Radiation Safety level 5 Frits Pleiter 02/07/2015radiation safety - level 51

Contents  atomic and nuclear physics (1)  interaction with matter (3) o sources and x-ray equipment (2) o shielding (3) o detection (4) o radiobiology (6) objective risk of radiation (6) subjective risk acceptation (6)  quantities and units (5)  regulations (7) o practical health physics (8 - 10) o waste (11) 02/07/2015radiation safety - level 52

Detection  ionization detector  scintillation detector  photographic emulsion  electronic equipment 02/07/2015radiation safety - level 53

Detection ionization detector gas filled detector ionization chamber proportional counter Geiger-Müller counter air, natural gas, noble gas, V semiconductor detector germanium (  -radiation) silicon (  -radiation, x-ray radiation) V 02/07/2015radiation safety - level 54 anode wire cathode wall counting gas

Detection ionization 02/07/2015radiation safety - level 55 gas atoom positive ion negative elektron ionizing radiation cathode wall anode wire ionization energy = 34 eV

Detection gas amplification primary electrons are accelerated collide with gas atoms and produce secundary ions 02/07/2015radiation safety - level 56 secundary charge positive ion negative electron 1 primary charge 2 cathode wall anode wire ionizing radiation

Detection influence of anode voltage I.recombination II.ionization chamber III.proportional counter IV.incomplete proportionality V.Geiger-Müller counter VI.continuous gas discharge 02/07/2015radiation safety - level 57  -particle III III IV V VI  -particle

Detection proportional counter 02/07/2015radiation safety - level 58 proportional counter energy resolution at 6.4 keV is 17%

Detection Geiger-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 02/07/2015radiation safety - level 59

Detection examples of ionization detectors 02/07/2015radiation safety - level 510

Detection semiconductor detector ionization energy  3 eV pros high efficiency excelent energy resolution cons no gas amplification must be cooled to 80 K expensive 02/07/2015radiation safety - level 511

Detection semiconductor detector 02/07/2015radiation safety - level 512 Ge-detector energy resolution at 661 keV is 0.4%

Detection scintillation detector inorganic scintillator NaI, BaF 2, 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) CaF 2, LiF, Li 2 B 4 O 7 02/07/2015radiation safety - level 513

Detection photomultiplier tube interaction of  -photon with scintillator  light photons interaction of light photon with cathode  photo-electron photo-electron hits electrodes at each collision secundary electrons are liberated in NaI, about 500 eV per photo-electron is required 02/07/2015radiation safety - level 514 ionizing radiation light photocathode dynode photomultiplier tube electrons anode contact pins scintillation crystal

Detection scintillation detector 02/07/2015radiation safety - level 515 NaI detector energy resolution at 5.9 keV is 43.5% energy resolution at 662 keV is 7%

Detection thermoluminescence 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 02/07/2015radiation safety - level 516 B A valence band conduction band ionizing radiation

Detection examples of scintillation detectors 02/07/2015radiation safety - level 517

Detection photographic 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 m 3 02/07/2015radiation safety - level 518

Detection detector for elementary particles 02/07/2015radiation safety - level 519

Detection proper 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 02/07/2015radiation safety - level 520

Detection proper 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 02/07/2015radiation safety - level 521

Detection proper 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  N pulse  N   E   dose 02/07/2015radiation safety - level 522 gas

Detection proper 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 02/07/2015radiation safety - level 523

Detection proper 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) 02/07/2015radiation safety - level 524

Detection  -spectroscopy  photopeak at E   escape peak at E  - E X  Compton-edge after electron capture and internal conversion  x-ray peak at E X after pair formation outside detector  annihilation peak at 511 keV line width is due to statistics 02/07/2015radiation safety - level 525

Detection multichannel analyzer 02/07/2015radiation safety - level 526

Detection energy calibration 02/07/2015radiation safety - level 527

Detection efficiency calibration 02/07/2015radiation safety - level 528