7.1-7.1.6 - Properties of Radiation

Question 1

What are atoms?

Answer 1

Atoms are the building blocks of all matter they have a tiny dense nucleus at their centre with electrons orbiting around the nucleus. The nucleus contains all the mass of the atom

Question 2

What are protons neutrons and electrons?

Answer 2

Protons - Positively charged particles with a relative atomic mass of one unit.

Neutrons - No charge and also with a relative atomic mass of one unit.

Electrons - Negative charge with almost no mass.

Question 3

What is the charge of an atom

Answer 3

Although atoms contain particles of different charge the total charge within an atom is zero because the number of electrons is equal to the number of protons.

Question 4

What is an ionised atom?

Answer 4

An Ionised atom is an atom that loses electrons.

Question 5

What is Nuclear notation?

Answer 5

Symbols that are used to describe particular nuclear by their elements symbol atomic and mass number.

Question 6

What is the atomic number?

Answer 6

The number of protons in an atom is the atomic number. Elements are arranged in order of atomic number in the periodic table.

The atomic number is equal to the number of electrons in an atom.

Question 7

What is the mass number?

Answer 7

The total number of particles in the nucleus of an atom is called its mass number. Mass number is the number of protons and neutrons in the atom.

Neutron = Mass number - Atomic number

Question 8

What are Isotopes?

Answer 8

Atoms of the same element that have an equal number of protons but a different number of neutrons.

Question 9

Why are Isotopes unstable?

Answer 9

Imbalance due to the imbalance of protons and neutrons.

Question 10

What can cause radiation?

Answer 10

Some atomic nuclei are unstable this is because there is an imbalance in the forces within the nucleus between the particles.

Question 11

What can happen to unstable nuclei?

Answer 11

Unstable nuclei can emit radiation to become more stable radiation can be in the form of high energy particles of wave. As the radiation moves away from the nucleus it takes energy with it reducing the overall energy of the nucleus, making it more stable

Question 12

What is Radioactive decay?

Answer 12

The process of emitting radiation is called radioactive decay it is a random process meaning it is not possible to know exactly when a particular nucleus will decay. When an unstable nucleus decays it emits radiation called nuclear radiation.

Question 13

What are the three types of radiation?

Answer 13

Alpha (α)
Beta (β-)
Gamma (γ)

Question 14

What are the properties of Alpha particles?

Answer 14

The symbol for alpha is α
An alpha particle is the same as a helium nucleus
This is because they consist of two neutrons and two protons
Alpha particles have a charge of +2
This means they can be affected by an electric field

Question 15

What are the properties of Beta particles?

Answer 15

The symbol for beta is β-
Beta particles are fast-moving electrons
They are produced in nuclei when a neutron changes into a proton and an electron
Beta particles have a charge of -1
This means they can be affected by an electric field

Question 16

What are the properties of Gamma rays?

Answer 16

The symbol for gamma is γ
Gamma rays are electromagnetic waves
They have the highest energy of the different types of electromagnetic waves
Gamma rays have no charge

Question 17

What is the range of Nuclear radiation in air?

Answer 17

Alpha - few cm
Beta - Few 10s of cm
Gamma - infinite

Question 18

What is the penetration of nuclear radiation?

Answer 18

Alpha - Stopped by paper
Beta - Stopped by a few mm of Aluminium
Gamma - Reduced by a few mm lead

Question 19

What is the ionising of nuclear radiation?

Answer 19

Alpha - high radiation
Beta - Medium radiation
Gamma - Low radiation

Question 20

What are the trends of the nuclear radiation particles?

Answer 20

The range increases
Penetrating power increases
Ionisation decreases

Question 21

What is penetrating power?

Answer 21

Alpha beta and gamma penetrate materials in different ways means they are stopped by different materials

Alpha stopped by paper whereas beta and gamma pass through it
Beta is stopped by a few millimetres of aluminium
Gamma can pass through aluminium
Gamma rays are only partially stopped by thick lead

Question 22

What is Ionising power?

Answer 22

All nuclear radiation is capable of ionising atoms that it hits
When an atom is ionised, the number of electrons it has changes
This gives it a non-zero charge Alpha radiation is the most ionising form of nuclear radiation
This is because alpha particles have a charge of +2
Gamma radiation is the least ionising form of nuclear radiation

Question 23

What happenes during alpha decay?

Answer 23

During alpha decay an alpha particle is emitted from an unstable nucleus
A completely new element is formed in the process.

An alpha particle is a helium nucleus
It is made of 2 protons and 2 neutrons
When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes
The mass number decreases by 4
The atomic number decreases by 2
The charge on the nucleus also decreases by 2
This is because protons have a charge of +1 each

Question 24

What happenes during Beta decay?

Answer 24

During beta decay, a neutron changes into a proton and an electron
The electron is emitted and the proton remains in the nuclei
A completely new element is formed because the atomic number changes.

A beta particle is a high-speed electron
It has a mass number of 0
This is because the electron has a negligible mass, compared to neutrons and protons
Therefore, the mass number of the decaying nuclei remains the same
Electrons have an atomic number of -1
This means that the new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay

Question 25

What happenes during Gamma decay?

Answer 25

During gamma decay, a gamma ray is emitted from an unstable nucleus
The process that makes the nucleus less energetic but does not change its structure

The gamma ray that is emitted has a lot of energy, but no mass or charge

Question 26

What is neutron emission?

Answer 26

A small number of isotopes can decay by emitting neutrons.
When a nucleus emits a neutron:
The number of protons does not change:
The atomic (proton) number does not change
The total number of particles (nucleons) in the nucleus decreases by 1:
The mass (nucleon) number decreases by 1

Question 27

How is radiation detected and why is it important humans are not exposed?

Answer 27

It is important to regulate the exposure of humans to radiation
The amount of radiation received by a person is called the dose and is measured in sieverts (Sv)
One sievert is a very big dose of radiation
It would cause acute radiation poisoning

To protect against over-exposure, the dose received by different activities is measured
Radiation can be measured and detected using a photographic film or a Geiger–Müller tube

Question 28

What is Photographic Film?

Answer 28

Photographic films detect radiation by becoming darker when it absorbs radiation, just like it does when it absorbs visible light
The more radiation the film absorbs, the darker it is when it is developed

To get an accurate measure of the dose received, the badge contains different materials that the radiation must penetrate to reach the film
These materials may include aluminium, copper, paper, lead and plastic

Question 29

What radiation are different areas of the films exposes to

Answer 29

Alpha radiation is unlikely to be detected at all as it will be absorbed / stopped by the paper
Beta radiation is absorbed by the aluminium
Gamma (or X-rays) affect all areas of the film but the lead will reduce some of the gamma radiation

Question 30

What is a Geiger- Muller tube?

Answer 30

The Geiger-Müller tube is the most common device used to measure and detect radiation
Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
This makes a clicking sound or displays the count rate
The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing
Therefore, it matters how close the tube is to the radiation source
The further away from the source, the lower the count rate detected

Question 31

What is Background radiation?

Answer 31

The radiation that exists around us all the time

There are two types of background radiation:
Natural sources
Man-made sources

Question 32

What are some natural sources of background radiation?

Answer 32

Radon gas from rocks and soil
Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground
Uranium decays into radon gas, which is an alpha emitter
This is particularly dangerous if inhaled into the lungs in large quantities

Carbon-14 in biological material
All organic matter contains a tiny amount of carbon-14
Living plants and animals constantly replace the supply of carbon in their systems hence the amount of carbon-14 in the system stays almost constant

Radioactive material in food and drink
Naturally occurring radioactive elements can get into food and water since they are in contact with rocks and soil containing these elements
Some foods contain higher amounts such as potassium-40 in bananas
However, the amount of radioactive material is minuscule and is not a cause for concern

Question 33

What are Man made sources of Nuclear radiation?

Answer 33

Medical sources
In medicine, radiation is utilised all the time
Uses include X-rays, CT scans, radioactive tracers, and radiation therapy

Nuclear fallout from nuclear weapons
Fallout is the residue radioactive material that is thrown into the air after a nuclear explosion,

While the amount of fallout in the environment is presently very low, it would increase significantly in areas where nuclear weapons are tested

Nuclear accidents
Accidents such as that in Chernobyl contributed a large dose of radiation into the environment
While these accidents are now extremely rare, they can be catastrophic and render areas devastated for centuries

Question 34

What is the correct count rate?

Answer 34

Background radiation must be accounted for when taking readings in a laboratory
This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present
This is known as the corrected count rate

Question 35

Explain Core practical 13: Investigating Radiation?

Answer 35

The aim of this experiment is to investigate the penetration powers of different types of radiation using either radioactive sources or simulations

Variables:
Independent variable = Absorber material
Dependent variable = Count rate
Control variables:
Radioactive source
Distance of GM tube to source
Location / background radiation

Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
Repeat this three times, and take an average
Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
Repeat the above experiment for other radioactive sources

Question 36

What is the analysis of core practical 13?

Answer 36

If the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
Note that some sources will emit more than one type of radiation
If the radiation is stopped by paper, the source will be emitting alpha
If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma

Question 37

What errors can occour during this experiment?

Answer 37

Systematic Errors:

Make sure that the sources are stored well away from the counter during the experiment
Conduct all runs of the experiment in the same location to avoid changes in background radiation levels
Random Errors:
The accuracy of such an experiment is improved with using reliable sources with a long half-life and an activity well above the natural background level

Question 38

What are the saftey concerns with this experiment?

Answer 38

When not using a source, keep it in a lead lined container
When in use, try and keep a good distance (a metre or so) between yourself and the source
When handling the source, do so using tweezers (or tongs) and point the source away from you