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In the search for scintillators that have a faster response than existing ones, better knowledge on the processes that take place during the first 100 ps of the scintillation process is required. For that one needs detailed information on the intrinsic rise time of a scintillation pulse. However, the observed rise time, also of direct importance to the timing resolution, is strongly affected by the time spread of photons leaving the scintillator. In this work we pioneered the use of a 120 fs Ti-sapphire laser in combination with a streak camera system to measure those photon time spreads with time resolution up to 5 ps. With this setup the photon time spread distributions of scintillator crystals with different size and/or surface treatment were measured. The potential to study the effect of Teflon packaging on this distribution was also investigated.

Three different methods to determine accurately the intensity of weak light pulses measured with various photomultiplier tubes are presented. The methods rely on a precise determination of the response of the PMTs to the detection of a single photon. 10 kHz LED pulses attenuated to a level where on average μ = 0.02 to 30 photons are detected per pulse were used. For weak intensity light pulses with μ

The thermal neutron detection, X-ray detection, gamma detection and the optical properties of the chloride scintillator Li3YCl6:Ce are reported. Photo-luminescence (PL) and luminescence excitation spectra together with X-ray excited emission studies provide information on the scintillation and luminescence mechanism. Thermal neutron scintillation performance was investigated and compared with the performance of scintillators like Rb2LiYBr6:Ce and Cs2LiYCl6:Ce from the elpasolite family. The estimated absorption length for thermal neutrons (1.8 Å wavelength or 25 meV energy) is 0.8 mm in 95 % 6Li-enriched Li3YCl6:Ce.

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.

We investigated gamma- and neutron-scintillation properties of A2LiLnX6:Ce3+ (A=Cs, Rb, K, Na, Li; Ln=La, Y, Lu, Sc; X=Br, I) with the aim to develop new scintillators with high neutron detection efficiencies. Among the investigated thermal neutron scintillators, Rb2LiYBr6:Ce3+ shows an excellent neutron peak resolution of 3.6%. This is the best neutron peak resolution ever reported. Together with the large alpha/beta ratio of 0.74, Rb2LiYBr6:Ce3+ offers the possibility of excellent neutron/gamma discrimination. The highest thermal neutron scintillation light yield of 83,000 photons/neutron is also reported for Rb2LiYBr6:Ce3+.

Future planetary missions such as BepiColombo are resource limited in both mass and power. Due to the proximity of the spacecraft to the Sun, the instrumentation will encounter harsh environments as far as radiation levels and thermal loads are concerned. Only radiation hard detectors that need little or no cooling will be able to successfully operate after long cruise times and over the expected mission lifetimes. The next generation of lanthanum halide scintillators promises to provide sufficient resolution in the spectral range between I and 10 MeV where most of the elemental gamma-ray emission lines can be detected. In order to be suitable for planetary gamma-ray spectrometers with sufficient sensitivity it had to be proven that larger crystals of size 3" can be produced and that they maintain their resolution of similar to 3% at 662 keV. For that purpose we have produced and characterized several larger LaBr3 : Ce crystals and assessed their radiation hardness by exposing the crystals to radiation doses that are representative of the expected conditions in the space environment. Systematic measurements on several crystals allowed the determination of the activation potential and the performance verification from which the consequences for instrument flight performance can be derived. From these investigations we conclude that these scintillators are well suited for planetary missions, with excellent and stable performance.

Photoelectron yields and energy resolutions of bare and packed LaBr3:Ce crystals are determined as function of proton irradiation dose, cerium concentration and sample height from 1 mm to 2 inch. A simple model is employed to predict light yield for Oslash3" times 3" size crystals, and to assess the quality of packaging. The effect of proton exposure on scintillation yield and resolution of LaBr3: Ce is investigated. Intense proton irradiation does not deteriorate yield or resolution. It also does not affect thermoluminescence behavior.

The scintillation properties of the first large O 1/spl times/1 inch/sup 3/ LaBr/sub 3/:5%Ce/sup 3+/ scintillator were studied under /spl gamma/-ray excitation. This crystal is a LaBr/sub 3/:5%Ce/sup 3+/ standard product from Saint Gobain company. The sample was cut and polished by the manufacturer from a larger size crystal boule. It was then assembled in a cylindric aluminum case with a front glass window. The results are compared with those recorded with a 0.4/spl times/0.3/spl bsol/,/spl times/0.5 inch/sup 3/ unpacked crystal. The highest light yield of 21500/spl plusmn/2200 photoelectrons per MeV (60500/spl plusmn/6000 photons per MeV) of absorbed /spl gamma/-ray energy was measured for the unpacked crystal-compared to 16800/spl plusmn/1700 photoelectrons per MeV for the O1/spl times/1 inch/sup 3/ sample. At room temperature the scintillation decays with a decay time of 16/spl plusmn/1 ns. The 0.4/spl times/0.3/spl times/0.5 inch/sup 3/ unpacked crystal-coupled to photomultiplier tube (Hamamatsu R1791) and measured at 662 keV-exhibited an energy resolution of 2.8%, better than the one of the O1/spl times/1 inch/sup 3/ crystal (3.1%). Special attention was devoted to energy and temperature dependencies of scintillation properties: the results show a good proportionality for light output versus /spl gamma/-ray energy. The light output deviates from the linear response of 5% between 20 keV and 2 MeV. Furthermore temperature dependency of gamma-ray excited decay time (80-700 K) does not indicate the presence of thermal quenching from the cerium 5d state. These characteristics suggest a broad range of applications for the LaBr/sub 3/:5%Ce/sup 3+/ scintillator.

The absolute light yield of four different scintillation materials measured with two photomultiplier tubes and two avalanche photodiodes is presented. Commonly, the photoelectron yields and electron–hole pair yields are corrected for the quantum efficiency of the detector, as specified by the manufacturer, to obtain the absolute photon yield. However, the effective quantum efficiency under scintillation measurement conditions is substantially higher due to back reflection. Only when back reflection is properly accounted for, the absolute photon yields obtained with the photomultipliers agree with those obtained with the photodiodes. The effect of optical coupling between the scintillator and detector is also discussed.

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.

A gaseous scintillation detector consisting of a Ar+CF4 filled GEM and a CCD camera has been investigated for the application as a position sensitive dosimeter in proton-beam radiation therapy. The light yield has been measured as a function of the CF4 concentration, operating voltage, beam intensity and beam energy. In conditions where the gas gain decreases due to a lower electric field, an increase of the amount of light per secondary electron is observed. The mixture of Ar+5% CF4 has the largest light output in absolute sense as well as per secondary electron. The scintillating Gas Electron Multiplier emits >1.5 times more light than needed and the signal-quenching in the Bragg peak which occurs in solid scintillators is reduced by a factor 4.

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.

Some scintillating materials offer the possibility of measuring well separated α and γ scintillation response using a single crystal. Eventually aiming at thermal neutron detection using 6Li or 10B admixture, pulse shape discrimination measurements were made on three scintillators: CsI:Tl, CsI:Na and pure BaF2 crystals. A very good α/γ discrimination was obtained using 22Na, 241Am (γ) and 244Cm (α) radioactive sources.

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.

We report on the scintillation properties of a LiBaF3 crystal when irradiated with thermal neutrons or gamma rays. This 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 LuAlO3:Ce (LuAP) crystals were first reported by Lempicki et al. [1]. The interest in this material is derived from the high light yield (above 20 000 photons/MeV), high density (8.34 g/cmι3 ) and short decay time (about 18 ns). These properties result in one of the highest figures of merit of any known scintillator and put LuAP in the forefront when high counting rates, fast timing, good stopping power, and energy resolution are of importance [1, 2]. Taking into consideration that this material is not fully optimized yet, and there is evidence that its performance may be highly improved [3, 4], it becomes exceptionally desirable to understand the physics which governs its behavior.

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.

Nonproportional response of the scintillation yield of un-doped SrI2 and SrI2:5o/oEu was studied using highly monochromatic synchrotron irradiation ranging from 10.5 to 100 keV. Measurements were performed at 80 K and 295 K for SrI , and at 80 K, 295 K, 450 K, and 600 K for SrI2:5o/oEu. By making a dense data sampling around the iodine K-edge and using the recently developed K-dip spectroscopy method, the K-shell photoelectron response curves were reconstructed down to 500 eV. Proportionalities of X-ray response and K-shell photoelectron response of both crystals reveal temperature dependence. Energy resolution of the X-ray photopeak was analyzed as a function of temperature and deposited energy. Energy resolution improves with better proportionality.

Lanthanum bromide scintillation detectors produce very high light outputs (∼60,000 ph/MeV) within a very short decay time (typically ∼20 ns) which means that high instantaneous currents can be generated in the photocathode and dynode chain of the photomultiplier tube (PMT) used for the scintillation readout. The net result is that signal saturation can occur long before the recommended PMT biasing conditions can be reached. In search of an optimized light readout system for LaBr3, we have tested and compared two different PMT configurations for detection of gamma-rays up to 15 MeV. This range was chosen as being appropriate for gamma-ray remote sensing and medium energy nuclear physics applications. The experiments were conducted at two facilities: the Laboratori Nazionali del Sud (LNS) in Catania, Italy [1] and the High Intensity Gamma-ray Source (HIγS) at Triangle University Nuclear Laboratory, in Durham, North Carolina, USA [2] . The PMT configurations we have tested are (1) a standard dynode chain operated under-biased; (2) a 4-stage reduced chain operated at nominal inter-dynode bias. The results are that shortening the number of active stages, as in configuration (2), has advantages in preserving energy resolution and avoiding PMT saturation over a large energy range. However, the use of an under-biased PMT, configuration (1), can still be considered a satisfactory solution, at least in the case of PMTs manufactured by Photonis. The results of this study will be used in support of the Mercury Gamma-ray and Neutron Spectrometer (MGNS) on board of BepiColombo, the joint ESA/JAXA mission to Mercury, scheduled for launch in 2014.

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 Ce doped Cs/sub 2/LiYBr/sub 6/, Rb/sub 2/LiScBr/sub 6/, Rb/sub 2/LiYBr/sub 6/, Rb/sub 2/LiLaBr/sub 6/, Rb/sub 2/LiYI/sub 6/ elpasolite, and Li/sub 3/YBr/sub 6/ monoclinic inorganic thermal-neutron scintillator crystals were investigated. Light yields and decay times were studied. Cs/sub 2/LiYBr/sub 6/:Ce and Rb/sub 2/LiYBr/sub 6/:Ce show a high light yield of /spl ges/64,000 photons per thermal neutron. More details will be presented and advantages and disadvantages of these new scintillator materials will be discussed.

Results of thermoluminescence (TL) studies on LuAlO 3 : Ce, a new fast and efficient scintillator, are reported. The simple model of TL is used for the glow-curve analysis, leading to the trap depth values of 0.7 and 1.6 eV. The influence of the traps on the scintillation process is also discussed.

We report on the scintillation properties of LiBaF 3 upon irradiation with thermal neutrons. For thermal neutron excitation cross luminescence is not observed, contrary to luminescence under X-ray or γ-ray excitation.

Scintillation properties like photoelectron yield and light yield of Ce3+-doped YAlO3 and mixed Lux(RE)1−xAlO3 (RE=Y3+ and Gd3+) perovskite crystals are presented. The photoelectron yields increase almost linearly with γ-ray energy but a small non-linearity is observed around 40 keV. Scintillation and spectroscopic properties like UV or X-ray excited emission, laser excited emission, excitation and absorption spectra and photo- and scintillation decay of the different crystals are compared. The influence of intrinsic absorption and reflecting tape on the yields are discussed. Selected YAlO3:Ce showed the highest light yield of 25,000 phels/MeV and an energy resolution of 4.5% for 662 keV γ-radiation. The γ-ray linear absorption coefficient increases with Lu content and that of LuAlO3:Ce is almost 10 times higher than that of YAlO3:Ce.

Cerium doped lutetium pyrosilicate Lu/sub 2/Si/sub 2/O/sub 7/ (Ce: LPS) scintillator presents high light output (average value: 26,300 ph/MeV), a relatively good energy resolution (10%) and a fast decay time (38 ns) without afterglow. The luminescence efficiency remains very high when the temperature increases up to 450 K. It makes this new scintillator very attractive. We compare its properties to those of another recently developed cerium doped silicate, Ce: Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO).

Data is presented on the proportionality of the light yield of Lu/sub 2/SiO/sub 5/(Ce/sup 3+/), Gd/sub 2/SiO/sub 5/(Ce/sup 3+/), CdWO/sub 4/, BaF/sub 2/, YAlO/sub 3/(Ce/sup 3+/), and Lu/sub 3/Al/sub 5/O/sub 12/(Sc/sup 3+/) scintillation crystals as a function of X-ray and /spl gamma/-ray excitation energy in the energy range from 5 keV to beyond 1 MeV. >

The first results of a study on the properties of a gaseous scintillation detector based on a Gas Electron Multiplier (GEM) are reported. The detector is designed for use in position-sensitive dosimetry applications in radiation therapy. A double GEM system, operating in a 90 10% Ar-CO2 gas mixture at a gas amplification factor of similar to 3000, emits a sufficient amount of detectable light to perform measurements of similar to 1 Gy doses in two dimensions. The light yield does not suffer from quenching processes when particles with high stopping power are detected. This operation mode of GEMs offers the dosimetric advantages of a gas-filled detector and the 2D read-out can be performed with a CCD camera. Compared to the existing dosimeters, this system is relatively simple and no complex multi-electrode read-out is necessary. (C) 2002 Elsevier Science B.V. All rights reserved.

Commercially available LaBr3:5% Ce3+ scintillators show with photomultiplier tube readout about 2.7% energy resolution for the detection of 662 keV γ-rays. Here we will show that by co-doping LaBr3:Ce3+ with Sr2+ or Ca2+ the resolution is improved to 2.0%. Such an improvement is attributed to a strong reduction of the scintillation light losses that are due to radiationless recombination of free electrons and holes during the earliest stages (1–10 ps) inside the high free charge carrier density parts of the ionization track.

Scintillation and luminescence characteristics of Rb2LiYBr6 doped with 0.1%, 0.5%, 1%, and 5%?Ce3+ are presented. Under optical and x-ray excitation, Ce3+ doublet emission is observed at 385 and 420 nm. Rb2LiYBr6:0.5%?Ce3+ shows very high thermal neutron scintillation light output of 83?000 photons/neutron. An excellent neutron peak resolution of 3.6% (full width at half maximum over peak position) is observed for the 4.8 MeV neutron-reaction products energy response in Rb2LiYBr6:0.1%?Ce3+. This peak shows up at 3.6 MeV ?-equivalent energy and therefore it gives an ?/? ratio of 0.74. The combination of a large fraction of neutron absorption in natural i?(62%), a sharp neutron response peak, high light yield, and large ?/? ratio makes Rb2LiYBr6:Ce3+ an efficient scintillator for thermal neutron detection.