Photodiode readout and pulse shape analysis of CsI(Tl) scintillator signals

The light output performance of CsI(Tl) scintillators coupled directly or via wavelength shifters to a photodiode is investigated. Using a photodiode readout system, the zero-crossing technique of pulse shape analysis has been employed to identify gammas, neutrons and charged particles (p, d, t, α) with a low energy threshold.     

Temperature dependence of pure CsI: scintillation light yield and decay time

The temperature dependence of the light emission for pure CsI crystals has been measured with photomultipliers, and photodiodes with wavelength shifters from 80–300 K. The light yield at 80 K is N_γ=50,000±5000 photons/MeV. This number was deduced from the number of electron–hole pairs produced in the photodiode, N_eh=39,600±1200. The light yield at room temperature is lower by a factor of 15.8±1.0, giving 3200±400 photons/MeV. Decay times were measured with a photomultiplier. At room temperature two fast decay components were observed with decay times of 6±1 and 28±2 ns. Below 180 K only one component is observed and at 80 K the decay time is 1015±17 ns.     

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.     

退火温度对CsI(Tl)薄膜微观结构和闪烁性能的影响

采用真空热蒸发法制备了CsI(Tl)薄膜, 然后进行了不同温度的真空热处理．用X射线衍射仪、扫描电子显微镜、X射线荧光光谱仪及正电子寿命谱仪对CsI(Tl)薄膜样品进行了分析, 并测得了样品的光产额．结果表明, 该CsI(Tl)薄膜沿(200)晶面择优取向生长．经过较低温度退火, CsI薄膜中的Tl⁺离子向薄膜表面扩散, 薄膜中缺陷数量增加, 且尺寸较大, 光产额略微增高．经过250℃退火, 薄膜中低温退火所形成缺陷得到恢复, 薄膜缺陷尺寸变小, 且数目减少, 具有较好的结晶状态, 光产额提高．经过400℃退火, 薄膜结构发生显著变化, 薄膜中缺陷大幅增加, 结晶状态变差, Ti+含量减少, 光产额急剧下降．     

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     

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.     

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.     

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.     

The use of silicon photodiodes in a CsI(Tl) calorimeter

The properties of silicon photodiodes and low-noise preamplifiers have been studied. The selection of optimal operating parameters for the use of photodiodes in a CsI shower detector is discussed.     

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.     

Effect of a nonuniform magnetic field on the time of longitudinal relaxation T 1 of a flowing liquid

The behavior of the time of longitudinal relaxation T₁ for a flowing liquid in the strong nonuniform magnetic field of the magnet polarizer of a nuclear-magnetic-resonance (NMR) flow meter is studied theoretically and experimentally. An increase in the nonuniformity of this field reduces T₁. The magnitude and nonuniformity of the field have an optimum whose criterion is the signal/noise ratio in the recording scheme for the NMR signal and the weight and dimension characteristics of the instrument. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 819–822, July–August, 2000.     

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.     

Resolution tests of CsI(Tl) scintillators read out by pin diodes

Cylindrical CsI(Tl) scintillators of 38 mm diameter and 100 mm length read out with PIN diodes of 400 mm² area were tested with respect to their response to medium energy light particles (p, d, t, α). Resolutions of better than 1% were achieved for 50 MeV protons and 90 MeV α-particles. For many crystals the resolution was found to be limited to 2–3% by local crystal nonuniformities which caused variations of the light output efficiency of several percent. A bench test is described which allows the detection of inhomogeneities to better than 0.5% accuracy. The quality of particle identification obtained with ΔE-E and pulse shape discrimination techniques are investigated as a function of count rate.     

Effect of impurity levels on the structure of solidified aluminum under pulse magneto-oscillation (PMO)

The effect of pulse magneto-oscillation (PMO) treatment on the solidified structure and the cooling curves of pure aluminum samples of two grades were investigated. The PMO treatment leads to decrease in the supercooling level and to refinement of the solidified structure. The effect of the PMO treatment strongly depends on the purity level of aluminum. A model is proposed to explain the effect of the PMO treatment on the structure of solidified metals.     

ZnO nanowire-based nano-floating gate memory with Pt nanocrystals embedded in Al(2)O(3) gate oxides

The memory characteristics of ZnO nanowire-based nano-floating gate memory (NFGM) with Pt nanocrystals acting as the floating gate nodes were investigated in this work. Pt nanocrystals were embedded between Al(2)O(3) tunneling and control oxide layers deposited on ZnO nanowire channels. For a representative ZnO nanowire-based NFGM with embedded Pt nanocrystals, a threshold voltage shift of 3.8?V was observed in its drain current versus gate voltage (I(DS)-V(GS)) measurements for a double sweep of the gate voltage, revealing that the deep effective potential wells built into the nanocrystals provide our NFGM with a large charge storage capacity. Details of the charge storage effect observed in this memory device are discussed in this paper.     

Effect of UV radiation on the behavior of CsI radioaerosols in the gas phase

¹³⁷Cs¹³¹I radioactive aerosols formed upon evaporating CsI from a Pt support to an Ar atmosphere or air under UV irradiation or without it are studied. Without UV radiation, the degree of localization of the aerosols in a bubbler filled with aqueous Na₂S₂O₃ varies from 30% in argon to 60% in air. In sublimation of ¹³⁷Cs¹³¹I from the Pt heater, a considerable amount of nanoparticles is formed, which are not absorbed by the aqueous solution in the bubbler and are even capable of penetrating through a combined filter fabricated from a Petryanov filter and a “White Ribbon” paper filter. In the Ar atmosphere, the conversion of CsI is minimal, being initiated by traces of oxygen and moisture, as demonstrated by data on the Cs/I ratio in various fractions. In both Ar and air, UV radiation increases the localization of the radionuclides in the bubblers, simultaneously decreasing practically by half the amount of ¹³⁷Cs penetrating across the combined filter. Evidently, this is due to the fact that photoactivation promotes coarsening of nanoparticles through self-agglomeration or interaction with some coarser aggregates. A conclusion is made that UV radiation affects essentially the kinetics of aggregation of the aerosols in the gas phase, but not the rate of the chemical reactions occurring in the gas phase with participation of the aerosols.