Radioactivity

Question 1

What is alpha decay?

Answer 1

The atom releases an alpha particle which has a mass of 4. It does this to become more stable.

Question 2

What is an alpha particle?

Answer 2

4
H
2

Question 3

What does the alpha particle do to the mass of the atom?

Answer 3

It decreases it by 4.

Question 4

What happens to the proton/atomic number of the atom when it loses an alpha particle?

Answer 4

It decreases by 2.

Question 5

What happens in Beta Decay?

Answer 5

It turns a neutron into a proton. When this happens an electron is also emitted. A beta particle is an electron created and emitted by a nucleus that has too many neutrons compared to protons.

Question 6

What does Beta decay occur?

Answer 6

When a nucleus has too many protons or too many neutrons. One of the protons/neutrons is transferred into the other.

Question 7

What happens in Beta Minus Decay?

Answer 7

A neutron decays into a proton, releasing an electron.

Question 8

What is the relative mass and charge of a beta particle (electron)?

Answer 8

The relative mass is 0
The relative charge is -1

0
B
-1

Question 9

What happens when an unstable nucleus emits a beta particle?

Answer 9

The atomic number of the nucleus goes up by 1. The mass number is unchanged.

Question 10

What is a gamma ray?

Answer 10

It is electromagnetic radiation from the nucleus of an atom. It is uncharged and has no mass. Therefore, it’s emission does not change the number of protons or neutrons in a nucleus. So the mass and charge of the nucleus is both unchanged.

Question 11

What is neutron emission?

Answer 11

Sometimes neutrons are emitted by some radioactive substances as a result of an alpha particle colliding with an unstable nuclei in the substance. If this collision happens it causes the unstable nuclei to become even more unstable and emit a neutron. As the emitted are uncharged they can pass through substances more easily than an alpha or beta particle can.

Question 12

What does a Geiger counter do?

Answer 12

It measures the count rate (the number of counts per second)
To take account of background radiation you must:
Measure the count rate without the radioactive source present. This is the background count rate.
Then measure the count rate with the source in place. Subtracting the background count rate from this gives you the count rate from the source alone.

Question 13

How do you calculate a radioactive substance penetrative power?

Answer 13

Add absorber materials between the Geiger counter and the substance. Then measure the count rate and continue to add layers of material until the count rate is zero. This means that the radiation from the source has been stopped by the absorber material.
To test the range that each type of radiation travels through air you need to move the tube away from the source. When the tube is beyond the range of the radiation, the count rate from the source is zero.

Question 14

What is ionisation?

Answer 14

The radiation from a radioactive substance can knock electrons out of atoms. The atoms become charged because they lose electrons. This process is caused ionisation.
When an object is exposed to ionising radiation it is said to be irradiated. However, it does not become radioactive.

Question 15

What is radioactive contamination?

Answer 15

Radioactive substances can contaminate other materials that they come into contact with. Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. This is a hazard due to the decay of the nuclei of the contaminating atoms.

Question 16

What is the most ionising radiation?

Answer 16

Alpha is the most dangerous as it’s ionising power is greater Han gamma or beta.

Question 17

What is the activity of a radioactive source?

Answer 17

The number of unstable atoms in the source that decay per second. The unit of activity is Becquerel (Bq) which is 1 decay per second.

Question 18

What is the count rate?

Answer 18

The number of counts in the Geiger counter per second. This is proportional to the activity of the source, as long as the distance between the tube and the source stays the same.

Question 19

What is the half life of a radioactive substance?

Answer 19

The average time taken for the count rate (and so the number of parent atoms) to fall by half.
The time it takes for the:
Number of nuclei of the isotope in a sample (and so the mass of parent atoms) to halve.
The count rate from the isotope in a sample to fall to half of its initial value.

Question 20

Talk about radioactive tracers?

Answer 20

They are used to trace the flow of a substance through an organ. The tracer contains a radioactive isotope that emits gamma radiation as it can be detected outside the system. The patient drinks some water counting the radioactive substance. If the kidney is blocked the detector will go up and stay up. This is because the radioactive substance does not flow back out of the kidney.

Question 21

Talk about gamma cameras?

Answer 21

They are used to take images of internal body organs. The patient is injected with a solution that contains a gamma emitting radioactive isotope. The solution is absorbed by the organ and a nearby gamma camera detects the gamma radiation emitted by the solution. The detector signals build up an image of where the radioactive isotope is located in the organ.

Question 22

Talk about a gamma beam/knife

Answer 22

Narrow beams are directed at tuberous cells in order to destroy it.

Question 23

Talk about radioactive implants?

Answer 23

Beta or gamma emitting isotopes are used in the form of small seeds or tiny rods.

Question 24

What is nuclear fission?

Answer 24

The nucleus of an atom is struck by a neutron, causing the nucleus to split into two smaller fragment nuclei.

Question 25

What is released during fission?

Answer 25

Two or three neutrons
Energy in the form of gamma radiation
Plus kinetic energy stored in the fission neutrons and the fragment nuclei.

Question 26

Why does a chain reaction occur during nuclear fission?

Answer 26

The neutrons released from each fission event can cause more fission events, to maintain the chain reaction.

Question 27

What does the nuclear core inside the nuclear reactor contain?

Answer 27

Fuel rods
Control rods
Water at a high pressure

Question 28

What is the purpose of water in a nuclear reactor?

Answer 28

It acts as a moderator because it slows down the fission neutrons. They are slowed down by collisions with the atoms in the water molecules.

Question 29

What is the job of control rods in a nuclear reactor?

Answer 29

They absorb surplus neutrons. This keeps the chain reaction under control. The depth of the rods can be adjusted to maintain a steady chain reaction.

Question 30

What is the job of the fuel rods in a reactor core?

Answer 30

They become very hot and the water acts a a coolant. It’s molecules kinetic energy stored increases as energy is transferred from the neutrons to the fuel rods. The water is pumped through the core, then it goes through sealed pipes to and from a heat exchanger outside the core. The water transfers energy from the core to the heat exchanger.

Question 31

Why is the reactor core surrounded by concrete?

Answer 31

To absorb ionising radiation that escapes through the walls of the steel vessel.

Question 32

What is nuclear fusion?

Answer 32

When two small nuclei release energy when they are fused together to form a single larger nucleus.

Question 33

What happens in a fusion reactor?

Answer 33

The plasma is heated by passing a very big electric current through it.
The plasma is contained by a magnetic field so that it doesn’t touch the reactor walls. If it did, it would go cold and the fusion would stop.

Question 34

Why are very high temperatures required for nuclear fusion to occur?

Answer 34

Two approaching nuclei will repel each other because of their positive charges. But if the nuclei are moving fast enough, they can overcome this force of repulsion and fuse together.

Question 35

What is activity?

Answer 35

The number of unstable atoms in the source that decay per second.