Dr Pusey

www.puseyscience.com

Syllabus points The measurement of absorbed dose and dose equivalence enables

the analysis of health and environmental risks

This includes applying the relationships:

𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 =𝐸

𝑚𝑑𝑜𝑠𝑒 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 = 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 × 𝑞𝑢𝑎𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟

Learning goals Define:

dose dose equivalent absorbed dose quality factor

Identify that all radiation delivers energy to cellular material Recall radiation can cause ionization which disrupts cellular process (e.g.

gene mutation) Identify that the degree of radiation damage depends on the amount of

energy (which is determined by half-life and time of exposure) Deduce the dose equivalence and its possible physiological consequences

by referring to a data table

Use and rearrange the following equations 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 =𝐸

𝑚𝑑𝑜𝑠𝑒 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 = 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 × 𝑞𝑢𝑎𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟

Give the SI units for: Absorbed dose, quality factor, dose equivalence

Exposure to radiation Effect of radiation on the body depends on:

the quantity of radiation absorbed

the type of radiation

the nature of organs, tissues, cells exposed to the radiation

Ionizing radiation = any type of radiation that can ionise cells. E.g. alpha, beta, gamma

Ionizing radiation removes (or adds) electrons from the cell, causing it to become charged (an ion)

Ions can cause unwanted chemical reactions, damaging or even killing cells, cell division can also be affected

Absorbed dose

Radiation dose is measured in terms of joules per kilogram of tissue

SI unit is the Gray (Gy)

1 Gy = 1 J/kg

Another unit you might see is the rad (1 Gy = 100 rad)

𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 =𝐸

𝑚

Energy absorbed by tissue (J)

Mass of tissue (kg)

(Gy)

Example 1

a) If a 30 kg child absorbed 200 J of radiation energy, what would their absorbed dose be?

b) If a 80 kg adult absorbed the same amount of energy, what would their absorbed dose be?

Example 1a) If a 30 kg child absorbed 200 J of radiation energy, what would their

absorbed dose be?

Example 1b) If a 80 kg adult absorbed the same amount of energy, what would their

absorbed dose be?

Example 2What is the mass of an adult who received an absorbed dose of 5 Gy and the energy from the radiation was 500 J.

Example 2What is the mass of an adult who received an absorbed dose of 5 Gy and the energy from the radiation was 500 J.

DOSE equivalence Different forms of radiation have

different ionisation abilities, so they can cause different amounts of damage

Quality factor – gives a weighting to the amount of damage caused by different types of radiation

Dose equivalent – takes into account absorbed dose and quality factor

Dose equivalence is measured in Sieverts (Sv)

Radiation Quality Factor

Alpha 20

Beta 1

Gamma 1

Neutrons (10 keV)

10

X-Rays 1

𝐷𝑜𝑠𝑒 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡= 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 × 𝑞𝑢𝑎𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟

(J/kg or Gy)

(Sv)

Example 3

Calculate the dose equivalent from a radiation source if the absorbed dose is 0.75 mGy and the radiation is:

a) Alpha radiation

b) Beta radiation

c) Gamma radiation

Example 3

Calculate the dose equivalent from a radiation source if the absorbed dose is 0.75 mGy and the radiation is:

a) Alpha radiation

Example 3

Calculate the dose equivalent from a radiation source if the absorbed dose is 0.75 mGy and the radiation is:

b) Beta radiation

c) Gamma radiation

From: http://en.wikipedia.org/wiki/Dosimetry#mediaviewer/File:SI_Radiation_dose_units.png

Radiation and the human body When sources of radiation are outside the

body: beta and gamma radiation are the most dangerous

because they can reach the cells of organs and may be absorbed by them

alpha radiation is least dangerous because it is unlikely to reach living cells

When sources of radiation are inside the body: alpha radiation is the most dangerous because it is so

strongly absorbed by cells, high ionisation ability

beta and gamma radiation are less dangerous because cells are less likely to absorb the radiation

Radiation from daily life

From: http://www.qpn.kyushu-u.ac.jp/message/info01/radiation_e.html

Story Time - Monitoring radiation at work People who work around radiation such as doctors, dentists, radiologists and

astronauts need to monitor their exposure to radiation for their safety Radiation is invisible and cannot be felt so radiation workers need to wear a

radiation monitoring badge A ‘film badge’ contains a photographic film in a light proof holder The badge has three filters to detect each type of radiation After being worn the film is developed to determine the amount and type of

radiation each person has been exposed to

From: http://www.mrcorfe.com/DAOS/Year11/Radioactivity/Ionising.html

Resources

AV Which Medical Device – real time radiation dose in medical

procedures (4:36)

Further Reading Science Media Centre of Japan – info about Fukushima Information is Beautiful - infographic about radiation doses Calculate your exposure to radiation in your daily life Radiation exposure for different activities

How did you go? Define:

dose

dose equivalent

absorbed dose

quality factor

Identify that all radiation delivers energy to cellular material

Recall radiation can cause ionization which disrupts cellular process (e.g. gene mutation)

Identify that the degree of radiation damage depends on the amount of energy (which is determined by half-life and time of exposure)

Deduce the dose equivalence and its possible physiological consequences by referring to a data table

Use and rearrange the following equations 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 =𝐸

𝑚𝑑𝑜𝑠𝑒 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 =

𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑑𝑜𝑠𝑒 × 𝑞𝑢𝑎𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟

Give the SI units for: Absorbed dose, quality factor, dose equivalence