Two isotopes of iodine are $^{125}_{53}I$ and $^{131}_{53}I$ - AQA - A-Level Physics - Question 1 - 2019 - Paper 1

The xenon nuclide formed from the beta ($\beta$) decay of iodine-131 has a nucleon number of 131, since beta decay does not change the nucleon count. This means that the nucleon number remains the same after the decay.

The iodine-125 nucleus has 53 protons and 72 neutrons, while the resulting tellurium nucleus after electron capture has:

• 52 protons (since one proton in iodine is transformed into a neutron)
• 73 neutrons (one additional neutron is formed)

Thus, the differences are:

1. The tellurium nucleus has one fewer proton than the iodine nucleus.
2. The tellurium nucleus has one more neutron than the iodine nucleus.

1. Energy Release:

   • Internal conversion involves the ejection of an electron from an atom when a nucleus in an excited state releases excess energy, without emitting a particle directly from the nucleus. In contrast, beta decay involves the transformation of a neutron into a proton or vice versa, emitting a beta particle (electron or positron) and an antineutrino.

2. Particle Emission:

   • During internal conversion, only an electron is released from the atom, while in beta decay, both a beta particle (electron or positron) and an antineutrino are released.

3. Change in Nucleus:

   • Internal conversion does not change the composition of the nucleus, whereas beta decay alters the number of protons and neutrons, resulting in a different element.