Radioactivity：練習題

A student uses a pair of long tongs to handle a radioactive source.
Why is this procedure considered a valid safety precaution?

A nucleus of radium-226 (\( ^{226}_{88}\text{Ra} \)) undergoes alpha (α) decay to form a nucleus of radon (Rn).

How many neutrons are present in the resulting radon nucleus?

A student uses a detector to measure the count rate from a radioactive source. The background count rate is constant at \( 30 \text{ counts/minute} \).

At \( t = 0 \), the detector shows a total count rate of \( 510 \text{ counts/minute} \).
After \( 6.0 \text{ hours} \), the detector shows a total count rate of \( 90 \text{ counts/minute} \).

What is the half-life of this source?

Which of the following is a significant natural source of background radiation?

During beta (̒) decay, a change occurs within the nucleus of an atom. Which of the following describes this change?

State one specific source of background radiation that originates from food and drink and explain how it enters the human body.

Explain why gamma (\(\gamma\)) radiation is significantly more penetrating than alpha (\(\alpha\)) radiation.

A radioactive source is used to monitor the thickness of paper in a factory. Explain why a beta (\(\beta^-\)) emitter is more suitable for this application than an alpha (\(\alpha\)) or gamma (\(\gamma\)) source.

A radioactive isotope has a half-life of \(8.0\text{ days}\). An initial sample of this isotope produces a count rate of \(640\text{ counts/s}\).

(a) Define the term half-life.
(b) Calculate the count rate of the sample after \(24\text{ days}\) have passed.
(c) State one safety precaution that should be taken when handling radioactive sources in a laboratory to reduce exposure.

A student uses a Geiger-M0ller tube to measure the activity of a radioactive sample. The results are shown in the table below:

Time (min): 0, 15, 30, 45
Measured Count Rate (counts/s): 145, 85, 55, 40
Background Count Rate: 25 counts/s

(a) Calculate the corrected count rate at each time interval. (2)
(b) Use the corrected values to determine the half-life of the sample. (2)
(c) Explain why radioactive decay is described as random. (2)