An Introduction to Radiation Safety2014

Ian Williamson / Steve Clipstone

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)

3

• Main requirements of legislation• Types of radiation• Health effects• Management arrangements• Risk control measures

This course will cover

AimThe aim of the session is to • Introduce you to some basic radiation principles • Inform you of the arrangements and control

measures in place to keep you safe when working with radiation

• Not to make you an expert!

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

• H&S Legislation needed?

Legislation• Ionising Radiation Regulations 1999 (IRRs)General and specific duties & rules about safe working practices, control measures, assessments, roles and responsibilities;Health and Safety Executive (HSE) enforcement

• Environmental Permitting Regulations 2010Regulates the holding, storage, accumulation and disposal of radioactive material;Environment Agency (EA) EnforcementReplaced the RSA93 Act

The Ionising Radiation Regulations• Risk assessments• Control of exposure to ALARP• Maintenance of control measures • Dose limitation• Contingency Plans and Local Rules• RPA and RPS defined roles• Information. Instruction and Training• Co-operation between employers• Designation of areas

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

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 – UK (IRRs)

Whole Body Extremities and skin Lens of the eye(new proposed limits in brackets)

Employees aged 18 and over 20 mSv 500 mSv 150 mSv (20)

Trainees aged 18 and under 6 mSv 150 mSv 50 mSv (15)

Any other person( e.g. Undergraduates)

1 mSv 50 mSv 15 mSv (15)

Women of reproductive capacity - exposure of abdomen limited to 13 mSv in any consecutive 3 month period. Women are legally obliged to inform their employer

Basic Radiological Safety Rules

• All work must be risk assessed• You MUST work within the Local Rules and

follow instructions• You MUST be a registered radiation worker• You MUST understand the instructions and

comply with them – if in doubt ask

The ALARP Principle

• Minimise the time you spend near a source• Maximise the distance between you and a

source of radiation• Maximise the shielding between you and a

source of radiation

Time

• Before the work make sure you know and plan what you are going to do! Minimise the time

• Practice the task beforehand• Do not linger in high dose rate areas

Distance

• Avoid working or standing in high dose rate areas, whenever possible by moving away from the source of radiation

• Use remote handling equipment• Observe from a separate area• Use minimal amounts / samples

Inverse Square Law

Distance Radiation Dose rate Double Reduced to ¼ Treble Reduced to 1/9 Quadruple Reduced to 1/16

Shielding

• Use shielding provided where possible • Do not tamper with equipment or defeat

interlocks• View behind protective screening• Make sure sealed sources are in good repair• PPE

Radiation UnitsActivity • Number disintegrations per second (Becquerel) – one Bq

means one atom/nucleus decays and emits radiation every second

• Characterised by the half lifeAbsorbed dose • Mean energy per unit mass absorbed by any medium by any

type of ionising radiation (Gray – Gy (or joules/kg)) Equivalent Dose• Dose allowing for type of radiation and effective biological

damage (Sievert - Sv)- absorbed dose by weighting factor

Old/US Units

• Rad 100 Rads = 1 Gray• Rem 100 Rem = 1 Sievert• Ci 1 Curie = 3.7 x 1010 Bq

(dps)

Types of radiation

alpha

• 2 protons + 2 neutrons tightly bound together- Helium nucleus

• High energy but low penetrating power• Range in air only a few cm• Internal hazard

beta

• Smaller than alpha • An electron (emitted from the nucleus)• Variable energy• Internal and external hazard

Gamma and x-rays

• Electromagnetic radiation• Variable energy with shorter wavelengths• External hazard• Penetrating – range in air m to km• Gamma rays emitted from the nucleus• X-rays emitted from electron orbital shells

Radiation

Penetration in air Stopped by

Alpha 3 – 5 cm of air Thin sheet of paper, outer layers of skin

Beta 3 m of air 1cm perspex3mm of aluminium sheet

Gamma Eventually stopped by air, depends on the energy of emission but can be big distances

40 cm of lead – stops almost all of the radiation

Not all of the atoms of a radioisotope decay at the same time, but they decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life.

The half-life of a radioisotope describes how long it takes for half of the atoms in a given mass to decay. Some isotopes decay very rapidly and, therefore, have a high specific activity. Others decay at a much slower rate – so decay at an “average rate”

After two half-lives, there will be one quarter the original sample, after three half-lives one eighth the original sample, and so forth.

It is an exponential decay process

Radioactive Half-Life

At start there are 16

radioisotopes

100%

After 1 half life half have

decayed. There are 8 remaining

50%

After 3 half lives another

2 have decayed.

There are 2 remaining

12.5%

After 2 half lives another

half have decayed.

There are 4 remaining

25%

= radioactive = stable, although not a precise figure

How can we work out the half-life of a radioisotope?We can plot a graph of activity against time

2 Half-Lives

1 Half-Life

Routes of exposure

Inhalation

IngestionSkin dose

Extremity dose

Abdomen/Foetal Dose

Eye dose

Injection

Whole body dose

Routes of Entry

• Ingestion• Inhalation• Puncture wounds or cuts• Absorption through the skin

Absorption of Nuclear Radiations

The most massive of the radioactive emissions – alpha particles – have the shortest range. Due to their size they interact strongly with matter (lots of collisions with atoms) causing large amounts of ionization. This makes them very harmful to living tissue.

Absorption of Radiation

Beta particles being smaller have a weaker interaction but can still cause ionization as they interact with the electrons surrounding atoms.

Since gamma radiation is electromagnetic waves it is the most penetrating and least ionizing. However the deep penetration makes it dangerous to living tissue.

Biological Effects of Ionising Radiation

• Health Effects are determined by the type and intensity of the radiation and the period of exposure.

Biological Effects The occurrence of particular health effects from exposure to ionizing radiation is a complicated function of numerous factors including:

•Type of radiation involved. All kinds of ionizing radiation can produce health effects. The main difference in the ability of alpha and beta particles and Gamma and X-rays to cause health effects is the amount of energy they have. Their energy determines how far they can penetrate into tissue and how much energy they are able to transmit directly or indirectly to tissues.  

•Size of dose received. The higher the dose of radiation received, the higher the likelihood of health effects.

•Rate the dose is received. Tissue can receive larger dosages over a period of time. If the dosage occurs over a number of days or weeks, the results are often not as serious if a similar dose was received in a matter of minutes.

•Part of the body exposed. Extremities such as the hands or feet are able to receive a greater amount of radiation with less resulting damage than blood forming organs housed in the torso.

•The age of the individual. As a person ages, cell division slows and the body is less sensitive to the effects of ionizing radiation. Once cell division has slowed, the effects of radiation are somewhat less damaging than when cells were rapidly dividing.

•Biological differences. Some individuals are more sensitive to the effects of radiation than others. Studies have not been able to conclusively determine the differences.

Radiation Effects• Direct ionisation

– Structural cell damage, weakens links between atoms

– Affects cellular function– DNA mutations

• Indirect ionisation– Damage to chemical

constituents, e.g. water– Formation of free radicals

Examples of various tissues and their relative radiosensitivities:

High Radiosensitivity - Lymphoid organs, bone marrow, blood, testes, ovaries, intestines

Fairly High Radiosensitivity- Skin and other organs with epithelial cell lining (cornea, oral cavity, esophagus, rectum, bladder, vagina, uterine cervix, ureters)

Moderate Radiosensitivity - Optic lens, stomach, growing cartilage, fine vasculature, growing bone (note optic lens may move up to high radiosensitivity)

Fairly Low Radiosensitivity - Mature cartilage or bones, salivary glands, respiratory organs, kidneys, liver, pancreas, thyroid, adrenal and pituitary glands

Low Radiosensitivity - Muscle, brain, spinal cord

Effects can take between 5 – 30 years

Radiation effects• Stochastic effects – somatic and hereditary effects• No safe dose or threshold – governed by chance• Deterministic effects – loss of function• There is no such thing as a safe level of radiation. A single electron

could damage a cell irreversibly and initiate cancer However the likelihood of damage and the severity of damage increases with the amount of radiation.

Types of exposure

• Acute exposureTakes place over a short period of timeUsually high exposures

• Chronic exposureTakes place over a long period of timeUsually low level exposures

Stochastic effects

Dose

ProbabilityEffect, e.g. malignancy and hereditary effects

Not immediately observable

probability increase as dose received increases

Deterministic Effects

Dose

Severity ThresholdEffect, e.g. cataracts, fetal damage, skin effects

Large dose can be fatal

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

Radiation Detectors

• Geiger counters, scintillation counters, ionisation chambers;

• Count and sensitivity of the detector to interpret the readings

Monitors• Use portable radiation detectors to monitor

laboratory or facility radiation levels• Use film badges or TLDs for retrospective

personal dose monitoring• Calibrated contamination monitors are only

valid for a particular type of radiation – there is no universal monitor

Work Areas

• Controlled areas• Supervised Areas

Dosimetry

• In controlled areas radiation dose is measured using dose meters or badges – you must wear them every time you enter a controlled area

• You will be given specific instructions by your RPS

Restricting Exposure

• All doses are kept to the ALARP principle Design – fail to safety and cannot be bypassed Engineered – shielded, fail to safety (interlocked), warning lights Administrative – Local Rules, supervision, disposal PPE – gloves , lab coats

• Dose limits should not be exceeded

Risk AssessmentAll work requires a risk assessment where the risk is significant and foreseeable. IRRs require: 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

Local Rules

• Brief and concise describing nature of work in the designated area

• Identify key work instructions to restrict exposure• Covers normal circumstances and contingency plans• Contains realistic and achievable work instructions• Reviewed periodically to ensure effectiveness• Summary of arrangements for access restriction• Name / contact details of RPS should be in the local rules

Waste

• Consult with your RPS regarding waste issues

Roles and responsibilities

• Keele University – VC and the Committee Structure

• Radiation Protection Advisor• University Radiation Protection Officer• Radiation Protection Supervisor• Registered Radiation Worker• Agencies / Regulatory bodies

Radiation Protection Advisor

• Legal requirement• Specialist role and appointed in writing• Accredited• Currently Radman Associates

Radiation Protection AdvisorConsulted on• Prior examination of plans for new facilities• Critical examination of equipment• Setting up of controlled or supervised areas• Calibration of monitoring equipment• Periodic examination and testing of control measures• Investigations• Compliance with IRRs

Radiation Protection Supervisor• Legal requirement• Training and development of staff / students in

correct working procedures• Some supervisory duties• Crucial role to ensure compliance with Local Rules,

Contingency Plans and general arrangements etc• Familiar with work in their area• Regular checks and record keeping

Key Contacts

• Radiation Protection Supervisors – list available• University Radiation Protection Adviser (RPA)- Radman

Associates• University Radiation Protection Officer – Steve Clipstone• Head of Occupational Health and Safety – Ian Williamson

Further information

• Keele webpages• HSE

Any questions?