Re: AW: Bismuth breaks half-life record

[BERNARD L COHEN <blc+@PITT.EDU>]

On Mon, 28 Apr 2003, Franz Schoenhofer wrote:

>

> 	--Every nucleus with mass above about 100 can decay by spontaneous

> fission. This is indisputable, just from measured masses.

>

> I cannot believe, that you are serious!!! Has it ever been observed that

> Cs-137, I-131, the stable isotopes of Cs, I, Hg, Cd, W, Rare Earths, Au, Pt,

> Ba, Ag etc etc decay by spontaneous fission???? I dispute it and you will

> hardly find anybody having common sense, who will not dispute it.



	--I did not say that the decay has been observed, only that it

must occur with some long half life. You can easily check this by

comparing the mass of the original nucleus with the sum of the masses of

the two fragments into which it would split; if the latter is smaller, the

decay can occur. No nuclear physicist would question this.

	As you well know, the binding energy per nucleon peaks at about

mass 60, so more binding energy per nucleon is obviously achieved if a

nucleus splits in half. Some correction is needed for the fact that the

product nucleus is off the line of stability, but this is relatively

small.

	As an example, using masses from Radiological Health Handbook, as

follows: Cd-112 has mass 111.9028; if it splits in half, the remains are

two nuclei of Cr-56 which have masses of 55.9046, so their combined mass

is 111.8812. Thus, 111.9028 - 111.8812 mass units are available as energy

release in the decay; this is 0.0216 atomic mass units, or about 20 MeV of

energy release. This decay is prohibited only by the Coulomb barrier,

which is what makes spontaneous fission so rare in uranium even though

uranium fission releases about 200 MeV.



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