The reading on a detector placed near a radioactive material is 740 counts per second740\text{ counts per second}740 counts per second. The background count rate is 60 counts per second60\text{ counts per second}60 counts per second. The half-life of the radioactive material is 15 days15\text{ days}15 days. What is the reading on the detector after 45 days45\text{ days}45 days?
85 counts per second85\text{ counts per second}85 counts per second
93 counts per second93\text{ counts per second}93 counts per second
145 counts per second145\text{ counts per second}145 counts per second
230 counts per second230\text{ counts per second}230 counts per second
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.