Suren Kandasamy Dissertation.pdf - University of Surrey

Characterisation of novel detector:LaCl 3 :Ce(10%)byKandasamy SurenA dissertation submitted to the Department of Physics,University of Surrey, in partial fulfilment of the degree ofMaster of Science in Radiation Detection and InstrumentationDepartment of PhysicsFaculty of Engineering and Physical SciencesUniversity of SurreyAugust 2010© Kandasamy Suren 2010

M.Sc DissertationAcknowledgementsI would like to give my deep gratitude to Dr. Z. Podolyak, Department ofPhysics University of Surrey for his help and guidance throughout this project.I express my sincere gratitude to my colleague Mr. G. R. Booker for helped meto carry out the experiments and also my special thanks to the radiation teachinglaboratory staff Mr. Gary Strudwick and Mr. John-Williams Brown for their helps andsupports throughout the project.And indeed I give my heartfelt thanks to all of my friends who helped me innumerous ways and of course I must extend my cordial thanks towards to my lecturersand administrative staff for their supports during my entire course time.Finally, warmly I am giving my thanks and deepest gratitude to my family fortheir supports and encouragements gives throughout my life.K. Suren ii

M.Sc DissertationTable of ContentsChapter 1 Introduction 1Chapter 2 Background 32.1 Types of detectors 32.2 Scintillators 42.2.1 Properties of Lanthanum halide scintillator 52.3 Gamma-Ray Interactions 62.4 Detector Characterisation 72.4.1 Energy Calibration 72.4.2 Energy Resolution 82.4.3 Detection efficiency 92.4.4 Photo-fraction 112.4.5 Time resolution 12Chapter 3 Experimental Apparatus and Method 133.1 To select the supply voltage of the LaCl 3 :Ce Detector 133.2 To get the optimum shaping time 143.3 Energy calibration of the LaCl 3 :Ce detector 143.4 Energy resolution 143.5 Detection efficiency 153.6 Self-counting of LaCl 3 :Ce detector 153.7 Time Resolution 15K. Suren iii

M.Sc DissertationChapter 4 Result and discussion 174.1 Select the supply voltage of the LaCl 3 :Ce(10%) 174.2 Select the optimum shaping time 194.3 Energy calibration of MCA 214.4 Energy resolution 244.5 Detection Efficiency 264.6 Photo-fraction 284.7 Internal Radioactivity 294.8 Time resolution 30Chapter 5 Conclusions 33Chapter 6 References 34Appendix A The present activity of used sources 36Appendix B Detectors and photomultipliers 37Appendix C Decay chain & background spectrum of 138 La 39Appendix D Spectrum collected with LaCl 3 :Ce detector 40K. Suren iv

M.Sc DissertationAbstractDelft and Bern Universities have invented LaCl 3 :Ce and LaBr 3 :Ce as scintillators,there are some other groups also had been further studied of their characteristics; andSaint-Gobain Crystals has made considerable progress in their commercial availabilityas BrilLanCe TM 350 and BrilLanCe TM 380 crystals. This report aims to examine theperformance of LaCl 3 :Ce scintillator detector for the gamma ray spectroscopy. Also thisstudy included selection of operating voltage, optimum shaping time, recordingspectrum, energy resolution, detection efficiency, photo-fraction and time resolution.LaCl 3 :Ce detector with the size of 44.450.8mmcontaining 10% of cerium (Ce) asan activator has high light output (~46,000 photons/MeV) and fast principal decay timeconstant (~28 ns). This scintillator crystal has very linear response and excellent energyresolution, operated with Hamamatsu R6231 photomultiplier at 950 Volts, and 1.0 sshaping time constant of ORTEC 672 shaping amplifier. For example, energyresolution of 3.70 ± 0.15% (FWHM) for 662 keV gamma-rays ( 137 Cs source) weremeasured with the LaCl 3 :Ce crystal at room temperature. The energy resolution asfunction of gamma-ray energy and the inverse square root of the incident photon energyshow a linear relationship. The photo-fraction and photopeak efficiency of 662 keVgamma-rays was measured with the LaCl 3 :Ce crystal as 27.06 ± 0.04 % and 11.43 ±0.01 % respectively. Also timing resolution of 876.0 ps has been recorded withLaCl 3 :Ce-PMT and BaF 2 -PMT detectors operating in coincidence using 1173.24 keV( 60 Co) gamma pairs. Furthermore, the radioactive background of the natural 138 Laradioactive isotope observed in LaCl 3 :Ce crystal, the integral background count ratewas determined to be about 1.17 cps/cm 3 .K. Suren v

M.Sc DissertationChapter 1IntroductionThe use of scintillators in gamma-ray spectroscopy is very wide spread. Theimportant properties for scintillation crystals are high light output, high stopping power,fast decay time, good linearity and low cost [13]. Depending on the intendedapplications, scintillators can be made by a variety of materials. Inorganic materialsusually an alkali halide, such as sodium iodide (NaI) or cesium iodide (CsI) are used tomake most common scintillators in gamma-ray spectroscopy. A bit of impurity, such asThallium and Sodium are often added with these materials to do their job properly. Thisimpurity material is called an “activator”. For example, sodium iodide crystal withthallium activator is denoted as NaI(TI) or cesium iodide crystal with a sodiumactivator is denoted as CsI(Na) [15].Scintillation spectrometers play a vital and ubiquitous role in detection andspectroscopy of energetic photons (γ-rays) as well as neutrons. The gamma-ray entersthrough the scintillator crystal where it produces charged particles. These chargedparticles interact with crystal and produce low energy photons. These photons arecollected by photomultiplier tubes (PMTs) and where they are amplified to yield acurrent pulse.Applications of this kind of detectors are high resolution X-ray and Gamma rayspectroscopy, nuclear and high-energy physics research, nuclear treaty verification andsafeguards, environmental monitoring, medical applications, diffraction, nondestructivetesting, national security and geological exploration. High detection andscintillation efficiency, good energy, time and spatial resolution, short dead-time, fastscintillation response and mechanical and chemical stability are the properties shouldhave to the scintillation crystals, when they are used in these kinds of applications.Though, until now there is no any detectors have been found with these allrequirements. Thus, there has been considerable research and development of newinorganic scintillators with enhanced performance [3].K. Suren 1

M.Sc DissertationThe most commonly used scintillator is NaI:Tl, which has a peak emission of 415nm, a light output of ~39,000 photons/MeV,. a density of 3.73gcm , and a decay time of240 nanoseconds. The energy resolution is typically 5−6 % FWHM for 662 keV gammarays with NaI:Tl [3].Recently, new cerium doped lanthanum halide scintillators, LaCl 3 :Ce(10%) andLaBr 3 :Ce(5%), have been discovered. LaCl 3 :Ce(10%) has a density of 3.93gcm , a lightoutput of 46,000 photons/MeV, and a decay time of 28 nanoseconds. Its peak emissionwavelength is 350 nm. On the other hand, LaBr 3 :Ce(5%) has a density of 5.33gcm , alight output of 60,000 photons/MeV, and a decay time of 26 nanoseconds. Its peakemission wavelength is 380 nm [13].Nowadays several groups are doing researches on the properties of LaCl 3 :Ce andLaBr 3 :Ce detectors, since Delft and Bern universities have discovered these scintillatordetectors. BrilLanCe TM 350 and BrilLanCe TM 380 crystals are the available crystals inthe commercial industry made by Saint-Gobain Crystal. Specifically, in this work,BrilLanCe B350 is LaCl 3 : Ce(10%) and BrilLanCe 380 is LaBr 3 :Ce(5%). These newscintillators have about 3% FWHM energy resolution for 662 keV gamma rays, andhave a more linear response with energy than NaI:Tl [5].The aim of this study is to evaluate and characterise of LaCl 3 :Ce(10%) with thesize of 44.450.8mmcrystal for gamma-ray spectroscopy application. For thisreport discuss about the characteristic of LaCl 3 :Ce detector, such as energy resolution,detection efficiency and time resolution.K. Suren 2

M.Sc DissertationChapter 2Background2.1 Types of detectorsDepending on the type, radiation detectors can be characterized into three majorgroups, such as Semiconductor detectors, Scintillator detectors and Gas Detectors. TheSemiconductor detectors are measure charge from the radiation event. The use ofsemiconductor materials as radiation detectors can result in a much larger number ofcarriers for a given incident radiation event than is possible with any other commondetector type. Consequently, the best energy resolution from radiation spectrometers inroutine use is achieved using semiconductor detectors. Of the available semiconductormaterials silicon predominates in the diode detectors used primarily for charged particlespectroscopy. Silicon detectors are most commonly used in α, β particle spectroscopy.But it is not suitable for X-rays and gamma rays because of it poor detection efficiency.Germanium is more widely used in gamma ray spectroscopy, since it has large volumeand high efficiency for X-rays and gamma rays. Though, highest energy resolution hasachieved for gamma ray spectroscopy by using HPGe (high purity germanium)detectors. All Germanium detectors should be cooled. Liquid nitrogen or cryo-coolers isusing for this purpose.Scintillator detectors measure light from the radiation event, which is convertedinto a current pulse via a photocathode. Normally two main types of Scintillatordetectors are available. They are Inorganic scintillators and Organic scintillators. Goodgamma efficiency, moderate/good energy resolutions are the best properties for theinorganic scintillators by using as detectors in gamma ray spectroscopy. Sodium Iodide(NaI), Barium Fluoride (BaF 2 ) and lately, cerium-doped lanthanum crystals, inparticular LaBr 3 :Ce and LaCl 3 :Ce are the good examples for inorganic scintillatordetectors. Also plastic scintillator (BC501) and liquid scintillator are the examples fororganic scintillator detectors. The organic scintillator detectors commonly called as“plastic” and have large volume, cheap, very fast pulses, poor energy resolution andlow gamma efficiency.K. Suren 3

M.Sc DissertationGas-filled Detectors are based on sensing the direct ionization created by thepassage of the radiation. These detectors can divide into three groups such as,Ionization chambers, proportional counters, and Geiger-Muller counters. TheIonization chambers are used to measure exposure to X-rays and gamma-rays. Oneimportant application of proportional counters has therefore been in the detection andspectroscopy of low-energy X-radiation. Proportional counters are also widely appliedin the detection of neutrons. Since helium-3 and boron have very high detectionefficiency for thermal neutrons, 3 He, BF 3 tubes are used as gas-filled detectors.2.2 ScintillatorsSome materials have the ability to release visible or UV light when de-excitedafter an excitation caused by a photon or charged particle. The emission of photons bythe atom of the materials is only a portion of the total energy deposited in the absorber.The rest of the energy is stored as thermal energy in the absorber. This type of materialsis called a scintillator and is widely used in nuclear medicine.The most widely applied scintillators include the inorganic alkali halide crystal.The inorganics tend to have the best light output and linearity, but with severalexceptions are relatively slow in their response time. Organic scintillators are generallyfaster but yield less light. The high Z-value of the constituents and high density ofinorganic crystal favour their choice of gamma-ray spectroscopy, whereas organics areoften preferred for beta spectroscopy and fast neutron detection [1]. The light yield(light output) of the scintillator is expressed as photons per MeV of absorbed gammarayenergy. The light output is the most important, as it affects both the efficiency andresolution of the detector. Main problems in creating effective scintillator gamma-raydetectors are the need for high energy resolution in order to make precise identificationof any source, and high efficiency in order to minimise the acquiring time needed forthe necessary resolution. This can be achieve with high light output scintillators, such asnew cerium doped lanthanum halide scintillators.K. Suren 4

M.Sc Dissertation2.2.1 Properties of Lanthanum halide scintillatorThe LaCl 3 :Ce +3 and LaBr 3 :Ce +3 crystal were grown from LaCl 3 /Br 3 and CeCl 3 /Br 3by the Bridgman technique. LaBr 3 :Ce and LaCl 3 :Ce crystal has hexagonal (UCl 3 type)structure with P63/m space group [12]. The compound melts congruently at 783 o C and860 o C respectively. The NaI:TI crystal has a decay time of 240 nanoseconds, whileBrilLanCe B350 LaCl 3 :Ce(10%) 28 nanoseconds and BrilLanCe B350 LaBr 3 :Ce(5%)26 nanoseconds. This difference becomes crucial high gamma ray fluxes, specificallywhen count rate of the gamma photons [6]. The fast decay time aids high rate detection.One advantage of using lanthanum halide scintillators is that the crystals of the samesize and shape can be mass produced with virtually identical properties. Thecomparative properties of LaBr 3 :Ce(5%), LaCl 3 :Ce(10%) and NaI:TI scintillator aresummarized in Table 2.1.Table 2.1 Summary of comparative properties of scintillators [2,3]Density (PropertyLaBr 3 :Ce(5%)BrilLanCe B380LaCl 3 :Ce(10%)BrilLanCe B350NaI:TI3gcm ) 5.29 3.79 3.67Decay time (ns) 26 28 240Light output (ph/MeV) 63,000 46,000 39,000Effective atomic number (Z eff ) 48.3 59.5 50.0Energy resolution (at 662 keV)

M.Sc Dissertation(A)(B)Figure 2.1 Scintillation emission spectrum of the (A) LaCl 3 :Ce and (B)LaBr 3 :Ce crystal [16]2.3 Gamma-Ray InteractionsA gamma-ray will interact with its medium in one of three different ways:photoelectric absorption, Compton scattering, and pair production. All these processlead to the partial or complete transfer of the gamma-ray photon energy to electronenergy [1]. These different interactions change their probability of occurring dependingon the energy of the gamma-ray and the atomic number of the material.As can be seen from Fig. 2.2, the line at the left represents the energy at whichphotoelectric absorption and Compton scattering are equally probable as a function ofthe absorber atomic number. The line at right represents the energy at which Comptonscattering and pair production are equally probable. The photoelectric effect isdominant for low energy photons and high Z materials. Pair production is dominant forhigh energy photons and high Z materials. The Compton scattering interaction isdominant for moderate energies. Compton continuum will be observed at the lowerenergy end of the spectrum.K. Suren 6

M.Sc DissertationFigure 2.2 A graph depicting the various regions where the different gamma-rayinteractions are dominant [1].2.4 Detector CharacterisationThe performance of a γ-ray spectroscopy system is generally characterised bythree properties. They are energy calibration, energy resolution and detectionefficiency. These quantities are dependent on the energy of the incident radiation andshould therefore be measured using several sources with different γ-ray energies [7]. .2.4.1 Energy CalibrationThe multichannel analyzer collects the voltage output from the amplifier anddivides in to a number of channels of the same width. The number of channel of ananalyzer gives an estimation of its sensitivity, which is increased with the numberchannel.The sensitivity of the analyzer Sandefined asVoutSan 2.1NchWhere, Voutoutput signal from the amplifier, Nchnumber channel of the analyzer.K. Suren 7

M.Sc DissertationA desirable feature of any γ-ray detector is linearity of energy response. That is,direct proportionality between the quantity of energy deposited in the detector by theincident radiation event and the height of the analogue output pulse. A detector energycalibration may be obtained by plotting incident photon energy versus the centralchannel number of the corresponding full energy peak. Using each of the sourcescollect an energy spectrum and determine the central channel of the full energy peak.Plot a graph of channel number versus energy, making sure to indicate all errors [7].Energy calibration is one of the most important factors that should be consideredbefore making any analysis. The gain of the system is given by the slope of thecalibration plot. The units are energy per channel (eg. keV per channel). Changing theamplifier gain is the most immediate way of altering the calibration of the system.2.4.2 Energy ResolutionOne important property of a detector in radiation spectroscopy can be examinedby noting its response to a monoenergetic source of that radiation. Statistical factors andelectronic noise affects the shape of the spectra obtained by a radiation detector. Sharplines and sharp edges would be the ideal spectrum, but in practice the lines are boardpeaks, and the edges are rounded. The energy resolution of a detector is a measure of itsability to resolve small differences in the energy of incident γ-rays, varies with theenergy and type of detector. Scintillator detectors tend to have lower energy resolutionin comparison with the solid state detectors at room temperature.An ideal photopeak will be close to Gaussian shape, because the total number ofcharge carriers N is typically a large number. In this case, the Gaussian function can bewritten with analytical parameter :A C exp 2 H H22022.2Where C is the number of count, H 0 is centroid channel number and A is peak area. Thewidth parameter determines the full width at half maximum (FWHM) of anyGaussian through the relation FWHM=2.35.K. Suren 8

M.Sc DissertationdNdHYY/2FWHMH 0HFigure 2.3 Representation of Gaussian shape peak with standard deviation , theFWHM is given by 2.35 [1].An ideal representation of the peak is shown in Fig. 2.3. A formal definition ofdetector energy resolution, R, is defined as:FWHMR 100%2.3H0The energy resolution R is thus a dimensionless fraction conventionally expressedas a percentage. Semiconductor diode detectors used in alpha spectroscopy can have anenergy resolution less than 1%, whereas scintillator detector used in gamma-rayspectroscopy normally show an energy resolution in the range 5-10% [1]. The value ofdetector resolution depends upon the size of detector and the energy of photons. Countsrates also affect the resolution and that‟s why it is better to use low rate sources forlonger time instead of using high rate sources. When using low rate source the signal tonoise ratio is better and the peak is closer to the Gaussian graph.2.4.3 Detection efficiencyDetection Efficiency describes the proportion of radiation events that recorded bya detector. It can include both geometric and radiation interaction effects. There arethree measurements of the efficiency of any detection system, Absolute totalefficiencyABS, Intrinsic efficiencyINT, and Intrinsic Peak efficiency P.K. Suren 9

M.Sc DissertationAbsolute total efficiency ABSis defined as the ratio of the pulses recorded by thedetector to the number of radiation quanta emitted from the source. This thereforeincludes solid angle effects, iefrom the source.ABSdecreases as the detector is moved further awayAbsolute total efficiency, ABS, expressed with the following formula:[7]where,C tABS100%2.4NCtis the number of counts recorded per unit time integrated over the wholerecorded spectrum, andtime.Nis calculated from:Nis the number of gamma rays emitted by the source per unitN D I E )2.5s ( Where,D is the disintegration rate of the source and I E ) is the fractional gammass( emitted per disintegration [7].Intrinsic efficiency is subdivided into two classes: intrinsic total efficiency andintrinsic photopeak efficiency. Intrinsic total efficiency, i, is defined as the percentageof radiation quanta incident on the detector, that are recorded and is expressed throughthe following formula:C ti 100%2.6NWhere,N is the total number of gamma rays that are incident on the detector and canbe calculated through the following expression:N DsI( E) N2.744Where, Ω is the solid angle subtended by the detector at the source position [7].K. Suren 10

M.Sc DissertationIntrinsic photopeak efficiency,quanta of a specific energyformula:P, is defined as the percentage of radiationEthat are recorded and is expressed by the followingC PP 100%2.8N Where,C is the net number of counts in a photopeak corresponding to energy E ,pandN is the total number of quanta of energyEwhich fall on the detector crystal,given by:N DsI( E)2.94Where, I ( E ) is the fractional number of photons of energy Eemitted perdisintegration [7].2.4.4 Photo-fractionPhoto-fraction is defined as the ratio between the total number of photons under aphotopeak to the total number of photons detected by the detector. In other words theperformance of the system is the peak-to-total ratio, also called the photo-fraction.Photo-fraction gives an estimation of the number of photons that deposit their totalenergy in the crystal as a comparison of the number of detected photons [8].Counts in the peakPhotofract ion 2.10Total number of CountsK. Suren 11

Counts per channelM.Sc Dissertation2.4.5 Time resolutionFigure 2.4 shows a simple system for recording a time spectrum. Twoindependent detectors are irradiated by a common radioisotope source that is assumedto emit at least two detectable quanta in true coincidence; that is both radiations arisefrom the same nuclear event within the source. The output signal from the each detectoris simultaneously sent down two signal branches such as Constant FractionDiscriminator (CFD). A CFD unit in each branch provides timing logic pulses that aresupplied to start and stop inputs of a Time-to-amplitude converter (TAC). A fixed timedelay is also present in the stop branch. The multichannel analyzer (MCA) records thenumber of time intervals [1].Detector 1 SourceDetector 2sourceCFDCFDFixed delayStartTACStopMultichannelanalyzerFigure 2.4 A simplified system for recording multichannel time spectra from asplit common source.FixeddelayFWHM=“time resolution ”Full width attenth maximumChannel numberor timeFigure 2.5 The multichannel time spectrum for the system of Fig. 2.4 [1].The full width at half maximum of the time distribution is often used as a measureof the overall timing uncertainty in the measurement system and is called the timeresolution [1].K. Suren 12

M.Sc DissertationChapter 3Experimental Apparatus and MethodH.VSourceDetectorPMTShapingAmplifierMCADisplayFigure 3.1 The schematic diagram is used to get the energy spectrum from theLaCl 3 :Ce(10%) detector.3.1 To select the supply voltage of the LaCl 3 :Ce DetectorAs shown in the Fig. 3.1 the LaCl 3 :Ce(10%) with the size of 44.450.8mmBrilLanCe B350 scintillator detector directly coupled with Hamamatsu R6231photomultiplier tube (PMT). Then the PMT tube was connected with Canberra 3102Dpositive high voltage power supply and ORTEC 672 shaping amplifier. The amplifieroutput signal was connected to ORTEC (1024 channel) Multi-Channel Analyser (MCA)and the data analyzed with the ORTEC Maestro for windows software.After that the shaping time and coarse gain of the shaping amplifier were set tolow values, such as 0.5 s and 20 respectively. Then the 137 Cs source was placed infront of the detector and the distance between source and detector was kept around 4cm. The voltage of the high voltage power supply was increased slowly from 0 Voltuntil get the signal in MCA. Then the corresponding voltage was noted down. After thatthis voltage was increased by 20 Volt and corresponding spectrum was collected in thecomputer. For each step the acquiring time was kept as 300 sec. Finally the totalnumber of net counts was noted down for each spectrum and then the graph of totalnumber of net counts versus supply voltage was plotted.K. Suren 13

M.Sc Dissertation3.2 To get the optimum shaping timeThe apparatus was setup as shown in Fig. 3.1. Then the positive high voltagepower supply was set to 950 Volts from the above experiment. After that shaping timeof the Amplifier was set to 0.5 s and the corresponding spectrum of the 137 Cs sourcewas collected in the computer. Then the previous step was repeated for differentshaping time as 1.0 s, 2.0 s, 3.0 s, 6.0 s and 10.0 s. Finally the FWHM was noteddown for each spectrum and then energy resolution was calculated for thecorresponding shaping time. Then the graph of energy resolution versus shaping timewas plotted.3.3 Energy calibration of the LaCl 3 :Ce detectorThe basic experiment apparatus setup was arranged as shown in Figure usingLaCl 3 :Ce detector. First 137 Cs (662 keV) source was used and the correspondingspectrum was collected in the computer. Then the 137Cs (662 keV) source was replacedas 60 Co (1173 keV, 1274 keV) and 22 Na (511 keV, 1332 keV) and in each step peakcentroid channel number was recorded from the corresponding spectrum. Then the fullpeak energy versus channel number graph was plotted.3.4 Energy resolution137 Cs (662 keV), 60 Co (1173 keV, 1274 keV), 22 Na (511 keV, 1332 keV) and 152 Eu(121.78 keV, 244.70 keV, 344.27 keV, 778.96 keV, 964.00 keV, 1112.05 keV, 1407.92keV) sources were used in the above experiment setup and the spectrum was collectedfor each sources. FWHM values were noted for each peak from the correspondingspectrum. Then the energy resolution was calculated for each FWHM values. Finallythe energy resolution versus peak energy graph was plotted.K. Suren 14

M.Sc Dissertation3.5 Detection efficiencyFirst the apparatus was setup as shown in the Fig. 3.1 and then the 137 Cs sourcewas placed in front of the detector. After that total number of counts was noted within agiven acquiring time. Then the number of counts in a photopeak was takencorresponding to the energy. Then the previous step was repeated for 60 Co, 22 Na and152 Eu sources. Finally diameter of the detector and the distance between the source anddetector were taken.3.6 Self-counting of LaCl 3 :Ce detectorTo measure the internal natural radioactivity, the Lanthanum detector was placed intoa well shielded chamber (lead castle) for self-counting. The acquisition time was kept 2days, in order to get a good statistics. Finally the spectrum was collected.3.7 Time ResolutionH.VH.VBaF 2 DetectorBaF 2 DetectorAnodePMT60 CoPMTAnodeCFDStartTACStopFixedDelayCFDInputMCAFigure 3.2 Schematic diagram of the experimental set-up using the slow fasttechnique. The anode signals pass through the fast channel which consists ofConstant Fraction Discriminator (CFD) and time-to-amplitude converter (TAC).The arrows in the figure indicate the direction in which the signal travelled [4].The basic experimental setup was arranged as shown in Fig. 3.2. Two BaF 2scintillators are directly coupled with XP2020 photomultiplier and S563 voltagedivider. One voltage divider (BaF 2 detector connected with start signal) connected withCanberra model 3102D high voltage power supply (H.V) operated at - 2000 Volts. Andother one (BaF 2 detector connected with stop signal) connected with ORTEC 456 H.VK. Suren 15

M.Sc Dissertationoperated at – 1800 Volts. Then 60 Co source was placed middle of the two BaF 2 detectorfront paces. The distance between the source and one detector was kept as 8 cm.The output of the each detector taken as two channels representing the fastchannel (anode or timing channel) and the slow channel (dynode or energy channel).The fast channel signal was connected to an ORTEC 934 EG&B constant fractiondiscriminator (CFD), while the energy channel signal was connected to the Canberra2022 shaping amplifier. Then the both signals were recorded using digital oscilloscope,which was triggered in a qualified mode incorporating level crossing of both signals,effectively acting as a coincidence gate to make sure they are in coincidence and passedto the MCA to adjust the CFD window to accept the 1173.24 keV peak only. Then theoutputs of the CFD were connected to the start and stop of the ORTEC 566 time-toamplitudeconverter (TAC) with the range of the TAC set at 50 ns. Finally, output ofthe TAC was connected to the input of an ORTEC (8192 channel) MCA, and the pulseheight spectrum was analysed using ORTEC Maestro for windows software [11].Then BaF 2 scintillator in the stop channel was replaced with the size of 44.450.8mmLaCl 3 :Ce(10%) scintillator directly coupled with Hamamatsu R6231photomultiplier tube operated at +950 Volts. Then the above step was done withLaCl 3 :Ce-BaF 2 detector. To obtain the time resolution in time scale (ps) the MCAsystem was calibrated using nanosecond delay at the stop signal.K. Suren 16

M.Sc DissertationChapter 4Result and discussionPerformance and the characterization of the gamma ray detection properties ofBrilLanCe B350 (LaCl 3 :Ce(10%)) with the size of 44.450.8mmscintillatordetector was studied. This study involved selection of operating voltage, optimumshaping time, recording spectrum, energy resolution, detection efficiency, photofractionand time resolution.4.1 Select the supply voltage of the LaCl 3 :Ce(10%)The energy spectrum of 137 Cs was collected using LaCl 3 :Ce(10%) detectordirectly coupled with Hamamatsu R6231 PMT and ORTEC 672 shaping amplifier, fordifferent positive supply voltages. The amplifier coarse gain was set to be 20. Table 4.1shows the total number of net count recorded from MCA maestro for windows softwarefor each spectrum.Table 4.1 Net count changes with supply voltageSupply Voltage(+V)Total number ofnet CountError in netcounts±860 96997 230880 101885 215900 128618 357920 262350 433940 282660 477960 283665 543980 286255 6181000 287726 4751020 290150 5571040 289232 4131060 289122 3251080 286799 6101100 287589 7251120 289420 4371140 287418 2651160 288120 3101180 285417 5471200 283274 526K. Suren 17

Total number of net countsM.Sc DissertationFigure 4.1 shows the graph of total number of net counts versus supply voltage.This graph was plotted using the values shown in Table 4.1 for LaCl 3 :Ce(10%)detector.29000024000019000014000090000850 900 950 1000 1050 1100 1150 1200 1250Supply voltage(V)Figure 4.1 The counting curve of LaCl 3 :Ce(10%) detector as a function ofsupply voltage.The operating voltage was chosen by the high voltage corresponding to the centrepoints on the plateaus [6]. According to the Fig. 4.1 for the LaCl 3 :Ce(10%) detector theoperating voltage has been found as 950 Volts. When using PMTs for scintillatordetectors, there is a trade between dynamic range, linearity (proportionality of response)and resolution. This can discussed as follows. The very high photon yields of thescintillator could with its fast emission time means that standard PMTs can easilysaturate when operated at nominal anode to cathode biases of ~ 1000 V purely due totheir very high gains [10]. This can result in gross non linearities being into spectra.Reducing the PMT bias may reduce these non linearities and extend the dynamic range,but at the expense of a deteriorated energy resolution. Therefore, a trade is requiredbetween range, linearity and resolution [10].From the Fig. 4.1 shows below 860 Volts less number of counts was recorded.From that point the recorded count was suddenly increased. That means the PMTworking active voltage bias region. The maximum recommended high voltage powerK. Suren 18

M.Sc Dissertationsupply of Hamamatsu R6231 PMTs is positive value of 1500 Volts. For this study thatoperating voltage is found positive value of 950 Volts. So this is good bias voltage ofLaCl 3 :Ce(10%) with the size of 44.450.8mmscintillator detector coupled withHamamatsu R6231 PMTs. For this positive high voltage supply was kept for otherstudies with LaCl 3 :Ce(10%) detector.4.2 Select the optimum shaping timeTo get the optimum shaping time of ORTEC 672 amplifier with LaCl 3 :Ce(10%),the 137 Cs spectrum was collected with different shaping time such as 0.5 s, 1.0 s, 2.0s, 3.0 s, 6.0 s, 10.0 s. For each spectrum was acquired same time period as 600sec. Table 4.2 shows the calculated value of energy resolution % (FWHM) for 137 Cs fullenergy peak of each spectrum.Table 4.2 Resolution changes with shaping time for peak energy of 662 keV ( 137 Cs)Shapingtime(µs)FWHM(Channel)PeakChannelnumberResolution %0.5 56.50 1405.41 4.021.0 42.18 1139.70 3.702.0 25.57 692.29 3.693.0 18.15 480.87 3.776.0 10.45 257.00 4.0710.0 6.74 148.92 4.53Using the values shown in Table 4.2 the graph of resolution versus shaping timeplotted for LaCl 3 :Ce(10%) detector, as shown in Fig. 4.2.K. Suren 19

Energy Resolution (%)M.Sc Dissertation4.604.404.204.003.803.600 2 4 6 8 10Shaping time (us)Figure 4.2 Variation of the Energy resolution of a LaCl 3 :Ce detector systems asthe amplifier shaping time is changedThe energy resolution (% FWHM) of the 662 keV ( 137 Cs) photopeak was studiedwith of LaCl 3 :Ce(10%) with the size of 44.450.8mmscintillator detector, atdifferent shaping time of amplifier. Figure 4.2 shows the value of energy resolution wasdecreased and increased as the shaping time increases. This gives good characteristic toselect optimum shaping time.Of all elements in pulse height analysis system, the linear amplifier presents theuser with the greatest variety of operational characteristics and, as result, the mostdifficult choices. One of the major „trade-offs‟ in using a linear amplifier is betweenevent rate and energy resolution. The best energy resolution is often with a long shapingtime (reduced noise), but high rates require short shaping time [1]. On manycommercial linear amplifiers, the shaping time is adjustable. Then the choice may beoptimized for a given application by measuring the pulse height resolution of thesystems as the shaping times are varied. This optimization is given in Fig. 4.2. Note theoptimum shaping time in case, where the energy resolution is a minimum. From theFig. 4.2 the optimum shaping time was selected as 1.0 s. This shaping time constant ofthe amplifier was kept for other studies.K. Suren 20

Peak energy (keV)M.Sc Dissertation4.3 Energy calibration of MCABefore starting the experiment it was essential to calibrate the systems to findwhether it is linear or not. The system was calibrated using the spectrum collected fromthe 22 Na, 137 Cs and 60 Co standard sources with LaCl 3 :Ce(10%) detector. Each spectrumwas collected for 600 sec.Table 4.3 Energy calibration for the detectorSourcePeak Energy(keV)Channel No22 Na 511.00 135.46137 Cs 661.67 176.8160 Co 1173.24 313.6360 Co 1274.50 337.1822 Na 1332.50 356.17Using the values shown in Table 4.3 the MCA calibration graph was plotted, as shownin Fig 4.3.13501250y = 3.7479x + 1.528211501050950850750650550450120 160 200 240Peak Channel No280 320 360Figure 4.3 The MCA calibration graph of LaCl 3 :Ce(10%) gamma-ray detectorK. Suren 21

Number of countsM.Sc DissertationFrom the energy calibration, Fig. 4.3 shows the relation between channel andenergy is linear (each channel has the same width of energy) and mathematicallyrepresented by the equation isEnergy ( keV) 3.7479Channelnumber 1.52824.1The implication of this equation is that for any given channel on the MCA, byplugging that channel number into Eq. 4.1, the energy that the MCA channel representhas been calculated. After the energy calibration of the system, the spectrum of 137 Cs,60 Co and 152 Eu was collected by LaCl 3 :Ce (10%) detector to check the linearity ofLaCl 3 (10%) detector. The Fig 4.4, 4.5, 4.6 show the spectrum of 137 Cs, 60 Co and 152 Eurespectively. For each spectrum the x-axis was converted into energy in keV. It showsthe full energy peak of each sources was collected their actual energy position. Thatmeans the LaCl 3 :Ce detector was give good linear response to MCA wide range from32 keV to 1407 keV.18000016000014000032 keVKα X-ray peak662 keVFull energy peak120000100000800006000040000Backscatter peakComptoncontinuumCompton edge2000000 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800Energy (keV)Figure 4.4 Pulse height spectrum for 662 keV gamma rays ( 137 Cs) taken with51 76mm LaCl 3 :Ce(10%) scintillator detectorFigure 4.4 represents the energy spectra of 662 keV gamma-rays from 137 Cssource, as collected with LaCl 3 :Ce(10%) detector with 1.0 s shaping time constant,acquired for 600 sec. For room temperature LaCl 3 :Ce(10%) detector have very goodK. Suren 22

Number of counts1436 keVInternal radioactivityM.Sc Dissertationenergy resolution 3.7 ± 0.15 % (FWHM) at 662 keV. And the spectrum shows the lowenergy peak at 32 keV due to barium K α X-ray.14000Kα X-ray peak120001000080001173.24 keVFull energy peak1332.5 keVFull energy peak60004000Backscatter peakComptoncontinuumCompton edge200000 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600Energy (KeV)Figure 4.5 Pulse height spectrum for 60 Co gamma rays source taken withLaCl 3 :Ce scintillator detector for 600 secFigure 4.5 presents the energy spectra of gamma-rays from a 60 Co source. Note avery high energy resolution of 2.78 ± 0.08 % for the 1332.5 keV peak measured withLaCl 3 :Ce crystal. In this spectrum there is an additional peak at 1436 keV due to internalradioactivity of lanthanum halide crystal. This is very useful for some other energycalibration application.K. Suren 23

Number of counts128.78 keV244.70 keV344.27 keV778.90 keV964.00 keV1112.05 keV1407.92 keVM.Sc Dissertation1600001400001200001000008000060000400002000000 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500Energy (keV)Figure 4.6 Pulse height spectrum for 152 Eu gamma rays source taken withLaCl 3 :Ce scintillator detector for 600 sec4.4 Energy resolutionAfter calibration of MCA the spectrum of 137 Cs, 60 Co, 22 Na and 152 Eu wascollected. For each spectrum the FWHM (keV) was recorded from the MCA, usingmaestro for windows software. Table 4.4 shows the values of FWHM (keV)corresponding peak energies. Then the resolution (%) was calculated using the Eq. 2.3.And also the resolution of constant times one over square root of energy was calculated.Table 4.4 Energy resolution of 137 Cs, 60 Co, 22 Na and 152 Eu for LaCl 3 :Ce detectorEnergy(keV)FWHM(keV)Resolution%ResolutionError (±)76.3energy ( keV )121.78 14.71 11.26 0.82 6.91244.70 18.41 7.52 0.41 4.88344.27 17.50 5.37 0.29 4.11511.00 20.36 4.18 0.20 3.38661.67 24.51 3.70 0.15 2.97778.96 25.23 3.24 0.13 2.73964.00 27.47 2.85 0.10 2.461112.05 31.95 2.87 0.09 2.291173.24 32.80 2.80 0.09 2.231274.50 35.34 2.77 0.08 2.141332.50 37.10 2.78 0.08 2.091407.92 38.04 2.70 0.07 2.03K. Suren 24

Resolution (%)M.Sc DissertationUsing the values shown in Table 4.4 the graph of energy resolution versus gammaray energy was plotted, as shown in Fig. 4.7.11.509.50Resolution% (FWHM)Resolution% (76.3/root(E))7.505.503.501.5050.00 250.00 450.00 650.00 850.00 1050.00 1250.00 1450.00Energy (keV)Figure 4.7 Energy resolutions as function of photon energyFigure 4.7 shows the energy resolution as function of photon energy between121.78 keV and 1407.92 keV. The energy resolution of 3.70 ± 0.15 % (FWHM) for 662keV gamma rays were calculated with the size of 44.450.8mmLaCl 3 :Ce(10%)scintillator detector coupled to an R6231 PMT at room temperature. Which is excellentfor scintillator based systems and it has been never achieved with established inorganicscintillator [11]. It should be noted the energy resolution obtained the size of 44.450.8mmLaCl 3 :Ce(10%) crystal approaches the energy resolution of roomtemperature semiconductor detectors such as CdTe and CdZnTe of similar size. Figure4.7 shows the energy resolution faithfully follows the statistical value of constant timesone over square root of energy [5]. That means the energy resolution of LaCl 3 :Ce(10%)is approximately inversely proportional to the square root of the energy [8].And also the energy resolution was characterized by LaCl 3 :Ce(10%) with the sizeof 44.450.8mmcrystal using other gamma ray energies such as 121.78 keV( 152 Eu), 511 keV ( 22 Na), and 1407.92 keV ( 152 Eu) and have found its energy resolutionto be 11.26 ± 0.82% (FWHM), 4.18 ± 0.20 % (FWHM) and 2.70 ± 0.07 % (FWHM),respectively, at room temperature. From the Fig. 4.7 it can be deduced that the energyresolution of LaCl 3 :Ce(10%) with the size of 44.450.8mmcrystal is poorer at lowK. Suren 25

M.Sc Dissertationenergies (approximately below 200 keV). This could be due to the fact thatLaCl 3 :Ce(10%) crystal has a significantly low light output approximately below 200keV. That means at low energies, the contribution of the intrinsic resolution is larger [8].4.5 Detection EfficiencyThe absolute efficiency ( ABS) of the detector can be calculated using Eq. 2.4, andare dependent not only on detector properties but also on the details of the countinggeometry (distance. between the source and detector). But in the case of intrinsicefficiency ( int) no longer includes the solid angle sustained by the detector as animplicit factor. These two efficiencies are simply related for isotropic sourcesby 4int ABS, where, is the solid angle of the detector seen from the actualsource position [1].The distance between the source and detector is 5.0 cm, and this was kept for allsources, and the diameter of the LaCl 3 :Ce detector is 51 mm. Table 4.5 shows theAbsolute total efficiency ABSand the Intrinsic efficiency INTcalculated for LaCl 3 :Cedetector.Table 4.5 Detection efficiency for LaCl 3 :Ce detectorSourceActivityD(s)BqI E ) N( N CtcpsC tABSN%100 100N137 Cs 259845 0.85 220868.25 12055.47 5092 2.31 42.24INTC t%60 Co 39928 2.00 79855.60 4358.69 1510 1.89 34.6422 Na 20045 2.80 56126.00 3063.48 366 0.98 17.93152 Eu 152911 1.24 189609.64 10349.31 5016 1.77 32.36The intrinsic photopeak efficiency was calculated using Eq. 2.8. The net countsunder the each peak are measured automatically by using maestro for windowssoftware.K. Suren 26

Peak efficiency (%)(%)M.Sc DissertationTable 4.6 Measured photopeak efficiency for LaCl 3 :Ce detector at various – rayenergiesPhoto peakefficiencySourceEnergy(keV)Activity(Bq)I( E )NN PhotopeakC P(cps)%152 Eu 121.78 152911 0.28 42815.08 2336.94 525 22.46 0.03152 Eu 244.70 152911 0.07 10703.77 584.24 84 14.38 0.07152 Eu 344.27 152911 0.27 41285.97 2253.48 247 10.94 0.0422 Na 511.00 20045 1.80 36081.00 1969.38 73 3.72 0.02137 Cs 662.00 259845 0.85 220868.25 12055.47 1378 11.43 0.01152 Eu 778.96 152911 0.13 19878.43 1085.01 123 11.38 0.05152 Eu 964.00 152911 0.15 22936.65 1251.93 86 6.90 0.04152 Eu 1112.05 152911 0.13 19878.43 1085.01 84 7.76 0.0360 Co 1173.24 39928 1.00 39927.80 2179.35 134 6.17 0.0322 Na 1274.50 20045 1.00 20045.00 1094.10 13 1.17 0.0260 Co 1332.50 39928 1.00 39927.80 2179.35 119 5.48 0.02152 Eu 1407.92 152911 0.21 32111.31 1752.71 59 3.36 0.02pError±%The full energy photopeak efficiency expresses the ability of the detector tomeasure photons at specific energies. From Fig 4.8 it was found that, as expected, itdecreases with the energy of the photons at specific energies. This result was expectedas the cross section of the photoelectric effect decrease with the energy of photons.30.0025.0020.0015.0010.005.000.00100.00 300.00 500.00 700.00 900.00 1100.00 1300.00 1500.00Photo peak energy (keV)Figure 4.8 Photopeak efficiencies as a function of peak energy.K. Suren 27

Photo-fraction %M.Sc Dissertation4.6 Photo-fractionThe photo-fraction was calculated using Eq. 2.10. The number of photonsdepositing their total energy into the detector is the number of events under thephotopeak after removing the background. This data is measured automatically by theMCA‟s software. The Table 4.7 give the photo-fraction ratio for LaCl 3 :Ce detector.Table 4.7 Measured photo-fraction of LaCl 3 :Ce detector at various – ray energiesSourceEnergy(keV)Photopeak countTotal countPhoto-fraction%Error±%152 Eu 121.78 314866 3009597 10.46 0.03152 Eu 244.70 50391 3009597 1.67 0.01152 Eu 344.27 147908 3009597 4.91 0.0322 Na 511.00 43988 219570 20.03 0.10137 Cs 661.67 826893 3055378 27.06 0.04152 Eu 778.96 74082 3009597 2.46 0.02152 Eu 964.00 51809 3009597 1.72 0.01152 Eu 1112.05 50494 3009597 1.68 0.0160 Co 1173.24 80628 905834 8.90 0.0422 Na 1274.50 7666 219570 3.49 0.0460 Co 1332.50 71604 905834 7.90 0.04152 Eu 1407.92 35347 3009597 1.17 0.01Using the values shown in Table 4.7 the graph of Photo-faction versus gamma rayenergy was plotted, as shown in Fig 4.9.25.0020.0015.0010.005.000.000.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1400.00 1600.00Energy (keV)Figure 4.9 Photo-fraction as a function of peak energyK. Suren 28

Number of countsM.Sc Dissertation4.7 Internal RadioactivityNaturally occurring lanthanum (La) is composed of one stable ( 139 La) and oneradioactive ( 138 La) isotopes with half life of 1.06×10 11 years. 139 La is the most abundantisotope (99.91%) and 138 La is very rare isotope. 138La decays both by electron capture(EC) decay (66.7%) and beta decay (33.3%). The EC decay is to a 1436 keV excitedstate in 138 Ba, which de-excites through a single 1436 gamma transition. The lesspreventbeta branch has a Q value of 1044 keV and populates the 789 keV state in 138 Ce,which decays through a single gamma transition to the 138 Ce state [9].10000090000800007000060000Beta continuum1436 Gamma+32 keV X-ray5000040000789 Gamma+Beta continuum30000200001000000 200 400 600 800 1000 1200 1400 1600Figure 4.10 Self-counting background spectrum from the LaCl 3 :Ce detector.The values of peak indicate their original values Ref [5]. But these values areslightly different with our calibrated systems.One of the major disadvantages of the lanthanum halide scintillator is their internalradioactivity. The background (internal radioactivity) spectrum easily measured by selfcounting for long time period. Fig. 4.10 shows such a spectrum collected byLaCl 3 :Ce(10%) with the size ofEnergy (keV) 44.450.8mm, BrilLanCe B350 crystal, countedfor about 2 days (154110 sec) in a very well shielded chamber (led castle). The energyaxis of the Fig. 4.10 shows the calibrated systems energy scale. Because of that the peakenergy values are shifted by some values, but the shape of the spectrum is similar to thestandard background spectrum of LaCl 3 :Ce crystal. For this period the total number ofnet counts per second/cm 3 was calculated, which is equal to 1.17 cps/cm 3 .K. Suren 29

M.Sc DissertationFigure 4.10 shows the self counting spectrum of LaCl 3 :Ce(10%) with the size of 44.450.8mmBrilLanCe B350 crystal. From left to right, first we can see a betacontinuum at low energies for 138 La decays to 138 Ce in which the 789 keV gamma hasescaped the detector altogether. This beta only spectrum continues to its end point of255 keV. From about 255 to 750 keV line is displays the Compton continua from the789 keV and 1436 keV gamma rays. The 789 keV line is continuum from the beta withthe coincident 789 keV gamma escaping the detector. Finally, the 1436 keV gamma, butdisplaced to a higher energy by approximately 37 keV to 1473 keV due to coincidentcapture of X-rays resulting when the Ba K level fills following K electron capture.Similarly, the hump near 1441 keV on the low energy side of the 1473 keV line is due tothe 1436 keV gamma plus 5 keV due to coincident capture of X-rays when the Ba Llevel fills following L electron capture. There is strong Ba K X-rays from 31-38 keV,but they are not seen due to the discriminator level setting of the MCA. The sum line at1473 keV might be used as a calibration peak [5].4.8 Time resolutionTime resolution of LaCl 3 :Ce(10%) with the size of 44.450.8mm, BrilLanCeB350 crystal was measured. Data was first recorded with two BaF 2 scintillator, one inthe start channel and the other one in the stop channel. In order to calculate timeresolution (FWHM) in ps, the system was calibrated using different delay time constant.Fig. 4.11 shows the MCA calibration curve of the spectrum. The slope of the curvegives the calibration constant per channel. For this time the full range of MCA wasselected as 50 ns.K. Suren 30

Delay time (ps)Number of countM.Sc Dissertation40000y = 6.2101x + 759.5635000300002500020000150002400 2900 3400 3900 4400 4900 5400 5900 6400channel numberFigure 4.11 Time calibration graph of counting systemFrom the time calibration shows Fig. 4.11 the relation between channel and timeis linear (each channel has the same width of time in ps) and the slope of the linear is6 .2101 ps channel . Fig. 4.12 shows the counting spectrum of the BaF 2 scintillator.From the Fig. 15 the coinciding timing resolution of BaF 2 scintillator was measured tobe 384.3 ps (FWHM)30252015105059 59.2 59.4 59.6 59.8 60 60.2 60.4 60.6 60.8 61 61.2 61.4 61.6 61.8 62Time (ns)Figure 4.12 Coincidence timing resolution result for two BaF 2 -PMT detectors,one in start channel and one in stop channelK. Suren 31

M.Sc DissertationChapter 5ConclusionsIn this project aim to investigate the characterisation of new scintillatorLaCl 3 :Ce(10%) with the size of 44.450.8mmBrilLanCe B350 detector for gammarayspectroscopy. The characterisation involved recording spectrum, calibration(linearity), measurement of energy resolution, detection efficiency, self counting andtiming properties. The calibration of systems showed a linear dependence of theincident photon and the MCA channels. LaCl 3 :Ce(10%) BrilLanCe B350 detector hasexcellent energy resolution, especially above 200 keV. The energy resolution ofLaCl 3 :Ce(10%) with the size of 44.450.8mm, was measured for the 662 keV peakis 3.70 ± 0.15 % (FWHM) at room temperature. This is very good agreement withmanufactured values [5]. Unfortunately, the lanthanum halide crystal has fewdrawbacks of their internal radioactivity and worst energy resolution for low energies(below 200 keV). But these drawbacks are likely to be serious only for a specificapplication such as long time measurement, low energy and low activity measurements.Time resolution of LaCl 3 :Ce(10%) was measured as 876.0 ps.K. Suren 33

M.Sc DissertationChapter 6References[1] G. Knoll, Radiation Detection and Measurement, 3 rd ed., John Wiley and Sons,2000[2] Alain Iltis, M.R. Mayhugh, P. Menge, C.M. Rozsa, O. Selles, V. Solovyev,Lanthanum halide scintillator: properties and application, Nuclear Instrumentsand Methods in Physics Research A 563 (2006) 359-363[3] K. Alzimami, E. Abuelhia, Z. Podolyak, A. Ionnou, N. M Spyrou,Characterization of LaBr 3 :Ce and LaCl 3 :Ce scintillator for gamma-rayspectroscopy, Journal of Radioanalytical and Nuclear Chemistry, Vol. 278, No.3(2008) 755-759[4] Lee Chow, Stephen Lukacs and Kent Hopkins ‘Speed of light’ measurement usingBaF 2 scintillator detectors, Eur. J. Phy 15 (1994) 49-52[5] C. M. Rozsa, Peter R. Menge, and M. R. Mayhugh, BrilLanCe TM Scintillator(Performance Summary), Scintillation Products Technical Note, Saint- Gobaindetector, January, 2009[6] Vladimir Solovyev, Performance of Sodium Iodide, BrilLanCe TM B350 andBrilLanCe TM B380 for High Count Rate Applications, Technical Information NoteDocument #519[7] Dr. Patrick Regan, REP 2 Gamma-Ray Spectroscopy, Laboratory scripts,University of Surrey, Sep. 2008[8] Marcin Balcerzyk, Marek Moszynski, Maciej Kapusta, Comparison of LaCl 3 :Ceand NaI(TI) scintillators in γ-ray spectrometry, Nuclear Instruments and Methodsin Physics Research A 537 (2005) 50-56[9] J. K. Hartwell, R. J. Gehrke, Observations on the background spectra of fourLaCl 3 (Ce) scintillators detectors, Applied Radiation and Isotopes 63 (2005) 223-228K. Suren 34

M.Sc Dissertation[10] Alan Owens, A.J.J. Bos, S. Brandenburg, C. Dathy, P. Dorenbos, S. Kraft, R.W.Ostendorf, V. Ouespenski, F. Quarati, γ-ray performance of a 1242 cm3 LaCl 3 :Cescintillation spectrometer, Nuclear Instruments and Methods in Physics ResearchA 574 (2007) 110-114[11] E. Abuelhia, K. Alzimami, M. Alkhorayef, Z. Podolyak, N. M. Spyrou,Measurement of coincidence timing resolution of scintillation detectors comparedto semiconductor detectors to image three-photon positron annihilation, Journalof Radioanalytical and Nuclear Chemistry, Vol. 278, No.3 (2008) 767-771[12] K. S. Shah, J. Glodo, M. Klugerman, L. Cirignano, W.W. Moses, S. E. Derenzo,and M.J. Weber LaCl 3 :Ce scintillator for Gamma ray Detection, Accepted byNuclear Instrument and methods,http://breast.lbl.gov/~wwwinstr/publications/Papers/LBNL-51369.pdf[13] Woon-Seng Choong, Stephen E. Derenzo, William W. Moses, Evaluation ofproduction samples of the scintillator LaBr 3 :Ce and LaCl 3 :Cehttp://www.escholarship.org/uc/item/2g77x1kh?display=all#page-1[14] http://sales.hamamatsu.com/en/products/electron-tube-division/detectors/photomultiplier- tubes/part-r6231-01.php[15] Dr. Jim Lochner, Scintillation as Gamma-ray Detectors, NASA GODDARDSPACE FLIGHT CENTER,http://imagine.gsfc.nasa.gov/docs/science/how_l2/gamma_scintillators.html[updated 27 sep 2008, cited 2 Aug 2010][16] C. M Rozsa, and M. R. Mayhugh, BrilLanCe TM 380 and BrilLanCe TM 350 Crystaldata sheet. Saint-Gobain 2006 [cited 15 Aug 2010]K. Suren 35

M.Sc DissertationAppendix AThe present activity of used sourcesAt the present project the experiment were held in the period between mid of June andmid of August 2010. The activity of the known sources wasn‟t considerably changed,for better accuracy on the experiment the activity was calculated each day. Table A.1shows the energies of the gamma photons, along the decay probability are illustrated.Table A.1 Present activity of used sources and photons energySourceIsotopeEnergykeVProbability %Activity (kBq)14/06/10 21/06/10 28/06/10 5/07/10 12/07/10 19/07/10S175.PH137 Cs 661.67 85.10 259.022 258.908 258.794 258.680 258.566 258.452S317.PH60 Co1173.24 99.851332.50 99.9838.220 37.540 36.872 36.216 35.571 34.938S311.PH22 Na511.00 180.761274.53 99.9419.754 19.654 19.554 19.454 19.355 19.256121.78 35.67244.70 7.61344.27 29.00S259.PH152 Eu778.96 12.96152.482 152.332 152.182 152.033 151.883 151.734964.00 14.651112.05 13.691407.92 21.07K. Suren 36

M.Sc DissertationAppendix BDetectors and photomultipliersFigure B.1 Dimensions of the LaCl 3 :Ce(10%) (BrilLanCe B 350) detectorFigure B.2 Dimensions of the Hamamatsu R6231 photomultiplier tube [14]K. Suren 37

M.Sc DissertationFigure B.3 Typical spectral response of the Hamamatsu R6231 photomultipliertube [14]Table B.1 Key Specifications of the Hamamatsu R6231 photomultiplier tube [14]Part Number R6231-01TypeSizeMinimum Maximum Peak Sens.GainRise TimeTransit TimeTransit Time SpreadNumber of Dynodes 8Applied voltageNotesHead on51 mm300 nm650 nm420 nm2.7E+055 ns48 ns11.6 ns+1000 VFor gamma camera andscintillation countingK. Suren 38

M.Sc DissertationAppendix CDecay chain & background spectrum of 138 LaFigure C.1 An Energy level diagram showing the decay branches of the metstable state 138 La [5].Figure C.2 Self-counting background spectrum for a BrilLanCe 380 detector[5].K. Suren 39

No of CountsNumber of countsM.Sc DissertationAppendix DSpectrum collected with LaCl 3 :Ce detector120000100000800006000040000V = 860 VoltsV = 880 VoltsV = 900 VoltsV = 920 VoltsV = 940 VoltsV = 960 VoltsV = 980 VoltsV = 1000 VoltsV = 1020 VoltsV = 1040 VoltsV = 1060 VoltsV = 1080 VoltsV = 1100 VoltsV = 1120 VoltsV = 1140 VoltsV = 1160 VoltsV = 1180 VoltsV = 1200 Volts2000000 50 100 150 200 250 300Channel numberFigure D.1 The spectrum of 137 Cs source with different supply voltage to theLaCl 3 :Ce detector40000035000010.0 us3000002500006.0 us2000003.0 us1500002.0 us100000500001.0 us0.5 us00 50 100 150 200Channel NumberFigure D.2 The spectrum of 137 Cs source with different shaping time at 950 Vsupply voltage to the LaCl 3 :Ce detectorK. Suren 40

No of CountsNumber of counts1274.5 keV1436 keVInternal radio activityM.Sc Dissertation3000025000200000.5us1.0us2.0us3.0us6.0us10.0us1500010000500000 50 100 150 200 250 300 350Channel NumberFigure D.3 The spectrum of 60 Co source with different shaping time at 950 Vsupply voltage to the LaCl 3 :Ce detector12000100008000511 keV60004000200000 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600Energy (keV)Figure D.4 The spectrum of 22 Na source collected by LaCl 3 :Ce detectorK. Suren 41