W. Klamra

Properties of the YAG:Ce scintillator

Abstract Light yield, light pulse shape due to γ-rays and α-particles, energy resolution and time resolution of the new YAG:Ce scintillator were studied using a light readout by means of the XP2020Q photomultiplier and the S3590-03 photodiode. The light yield of 20 300 ± 2000 photons/MeV was determined using three independent methods. The light pulse produced by γ-rays consists of two components with the decay time constants of 87.9 ns and 302 ns respectively. The light pulse measured for α-particles exhibits a faster and less intense fast component with the decay time constant of 68.4 ns. The energy resolution obtained was 11.1% and 11.7% for the 662 keV γ-rays from a 137 Cs source as measured with the photomultiplier and the photodiode readout, respectively. A time resolution of 1.3 ns was observed for 60 Co γ-rays (at 100 keV threshold) with the crystal coupled to the XP2020Q photomultiplier. The YAG:Ce scintillator with the peak emission at 550 nm is a good candidate to replace CsI(T1) and BGO scintillators in detection of light charged particles when photodiode readout is of importance. The observed difference in the light pulse shape due to γ-rays and α-particles suggests good performance of the crystal in the pulse shape discrimination method for the particle identification.

Blue enhanced large area avalanche photodiodes in scintillation detection with LSO, YAP and LuAP crystals

Scintillation detectors consisting of LSO, LuAP and YAP crystals fitted to bevelled-edge large area avalanche photodiodes of 10 mm in diameter characterised by a high quantum efficiency up to 68% at 350 nm wavelength were studied. Among the properties measured were the number of electron-hole pairs, energy resolution and noise contribution of the LAAPDs at shaping time constants down to 20 ns at different gains. High electron-hole pair numbers of 11000/spl plusmn/550 e-h/MeV and 19500/spl plusmn/980 e-h/MeV for the YAP and LSO crystals were measured, respectively. The energy resolution for /sup 137/Cs /spl gamma/-rays of 5.9% in FWHM for the YAP crystal, much better than that of 9.9% for the LSO crystal were measured at 0.5 /spl mu/s shaping time constant and the APD gain of 40. The same study done with a fast shaping of 20 ns and the APD gain of 160 showed the energy resolution of 6.7%.

Properties of the YAP : Ce scintillator

Abstract Light yield, light pulse shape due to γ-rays and α-particles, energy and time resolutions for a 10 × 10 × 5 mm 3 YAB crystal coupled to the XP2020Q photomultiplier were studied. The measured light output of 17000 ± 850 photons/MeV includes a correction for the calibrated quantum efficiency of the XP2020Q. The fast component of the light pulse with the decay time constant of 26.7 ± 0.12 ns also shows a finite rise time described approximately by the time constant of 380 ± 45 ps. The YAP crystal which was studied exhibited an energy resolution of 5.7% for 662 keV γ-rays fron a 137 Cs source. This very good energy resolution is due to a low intrinsic energy resolution of 3.4%. These characteristics, together with a good time resolution for 60 Co γ-rays of 160 ps measured at the threshold of 1 MeV, suggest a broad range of applications for the YAP scintillator.

Energy resolution of scintillation detectors readout with large area avalanche photodiodes and photomultipliers

The energy resolution of small NaI(Tl), CsI(Tl), BGO, GSO, YAP and LSO crystals has been studied using 16 mm diameter large area avalanche photodiodes (LAAPD) and a 52 mm diameter photomultiplier. The best result of 4.8% for 662 keV /spl gamma/-rays from a /sup 137/Cs source was obtained with a 9 mm in diameter by 9 mm high CsI(Tl) scintillator coupled to an LAAPD. Measuring the number of primary electron-hole pairs produced in the LAAPD and photoelectrons in the photomultiplier, as well as the noise contribution of the LAAPD, allowed a quantitative discussion of the results. The energy resolutions measured with LAAPDs are comparable to, or significantly better (at certain emission wavelengths) than, those obtained with the photomultiplier. At energies above 100 keV the energy resolution measured with the majority of crystals and the LAAPD was weakly affected by the photodiode noise contribution. The advantages and limitations of LAAPDs in energy spectrometry with scintillation detectors are also discussed.

Low energy /spl gamma/-rays scintillation detection with large area avalanche photodiodes

The energy resolution of NaI:Tl, CsI:Tl, LSO and YAP crystals coupled to 16 mm diameter large area avalanche photodiodes (LAAPD) was studied for low energy /spl gamma/-rays. Energy resolutions of 11.3% and 8.4% were obtained for 59.6 keV /spl gamma/-rays from /sup 241/Am and 122 keV /spl gamma/-rays from /sup 57/Co sources, respectively, as measured with a 10 mm diameter by 10 mm high NaI:Tl crystal. The optimization of the LAAPD performance is presented, being essential for improvement of energy resolution at low energy /spl gamma/-rays. Measured numbers of primary electron-hole pairs produced in LAAPDs and evaluation of the noise contribution of these devices allowed for quantitative discussion of the results. Particularly, the intrinsic energy resolution of the crystals vs. the energy of /spl gamma/-rays has been evaluated. Obtained data for a NaI:Tl crystal showed a good agreement (within 30%) with the calculated component due to nonproportional light yield for energies above 50 keV.

Comparison of n-γ discrimination by zero-crossing and digital charge comparison methods

Abstract A comparative study of the n-γ discrimination done by the digital charge comparison and zero-crossing methods was carried out for a 130 mm in diameter and 130 mm high BC501A liquid scintillator coupled to a 130 mm diameter XP4512B photomultiplier. The high quality of the tested detector was reflected in a photoelectron yield of 2300 ± 100 phe/MeV and excellent n-γ discrimination properties with energy discrimination thresholds corresponding to very low neutron (or electron) energies. The superiority of the Z C method was demonstrated for the n-γ discrimination method alone, as well as, for the simultaneous separation by the pulse shape discrimination and the time-of-flight methods down to about 30 keV recoil electron energy. The digital charge comparison method fails for a large dynamic range of energy and its separation is weakly improved by time-of-flight method for low energies.

Advantages and limitations of LSO scintillator in nuclear physics experiments

Light yield, light pulse shape due to /spl gamma/-rays and /spl alpha/-particles, energy and time resolutions for three different samples of the LSO scintillator were studied using an XP2020Q photomultiplier and an S3590-03 photodiode. Light yields of 4200/spl plusmn/200 phe/MeV and 18500/spl plusmn/900 e-h pair/MeV were measured for the PM tube and the photodiode, respectively. The light pulse shape exhibits a pure exponential decay with a time constant of 47.2/spl plusmn/1.3 ns for both /spl gamma/-rays and /spl alpha/-particles. Energy resolutions of 10% and 14.6% for the 662 keV /spl gamma/-rays from a /sup 137/Cs source were obtained for the photomultiplier and the photodiode readout, respectively. A time resolution of 180 ns was observed for /sup 60/Co /spl gamma/-rays at 1 MeV threshold and 400 ps for 100 keV threshold. The study confirmed a number of advantages of the LSO scintillator for nuclear physics experiments, however, for small size samples. For larger volumes the natural radioactivity of the LSO, about 300 counts/s/cm/sup 3/, may limit possible applications. The high number of e-h pairs produced in the photodiodes makes LSO very attractive for small compact scintillation probes. >

The EUROBALL neutron wall - design and performance tests of neutron detectors

The mechanical design of the EUROBALL neutron wall and neutron detectors, and their performance measured with a Cm-246,Cm-248 fission source are described. The array consists of 15 pseudohexaconical detector units subdivided into three, 149 mm high, hermetically separated segments and a smaller central pentagonal unit subdivided into five segments. The detectors are filled with Bicron BC501A liquid scintillator. Each section of the hexaconical detectors is viewed by a 130 mm diameter Philips XP4512PA photomultiplier while the sections of pentagonal detectors are viewed by Philips XP4312B PMTs. The tests of n-gamma discrimination performed by zero-crossing and time-of-flight methods show a full separation of gamma- and neutron events down to 50 keV recoil electron energy. These tests demonstrate the excellent timing properties of the detectors and an average time resolution of 1.56 ns. The factors determining the efficiency of neutron detectors are discussed. The total efficiency for the full array for a symmetric fusion-evaporation reaction is predicted to be 0.30

Light output and energy resolution of CsI, YAG, GSO, BGO and LSO scintillators for light ions

The light output and energy resolution for the scintillators CsI(Tl), YAG(Ce), GSO(Ce), BGO and LSO(Ce) have been measured with 1H, 2H and 3He ions in the energy region ∼ 3–20 MeV/nucleon using photodiodes for the light readout. A very good energy resolution of ∼ 0.62% for 45 MeV 3He-particles has been obtained for CsI. The YAG(Ce), GSO(Ce) and LSO(Ce) crystals are non-hygroscopic, have fast decay time as main component and are well suited for experiments with high counting rates and strict timing requirements. The LSO crystal gives the best energy resolution, but reveals strong quenching for heavy ions. The GSO crystal is a good candidate for operation in UHV environment and has high stopping power, short decay time (56 ns) and moderate quenching.

Investigation of some scintillation properties of YAG:Ce crystals

Abstract A light output expressed in the photoelectron (phe) number, a relative light yield for α-particles and light pulse shapes for γ-rays and α-particles excitation of the YAG:Ce crystals with different Ce doping between 0.012 and 1.08 mol% were studied. The highest light output of 1420 ± 70 phe/MeV was measured for the sample doped with 0.21 ± 0.03 mol% Ce, while the fastest pulse was observed for the sample doped with 1.08 ± 0.08 mol% Ce showing, however, lower light yield by 10%. The relative light yield for α-particles of 0.21 ± 0.03 as compared to γ-rays was approximately the same for all the samples studied. In conclusion, the YAG:Ce crystal doped with about 1 mol% of Ce is the most appropriate for different applications. For this crystal the α-γ discrimination by digital charge comparison method was studied. A clear separation was observed with the YAG crystal coupled to the XP2020Q photomultiplier for 5.49 MeV α-particles from 241 Am source and 6.04 MeV as well as 8.77 MeV from ThC source. However, this separation was inferior compared to that known for CsI(Tl).