IGCSE Physics Nuclear physics topical questions

Answer these atom-counting questions for the nuclide ¹⁹₉F.

1. (a)State the proton number of fluorine.[1]
2. (b)State the nucleon number of fluorine-19.[1]
3. (c)Calculate the number of neutrons in the nucleus.[1]

Match each radiation to one property.

1. (a)Which radiation is stopped by a few millimetres of aluminium?[1]
2. (b)Which radiation is an electromagnetic wave?[1]
3. (c)Which radiation is a helium nucleus?[1]

A Geiger counter near a rocky area records 74 counts per minute with no source present.

1. (a)State the name for this radiation the counter picks up with no source.[1]
2. (b)Name two of its sources.[2]

A lithium atom contains 3 protons, 4 neutrons and 3 electrons.

1. (a)State the nucleon number of this lithium atom.[1]
2. (b)State the charge of the nucleus, including its sign.[1]
3. (c)Explain why the whole atom is uncharged.[2]

The nuclide ²¹⁴₈₂Pb decays by beta emission to form bismuth (Bi, Z = 83).

1. (a)State the nucleon number and proton number of the bismuth nucleus formed.[2]
2. (b)Write the full decay equation in nuclide notation.[2]

A sample of a radioactive isotope has an initial corrected count rate of 960 counts/s. Its half-life is 15 minutes.

1. (a)Calculate the count rate after 45 minutes.[2]
2. (b)Calculate how long it takes the count rate to fall to 15 counts/s.[3]

A radioactive source is placed in front of a detector. With no absorber the count rate is 500 counts/s. With a sheet of paper the rate is unchanged. With 5 mm of aluminium the rate falls to 60 counts/s. With 5 cm of lead it falls to 55 counts/s.

1. (a)Identify which emissions the source produces, quoting the evidence.[3]
2. (b)Explain why the count rate does not reach the background level with the lead in place.[2]

A nucleus of radon-222 is written ²²²₈₆Rn. It emits an alpha particle; the product then emits a beta particle.

1. (a)State the nucleon number and proton number of the nucleus formed in the alpha decay.[2]
2. (b)State the nucleon number and proton number after the beta decay.[2]
3. (c)Write the beta-decay equation in nuclide notation and show that both numbers balance.[2]

A school laboratory keeps a beta-emitting source for class experiments.

1. (a)Give two reasons why a student must never hold this source in bare hands.[2]
2. (b)State two precautions for handling it correctly.[2]
3. (c)Explain why the school chose a source with a long half-life.[1]

A factory measures the count rate from a radioactive tracer placed in a pipe. The detector reading is 850 counts/min, and the background count rate is 50 counts/min. The tracer has a half-life of 6.0 hours.

1. (a)Calculate the corrected count rate at the start.[1]
2. (b)Calculate the corrected count rate after 18 hours.[2]
3. (c)Calculate the total detector reading (including background) after 18 hours.[2]
4. (d)State why the background must be subtracted before working out half-lives from readings.[1]

A hospital chooses isotopes for four jobs: sterilising surgical instruments in a sealed source; checking the thickness of aluminium foil as it rolls; a smoke alarm; and delivering a focused dose to a tumour. All four use gamma or beta or alpha sources with chosen half-lives.

1. (a)State which radiation each job needs, with one reason each.[4]
2. (b)For the foil-thickness gauge, explain what happens to the detected count rate if the foil becomes too thick.[2]
3. (c)State why a very short half-life would be a poor choice for a factory gauge.[1]

A detector beside a weak source records counts in four consecutive 10-second intervals: 34, 29, 36 and 31 counts. A 10-second reading with the source removed gives 2 counts.

1. (a)Explain why the four readings are not identical.[1]
2. (b)Calculate the mean raw count per 10-second interval.[2]
3. (c)Calculate the corrected count rate due to the source alone, in counts per second, to 2 significant figures.[2]
4. (d)State why averaging over a longer time improves the result.[1]