotons to, in a lesser amount, megatons range, but the absurdly large ones are retired.

It's (in my view) the downsized weapons that must be feared most.
Once, "nuclear artillery" really existed, for obvious military reasons, and indeed in howitzer form.
The shells were in the sub-kiloton range.

If you did not knew this fact, aren't you amazed by that?

But today, very small tactical nuclear weapons (delivered by rockets) exist.
Not only rockets, but even torpedoes and you name it...

Smaller rockets, and devices that can be mounted on stealthy jets, or drones, invite any potential
enemy to do the same.
Risks of escalation is very high. Risks for public acceptence cannot even be ruled out.
The latter may seem very strange at first sight. Don't forget we are already used to armour piercing
Uranium based ammonition. Don't forget that firing 100 conventional cruise missiles,
might "just as well" be done by a "cute" sub-kiloton device, especially if fall-out is "acceptable".

I agree: what you have seen in this section, is not awfully much.
If you were relatively new, I really wonder whether this section brought any clarity.

However: My sole mission was to demonstrate, to a very limited extend, that humanity is still not
safeguarded by solid treaties or agreements.
I think that rather recently, actually the situation deteriorated.
From almost all nuclear capable nations, almost none is willing to consider the latest
UN proposal of the "Ban on nuclar Arms" (early 2017).

5. Overview Nuclear capabilities per Nation.

Hope that this simple note is not too boring up to now.

However, this section, as I feel it, might be percieved as a bit "grim".

It's indeed a bit dissapointing that quite a few nations invest rather heavily in defense,
that is in conventional weapons, but some nations in nuclear weapons too.

First a few warnings and remarks:

Warning (1):

-For nations like Israel, South-Africa, India, Pakistan, North-Korea, it's not possible
to write down "exact" statements. Here, in most cases, "reasonble" estimations (also based on the
probable amount of weapon grade fissile material, and supporting material) is the best to offer.
But we still can see some trends, and purchases (as far as is known), and facilities.

-North-Korea is rather special, since hoaxes and reality are probably a bit mixed.
It's extremely difficult to say anything usefull here.
Although, following the latest news, they seem to make steps in missile technology.
However, an armed conflict between the US and North-Korea must be avoided with "Galactic" effort.

Since North-Korea is so intensively "in the news", I will try to say something useful later this note.

-Israel will be fully left out, since possible information would be too speculative anyway.

-Great-Britain and France, have a tiny bit of a sort of special status.
As much as is possible, will be presented here.

Even so, all provided information can still be flawed, or biased.

Warning (2):

Since I believe weapon research got a new impetus, since the '90's, and even more so since rather
recently, the US (and possible consumerstates in NATO), Russia (Russian Federation),
and China, it is quite sure that those nations are evaluating, planning, and doing research.

Even so, all provided information can still be flawed, or biased.

Ok, here are my investigations:

1. India:

Accent on: Conventional and Nuclear:

It's amazing how fast the conventional forces has grown the last years.

1.1 Navy:

Let's take a quick look at the Indian Navy. It has become a very serious force on our Globe.

Blue Navy:

1.1.1. Modern Carriers:

Certainly their two new Aircraft carriers are very impressive.
The new carriers are replacments of older British ships, like the Viraat and Vikant (former Royal Navy's HMS Hermes,
and the former HMS Hercules) which are retired.

- The INS Vikramaditya: A modern aircraft carrier which entered service, in 2013.

Some details: displacement 45400 tons, length, 283.5m, max speed 30 knots, crew around 1600.
It's is a rebuild/modified/modernized Russian Kiev class carrier.

It has a capacity for about 26 MiG 29K fighterjets and about 10 Kamov Ka-31 AEW / Ka-28 ASW helicopters,
of which anti-submarine capabilities is a strong feature of those helicopters.
The propulsion is traditional, that is, non-nuclear.

Local armament: at least: 4x AK-630 CIWS (30mm gatling), Barak 1, Barak 8 SAM missiles.

- The INS Vikrant: Another very modern aircraft carrier, is about to step into service (2019-2023).

INS Vikrant": displacement 40000 tons, length, 262m, max 28 knots, crew around 1400.

It has a capacity for about 26-30 MiG 29K fighters and about 10 Kamov Ka-31 AEW / Ka-28 ASW helicopters.
The propulsion is traditional, that is, non-nuclear too.

This ship is "home" build, but weapon guiding systems are still partly Russian.

Local armament: 4 x Otobreda 76 mm, 4x AK-630 CIWS (30mm gatling), Barak 1, Barak 8 SAM missiles.

There seem to be no indication that nuclear devices will be stored on board. The Mig 29K is capable
of carying various nuclear devices. Jet experts generally type the Mig 29K as a very capable fighter.

Even only those ships, delever already an airforce capability, that would be quite similar to the capabilities
of smaller NATO members like The Netherlands, Belgium and the like.

1.1.2. Modern Frigates (> year 2000):

The "Shivalik class" (142m, 6200 tons) has three ships operational at this point in time. The planned capacity was 7,
but that figure seems to be debated nowadays (due to Project 17A-class frigate).
These are very modern frigates, having a low profile, and a large surface to air capability,
but it has in fact a strong air defence, and land-strike capabilities.

Originally, Shivalik seem to fall under the "Project 17A-class frigate" design, however (as I understand it),
it seems that this project now may be regarded as a follow-up of the Shivalik design.

1.1.3. Older frigates:

About 11 pre-2000 frigates are in service right now. In total thus about 15, or 16 frigates.

1.1.4. Modern Destroyers (> year 2000):

Right now, India has the "Kolkata class" (163m, 7300 tons). There are 3 ships in operation.
Everything that might be expected from a modern destroyer, can be found in this class.

1.1.5. Older Destroyers:

About 8 pre-2000 destroyers are in service. In total thus about 11 destroyers.

1.1.6. Modern Nuclear Submarines (> year 2000):

A very ambitious plan exists for the development of the nuclear powered submarine of the "Arihant class".
The first one, out of (likely) 6, the "INS Arihant" is in operation since 2016.
The second one, is now in the building phase.

The whole project is rather remarkable, or possibly even somewhat strange. The ATV (Advanced Technology vehicle) Program
exists since 1974, having various members from many technical institutions and industries from the Country.

While several nuclear subs were already "leased" from Russia, India, so it seems, desperately wanted
nuclear subs themselves. It's very likely, that Russian cooperation made the project possible.
It's namely very difficult to develop a compact reaktor for such a ship, and integrate it with all the interfacing to
for example to propulsion etc.. etc.. A nation with extensive experience might pull it off.

Warning: the alinea above might contain "coloured" or biased information.

The "Arihant class" is likely to have a number (8?) of K15 ballistic missiles, but with a limited range,
in the order of 1000km.
The K15 ballistic missile, is believed to carry a nuclear warhead, but information on type and explosive power
is rather unclear.
Since India is also rather active in development of missiles, the sub might also be equipped with K4 missiles
having a very serious range of over 3000km.

It's very well possible, that presently nuclear warheads are not mounted (yet), in normal operation
of this class of subs. It's might be that more tests are needed.

In "lease" is also an advanced nuclear powered Russian Attack sub, with a multitude of torpedoes and cruise missiles.
A lease sounds remarkable, but the Russian Akula class was partly financed by India.

1.1.7. Older submarines:

There is a rather wide range of conventional Attack subs, of Russian origin.
Most of them, are equipped with anti-vessl cruise missiles and various torpedo systems.

Green Navy:

1.1.8. A very large mix of green fleet:

There exists nummerous vessels for costal operations, patrol- and attack, and landing operations.
Among them, a series of Corvettes is present, but it seems fair to categorize them in the green fleet too.

1.1.9. Conclusions:

One should always be very careful in making conclusions, but certain facts seem to point towards to:

Conclusion 1:
Presently, Naval Nuclear striking capabilities seem to exist only in the nuclear subs, as mentioned in 1.1.6.

Conclusion 2:
There seems to exist a strong commitment in enhancing Naval nuclear striking capability.

Warning: These statements might be flawed or biased.

1.2 Missiles:

At November 2008, the Moon Probe "Chandrayaan-1" struck the south pole of the Moon. It was a rather controlled manouvre.
India used the PSLV-XL rocket, to accomplish this. This rocket, 44m length, and having a max payload of 3800kg for a
Low Earth Orbith (LEO), is serious business.

The PSLV rocket series, was at least launched 40 times, at the time of this writing.

By the way, the whole Spaceprogram of India, is serious business.
There exists a whole list of scientific explorations, for the near future.

Planned for december 2017,is India's first full private mission to the moon by Team "Indus".
It seems (for now) that more than one rovers (from Japan and one of Team Indus) will perform explorations.

This is science. But the missile technology, or India's technology in general, surely is impressive.
Scientific purposes are often different from military objectives. However, unfortunately, science and the military,
are sometimes "pretty close".

1.3 Army & Airforces:

1.4 Reactors:

1.5 Imports / Exports as far as is known:

1.6 Possible Conflict area's:

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