Radiation Safety level 5

1. Radiation Safetylevel 5 Frits Pleiter radiation safety - level 5

2. Contents • atomic and nuclear physics (1) • interaction with matter (3) • sources and x-ray equipment (2) • shielding (3) • detection (4) • radiobiology (6) • objective risk of radiation (6) • subjective risk acceptation (6) • quantities and units (5) • regulations (7) • practical health physics (8 - 10) • waste (11) radiation safety - level 5

3. Detection • ionization detector • scintillation detector • photographic emulsion • electronic equipment radiation safety - level 5

4. cathode wall anode wire counting gas Detectionionization detector gas filled detector ionization chamber proportional counter Geiger-Müller counter air, natural gas, noble gas, ... 100 - 1500 V semiconductor detector germanium (-radiation) silicon (-radiation, x-ray radiation) 500 - 3000 V radiation safety - level 5

5. cathode wall ionizing radiation anode wire cathode wall Detectionionization gas atoom positive ion negative elektron ionization energy = 34 eV radiation safety - level 5

6. cathode wall ionizing radiation 1 2 2 2 anode wire primary charge 1 secundary charge 2 positive ion negative electron cathode wall Detectiongas amplification primary electrons are accelerated collide with gas atoms and produce secundary ions radiation safety - level 5

7. VI V IV III I II -particle -particle Detectioninfluence of anode voltage • recombination • ionization chamber • proportional counter • incomplete proportionality • Geiger-Müller counter • continuous gas discharge radiation safety - level 5

8. Detectionproportional counter proportional counter energy resolution at 6.4 keV is 17% radiation safety - level 5

9. DetectionGeiger-Müller counter simple construction and cheap anode field is shielded by positive ions which reduces gas amplification constant pulse height > 10 V dead time  > 0.1 ms  true count rate > measured count rate secundary electrons from cathode wall are accelerated and produce a new signal, etcetera to prevent this, a (multiatomic) quench gas is added radiation safety - level 5

10. Detectionexamples of ionization detectors radiation safety - level 5

11. Detectionsemiconductor detector ionization energy  3 eV pros high efficiency excelent energy resolution cons no gas amplification must be cooled to 80 K expensive radiation safety - level 5

12. Detectionsemiconductor detector Ge-detector energy resolution at 661 keV is 0.4% radiation safety - level 5

13. Detectionscintillation detector inorganic scintillator NaI, BaF2, ZnS, BGO often contains a fluorescent additive, e.g. NaI(Tl) organic scintillator anthracene, stilbene, plastic, liquid often contains a fluorescent additive chemical and optical quenching thermoluminescence detector (TLD) CaF2, LiF, Li2B4O7 radiation safety - level 5

14. anode photocathode electrons ionizing radiation light dynode contact pins scintillation crystal photomultiplier tube Detectionphotomultiplier tube interaction of -photon with scintillator  light photons interaction of light photon with cathode  photo-electron photo-electron hits 10 - 14 electrodes at each collision 2 - 3 secundary electrons are liberated in NaI, about 500 eV per photo-electron is required radiation safety - level 5

15. Detectionscintillation detector NaI detector energy resolution at 5.9 keV is 43.5% energy resolution at 662 keV is 7% radiation safety - level 5

16. conduction band ionizing radiation B A valence band Detectionthermoluminescence detector (TLD) interaction lifts an electron into a metastable state if TLD material is heated, electron returns to ground state during this proces infrared light is emitted radiation safety - level 5

17. Detectionexamples of scintillation detectors radiation safety - level 5

18. Detectionphotographic emulsion film badge as personal dose registration tool completely replaced by TLD badge autoradiogram analytic tool in chemistry and biochemistry more and more replaced by semiconductor tools x-ray picture medical diagnostic tool more and more replaced by semiconductor devices nuclear emulsion detector for elementary particles in cosmic radiation replaced by equipment with volumes > 1000 m3 radiation safety - level 5

19. Detectiondetector for elementary particles radiation safety - level 5

20. Detectionproper choice of detector which detector to choose depends largely on what has to be measured (and on the available amount of money) dose of dose rate contamination -, -, -radiation identification of a nuclide in the last case, energies must be measured (spectroscopy) with the aid of a multichannel analyser nowadays hardly more than an interface card in the computer radiation safety - level 5

21. Detectionproper choice of detector dose rate meter reading in sievert per unit of time not suited for contamination measurements contamination monitor reading in number of counts per unit of time not suited for dose rate measurements radiation safety - level 5

22. gas Detectionproper choice of detector -dose measured with Geiger-Müller counter signal provides no energy information photo-effect and Compton-effect create electrons in the tube wall electrons that escapes into the gas cause an electric pulse the larger E, the thicker the layer from which electrons can escape  Npulse  N  E  dose radiation safety - level 5

23. Detectionproper choice of detector -contamination ZnS with extremely thin window gas filled detector with extremely thin window liquid scintillation counter -contamination gas filled detector with thin window Si-detector with thin window (no Ge since it is more sensitive to -ray background) liquid scintillation counter radiation safety - level 5

24. Detectionproper choice of detector -contamination NaI-detector gas filled detector with large area and low background Ge-detector Si-detector with thin window (especially for x-ray radiation) liquid scintillation counter (if E < 50 keV) radiation safety - level 5

25. Detection-spectroscopy • photopeak at E • escape peak at E - EX • Compton-edge after electron capture and internal conversion • x-ray peak at EX after pair formation outside detector • annihilation peak at 511 keV line width is due to statistics radiation safety - level 5

26. Detectionmultichannel analyzer radiation safety - level 5

27. Detectionenergy calibration radiation safety - level 5

28. Detectionefficiency calibration radiation safety - level 5