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 November 26 th, 13:30 – 15:20: lab groups B1 & B2 December 3 rd, 13:30 – 14:20: report back

Contamination Contamination of surfaces, tools, equipment Check integrity of sealed sourcs

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

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 Bq cm -2 – (iii) class C radionuclides  300 Bq cm -2 Averaged over area  100 cm 2

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

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

Contamination criteria 0.3 Bq cm -2 !? Compare 40 K: 31.7 kBq kg -1 (natural K) Natural uranium: 238 U 12.3 MBq kg -1 (+ all daughters[7 , 6  ] if in secular equilibrium); 235 U 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 )

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!

Measuring contamination

Remember criterion “averaged over area  100 cm 2 ” Personal protective equipment? Properties of “swipe”?

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”.

125 I brachytherapy seed

238 Pu-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 241 Am-Be?)

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

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

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