This question is about the nucleus of uranium- $235\left({}_{92}{}^{235}\mathrm{U}\right)$, which has a mass of $3.89\times {10}^{-25} \mathrm{kg}$.

(b) The radius r of a nucleus is given by the equation:

$r=1.41\times {10}^{-15}{A}^{\frac{1}{3}}$

where A is the nucleon number of the nucleus.

Calculate the density of the ${}_{92}{}^{235}\mathrm{U}$ nucleus.

This question is about the nucleus of uranium- $235\left({}_{92}{}^{235}\mathrm{U}\right)$, which has a mass of $3.89\times {10}^{-25} \mathrm{kg}$.

(c) Explain why the total mass of the nucleons is different from the mass of the $\mathrm{U}$ nucleus.

This question is about the nucleus of uranium- $235\left({}_{92}{}^{235}\mathrm{U}\right)$, which has a mass of $3.89\times {10}^{-25} \mathrm{kg}$.

(d) Without calculations, explain how you can determine the binding energy per nucleon for the uranium-235 nucleus from its mass and the masses of a proton and a neutron.

(b) The main reactions that fuel the Sun are the fusion of hydrogen nuclides to form helium nuclides. However, other reactions do occur. In one such reaction, known as the triple alpha process, three helium nuclei collide and fuse to form a carbon-12 nucleus.

(i)Explain why temperatures higher than those required for the fusion of hydrogen are needed for the triple alpha process?

(b) The main reactions that fuel the Sun are the fusion of hydrogen nuclides to form helium nuclides. However, other reactions do occur. In one such reaction, known as the triple alpha process, three helium nuclei collide and fuse to form a carbon-12 nucleus.

(ii) Calculate the energy released in the triple alpha process.

The isotope of polonium, ${}_{81}^{218}\mathrm{Po}$, decays by the emission of an $\alpha$ -particle with a half-life of $183 \mathrm{s}$.

(a) In an accident at a reprocessing plant some of this isotope, in the form of dust, is released into the atmosphere. Explain why a spillage in the form of a dust is far more dangerous to health than a liquid spillage.

The isotope of polonium, ${}_{81}^{218}\mathrm{Po}$, decays by the emission of an $\alpha$ -particle with a half-life of $183 \mathrm{s}$.

(b) It is calculated that $2.4 \mathrm{g}$ of the isotope is released into the atmosphere. The molar mass of polonium is $218 \mathrm{g}{ \mathrm{mol}}^{-1}$. Calculate the initial activity of the released polonium.

Avogadro's number $=6.63\times {10}^{21}$

The isotope of polonium, ${}_{81}^{218}\mathrm{Po}$, decays by the emission of an $\alpha$ -particle with a half-life of $183 \mathrm{s}$.

(c) It is felt that it would safe to re-enter the laboratory when the activity falls to background, about $10 \mathrm{Bq}$. Calculate how many hours must pass before it is safe to re-enter the laboratory.