NaI Scintillation Research Articles

Efficiency calibration of LaBr3(Ce) and NaI(Tl) scintillation detectors with MCNP6 for various in-situ measurements for NPP decommissioning purposes

During a decommissioning of nuclear facilities, rapid in-situ methods are highly desirable to support the characterization of material and sites. Mathematical efficiency calibration is suitable for in-situ measurements due to its ability to determine the efficiency for any geometry arrangement without the need to procure expensive calibration standards. During the characterization, the geometry of the measurement can change significantly, so from the dynamics and time-consumption point of view, mathematical calibration is advantageous. Paper presents the efficiency calibration of LaBr3(Ce) and NaI(Tl) detectors with MCNP6 in the range of 59.5–1332.5 keV. These detectors are widely used for in-situ measurements. The relative deviations between the calculated and measured efficiencies were analyzed. The relative deviations are up to 10% throughout the energy spectra, and up to 5% for full energy peak efficiencies. Paper provides instructions on preparation of the model of these detectors in MCNP6 for in-situ soil and concrete measurements.

Determination of the activity concentration of 226Ra, 232Th, 40K and the concentration of 222Rn in soil samples of the Campos Gerais region (Paraná)

In the Campos Gerais region of Paraná there are few literature that evaluate the concentrations of natural radioactivity. Thus, the aim of the present work was to determine activity concentrations of 226Ra, 232Th, 40K and 222Rn concentration in soil samples from Telêmaco Borba, Tibagi, Curiúva, Ventania, Lageado Bonito and Ortigueira. The soil samples, with about 2 kg, were collected on the surface at points near the river bed, making sure that the soil is not under the agriculture influence. Gamma-ray spectrometry analyzes were performed with a NaI(Tl) scintillation detector, with dimensions of 76 mm in diameter, 152 mm in height and 8 cm of lead shield. The 222Rn concentration determinations were performed by means of the sealed can technique, using as track detector a polycarbonate of domestic manufacture. The results obtained for the activity concentration varied from <4.2 ± 1.2 Bq.kg-1 to 290.2 ± 1.7 Bq.kg-1 for the 40K, of 23.3 ± 1.1 Bq. kg-1 to 36.5 ± 1.1 Bq.kg-1 for the 226Ra and from 52.6 ± 1.9 Bq.kg-1 to 70.5 ± 2 Bq.kg-1 for the 232Th. The results for the 222Rn concentration ranged from 4 ± 3 Bq.m-3 to 1147 ± 326 Bq.m-3. Two of the six soil samples presented radon concentrations above the threshold established by the European Commission for Radiological Protection of 200 Bq.m-3, for internal environments. The concentrations of 226Ra and 232Th are within the limits, showing the importance of future investigating the origin of this radon.

Source-detector effective solid angle calculation using MCNP6 code

Nuclear techniques based on the attenuation of gamma radiation are used in the industry to calculate flow rate, determine fluid density, predict inorganic scale in oil pipelines, evaluate industrial mixers, among other applications. In order to use these nuclear techniques is necessary to perform studies of important parameters of radioactive source and radiation detectors, which are part of the measurement geometry, such as detection efficiency and solid angle. The aim of this study is to calculate the solid angle and the effective solid angle subtended by a NaI(Tl) detector. The effective solid angle considers attenuation in the medium (between source and detector) and other effects of radiation interaction with matter. Mathematical models were developed using the MCNP6 code in order to evaluate the proposed measurement geometry. The source was placed in different positions to the detector to evaluate frontal and lateral solid angle contributions, which is an important parameter to obtain the intrinsic efficiency response function. The simulated model consists of a NaI(Tl) scintillator detector and two point isotropic sources (241Am and 137Cs). The results for the geometry used in this study showed that the difference between solid angle and effective solid angle reached 20.17% for 241Am and 2.58% for 137Cs, which means that it is highly recommended to consider the effective solid angle in the calculations.

Use of the Grubbs test to study the homogeneity of a NaI(Tl) detector

The NaI(Tl) detector is one of the most used in gamma ray spectrometry because it presents high counting efficiency for gamma rays in a wide range of energy. The crystal can have a lower efficiency that can be indicated by the effects of its aging by several factors such as: the reaction of sodium iodide with magnesium oxide, absorption of water vapor by crystal, and problems related to photomultiplier. In an experiment, several measures can be take and when a doubt exists between one of the measured values it is possible to use a statistical test. Grubbs test is designed to verify the presence of extreme values in sample observations. This paper presents a methodology that has the objective of evaluating the homogeneity of a NaI(Tl) scintillation detector using the Grubbs test to validated the crystal homogeneity. The study pre-established five differents locations in frontal area of detector where measurements were performed using a 137Cs standard source in order to calculate the standard deviation.

The Future Role of Inorganic Crystal Scintillators in Dark Matter Investigations

Crystal scintillators and in particular inorganic scintillators play an important role in the investigation of Dark Matter (DM) and other rare processes. The investigation of a DM signature, as the annual modulation, or the directionality technique requires the use of highly radiopure detectors able to explore the very low energy region maintaining a high stability of the running conditions. In this paper, the cases of NaI(Tl), ZnWO4 and SrI2(Eu) crystal scintillators are described in the framework of our activities at the Gran Sasso National Laboratory of the INFN. Their role, the obtained results in DM investigation, as well as their potential and perspectives for the future are reviewed.

Development of neutron time-of-flight measurement system for 1.7-MV tandem proton accelerator with lithium target

In this study, we developed a neutron time-of-flight (nTOF) measurement system for a 1.7-MV tandem proton accelerator with a target covered with 300-nm-thick lithium (Li) layer. With implementation of beam chopping module after its ion source, the accelerator is configured to operate in pulsed-beam mode with a pulse width <50 ns at 20-kHz repetition rate. This enables the gamma flash-type nTOF measurement system to identify the neutron generated with 3-MeV proton beam energy. The nTOF system consists of a 3″ cylindrical NaI(Tl) and four stilbene scintillation detectors. The NaI(Tl) scintillator is placed 50 cm from the Li target to measure the time of beam irradiation on the target, and the stilbene detectors are placed 2 and 2.4 m away to measure nTOF at each location. The nTOF system successfully measured the generated neutron energy at irradiated proton energies of 2.6 and 3.0 MeV with an average energy resolution of 15%.

Fabrication, characterization, simulation and experimental studies of the ordinary concrete reinforced with micro and nano lead oxide particles against gamma radiation

The concrete is considered as an important radiation shielding material employed widely in nuclear reactors, particle accelerators, laboratory hot cells and other different radiation sources. The present research is dedicated to the shielding properties study of the ordinary concrete reinforced with different weight fractions of lead oxide micro/nano particles. Lead oxide particles were fabricated by chemical synthesis method and their properties including the average size, morphological structure, functional groups and thermal properties were characterized by XRD, FESEM-EDS, FTIR and TGA analysis. The gamma ray mass attenuation coefficient of concrete composites has been calculated and measured by means of the Monte Carlo simulation and experimental methods. The simulation process was based on the use of MCNP Monte Carlo code where the mass attenuation coefficient (μ/ρ) has been calculated as a function of different particle sizes and filler weight fractions. The simulation results showed that the employment of the lead oxide filler particles enhances the mass attenuation coefficient of the ordinary concrete, drastically. On the other hand, there are approximately no differences between micro and nano sized particles. The mass attenuation coefficient was increased by increasing the weight fraction of nanoparticles. However, a semi-saturation effect was observed at concentrations more than 10 wt%. The experimental process was based on the fabrication of concrete slabs filled by different weight fractions of nano lead oxide particles. The mass attenuation coefficients of these slabs were determined at different gamma ray energies using 22Na, 137Cs and 60Co sources and NaI (Tl) scintillation detector. The experimental results showed that the HVL parameter of the ordinary concrete reinforced with 5 wt% of nano PbO particles was reduced by 64% at 511 keV and 48% at 1332 keV. Reasonable agreement was obtained between simulation and experimental results and showed that the employment of nano PbO particles is more efficient at low gamma energies up to 1Mev. The proposed concrete is less toxic and could be prepared in block form instead of toxic lead blocks.

High count-rate digital gamma-ray spectroscopy using a low-cost COTS digitizer system

A combination of publicly-available digitizers (COTS) has been used in digital gamma-ray spectroscopy in recent years. In this work, a feasibility study was undertaken to use a personal computer (PC) sound card as a digitizer in digital gamma-ray spectroscopy with NaI(Tl) scintillation detector. To this end, the duration of the output pulses of the NaI detector was increased to 300 μs by the preamplifier. Also, the algorithms for correcting and rejecting pile-up events at a low sample rate (96 kHz) were investigated. A new method based on a high-pass filter was developed to detect the pulse start time. Moreover, a new fast-fitting method based on the Integrodifferential equation was introduced, which represented a good performance at a low sample rate. An approximate method of applying the MLE method of long waveforms was also implemented. Wong's method was analytically rewritten assuming that there were more neighbors and it was shown that this result was independent of the assumption of a different number of close neighbors. The performance of these three methods in correcting the energy spectrum of the Cs-137 source, which was disturbed due to the presence of pile-up events and achieving high energy resolution, was compared. Finally, a new method based on the full width at half maximum of preamplifier pulses was also introduced to reject pile-up events.

Building a VME spectrometer and testing Si PIN diode detector: a feasibility study for the first nuclear astrophysical experiments using a pelletron

This work presents the logical design, connections between NIM and VME elec­tronic modules, and the data acquisition programming to build a complete detector readout system. The test experiments were carried out with commercial silicon PIN diode S3590-09 bare detectors bombarded by charged particles from a 241Am α-source and Rutherford elastic backscattering (RBS) protons induced by 2.5 MeV proton beam bombarding on an Au-on-glass target, and with a NaI scintillation detector bombarded by gammas from 27Al(p, γ)28Si reaction with proton beam energy of 1.379 MeV. The test showed that the spectrometer operated steadily and its versatility for different kind of detector. The energy resolutions of the Si diodes were less than 0.5% energy of a charged particle, which satisfies the foreseen requirement for the upcoming experiments.

Моделирование аппаратурных спектров гамма-излучения для упрощенных моделей облака радиоактивного выброса

The paper considers the issues of determining the pulse height spectra of gamma detector from a radioactive cloud. This task is of interest from the point of view of possible improvement of existing systems for monitoring the radiation situation around nuclear power plants and nuclear industry enterprises due to the wider use of gamma-spectrometric equipment. Modeling of pulse height spectra will allow conducting research on the capabilities of monitoring system posts for detecting radionuclides in the radioactive cloud. A general approach to modeling pulse height spectra using division of the radioactive cloud into elementary gamma sources is developed. The pulse height spectra of scintillator NaI ∅63×63 mm are calculated for simplified models of the radioactive cloud in the form of a linear gamma source and a semi-infinite space. The obtained data can be used for rapid estimates of pulse height spectra, while the formulated approach to spectra modeling also allows for more time-consuming calculations for an arbitraryshaped radioactive cloud with an arbitrary radionuclide composition.

In situ determination of 137Cs inventory in soil using a field-portable scintillation gamma spectrometer-dosimeter

A new empirical method for in situ determination of the inventory of 137Cs in soil (ACs, kBq m−2) at grasslands and forests using a field-portable NaI(Tl) scintillation spectrometer-dosimeter was developed. The method is based on evaluation of the ambient dose equivalent build-up factor. The practical implementation of the new method with the spectrometer-dosimeter does not require a priori knowledge of the vertical distribution of 137Cs in soil. Moreover, the method allows assessing a value of the mean migration depth of 137Cs in soil (Z) in terms of g cm−2. The 95% confidence interval for the mean value of the conversion coefficients from the ambient dose equivalent build-up factor to ACs and to Z is less than 10%. The new method has been developed and verified using published data that where obtained at territories in Russia and Belarus heavily contaminated with 137Cs (ACs > 37 kBq m−2) due to the Chernobyl accident. Therefore, the survey of less contaminated areas requires additional validation of this method.

A Passive Shield for the RED-100 Neutrino Detector

A combined passive shield of the RED-100 two-phase emission neutrino detector has been developed and built for suppressing the background of external γ rays and neutrons. The shield is composed of a 5‑cm-thick copper layer (the inner layer is adjacent to the detector) and a water layer with a total thickness of approximately 70 cm (including the water inside the copper shield). The Monte Carlo simulation of the shielding efficiency has been performed. The obtained attenuation factor of the copper shield for the γ-ray background has been experimentally verified in a laboratory test using a NaI(Tl) scintillator detector. The γ‑ray background rejection factor of the full shield has also been calculated.

Transit of the Sun across constellation Libra and variation of secondary gamma radiation flux in the month of October and November, 2020 at Udaipur, India

Background: During transit of the Sun across the constellation Libra in the month of October and November 2020 we experimentally observed the variation of secondary gamma radiation flux (SGR) at Udaipur (270 43’ 12.00”N, 750 28’ 48.01” E), India. We interpret such variation of SGR flux on the basis of gravitational lensing effect produced by the Sun and constellation Libra, radiation from constellation and gravitational pull-on background radiation by constellation Libra and Sun. Objective: The study is to observe secondary gamma radiation flux during transit of the Sun across the constellation Libra. Method: For this experimental study we used ground based NaI (Tl) Scintillation detector. Data were collected around time from 17.0 IST to 17.30 IST on date October 27, 28, 29, 30, 31 and November 2, 4, 6, 11, 12, 13, 14, 2020. The detector was pointed towards the Sun in this whole experimental study. Finding: Analyzed data showed significant variation of secondary gamma radiation flux (SGR) in month of October and November. Novelty: Due to transit of the Sun across the constellation Libra on the surface of Earth secondary gamma radiation flux varies. In the Month of October from 27 October to 31 October secondary gamma radiation flux decreases from 240084 to 230424 while in the month of November from November 2 onward dates up to 12 November the secondary radiation flux increases from 234414 to 242816 and then started to decrease on date 13, 14 November 2020. Keywords: Cosmic radiation; solar radiation; secondary gamma radiation; the Sun; Libra constellation; gravitational pull; radiation from constellation; gravitational lensing effect

Operation of scintillators and SiPMs at high temperatures and their application for borehole logging

Gamma-ray detection is extensively used in borehole logging — a technique widely employed in oil and gas, and mineral exploration. The workhorse of this detection application for many years has been traditional NaI(Tl) scintillators coupled to photo-multiplier tubes (PMTs) which can provide the performance and energy resolution required in this application. PMTs are a well proven technology which can operate in the high temperature conditions (typically of order 100 °C) and pressures (10 MPa) encountered during logging activities. PMTs are, however, fragile in that they incorporate an evacuated tube. They also have a large form factor and require ancillary electronics such as a high-voltage supply meaning they occupy significant space within the borehole probe. It would be advantageous to have a compact replacement to allow additional instruments to be included within the borehole probe. Silicon photo-multipliers (SiPMs) are an attractive PMT replacement since they are robust, compact and operate at low voltage. However, SiPMs suffer from dark current which increases rapidly with temperature leading to increased noise and degraded energy resolution. We have evaluated CsI(Tl) scintillators coupled to standard 6 × 6 mm2 SiPMs from Hamamatsu and SensL as a function of temperature. We have shown that these prototypes operate effectively up to a temperature of 80 °C which could satisfy the requirements of some applications of borehole logging where the maximum temperature encountered is 75 °C.

A preliminary investigation on gamma-rayattenuation of alkali-activated concrete waste based-geopolymer modified with pozzocrete-fly ash

In the current investigation, pozzocrete fly ash (PFA) was employed to assess its effects on physical, mechanical and radiation shielding properties of alkali-activated geopolymer mixtures prepared using calcined concrete waste-based dolomite aggregate (DCW). Two series of geopolymer samples comprising 6% and 10% sodium hydroxide as alkaline activator were designed. Concrete waste was partially substituted by PFA at levels of 0%, 10%, 15%, 20% and 30%, by weight. Bulk density, compressive strength, attenuation coefficients (μ & μm) as well gamma transmission factors (half-value layer, HVL; tenth-value layer, TVL and mean free path, MFP) of studied samples were determined at different hydration times. The gamma attenuation coefficients of the blend were experimentally conducted with NaI (Tl) scintillation detector utilizing radiation sources namely Cs-137 with photon energy of 0.662 MeV and Co-60 with photon energies of 1.173 and 1.333 MeV. The inclusion of 15% PFA in DCW-geopolymer system alkali-activated with 10% NH has resulted in the enhancement of both physical and mechanical properties. In a similar fashion, this geopolymer composite demonstrated superior performance in terms of attenuation of gamma rays through a 5 cm thickness shield over the corresponding mixtures.

Analysis of radioactive cesium-enriched particles and measurement of their distribution in marine sediment near Fukushima Daiichi nuclear power plant

ABSTRACT Cesium-enriched particles released from the Fukushima Daiich Nuclear Power Plant (NPP1) exist in the Fukushima coastal waters and offshore, and they possibly affect the wide-area distribution of the radioactive cesium measured by the towed spectrometer. Therefore, the distribution of them in marine sediment was measured near NPP1 in November, 2016. We scanned the seafloor using a remotely operated vehicle (ROV) equipped with a NaI(Tl) scintillation detector. The sediment samples were obtained on the survey line by the ROV’s suction-type sampler. Five cesium particles, with diameters of approximately 400 m, were isolated from the samples. The radioactivity of was less than 360 Bq, and no nuclides other than , , and natural radioactive ones were found from gamma-ray spectroscopy. In the particles, titanium and calcium were commonly detected by energy-dispersive X-ray spectrometry. We also estimated the particles’ presence from the change in the total counting rate of the scintillation detector. The average particle density is found to be 3.45 m at most. The average increase in the counting rate directly above the cesium-enriched particles in the sediment was less than double. Therefore, the effect of such particles on the distribution of radioactive cesium is limited.

Development and performance evaluation of large-area hybrid gamma imager (LAHGI)

We report the development of a gamma-ray imaging device, named Large-Area Hybrid Gamma Imager (LAHGI), featuring high imaging sensitivity and good imaging resolution over a broad energy range. A hybrid collimation method, which combines mechanical and electronic collimation, is employed for a stable imaging performance based on large-area scintillation detectors for high imaging sensitivity. The system comprises two monolithic position-sensitive NaI(Tl) scintillation detectors with a crystal area of 27 × 27 cm2 and a tungsten coded aperture mask with a modified uniformly redundant array (MURA) pattern. The performance of the system was evaluated under several source conditions. The system showed good imaging resolution (i.e., 6.0–8.9° FWHM) for the entire energy range of 59.5–1330 keV considered in the present study. It also showed very high imaging sensitivity, successfully imaging a 253 μCi 137Cs source located 15 m away in 1 min; this performance is notable considering that the dose rate at the front surface of the system, due to the existence of the 137Cs source, was only 0.003 μSv/h, which corresponds to ∼3% of the background level.

Decrement of secondary gamma radiation flux during lunar eclipse June 16, 2011

The lunar eclipse at Udaipur (27◦ 43’ 12.00” N, 75◦ 28’ 48.01” E), India was experimentally observed on June16, 2011 using ground based NaI (Tl) Scintillation detector. We interpret such decrement of secondary gamma radiation flux (SGRF) on the basis of obstruction effect produced by Earth and Moon during lunar eclipse on radiation. Objective: To observe secondary gamma radiation flux during lunar eclipse day on comparison to pre and post eclipse days. Methods: For this experimental study we used ground based NaI (Tl) Scintillation detector. The data files were stored in computer for thirty minutes duration from 1.00 AM to 2.00 AM (Indian Time) on pre-eclipse normal days June 14 and 15, 2011 as well as on post eclipse normal day June 17 and also on eclipse day June 16, 2011. Finding: The analyzed data reveal significant decrement of secondary gamma radiation flux (SGRF) on lunar eclipse day about 6% on comparison to pre and post lunar eclipse days. Novelty: In this experimental study first time we reported about 6% decrement of secondary gamma radiation flux on lunar eclipse day on comparison to pre and post lunar eclipse days. Keywords: Lunar eclipse; cosmic radiation; reflected solar radiation; secondary gamma radiation; obstruction effect by Earth and Moon

Experimental evaluation of the GE NM/CT 870 CZT clinical SPECT system equipped with WEHR and MEHRS collimator.

PurposeA high‐energy‐resolution whole‐body SPECT‐CT device (NM/CT 870 CZT; C‐SPECT) equipped with a CZT detector has been developed and is being used clinically. A MEHRS collimator has also been developed recently, with an expected improvement in imaging accuracy using medium‐energy radionuclides. The objective of this study was to compare and analyze the accuracies of the following devices: a WEHR collimator and the MEHRS collimator installed on a C‐SPECT, and a NaI scintillation detector‐equipped Anger‐type SPECT (A‐SPECT) scanner, with a LEHR and LMEGP.MethodsA line phantom was used to measure the energy resolutions including collimator characteristics in the planar acquisition of each device using 99mTc and 123I. We also measured the system's sensitivity and high‐contrast resolution using a lead bar phantom. We evaluated SPECT spatial resolution, high‐contrast resolution, radioactivity concentration linearity, and homogeneity, using a basic performance evaluation phantom. In addition, the effect of scatter correction was evaluated by varying the sub window (SW) employed for scattering correction.ResultsThe energy resolution with 99mTc was 5.6% in C‐SPECT with WEHR and 9.9% in A‐SPECT with LEHR. Using 123I, the results were 9.1% in C‐SPECT with WEHR, 5.5% in C‐SPECT with MEHRS, and 10.4% in A‐SPECT with LMEGP. The planar spatial resolution was similar under all conditions, but C‐SPECT performed better in SPECT acquisition. High‐contrast resolution was improved in C‐SPECT under planar condition and SPECT. The sensitivity and homogeneity were improved by setting the SW for scattering correction to 3% of the main peak in C‐SPECT.ConclusionC‐SPECT demonstrates excellent energy resolution and improved high‐contrast resolution for each radionuclide. In addition, when using 123I, careful attention should be paid to SW for scatter correction. By setting the appropriate SW, C‐SPECT with MEHRS has an excellent scattered ray removal effect, and highly homogenous imaging is possible while maintaining the high‐contrast resolution.

Design of nuclear radiation detector for stack exhaust of plasma melting system

The Plasma melting technology can reduce the low and medium level radioactive waste to a minimum. The emission of high-temperature radioactive aerosol generated in the process of treatment needs to be monitored. After treatment with a high efficiency filter and meeting national standards for gaseous effluents, it will be allowed to be discharged into the atmosphere. In order to achieve stable and reliable radiation monitoring, through the research on the radionuclide analysis of stack exhaust and the design of detector selection, the combined design of plastic scintillator &amp; NaI scintillator is adopted. At the same time, the real-time and reliable monitoring of radioactive aerosols in stack gases under high temperature environment is also solved.