CIE iGCSE Co-Ordinated Science P5.2.3 Radioactive decay Exam Style Questions Paper 4
Question
Tritium ($_{3}^{1}\textrm{H}$) is an isotope of hydrogen.
(a) Tritium decays by beta (β) emission.
(i) Use correct nuclide notation to complete the decay equation for tritium.
$_{1}^{3}\textrm{H}\to He +\beta $
(ii) The half‐life of tritium is 12.3 years.
Calculate the time taken, in years, for 87.5% of a sample of tritium to decay.
time = ……………………………………….. years
(b) A beta particle is emitted from a tritium nucleus with a speed of 2.0 × 10$^{8}$m/ s and a kinetic energy of 1.8 × 10$^{-14}$ J.
(i) Calculate the distance travelled by the beta particle in 3.5 × 10$^{-10}$ s.
distance = …………………………………………….. m
(ii) Calculate the mass of the beta particle.
mass = ……………………………………………. kg
▶️Answer/Explanation
Ans :
9(a)(i)
$_{3}^{1}\textrm{H}{\rightarrow}_{3}^{2}\textrm{He}+_{0}^{-1}\textrm{β} $
1 mark for correct nucleon number for He ;
1 mark for correct proton number for He ;
1 mark for correct beta particle ;
9(a)(ii) reference to 3 half-lives or 12.3 × 3 ;
36.9 (years) ;
9(b)(i) (d =) v × t or 2.0 × 10$^{8}$ × 3.5 × 10$^{-10}$ ;
(d =) 0.070 (m) ;
9(b)(ii)
evidence of KE = 1⁄2 mv$^{2}$ or $\frac{(2\times1.8\times 10^{-14} )}{(20)\times 10^{8})2}4;
9.0 × 10$^{-31}$ (kg)