Radioactivity | OCR GCSE Physics A, Higher tier (J249)

Radioactivity

139 questions
9 subtopics
Paper 4
Paper 4

Radioactivity is examined in Physics A Paper 4.

It covers protons, neutrons and isotopes, unstable nuclei and the emissions they give out, balancing nuclear equations, electron energy levels, and radiation from atoms, half-life and the randomness of decay, penetration of alpha, beta and gamma, contamination and irradiation, and half-life as a hazard, uses of nuclear radiation and nuclear fission and fusion.

Sample questions from Radioactivity

Answer each one closed book first, then open the answer.

Protons, neutrons and isotopes

What is an isotope?

Show the answer
An isotope is an atom of an element that has the usual number of protons but a different number of neutrons.
Unstable nuclei and the emissions they give out

What is the charge on an alpha particle?

Show the answer
It has a charge of +2, because it carries two protons and no electrons.
Balancing nuclear equations

Which two totals must be the same on both sides of a nuclear decay equation?

Show the answer
The total mass number and the total charge must be the same on each side.
Electron energy levels, and radiation from atoms

What charge does an atom have once it has lost an outer electron?

Show the answer
It has a positive charge, because it then has more protons than electrons.
Half-life and the randomness of decay

Does the half-life of a source change as more and more of its nuclei decay away?

Show the answer
No, the half-life stays the same throughout, even though the number of undecayed nuclei is falling.
Penetration of alpha, beta and gamma

Which of the three radiations is the most penetrating?

Show the answer
Gamma radiation is the most penetrating.
Contamination and irradiation, and half-life as a hazard

Why is a gamma source the greater hazard when it is outside the body?

Show the answer
Gamma radiation is very penetrating, so it passes through skin and reaches organs deep inside.
Uses of nuclear radiation

How is the radiation from a tracer detected once it has been given to a patient?

Show the answer
A detector or camera outside the body picks up the gamma radiation and builds a picture of where the tracer has collected.

The 9 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Protons, neutrons and isotopes	The particles in a nucleus and their charges and masses, what nucleons are, what an isotope is, and how mass number and atomic number give the neutron count and nuclear charge.	21
Unstable nuclei and the emissions they give out	Why unstable nuclei emit radiation, what alpha and beta particles, gamma rays and neutrons are and the charge each carries, and how the mass number and atomic number change with each emission, including why beta emission leaves the mass number unchanged.	16
Balancing nuclear equations	How alpha, beta, gamma, neutrons and protons are written in decay equations, which totals must balance, and worked examples for radium, carbon, uranium, polonium and iodine decays.	16
Electron energy levels, and radiation from atoms	Electrons in energy levels, excitation by absorbing radiation and emission on falling back, ionisation and the positive ion it leaves, the wide range of frequencies atoms and nuclei emit, gamma rays from the nucleus, the spectrum in order of frequency, and what sets the frequency emitted.	16
Half-life and the randomness of decay	Half-life in terms of nuclei and count rate, why decay is random yet a sample has a reliable half-life, finding a half-life from count rates and graphs, the net decline in activity as a ratio after several half-lives, activity calculations, and modelling decay with dice.	18
Penetration of alpha, beta and gamma	What absorbs alpha, beta and gamma radiation, which is most and least penetrating, which ionises most strongly, how far each travels in air, and reading absorption tests.	10
Contamination and irradiation, and half-life as a hazard	Irradiation and contamination and which is the greater long-term hazard, why alpha is most dangerous inside the body and gamma outside it, reducing exposure and avoiding contamination, and why sources with long or short half-lives are hazards in medicine, nuclear waste, spills and smoke alarms.	16
Uses of nuclear radiation	Medical tracers, why gamma emitters suit them and alpha emitters do not, how a tracer is detected and used to check the thyroid, radiotherapy with external beams from several directions and with implanted sources, and why the dose must be controlled carefully.	10
Nuclear fission and fusion	Nuclear fission, the neutron that starts it and what it releases, chain reactions and how control rods keep them steady, uranium and plutonium fuels, fusion in stars and the mass converted to energy, why fusion needs extreme conditions, and how fission and fusion differ.	16

Radioactivity is 139 of the 1,584 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.