Question

Some uranium samples from the natural reactor site described in Module 43-3 were found to be slightly enrichedin ${\mathbf{}}^{\mathbf{235}}\mathbf{U}$, rather than depleted. Account for this in terms of neutron absorption by the abundant isotope ${\mathbf{}}^{\mathbf{238}}\mathbf{U}$and the subsequent beta and alpha decay of its products.

Short answer

The neutron absorption by the abundant isotope of ${}^{238}\mathrm{U}$is substantially increased resulting in a faster decay rate for the beta and alpha processes.

Step-by-step solution

Write the given data

Some uranium samples from the natural reactor site were described in Module 43-3.

Determine the concept of enrichment of an isotope

An isotope of a radionuclide is defined as enriched or abundant relating to various factors that occur in their beta or alpha decay processes. The availability of higher neutrons causes the fission reaction of a radionuclide resulting in their decay and thus, it causes their decay rate to be faster than others. Thus, a nuclide with faster decay is depleted by neutrons while a lower decay rate describes enrichment in the nuclide's nuclei number.

Calculate the neutron absorption by the uranium-238 isotope

The nuclei of${}^{238}\mathrm{U}$can capture neutrons and beta-decay. With a large amount of neutrons available due to the fission of ${}^{235}\mathrm{U}$, the probability for this process is substantially increased, resulting in a much higher decay rate for${}^{238}\mathrm{U}$and causing the depletion of${}^{238}\mathrm{U}$(and relative enrichment of ${}^{235}\mathrm{U}$).

Hence, the neutron absorption by the abundant isotope of ${}^{238}\mathrm{U}$is substantially increased resulting in a faster decay rate for the beta and alpha processes.