IGCSE Physics (0625) 5.2.3 Radioactive decay Paper 3

Question

A teacher determines the types of emission from a radioactive source. He uses different materials to absorb the emissions. Fig. 11.1 shows the equipment.

The teacher places a material between the radioactive source and the detector. The counter shows the count rate for the emission that reaches the detector. The teacher records the count rate. He repeats the experiment for different materials.
Table 11.1 shows the results.

(a) State whether the source emits α (alpha)-particles.
Use information from Table 11.1 to give a reason for your answer.

Answer/Explanation

Ans: alpha (particles) not emitted
any one from
idea that count rate for paper is similar to count rate for air OR
if alpha emitted count rate for paper would decrease/be less (than 480)

(b) State whether the source emits γ (gamma)-rays.
Use information from Table 11.1 to give a reason for your answer.

Answer/Explanation

Ans: gamma (rays) emitted
any one from
idea that count rate for (10 mm) lead is less (than count rate for (2 mm) aluminium/air/paper owtte)
OR (most/some of) gamma (rays) are absorbed by lead

Question

(a) Table 12.1 describes four nuclides.

(i) State which two nuclides have the same number of protons.

   …………………………………………………………………………………………………………………….                                                                                              [1]

(ii) State which two nuclides have the same number of nucleons.

    …………………………………………………………………………………………………………………….                                                                                             [1]

(iii) State which one of the four nuclides has the most electrons orbiting when it is in a neutral atom.

      …………………………………………………………………………………………………………………….                                                                                           [1]

(b) Thorium-234 has a half-life of 24 days. A sample of radioactive material contains 40 mg of  thorium-234.

Calculate the mass of thorium-234 remaining after 72 days.

mass of thorium-234 remaining = …………………………………………… mg [3][Total: 6]

Answer/Explanation

Ans: (a)(i) uranium-235 AND uranium-238

(a)(ii) plutonium(-238) AND uranium-238

(a)(iii) plutonium(-238)

(b) idea of 3 half-lives OR 72 ÷ 24 40 ÷ 8 5(.0) (mg)

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