Radiation practical course (Dr Gordon Parker 2012)
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Transcript of Radiation practical course (Dr Gordon Parker 2012)
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