1. Hydrogen exists as three isotopes, with 0, 1 and 2 neutrons. Deuterium is used as a nuclear fusion fuel and in H-bombs, and tritium is a radioactive isotope useful in biochemical tracing. Fill in the following table to describe their nuclei.

    Name

    Neutrons

    Atomic number (Z)

    Atomic mass (A)

    Symbol

    Protium (H)

    0

    1

    1

    1H

    Deuterium (D)

    1

    1

    2

    2H

    Tritium (T)

    2

    1

    3

    3H
  2. 238U is a very large nucleus, and is unstable because the short-range of the strong force cannot hold together electrically repulsive protons when they are so far separated. Consequently, the nucleus preferentially decays by losing mass, reducing the size of the nucleus, and hence the electrical repulsion of the protons. 14C decays by β emission because it is a very light nucleus, with an excess of neutrons. These loosely-bound neutrons at the top of the nucleon 'stack' can decay to lower energy bound protons by the emission of an electron (and an antielectron neutrino).