Safety regulations or Radiation protection 26/04/2016

Transkript

1 Safety regulations or Radiation protection 26/04/2016 Holger Jensen, Ph.D. Chief Cyclotron Physicist, The Centre of Diagnostic Investigations The PET and Cyclotron unit, 3982 Blegdamsvej 9, DK2100 Copenhagen Denmark. Tel

2 Radiation protection Agenda Why care about safety? ICRP recommendations Legislation Equipment How to minimize dose and some basic laboratory rules Page 2

3 Radiation protection Appetizer Typical producers of PET isotopes have production capacities of GBq 18 F and 100 GBq 11 C. Some facilities are approaching 1000 GBq 18 F. Can this be dangerous? YES Effective dose rate D from a 18 F point source, A = 1 MBq, at a distance of r=30 cm is D = msv/h For 500 GBq we obtain D = msv/h = 905 msv/h or the allowed annual dose in 20/905*60 = 1.3 minutes! This is a good argument for this safety lecture Page 3

4 Radiation protection Types of decay β - : β + : n p + e - + ν p n + e + + ν ε (EC): p + e - n + ν Side 4

5 Radiation protection Example of decay, β + 18 F 18 O + e + + ν T ½ = 109,728 m 2h 18 9 F O 10 + e + + ν β + : p n + e + + ν ε (EC): p + e - n + ν The annihilation of an electron and a positron results in 2 gamma rays, each with energies of E γ = 511 kev or C J C = J But what is typical binding energies B involved in atoms and molecules /chemistry??? With B 1 ev one single PET gamma-foton can potentially break or damage ~ molecules/atoms/ Side 5

6 Radiation protection Ionizing radiation Ionizing radiation Original molecules Ionizing Ionizing Free radicals Repair Radiation damage, DNA and RNA damage, changed molecules, No repair or wrong repair Normal celle Side 6 Mutant celle Dead celle

7 Radiation protection IAEA Nuclear Medicine Physics Side 7

8 Radiation protection IAEA Side 8

9 Radiation protection IAEA Side 9

10 Radiation protection IAEA Side 10

11 Radiation protection IAEA Side 11

12 Radiation protection IAEA Side 12

13 Radiation protection IAEA Side 13

14 Radiation protection recommended dose limits Side 14

15 Radiation protection Background radiation/dose: Side 15

16 Radiation protection what is the risk? Estimated riskfactor P = 0,00005/mSv Statistically it is expetcted to find 5 death in a population of inhabitants if they each receive 1 msv. With 5 million inhabitants in Denmark and a background of 4 msv/year 1000 death per year is expected. (Radon is the big killer). A received dose of 6 msv gives 0,3 permille risk of developing a mortal cancer. This corresponds to: Going on canoe vacation for 5 days Being 60 years old in 4,5 days Drinking 20 bottles of vine Smoking 15 packs of cigarettes Side 16

17 Radiation protection Legislation, procedures, A collection of the most important laws, procedures, results can be found at: In order to be allowed to work with open radioactive sources it is requested by the law to read and understand major parts of Examples of links, procedures, graphs, data,, Vores gældende isotoptilladelse - part A BEK_954_231000_aabne_kilder PET_Cyklotron_Sikkerhedsinstruks_vers 5.pdf 14.2.RH.0.01 Dekontaminering.pdf Forskrift for opbevaring af radioaktive kilder.pdf Haandtering og bortskaffelse af radioaktivt affald version 1.pdf Helkropsdoser_Cyklotron Helkropsdoser_Kemi Grafisk fremstilling af doser Fingerdoser_2015 Side 17 BEK_954_231000_aabne_kilder

18 Radiation protection surveillance and reporting Thermo Luminescence based Dosimetry (TLD): Whole body dose: 1 month Finger dose: 2 weeks. Electronic RAD-60 Dosimeter: Online monitoring and alarm function Side 18

19 Whole body dose [msv] Radiation protection whole body dose Total Mean Max. Nucl. Med. i DK Whole body dose cyclotron+chemistry Year Average: 1,7 ±1,5 / 1,2 ±1,1 and max. 5,5 /4,0 for Cyclotron/Chemistry. Side 19

20 Radiation protection Equipment Always check staff, tools and equipment for contaminations before leaving a isotope laboratory. Side 20

21 Radiation protection The decay law of radioactivity Radioaktivt materiale: antal henfald ΔN per tidsenhed Δt må nødvendigvis være proportionalt med antallet af kerner N: N = λ N N t = N 0e λt t Aktiviteten er givet som ændringen i antallet af kerner N per tidsenhed: A(t) = dn = λ N dt 0e λt = λ N t A t = A 0 e λt Halveringstid T ½ og λ hænger sammen λ = ln(2) / T ½ og er en kernefysisk konstant som ikke kan ændres! Aktiviteten kan med fordel udtrykkes ved potenser af ½: A t = A 0 e λt t ln 2 = A 0 e T½ = A 0 (e ln 2 t 1 ) T½ = A 0 2 t T½ Side 21

22 Radiation protection The decay law of radioactivity Activity law expressed in powers of ½ : A t = A 0 e λt t ln 2 = A 0 e T½ = A 0 (e ln 2 t ) T½ = A t T½ Example: 11 C, T ½ =20min, A 0 =64 GBq, what is the activity A after 2 hours? A t = 2h = A t T½ = A 0 ( 1 2 )120/20 = A 0 ( 1 2 )6 = 64 GBq 1 64 = 1 GBq If you have an accident and need to clean up wait until the activity has decayed. Side 22

23 Radiation protection Radiation Protection Data Handbook F 18 O + e + + ν T ½ = 109,728 m 2h ISBN RADIATION PROTECTION DOSIMETRY Vol. 98 No 1, 2002 Published by Nuclear Technology Publishing Side 23

24 Radiation protection Radiation Protection Data Handbook H β = 120 μsv/h or H γ /H β = 1/66 H γ = 1,81 μsv/h Side 24 Distance and/or geometry VERY important.

25 Radiation protection Radiotoksicitetsgrupper The risk and danger is different for different isotopes: Classification of isotopes Group 1 Group 2 Group 3 Group 4 11C, 13N, 83Rb, 84Rb 131I, 211At 223Ra 15O, 18F 64Cu 68Ga, 81Kr 89Zr Contamination limits [Bq/cm2] Skin 50 5 Surfaces Side 25

26 Radiation protection Time factor Side 26 Received dose is proportional to time: ΔE = E Δt You should always estimate expected dose before any new task. Train the work cold or with experimental activities only. If you are in doubt do not take any risk and ask for help! Example: Point source, 11 C r = 30 cm, A = 1 MBq, E = 1, msv/h For 100 GBq we have E =187 msv/h In 2 minutes you will receive ΔE = 187 msv/h 2/60 h = 6,2 msv corresponding to the allowed annual dose.

27 Radiation protection Distance square law Received dose is inversely proportional to the distance squarred: E (r) = E (r=a) ( a r )2 Example 1: Double distance = one forth dose 10 times distance = reduction to 1% Keep distance. Use tweezers, tongs, If possible use/develop automation of the labelling procedure. Example 2 (100 GBq 11 C, a= cm): E (r) = E (r=a) ( r a )2 = 187 msv/h ( 0,3 1,0 )2 = 16,8 msv/h Now the annual dose is received in 21 minutes rather than in 2 minutes as in the former example. Side 27

28 Radiation protection Distance square law Distance and/or geometry VERY important for received dose. Example: E point source / E syringe = 1/1600 Side 28

29 Radiation protection Shielding I 0 Δx absorbed I 0 * e -mx detected scattered S. Holm. Reduction in intensity ΔI per thickness Δx is proportional to the incomming intensity I 0 : I ΔI = μ I Δx = μ I I x = I x 0e μx Linear attenuation coefficient µ and half-thickness X ½ is related: μ = ln(2) / X ½ Side 29

30 Radiation protection Shielding γ The linear attenuation coefficient µ is a material constant and depends on both radiation type and energy. X ½ (E γ =511keV) = 4,2 mm for lead X ½ (E γ =511keV) = 3,4 cm for concrete X ½ (E γ =511keV) = 7,2 cm for water/tisue I x = I 0 e μx μ = ln(2) / X ½ I x = I x X½ Linear- (µ) or mass attenuation - (µ/ρ) coefficients can be found at: Side 30

31 Radiation protection Shielding γ Example: Hot-celle, ΔX = 70 mm, X ½ (E γ = 511keV) = 3,8 mm for lead X ½ (E γ =1.0 MeV) = 8,6 mm for lead X ½ (E γ =1.5 MeV) = 11,7 mm for lead I x 1 I , 8 = = I x 1 I , 7 = = 1 63 If the dose rate from a 511 kev source is 1 µsv/h on the out side of the hot-celle it will be 350 msv/h in side the hot-cellen. Never open a hot cell with a full batch inside. Be careful the shielding is VERY energy dependent. Side 31

32 Radiation protection Shielding α and β R β (0,5 / 1 MeV) = 1,6 / 4,1 m in air R β (1 MeV) = 2,3 mm in pyrex glass R β (1 MeV) = 2,1 mm in aluminum Glasses are good for protecting your eyes. Side 32 Linear- (µ) and/or mass attenuation - (µ/ρ) coefficients can be found at:

33 Radiation protection Shielding α and β We are now talking about µm and mm. External radiation is no problem, but inhalation and/or ingestion can be VERY serious. Linear- (µ) and/or mass attenuation - (µ/ρ) coefficients can be found at: Side 33

34 Finito, basta, Finito, basta, Side 34

35 Diverse observationer/anbefalinger - 1 Læs 954 om hvad I må og ikke må I vore isotoplaboratorier. Brug af helkrops-tld obligatorisk for alle. Brug af finger-tld obligatorisk for de fleste. Husk at aflevere TLD og finger-tld til tiden. Brug af elektronisk dosismeter obligatorisk. Check dagligt at den virker. Kontrolmåling (af personer og ting) efter besøg i isotoplaboratorier. De-kontamineringsprocedure. Undgå panik. Sæt jer ind I brugen af vort måleudstyr. Vejledninger findes. Rapporter i log-bog. Underret ansvarlig i forbindelse med kontamineringer og ryd op efter jer. Rapporter fejl på måleinstrumenter. Skift f.eks. selv batterier. Side 35

36 Diverse observationer/anbefalinger - 2 Overvej jævnligt jeres arbejdsrutiner. Selvkontrol. I udviklingslaboratoriet må der kun arbejdes med små aktivitetsmænger. Kender du de typiske strålingsniveauer i dit arbejdsområde? Regler for håndtering af radioaktivt affald. Automatisering af processer. Afskærmning af kilder. Hjælpeudstyr. Hjælp fra mere erfarne kemikere. Analyser forventet dosis før alle nye arbejdsprocesser. Side 36