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Med Phys 3A03/3AA1

Med Phys 3A03/3AA1. Practical Health & Medical Physics Communications D.R. Chettle , with D.F. Moscu TA: Helen Moise. Contamination. Module 3 November 12 th , 13:30 – 14:20: introduction November 19 th , 13:30 – 15:20: lab, groups A1 & A2

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Med Phys 3A03/3AA1

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  1. Med Phys 3A03/3AA1 Practical Health & Medical Physics Communications D.R. Chettle, with D.F. Moscu TA: Helen Moise

  2. Contamination Module 3 November 12th, 13:30 – 14:20: introduction November 19th, 13:30 – 15:20: lab, groups A1 & A2 November 26th, 13:30 – 15:20: lab groups B1 & B2 December 3rd, 13:30 – 14:20: report back

  3. Contamination • Contamination of surfaces, tools, equipment • Check integrity of sealed sourcs

  4. Contamination • Can it easily be removed and so transferred to another surface, area or person? • So, is it “non-fixed” wipeable? • McMaster licence has “Contamination criteria” • two levels, controlled areas, all other areas

  5. Contamination criteria – a) • Non-fixed contamination in all areas where unsealed nuclear substances are used or stored • (i) class A radionuclides 3 Bq cm-2 • (ii) class B radionuclides 30 Bqcm-2 • (iii) class C radionuclides 300 Bqcm-2 Averaged over area  100 cm2

  6. Contamination criteria – b) • Non-fixed contamination in all other areas • (i) class A radionuclides 0.3 Bq cm-2 • (ii) class B radionuclides 3 Bqcm-2 • (iii) class C radionuclides 30 Bqcm-2 Averaged over area  100 cm2

  7. What are class A, B, C radionuclides? • Class A, eg:  emitters, 18F, 24Na, 60Co • Class B, eg: 131I, 90Sr, 198Au, 59Fe • Class C, eg: 14C, 109Cd, 99mTc, 32P • Classification appears to depend on emissions, half life, physical form and chemical and physical behaviour

  8. Contamination criteria • 0.3 Bq cm-2!? • Compare 40K: 31.7 kBq kg-1 (natural K) • Natural uranium: 238U 12.3 MBq kg-1 (+ all daughters[7, 6] if in secular equilibrium); 235U 0.568 MBq kg-1 (+ daughters) • Natural thorium: 4.07 MBq kg-1 (+ daughters) • Maybe think of it as 3 kBq m-2 (to 3 MBq m-2)

  9. Measuring contamination

  10. Measuring contamination • Using “pancake” detector, as in module #1 • Scan over suspect area • Careful not to allow detector to touch surface (or object) • Contaminated detectors do not help!

  11. Measuring contamination

  12. Measuring contamination • Remember criterion “averaged over area  100 cm2” • Personal protective equipment? • Properties of “swipe”?

  13. Checking sealed sources • “a radioactive nuclear substance in a sealed capsule or in a cover to which the substance is bonded, where the capsule or cover is strong enough to prevent contact with or the dispersion of the substance under the conditions for which the capsule or cover is designed”.

  14. 125I brachytherapy seed

  15. 238Pu-Be • Double stainless steel encapsulation, meets drop test, fire test, water test • What is decay mode? • Another name? • What happens to that substance? • How many years might this source be around? • (Also, what about 241Am-Be?)

  16. Checking sealed sources • Precautions as for swipe test of surface • Checking source directly will give dose • Sources are kept in appropriate containers • If source has retained its integrity, container will not have any contamination

  17. Checking sealed sources • Swipe container and check as for contaminated surfaces • If any suspect contamination, check whether it is same isotope as sealed source, may well need different type(s) of detector

  18. Self-assessment/peer-assessment • Module 1: received 12, missing 3 • Module 2: received 6, awaiting 9

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