Tl Crystals Research Articles

Signals features extraction in liquid-gas flow measurements using gamma densitometry. Part 1: time domain

Knowledge of the structure of a flow is really significant for the proper conduct a number of industrial processes. In this case a description of a two-phase flow regimes is possible by use of the time-series analysis e.g. in frequency domain. In this article the classical spectral analysis based on Fourier Transform (FT) and Short-Time Fourier Transform (STFT) were applied for analysis of signals obtained for water-air flow using gamma ray absorption. The presented method was illustrated by use data collected in experiments carried out on the laboratory hydraulic installation with a horizontal pipe of 4.5 m length and inner diameter of 30 mm equipped with two 241Am radioactive sources and scintillation probes with NaI(Tl) crystals. Stochastic signals obtained from detectors for plug, bubble, and transitional plug – bubble flows were considered in this work. The recorded raw signals were analyzed and several features in the frequency domain were extracted using autospectral density function (ADF), cross-spectral density function (CSDF), and the STFT spectrogram. In result of a detail analysis it was found that the most promising to recognize of the flow structure are: maximum value of the CSDF magnitude, sum of the CSDF magnitudes in the selected frequency range, and the maximum value of the sum of selected amplitudes of STFT spectrogram.

Comparative Studies of CsI(Tl), LYSO and BGO Scintillators

Inorganic scintillators of CsI(Tl), LYSO and BGO crystals were characterized using photomultiplier tube R1306 PMT readout for gamma ray detection. The photoelectron yield, light yield and photofraction were measured at gamma energies in range 59.5 keV to 1332 keV. It is found that the photoelectron yield of LYSO is much better than that of CsI(Tl) and BGO crystals. CsI(Tl) crystal showed the high light yield of 63855.25 ph/MeV in this energy range, which is better than that of LYSO and BGO crystals. The photofraction for all crystals was determined and compared with the cross-section ratio for the photoelectric effect to the total one which calculated by WinXCom program.

First experiment with the NUSTAR/FAIR Decay Total Absorption [formula omitted]-Ray Spectrometer (DTAS) at the IGISOL IV facility

The new Decay Total Absorption Spectrometer (DTAS) has been commissioned with low energy radioactive beams at the upgraded IGISOL IV facility. The DTAS is a segmented detector composed of up to 18 NaI(Tl) crystals and it will be a key instrument in the DESPEC experiment at FAIR. In this document we report on the experimental setup and the first measurements performed with DTAS at IGISOL. The detector was characterized by means of MC simulations, and this allowed us to calculate the response function of the spectrometer and analyse the first cases of interest.

A new 4π(LS)-γ coincidence counter at NCBJ RC POLATOM with TDCR detector in the beta channel

A new 4π(LS)-γ coincidence system (TDCRG) was built at the NCBJ RC POLATOM. The counter consists of a TDCR detector in the beta channel and scintillation detector with NaI(Tl) crystal in the gamma channel. The system is equipped with a digital board with FPGA, which records and analyses coincidences in the TDCR detector and coincidences between the beta and gamma channels. The characteristics of the system and a scheme of the FPGA implementation with behavioral simulation are given. The TDCRG counter was validated by activity measurements on 14C and 60Co solutions standardized in RC POLATOM using previously validated methods.

Back-thinning process research and characteristics measurement of thin sensor

It is important to develop a thin silicon detector using a large silicon wafer to reduce multiple Coulomb scattering and the material budget. A Si-CsI detector in a large acceptance multi-purpose spectrometer (LAMPS) is considered to identify isotopes. The thickness of the first of three silicon sensors in front of the CsI(Tl) crystal is 100 μm. We aim to establish a manufacturing process for thinning using a 6-inch silicon wafer that provides the characteristics of a photodiode. In this paper, we present a back-thinning process of the photodiode, and comparisons of its electrical characteristics and signal-to-noise ratios before and after the thinning process.

New electronics of the spectrometric channel for the SND detector electromagnetic calorimeter

The Spherical Neutral Detector (SND) is intended for study of electron–positron annihilation at the VEPP-2000 e+e− collider (BINP, Novosibirsk) in the center-of-mass energy region below 2GeV. The main part of the detector is a three-layer electromagnetic calorimeter based on NaI(Tl) crystals. The physics program of the SND experiment includes a high statistics study of neutron–antineutron production near threshold, for which time measurements in the calorimeter are required. In this paper we describe new shaping and digitizing calorimeter electronics, which allow to reach a time resolution of about 1ns for 100MeV signal and an amplitude resolution of about 250keV.

Search for a new Li-based scintillator for neutron detection

Li-based scintillators are promising candidates for thermal neutron detection due to the presence of 6Li nuclei in the host lattice. In this study, pure and doped lithium iodide (LiI) crystals are grown by using the two-zone vertical Bridgman technique with diameters of ~1 cm and lengths of ~4 cm. The crystals were doped with Na, CO3 and Tl activators with the aim to develop a scintillator having enhanced neutron detection efficiency. Among the grown crystals, LiI(Tl) showed the highest luminescence intensity under X-ray excitation. The LiI(Tl) crystal exhibited a broad emission spectrum between 300 and 700 nm peaking at 470 nm. Under γ-ray excitation, The LiI(Tl) crystal showed two decay-time components of 180 ns and 900 ns, respectively. The response of the LiI(Tl) crystal to spallation neutrons and the radiation damage effects were determined at the Korea Multi-purpose Accelerator Complex (KOMAC). A clear neutron capture peak was measured at 3 MeVee under spallation-neutron irradiation.

In situ gamma ray survey for geological mapping of Kmetasomatized metavolcanics at Bükkszentkereszt, Bükk Mts, Hungary

Abstract The Middle-Upper Triassic Bagolyhegy Metarhyolite Formation of the Bükk Mts. (Hungary) hosts silicified bodies with high potassic feldspar content formed by Kmetasomatism. The rocks underwent a multistage deformation history including syn- and postmetamorphic folding and faulting. As the outcrop area is covered by soil and debris with some exposed silicified cliffs only, and potassium content is a characteristic feature of the metasomatized rocks, geological mapping was supported by a spectral gamma ray survey with a scintillation detector of NaI(Tl) crystal. A thunderstorm felling the beech forest made the soil horizon B also accessible in several pits, providing the opportunity to make measurements on the weathered debris instead of the topsoil (horizon A). Measurements in different arrangements were designed to test the effects of measuring time, measuring geometry and soil horizon. Our results show that concentration values obtained on the debris with a 2 min measuring time can be compared with those measured on exposed rock surfaces, producing a more reliable geological map than measurements on the topsoil with randomly variable K depletion. Pit geometry effects can be eliminated by the K/(eU+eTh) ratio. This results in a more realistic K distribution map if neither U nor Th enrichments are present. The survey successfully delineated the unexposed outcrop of K-enriched rocks on the survey area.

Optimal design of a CsI(Tl) crystal in a SiPM based compact radiation sensor

In this study, a compact radiation sensor for integration into mobile applications is proposed consisting of a CsI(Tl) crystal and a silicon photomultiplier with a 3 × 3 mm2 active area. Considering the size limit of mobile devices, the optimal size of the CsI(Tl) crystal was determined so that it has the best figure of merit (the absolute detection efficiency over the relative energy resolution) in the gamma energy spectrum while satisfying the criteria for the uniformity of the angular response. The final suggested dimensions consist of a cylindrically shaped crystal with a diameter of 5 mm, a total length of 5 mm and a tapered head length of 1 mm.

Compton background suppression with a multi-element scintillation detector using high speed data acquisition and digital signal processing

A multi-element scintillation detector, consisting of eight NaI(Tl)/BGO scintillators surrounding a single NaI(Tl)/CsI(Tl) scintillator, was initially developed for locating and measuring concealed special nuclear materials that emit primarily low energy photons. Signal digitizers and LabView virtual instrument (VI) subroutines process and analyze pulses from each of the dual scintillators to suppress Compton interactions occurring in the central detector and discriminate between low and high energy photon events occurring within NaI(Tl) and CsI(Tl) crystals, respectively. Digital signal processing significantly improved the signal-to-noise ratio of the central detector and greatly reduced the analog electronic equipment required in the same time.

Pulse-shape discrimination between electron and nuclear recoils in a NaI(Tl) crystal

We report on the response of a high light-output NaI(Tl) crystal to nuclear recoils induced by neutrons from an Am-Be source and compare the results with the response to electron recoils produced by Compton scattered 662 keV $\gamma$-rays from a $^{137}$Cs source. The measured pulse-shape discrimination (PSD) power of the NaI(Tl) crystal is found to be significantly improved because of the high light output of the NaI(Tl) detector. We quantify the PSD power with a quality factor and estimate the sensitivity to the interaction rate for weakly interacting massive particles (WIMPs) with nucleons, and the result is compared with the annual modulation amplitude observed by the DAMA/LIBRA experiment. The sensitivity to spin-independent WIMP-nucleon interactions based on 100 kg$\cdot$year of data from NaI detectors is estimated with simulated experiments, using the standard halo model.

Numerical Simulation of Terrestrial Radiation over a Snow Cover

AbstractThe intensity of terrestrial gamma radiation is a function of a number of parameters: emissivity and spatial distribution of the radioactive material in the soil, snow/water cover above ground, soil moisture content, type, and height above ground of the detector. Thus, the conversion of gamma measurements into reliable information must be based on a solid knowledge of the behavior of the gamma detector under different conditions. Such a detector, using a cylindrical NaI(Tl) crystal, was developed to remotely and automatically provide information on snow water equivalent (SWE) and soil moisture content (M). It became rapidly obvious that the behavior of the detector [gamma monitor (GMON)] over an infinite source could not be exactly reproduced in a laboratory. Therefore, a relatively simple model to simulate the behavior of GMON and to establish the relevant data analysis algorithms was conceived. This paper presents the basic assumptions for developing the model, the resulting algorithms, a comparison with field measurements, and some useful information on how GMON reacts to various field conditions.

Studying the D(p, γ)3He reaction in zirconium deuteride within the proton energy range of 9–35 keV

This work is dedicated to measuring the dependences of the effective cross section and the astrophysical S factor for the pd reaction that proceeds in zirconium deuteride upon the proton-deuteron collision energy within a range of 6.0–23.3 keV. The experiment was performed using the heavy-current plasma Hall accelerator at the National Research Tomsk Polytechnic University. The gamma quanta produced in the pd reaction with the energy of 5.5 MeV was recorded using eight scintillation spectrometers based on NaI(Tl) crystals (400 × 100 × 100 mm), which were located around the target. The result of this work coincides with the result of our previous work obtained within a range of proton-deuteron collision energies of 7.3–12.7 keV and agrees well with the result obtained by the LUNA collaboration with the use of the gaseous deuterium target.

Timing characteristics of Ce doped Gd3Ga3Al2O12 single crystals in comparison with CsI(Tl) scintillators

Single crystals of Gd3Ga3Al2O12:Ce with B codopants were successfully grown using the Czochralski technique. The timing characteristics of the crystal was measured by coupling the crystal to photomultiplier tubes (PMT) or silicon photodiodes [Si(PIN)]. The two prompt γ‐rays emitted in a cascade from 60Co or 22Na source were detected in coincidence using Gd3Ga3Al2O12:Ce,B crystal detectors and a BaF2 detector. The time resolution of these crystals are observed to be better than that measured for CsI:Tl crystal coupled to PMT or Si(PIN) in an identical measurement setup.

Three-Dimensional Event Localization in Bulk Scintillator Crystals Using Optical Coded Apertures

Scintillator-based detectors are among the most commonly used methods for detecting ionizing radiation. Scintillators provide a reliable, cost-effective, and simple way to make large-volume detectors. Furthermore, localizing the position of the interactions in three dimensions within the crystals is useful to a wide array of fields. The most straightforward way of doing this is to pair the crystal with a position-sensitive phototransducer (PT). This allows for measurement of the shape of the light spot at the PT plane. Using this information, various methods exist to localize the gamma-ray interaction in the crystal; however, the position resolution worsens the farther the event occurs from the PT plane. To improve on the localization ability, this work uses an optical coded-aperture shadow mask between the crystal and the PT. The recorded detector response is used in reconstructing the event over the entire depth of the crystal, and the “sharpest” reconstructed image gives an event’s depth. The lateral position is given from the standard coded-aperture image reconstruction. Experimental results obtained by emulating a 26-mm-thick crystal using a thin 1-mm-thick NaI(Tl) crystal and different amounts of light pipe between the crystal and the PT plane achieved $\sim $ 1 to 2-mm resolution in all three dimensions throughout most of the 26-mm-thick crystal.

Detection system of the COMBAS fragment separator

The (ΔE1, ΔE2, E) multidetector telescope has been developed and tested. The telescope is a compact combination of two 32-strip silicon ΔE1-, ΔE2-detectors and a scintillation E-detector, which is a 3 × 3 array of CsI(Tl) crystals. A timing signal can be obtained from any of the Si detectors for time-of-flight (TOF) measurements. Single-channel and 32-channel charge-sensitive preamplifiers have been developed and manufactured for the multidetector module to serve the ΔE- and E-detectors with high efficiency and sensitivity. Reaction products obtained in the 40Ar (35 MeV/nucleon) + 9Be reaction have been unambiguously identified in the experiment by mass number A and atomic number Z.

Measurement of intrinsic radioactive backgrounds from the 137Cs and U/Th chains in CsI(Tl) crystals**Supported by National Natural Science Foundation of China (11275107, 11175099)

The inorganic CsI(Tl) crystal scintillator is a candidate anti-compton detector for the China Dark matter Experiment. Studying the intrinsic radiopurity of the CsI(Tl) crystal is an issue of major importance. The timing, energy and spatial correlations, as well as the capability of pulse shape discrimination provide powerful methods for the measurement of intrinsic radiopurities. The experimental design, detector performance and event-selection algorithms are described. A total of 359×3 kg-days data from three prototypes of CsI(Tl) crystals were taken at China Jinping Underground Laboratory (CJPL), which offers a good shielding environment. The contamination levels of internal isotopes from 137Cs, 232Th and 238U series, as well as the upper bounds of 235U series are reported. Identification of the whole α peaks from U/Th decay chains and derivation of those corresponding quenching factors are achieved.

Investigation of ion induced damage in KBr, YAG:Ce, CaF2:Eu and CsI:Tl irradiated by various-energy protons

New experimental results on the scintillation processes for KBr, YAG:Ce, CaF2:Eu and CsI:Tl crystals under H2+ irradiation for the energy range of 600-2150 keV/u are systematically reported. The scintillation light yield was measured as a function of accumulated particle fluence at the rare isotope ReAccelerator (ReA) facility of the National Superconducting Cyclotron Laboratory (NSCL). The data indicates that YAG:Ce and CsI:Tl can maintain stable luminescence under continuous ion bombardment for at least a total fluence of 1.8×1012 ions/mm2 in the energy range used for this experiment. On the other hand, the luminescence of CaF2:Eu shows a rapid initial decay but then maintains a nearly constant luminescence yield. The extraordinary scintillation response of KBr is initially enhanced under ion bombardment, approaches a maximum, and then eventually decays. The scintillation efficiency of the CsI:Tl scintillator is superior to the other materials. The stability of the measured beam profile width deducted from the different scintillator materials in static beam conditions was also investigated as a function of irradiation time. We observed that the low-energy H2+ bombardment (25 keV/u) on the YAG:Ce scintillator can lead to the significant degradation of the scintillation yields. Different scintillation degradation responses for the low- and high-energy bombardments can be attributed to the transmission loss of the emitted light inside the crystal caused by displacement damages.

IPhos, a new technique for the CALIFA CsI(Tl) calorimeter

Within this paper we will present an entirely new energy reconstruction method iPhos for charged particles detected in CsI(Tl) crystals. Based on pulse shape analysis of CsI(Tl) scintillation signals [1] protons that cannot be stopped within the active detector material can be distinguished from those fully stopped. Due to a special signature of punch-through protons, they can be identified and their full energy is reconstructed from their specific energy loss. In a dedicated experiment at the Cyclotron Center Bronowice, Krakow the first proof of this method was achieved.

Application of the Hilbert Transform to measurements of liquid–gas flow using gamma ray densitometry

Measuring parameters of two-phase flows usually requires contactless measuring techniques to be used together alongside advanced methods of signal processing. One of these techniques, which has been employed for many years in measurements of liquid–gas, liquid–solids and gas–solid flows is a method of gamma-ray densitometry. Frequently in such measurements mutually delayed stochastic signals are received from the scintillation detectors. For the analysis of such signals a well-known cross-correlation function (CCF) is used due to the random nature of the signals and the presence of disturbances.This paper applies the Hilbert Transform to the time delay estimation in measurements of two-phase flow performed by using gamma-ray absorption. It presents the selected results of study of the modified CCFHT cross-correlation method, in which a Hilbert Transform of one measured signal is used. The experiments have been carried out for two-phase water–air flow through a horizontal pipeline of 30mm inner diameter. A sealed 241Am gamma ray source of 59.5keV energy has been used in the experiments mentioned above, together with scintillation detectors based on NaI(Tl) crystals. Based on obtained values of time delay the mean velocity of gaseous phase transported by liquid was calculated. It is stated, that the CCFHT method provides better metrological properties than the classical CCF. In the presented experiments combined uncertainties of the gas phase average velocity did not exceed 3.1% for CCF and 0.05% for CCFHT.