Nuclear Physics

Beta is produced by the weak nuclear force.

• n --> p + e- + v, decay to electron & antineutrino
• p --> n + e+ + v, decay to positron & neutrino

The leptons do not preexist in the nucleus, their wavelength would be too long for that.

I think you are confused when you say "contain no elements". No nucleus contains elements, the nucleus is part of an atom and atoms are part of elements & compounds.

Perhaps you meant to say "contain no electrons". If so you are right, see above. The leptons (electron, positron, neutrinos) are created by a decay process mediated by the weak nuclear force.

Yes, absolutely. Los Alamos had many ideas even before the war ended for improvements on the two rather primitive atomic bombs used during the war. Had the Japanese not surrendered the first of these (composite plutonium/uranium core) would have gone into production and use in the bombs scheduled for November 1945.

Immediately after the war ended activity was scaled back at all Manhattan Project sites, but work did not stop on improvements. The first new atomic bomb, the MK-4 entered the stockpile in 1949 and incorporated the following improvements:

• Factory assembled (the earlier bombs were delivered in kits requiring field assembly)
• Interchangeable parts (the earlier bombs used custom hand fitted parts that were not interchangeable)
• In Flight Insertion of nuclear core (the earlier bombs were designed for insertion on the ground before takeoff)
• Composite plutonium/uranium core
• Levitated-pit core
• Variable yield by a selection of different pits (1 kt, 3.5 kt, 8 kt, 14 kt, 21 kt, 22 kt, or 31 kt)
• Battery that could could be replaced without requiring complete disassembly of the bomb (as was required in the MK-III)
• Improved fin structure
• Internal RADAR antennas in the flat nose (the earlier bombs used external RADAR antennas that were easily damaged)

Additional improvements incorporated in later bombs:

• External electronic pulsed neutron sources that could be precisely timed to fire when the core is optimally supercritical to get the best and more repeatable yield (earlier bombs used an internal mechanically pulsed neutron source triggered when crushed by the shock wave from the chemical explosives and also had to be replaced roughly twice a year making both maintenance and stockpiling complicated)
• Variable yield by injection of deuterium and/or tritium gas into the pit (physically changing the pit was no longer required)
• 64 lens and 92 lens chemical explosive systems to produce a more smooth implosion shockwave than the original 32 lens system
• Many improvements in batteries, ultimately resulting in batteries that were installed once at the factory and never needed either maintenance or replacement
• Advanced fusing systems suitable for different targets: surface burst, delayed surface burst, depth charge, ground penetration, antitank mines, etc. (earlier bombs were all fused for optimal damage airburst and could not be changed)
• Weight and size reductions, permitting use of different delivery vehicles, not just large bomber airplanes (e.g. fighter airplanes, torpedoes, ballistic missiles, artillery pieces, even a man carried backpack for special forces use)
• Multi-staging radiation implosion, essential to the hydrogen fusion bomb but originally worked on as a possible means of making fission bombs of very high yield (perhaps breaking the 1 Mt theoretical yield limit for a pure fission bomb)
• Development of "single-point safe" implosion designs that could not produce any nuclear yield if only one explosive lens was detonated
• Use of more stable chemical explosives that could not detonate when exposed to fire or mechanical shocks
• Use of machinable chemical explosives, permitting more precise manufacture of the explosive lenses (earlier bombs used explosives that had to be melted and cast in molds; which was hazardous, hard to maintain precision, and often left bubbles in the casting causing a high rejection rate)
• etc.