Re: U236 and long half life

Rex,

The answer to your puzzlement is the hidden parts of the descriptions that you might find in the explanation booklet that comes with the General Electric Chart of the Nuclides or a text on Nuclear and Radiochemistry. There are a couple of internet references at the bottom of this message that talk about the fission process, giving the energetics of the fission process.

The half life given in tables of nuclei refer to the ground state of the nucleus, the most stable state of the nucleus. The ground state almost always has the longest half life of all states possible for that nuclide. In this case, that is the millions-of-years half life for U-236 that is given in tables of nuclides.

What happens in the reaction U-235 + n ==> U-236 is that the initial U- 236 nucleus is formed in an excited state, sometimes designated as U-236*. The energy comes from the kinetic energy of the neutron plus the energy gained when the neutron "binds" to the nucleus (no matter how long this lasts). While most excited nuclei decay by alpha, beta, or gamma radiation, some, such as U-236*, have other pathways--in this case fission is the most probable decay when U-236* is formed by U-235 + n.

http://www.users.bigpond.com/Sinclair/fission/Fission5.html

http://library.thinkquest.org/17940/texts/fission/fission.html

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fission.html