The background count rate measured by a radiation counter is 40 counts per minute (cpm). With the counter close to a radioactive source, the counter reading is $$$960 \mathrm{cpm}$$$. The half-life of the source is 20 minutes. What is the counter reading one hour later?

$115 \mathrm{cpm}$

$120 \mathrm{cpm}$

$155 \mathrm{cpm}$

$160 \mathrm{cpm}$

Physics

IGCSE&ALevel

CAIE

Exam No：0625_s23_qp_21 Year：2023 Question No：36

Answer:

5.2.1.1 Demonstrate understanding of background radiation

5.2.1.2 Describe the detection of α-particles

5.2.2.1 Discuss the random nature of radioactive emission

5.2.2.2.1 their nature

5.2.2.2.2 their relative ionising effects

5.2.2.2.3 their relative penetrating abilities

5.2.2.3 Describe their deflection in electric fields and in magnetic fields

5.2.2.4 Interpret their relative ionising effects

5.2.2.5 Give and explain examples of practical applications of α-

5.2.3.1 State the meaning of radioactive decay

5.2.3.2 State that during α- or -decay the nucleus changes to that of a different element

5.2.3.3 Use equations involving nuclide notation to represent changes in the composition of the nucleus when particles are emitted

5.2.4.1 Use the term half-life in simple calculations, which might involve information in tables or decay curves

5.2.4.2 Calculate half-life from data or decay curves from which background radiation has not been subtracted

5.2.5.1 Recall the effects of ionising radiations on living things

5.2.5.2 Describe how radioactive materials are handled, used and stored in a safe way