Biological Effects of Radiation

Question 1

What are the two main effect of radiation on organisms?

Answer 1

Direct damage to molecules and the generation of highly active chemicals (free radicals)

Question 2

What are free radicals?

Answer 2

Neutral atoms or molecules with an unpaired electron. They are extremely chemically reactive and diffuse through the body, inducing chemical changes in critical biological structures.

Question 3

Why is radiolysis dangerous?

Answer 3

Radiolysis is the ionisation of water molecules by radiation. These water ions can break up into either an H+ ion or OH- ion and a free radical

Question 4

What is the oxygen effect?

Answer 4

Oxygen reacts with free radicals, forming reactive organic proxy radicals which can produce further free radicals.

Question 5

What is linear energy transfer (LET)?

Answer 5

The energy deposited along a path travelled, typically measured in keV / mm. Similar to stopping power but in a biological context.

Question 6

Difference between high and low LET?

Answer 6

High LET radiation produces more irreparable damage than low LET radiation of the same dose.

Question 7

Absorbed dose

Answer 7

The amount of radiation deposited in a mass of tissue. Measured in gray (Gy) (J/kg)

Question 8

Equivalent dose

Answer 8

Absorbed dose weighted by a relative radiation weighting factor depending on the type of radiation. Measured in sieverts (Sv)

Question 9

Effective dose

Answer 9

All the different equivalent doses further weighted by a tissue weighting factor to account for the susceptibility of different tissues to radiation. Measured in sieverts (Sv)

Question 10

Acute vs Chronic doses

Answer 10

Acute doses are sudden, short doses. Chronic doses are long-term, often more low level, doses.

Question 11

What is fractionation?

Answer 11

A single, lethal dose is split into smaller doses with a time interval in between to reduce the dose rate and allow the body to recover in the intervals.

Question 12

Deterministic effects of radiation?

Answer 12

Effects which over a given threshold will always reliably occur, and severity increases with dose.

Question 13

Stochastic effects of radiation?

Answer 13

Effects which increase in probability with dose, but the severity does not change. (eg cancer)

Question 14

What are the 3 sub-groups of acute radiation syndrome (ARS)?

Answer 14

Haematopoetic (decrease in no. of blood cells), Gastrointestinal (nausea, vomiting etc) and Neurovascular (dizziness and loss of consciousness)

Question 15

Dose limits?

Answer 15

The recommended maximum radiation dose for a person per year. Measured above the background and exclude any medical reasons.
In the UK the whole-body dose limit is 1 mSv/yr for a member of the public

Question 16

Sources of background radiation?

Answer 16

Radon and Thoron gas (~48%), Medical exposures (~16%), Terrestrial gamma radiation (~13%), Cosmic rays (~12%), Intake of natural radionuclides (~11%) and other trace amounts from weapons testing and power plants.

Question 17

3 ways to protect from radiation?

Answer 17

Time, distance and shielding