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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: Maxwell who wrote (39121)	10/13/1998 1:20:00 AM
From: Paul Engel	Read Replies (2) \| Respond to of 1572389

Maxwell - Re: "So why was Uranium 235 was used instead of Uranium 238 even though Uranium 238 is more abundant than Uranium 235? This question is most often asked and few ever get it right. " There are basically two reasons. 1. U238 will result in fission ONLY with FAST Neutrons with energy above 1 MeV. U235 will fission when bombarded with slow neutrons (a few KeV) as well as fast neutrons and any neutrons in between. The use of slow neutrons makes U235 amenable to CONTROLLED nuclear fission because slow neutrons ( a few KeV) can easily be moderated (i.e., absorbed or removed from the reaction chain) for controlling the sustained nuclear reaction. Fast neutrons are "too hot too handle". 2. When U238 fissions, it captures a neutron and becomes U239. The number of neutrons in the nucleus changes from even to odd. However, when U235 fissions to U236, its nucleus also captures a neutron but the nucleus changes from an ODD number of neutrons to an EVEN number of neutrons. This Odd-To-Even change in the number of neutrons in the nucleus of U236 releases 1 or 2 MeV of energy via nuclear reactions, giving U235 a built in energy advantage, which could also result in the eventual co-generation of heat - for power generation. Paul