Well i suppose u know the concept of a nuclear fission. Well then on those grounds let me brush a few basics.The basic fission reaction that occurs in a nuclear explosion involves
(Neutron) + (Fissionable Isotope of large atom) → (Isotope of medium sized atom) + (Isotope of medium sized atom) + 3 or 4 (Neutron)
For a nuclear explosion to occur, the average number of the product neutrons that trigger another reaction needs to be greater than 1.
There are several things that can happen to neutrons that are produced as a product of a fission reaction
(1) They can move out of the region where the fissionable material is
(2) They can be absorbed by atoms other than the fissionable ones
(3) They are usually very fast moving -- they can bounce around off other atoms a bit and gradually get slowed down, OR
(4) If conditions are just right, they can collide with another fissionable atom, and produce another fission reaction.
If each reaction produces, say, 3.5 neutrons out for each neutron in, then there will only be a nuclear explosion if about 30% or more of those neutrons trigger another fission.
With a small lump of fissionable material, you will not get a nuclear hand grenade, Nearly all of the neutrons will travel straight out of the lump, maybe having a few collisions and warming things up, but more than 90% will take route (1) above.
For a medium size lump, routes (2) and (3) become more important. The lump will probably melt and make a bit of a mess, but not an explosion.
Quite a sizable lump of material is required for there to be any chance of an explosion. The actual size needed depends on shape and purity, but for a 100% pure sphere of fissionable material there is a "critical mass" (you may be able to find how much on the web -- I think it is somewhere in the region of 10-15 kg) required.
Now let's take 10Kg for the sake of discussion. I have not added to it the wight of firing mechanisms, shielding [Yup weapons too have shielding], safeguards and redundancies. So the question arises, what weight should a small self contained nuke weigh? Smallest, that can make a impact, 100 kg but it used ~100% enriched U235 and 350kg with abt 98.3% enrichment.
So at last, how much can Nasr carry as a warhead ? Sadly just 50kg.
So I suppose Pakistan are producing Californium-251 (cost of production $10,000,000 Per gram) for the warheads for Nasr ?
Pls shed some light on the topic
(1). Type of Fission material ?
(2). Fission material weight ?