Radiation

Question 1

Why does the nucleus have an overall positive charge?

Answer 1

The protons.

Question 2

Compare the energy of the energy levels depending on their distance from the nucleus?

Answer 2

Energy levels which are further from the nucleus are at a higher energy than those which are closer to the nucleus.

Question 3

What happens if an atom absorbs electromagnetic radiation e.g. light?

Answer 3

An electron can move from a lower energy level to a higher energy level.
Now the atom can emit electromagnetic radiation, and the electron returns back to the lower energy level.

Question 4

Why do atoms have no overall charge?

Answer 4

Number of protons is equal to the number of electrons.

The negative charges on the electrons cancel out the positive charges on the protons.

Question 5

What are isotopes?

Answer 5

Atoms of the same element that have a different number of neutrons.

Question 6

What is the plum-pudding model?

Answer 6

An atom is a ball of positive charge with negative electrons embedded in it.

Question 7

What is the nuclear model?

Answer 7

Mostly empty space
Tiny positive nucleus in the centre.
Negative electrons around the edge.

Question 8

What did Niels Bohr propose?

Answer 8

Electrons orbit the nucleus at specific distances.

His work agreed with the results of other scientists.

Question 9

What did James Chadwick discover?

Answer 9

Nucleus also contained neutrons, which have no charge.

Question 10

What is meant by radioactive decay?

Answer 10

Some isotopes have an unstable nucleus.
To become stable, the nucleus gives out radiation.

This is a completely random process.

Question 11

What is meant by activity?

Answer 11

The rate at which a source of unstable nuclei decay.
Measured in becquerel (Bq)
1 Bq= 1 decay per second.
Activity is measured by a Geiger-Muller tube.

Question 12

What is count-rate?

Answer 12

The number of decays recorded each second by a detector e.g. Geiger Muller tube.

Question 13

Describe Alpha particles

Answer 13

Consist of two neutrons and two protons.

The same as a helium nucleus.

Question 14

Describe a Beta particle

Answer 14

An electron which is ejected from the nucleus at very high speed.
It is formed inside the nucleus when a neutron changes into a proton and an electron.

Question 15

Describe gamma rays

Answer 15

A type of electromagnetic radiation from the nucleus.

Question 16

List the four types of radiation

Answer 16

Alpha particles
Beta particles
Gamma rays
Neutrons

Question 17

Describe the properties of Alpha particles:

Answer 17

Large
Range in air:
They can travel around 5cm in air before they collide with air particles and stop.
Penetrating power:
Stopped by a single sheet of paper.
Ionising power:
Very strongly ionising.

Question 18

What is ionising power?

Answer 18

When radiation collides with atoms, that can cause atoms to lose electrons and form ions.
So if something has a high ionising power, it means they can produce a lot of ions if they collide with a material.

Question 19

Describe the properties of Beta particles:

Answer 19

Range in air:
Can travel around 15cm in air before stopping.
Penetrating power:
Stopped by a few mm of aluminium.
Ionising power:
Quite strongly ionising.

Question 20

Describe the properties of gamma rays:

Answer 20

Range in air:
Several metres in air before stopping.
Penetrating power:
Stopped by several cm of lead.
Ionising power:
Weakly ionising

Question 21

What is alpha decay?

Answer 21

Mass number decreases by 4.

Atomic number decreases by 2.

Question 22

What is beta decay?

Answer 22

Because a neutron changes into a proton, the atomic number increases by 1.

Mass number doesn’t change because the total number of protons and neutrons in the nucleus stays the same.

Question 23

What is gamma decay?

Answer 23

Both the atomic number and mass number are not changed at all.

Question 24

What is meant by the half-life of a radioactive isotope?

Answer 24

The time it takes for a the number of nuclei of the isotope in a sample to halve.

or

The time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.

Question 25

What is meant by irradiation?

Answer 25

Exposing an object to nuclear radiation.

Question 26

How is irradiation used for sterilisation?

Answer 26

The object is placed inside a sealed plastic wrapper to stop bacteria from entering. Place the object near a radioactive isotope which emits gamma radiation. The isotope is inside a lead shield to protect workers from the radiation. Withdrawing the internal lead shield allows gamma radiation to irradiate the object. This kills any bacteria present. The object does not become radioactive as the object hasn't come into contact with the isotope itself.

Question 27

What precautions do people who work with radioactive isotopes have to take?

Answer 27

Ionising radiation can increase the risk of cancer. Gloves can protect against alpha radiation. (Low penetrating power) Beta and gamma radiation can be reduced using a lead apron. With high levels, use lead walls and lead-glass screens Radiation monitors can measure how much radiation has been received. This means we can stop people working with radioactive isotopes if they absorbed too much.

Question 28

What is meant by radioactive contamination?

Answer 28

When unwanted radioactive isotopes end up on other materials. This is dangerous because the radioactive atoms decay and emit ionising radiation.

Question 29

How hazardous is each type of radiation?

Answer 29

Alpha: Strongly ionising but easily stopped by dead cells on the skin surface. Alpha emitters are dangerous when inhaled or swallowed. Beta: Quite ionising and can penetrate skin into the body. Gamma radiation: Weakly ionising. Can penetrate the body but likely to pass straight through.