Charged particles identification with a CsI(Tl) scintillator

A CsI(Tl) scintillator with two light decay components is used to detect and identify p, d, t, ³He and α particles with a low energy threshold. Besides, the addition of a thin plastic scintillator in front of the CsI(Tl) crystal allows charge identification for ions with Z up to 19.     

CsI(Tl)/plastic phoswich detector enhanced in low-energy gamma-ray detection

A phoswich detector composed of a thin plate CsI(Tl) scintillator and a plastic scintillator (BC-400) has been designed and evaluated in order to improve the sensitivity in the low-energy region of a large-area plastic scintillation detector. This newly designed phoswich detector can be applied to both gross gamma measurement and energy spectrometry for low-energy gamma-ray emitters. Judging by estimations of minimum detectable activity, the lower measurable energy of a large-area plastic scintillation detector can be expanded down to a few tens of keV by adding a thin plate CsI(Tl) scintillator.     

Improvement on the light yield of a high-Z inorganic scintillator GSO(Ce)

Cerium-doped gadolinium silicic dioxide crystal, GSO(Ce), is a high-Z non-hydroscopic scintillator that gives higher light yield than BGO, and can potentially replace NaI(Tl), CsI(Tl) and BGO in many applications. Its production cost, however, has been substantially higher than any of them, while its energy resolution has been worse than that of NaI(Tl) or CsI(Tl). The merit did not overcome these deficiencies except in limited applications.

We developed a low background phoswich counter (the well-type phoswich counter) for the Hard X-ray Detector of the Astro-E project based on GSO scintillator. In the developmental work, we have succeeded in improving the light yield of GSO(Ce) by 40–50%. For energies above 500 keV, a large GSO(Ce) crystal (4.5 cm×4.5φ cm) now gives energy resolution comparable to or better than the best NaI(Tl) when read out with a phototube. With a small GSO(Ce) crystal (5×5×5 mm³) and a photodiode, an energy resolution comparable to or better than the best CsI(Tl) has been obtained. With this improved performance, we find that the much higher photopeak efficiency and the shorter scintillation decay time of GSO(Ce) offsets its higher cost for many applications.

We summarize our past developmental work to decrease radioactive contamination and to increase light yield of GSO(Ce) for astronomical hard X-ray detection. Included also are measurements done after the unsuccessful launch of the Astro-E mission. The work is still continuing for the remake version of Astro-E Hard X-ray Detector.     

New idea of a small-sized neutron detector with a plastic fibre

A small-sized thermal neutron detector based on a (6)Li-glass scintillator and a plastic optical fibre has been developed for precise measurement of the spatial distribution of thermal neutron fluence rate. This detector was tested in experiments performed using thermal neutrons. The detector is useful in a thermal neutron field. However, the gamma-ray discrimination ability of the (6)Li-glass scintillator is not good in a low-intensity thermal neutron field. A new idea using a gamma-ray suppression method is proposed to reduce the uncertainty in the neutron counts due to the gamma-ray background. A novel small-sized thermal neutron detector consists of a (6)Li-glass scintillator, a hollow CsI(Tl) scintillator and plastic optical fibres. The evaluation of the gamma-ray suppression ability of the detector using the EGS4 code indicates that the gamma-ray suppression is effective.     

Optimisation on the two-layer stack gamma detectors of CsI(Tl) coupled with a pin photodiode for non-destructive testing

This paper proposed the two-layer stack scintillator-coupled photodiode detector to improve the measurement accuracy of the gamma-ray scanning. Both MCNPX and DETECT97 code were used to design the detector. The two manufactured two-layer stack gamma detectors were used to measure the density profile of the distillation column of the radiographic non-intrusive process diagnostic area. To compare the measurement accuracy of the density profile through the non-destructive transmission test, the relative error of the four fluids used for the process diagnostics was analysed. To summarise the measurement results with regard to the relative error of the NaI(Tl) detector and the manufactured detector by material as well as the total relative error, the total relative error of the NaI(Tl) detector was about 15.7 %, whereas that of the two-layer stack CsI(Tl) with photodiode detectors were about 5 %. This paper confirmed that the measurement accuracy of the detector proposed was improved by about three times as compared with the NaI(Tl) detector mostly used for non-destructive testing.     

A new hybrid photomultiplier tube as detector for scintillating crystals

In this work, we have attentively studied the performance of a new hybrid photomultiplier tube (HPMT) as detector for photons from scintillating crystals. The HPMT is equipped with a YAP window in order to improve light collection and increase measured light response from scintillating crystals. Several measurements have been performed on BGO, LSO, CsI(Tl) and NaI(Tl) planar crystals having three different surface treatments as well as on YAP : Ce and CsI(Tl) matrices. Such crystals have been coupled to two HPMTs, one equipped with a YAP window (Y-HPMT) and the other with a conventional quartz window (Q-HPMT). Measurements on crystals coupled to the Y-HPMT have shown a consistent improvement of the light response, thanks to the presence of the YAP window. Indeed, the light response measured with the Y-HPMT was on average equal to 1.5, 2.1 and 2.6 times that obtained with the Q-HPMT for planar crystals with white painted (diffusive), fine ground and polished rear surfaces, respectively. With regards to crystal matrices, we measured a light response increase of about 1.2 times.     

Electronics for A SiCsI(Tl)-photodiode multidetector system

Preamplifiers, computer-controlled main amplifiers and trigger electronics have been designed and built for our charged particle multidetector system (MDS). These electronic process signals from the individual detection elements of the MDS, each consisting of a silicon surface-barrier detector and a CsI(Tl) scintillator with photodiode readout. Our design is compact, reliable, cheap, and well-suited for the multidetector system.     

Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals

A new large area detector of high-energy X-ray and β-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed β-sensitivity . The spectrograms of a ⁹⁰Sr+⁹⁰Y β-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum.

The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of γ-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of - and γ-radiation has been achieved under simultaneous excitation by ²³⁹Pu (ZnSe(Te), R=6%) and ²⁴¹Am (CsI(Tl), R_γ=20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition.     

CsI(Tl)-241Am calibration source for Pb-glass detectors

A light pulser for calibrating Pb-glass detectors has been designed consisting of a 3 mm diameter by 1 mm thick CsI(Tl) scintillation crystal positioned in an Al cup 1 mm from an ²⁴¹Am α-emitting source. Optical coupling to a Pb-glass detector is provided by a glass window and epoxy. Calibration consists of exposing the Pb-glass detector to high-energy electrons, typically 2 GeV, and comparing the Cherenkov pulse with the line from the CsI(Tl)-²⁴¹Am source. The advantages of this source are its expected long-term stability of light output, simplicity, and low cost.     

Performance of different phoswich configurations in a balloon flight experiment

Four different phoswich units were included in a modular hard X-ray balloon experiment launched on August 10, 1982 in order to check the dependence of background level and rejection efficiency of NaI(Tl)/CsI(Na) phoswich detectors on scintillator thicknesses. The results concern the dependence of the background intensity on both the thickness of the active shield, for a fixed primary detector thickness, and on the thickness of the primary detector, given the active shield thickness. A direct comparison of phoswich detectors with passively shielded NaI(Tl) crystals is also given. As a consequence practical hints for designing new phoswich detectors are derived and the limiting sensitivity of these detectors for hard X-ray observations of celestial sources is inferred.     

Radioluminescent light source for the development of optical sensor arrays

A radioluminescent (RL) light source is evaluated for the development of photonically based chemical-responsive sensor arrays (CRSAs). The RL light source is comprised of a strontium-90 (90Sr) radionuclide and a plastic scintillator. The beta particles emitted from the 90Sr generate blue light (lambda(max) = 435 nm) from the plastic scintillator, and the blue light excites the analyte-responsive luminophores within the CRSA. To assess the RL light source utility, we have determined the analytical figures of merit from two tris(4,7'-diphenyl-1,10'-phenathroline)ruthenium(II)-doped xerogel-based sensor platforms: (i) a planar 5 x 5 multielement array and (ii) a discrete sensor element formed on the proximal face of poly(styrene) pillars that have a frustrated cone (frustum) geometry. We compare the performance from each platform when it is excited by a He-Cd laser (442 nm), a blue light-emitting diode (460-470 nm), and the RL light source. The RL light source yields results that are statistically equivalent to results from either electrically powered light source. The RL light source consumes no electrical power, is compact and simple, and has an extremely stable time-averaged signal. The primary trade-offs for these advantages are the RL light source's lower radiant power and the corresponding longer data acquisition times.     

Beam test of the CsI(Tl) calorimeter for the BELLE detector at the KEK-B factory

We studied the performance of a prototype electromagnetic calorimeter for the BELLE detector at the KEK proton synchrotron for an energy range of 0.25–3.5 GeV. The prototype consisted of an array of 6 × 5 CsI(Tl) crystals with 30 cm length (16.2 radiation lengths) and about 6 cm × 6 cm cross section. The scintillation light of each CsI(Tl) crystal was read out by two large-area PIN photodiodes and charge-sensitive preamplifiers attached at the rear face of the crystal. We measured the energy and position resolution for electrons and the e/π separation for two sets of matrix configurations: one corresponded to the center and the other to the edge of the barrel calorimeter. The overall performance measured by the test proves that the prototype calorimeter is satisfactory for the use in the BELLE detector.     

The use of CsI(Tl) scintillators with photodiode readout in heavy ion experiments

The performance of a ΔE−E telescope consisting of transmission silicon detector and CsI(Tl) scintillators with photodiode read out investigated in 46.7 MeV/u ¹²C induced reaction. The zero-crossing technique of pulse shape analysis has been employed to identify the light charged particles (p, d, t, ) with a low energy threshold, and a detector array composed of nine elements of CsI(Tl) scintillators with photodiode readout have been developed to measure the light charged particle interferometry in intermediate energy heavy ion induced reaction.     

CdWO4 scintillator as a compact gamma ray spectrometer for planetary lander missions

The objective of this work is to develop a gamma ray spectrometer (GRS) suitable for use on planetary rover missions. The main characteristics of this detector are low weight, small volume low power and resistance to cosmic ray radiation over a long period of time. We describe a 3 cm diameter by 3 cm thick CdWO₄ cylindrical scintillator coupled to a PMT as a GRS for the energy region 0.662–7.64 MeV. Its spectral performance and efficiency are compared to that of a CsI(Tl) scintillator 2.5 cm diameter by 6 cm thick coupled to a 28 mm×28 mm PIN photodiode. The comparison is made experimentally using ¹³⁷Cs, ⁶⁰Co, 6.13 MeV gamma rays from a ¹³C(,γn)O¹⁶* source, 7.64 MeV thermal neutron capture gamma rays emitted from iron bars using a ²⁵²Cf neutron source, and natural radioactivity 1.46 MeV ⁴⁰K and 2.61 MeV ²³²Th gamma rays. We use a Monte Carlo method to calculate the total peak efficiency of these detectors and the full energy, first and second escape peak efficiencies. The experimental and calculated results agree well. We investigated the usefulness of these detectors for a GRS on a Mars lander mission. Although both detectors meet desired specifications, it was found that CdWO₄ has advantages over CsI(Tl) being a more compact detector of higher efficiency. Using a shaping amplifier of 24 ms, CdWO₄ spectrometer exhibited a 6.8% FWHM at 662 keV. At 6.13 MeV, CdWO₄ detector possesses an intrinsic total and full energy peak efficiencies of 16.7% and 6.3%, respectively. These efficiencies are nearly a factor of 1.6 and 4 greater than the corresponding efficiencies of the CsI(Tl) detector.

A proposed gamma ray spectroscopy system to be placed on a rover, consists of a central detector surrounded by a Compton suppressor shield. The central detector is a cylindrical CdWO₄ detector and the Compton suppressor shield is made of segmented CdWO₄, coupled to PIN photodiodes. The shield also prevents thermal neutron activation of the central detector.     

Ultralow-concentration Sm codoping in CsI:Tl scintillator: A case of little things can make a big difference

CsI:Tl scintillators were hindered from computer tomography and high-speed imaging applications by a serious afterglow problem. In this study, the effects of ultralow-concentration Sm codoping on the scintillation characteristics of CsI:Tl were investigated. Pulsed X-ray excited afterglow after 50 ms in 0.005 mol% Sm-codoped CsI:Tl was lowered by over one order of magnitude in comparison with Sm-free one. The beneficial effects of ultralow-concentration Sm codoping also appeared to be maintaining the light yield and energy resolution. The light yield and energy resolution after 0.005 mol% Sm codoping were 71,700 ± 6000 photons/MeV and 6.9% at 662 keV, respectively.     

The response of a CsI(Tl) scintillator with photodiode readout to light particles and heavy ions

The response of a small (1 cm³) CsI(Tl) crystal coupled to a silicon photodiode to light particles and heavy ions has been investigated using proton, alpha and oxygen beams in the energy range 10–25 MeV/n.Pulse-height resolution of 1.2 and 2.9% [fwhm] have been measured for 98 MeV ⁴He and 278 MeV ¹⁶O. The use of CsI(Tl)-photodiode assembly in nuclear physics experiments with intermediate energy heavy-ions beams is envisaged     

Results from a CsI(Tl) test calorimeter with photodiode readout between 1 and 20 GeV

Results from a test with a CsI(Tl) calorimeter will be presented. The purpose was to evaluate the use of CsI(Tl) for high resolution electromagnetic calorimetry. A resolution of about 1% has been measured between 4 and 20 GeV. A very high electron/hadron separation of > 1 : 1000 has been observed. Prospects and limitations for large scale applications will be discussed.     

CsI(Tl)晶体发光均匀性的研究

本文对Tl分布、几何形状以及表面条件对大尺寸锥形CsI（Tl）晶体的闪烁发光均匀性的影响进行了研究,提出了改善大尺寸锥形CsI（Tl）晶体的发光均匀性的措施.     

Multiscale patterning of plasmonic metamaterials

The interaction of light with surface plasmons--collective oscillations of free electrons--in metallic nanostructures has resulted in demonstrations of enhanced optical transmission, collimation of light through a subwavelength aperture, negative permeability and refraction at visible wavelengths, and second-harmonic generation from magnetic metamaterials. The structures that display these plasmonic phenomena typically consist of ordered arrays of particles or holes with sizes of the order of 100 nm. However, surface plasmons can interact with each other over much longer distances, so the ability to organize nanoscale particles or holes over multiple length scales could lead to new plasmonic metamaterials with novel optical properties. Here, we present a high-throughput nanofabrication technique-soft interference lithography-that combines the ability of interference lithography to produce wafer-scale nanopatterns with the versatility of soft lithography, and use it to create such plasmonic metamaterials. Metal films perforated with quasi-infinite arrays of 100-nm holes were generated over areas greater than 10 cm(2), exhibiting sharp spectral features that changed in relative amplitude and shifted to longer wavelengths when exposed to increased refractive index environments. Moreover, gold nanohole arrays patterned into microscale patches exhibited strikingly different transmission properties; for instance, patches of nanoholes displayed narrow resonances (<14.5 nm full-width-at-half-maximum) that resulted in high refractive index sensitivities far exceeding those reported previously. Soft interference lithography was also used to produce various infinite and finite-area arrays of nanoparticles, including patterns that contained optically distinct particles side by side and arrays that contained both metallic and dielectric materials.     

Preparation of CsI(Tl) for charged particle detection

For packaging CsI(Tl) scintillators, thin aluminum leaf, rather than aluminized Mylar, is used as the reflective entrance window and as a light barrier between crystals. A uniform, thin, diffuse reflective layer on the sides of the crystals is made from a mixture of TiO₂ powder and low-viscosity epoxy.