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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.

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.

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.

Optical spectroscopy of LuI 3 doped with Ce 3 + using ultraviolet and visible light excitation is reported. LuI 3 host excitation and emission and 4f–5d excitation and emission of Ce 3 + are observed. An empirical model based on crystal field splitting was used to estimate the energy of the highest 4f–5d excitation band. The crystal field splitting and centroid shift were compared to those of LuCl 3 : Ce 3 + and LuBr 3 : Ce 3 + . Temperature dependence of X-ray excited luminescence spectra shows thermal quenching, whereas that of the decay curve of Ce 3 + emission excited at the lowest 5d band of Ce 3 + does not indicate the presence of quenching of Ce 3 + emission for temperature below 625 K. The quenching in LuI 3 : Ce 3 + therefore occurs before the 5d Ce 3 + emission takes place.

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.

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.

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 optical and scintillation properties of LaCl3 : 0.57% Ce, LuBr3 : 0.021%, 0.46%, 0.76% Ce and LuCl3 : 0.45% Ce are studied under optical, X- and γ-ray excitation. The highest light yield of 40000±4000 photons per MeV (ph/MeV) of absorbed γ-ray energy was measured for LaCl3 : 0.57% Ce. An energy resolution (FWHM over peak position) of, respectively, 7.0±0.5%, 6.0±0.1%, 7.8±0.3%, 6.5±0.5% and 18.0±0.5% was observed for the 662 keV full absorption peak. The scintillation decay curves can be described with three components: 20±2, 330±30 ns and 2.2±0.2 μs for LaCl3 : 0.57%; 32±3, 450–550 ns and >5 μs for LuBr3 : 0.76%; 50±5, 250–350 ns and >4 μs for LuCl3 : 0.45%.

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.

The absolute yields of excited states formed in benzene solutions by photons with energy varying from 17.5 to 122 keV were determined using a liquid scintillation method with photopeak detection. Radiation energy was accurately defined by using radioactive sources with mono-energetic g- or X-ray emission. From these results the absolute yields of excited states in pure benzene, G(B), were calculated for photon energies of 17.5, 32, 59.5, and 122 keV as respectively 0.98, 1.11, 1.12, and 1.15 (100 eV) ˇ1 . The 22s error limits are 215% with 95% confidence. These results are discussed in comparison with former determinations, taking their dependence on excitation photon energy, due to track eAects, into account. The new results used as reference for fluorescence yields in alkanes, namely decalins, lead to a better agreement between earlier measurements of the eAciencies for excited state formation in the decalins from ion recombination and more recent simulation calculations based on spin correlation. # 1999 Elsevier Science Ltd. All rights reserved.

We have measured for the first time the temperature dependence of LaBr3:5% Ce3+ and LaCl3:10% Ce3+ gamma-ray excited light yields and decay curves between 100 and 600 K. Under gamma-ray excitation, both scintillators present a very good thermal stability over the entire temperature range. The light yield of LaBr3 is maximum at 100 K and decreases monotonously from 100 to 600 K. The decrease at 600 K does not exceed 15% of the maximum value. The light yield of LaCl3 is maximum at 600 K and decreases with decreasing temperatures. The lowest value is reached at 150 K and corresponds to 90% of the maximum light yield recorded at 600 K. Our results show that LaBr3:5% Ce3+ and LaCl3:10% Ce3+ crystals can be used in applications where temperature conditions are extreme such as in oil well logging. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Results are presented on the scintillation properties of LaF 3 crystals doped with Nd 3+ concentrations ranging from 0.1 to 15 mol%. Attention will be focussed on the absolute light output in photons/MeV contained in the 173 nm emission band, caused by dipole allowed 5d-4f transitions in the Nd 3+ ions.

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.

Data are presented on the relative photon yield of Lu 2 SiO 5 (Ce 3+ ), Cd 2 SiO 5 (Ce 3+ ), CdWO 4 , BaF 2 , YAlO 3 (Ce 3+ ) and Lu 3 Al 5 O 12 (Sc 3+ ) scintillation of crystals on absorption of X-ray and γ-ray photons at energies ranging from 5 keV to beyond 1 MeV.

The diffuse reflectance and photoluminescence (PL) spectra of NdI(2), SmI(2), EuI(2), DyI(2), TmI(2) and YbI(2) were measured between 225 and 12 500 nm in order to determine their 4f(n) → 4f(n-1)5d(1) optical bandgaps. The results were compared with those obtained using an empirical model of the electronic structure of LnI(2). The results can be used to explain the lanthanide valency and crystalline structure changes of other lanthanide diiodides such as PrI(2).

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.

The quantum efficiency curves of five Philips XP2020Q photomultiplier tubes (PMTs), one Hamamatsu R2059 PMT, and a Na-salicylate coated glass window are determined using a calibrated Thorn EMI 9426 PMT as a reference. The QE of XP2020Q PMTs at wavelengths smaller than 230 nm appears much better than the values specified by the manufacturer. Consequently, the often reported photon yield of 2000 photons/MeV for the fast component of the scintillation pulses from pure BaF/sub 2/ crystals determined with this tube is overestimated. The authors' results, obtained by means of calibrated equipment and using 662-keV gamma -rays, yield a value of 1400 photons/MeV. >

Using a conventional fast-shuttered laboratory X-ray source in combination with pulsed laser diode modules, the possibilities for undertaking X-ray/laser interaction spectroscopy in wide band-gap luminescent materials are explored. It is shown that in such materials, a variety of X-ray/laser timing sequences can extract complimentary information regarding the charge-carrier trapping, de-trapping and recombination processes. The effects on the luminescence are illustrated for six example materials (YPO 4 :Ce,Sm, Lu 3 Al 5 O 12 :Pr, Al 2 O 3 :C, natural sodium feldspar NaAlSi 3 O 8 , cubic BN and type IIa natural diamond). By ramping the temperature from 10 to 320 K during repeated X-ray pump/laser-probe activation cycles, a rapid assessment can be made of the important thermally dependent changes to the charge carrier trapping competition processes.

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.

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce3+ in LaAlO3:Ce3+. It is demonstrated that the absence of luminescence is the result of Ce3+ ionization from the 5d excited states, which are all located in the conduction band. Ce3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce3+ to traps and vice versa, from traps back to Ce4+. The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band.

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.

A combined photoconductivity and luminescence quenching study, both temperature and spectrally resolved, has revealed the role played by electron delocalization in luminescence quenching of Ce{sup 3+} impurities in the wide band-gap inorganic insulator GdAlO{sub 3}. The anticorrelation found between the temperature behavior of photocurrent and luminescence intensity strongly suggests that luminescence quenching and photoconduction are intimately related by the same process, i.e., thermal stimulated ionization of optically excited Ce{sup 3+} centers: Ce{sup 3+}{yields}Ce{sup 4+}+electron. Quantitative modeling of experimental data using rate equations, however, reveals a 0.05-eV smaller activation energy for luminescence quenching than for photocurrent generation which indicates that quenching predominantly proceeds via the formation of a Ce bound exciton at the originally excited Ce ion. A second quenching process, dominant below 230 K, seems mediated by energy transfer from Ce{sup 3+} via the Gd{sup 3+} sublattice to Ce{sup 4+} centers resulting in hole conductivity via a charge transfer excitation: Ce{sup 4+}{yields}Ce{sup 3+}+hole.

The scintillation properties of GdAlO3 single crystals doped with different concentrations of Ce3+ are reported. Dipole allowed transitions in Ce3+ ions from the lowest 5d to the two 4f levels cause luminescence between 320 and 400 nm.

In this work we present the scintillation properties of K 2 LaCl 5 doped with Ce 3+ concentrations of 0, 0.1, 1 and 10%. Under X-ray excitation the crystals show the efficient Ce 3+ (5d–4f) luminescence between 340 and 400 nm. Depending on the Ce concentration, the light yields vary between 24,000 and 50,000 photons/MeV (ph/MeV). Experiments with 662 KeV gamma ray excitation show light yields varying between 13,000 and 30,000 ph/MeV. For Ce luminescence a single exponential decay time of approximately 40 ns is expected. However, for K 2 LaCl 5 :10%Ce, the decay is not single exponential. As a function of the time t , it can be described by a 1/ t 1.63 behaviour for large t . With a crystal of K 2 LaCl 5 :10%Ce we obtained an energy resolution of 5.1% for 662 KeV gamma ray excitation of 137 Cs.

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).

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. >

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.

The quantum efficiencies (QEs) of several VUV sensitive photon detectors were determined and compared with each other. We tested the following photomultiplier tubes (PMTs): five Philips XP2020Qs, one Hamamatsu R2059, and one Thorn EMI 9426. We also tested a Na-salicylate coated glass window combined with a Philips XP2020 PMT. At wavelengths smaller than 230 nm, the QEs of both the Thorn EMI and Philips PMTs appear significantly better than the QE of the Hamamatsu PMT. Furthermore, at these wavelengths, the QE of the XP2020Q PMTs was found to be much higher than advertised in the manufacturers catalogues.

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.

A review and new data are presented on the absolute photon yield emitted by "classical" (NaI(Tl/sup +/), CsI(Tl/sup +/), CsI(Na/sup +/), CaF/sub 2/(Eu/sup 2+/), Bi/sub 4/Ge/sub 3/O/sub 12/, and CdWO/sub 4/) and "modern" (BaF/sub 2/, Gd/sub 2/SiO/sub 5/(Ce/sup 3+/), YAlO/sub 3/(Ce/sup 3+/), Lu/sub 2/SiO/sub 5/(Ce/sup 3+/), Lu/sub 3/Al/sub 5/O/sub 12/(Sc/sup 3+/), and K/sub 2/LaCl/sub 5/(Ce/sup 3+/)) scintillation crystals after absorption of X-rays and /spl gamma/-rays of energies ranging from 5 keV to 1 MeV. Factors influencing the energy resolution with which high energy photons can be detected with scintillator-photomultiplier combinations are reviewed. Attention is especially focused on the effects of nonproportionality in the scintillation response on the energy resolution.

To achieve optimal use of the capabilities of a robot it has become increasingly important to include the dynamical behaviour of the robot in control strategies. In this case a dynamic model is needed for collision-free motion planning and control of two cooperating robots in an assembly cell. The two robots are of different types, an anthropomorphic type and a SCARA type. In this paper the derivation and identification of the dynamical model for the industrial Bosch SR800 TurboScara robot is described. The robot has 4 degrees of freedom of which the first two are the most important. Both these degrees consist of joints that are actuated with DC-motors and use harmonic-drives for speed reduction. In recent literature [1],[2] it is shown that the use of harmonic-drives can introduce considerable flexibility. Analyses of the actuator response after a step input shows flexibility in the first joint. This flexibility will be incorporated in the model. The model has been identified using black-box identification and parameter optimization. With the black-box model orders and rough parameter values are estimated. With a parameter optimization method the individual parameters, like link inertia, are estimated through minimizing the difference between measured and simulated time response. The use of time responses enables the individual estimation of parameters with an influence on a specific part of the respons.

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.

Optical absorption spectra of irradiated single crystals of LiF:Mg,Ti have been studied while the sample temperature has been raised during the measurement. Nine absorption bands could be distinguished. Careful computerized curve fitting of the spectra allow for the behaviour of the various bands during heating. The absorption spectra have been compared with spectra measured after a pulse anneal. Clear differences have been observed between the continuous and pulse anneal spectra indicating that the defect state of the sample at room temperature after a pulse anneal is not the same as during TL emission. A striking result is the rise and fall during the heating process of the absorption bands at 4.50 eV (not noticed before) and 5.54 eV (known from the literature). Similarities between the pulse and continuous anneal spectra have been observed for the behaviour of the 4.00 and 5.10 eV bands.