A hand of mass 0.50 kg absorbs 1.5 mJ of energy from a radiation source. Calculate the absorbed dose.

The absorbed dose is 1.5 × 10⁻³ ÷ 0.50 = 3.0 × 10⁻³ Gy, which is 3.0 mGy.

What is meant by effective dose, and what is its unit?

Effective dose measures the biological harm done by a given absorbed dose, allowing for how damaging the type of radiation is, and it is measured in sieverts.

Write the relationship between effective dose and absorbed dose.

The effective dose in sieverts is the absorbed dose in grays multiplied by the quality factor of the radiation concerned.

State typical quality factors for beta, gamma and alpha radiation.

Beta and gamma radiation both have a quality factor of about 1, whereas alpha radiation has a quality factor of about 20.

OCR A-Level Physics B H557

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Ionising Radiation and Risk

Absorbed dose, effective dose and risk

3 things to know
Components 01, 02 and 03

Overview

Recall questions on absorbed dose and the gray, effective dose and the sievert, quality factors for alpha, beta and gamma radiation, absorbed and effective dose calculations, why two quantities and two unit names are needed, risk as probability times consequence, the chance of harm from an 8.0 mSv procedure, and the judgement involved in assessing risk.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why are two separate quantities needed to describe a radiation exposure?

Key term

Define absorbed dose and state its unit.

Key term

Express the gray in terms of joules and kilograms.

Questions from this subtopic

Each one with the model answer underneath.

1
Define absorbed dose and state its unit.
Model answer
Absorbed dose is the energy deposited by ionising radiation per unit mass of the absorbing material, measured in grays.
2
Express the gray in terms of joules and kilograms.
Model answer
One gray is one joule of energy deposited per kilogram of material, so 1 Gy = 1 J kg⁻¹.
3
A hand of mass 0.50 kg absorbs 1.5 mJ of energy from a radiation source. Calculate the absorbed dose.
Model answer
The absorbed dose is 1.5 × 10⁻³ ÷ 0.50 = 3.0 × 10⁻³ Gy, which is 3.0 mGy.
4
What is meant by effective dose, and what is its unit?
Model answer
Effective dose measures the biological harm done by a given absorbed dose, allowing for how damaging the type of radiation is, and it is measured in sieverts.
5
Write the relationship between effective dose and absorbed dose.
Model answer
The effective dose in sieverts is the absorbed dose in grays multiplied by the quality factor of the radiation concerned.
6
State typical quality factors for beta, gamma and alpha radiation.
Model answer
Beta and gamma radiation both have a quality factor of about 1, whereas alpha radiation has a quality factor of about 20.

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