Describe what is meant by

(i) radioactive decay.

(ii) nuclear fusion.

Tritium is a radioactive nuclide with a half-life of 4500 days. It decays to an isotope of helium.

Determine the time taken for 90% of a sample of tritium to decay.

A nuclide of deuterium $\left( {{}_1^2{\rm{H}}} \right)$ and a nuclide of tritium $\left( {{}_1^3{\rm{H}}} \right)$ undergo nuclear fusion. The reaction equation for this process is

$${}_1^2{\rm{H + }}{}_1^3{\rm{H}} \to {}_2^4{\rm{He + X}}$$

Identify X.

(i) refers to unstable nucleus/isotope / refers to spontaneous/random process;
which emits named radiation (from nucleus) / forms different nucleus/isotope;

(ii) combination of two nuclei / OWTTE; (do not allow “particles” or “atoms”)
to form new nuclide with greater mass/larger nucleus/greater number of nucleons;

$\lambda  = \frac{{\ln 2}}{{4500}}\left( { = 1.54 \times {{10}^{ - 4}}} \right)$;
$0.1{N_0} = {N_0}{{\rm{e}}^{ - 1.54 \times {{10}^{ - 4}}t}}$;
1.5×10⁴(d) or 1.3×10⁹(s);
Award [2 max] if answer is time to lose 10% (680 d).
Allow answer to be expressed in any time units.
Award [3] for a bald correct answer.

or

$\ln 0.1 = \frac{{ - 0.69t}}{{{t_{\frac{1}{2}}}}}$;
t=3.3×4500;
1.5×10⁴(d);
Award [2 max] if answer is time to lose 10% (680 d).
Allow answer to be expressed in any time units.
Award [3] for a bald correct answer.

${}_0^1n$/neutron;