Light Yield Measurements Research Articles

An analytical model of nonproportional scintillator light yield in terms of recombination rates

Analytical expressions for the local light yield as a function of the local deposited energy (−dE/dx) and total scintillation yield integrated over the track of an electron of initial energy E are derived from radiative and/or nonradiative rates of first through third order in density of electronic excitations. The model is formulated in terms of rate constants, some of which can be determined independently from time-resolved spectroscopy and others estimated from measured light yield efficiency as a constraint assumed to apply in each kinetic order. The rates and parameters are used in the theory to calculate scintillation yield versus primary electron energy for comparison to published experimental results on four scintillators. Influence of the track radius on the yield is also discussed. Results are found to be qualitatively consistent with the observed scintillation light yield. The theory can be applied to any scintillator if the rates of the radiative and nonradiative processes are known.

Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals

We report on measurements of the absolute light output from LSO crystals for irradiation with 511 keV gamma rays as a function of interaction position, reflector arrangement, detector coupling geometry and optical coupling to an adjacent crystal. The light output for this series of geometrical configurations is simulated with the ZEMAX ray-tracing software. By fine-tuning the optical parameters of the bulk and at the interfaces of the crystal, a model is obtained which yields good agreement with experimental data for all configurations. The resulting parameter set is applied to calculate the light distribution in a 12 times 12 crystal block detector. A comparison of measured and calculated block position profiles shows good agreement, demonstrating the potential of the simulation model to predict block detector performance data and provide guidelines for future array designs.

Spectral properties and thermoluminescence of codoped PbWO4:(Mo,Y) and PbWO4:(F,Y) crystals

AbstractLead tungstate, PbWO4 single crystals codoped with Mo6+/F– and Y3+ ions were grown using the modified Bridgman method. Optical transmission, X‐ray excited luminescence, photoluminescence, ultrashort pulsed X‐ray excited fluorescent lifetime and thermoluminescence have been investigated. Compared to pure PbWO4, the codoped PbWO4:(Mo,Y) and PbWO4:(F,Y) crystals exhibit improved transmittance in the short‐wavelength region. Luminescence and light‐yield measurements demonstrated that Mo6+/F– and Y3+ codoping could enhance the luminescence of PbWO4 and reduce slow decay components. Doped Mo6+ and F– ions in PbWO4 were tentatively considered to occupy W and O sites, while Y3+ ions codoped in PbWO4:Mo/F mostly occupy Pb sublattice sites. The second excitation peak at 335 nm, which is the second effective excitation for the enhanced blue‐green emission in as‐grown PbWO4:(Mo,Y) and PbWO4:(F,Y) crystals, should be related to MoO42– groups and O vacancies (VO). Thermoluminescence glow curve measurement between RT and 400 °C provides complementary information about trapping states and the effect of Y3+ ion codoping resulting in the reduction of stable and temporary hole centers. Further work is needed to explain the doping and energy‐transfer mechanism. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nd loaded liquid scintillator to search for 150Nd neutrinoless double beta decay

The 150Nd is considered one of the most attractive candidate for searching neutrinoless double beta (0νββ-) decay, thanks to its high Q-value (3.367 MeV), that makes the external background issue less significative respect to other isotopes, and favorable computed matrix elements. The isotopic abundance of this isotope in natural neodimium is only 5.6% and up to now, it has been investigated only in low mass experiments. The next step is to increase the sensitivity of the experiments using larger mass of neodymium (10 ton-1 kton). This could be possible with a Nd loaded liquid scintillator (LS). At the Gran Sasso National Laboratory (LNGS), a joint INFN (Istituto Nazionale di Fisica Nucleare) and INR (Institute for Nuclear Research of Moscow) working group has been carrying out since 2001 an R&D activity aiming to develop organic liquid scintillators (LS) doped with metals. The achieved know-how and the satisfactory results obtained both with In and Gd allowed to face the development and production of Nd doped LS. The development of metal doped LS is challenging because the metal has to be embedded in a proper organic system that makes it soluble in an organic solvent minimizing the impact of the metal-organic compound on the optical and scintillation properties of the LS. A further challenge in the case of Nd is the presence of absorption bands of this element in the optical region with a transparent region around 400 nm, which is about at the maximum of the scintillator emission spectrum. A 2.5 1 Nd loaded LS has been produced diluting an originally developed Nd-Carboxylic (Nd-CBX) salt in pseudocumene (PC), the solvent of the Borexino liquid scintillator. The measured light yield, at [Nd] = 6.5 g/1 and [PPO] = 1.5 g/1, is ∼ 75% of pure PC at the same fluor concentration (~ 10000 ph/MeV). The Nd doped LS has been tested in a 2 1 quartz cell (wrapped by VM2000 reflector film) having dimensions 5x5x100 cm3. The light propagates in the cell by total internal reflection at the external quartz/air interface and is reflected by the VM2000 foil. The light is trasmitted at the windows of the cell where 3-inch PMTs (one for each end) are coupled. Two fillings have been performed: distilled PC (PPO-1.5 g/1) and Nd loaded LS (Nd-6.5 g/1, PPO-1.5 g/1, MSB-30 mg/1). In both cases, the cell is irradiated with a 137Cs source, scanning different positions along the cell axis. For each position the Compton Edge (CE) in the spectrum has been fitted. The optical attenuation length measured with this methodic is: 210±10 cm (only stat error, systematics not yet investigated). The measurements performed by ICP-MS of the radiopurity of the Nd2O3, that is the compound from which the Nd-CBX salt is synthesized, and of the content of optically active impurities show that a purification procedure is needed. Further investigations, at the ppt level, on the Th content in Nd2O3 is planned with the Borexino CTF.

Nanostructuring of an AlGaInP light emitting diode for surface plasmon enhanced emission of light output

AbstractThis work describes a successful post fabrication method of applying a plasmonic grating to the surface of a mounted AlGaInP LED device. A Carl Zeiss 1540 XB Focused Ion beam system was used to mill holes in a thin gold layer with a periodicity of around 540 nm. Measurements of the total light output of the device compared with a standard un‐textured device show that the plasmonic grating was found to significantly affect the light output characteristics such that the overall light output was reduced. This is attributed to the fact that only p‐polarised light can interact with the hole array. Furthermore, the onset of saturation in the textured device was not evident as compared with the un‐textured device. This is attributed to improved current spreading in the device due to the top gold layer. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Scintillation yield of liquid xenon at room temperature

The intensity of scintillation light emission from liquid xenon at room temperature was measured. The scintillation light yield at 1 ∘ C was measured to be 0.64 ± 0.02 (stat.) ± 0.06 (sys.) of that at - 100 ∘ C . Using the reported light yield at - 100 ∘ C (46 photons/keV), the measured light yield at 1 ∘ C corresponds to 29 photons/keV. This result shows that liquid xenon scintillator provides high light yield even at room temperature.

Energy and Timing Response of Six Prototype Scintillators for TOF-PET

The recent development of fast scintillating crystals with high light output (such as LaBr3, LYSO, and LSO) has made it possible to incorporate time-of-flight information into whole-body positron emission tomography scanners (TOF-PET). The development of fast scintillators has continued, and scintillators such as CeBr3 and the six crystals we report on here are candidates for future TOF-PET scanners. We have performed preliminary tests on six prototype scintillating crystals composed of YI3 (2% Ce), (Lu,Gd)I3 (2% Ce), Lul3 (10% Ce), Lul3 (5% Ce), Lul3 (2% Ce), and Ce(Br,Cl)3. The crystals were coupled to a PMT to observe 511 keV photons produced by positron captures in a 22Na point source. A LaBr3 coincidence detector was used in order to make timing resolution measurements. The prototype samples had a range of timing resolutions from 160 ps to 250 ps (FWHM). Ce(Br,Cl)3 was found to have the best timing resolution, with 160 ps, followed by Lul3 (2% Ce) with 180 ps. These results are competitive with the 160 ps we observed for a pair of LaBr3 crystals in coincidence with each other. The 2% Ce doped Lul3 sample was found to have the best overall energy response, with an energy resolution (FWHM) of 6% at 511 keV. Energy resolution and light yield measurements are presented for each of the crystals.

Large Size CdWO4 Crystal for Energetic X- and γ-Ray Detection

A Large size of Φ70 mm × 71 mm (2.1 kg) CdWO4 crystal with excellent quality was studied for the energy response of the crystal to the γ-rays. The large crystal was coupled with a green-extended Photomultiplier tube (PMT) and tested at room temperature. We measured light yield and energy resolution of the crystal using various radioactive sources. The energy resolutions of the CdWO4 crystal were obtained to be 9.5 % and 5.3% for 662 keV and 2614 keV, respectively. Linearity of the crystal in different γ-ray energy was also measured. In the environmental background spectrum, well defined peaks of 1461 keV by 40K decay and 2614 keV by 208Tl decay were identified. A simulation study with GEANT4 package was performed for the efficiency comparison with commonly used NaI(Tl) crystal scintillators. The study showed that the CdWO4 crystal is the promising candidate for the boarder control and energetic X-and γ-ray detection equipment.

Scintillation light yield of BaF 2:Ce

BaF 2:Ce scintillator is a well-known, reasonably fast and efficient scintillator characterized by a decent stopping power and availability of large size crystals. In this communication we report scintillation light yield measurements on a number of BaF 2:Ce samples cut from one larger boule. We interpret these measurements in a frame of a simple one-dimensional model developed and first tested on LuAP and LuYAP samples. The model is expected to reproduce the observed strong dependence of the effective scintillation light yield against the height of the sample. The fit to experimental points provides a value of the “intrinsic” light yield LY(0), as well as a value of the “loss” parameter μ (scattering and absorption of scintillation light in the sample). Although the value of the loss parameter μ, at around 0.5 cm −1, found from the fit for BaF 2:Ce is clearly lower than a typical value in LuAP and LuYAP, it is, nevertheless, much higher than the value of about 0.05–0.07 cm −1 measured in Delft for LaBr 3:Ce. We have also measured the absorption spectra of BaF 2:Ce crystals. The corrected spectra have been used to estimate contributions from scattering, self-absorption (by Ce-ions) and parasitic absorption from unidentified centers in order to establish physical limits imposed on the light yield from these crystals.

Scintillation response of CaF2 to H and He over a continuous energy range

Recent demands for new radiation detector materials with improved γ-ray detection performance at room temperature have prompted research efforts on both accelerated material discovery and efficient techniques that can be used to identify material properties relevant to detector performance. New material discovery has been limited due to the difficulties of large crystal growth to completely absorb γ-energies; whereas high-quality thin films or small crystals of candidate materials can be readily produced by various modern growth techniques. In this work, an ion-scintillator technique is demonstrated that can be applied to study scintillation properties of thin films and small crystals. The scintillation response of a benchmark scintillator, europium-doped calcium fluoride (CaF2:Eu), to energetic proton and helium ions is studied using the ion-scintillator approach based on a time-of-flight (TOF) telescope. Excellent energy resolution and fast response of the TOF telescope allow quantitative measurement of light yield, nonlinearity and energy resolution over an energy range from a few tens to a few thousands of keV.

LED projector with two liquid crystal on silicon light valves and a fly’s eye integrator

We present a projection system with two liquid crystal on silicon light valves that are illuminated by light-emitting diode light sources (LEDs). The LED illumination system is designed with a fly’s eye integrator. Using this integrator we combine for each primary color two LEDs into one bright source to illuminate the light valve. In the color management system a wire-grid polarizer is used to combine two beams with opposite state of polarization. The contrast behavior of our two LCOS approach is investigated with a basic model and ray tracing. The consequences of using this polarizer are discussed. We present contrast, uniformity and light output measurements of a concept demonstration set-up.

On the aging of the scintillation counters for RUN II Muon System at CDF

The CDF II Muon System has an important role in the CDF detector, particularly in investigations of processes, as with heavy quarks. JINR and INFN physicists at FNAL are responsible for maintenance to perform the highly efficient functioning of the scintillation counters involved into the CDF Muon system. In the course of several years, we carried out the light yield measurements, at ends farthest from photomultiplier, of the various types of scintillation counters installed at CDF. On the basis of the results obtained, conclusions about the aging rate of the counters and long-range forecast of their efficiency during physics data taking at CDF RUN II could be made. One can see that the new generation counters with wavelength-shifter fibers technology for light collection have higher long-range efficiency compared to counters using a classic plexiglas light-guide for light propagation.

Growth and Luminescence Properties of Pr-doped Lu3(Ga,Al)5O12 Single Crystals

Single crystals with the nominal composition of (Pr0.01,Lu0.99)3(Gax,Al1-x)5O12 (Pr:LuGAG) were grown by the micro-pulling-down (µ-PD) method with RF heating and their luminescence properties were characterized. Transparent and crack free crystals that were slightly yellowish green were obtained. Lattice constants and densities systematically increased with increasing of Ga concentration. The luminescence properties of Pr:LuGAG were characterized by photoluminescence spectra and decays, radioluminescence spectra and light yield measurements. 5d–4f luminescence was observed for the x≤0.6 samples. It was found that the 5d–4f emission of Pr3+ is quenched only slightly up to x≤0.4 whereas density systematically increased in the range of 0≤x≤1.0.

Cerium-doped mixed-alkali rare-earth double-phosphate scintillators for thermal neutron detection

Previous measurements of the scintillation properties of members of the single-alkali, rare-earth double-phosphate family have demonstrated high light output and fast decay times when exposed to ionizing radiation. Because of the ease with which the alkali constituents (Li, Na, K, Rb, Cs) of the crystal matrix may be interchanged (e.g. K 2CsLu(PO 4) 2 and CsLi 2Lu(PO 4) 2), the rare-earth double-phosphate family of scintillators provides an ideal system for the study of matrix effects on scintillation efficiency and kinetics. New members of the rare-earth double-phosphate family have been synthesized by high-temperature flux growth. These new samples, represented by the general formula (A,B) 3Lu(PO 4) 2:Ce where A and B are alkali elements, incorporate lithium as one of the components and varying levels of Ce doping. Characteristics important to gamma-ray and thermal neutron excitation are calculated for three model systems which incorporate total lithium-ion substitution. Light output, scintillation decay times, and photoluminescence measurements for the most promising of the samples to date are reported. Future work includes (1) synthesis of mixed-alkali scandium and yttrium double-phosphates in which Li ions are substitutional in the structure with varying lithium-ion content up to and including total lithium–ion substitution on the alkali ion site and (2) measurements of light output and pulse shape using thermal neutron excitation.

Challenge and study for developing of novel single crystalline optical materials using micro-pulling-down method

Micro-pulling-down (μ-PD) method is a useful tool to search for new materials. This method allows us to prepare single crystalline materials quickly and relatively inexpensively. Grown crystals are of sufficient dimensions for all the necessary characterization by optical and luminescence methods, including photo- and radio-luminescence, decay kinetics and light yield measurements. Recent results obtained for laser and scintillator materials at Pr-doped Y3Al5O12, Lu3Al5O12, YAlO3, Y2SiO5, Lu2SiO5, fluorides like Ce-doped PrF3, mixed binary fluorides AEF2–REF3, (Ce:AE:(Gd,Y)F3, AE=Ba, Sr, Ca) and Yb- and Tm-doped RE2O3 (RE=Y, Lu, Sc) are summarized here. Practical importance of μ-PD method follows also from the shaped crystal growth aspect. It is possible to grow shaped and/or device-size crystals from the melt using a single step process. Recent improvement of μ-PD method makes the quality of μ-PD crystals comparable with those prepared by Czochralski (Cz), Bridgeman, or other classical growth techniques.

Measurement of air and nitrogen fluorescence light yields induced by electron beam for UHECR experiments

Most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, EUSO, TUS, etc.) use air fluorescence to detect and measure extensive air showers (EAS). The precise knowledge of the Fluorescence Light Yield (FLY) is of paramount importance for the reconstruction of UHECR. The MACFLY—Measurement of Air Cherenkov and Fluorescence Light Yield—experiment has been designed to perform such FLY measurements. In this paper we will present the results of FLY in the 290–440 nm wavelength range for dry air and pure nitrogen, both excited by electrons with energy of 1.5 MeV, 20 GeV and 50 GeV. The experiment uses a 90Sr radioactive source for low energy measurement and a CERN SPS e − beam for high energy. We find that the FLY is proportional to the deposited energy ( E d) in the gas and we show that the air fluorescence properties remain constant independently of the electron energy. At the reference point: atmospheric dry air at 1013 hPa and 23 °C, the ratio FLY/ E d = 17.6 photon/MeV with a systematic error of 13.2%.

The Monte-Carlo refractive index matching technique for determining the input parameters for simulation of the light collection in scintillating crystals

The Monte-Carlo refractive index matching (MCRIM) technique was developed to determine the physical properties of heavy inorganic scintillators (HIS) which are difficult to measure experimentally. It was designed as a method for obtaining input parameters for Monte-Carlo (MC) simulations of experimental arrangements incorporating HIS in their setups. The MCRIM technique is used to estimate the intrinsic light yield, the scattering coefficient and the absorption coefficient, herein referred to as indirect measurement properties. The MCRIM technique uses an experiment/MC combination to determine these indirect measurement properties. The MCRIM experimental setup comprises a crystal placed on a photomultiplier tube window with the possibility of introducing materials of different refractive indices in a small gap between the crystal and photomultiplier tube (PMT) window. The dependence of the measured light yield on the refractive index of the material in the gap can only be reproduced by simulations if the correct values of scattering, absorption and intrinsic light yield are used. The experimental setup is designed to minimise the presence of optical components such as unpolished surfaces and non-ideal reflectors, which are difficult to simulate. The MCRIM technique is tested on a 1.03×1.00×0.82 cm 3 crystal of CaWO 4 which is found to have a scattering coefficient of 0.061±0.005 cm −1, an absorption coefficient of 0.065±0.005 cm −1, and an intrinsic light yield of 22700±1700 photons/MeV.

Growth and scintillation properties of F-doped PWO crystals

The application of PbWO 4-based scintillators in inexpensive positron emission tomography is strongly limited by their poor light yield; an effort has been made at the Shanghai Institute of Ceramics to overcome this problem. By using F ion doped, a factor of 2.5 increase of the light yield (within 200 ns) can be achieved compared with undoped PbWO 4 crystals. X-ray diffraction patterns, transmittance, luminescence (X-ray and UV excited) spectra and light yield measurements of PWO:F crystals are presented. This increase of fast scintillation component of PbWO 4 may open up a wide field of practical applications in medical imaging.

High-energy proton induced damage study of scintillation light output from [formula omitted] calorimeter crystals

Eight PbWO 4 crystals produced for the electromagnetic calorimeter of the CMS experiment at LHC have been irradiated in a 20 GeV / c proton beam up to fluences of 5.4 × 10 13 p / cm 2 . The damage recovery in these crystals, stored in the dark at room temperature, has been followed for over a year. Comparative irradiations with 60Co photons have been performed on seven other crystals using a dose rate of 1 kGy/h. The issue whether hadrons cause a specific damage to the scintillation mechanism has been studied through light output measurements on the irradiated crystals using cosmic rays. The correlation between light output changes and light transmission changes is measured to be the same for proton-irradiated crystals and for γ -irradiated crystals. Thus, within the precision of the measurements and for the explored range of proton fluences, no additional, hadron-specific damage to the scintillation mechanism is observed.

Study of scintillator strip with wavelength shifting fiber and silicon photomultiplier

The performance of the 200 × 2.5 × 1 cm 3 plastic scintillator strip with wavelength shifting fiber read out by two novel photodetectors called Silicon PhotoMultipliers (SiPMs) is discussed. The advantages of SiPM relative to the traditional multichannel photomultiplier are shown. Light yield and light attenuation measurements are presented. This technique can be used in muon or calorimeter systems.