SPM Trial MARA 2010 ~ paper 2 ( Radioactivity )

Question 3

Diagram 3 shows a Geiger-Muller tube (GM tube) and a rate meter which are used to detect the level of milk in containers in a factory.

Table 3 shows the readings recorded by the rate meter for four containers P, Q, R and S when a radioactive source is placed near the containers. The rate meter records a reading of 100 counts per minute when there is no radioactive source nearby.

Rajah 3 menunjukkan sebuah tiub GM dan alat meter kadar digunakan untuk mengesan paras susu di dalam bekas di sebuah kilang.

Jadual 3 menunjukkan bacaan meter kadar bagi empat bekas P, Q, R dan S bila suatu sumber radioaktif diletakkan berhampiran bekas. Meter kadar mencatatkan bacaan 100 bilangan per minit jika tiada sumber radioaktif diletakkan berdekatan.

(a)

Name the radiation emitted by the radioactive source.

Namakan sinar radiasi yang dikeluarkan oleh sumber radioaktif itu.

Hints for solving the problem :
Beta or gamma source are used, depending on the thickness and the density of the material to be measured.

(b)

(i)

Based on Table 3, which container has the least amount of milk?

State one reason for your answer.

Berdasarkan Jadual 3, bekas yang manakah mempunyai kuantiti susu paling kecil?

Beri satu sebab bagi jawapan anda.

Hints for solving the problem :

The reading depends on the milk quantity in the container and it gets higher as the milk is under level.

(ii)

State the actual rate meter reading for Q.

Nyatakan kadar bacaan sebenar bagi Q

Hints for solving the problem :

When there is no radioactive source nearby the detector detect natural background radiation . (cosmic radiation, solar radiation, etc)

(c) The mass of a radioactive source is reduced from 80.0 g to 20.0 g in 30

seconds. Calculate its half-life.

Jisim suatu sumber radioaktif menyusut dari 80.0 g kepada 20.0 g dalam masa 30 saat.

Hitungkan setengah hayat bagi bahan radioaktif tersebut.

Hints for solving the problem :

The half-life of a radioisotope is the average time it takes for half of the remaining radiative atoms to decay to a different atom.

Suggested answers:

a) beta because it can penetrate box and liquid and is less
dangerous than gamma.
b)
(i) R has the least a mount of milk. highest mean it allow more beta to passes though.
(ii) 566 - 100 = 466 counts per second
c) 80 --> 40 --> 20
it undergo 2 half-life.
half life = 30/ 2 = 15 secs