Background Radiation, Correct Count-Rate, Uses and Risks of Radiation

Question 1

What is background radiation?

Answer 1

A combination of natural and man-made low-level radiation that exists around us at all time.

Question 2

What are some natural sources of background radiation?

Answer 2

• radon gas (from the ground)
• buildings
• cosmic rays from space (e.g: sun-rays)
• rocks
• food and drink

Question 3

What are some man-made sources of background radiation?

Answer 3

• fallout (radioactive material that falls back to Earth) from nuclear weapons testing
• nuclear accidents (e.g: Chernobyl)
• radiotherapy
• exposure from medical testing (e.g: x-rays)

Question 4

What factors affect the amount of background radiation a person receives?

Answer 4

• where they live
• their occupation
• other environmental factors

Question 5

Through which method of radioactive exposure does background radiation mainly affect people?

Answer 5

Mostly by irradiation, since background radiation isn’t directly in contact, but there’s a smaller contribution from contamination via radioactive atoms in food and drink.

Question 6

How does location influence background radiation?

Answer 6

Some areas have higher natural background radiation because they are closer to natural sources of radiation.

Question 7

How does occupation influence radiation exposure?

Answer 7

People who work with nuclear radiation receive higher doses.

Question 8

What is the amount of radiation a person receives called?

Answer 8

Dose

Question 9

What is radiation dose measured in?

Answer 9

Sieverts (Sv)

Question 10

1 Sievert = ? milliSieverts

Answer 10

1000

Question 11

What’s the difference between activity and count-rate?

Answer 11

Activity - total number of nuclear decays per second in a radioactive source; measured in Becquerels (Bq), where 1Bq = 1 decay per second

Count-Rate - number of decays actually detected per second by a G-M tube; measured in counts per second (cps)

Question 12

Why is count-rate usually less than the activity?

Answer 12

Because not all emitted radiation is detected (some may escape or be blocked)

Question 13

Why must background radiation be considered when measuring a sample with a G-M tube?

Answer 13

Since background radiation contributes to the readings, it must be subtracted to find the true count rate of a sample.

Question 14

What steps are taken to calculate the corrected count rate?

Answer 14

1. Measure background radiation by pointing G-M tube into the air
2. Point G-M tube at the sample being measured - this will give the reading of the sample AND background radiation combined.
3. Subtract the sample reading by the background radiation reading to give the corrected count rate.

Question 15

Why is milliSieverts often used?

Answer 15

The dose from background radiation is small.

Question 16

Why are alpha particles used in smoke detectors?

Answer 16

They have a high ionising power, which ionises air to create a current. Smoke blocks these ions, and a drop in current is detected, which is what triggers the alarm.

Question 17

Why is alpha radiation the most suitable for detecting smoke?

Answer 17

Alpha particles are the largest of the three types, so they interact most strongly with matter, so are very sensitive to changes in air composition, which is crucial for the early detection of fires..

Question 18

Why are beta particles used to measure material thickness?

Answer 18

Beta particles have moderate penetration and ionising power, so are absorbed at predictable rates, allowing for precise measurements.

Also, beta particles penetrate materials enough to provide information without passing completely through, which is ideal for non-destructive testing of materials, like sheets of metal.

Question 19

Why are gamma rays used in medical tracers?

Answer 19

They penetrate living tissue and exit the body with being absorbed as much as alpha/beta, so can be detected externally, allowing for images of internal organs to be produced.

Question 20

How is a medical tracer used?

Answer 20

• a radioactive substance (e.g: iodine-123) is injected/ingested
• it flows through the blood
• is absorbed by specific organs
• emits gamma rays
• is detected by an external detector to monitor organ functions or detect abnormalities

Question 21

How does the low ionising power of gamma radiation make it suitable for use in medical tracers?

Answer 21

• reduces the risk of damage to healthy tissues

Question 22

Why do medical tracer isotopes have a short half-life?

Answer 22

They decay quickly, so only emit radiation for a short period of time, so still gives a clear signal for imaging, but the patient’s total exposure to radiation stays low.

Question 23

How is irradiation used to preserve food?

Answer 23

Gamma rays (e.g: from cobalt-60) are highly penetrating, so pass through food packaging and kill bacteria, preserving food without changing it significantly, and the object doesn’t become radioactive itself.

Question 24

How is medical equipment sterilised using irradiation?

Answer 24

Gamma rays have high penetrating power, so can pass through packaging and reach all surfaces of medical instruments, killing bacteria without opening the packaging, and the instruments don’t become radioactive.

Question 25

Advantages of the uses of irradiation?

Answer 25

- kills bacteria without high heat - preserves food - sterilises medical equipment

Question 26

Disadvantage of the uses of irradiation?

Answer 26

- may not kill all bacteria - harmful to human cells if exposed for too long - careful handling needed

Question 27

How is external radiotherapy used to treat cancer?

Answer 27

Beams of high doses of radiation of gamma rays are directed from multiple angles to maximise the dose on tumour cells, whilst minimising exposure to soft, healthy tissue.

Question 28

How is internal radiotherapy used?

Answer 28

Radioactive pellets are implanted into tumours to expose them directly to radiation.

Question 29

Risks of radiotherapy?

Answer 29

- if careful dose calculations aren't made, healthy tissue can be irradiated - can cause side effects

Question 30

How can gamma-emitting isotopes detect leaks?

Answer 30

- gamma-emitting isotope is added to water - if a pipe leaks, contaminated water seeps into the ground - causes a build-up of gamma emissions - this build-up can be found using a G-M tube - helps workers locate exactly where to dig

Question 31

What are the requirements for the isotopes used in leak detection?

Answer 31

- must emit gamma - non-toxic, since it will form part of the water supply - half-life at least several days to allow the emissions to build up in the soi

Question 32

How does nuclear radiation affect human tissues?

Answer 32

- ionises chemicals within a body - which changes the way cells behave - deposits large amounts of energy into the body - which can damage/destroy cells completely

Question 33

What can high doses of radiation cause to the eye?

Answer 33

forms cataracts (cloudy area in lens of the eye)

Question 34

What can radioactive iodine cause to the thyroid gland?

Answer 34

- can build up and cause cancer - particularly during growth

Question 35

What can breathing in radioisotopes do to the lungs?

Answer 35

damage DNA

Question 36

What can radioisotopes do to the stomach?

Answer 36

-can sit in the stomach and irradiate for a long time

Question 37

What can high doses of radiation do the reproductive organs?

Answer 37

can cause sterility or mutations

Question 38

What can radiation do to the skin?

Answer 38

can burn skin, or cause skin cancer

Question 39

What can radiation do to bone marrow?

Answer 39

can cause leukaemia and other diseases of the blood

Question 40

What is the disadvantage of using contamination for medical tracers?

Answer 40

May not go where they are wanted.

Question 41

What is the disadvantage of internal radiotherapy?

Answer 41

It can be difficult to ensure that the contamination is FULLY removed, so small amount of radioisotope may still be left behind.

Question 42

Why is radiation still used in medicine despite its risks?

Answer 42

For many, the benefits of diagnosing and treating serious conditions, like cancer, often outweigh the small risks of radiation exposure.

Question 43

Why must radiation exposure in medicine be carefully controlled?

Answer 43

Any prolonged or unnecessary exposure increases the risk of future health problems, so radiation must only be used when the medical benefits are greater than the potential harm.

Question 44

Even though the low doses of radiation reduce the damage to healthy tissues, what can it cause?

Answer 44

can cause minor damage without killing the cells, so gives rise to mutant cells, which divide uncontrollably, leading to cancer

Question 45

What do high doses of radiation lead to in the body?

Answer 45

- kills cells completely - causing radiation sickness - includes vomiting, tiredness, hair loss - but only if a lot of cells get killed at once