Radioactivity：练习题

Which type of ionising radiation has the highest penetrating power, capable of passing through several centimetres of lead?

A nucleus of Plutonium-239 is represented by the symbol \(^{239}_{94}\text{Pu}\). It undergoes alpha (\(\alpha\)) decay to form a nucleus of Uranium (U).
What are the mass number and atomic number of the resulting Uranium nucleus?

A sample of a radioactive isotope is monitored over time. After \(24 \text{ days}\), the activity has decreased to \(\frac{1}{16}\) of its original value.
What is the half-life of this isotope?

Which of the following describes the difference between contamination and irradiation?

When a nucleus undergoes beta (\(\beta^{-}\)) decay, what happens to its atomic (proton) number and its mass (nucleon) number?

Ionising radiation is part of the natural environment and is known as background radiation.
Name one source of background radiation originating from Earth and one source originating from space.

Radioactive decay is defined as a random process.
Explain what the term random means in the context of the decay of individual unstable nuclei in a sample.

A nucleus of Carbon-14 is represented by the symbol \(^{14}_{6}\text{C}\).
(a) Describe the structure of this nucleus by stating the number of protons and the number of neutrons it contains.
(b) Carbon-12 is another isotope of carbon. State what is meant by the term isotope.

A student performs an experiment to identify the types of radiation emitted by two different unknown sources, A and B. They measure the count rate (counts per minute, cpm) using various absorbers. The background radiation is constant at 25 cpm. The results are shown in the data table below:

Source A: No absorber = 450 cpm; Paper = 448 cpm; 5mm Aluminium = 30 cpm.
Source B: No absorber = 600 cpm; Paper = 28 cpm; 5mm Aluminium = 26 cpm.

(a) Identify the type of radiation emitted by Source A and justify your answer using the data.
(b) Identify the type of radiation emitted by Source B and justify your answer using the data.
(c) Source B is placed 10 cm away from the detector. Predict what would happen to the count rate and explain why.