Large Scintillator Research Articles

Large area position sensitive β-detector

A new conceptual design of a large area electron detector, which is position and energy sensitive, was developed. This detector is designed for beta decay energies up to 4MeV, but in principle can be re-designed for higher energies. The detector incorporates one large plastic scintillator and, in general, a limited number of photomultipliers (7 presently). The current setup was designed and constructed after an extensive Geant4 simulation study. By comparison of a single hit light distribution between the various photomultipliers to a pre-measured accurate position-response map, the anticipated position resolution is around 5mm. The first benchmark experiments have been conducted in order to calibrate and confirm the position resolution of the detector. The new method, results of the first test experiments and comparison to simulations are presented.

The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET

In this work, a method is presented that can calculate the lower bound of the timing resolution for large scintillation crystals with non-negligible photon transport. Hereby, the timing resolution bound can directly be calculated from Monte Carlo generated arrival times of the scintillation photons. This method extends timing resolution bound calculations based on analytical equations, as crystal geometries can be evaluated that do not have closed form solutions of arrival time distributions. The timing resolution bounds are calculated for an exemplary 3 mm × 3 mm × 20 mm LYSO crystal geometry, with scintillation centers exponentially spread along the crystal length as well as with scintillation centers at fixed distances from the photosensor. Pulse shape simulations further show that analog photosensors intrinsically operate near the timing resolution bound, which can be attributed to the finite single photoelectron pulse rise time.

Statistics of ionospheric scintillation occurrence over European high latitudes

Rapid fluctuation in the amplitude and phase of transionospheric radio signals caused by small scale ionospheric plasma density irregularities is known as scintillation. Over the high latitudes, irregularities causing scintillation are associated with large scale plasma structures and scintillation occurrence is mainly enhanced during geomagnetic storms. This paper presents a statistical analysis of scintillation occurrence on GPS L1C/A signal at a high latitude station located in Bronnoysund (geographic latitude 65.5°N, geographic longitude 12.2°E; corrected geomagnetic (CGM) latitude 62.77°N), Norway, during the periods around the peaks of solar cycles 23 (2002–2003) and 24 (2011–2013). The analysis revealed that the scintillation occurrence at Bronnoysund during both the solar maximum periods maximises close to the midnight magnetic local time (MLT) sector. A higher occurrence of scintillation is observed on geomagnetically active days during both the solar maximum periods. The seasonal pattern of scintillation occurrence indicated peaks during the summer and equinoctial months. A comparison with the interplanetary magnetic field (IMF) components By and Bz showed an association of scintillation occurrence with the southward IMF Bz conditions.

A Monte Carlo calibration of a whole body counter using the ICRP computational phantoms.

A fast and versatile calibration of a whole body counter (WBC) is presented. The WBC, consisting of four large plastic scintillators, is to be used for measurements after accident or other incident involving ionising radiation. The WBC was calibrated using Monte Carlo modelling and the ICRP computational phantoms. The Monte Carlo model of the WBC was made in GATE, v6.2 (Geant4 Application for Tomographic Emission) and MATLAB. The Monte Carlo model was verified by comparing simulated energy spectrum and simulated counting efficiency with experimental energy spectrum and experimental counting efficiency for high-energy monoenergetic gamma-emitting point sources. The simulated results were in good agreement with experimental results except when compared with experimental results from high dead-time (DT) measurements. The Monte Carlo calibration was made for a heterogeneous source distribution of (137)Cs and (40)K, respectively, inside the ICRP computational phantoms. The source distribution was based on the biokinetic model for (137)Cs.

POLITRANI, A New Toolkit to Simulate Organic Scintillator Pulses

3He shortage has provoked a renewed interest for organic scintillation detectors (good neutron detection efficiency) with neutron-gamma discrimination capability. Pulse Shape Discrimination (PSD) with plastic scintillators has recently shown important progresses and raises a great interest as plastic detectors are not toxic and not inflammable contrary to liquid scintillation detectors. In this context, the French Alternative Energies and Atomic Energy Commission (CEA), within the FP7 European project SCINTILLA, is studying the possibility to produce large size plastic scintillators as candidates for 3He tube replacements together with the related FPGA electronics. To support the design of plastic scintillators with enhanced neutron-gamma discrimination power, software based on ROOT data analysis software was developed to couple photon-neutron transport with MCNP PoliMi and optical photon tracking in the scintillator with Litrani. This new tool called “POLITRANI” allows to build realistic electronic pulses delivered by radiation detectors, and thus to study PSD sensitivity to various factors such as plastic shape, size, coating, scintillation decay time for neutrons vs. gamma rays, and radiation scattering in the detector. Parameters of the FPGA-based electronics can also be investigated, such as sampling frequency, trigger, and length of the integration gate.

Digital electronics for 256 anode Hamamatsu H9500 PSPMT arrays in full-volume Compton imagers

Ziock et al.'s [1] recent Monte Carlo study of a proposed ``full-volume'' Compton Imaging Camera concluded that simultaneously locating a Compton scatter event's multiple interaction points within a single large scintillator crystal might be possible at 1 mm spatial resolution using a coded aperture mask sandwiched between two light guides and coupled to a position sensitive photomultiplier (PSPMT) to record the output light pattern. The method promises high efficiency at a relatively low cost. They are currently developing a lower resolution prototype using a large cubic scintillator (25.4 cm/side) whose masked face will be tiled with 25 Hamamatsu H9500 PSPMTs (6,400 outputs). XIA has contracted to develop and produce the readout electronics, which present several significant design challenges, including capturing all 6,400 anode outputs individually, with single photon sensitivity, in a compact format that will fit behind the tiled PSPMTs. 10,000 event/sec operation is desired, as is a cost of less than about $50/channel.In our approach, each PSPMT front end integrates the 256 anode signals and 8-1 multiplexes them to 32 differential outputs that are digitized in a PXI card using 4 octal 50 MHz ADCs. The multiplexers run at 8 MHz, sampling each anode at 1 MHz, which becomes the image frame rate. The ADC signals are demultiplexed and digitally filtered to extract the number of photons in each pixel in the full 2-D image. The design has been completed and built and is undergoing evaluation tests at the single PSPMT level.

Large plastic scintillator panels with WLS fiber readout: Optimization of components

Results are presented on R&D efforts to design and build large size veto panels, optimized for underground low background experiments, in the most efficient and economical way using commercially available components. A variety of plastic scintillators, photomultiplier tubes, wavelength shifting fibers, and light reflector combinations were tested. Results of these studies and performance of a 2.2m long panel are presented.

Study of the soft dipole modes in 140Ce via inelastic scattering of 17O

The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in Ce, excited via inelastic scattering of weakly bound O projectiles. An important aim was to investigate the ‘splitting’ of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (α, α′) and (γ, γ′) experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of O ion beam at was used to excite the resonance modes in the Ce target. Gamma-rays were registered by five triple clusters of AGATA-Demonstrator and nine large volume scintillators (). The scattered O ions were identified by two Si telescopes of the TRACE array mounted inside the scattering chamber. The telescopes consisted of two segmented Si-pad detectors, each of 60 pixels. Very preliminary data have shown a strong domination of the E1 transitions in the ‘pygmy’ region with a character more similar to the one obtained in alpha scattering experiment.

Precisionν¯e-electron scattering measurements with IsoDAR to search for new physics

IsoDAR provides a pure and intense $\bar \nu_e$ source with an average energy of 6.5 MeV produced through $^8$Li $\beta$-decay. This source can be paired with a large scintillator detector, such as KamLAND, to produce a sample of $\bar \nu_e$-electron scatters that is more than five times larger than what has been collected before. Such a sample would allow for a 3.2% measurement of $\sin^2\theta_W$ and a sensitive search for non-standard interactions.

Novel High Efficiency Microcolumnar LuI3:Ce for Hard X-ray Imaging

We have developed a structured scintillator using a vacuum deposition technique that is suitable for manufacturing large area scintillators in a microcolumnar form. While providing high absorption efficiency, it also allows great temporal and spatial resolution X-ray imaging. Microcolumnar films of extremely fast and bright cerium-doped lutetium iodide (LuI3:Ce) scintillator were synthesized. It has high density (~5.6 g/cm3), high effective atomic number (59.7), bright green emission (540 nm range, well matched to commercial optics and CCD sensors), light yield exceeding 115,000 ph/MeV, and rapid, afterglow-free decay (~28 ns). This new scintillator could resolve the 153 ns bunch structure of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Due to the fast, afterglow-free decay, and high efficiency of LuI3:Ce, during the experiments performed at the 1-ID hard X-ray beamline at the APS, single 65 keV X-ray photons could be resolved with high signal-to-noise ratio and with temporal resolution better than 20ns. In the future, it will enable a wide range of hard X-ray (20 keV to 100 keV) imaging and/or high frame-rate applications such as dynamic studies of the structural and electrochemical properties of batteries using microtomographic X-ray imaging, internal corrosion in fuel cells, and time-resolved muscle diffraction experiments.

A Photo-Multiplier Testing Device

The paper reports the design of a photo-multiplier testing device constructed to assess long term stability and suitability of 53 AVP photo-multipliers for use with singles counting, scintillation counter arrays and large plastic scintillation counter arrays (in coincidence) in high energy physics experiments (with muons). The device can be used for routine checking of such phototubes in laboratory.

The design of a low activity laboratory housing a whole body counter consisting of large plastic scintillators and the work towards a flexible Monte Carlo calibration

137 Cs point source. The measured spectra were compared to Monte Carlo simulated spectra. The Monte Carlo code GATE v6.1 was used to simulate the energy deposition with the following optical transport in the scintillator material and detection of optical photons at the photocathode. MATLAB R2012a was used to calculate the multiplication in the photomultiplier tube. The results show the benefits of incorporating optical transport in the Monte Carlo simulations; the resolution in the simulated spectra changed drastically between energy deposition spectra and spectra of detected optical photons at the photocathode and; the measured spectra showed a source position dependence which was not noticed in the energy deposition spectra but first after the optical transport. A detailed description is given of the detector system and surrounding facilities because of their rather unique design.

Shielding benchmark experiment using hundreds of MeV quasi-monoenergetic neutron source by a large organic scintillator

aHigh Energy Accelerator Research Organization, 1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305-0801, Japan; bJapan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195, Japan; cNational Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki-ken, 305-8561, Japan; dResearch Reactor Institute, Kyoto University, 2-1010 Asashiro-nishi,Kumatori-cho, Sennan-gun, Osaka-hu, 590-0494, Japan; eResearch Center for Nuclear Physics,10-1 Mihogaoka, Ibaraki-shi, Osaka-hu. 567-0047, Japan; fShimizu Corporation,4-17, Etchujima 3-Chome, Koto-ku, Tokyo-to, 135-8530, Japan

Annihilation Radiation Gauge for Relative Density and Multiphase Fluid Monitoring

The knowledge of the multi-phase flow parameters are important for the petroleum industry, specifically during the transport in pipelines and network related to exploitation's wells. Crude oil flow is studied by Monte Carlo simulation and experimentally to determine transient liquid phase in a laboratory system. Relative density and fluid phase time variation is monitored employing a fast nuclear data acquisition setup that includes two large volume BaF2 scintillator detectors coupled to an electronic chain and data display in a LabView® environment. Fluid parameters are determined by the difference in count rate of coincidence pulses. The operational characteristics of the equipment indicate that 2 % deviation in the CCR corresponds to a variation, on average, of 20 % in the fraction of liquid of the multiphase fluid.

A full digital approach to the TDCR method

Current state of the art solutions based on the Triple to Double Coincidence Ratio method are generally large size, heavy-weight and not transportable systems. This is due, on one side, to large detectors and scintillation chambers and, on the other, to bulky analog electronics for data acquisition. CAEN developed a new, full digital approach to TDCR technique based on a portable, stand-alone, high-speed multichannel digitizer, on-board Digital Pulse Processing and dedicated DAQ software that emulates the well-known MAC3 analog board.

6Li Embedded Biaxially Stretched Scintillation Films for Thermal Neutron Detection and Neutron/Gamma Discrimination

Biaxially stretched composite polyethylene naphthalate (PEN) films (BSCPF) embedded with submicron lithium fluoride (6LiF) particles and luminescent molecules were fabricated to make large area scintillation films (≈1 m × 1 m) for thermal neutron detection. BSCPF had 20.2% higher neutron light yield as compared to unstretched composite film (UCPF), and were 2.46 ± 1.47 times more efficient for detecting thermal neutrons than lithiated glass GS20 above lower level discriminator corresponding to an intrinsic efficiency for gamma <10−6. MCNPX simulations for a layered BSCPF detector resulted 6.1 cps for 1 ng 252Cf, thus meeting the Pacific Northwest National Laboratory criteria for absolute neutron detection efficiency and intrinsic gamma‐neutron discrimination. BSCPF have alpha to beta ratio of 0.25, which is higher than that for UCPF (0.11), and also for GS20 (0.22), which offers the possibility of excellent neutron/gamma discrimination.

Evaluation of LGSO:Ce scintillator for high energy physics experiments

The work is focused on the development of production methods of large scintillators based on lutetium-gadolinium oxyorthosilicate doped with cerium Lu2xGd2−2xSiO5:Ce (LGSO:Ce). Large LGSO:Ce crystals were grown by the Czochralski method, and a set of experimental samples for testing of scintillation characteristics was produced. Possibilities are discussed to use this scintillator in high energy physics experiments. In particular, an electromagnetic calorimeter to search for conversion of electrons into muons, which is forbidden in the Standard Model.

KASCADE-Grande measurements of energy spectra for elemental groups of cosmic rays

The KASCADE-Grande air shower experiment [1] consists of, among others, a large scintillator array for measurements of charged particles, Nch, and of an array of shielded scintillation counters used for muon counting, Nμ. KASCADE-Grande is optimized for cosmic ray measurements in the energy range 10PeV to about 2000PeV, where exploring the composition is of fundamental importance for understanding the transition from galactic to extragalactic origin of cosmic rays. Following earlier studies of the all-particle and the elemental spectra reconstructed in the knee energy range from KASCADE data [2], we have now extended these measurements to beyond 200PeV. By analysing the two-dimensional shower size spectrum Nch vs. Nμ for nearly vertical events, we reconstruct the energy spectra of different mass groups by means of unfolding methods over an energy range where the detector is fully efficient. The procedure and its results, which are derived based on the hadronic interaction model QGSJET-II-02 and which yield a strong indication for a dominance of heavy mass groups in the covered energy range and for a knee-like structure in the iron spectrum at around 80PeV, are presented. This confirms and further refines the results obtained by other analyses of KASCADE-Grande data, which already gave evidence for a knee-like structure in the heavy component of cosmic rays at about 80PeV [3].

Optimization of the Scintillator Size for Positron Lifetime Measurements

Optimization of the measurement condition for positron annihilation lifetime spectroscopy (PALS) is discussed from the viewpoint of non-destructive "on-site" material inspection. Numerical analysis based on a least-squares estimation and experiments with various sizes of BaF2 scintillators by conventional PALS suggested that the use of relatively large BaF2 scintillators enables on-site material inspection by PALS with reasonable accumulation time and time resolution.

Characterization of the Hamamatsu R11780 12 in. photomultiplier tube

Future large water Cherenkov and scintillator detectors have been proposed for measurements of long baseline neutrino oscillations, proton decay, supernova and solar neutrinos. To ensure cost-effectiveness and optimize scientific reach, one of the critical requirements for such detectors are large-area, high performance photomultiplier tubes (PMTs). One candidate for such a device is the Hamamatsu R11780, a 12 in. PMT that is available in both standard and high quantum efficiency versions. Measurements of the single photoelectron response characteristics, relative efficiencies of the standard and high quantum efficiency versions, a preliminary measurement of the absolute quantum efficiency of the standard quantum efficiency version, and a two-dimensional scan of the relative efficiency across the photocathode surface are presented in this paper. All single photoelectron investigations were made using a Cherenkov light source at room temperature at a gain of 1×107. These results show that the R11780 PMT is an excellent candidate for such large optical detectors.