Buxton & District Science Discussion 1 Radiation Protection Marge Rose August 2013.

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Radiation Protection

Marge RoseAugust 2013

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Protection of people

From ionising radiation

Scope of talk

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Ionisation

Certain types of radiation can ionise atoms

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Types of ionising radiation

X-raysGamma rays

Alpha particlesBeta particles (or radiation)

Neutrons, protons etc.

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Types of ionising radiation

X-raysGamma rays

Alpha particlesBeta particles (or radiation)

Neutrons, protons etc.

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Fear and the Perception of riskEating a banana Going to Cornwall on holiday

for a fortnight

Living within 50 miles of a nuclear power plant for a year

Having a PET scan of the head

Working as an airline pilot for a year

Having a dental x-ray

Having a CT scan of the head Working in a nuclear power station for a year

Standing in the grounds of Chernobyl for an hour

Living in Buxton for a year

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Estimated doses in mSvLiving within 50 miles of a nuclear power plant for a year

0.00009 Working as an airline pilot for a year

2.2

Eating a banana 0.0001 Having a CT scan of the head

2.3

Having a dental x-ray 0.005 Living in Buxton for a year 3.1

Working in a nuclear power station for a year

0.18 PET scan of the head 5

Going to Cornwall on holiday for a fortnight

0.3 Standing in the grounds of Chernobyl for an hour

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History

1895 X-rays Röntgen

1895 Radioactivity Becquerel

1898 Radium Curies

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Recognition of use in Medicine

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The pioneering daysSome conditions recommended for

treatment with radium in 1906

Lupus vulgarisEczemaAcne

Psoriasis Pain

ArthritisInfectious diseases

x-rays Radium

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Radium dial painters

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Legislation1960 Radioactive Substances Act

(Updated in 1993)Keeping, storage, disposal of waste

1978 The Medicines (Administration of Radioactive Substances) Regulations

Administration of radioactivity to patients

1985 Ionising Radiation Regulations(Updated in 1999)

Work

2001 Ionising Radiations (Medical Exposures) Regulations

Medical exposures

2001 Radiation (Emergency Preparedness and Public Information) Regulations

Emergency Preparedness

2004 Justification of Practices involving Ionising Radiations

Justification

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Radiation Dose

Internal : from unsealed radioactive substances

Modes of exposure to ionising radiation

External : from x-rays & sealed radioactive substances

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Protecting yourself from ionising radiation

TimeDistanceShielding

And, to reduce internal irradiation you needGood housekeeping

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Radiation can only cause harm if at least some of its energy is

absorbed within the body

Type of radiation Outside the body Inside the body

Alpha Stopped by thin sheet of paper

Imparts all its energy to a tiny area

Beta Stopped by a few mm aluminium

Almost all of the energy is absorbed

close to the site

Gamma(sim. X-ray)

Shielding needs may be substantial

depending on energy

A sizeable proportion may escape the body, depending on energy

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What sort of damage can radiation do to humans?

Acute effects (Radiation sickness)

Skin reddening, cataracts (Tissue reactions)

Increased probability of certain kinds of cancer – avoidance is main aim of radiation protection

(Stochastic effects)

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There is hard evidence for radiation sickness and the so-called tissue reactions

(were called deterministic and, before that, non-stochastic)

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Stochastic effect – Increased probability of cancer

Overall, it is estimated that more than one in three people will be

diagnosed with some form of cancer during their lifetime.

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At 200 mSv, we have reasonably good evidence that death from cancer as a result of radiation exposure is under

9000 in a million to add to underlying incidence of 250,000

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Linear No Threshold Model

0

Dose (mSv)

Relative increase in risk Linear-No-Threshold (LNT)

Supralinear

Sublinear Threshold

HormesisRelative benefit

www.llrc.org

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Units of effective radiation dose

Rem/Sievert(1 Sievert = 100 Rem)

Whole body or part

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Rolf Maximilian Sievert

Doses talked about so far are whole body effective dose. This is

the energy absorbed per mass taking into account the type of

radiation and the part of the body irradiated – a measure of harm

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There are many assumptions that go into effective dose estimations

1. Energy deposited per unit mass – accurate measure

2. What kind of radiation – α particles are 20 times more damaging than x or γ

3. Which part of the body – gonads more sensitive, liver less so

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Tissue weighting factorsGonads 0.20 Red bone

marrow 0.12 Colon 0.12

Lungs 0.12 Stomach 0.12 Bladder 0.05

Breast 0.05 Liver 0.05 Oesophagus 0.05

Thyroid 0.05 Skin 0.01 Bone surfaces 0.01

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Be wary of mSv estimates

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Average annual doses

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• Radon Map

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Detailed Radon Map

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The Uranium decay chain

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The basic assumption behind all the radiation protection precautions we take these days is that all radiation is

harmful. Even if it is naturally-occurring like Radon, we seek to

limit it as far as possible.

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Control of exposure is based on 3 tenets

1. Justification (Risk v Benefit)2. Optimisation3. Limits (but ALARP)

ALARP = as low as reasonably practicable

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Referral guidelines

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Data from the NRPB – National Radiological Protection Board (which became part of the HPA - Health Protection Agency and is now, from April 2013, part of Public Health England)

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Annual dose limits

Classified workers (must be over 18) 20 mSv

Unclassified workers and trainees 6 mSv

All others (including members of the public*)

1 mSv

* There are no specified limits for patients or ‘carers’

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Why does the radiographer go behind a lead screen when an x-ray is taken? It

must be dangerous so why isn’t it dangerous for me as the patient ?

It’s true of course - the patient will get more dose than the member of staff for that one exposure

But the member of staff will be present at many such exposures over the year and the only benefit they receive is that it is their job. There is no

justification for irradiation of the member of staff when it can be avoided by standing behind a lead screen.

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Ex-Russian agent Alexander Litvinenko died in a London hospital on 23 November 2006 from poisoning with Polonium 210

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Polonium 210 absorbed into the body cannot be detected from the outside – the way to check for it is

to monitor the urine

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The Radioactive Boy Scout

David Hahn was 17 when he built a nuclear breeder reactor in his mother’s backyard.