Highworth Physics - Radiation - Ionising Power

Front 1

State the three ways an unstable nucleus can decay.

Back 1

It may give out:

An alpha particle

A beta particle

A gamma ray

Front 2

Describe the types of radiation?

Back 2

Alpha particle - Two protons and two neutrons – the same as a helium nucleus

Beta particle - Fast-moving electron

Gamma ray - High energy electromagnetic radiation

Front 3

What is Ionising radiation?

Back 3

Ionising radiation is radiation that has enough energy to cause other atoms to lose electrons and form ions.

Front 4

The different forms of radiation have different levels of ionisation abilities - what are they?

Back 4

Alpha particles – very ionising

Beta particles – moderately ionising

Gamma rays – weakly ionising

Front 5

The nucleus of an atom can be represented like the image.

Explain what it means.

Back 5

A = atomic mass (number of protons + neutrons)

Z = atomic number (number of protons)

X = chemical symbol (as shown on the periodic table)

Front 6

Describe Alpha decay.

Back 6

When an alpha particle is emitted from a nucleus the nucleus loses two protons and two neutrons.

This means the atomic mass number decreases by 4 and the atomic number decreases by 2.

A new element is formed that is two places lower in the Periodic Table than the original element.

Front 7

Describe Beta decay.

Back 7

In Beta decay a neutron changes into a proton plus an electron.

The proton stays in the nucleus and the electron leaves the atom with high energy, and we call it a beta particle.

When a beta particle is emitted from the nucleus the nucleus has one more proton and one less neutron.

This means the atomic mass number remains unchanged and the atomic number increases by 1.

Front 8

Describe Gamma decay.

Back 8

Rather than producing atomic particles, gamma radiation gives off high-energy electromagnetic waves, more energetic than X-rays.

Front 9

Summarise the different properties of nuclear radiation.

Back 9

Front 10

What is the range of different types of radiation?

Back 10

Front 11

What is the hazard symbol that is shown on containers of radioactive substances to warn of the danger.

Back 11

Front 12

The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body.

Describe the dangers if the radioactive source is inside the body, perhaps after being swallowed or breathed in:

Back 12

If the radioactive source is inside the body, perhaps after being swallowed or breathed in:

Alpha radiation is the most dangerous because it is easily absorbed by cells.

Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it.

Front 13

The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body.

Describe the dangers if the radioactive source is outside the body.

Back 13

If the radioactive source is outside the body:

Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body.

Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside.

Front 14

How is radiation affected by electric fields?

Back 14

Alpha particles are positively charged, beta particles are negatively charged and gamma radiation is electrically neutral.

This means that alpha radiation and beta radiation can be deflected by electric fields, but gamma radiation is not deflected.

Beta particles are negatively charged so they will be attracted towards a positively charged plate.

Positive alpha particles will be attracted towards a negatively charged plate.

Front 15

How is radiation affected by magnetic fields?

Back 15

Because they consist of charged particles, alpha radiation and beta radiation can also be deflected by magnetic fields.

Just as with electric fields, gamma radiation is not deflected by magnetic fields.

Front 16

State two methods of detecting radiation.

Back 16

Photographic film

Photographic film goes 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.

Geiger-Muller tube

The Geiger-Muller tube detects 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-Muller tube is absorbing.

Front 17

A student asks you to describe the size of each type of ionising radiation.

Describe the ‘size’ of each type of radiation to the student.

Back 17

An alpha particle is made up of four particles (two protons, two neutrons) and is the biggest.

It is much larger than a beta particle, which is a single electron.

Gamma rays have no actual size as they are pure energy.

Front 18

Some people think that an alpha particle is a helium atom.

Explain why they are mistaken.

Back 18

An alpha particle is not the same as a helium atom because it has no electrons.

Front 19

Explain why beta particles have a much larger range in air than alpha particles.

Back 19

Beta particles have less charge than alpha particles and they only have 1/1800 the mass so they are much more likely to miss atoms in air than alpha particles are.

This means they will travel further.

Front 20

Explain why being far away is the best protection against gamma radiation, while a paper towel will protect against alpha particles.

Back 20

A emitted from a source so the further away you are, the fewer rays hit you.

Also, gamma rays are difficult to stop, so shielding is not that useful.

Alpha particles are stopped by paper, so a paper towel will stop them ionising you.

Front 21

Gamma radiation is pure energy, just like light. Gamma radiation comes in packets called photons.

Each photon’s energy must all be transferred at once when it interacts with an atom.

How many atoms do you think a gamma ray will ionise?

Back 21

A gamma ray is a single photon of energy.

When it hits an atom and ionises it, all of its energy is transferred so it only ionises one atom.

Front 22

Describe what you think will happen to an alpha particle that travels close to the nucleus of an atom but does not ionise the atom.

Back 22

The alpha particle would be repelled by the nucleus of the atom because they are both positively charged.

Front 23

Explain why ionising radiations tend to travel less far in dense materials like lead compared with less dense materials like air.

Back 23

In dense materials the probability of ionising an atom is much higher because the radiation comes across atoms more frequently.

Front 24

The analogy of the radiations travelling through the forest in the figure, has several shortcomings.

Explain one of these shortcomings.

Back 24

Any clearly explained problem with the forest model will do, e.g. the discus bouncing off trees suggests that beta particles bounce off atoms.

Also, if knocking down a tree is ionising an atom, then a laser beam would not damage a tree in the same way as an alpha particle would.

Front 25

What are the key points to remember?

Back 25

Different types of ionising radiation have very different ranges and penetrating powers.
Ionising radiation can be very damaging to cells.

Alpha and beta particles are both deflected by electric and magnetic fields.1