物理輻射與放射性 DSE、CE 選擇題（第 4 頁）

31.

Arrange $\alpha$ , $\beta$ and $\gamma$ radiation in ascending order of their ionizing powers :

32.

The activity of a radioactive source drops from $640$ Bq to $40$ Bq in $2$ hours. Find the half-life of the source.

33.

Which of the following signs is used to indicate radioactive material ?

Four signs: A skull and crossbones, B radiation trefoil, C letter R, D a lamp with rays

34.

Which of the following diagrams correctly shows the deflections of $\alpha$ , $\beta$ and $\gamma$ rays in a uniform magnetic field pointing into the paper ?

Four diagrams A to D showing tracks of alpha, beta and gamma rays through a circular region with a magnetic field into the paper

35.

Graph of activity (Bq) against time (minute): exponential decay from 40 Bq at 0 to about 4 Bq at 100 minutes

The activity of a radioactive source is recorded on a graph as shown above. What is the half-life of the source ?

36.

In an experiment to measure the half-life of a radioactive isotope in a place where the background count rate is $20$ counts per minute, the following results are recorded :

Time / minute	0	2	4	6	8	10	12
Total count rate / counts per minute	116	96	80	69	58	50	44

The half-life is about

37.

A radioactive source has a half-life of $22$ years. After $66$ years, what fraction of the source remains undecayed ?

38.

The activity of a radioactive source falls to $\frac{1}{8}$ of its original value in $24$ minutes. The half-life of the source is

39.

Which of the following descriptions of the half-life of a sample of radioactive isotope is/are correct ? The half-life is

(1)the time taken for the mass of the sample to fall to half of its initial value.

(2)the time taken for the activity of the sample to fall to half of its initial value.

(3)half of the time taken for the sample to decay completely.

40.

Which of the following about $\alpha$ radiation is/are correct ?

(1)The mass of an

\alpha

particle is about four times that of a proton.

(2)It has a stronger ionizing power than

\beta

radiation.

(3)It has a greater penetration power than

\gamma

radiation.