5. Uses of Radioactivity

Question 1

How is alpha radiation used in smoke alarms?

Answer 1

1. Alpha particles pass through two charged plates and ionises the atoms in the air.
2. The ions flow towards the oppositely charged plate. This causes a current to flow .
3. If smoke is present it will absorb some of the alpha particles resulting in less ionisation, which means a smaller current flows, so the alarm sounds.

Question 2

Why is alpha used in smoke alarms?

Answer 2

It has a low penetrating power so it will be absorbed by the smoke and also it is absorbed by a few cm of air, so as long as the detector is high up on a wall it is safe for humans to be in the same room.

Question 3

Why is a source with a long half life used for the smoke detector?

Answer 3

So that the smoke detector does not have to be replaced too frequently

Question 4

How is beta used in gauging?

Answer 4

1. Aluminium is placed between a radioactive source and a detector, and the thicker the sheet, the lower the count rate since more beta is absorbed

Question 5

What would happen if alpha particles were used for gauging?

Answer 5

Have a low penetrating power so would be absorbed by the aluminium, there will be no change in the cam reading so you can’t determine the thickness

Question 6

How is gamma radiation used in crack detection?

Answer 6

1. Gamma emitter injected into pipeline downstream, so it flows
2. As gamma has a high penetrating power, it can be transmitted by rocks and earth surrounding the pipe
3. Where there is a crack in the pipe, gamma radiation will penetrate more easily, and collect outside the pipe, and more radiation will be detected at that point

Question 7

What would happen if alpha particles were used for crack detection?

Answer 7

Low penetrating power, so the radiation would not make it to the surface and be detected

Question 8

Why would a source with a half life of several hours or days be used?

Answer 8

Too long- environmental damage

Too short- not long enough for experiment

Question 9

How is beta and gamma radiation used as a medical tracer?

Answer 9

1) beta and gamma penetrate the skin and tissue
2) source injected, penetrates skin and tissues
3) the source’s movement in the body is detected and monitored on a computer
4) used to see if there are any bodily issues

Question 10

Why does the source have a short half life for a medical tracer?

Answer 10

So that the initial levels are high enough to be detected, but then decrease quickly so as not to cause too much damage to healthy tissues

Question 11

Why would you not use alpha for a medical tracer?

Answer 11

Wouldn’t be able to penetrate organs and tissues

High ionising power makes it harmful if it is inside you

Question 12

How is gamma radiation used to kill cancerous cells?

Answer 12

Beam of gamma radiation is rotated around the body with the tumour as the focus

• where gamma rays intersect = high dose of radiation
• but doesn’t damage healthy tissue, low dose

Question 13

How can gamma rays be used to sterilise food and equipment?

Answer 13

• food can be irradiated to kill bacteria and to keep it fresh, doesnt involve high temps so fresh fruit can be sterilised without being damaged
• medical equipment can be sterilised

Question 14

What is the difference between contamination and irradiation?

Answer 14

Irradiation -> exposed to ionising radiation, not dangerous as not EMITTING ionising radiation

• contamination -> when some of radioactive isotope has been transferred to object IT WILL CONTINUE TO EMIT IONISING RADIATION it is dangerous to us