A possible nuclear fission equation is $^{235}_{92}\text{U} + ^{1}_{0}\text{n} \rightarrow ^{141}_{56}\text{Ba} + ^{92}_{36}\text{Kr} + 3^{1}_{0}\text{n} + \text{energy}$. Barium-141 ($^{141}_{56}\text{Ba}$) together with krypton-92 ($^{92}_{36}\text{Kr}$) are both $\beta$-emitters. Barium-141 has a half-life of 18 minutes and a decay constant of $6.4 \times 10^{-4}\,\text{s}^{-1}$. Krypton-92 has a half-life of 3.0 seconds.
(a)[2]
State what the term decay constant means.
(b(i))[2]
A $1.2\,\text{g}$ sample of uranium-235 undergoes this nuclear reaction in a very short time (a few nanoseconds). Calculate the number of barium-141 nuclei present immediately after the reaction has finished.
(b(ii))[4]
Using your answer to (b)(i), calculate the total activity of the barium-141 and the krypton-92 at $1.0\,\text{hours}$ after the fission reaction has taken place.
(b)
A $1.2\,\text{g}$ sample of uranium-235 undergoes this nuclear reaction in a very short time (a few nanoseconds).
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Probability that a nucleus decays per unit time / fraction of nuclei decaying per unit time” …