Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 4

An alpha decay decreases mass number by four and atomic number by two; a beta-minus decay keeps the mass number fixed and increases atomic number by one. ThereforeThe beta-minus step converts a neutron to a proton with emission of an electron and an electron antineutrino. It is not capture of an orbital electron, which would change the atomic number in the opposite direction.

Radiation changes the solution's chemistry by radiolysis; it does not turn Am(VI) nuclei into Am(V) nuclei. An emitted alpha particle deposits energy into many water and solute molecules, generating ionized/excited species, hydrated electrons, hydrogen atoms and molecular products including hydrogen peroxide. Reducing products can supply the electron needed forFor example, hydrogen peroxide can be oxidized while reducing two americyl(VI) ions:The $0.3$ mM loss of Am(VI) equals the $0.3$ mM appearance of Am(V), preserving the measured dissolved americium total while transferring $0.3\mathrm{mmol}{\mathrm{L}}^{-1}$ of electron equivalents. Oxidizing radiolysis products are also present, and the net reduction depends on acid, dissolved gases and scavengers; not every radiolytic event is reducing. In nitric acid, primary kinetic work identifies hydrogen peroxide and radiolytically produced nitrous acid as important reductants, with a rate controlled by total americium activity rather than necessarily by the instantaneous Am(VI) concentration.^[ref]