J.T.M. de Haas

Advances in Yield Calibration of Scintillators

By means of a photomultiplier tube, a Si-photodiode, and a Si-avalanche photodiode, the absolute scintillation yield of recently developed LaBr₃:Ce, LaCl₃:Ce, and (Lu,Y)₂SiO₅:Ce scintillators and traditional Lu₂SiO₅:Ce, Bi₄Ge₃O₁₂, NaI:Tl, CsI:Tl, and CsI:Na scintillators were determined. These are all well known scintillators that cover emission wavelengths from 250 nm to 750 nm. By comparing the scintillation yield independently measured with the three different photon detectors reliable yield values are obtained.

Scintillation properties of Lu2Si2O7:Ce3+, a fast and efficient scintillator crystal

Cerium doped lutetium pyrosilicate Lu2Si2O7:Ce3+ (LPS), a new inorganic scintillator, displays particularly promising performance. This material can be readily pulled from the melt. A high light output (average value: 26 300 ph MeV−1), a relatively good energy resolution (9%) and a fast decay time (38 ns) without afterglow make this new scintillator very attractive, in particular for medical imaging. Optical characterizations and scintillation properties of LPS:Ce large single crystals are presented, including timing properties and study of the scintillation yields as a function of incident energy.

High efficiency of lutetium silicate scintillators, Ce-doped LPS, and LYSO crystals

We have introduced a new scintillator: cerium doped lutetium pyrosilicate Lu/sub 2/Si/sub 2/O/sub 7/ (Ce: LPS). A high light output (average value: 26,300 ph/MeV), a relatively good energy resolution (10%) and a fast decay time (38 ns) without afterglow make this new scintillator very attractive. We compare its properties to those of another recently developed cerium doped lutetium based silicate, Ce: Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO).

Gamma ray spectroscopy with a O19/spl times/19 mm/sup 3/ LaBr/sub 3/:0.5% Ce/sup 3+/ scintillator

Pulse height spectra of various sources covering X-ray and gamma ray energies from 10 keV to 6.1 MeV were measured by the first large O19/spl times/19 mm/sup 3/ LaBr/sub 3/:0.5% Ce/sup 3+/ scintillator. The spectra are compared with that recorded with a same sized NaI:Tl/sup +/ scintillator. Excellent energy resolution pulse height spectra are obtained showing that the scaling up from a small (/spl ap/3/spl times/3/spl times/10 mm/sup 3/) sized LaBr/sub 3/:Ce/sup 3+/ scintillator studied initially up to an /spl ap/6 cm/sup 3/ scintillator does not lead to much deterioration of resolution and light output. Special attention is devoted to the nonproportionality in the response of LaBr/sub 3/:Ce/sup 3+/ and related energy resolution. At high energy LaBr/sub 3/:Ce/sup 3+/ is far superior above NaI:Tl/sup +/ in terms of energy resolution and scintillation speed. At energies below 100 keV, NaI:Tl/sup +/ shows a better energy resolution.

Scintillation Properties of Praseodymium Activated

Scintillation properties of LuAG:Pr grown by Furukawa Co. Ltd., Japan, have been studied. The best crystals display light outputs up to 19000 ph/MeV and an energy resolution of 4.6% at 662 keV. The scintillation yield is found to be a function of size and temperature of the sample; it can be enhanced by 40% upon heating to 450 K. Radioluminescence spectra show both d- f and f-f transitions of Pr3+ ions; the contribution of the latter increases with temperature. The scintillation decays are complex, with a fast decay constant of 20 ns. The presence of 176Lu induces high background activity.

{\rm Lu}_{3}{\rm Al}_{5}{\rm O} _{12}

The absolute light yield of cerium doped lutetium oxyorthosilicate Lu/sub 2/SiO/sub 5/:Ce/sup 3+/ (LSO:Ce) scintillation crystals is presented. From 60 keV to above 1 MeV the light output increases linearly with the gamma-ray energy and is about 67% of that of NaI(Tl/sup +/). However, a nonlinear response is observed for X-ray energies between 5 and 60 keV. For comparison, we also studied the light yield of a Gd/sub 2/SiO/sub 5/:Ce/sup 3+/ crystal and a CsI:Tl crystal as a function of excitation energy. >

Single Crystals

The scintillation properties of RbGd/sub 2/Br/sub 7/ crystals, doped with Ce/sup 3+/ concentrations of 0.02, 0.11, 0.88, 2.05, 4.1, and 9.8%, are studied under X-ray and /spl gamma/-quanta excitations. For the RbGd/sub 2/Br/sub 7/ sample doped with 9.8% Ce, the authors measured a light yield of 56000/spl plusmn/6000 photons per MeV of absorbed /spl gamma/-ray energy with a main decay time of 43/spl plusmn/1 ns, using a Hamamatsu R1791 photomultiplier (PMT), a /sup 137/Cs radioactive source, and a shaping time of 10 /spl mu/s. A time resolution of 790/spl plusmn/10 ps was measured for the RbGd/sub 2/Br/sub 7/:9.8% Ce compound, using BaF/sub 2/ as second scintillator, two XP2020Q PMTs, a /sup 22/Na source, and an energy threshold set at E/spl ges/511 keV. With the R1791 PMT, an energy resolution of 4.1% (FWHM over peak position) for the 662-keV full absorption peak has been observed for two crystals of 7/spl times/4/spl times/2 mm/sup 3/ and 15/spl times/5/spl times/1 mm/sup 3/ with 4.1 and 9.8% Ce content, respectively. Moreover, the nonproportional responses of three RbGd/sub 2/Br/sub 7/:Ce compounds with different concentrations (0.11, 2.05, and 9.8%) were studied revealing an almost-constant light output response from 17.4 keV to 1 MeV. These properties are compared to three other well-known scintillators: NaI:Tl, CsI:Tl, and Lu/sub 2/SiO/sub 5/:Ce.

Non-linear Response In The Scintillation Yield Of Lu/sub 2/ SiO/sub 5/ O:Ce/sup 3+/

Abstract We report on the scintillation properties of a LiBaF3 crystal when irradiated with thermal neutrons or gamma rays. The scintillator exhibits cross luminescence and self-trapped-exciton luminescence. The former does not show up under thermal neutron irradiation, whereas both give a response under gamma irradiation. This offers a unique opportunity for thermal neutron-gamma discrimination. The effectiveness of the method is demonstrated.

Scintillation properties of RbGd/sub 2/Br/sub 7/:Ce. Advantages and limitations

The scintillation properties of pure SrI2 and SrI2 doped with 0.5%, 0.86%, 2%, and 5% europium were studied. Different techniques were used to measure γ-ray excited pulse-height and scintillation decay time spectra, and to perform X-ray excited and optically excited emission spectroscopy. Eu2+ emission and trapped exciton (TE) emission was observed in SrI2:Eu2+ samples. These emissions were studied as a function of temperature, Eu concentration, and sample size. A spectral overlap was observed between Eu2+ excitation and emission spectra, the amount of overlap depends on temperature. The light yield, energy resolution and luminescence decay profiles reveal also a dependence on temperature, sample size, and Eu concentration. The observations were analyzed and interpreted in terms of two separate models. One model consists of the relation between TE and Eu2+ emission and the other deals with self absorption processes.

LiBaF3, a thermal neutron scintillator with optimal n-γ discrimination☆

The optical properties of SrAlF5:Pr3 + are studied. Emission measurements up to 1200 nm under blue-light excitation in the3P2 level reveal a large number of emissions all originating from the3P0 level and the1D2 level. Under vacuum ultraviolet excitation in the 4f15d1 bands, emission from the1S0 level, followed by emission from the3P0 level and the1D2 level takes place. This is known as the photon cascade emission process. The excitation spectrum of the1S0 emission was measured and was compared with the excitation spectrum of SrAlF5:Ce3 +. The spectrum for SrAlF5:Pr3 + compared to SrAlF5:Ce3 + is at about 12 240 cm−1 higher energy. A study of the x-ray-excited emission in the temperature region from 100 to 350 K was performed, determining the processes responsible for both1S0 and3P0/1D2 emissions.