working with radiation in the university of bristol department of physics
TRANSCRIPT
Working with Radiation in the University of Bristol
Department of Physics
Aim
The aim of the session is to introduce you to radiation, the structures in place to keep you safe when working with radiation, and to point you in the right direction if further training is needed.
Objectives
• Remind you that radiation can be a hazard
– Introduction to types of radiation
– Health effects.
• Illustrate potential risks involved with handling radioactive sources.
• Outline the structure for keeping people safe.
• Hand over to X-ray talk.
Early uses of radioactivity
Radium and thorium
Radiation Injuries
• 1896 - first injuries due to radiation recorded
• 1902 - first skin cancers seen
• 1911 – 94 cases of skin carcinomas and sarcomas reported
Radiation Units
Activity Number disintegrations per second (Becquerel)
Absorbed dose Energy deposited in any medium by any type of ionising
radiation (Gray)
Dose equivalent Dose allowing for type of radiation and biological damage
(Sievert)
Equivalent Dose
Equivalent dose (HT) is the absorbed dose in tissue or organ T weighted for the type and quality of radiation R.
HT,R = WRDT,R
Where DT,R is the absorbed dose averaged over organ
or tissue T, due to radiation R
WR is the radiation weighting factor
Equivalent Dose
Radiation Type Weighting Factor
(ICRP 103, 2007)
Beta, Gamma, X-ray 1
Alpha 20
Neutrons Between 2.5 & 20
Old/US Units
• Rad 100 Rads = 1 Gray
• Rem 100 Rem = 1 Sievert
• Ci 1 Curie = 3.7 x 1010 Bq (dps)
1 mCi = 3.7 x 107
( to avoid confusion, steer clear of CGS units if possible)
Dose Limits – For Workers
• 1934 2 mSv per day or 730 mSv per year
• 1937 2 mSv per day or 10 mSv per week
• 1950 3 mSv per week or 150 mSv per year
• 1956 1 mSv per week or 50 mSv per year
• 1977 50 mSv per year
• 2000 20 mSv per year
ICRP 60 (Published 1990)
• Justification – there should be a net benefit
• Optimisation – restriction of exposure
• ALARP/ALARA
Average annual dose to UK population (2.6 mSv)
Radon gas from the ground 50%
Food and drink 11.5%
Nuclear discharges <0.1%
Products 0.1%Fallout 0.2%
Occupational 0.3%
Gamma rays from ground and buildings
14%
Medical 14%
Cosmic rays 10%
Annual Dose Limits
Whole Body Extremities and skin Lens of the eye
Employees aged 18 and over
20 mSv 500 mSv 150 mSv
Trainees aged 18 and under
6 mSv 150 mSv 50 mSv
Any other person ( e.g. Undergraduates)
1 mSv 50 mSv 15 mSv
Women of reproductive capacity - exposure of abdomen limited to 13 mSv in any consecutive 3 month period.
Properties of Radiation
Biological Effects of Ionising Radiation
Introduction
• Health Effects are determined by the type and intensity of the radiation and the period of exposure.
Radiation Effects
• Direct ionisation– Structural cell damage,
weakens links between atoms
• Indirect ionisation– Damage to chemical
constituents, e.g. water– Formation of free
radicals
Radiation effects
• Stochastic effects – somatic and hereditary effects
• Deterministic effects – loss of function
Stochastic effects
Dose
ProbabilityEffect, e.g. malignancy and hereditary effects
No threshold for an effect to occur, probability increase as dose received increases
Deterministic Effects
Dose
Severity ThresholdEffect, e.g. cataracts, fetal damage, skin effects
Degree of cells killed increases with dose impairing organ function
Deterministic Effects
• 50 mSv body repairs itself• 1 Sv nausea and vomiting• 3 Sv Erythema, blistering and ulceration• 6 Sv LD50 depletion white blood cells,
50% population exposed die of infection death
• 10 Sv severe depletion of cells lining intestine, death due to secondary infections
Routes of exposure
Inhalation
IngestionSkin dose
Extremity dose
Abdomen/Foetal Dose
Eye dose
Injection
Whole body dose
External Dosimetry (,X & )
• Whole body/skin – TLDs, PLDs
• Eye dose – TLD chips
• Extremities – Ring badges or TLD chips
Environmental Monitoring
• radiation exposure
• surface contamination
• airborne activity
Restricting Exposure Alle Ding' sind Gift, und nichts ohn'
Gift; allein die Dosis macht, daß ein Ding kein Gift ist.
"All things are poison and nothing is without poison, only the dose permits something not to be
poisonous."(Paracelsus, 1493 - 1541)
Risk AssessmentUnder the Health and Safety at Work, etc. Act 1974, all work requires a risk
assessment.
The risk assessment should address the following: nature and source of ionising radiation to be used estimated dose rates to anyone exposed likelihood of contamination arising and being spread results of previous monitoring if relevant control measures and design features requirement to designate areas and personnel planned systems of work estimated levels of airborne or surface contamination likely to be
encountered requirement for PPE possible accident situations, potential severity consequences of failure of control measures steps to limit consequences of accident situations
Restricting Exposure
• Radiation – Time, distance and shielding
• Contamination – make sure sealed sources are in good repair.
Calculating Dose Rates
Dose Rate = A x E Sv/h where A = activity of source
6r2 (MBq)
E = energy of radation (MeV)
r = distance from source (m)
Inverse Square Law
D1R12 = D2R2
2 where R = distance and D = dose
Who ya gonna Call?
• Local Radiation Protection Supervisor (LRPS)
– X-Rays: Dr Adrian Barnes
– Radioactive Materials: Prof. Denis Henshaw
– IAC labs: Dr Keith Hallam
• Departmental Radiation Protection Supervisor (DRPS)
– Dr David Cussans
• University Radiation Protection Adviser (RPA)
– Dr Tony Butterworth
University Arrangements• To work with ionising radiation you must register
via the online database using form RP1.• Prior to working with radioactive material you
will be required to complete, or be added to, a risk assessment using form RP2. Attached to the RP2 will be your dose calculations and work protocol including risk evaluation.
• Acquisition of radioactive material is done using form RP3 and will need approval by your DRPS.
• Stock records are recorded using form RP4• Waste disposals are recorded using form RP5
Any questions?