working with radiation in the university of bristol department of physics

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?