Radioactivity

What is ionising radiation?

Radiation that can ionise atoms by removing an electron to leave a positive ion

Describe how a cloud chamber allows us to see tracks of ionising radiation

• The cloud chamber contains air saturated with vapour at a very low temperature.

• The radiation ionises air molecules in the chamber

• Liquid condenses onto the ions to leave tracks of droplets marking the path of the radiation

What are the two types of beta radiation?

• Beta minus

• Beta plus

Gamma radiation can also be called gamma ____

Gamma rays

What does alpha radiation consist of?

• Fast moving, positively charged alpha particles

• Each alpha particle contains two protons and two neutrons (it is a helium nucleus)

What does beta minus radiation consist of?

Fast moving electrons

What does beta plus radiation consist of?

Fast moving positrons

What does gamma radiation consist of?

High energy photons with wavelengths less than ~10^-13 m

What is the charge of an alpha particle?

+2e

What is the charge of a beta minus particle?

• -e

• Not the same as β⁺

What is the charge of a beta plus particle?

• +e

• Not the same as β^-

What is the charge of a gamma ray?

0; they have no charge

What is the typical speed of alpha radiation?

~10⁶ ms^-1

What is the typical speed of beta radiation?

• ~10⁸ ms^-1

• Same for both β^- and β⁺

What is the typical speed of gamma radiation?

• Speed of light

• 3.00 × 10⁸ ms^-1

What is the name of the unit u?

Unified atomic mass unit

What is 1u in kg?

1.661 × 10^–27

What is the mass of alpha radiation in u?

4u

What is the mass of beta radiation in u?

• 1/2000 u

• Same for both β^- and β⁺

What is the mass of gamma radiation in u?

0

What is the range of alpha radiation in air?

Very short range - a few centimetres

What is the range of beta radiation in air?

• ~1m

• Same for both β^- and β⁺

What is the range of gamma radiation in air?

Very long range

What is the penetration of alpha radiation?

Thin sheet of paper

What is the penetration of beta radiation?

• 4-5 mm of aluminium

• Same for both β^- and β⁺

What is the penetration of gamma radiation?

A few centimetres of lead

What force is responsible for beta decay?

Weak nuclear force

What is the nuclear decay equation for the alpha decay of the nucleus X?

What is the nuclear decay equation for the beta minus decay of the nucleus X?

What is the nuclear decay equation for the beta plus decay of the nucleus X?

What is the nuclear decay equation for the gamma decay of the nucleus X?

What is the parent nucleus?

A nucleus before the occurence of radioactive decay

What is the daughter nucleus?

A new nucleus formed following a radioactive decay

What is the parent nucleus in the decay equation shown?

What is the daughter nucleus in the decay equation shown?

What is the parent nucleus in the decay equation shown?

What is the daughter nucleus in the decay equation shown?

Draw a diagram of a Geiger-Müller tube

How is radiation detected by a Geiger-Müller tube?

• When alpha, beta or gamma radiation enters the tube it produces ions in the gas.

• The ions created in the gas enable the tube to conduct. A current is produced in the tube for a short time.

• The current produces a voltage pulse. Each voltage pulse corresponds to one ionising radiation entering the GM tube.

• The voltage pulse is amplified and counted.

Radioactive decay is a _____ and spontaneous event

Random

Radioactive decay is a random and _____ event

spontaneous

Radioactive decay is a _____ and _____ event

• Random

• Spontaneous

Why is radioactivity described as a random process?

• We can’t predict when a particular nucleus in a sample will decay or which one will decay next

• Each nucleus within a sample has the same chance of decaying per unit time

Why is radioactivity described as a spontaneous process?

Because the decay of nuclei is not affected by:

• The presence of other nuclei in the sample

• External factors such as pressure.

Define activity

The rate at which nuclei decay or disintegrate in a radioactive source

Define the Becquerel

One becquerel is an activity of one decay per second

What is the symbol for Becquerel?

Bq

What is the decay constant?

The probability of decay of an individual nucleus per unit time

What is the unit of the decay constant?

s^-1 (NOT Bq)

What is the symbol for the decay constant?

λ

What is the relationship between activity and the decay constant?

• A = λN

• A is activity in Bq

• λ is the decay constant in s^-1

• N is the number of undecayed nuclei