# 31.1 Nuclear radioactivity  (Page 5/13)

 Page 5 / 13

## Phet explorations: beta decay

Watch beta decay occur for a collection of nuclei or for an individual nucleus.

## Test prep for ap courses

A nucleus is observed to emit a $\gamma$ ray with a frequency of What must happen to the nucleus as a consequence?

1. The nucleus must gain 0.26 MeV.
2. The nucleus must also emit an α particle of energy 0.26 MeV in the opposite direction.
3. The nucleus must lose 0.26 MeV.
4. The nucleus must also emit a β particle of energy 0.26 MeV in the opposite direction.

(c)

A uranium nucleus emits an α particle. Assuming charge is conserved, the resulting nucleus must be

1. thorium
2. plutonium
4. curium

## Section summary

• Some nuclei are radioactive—they spontaneously decay destroying some part of their mass and emitting energetic rays, a process called nuclear radioactivity.
• Nuclear radiation, like x rays, is ionizing radiation, because energy sufficient to ionize matter is emitted in each decay.
• The range (or distance traveled in a material) of ionizing radiation is directly related to the charge of the emitted particle and its energy, with greater-charge and lower-energy particles having the shortest ranges.
• Radiation detectors are based directly or indirectly upon the ionization created by radiation, as are the effects of radiation on living and inert materials.

## Conceptual questions

Suppose the range for ray is known to be 2.0 mm in a certain material. Does this mean that every a ray that strikes this material travels 2.0 mm, or does the range have an average value with some statistical fluctuations in the distances traveled? Explain.

What is the difference between $\gamma$ rays and characteristic x rays? Is either necessarily more energetic than the other? Which can be the most energetic?

Ionizing radiation interacts with matter by scattering from electrons and nuclei in the substance. Based on the law of conservation of momentum and energy, explain why electrons tend to absorb more energy than nuclei in these interactions.

What characteristics of radioactivity show it to be nuclear in origin and not atomic?

What is the source of the energy emitted in radioactive decay? Identify an earlier conservation law, and describe how it was modified to take such processes into account.

Consider [link] . If an electric field is substituted for the magnetic field with positive charge instead of the north pole and negative charge instead of the south pole, in which directions will the $\alpha$ , $\beta$ , and $\gamma$ rays bend?

Explain how an $\alpha$ particle can have a larger range in air than a $\beta$ particle with the same energy in lead.

Arrange the following according to their ability to act as radiation shields, with the best first and worst last. Explain your ordering in terms of how radiation loses its energy in matter.

(a) A solid material with low density composed of low-mass atoms.

(b) A gas composed of high-mass atoms.

(c) A gas composed of low-mass atoms.

(d) A solid with high density composed of high-mass atoms.

Often, when people have to work around radioactive materials spills, we see them wearing white coveralls (usually a plastic material). What types of radiation (if any) do you think these suits protect the worker from, and how?

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And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
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