Ionising RadiationsPractical aspects

Dr Gordon Parker

The physics

Properties of radiation 1

• Alpha particles – α– heavy, two positive charges– don’t penetrate materials very far– easy to shield

• Beta particles – β– light, one negative charge (i.e. electron)– more penetrating than alpha– can be shielded by low density materials

Properties of radiation 2

• Gamma and x-rays – γ & x– uncharged waves– very penetrating– shielded by dense materials

• Neutrons– uncharged particles– cause indirect ionisation– very penetrating– shielded by hydrogenous materials

Radiation penetration

Activity and half life

• Activity– number of decaying atoms per second– unit – Becquerel (Bq)

• Half life – the time for half the atoms to decay– unique to the isotope

Typical half lives

• Physical half lives:

• Uranium 238 4,500 million years

• Tritium (H3) 12.3 years

• Iodine 131 8.05 days

• Fluorine 18 1.83 hours

Biological and effective half lives

Isotope T (physical)

hours

T (biological)

hours

T (effective)

hours

3H 1.1x 105 2.8x102 2.8x102

90Sr 2.6x105 4.3x105 1.6x105

99Tc 6 24 4.8

18F 1.83 6 1.4

Units – absorbed dose (D)

• Energy is measured in Grays (Gy)

• Absorbed dose (D)– the measure of energy deposition in any

medium by any type of radiation (i.e. not directly related to ‘biological’ effect)

– important in emergencies “what is the total energy in this event?”

Units – equivalent dose (H)

• Equivalent dose is measured in Sieverts (Sv)– the extent to which biological matter has been

exposed– Sv = Gy x weighting factor (WR)

WR = 1 for β, γ and x radiation

WR = 20 for α particles

WR = 5-20 for neutrons

Effective dose (E)

• Measured in Sieverts (Sv)– the measure of varying risk to different organs

– depends on tissue weighting factor (WT)

WT Gonads 0.2

Lung 0.12

Breast 0.05

Skin 0.01

E = H x WT

Radiation interaction with matter

How does radiation damage a living cell?

• Ionisation in the cell

• Damage to DNA (direct and indirect)

• Cell death – deterministic effect

• Cell reproduction – stochastic effect

Deterministic effects

• Death with increasing dose:

Pro

babi

lity

of

effe

ct

Dose

Stochastic effectsστοχος = “guess”

• Stochastic risk is due to cell damage and repair.

• Probability of cancer increases with increasing dose.

• No threshold?

• Is it linear?

Dose

Effect

Part 2 Practical aspects of radiation doses

• What are the likely effects of exposure?

• What is a ‘big’ dose?

• What is a ‘dangerous’ dose?

Comparative risks

• 1 Sv = 5% increased cancer risk – (general population)

• 1 Sv = 4% increased cancer risk– (occupational)

• Risk of dying of cancer (UK) = 23%

• Adding 1 Sv radiation increases your risk to 27%

Radiation doses

• Banana• Background 2.70mSv (range 1 -13)

• Flying to US 0.07mSv• CXR 0.10mSv• Nuclear Power Station 0.18mSv• Living in Cornwall 7.80mSv • Abdominal CT 8.00mSv• LD50 5Sv

1μSv Banana Equivalent Dose

Dose limits

• Employees over 18• Trainees under 18• Women

• Skin & extremities• Eyes

• Investigation levels

Exposure limits in exceptional circumstances

Type of Exposure Immediate Recovery

Emergency Dose

Extreme

Authorised by Senior Fire Officer

Incident Controller

Emergency controller

Who Fire Personnel

Volunteers (?)

Max dose 20 mSv 100 mSv 500 mSv

Radiation protection

• The three principles of radiation protection are:

Irradiation and contamination

• General PPE– rubber gloves– overalls or Tyvek suits, air-cooled suits– full face respirators, BA – Wellington boots

The monitoring alarms sound…

• What do you do…?

Overexposures

Investigating overexposures

• What do you do?

– history– examination– biological investigations

Part 3 – Fitness for work

• The Classified Worker

• The work of an Appointed Doctor

The role / responsibilities of the employer

• Designating workers as classified persons• Consulting the RPA about doses to which female

employees may be exposed• Arranging medical surveillance and providing facilities

and/or time• Maintaining a valid health record and ensuring that any

conditions specified in the health record are observed• Furnishing the doctor with relevant information• Permitting appointed doctors to view the workplace• Notifying the AD or EMA of any suspected

overexposures• Cooperating with other employers as necessary

The role / responsibilities of the AD

• Liaising with the employer to ensure that the AD has an understanding of the work and the risks

• Liaising with the HSE• Conducting the medical examinations and health

reviews; maintaining adequate clinical records• Specifying any conditions on the Health Record• Conducting special medical examinations following

overexposures• Submitting statistical returns to the HSE• Undergoing training and maintaining up-to-date

knowledge

Classified Person

• Regulation 20

• “…the employer shall designate as classified persons those of his employees who are likely to receive an effective dose in excess of 6mSv per year or an equivalent dose which exceeds three-tenths of any relevant dose limit…”

Outside workers

Termination of Classification

Cases

Example 1

• A 28 year old lady with hand dermatitis applies for a laboratory job involving handling sources in a glove box:

Fit without restriction?Fit subject to regular health surveillance?Unfit?Other suggestions?

Cases

Example 2• A 45 year old man applies for a job as

general duties assistant in a nuclear power station. He has a long history of asthma, using regular inhaler steroids and beta-agonists, several short spells of absence from previous job (usually in the winter) and two admissions to hospital in the past 6 years.

• Fit without restriction?

• Fit with restrictions?

• Fit subject to regular health surveillance?

• Unfit?

• Other suggestions?

Cases

Example 3

• 32 year old lady with a history of melanoma – has had two abdominal CTs in the past two years – applies for a job as a PET CT technician…

18F-FDG fludeoxyglucose

200-400 MBq

High energy, needs significant shielding: thickness of lead

Thickness of lead (mm)

Coefficient of attenuation

4.1 0.50

8.3 0.25

13.2 0.10

26.4 0.01

52.8 0.001

Doses for PET CT scanner

Jan 11 Feb 11 Mar 11 Apr 11

Whole body

0.11mSv 0.08mSv 0.10mSv 0.04mSv

Eye 0.15mSv 0.10mSv 0.05mSv 0.06mSv

Right index finger TLD

2.8mSv 1.80mSv 2.40mSv 1.75mSv

Right index finger ring

0.8mSv 0.3mSv 0.7mSv 0.10mSv

• Fit without restriction?

• Fit with restrictions?

• Fit subject to regular health surveillance?

• Unfit?

• Other suggestions?

Cases

Example 4

• 43 year old man with a long history of anxiety and depression treated with antidepressants. One suicide attempt two years ago. Applies for a job as an industrial radiographer. Will be working on site, sometimes offshore…

• Fit to become a classified worker

• Unfit to become a classified worker

• Fit for job without restrictions

• Fit for job with restrictions

• Other suggestions?

Questions / discussion