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Basic Radiation Protection

Basic Radiation Protection. Radioactivity. Nuclide – a particular atomic nucleus with a specific number of protons (p) and neutrons (n). For example 31 P 32 P 33 P Approximately 1700 known nuclides. About 1400 are unstable – RADIONUCLIDES .

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Basic Radiation Protection

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  1. Basic Radiation Protection

  2. Radioactivity Nuclide – a particular atomic nucleus with a specific number of protons (p) and neutrons (n). For example31P32P 33P Approximately 1700 known nuclides. About 1400 are unstable – RADIONUCLIDES. Radionuclides - imbalanced numbers of p and n. - emit particles/energy to improve stability

  3. Radioactivity Gamma photon Radionuclide Excess energy Disintegration Stable daughter Excited daughter Charged particle

  4. Sources SEALED – a radioactive source containing radioactive materialwhere the structure is designed to prevent, under normal use, any dispersion of radioactive substances e.g. Am/Be sealed in stainless steel capsule UNSEALED - dispersible Solids – powders Liquids – aqueous or organic Gases – e.g. Xe-133 MACHINES – e.g. x-ray and neutron generators

  5. Main Emissions Helium nuclei (2p + 2n) + 2 positive charge 4 mass units Alpha (a) High speed electrons • 1 negative charge • 0.0005 mass unit Beta (b) Electromagnetic photons No charge No mass Gamma (g)

  6. energy gained by an electron passing through an electrical potential of 1 volt 1 eV = Energy Energy of emissions ÞELECTRONVOLTS (eV) 1 eV is a very small energy = 1.6 x 10-19 joules. Normally emission energies are in keV or MeV range.

  7. Ranges Particle Energy (MeV) Range Tissue Air Alpha 3 - 7 < 1mm few cm Beta H3 0.018 0.05mm 4mm C14 0.156 0.3mm 2cm P32 1.70 8mm 600cm Gamma 0.1 – 0.6 V. Large V.Large

  8. Activity (A) Rate of disintegrations in a large group of nuclei. A(t) µ N(t) which means EXPONENTIAL DECAY. SI unit is BEQUEREL(Bq) 1 Bq = one disintegration per second. Another commonly used but old unit is CURIE (Ci) 1 Ci = 3.7 x 1010 Bq or 1 mCi = 37 MBq

  9. Ao A(t) = Ao exp (- lt) ½Ao T½ = 0.693 / l Half-Life where l is the radioactive decay constant

  10. Radionuclide Half-Life H3 12.3 years C14 5760 years P32 14.3 days S35 87.2 days Cs137 30.2 years Eu152 13.5 years I131 8.04 days Typical Half-Lives

  11. Bremstrahlung • “Breaking Radiation” • X-rays produced when b particles are • slowed down very rapidly as they come • very close to an atomic nucleus. • shielding materials (e.g. perspex) have • relatively low atomic numbers in order to • slow them down more gradually.

  12. Absorbed Dose (D) • Energy imparted to matter in small volume • Mass of the small volume • 1 Gray (Gy) = 1 Joule of energy absorbed • in 1 kg of matter i.e. 1 J / kg • Gy is a HUGE dose of radiation. • (Old units : 1 gray = 100 rads)

  13. Equivalent Dose - H Absorbed Dose x Radiation Weighting (Grays) Factor (WR) Sieverts (Sv) which are still J / kg WR = 1 for photons and betas of any energy. (Old units : 1 Sv = 100 rem) H =

  14. Effective Dose (E) Accounts for uneven irradiation of the body. Represents overall risk from a whole body exposure. E = wTx HT where HT = Equivalent dose to tissue / organ “T” wT = Tissue weighting factor Tissue weighting factors represent risks of detrimental radiation effects to different organs or tissue S T

  15. Tissue Weighting Factors • Gonads 0.08 Breast 0.12 • Red bone marrow 0.12 Liver 0.04 • Colon 0.12 Oesophogus 0.04 • Lung 0.12 Thyroid 0.04 • Stomach 0.12 Skin 0.01 • Bladder 0.04 Bone surfaces 0.01 • Brain 0.01 Salivary glands 0.01 • Remainder 0.12 • includes: Adrenals Upper large intestine • Small intestine Muscle • Kidney Spleen • Pancreas Uterus • Thymus å WT = 1

  16. Internal Radiation Amount of radionuclide in body Dose rate in organ lEFF = lR + lB exp(-lRt) exp(-lBt) exp(-lEFFt) exp(-lEFFt) Time Time (post ingestion)

  17. Equivalent dose summed over a 50 year period. HT(50) = Committed Equivalent Dose AlsoCommitted Effective Dose

  18. Annual Limit of Intake (ALI) The amount of radionuclide (in Bq) which when taken into the body will result in : Committed Effective Dose = Dose Limit (20mSv) Radionuclide ALI (MBq) Inhalation Ingestion Sodium-22 10 7 Iodine-131 1 0.8 Also depends on chemical compound.

  19. X-ray Generators • Typically Controlled Area is: • Anywhere in the primary beam direction • 150cm around scattering object • Inside a shielded interlocked enclosure Hand-held XRF analyser Niton XL2 GOLDD (from www.nitonuk.co.uk with permission) NOMAD Pro Hand-held Dental Unit Desk-top XRF Unit (totally shielded enclosure) Mobile Diagnostic X-ray Machines

  20. Lead Aprons • Only protect from scatter (95%) • Minimum of 0.25mm lead equivalence • Visually inspected for damage • Worn correctly - closed with no gaps

  21. Radiation Damage to Tissue X-ray interacts and loses energy along its path. Ionisation : dominant interaction  damage. Energy loss random process - only some molecules effected. Cellular damage either : - direct or - indirect

  22. Direct Damage Ionisation in important macromolecules e.g. - Breaks in DNA strands - Chromosomal aberrations Repair processes may not work - death of cell - failure to reproduce

  23. Indirect Damage Ionisation of cellular water  free radicals Very reactive Move through cell  chemical reactions  similar DNA damage Dominant mechanism for X-rays

  24. Sensitivity Actively dividing cells most radiosensitive - Bone marrow - Germinal cells in testis/ovaries - Intestinal epithelium - Foetus - Children Effects appear within hours or days Slow dividing cells - months to years

  25. Hazardous Effects Detrimental to : - Individual exposed :SOMATIC - Descendants :HERITABLE Need certain radiation exposures BUTneed to protect : - Individuals exposed - Their offspring - Mankind generally

  26. Deterministic Effects Severity Dose Threshold Thresholds well above both typical dose limits for workers Dose

  27. Stochastic Effects Probability Natural Occurence Dose

  28. Stochastic Effects Probability of effect  as dose  Linearly i.e. 2 x dose  2 x more likely to occur. NO Threshold. NO direct cell killingBUTmutations : - cancer (years later!!) - birth abnomalities(physical+mental) Effect of concern with low doses

  29. Stochastic damage toGERM CELLS Disorders inDESCENDANTS of person exposed Heritable Effects These effects not yet proved in humans but likely

  30. Risk Likelihood (or probability) of exposure to radiation harmful stochastic effect e.g. fatal cancer.

  31. Risk Factors (whole popn) Occurrence of % per Sv Fatal Cancer 5.0 Non-fatal Cancer 1.0 Hereditary effects 1.3 TOTAL 7.3 100 people. Each given 1Sv. On average 5 will get fatal cancer eventually due to that exposure.

  32. RIP Natural Fatal Cancers ~ 90,000 1 million people Over 30 Years ~ 500 cancer deaths + ~ 100 genetic abnormalities Give each 10mSv (a lot but still within workers annual limit) Additional

  33. 1 million foetuses in utero 40,000 abnormalities NATURALLY Risks to Foetus Extra care with STAFF and PATIENTS who PREGNANTorREPRODUCTIVE CAPACITY ~ 2500 extra abnomalities ADDITIONALLY Each receive 10mSv

  34. Comparable Risks Activity Risk of Death per year (1 in N) 300 miles car travel 100000 Accidents in home 10000 Smoking 10 a day 6500 Coal mining 6500 Deep sea fishing 500

  35. Principles of Radiation Protection • Justification – Benefits > Risks • Optimisation - ALARP • Dose Limitation

  36. Practical Protection Measures External Radiation Distance: inverse square law. : always use remote handling (if poss). Shielding: placed between worker & source. : attenuates the radiation. : lead for g : Perspex for energetic b : B-polythene for neutrons Time : be as quick as safely possible.

  37. To use tongs or not to use tongs? 30cm 10mins @ 1mSv/min Þ 10 mSv 1cm 1min @ 900mSv/min Þ 900 mSv

  38. Practical Protection Measures Internal Radiation Use all appropriate protective equipment e.g. gloves. Only handle radioisotopes in designated areas. Monitor for contamination. Know the whereabouts and how to use the decontamination kit Monitoring for contamination must be done regularly

  39. Do NOT eat drink or smoke in an area where unsealed radioactive substances are handled. “What the? …… This is lemonade! Where’s my preparation of tritiated thymidine?”

  40. DO NOT WEAR LAB COATS IN THIS ROOM

  41. Personal Monitoring • Normally TLD badges. • Worn as instructed in local rules. • Do not try to remove TLDs from holder. • Damaged holders replaced immediately. • NOT left in radiation areas, left on radiators, washed etc. • Returned for reading promptly. • Special monitors for wrists, eyes etc. NOT whole body one.

  42. Legislation The Environmental Permitting Regulations 2010 (EPR2010) + 2011 Amendment The Ionising Radiations Regulations 1999 (IRR99)

  43. EPR2010 (was RSA93) Protection of General Public and Environment. PERMITS: to keep & use sealed radioactive sources. Subject to national security SEALED : to keep and use unsealed radioactive substances and accumulate/dispose of waste OPEN : Policed by The Environment Agency (EA)

  44. Record Keeping • Date received, radionuclide, activity • Location stored • Details of removal for use, date, activity • Activity present in stock at end of month • Dates of disposal • Total activity disposed of and by which route each month • Total activity of waste accumulated at end of each month

  45. Where does all the waste go ? SOLID : Very Low Level Waste (VLLW) Þ skip by user. Low Level Waste (LLW) from bins in labs collected and taken for incineration (or landfill burial) Sealed sources – specialist contractor LIQUID : Aqueous – down the drain Organic – collected and sent for incineration

  46. Waste Disposal IS VERY EXPENSIVE: When buying new sources – think about disposal costs and work this into the grant application

  47. Orphans Radioactive sources or materials or waste that does not have an ‘owner’ Creates a lot of work for RPO RPO has to pay for its legal disposal PLEASE NO ORPHANS X

  48. When an Inspector Calls !! • Poor accounting of sources and waste • Lost sources • Unauthorised disposal of waste • Over-accumulation of waste • Failure to keep suitable and sufficient records • Failure to use best practicable means (BPM)

  49. Offences Variety of offences & penalties Penalties can be applied to anyone within the University - not just the COO or Department Head Non-compliance with Permit conditions/schedules - up to £20,000 fine and/or up to 6 months in prison Failure to keep records - a fine and/or up to 3 months imprisonment

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