Question

A nucleus Pu emits an alpha particle and changes to U, which emits a beta particle and then a gamma particle to change into \[\ce{^235_93Np}\]. Write the above nuclear changes in the form of an equation stating the atomic number and mass number of each nucleus.

Answer 1

By tracing the decay steps backward from the final product\[\ce{^235_93Np}\]:

1. Gamma emission (γ) does not change the mass or atomic number, so the precursor was also mass 235 and atomic number 93.
2. Beta emission (β) increases the atomic number by 1 while mass stays the same. Working backward, the nucleus U has an atomic number of 93 − 1 = 92 and a mass number of 235.
3. Alpha emission (α) decreases mass by 4 and atomic number by 2. Working backward, the original nucleus Pu has a mass number of 235 + 4 = 239 and an atomic number of 92 + 2 = 94.

Complete Nuclear Equations:

\[\ce{^239_94Pu ->[\alpha-decay] ^235_92U + ^4_2He}\]

\[\ce{^235_92U ->[\beta-decay] ^235_93Np + ^0_{-1}e}\]

\[\ce{^235_93Np ->[\gamma-decay] ^235_93Np + gamma}\]