Presentation on theme: "Working with Radiation in the University of Bristol Department of Physics."— Presentation 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 first injuries due to radiation recorded 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 (H T ) is the absorbed dose in tissue or organ T weighted for the type and quality of radiation R. H T,R = W R D T,R Where D T,R is the absorbed dose averaged over organ or tissue T, due to radiation R W R is the radiation weighting factor
Old/US Units Rad100 Rads = 1 Gray Rem100 Rem = 1 Sievert Ci1 Curie = 3.7 x Bq (dps) 1 mCi = 3.7 x 10 7 ( to avoid confusion, steer clear of CGS units if possible)
Dose Limits – For Workers mSv per day or 730 mSv per year mSv per day or 10 mSv per week mSv per week or 150 mSv per year mSv per week or 50 mSv per year mSv per year mSv per year
ICRP 60 (Published 1990) Justification – there should be a net benefit Optimisation – restriction of exposure ALARP/ALARA
Annual Dose Limits Whole BodyExtremities and skinLens of the eye Employees aged 18 and over 20 mSv500 mSv150 mSv Trainees aged 18 and under 6 mSv150 mSv50 mSv Any other person ( e.g. Undergraduates) 1 mSv50 mSv15 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 Probability Effect, e.g. malignancy and hereditary effects No threshold for an effect to occur, probability increase as dose received increases
Deterministic Effects Dose Severity Threshold Effect, 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 LD 50 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 Ingestion Skin dose Extremity dose Abdomen/Foetal Dose Eye dose Injection Whole body dose
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, )
Risk Assessment Under 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 6r 2 (MBq) E = energy of radation (MeV) r = distance from source (m)
Inverse Square Law D 1 R 1 2 = D 2 R 2 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