Nuclear Fission & Fusion (OCR A Level Physics)

A researcher is doing an experiment on a radioactive solution in a thin glass tube. The solution has two radioactive materials X and Y. The table below shows some data on these two materials.

The solution has the same number of nuclei of X and Y at the start.

i) State and explain which material has the greatest activity at the start.

[1]

ii) State why it is dangerous for the researcher to handle the test tube with bare hands.

[1]

Carbon-14 is produced in the upper atmosphere of the Earth by collisions between nitrogen nuclei and fast-moving neutrons. The nuclear transformation equation below shows the formation of a single carbon-14 nucleus.

i) State the proton number of particle X.

proton number = .......................................................... [1]

ii) Use the data below to determine the binding energy per nucleon of the 146C nucleus.

Write your answer to 3 significant figures.

• mass of neutron = 1.675 × 10^–27 kg

• mass of proton = 1.673 × 10^–27 kg

• mass of nucleus = 14.000 u

• 1 u = 1.66 × 10^–27 kg

binding energy per nucleon = ................................... J per nucleon [4]

Fig. 21 shows stable and unstable nuclei of some light elements plotted on a grid. This grid has number of neutrons N on the vertical axis and number of protons Z on the horizontal axis.

Fig. 21

The key on Fig. 21 shows whether a nucleus is stable, emits a beta-plus particle or emits a beta-minus particle to become stable. For Z = 7, suggest in terms of N why an isotope may emit

i) a beta-minus particle [1]

ii) a beta-plus particle. [1]

Inside a nuclear reactor, fission reactions are controlled and chain reactions are prevented. A typical fission reaction of the uranium-235 nucleus () is illustrated below.

The neutron triggering the fission reaction moves slowly. The neutrons produced in the fission reaction move fast.

i) Describe what is meant by chain reaction.

[2]

ii) Explain how chain reactions are prevented inside a nuclear reactor.

[2]

iii) The energy released in each fission reaction is equivalent to a decrease in mass of 0.19u.

A fuel rod in a nuclear reactor contains 3.0% of uranium-235 by mass. Estimate the total energy produced from 1.0 kg of fuel rod. molar mass of uranium-235 = 0.235 kg mol^–1 1u = 1.66 × 10^–27 kg

energy = .......................................... J  [4]

Stars produce energy by nuclear fusion. One particular fusion reaction between two protons () is shown below.

In this reaction 2.2 MeV of energy is released.

Only one of the particles shown in the reaction has binding energy. Determine the binding energy per nucleon of this particle. Explain your answer.

[2]

Explain why high temperatures are necessary for fusion reactions to occur in stars.

[2]

A gamma photon in a star can spontaneously create an electron-positron pair. Calculate the maximum wavelength of a gamma photon for this creation event.

maximum wavelength = ......................................... m [3]