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Name: Bob B.
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: Thursday, August 22, 2002


Question:
Does the decay rate of U238 vary with temperature and pressure?


Replies:
Not significantly. U238 decays by emitting an alpha particle (a helium nucleus). The decay rate is determined almost entirely by the environment in the nucleus. Temperature and pressure changes that we are capable of making affect the electron cloud and do not affect the nucleus.

Maybe the sorts of temperatures and pressures you could get in a fusion reactor would measurably affect the decay rate, but I doubt it.

Tim Mooney


No.

Richard E. Barrans Jr., Ph.D.
Director of Academic Programs
PG Research Foundation, Darien, Illinois


Radioactive decay is a nuclear process. The rate of fission (in the case of U238 as well as other decays is proportional to the concentration of nuclei. So the rate will change slightly with large changes in the temperature and pressure because the volume of the fissionable material increases with increasing pressure and decreasing temperature. However, this is a minor effect if the concentration of nuclei is significantly less than the so-called critical mass.

When the concentration of nuclei reaches the critical mass, the decay events produce sufficient neutrons to cause a chain reaction, i.e. the neutrons strike other nuclei causing them to decay, which produces more neutrons which cause other nuclei to decay,......

This is what happens in an atomic bomb, and under more controlled conditions in a nuclear reactor. You can find this discussed in lay terms in the book: "The Making of the Atomic Bomb" by Richard Rhodes.

However, the temperatures and pressures that can be obtained with standard equipment do not affect the rate of radioactive decay. What happens in stars etc. where enormous pressures are generated is also excluded.

Vince Calder


Bob,

So far as is known, decay rates of radioactive elements are constant and independent of the conditions about which you ask. If decay rates were found to be temp/pressure dependent, a good deal of geologic dating work would be rendered meaningless.

Regards,
ProfHoff 450



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