Aluminium-26 decays into an isotope of magnesium (Mg) by ${\beta ^ + }$ decay.

$$_{{\text{13}}}^{{\text{26}}}{\text{Al}} \to _{\text{Y}}^{\text{X}}{\text{Mg}} + {\beta ^ + } + {\text{Z}}$$

Identify X, Y and Z in this nuclear decay process.

X:

Y:

Z:

Explain why the beta particles emitted from the aluminium-26 have a continuous range of energies.

State what is meant by half-life.

A meteorite which has just fallen to Earth has an activity of 36.8 Bq. A second meteorite of the same mass, which arrived some time ago, has an activity of 11.2 Bq. Determine, in years, the time since the second meteorite arrived on Earth.

X: 26 and Y: 12; (both needed for [1])

Z: v/neutrino;

Do not allow the antineutrino.

total energy released is fixed;

neutrino carries some of this energy;

(leaving the beta particle with a range of energies)

the time taken for half the radioactive nuclides to decay / the time taken for the activity to decrease to half its initial value;

Do not allow reference to change in weight.

$\lambda  = \left( {\frac{{\ln 2}}{{7.2 \times {{10}^5}}} = } \right){\text{ }}9.63 \times {10^{ - 7}}$;

$11.2 = 36.8{e^{ - (9.63 \times {{10}^{ - 7}})t}}$;

$t = 1.24 \times {10^6}{\text{ (yr)}}$;

This was generally well answered, although a significant minority insisted that nuclear half-life is defined by a loss of mass.

This was generally well answered, although a significant minority insisted that nuclear half-life is defined by a loss of mass.

This was generally well answered, although a significant minority insisted that nuclear half-life is defined by a loss of mass.

This was generally well answered, although a significant minority insisted that nuclear half-life is defined by a loss of mass.