Ionising Radiation Revised January 2012 John Sutherland, - PowerPoint PPT Presentation

Safe Working With Ionising Radiation Revised January 2012 John Sutherland, University Safety and Radiation Protection Officer

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Programme  What is radiation?  How is it measured?  Biological harm  Doses into perspective  Legislation  Unsealed work  X-ray/Sealed - Harry Zuranski, Safety Office.

Objectives  Foundation for Training in School  Understand principles  radiation types and effects  biological effects  relative risk  legislation  university arrangements  Safe Practice

Atomic Structure X a, B, Y neutron

Isotopes • Variable neutron number • Unstable nuclei transform • Ionising radiation emitted

Ionisation • Energy transfer • Enough energy ~ 13+ eV

Half - life Isotope Half-Life Tritium 12.4 y Carbon 14 5730 y Sulphur 35 87.4 d Phosphorus 33 25.6 d Phosphorus 32 14.3 d Iodine 125 60.1 d

Types of Radiation  Video

Types of Radiation  Alpha  From heavy nuclei (e.g. Americium 241)  Helium nuclei (2P+2N)  1500 ionisations  Dangerous internally  Easily shielded as very large particles  Sheet of paper or plastic film  Small distance of air  Dead outer layer of skin

Types of Radiation  Beta Par articles es (B) (B)  High speed electrons from nucleus  Identical to orbital electrons Proton + B -  Neutron  Energy dependent penetrating power  3H - 18.6 KeV  14C - 156 KeV  32P - 1.71 MeV  Rule of thumb for maximum range of beta particles  4 metres in air per MeV of charge  P32 can travel up to 7 m in air but 3H only 6mm!  Easily shielded with perspex, higher energy needs greater thickness  10 mm will absorb all P32 betas  Cannot reach internal organs

Types of Radiation  Bremsstra msstrahlun hlung  X-radiation resulting from high energy ß particle absorption in high density shielding, e.g. lead.  Risk with 32P and similar high energy ß emitters.  Shield ß with lightweight materials such as perspex.  Very large activities can still produce some Bremsstrahlung from perspex - supplement perspex with lead on outside to absorb the X-rays.

Types of Radiation  Gam amma ma Rad adia iati tion on (Y)  Electromagnetic radiation  Emitted from nucleus  Readjustment of energy in nucleus following a or ß emission  Variable energy characteristic of isotope  Highly penetrating  5 - 25 cm lead  3m concrete  Can reach internal organs  Can pass through the body

Types of Radiation  X-Radiat adiation ion  Similar to gamma but usually less energetic  Originates from electron cloud of the nucleus  Produced by machines - can be switched off!  Also produced by some isotopes  Iodine-125 produces both gamma and x-rays  Broad spectrum of energy

Types of Radiation  X-rays  Incident radiation ejects electron  Outer electron fills gap  X-ray energy = difference between orbital energy levels - characteristic  Bremsstrahlung also produced

Types of Radiation  Neutrons  Large, uncharged, physical interaction.  Spontaneous fission (Californium 252)  Alpha interaction with Beryllium (Am-241/Be)  Shield with proton-rich materials such as hydrocarbon wax and polypropylene.  Americium/Beryllium sources are used in neutron probes for moisture or density measurement in soils and road surfaces etc. These also emit gamma radiation.

Uni nits ts of of Rad adiat ation on  SI units Becquerel, Gray, Seivert  replaced Curies, Rems, Rads  Activity  Dose  absorbed  equivalent  committed

Uni nits ts of of Rad adiat ation on - ac activity ity  Quantity of r/a material  Bequerel (Bq; kBq; MBq)  1 nuclear transformation/second  3.7 x 10 10 Bq = 1 Curie  Record keeping  Stock, disposals  Expt protocols

Uni nits ts of of Rad adiat ation on - do dose  Absorbed - Gray (Gy)  Radiation energy deposited  1 Gy = 1 joule/kg  Dose Equivalent - Seivert (Sv)  modified for relative biological effectiveness  beta, gamma, X = 1  alpha, neutrons = 10-20

Uni nits ts of of Rad adiat ation on - com ommi mitted tted  Internal  irradiation until decay or elimination  radiological and biological half-lives  data for 50-year effect  Annual Limit on Intake (ALI)  limit on committed dose equivalent  quantity causing dose limit exposure

Exposure to Ionising Radiation  Environment  Naturally occurring radioactive minerals remaining from the very early formation of the planet.  Outer space and passes through the atmosphere of the planet – so-called cosmic radiation.  Man-made  medical treatment and diagnosis.  industry, primarily for measurement purposes and for producing electricity.  fallout from previous nuclear weapon explosions and other accidents/incidents world-wide.

Biological Effects of Radiation Exposure  Ionising radiation affects the cells of the body through damage to DNA by:  Direct interaction with DNA, or  Through ionisation of water molecules etc producing free radicals which then damage the DNA.  Some damaged cells might be killed outright so do not pass on any defect.  In some cases cell repair mechanisms can correct damage depending on dose.

Biological Effects of Radiation Exposure  Deterministic Effects.  Threshold beneath which there is no effect and above which severity increases with exposure.  High dose effects - cells may be killed by damage to DNA and cell structures.  Clinically observable effects include:  5 Sv to whole body in a short time is fatal.  60 Sv to skin causes irreversible burning.  5 Sv to scalp causes hair loss  4 Sv to skin causes brief reddening after three weeks  3 Sv is threshold for skin effects.

Biological Effects of Radiation Exposure  Stochastic (Chance) Effects  No threshold dose, probability of effect increases with dose but severity of effect remains unchanged  Lower dose effects  No obvious injury,  Some cells have incorrectly repaired the DNA damage and carry mutations leading to increased risk of cancer.  Rapidly dividing cells most at risk – blood forming cells in bone marrow; gut lining.

Cancer Risk at Low Doses  Evaluation of Cancer Risk  Studied for decades.  atomic bomb explosions in Main Area of Available Data for Japan, Study E  fallout from nuclear F weapons tests F  radiation accidents. E C  medical irradiations, T  work (e.g. nuclear power industry) Main Area of Interest for Radiation  living in a region that has Protection unusually high levels of radioactive radon gas or RADIATION DOSE gamma radiation.

Cancer Risk at Low Doses  Life-time risk of cancer from all causes of about 20 – 25%.  Exposure to all sources of ionising radiation (natural plus man-made) could be responsible for an additional risk of fatal cancer of about 1%  Dose from natural background radiation is about 2.2 mSv per year.  Dose from non-medical, man-made radiation  0.02 to 0.03 mSv per year (1/100 th natural background),  0.01% of additional cancer risk.  More significant cancer risk factors include:  cigarette smoking,  excessive exposure to sunlight, and  poor diet.

Biological Effects  4-10 Sv - death  1 Sv - clinical effects  100 mSv - clinical effects on foetus  50 mSv - max lifetime univ. dose  20 mSv - annual whole body dose limit  6 mSv - classified worker  2.5 mSv - average annual exposure (UK)  1 mSv - foetus after pregnancy confirmed  150 - 250 uSv - max annual dose at univ.  20 uSv – average annual dose at univ.

Perspective on Exposures  Nature of work AND precautions in place show risk from exposure at work is extremely low.  10-15% of those subject to dosimetry receive a measurable dose,  Average dose ~ 18uSv  0.1% of the dose limit of 20 mSv,  1% of that received from natural background radiation (2.2 mSv). Follow Safe Procedures

Properties of Main Isotopes Isotope Half- Radi Energy Range in Dose Annual Life ation Air Rate at Limit on Type 10 cm Intake* from 1 MBq** Tritium 12.4 y B 18.6 keV 6 mm Water 1 GBq (organic) 480 MBq Carbon 14 5730 y B 156 keV 24 cm 15 MBq Sulphur 35 87.4 d B 167 keV 26 cm 34 MBq Phosphorus 25.6 d B 250 keV 46 cm 14MBq 33 1 mSvh -1 Phosphorus 14.3 d B 1.71 MeV 790 cm 6 MBq 32 14 uSvh -1 1 MBq Iodine 125 60.1 d X 30 keV metres Y 35 keV

Legislation  Health and Safety  Ionising Radiations Regulations 1999  Environmental  Environmental Permitting Regulations 2010  (Supersede Radioactive Substances Act 1993)

Ionising Radiations Regulations 1999  Worker protection  dose limits  Justification  Radiation Project Proposal Forms (Rad 1-3)  risk assessment for exposure  Risk Assessment Forms (Rad 5 or 6)  restrict exposure through  equipment, procedure, experimental design  time,  shielding,  distance (inverse square law)

Protection through distance  Inverse square law applies Distance Dose rate (uSv/hr) 1m 1 2m 0.25 4m 0.06