aton, In the fission bomb, ttre process involved. 1s the spli.tting of uraniun or plutonium nucl"ei into lighter fragments, fission Products. fn a thermonucl-ear or hydrogeD bomb, nuclei of heavy hydTogen isotopes - deuterium and tritiun - *re irr".d together at the very high terrperatures triggered through the fission I)rocess. 13. Th€ speed of the uuclear reactions is enormous. Both in a fission and a fusion explosive, the eotire nuclear ener8-y is released in about one millionth of a second. with todayts technique, it is tbus possible to release by one weapon nol'e energy in one microsecond than that fron all conventional veapons in al-l wars of history. Ifl:i1::' 5-nnez a' . i_L l-4. In order to sustain the chain reaction in a fission explosion" it i.s necessarJ- lo have more than a certain minimurn anount of fissile naterial, thecritical nass. This nass depends ulon the purity and d.ensity of the material,its leor.etrical- shape: the possible presence of neutron reflectin5 nateriols a.r:jother factors. The fissile material has to be brought together very quickly ifthe l,'eapon is to explode rrith great force. Conwentional expfosives are used fot:this prrrpose and the fissile rrraterial put together, with or vithout compression,to a size vhich, fo} a plutonium bomb, needs to be no larger in volume than a marl sfist. At this tine the chain reaction is inj.tiated. The 1968 United liations stud.r on nuclearweapons (see para. 4 above) set 8 hg. of plutonium containing !0 to 95 per cent of llutonj.um-239 and 25 kg. of highly enriched uranium-235 a: thc amcunts necessary to achieve an explosion with a yield correspcnding to 20 kt. of high explosive. Depending on the design sophistication and r,rith hinh quality t-alerial , this nass can range from It to 25 kg. for uranium 235 and fxon )r to C lS-for plutonium.-239. 1/
**Analysis**
The text appears to be a technical description of nuclear weapons, discussing the process of fission and fusion reactions, the critical mass of fissile materials, and the design of nuclear explosives. The language used is formal and scientific, suggesting a technical or academic context. The text does not mention economic, social, or environmental impacts, but rather focuses on the physical and technical aspects of nuclear weapons.

**Category**
Science and technology