Large CsI Research Articles

Search for Light Neutral Bosons in the TREK/E36 Experiment at J-PARC

The Standard Model (SM) represents our best description of the subatomic world and it has been very successful in explaining how elementary particles interact under the influence of the fundamental forces. Despite its far reaching success in describing the building blocks of matter, the SM is still incomplete; falling short to explain dark matter, baryogenesis, neutrino masses and much more. The E36 experiment conducted at J-PARC in Japan, allows for sensitivity to search for light U(1) gauge bosons, in the muonic K + decay channel. Such U(1) bosons could be associated with dark matter or explain established muon-related anomalies such as the muon gµ − 2 value, and the proton radius puzzle. A scintillating fiber target was used to stop a beam of positively charged K mesons. The K + products were detected with a large-acceptance toroidal spectrometer capable of tracking charged particles with high resolution, combined with a large solid angle CsI(TI) photon detector and particle ID systems. A realistic simulation was employed to search for these rare decays in the mass range of 20–100 MeV/c 2. Preliminary results of the upper limits for the A′ branching ratio Br(A′ ) extracted at 95% CL, will be discussed.

Measurement of delayed neutron emission from water activated by 14 MeV neutrons in a FW mock-up of ITER

Water activated by 14 MeV neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The isotopes 16,17N are produced through the 16O(n,p)16N (T1/2 = 7.13 s) and 17O(n,p)17N (T1/2 = 4.1 s) reactions, respectively. These sources of radiation represent one of the main issues for ITER having large impact on the design of the machine and on the qualification of components. To validate the calculation methodology used for ITER and to reduce the safety factors applied to the calculation results a water activation experiment was commissioned by F4E to ENEA and performed at the 14 MeV Frascati neutron generator (FNG). The experimental set-up consisted of a closed water loop, about 40 m long, where the cooling water, while transiting through an ITER FW mock-up, was irradiated by the D-T neutrons produced at FNG. 6.73 MeV gamma-rays from 16N and delayed (fast) neutrons from 17N were measured using a large CsI gamma-ray detector and an array of absolutely calibrated 3He detectors, respectively. This paper reports on the measurements of the delayed neutrons emission from 17N. The calibration of the 3He detector array and the experimental set-up are first discussed. Then the experimental results (E) for the delayed neutrons as well as the comparison with the calculation (C) performed using the MCNP Monte Carlo code (coupled to the FENDL3.1 data library) and the EASY-2007 inventory code are presented. The C/E ratio results close to unity, however it is affected by a very large error (> ±60 %) to be ascribed mainly to the uncertainty on the nuclear data used for calculation.

Comparison between measurement and calculations for a 14 MeV neutron water activation experiment

The nuclear heat loads due to gamma rays emitted from the decay of 16N and delayed neutrons from17N, generated by the activation of water in cooling circuits, are critical for ITER design. The assessment of nuclear heating from activated water is complex; it requires temporal and spatial dependent transport and activation calculations taking into account variation of irradiation, water flow conditions and cooling circuits’ parameters. A water activation experiment has been recently conducted at the14 MeV Frascati Neutron Generator (FNG) in order to validate the methodology for water activation assessment used for ITER and to reduce the safety factors applied to the calculation results, which have a large impact on the schedule, commissioning and licensing. Water circulating inside an ITER First Wall (FW) mock-up was irradiated with 14 MeV neutrons and then measured using a large CsI scintillator detector. The system consists of a closed water loop where the cooling water, transiting through an ITER FW mock-up, is irradiated by FNG. The induced 16N activity via 14 MeV neutrons interactions with 16O via the 16O(n,p)16N reaction is measured in a dedicated counting station via an expansion volume. The water then passes to a much larger holding delay tank, and after several 16N half-lives decay time, it is then recirculated and exposed again to neutrons in the ITER First Wall (FW) mock-up. The measured 16N activity is obtained measuring the emitted characteristic 6.13 and 7.12 MeV gamma-rays. Calculations were performed in an accurate model of the FW mock-up using the MCNP Monte Carlo code and FENDL-3.1 nuclear data library to obtain the predicted flux impinging on the water. The EASY-2007 inventory code was used to predict the 16N activity. In this work, a comparison between measurements and calculations is reported together with associated uncertainty analysis.

Estimation of the detected background by the future gamma ray transient mission CAMELOT

AbstractThis study presents a background estimation for the CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all‐sky monitoring and timing‐based localization of gamma ray transients with precise localization capability at low Earth orbits. CAMELOT will allow us to observe and precisely localize short gamma ray bursts (GRBs) associated with kilonovae, long GRBs associated with core‐collapse massive stars, magnetar outbursts, terrestrial gamma ray flashes, and gamma ray counterparts to gravitational wave sources. A fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multipixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and minimize the effect of the radiation damage of MPPCs.

Performance study of a large CsI(Tl) scintillator with an MPPC readout for nanosatellites used to localize gamma-ray bursts

We are designing a fleet of nanosatellites to perform accurate position determinations of short-duration gamma-ray bursts by measuring arrival time differences. To achieve sufficient photon statistics to measure the arrival times precisely under the severe limitations of size, mass and power consumption, we propose the use of large-area CsI(Tl) scintillators which provide a high light output and the use of a small-sized multipixel photon counters (MPPC), a kind of SiPM, that have low power consumption. We plan to use one of the latest-model MPPCs provided by Hamamatsu Photonics, namely, S13360-6050CS, which has an active area of 6×6 mm2. We have compared the performance of two scintillators of different sizes (150×75×5 mm3 and 100×75×5 mm3); the bigger one is the maximum size that can be mounted on a three-unit satellite, according to CubeSat standards. We have found that the light yield of the bigger scintillator is lower than that of the smaller one, but the difference is only approximately 13%, and each has an energy threshold of ∼10 keV at 25∘C. We have tested one- and two-MPPC readout and confirmed the same energy thresholds. The light yield for the two-MPPC readout is 1.4 times as high as that for the one-MPPC readout. We have also examined the position dependence of the light yield by using radiation from a 241Am (59.5 keV) source, and confirmed that uniformity was improved, and energy resolution got better by ∼7% for two-MPPC readout.

Performances of Crystal Scintillators in a Severe Radiation Environment Caused by Gamma Rays

Because of their superb energy resolution and detection efficiency crystal scintillators are widely used in high energy and nuclear physics experiments. A crucial issue is radiation damage. We report an investigation on γ-ray induced radiation damage in crystal scintillators of large size, including BaF2, BGO, CeF3, pure CsI, LSO/LYSO/LFS and PWO with an integrated dose up to 340 Mrad at a dose rate up to 1 Mrad/h. Optical and scintillation properties of these crystal samples were measured before and after irradiations. The result shows that pure CsI crystals have good radiation hardness below 100 krad. BaF2, BGO and LYSO crystals show good radiation hardness beyond 1 Mrad. In terms of light output degradation LSO/LYSO/LFS is clearly the best among all scintillation crystals.

Characterization of a CsI(Tl)-SiPM detector to low energy protons for light dark matter search in a future Beam Dump eXperiment

The silicon Photomutiplier (SiPM) is a successful solid-state light detector. Thanks to its characteristics, especially the high quantum efficiency, comparable to that of PMTs, and the much higher gain compared to APDs, it can play an important role in many physics fields. For example a calorimeter read out by SiPMs is the proposed solution for the detection light dark matter in a future beam dump experiment. Although scintillating crystals coupled to SiPMs are widely used, they have been scarcely characterized as low energy (∼ MeV) ion detectors. In the present work we report a study of the light response of a large volume CsI(Tl) crystal, read out by a small area SiPM to low energy protons of different kinetic energies, from 2.5 MeV to 24 MeV . The results of the measurements allowed us to qualify the CsI(Tl)-SiPM solution in an unmeasured energetic regime.

Scintillation γ spectrometers for use at nuclear power plants (review)

In this review, it is shown that out of the 300 scintillators synthesized to date only LaBr3:Ce, CeBr3, YAlO3: Ce, and CsI:Tl crystals with the corresponding silicon photosensors (SiPSs) can be used as detectors in industrial γ-ray spectrometers intended for nuclear power plants. They are superior in their energy resolution and their resistance to mechanical and electromagnetic effects to spectrometers used today with a NaI:Tl crystal and a photomultiplier tube (PMT). A p–i–n photodiode (PD), an avalanche photodiode (APD), and a silicon photomultiplier (SiPM) are promising SiPSs. The properties of various assemblies of listed scintillators and photosensors are analyzed. A PD matches well with any scintillator. A spectrometer does not require LED stabilization of the scale, but its noise level must be reduced by selective PD cooling and the use of a light guide for coupling a massive scintillator and a SiPS with a small area of its sensitive surface. A spectrometer with an APD does not require photosensor cooling; however, LED stabilization of its energy scale is necessary. Application of an SiPM can rule out the use of a light concentrator (which is important for large CsI:Tl scintillators) and selective cooling, but this introduces nonlinearity at a short decay time and a high light yield in the scintillator (LaBr3:Ce and CeBr3) and also calls for an LED stabilization system for the spectrometer. The prospects for the development and application of new scintillation γ-ray spectrometers are discussed in this review.

A CsI low-temperature detector for dark matter search

Cryogenic detectors have a long history of success in the field of rare event searches. In particular scintillating calorimeters are very suitable detectors for this task since two signals are induced by a particle interaction in a scintillating crystal. The thermal signal provides a precise measurement of the deposited energy while the simultaneously measured scintillation light signal yields particle discrimination as the amount of produced scintillation light depends on the nature of the interacting particle. We investigate the calorimetric properties and background rejection capabilities of two large CsI (undoped) crystals (∼122 g each) operated as scintillating calorimeters at milli-Kelvin temperatures. Furthermore, we discuss the feasibility of this detection approach towards a future background-free dark matter experiment based on alkali halide crystals, with active particle discrimination via the two-channel detection.

Development of a low-cost-high-sensitivity Compton camera using CsI (Tl) scintillators (γI)

We have developed a novel low-cost gamma-ray imaging Compton camera γI that has a high detection efficiency. Our motivation for the development of this detector was to measure the arrival directions of gamma rays produced by radioactive nuclides that were released by the Fukushima Daiichi nuclear power plant accident in 2011. The detector comprises two arrays of inorganic scintillation detectors, which act as a scatterer and an absorber. Each array has eight scintillation detectors, each comprising a large CsI (Tl) scintillator cube of side 3.5cm, which is inexpensive and has a good energy resolution. Energies deposited by the Compton scattered electrons and subsequent photoelectric absorption, measured by each scintillation counter, are used for image reconstruction. The angular resolution was found to be 3.5° after using an image-sharpening technique. With this angular resolution, we can resolve a 1m2 radiation hot spot that is located at a distance of 10m from the detector with a wide field of view of 1sr. Moreover, the detection efficiency 0.68cps/MBq at 1m for 662keV (7.6cps/μSv/h) is sufficient for measuring low-level contamination (i.e., less than 1μSv/h) corresponding to typical values in large areas of eastern Japan. In addition to the laboratory tests, the imaging capability of our detector was verified in various regions with dose rates less than 1μSv/h (e.g., Fukushima city).

A Compton-vetoed germanium detector with increased sensitivity at low energies

The difficulty to directly detect plutonium in spent nuclear fuel due to the high Compton background of the fission products motivates the design of a gamma detector with improved sensitivity at low energies. We have built such a detector by operating a thin high-purity Ge detector with a large scintillator Compton veto directly behind it. The Ge detector is thin to absorb just the low-energy Pu radiation of interest while minimizing Compton scattering of high-energy radiation from the fission products. The subsequent scintillator is large so that forward-scattered photons from the Ge detector interact in it at least once to provide an anti-coincidence veto for the Ge detector. For highest sensitivity, additional material in the line of sight is minimized, the radioactive sample is kept thin, and its radiation is collimated. We will discuss the instrument design, and demonstrate the feasibility of the approach with a prototype that employs two large CsI scintillator vetoes. Initial spectra of a thin Cs-137 calibration source show a background suppression of a factor of ~2.5 at ~100 keV, limited by an unexpectedly thick 4 mm dead layer in the Ge detector.

Chang’E-1 gamma ray spectrometer and preliminary radioactive results on the lunar surface

The Chang’E-1(CE-1) spacecraft took a gamma-ray spectrometer (hereafter, CGRS) to detect the element distributions on the lunar surface in a circular, 200 km altitude, polar orbit with approximately 2 h periodicity. CGRS consists of two large CsI(Tl) crystals as the main and anticoincidence detectors. The large CsI crystal of CGRS has a higher detector effective area than other lunar gamma ray spectrometers. For its 1-year mission, gamma ray spectra including many peaks of major elements and trace elements on the lunar surface have been measured by CGRS. Global measurement within 0.55–0.75 MeV is given here to describe the distribution of radioactive composition (e.g., uranium and thorium) on the lunar surface. Although CGRS has a lower energy resolution that cannot separate the uranium peak from others in this energy region, 609 keV uranium gamma ray line dominates the shape of the spectrum in this energy region. Therefore, the radioactive map can indirectly describe the uranium distribution on the lunar surface. The radioactive map shows that the higher radiation is concentrated in the Procellarum KREEP Terrene (PKT) on the nearside with an oval shape. The secondary high-radiation is located in South Pole-Aitken (SPA) basin. Lunar highlands have lower concentration. The relationship between radiation and topography displays different linear correlations for lunar highlands and SPA basin, which imply the different processes for these two regions.

An upgrade of the SCANDAL setup for measurements of elastic neutron scattering at 175 MeV

The experimental setup SCANDAL, used for measurements of the differential cross section for elastic and inelastic neutron scattering, has recently been upgraded with larger CsI scintillating detectors to enable measurements at energies up to 175 MeV. Measurements on Fe, Bi and Si have been carried out using the quasi mono-energetic neutron beam at the The Svedberg Laboratory, and data is under analysis. The experimental setup can be used for measurements on a wide range of target nuclei, including C and O, which are important for dosimetry applications. SCANDAL can also run in proton mode, for measurements of the (n,p) reaction. This paper describes the new experimental setup, and reports on its properties, such as energy resolution.

Can large scintillators be used for solar-axion searches to test the cosmological axion–photon oscillation proposal?

Solar-axion interaction rates in NaI, CsI and Xe scintillators via the axio-electric effect were calculated. A table is presented with photo-electric and axio-electric cross sections, solar-axion fluxes, and the interaction rates from 2.0 to 10.0 keV. The results imply that annual-modulation data of large NaI and CsI arrays, and large Xe scintillation detectors, might be made sensitive enough to probe coupling to photons at levels required to explain axion–photon oscillation phenomena proposed to explain the survival of high-energy photons traveling cosmological distances. The DAMA/LIBRA data are used to demonstrate the power of the model-independent annual modulation due to the seasonal variation in the earth-sun distance.

Gas Cherenkov detectors for high momentum charged particle identification in the ALICE experiment at LHC

Protons identification up to 10 GeV / c and more is a challenge. We present here an exhaustive study of the possibilities offered by a combination of a gaseous radiator having low index of refraction (C 5F 12) with the proven concept of large area CsI photocathodes, instrumenting either a multiwire chamber or a GEM detector. We present two geometries. One of them is proximity-focusing, nevertheless allows identification in a large momentum range. The second one deals with a focusing geometry with a spherical mirror. Simulations of the performance of both types are presented.

Study of gas Cherenkov detectors for high momentum charged particle identification

We present here an exhaustive study of the possibilities offered by a combination of a gas radiator of the highest index of refraction commercially available ( C 5 F 12 ) with the proven concept of large area CsI photocathodes instrumenting either a multiwire chamber or a GEM detector. We will present two geometries. One of them is proximity-focusing, nevertheless allows identification in a large momentum range. The second geometry deals with the possibilities of using focusing with a spherical mirror. Simulations of the performance are presented.

Photo-current scanner system for in situ quality assessment of large area CsI photocathodes

The facility for the production of the large area ( 64 × 42 cm 2 ) CsI photocathodes (PCs) for the ALICE/HMPID detector has been equipped with a photo-current scanner system for the in situ measurement of the CsI response over the full photo-sensitive area before transfer to the detector. This paper provides a detailed description of the experimental setup. Measurements of variations in the photo-current due to the pad structure of the PCs as well as due to heat treatment and ageing effects of the CsI PCs demonstrate the sensitivity of the instrument to changes in quantum efficiency (QE). The usability of the scanner to perform quality monitoring during the series production of PCs for the detector is shown in a comparison of scanner measurements and beam test results for 17 PCs.

Production technique and quality evaluation of CsI photocathodes for the ALICE/HMPID detector

The ALICE/HMPID detector has been equipped with 42 large area CsI photocathodes providing a total of 11 m 2 of photosensitive area for the detection of Cherenkov light. This production summary reports on the CsI coating procedure and provides results of the quality monitoring measurements by means of a photocurrent scanner system. The importance of the heat enhancement of CsI PCs is stressed and difficulties due to variations in this process are presented, followed by a discussion of possible influences of production parameters on this process.

Non-uniformity of light output in large-sized CsI(Tl) crystals grown by non-vacuum Bridgman method

CsI crystals doped with different concentration of Tl were grown with non-vacuum Bridgman method, so-called as the modified Bridgman method. The dependence of the light output on Tl content was studied and 1000 ppm (mol) of TlI was suggested as a suitable doping level for growing large CsI(Tl) crystals with this crystal growth technique. The distribution of thallium along the longitudinal direction of the CsI crystal was analyzed by the Atomic Absorption Spectrometry (AAS) and has been proved to be inhomogeneous. The non-uniformity of light output along the longitudinal axis of a large crystal with dimension of 80×80×400 mm 3 was rather evident, however, it could be amended, during the mechanical processing of the boule, by properly defining one of the end faces (tail side) as the particle incident face, named as front face, and another end face (seed side) for attached by PMT or photodiode to be named as rear face. The influence of irradiation on the non-uniformity of light output was investigated as well.

Results from the ageing studies of large CsI photocathodes exposed to ionizing radiation in a gaseous RICH detector

We studied the ageing of large CsI photocathodes induced by ionizing particles ( 90Sr) by correlating the integrated charge dose of the ionic avalanches hitting the photocathode to the local changes of the Quantum Efficiency (QE). The drop of the QE of the irradiated CsI spots is reported as a function of the charge dose. It was found that the ageing process continues even in absence of irradiation.