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Characterization of a tin-loaded liquid scintillator for gamma spectroscopy and neutron detection
Abstract
A tin-loaded liquid scintillator has been developed for gamma spectroscopy and neutron detection. The scintillator was characterized in regard to energy resolution, pulse shape discrimination, neutron light output function, and timing resolution. The loading of tin into scintillators with low effective atomic number was demonstrated to provide photopeaks with acceptable energy resolution. The scintillator was shown to have reasonable neutron/gamma discrimination capability based on the charge comparison method. The effect on the discrimination quality of the total charge integration time and the initial delay time for tail charge integration was studied. To obtain the neutron light output function, the time-of-flight technique was utilized with a ²⁵²Cf source. The light output function was validated with the MCNPX-PoliMi code by comparing the measured and simulated pule height spectra. The timing resolution of the developed scintillator was also evaluated. The tin-loading was found to have negligible impact on the scintillation decay times. However, a relatively large degradation of timing resolution was observed due to the reduced light yield.
... 75) Other elements have been loaded in liquid scintillators mainly applied to search for neutrinoless double beta decay. 10,11) Sn-loaded liquid scintillators have been developed using tetramethyltin 76) or tetra-n-butyltin 77) as the loaded compounds. Similarly, Zr-loaded liquid scintillators have been developed using Zr acetylacetonate, 78,79) tetrakis(isopropyl acetoacetato)zirconium, 79) and tetrakis(ethyl acetoacetato) zirconium 79) as the loaded compounds. ...
Recent development of organic scintillators is reviewed from the viewpoint of materials science. Design and crystal growth of organic crystalline scintillators, use of novel solvents and solutes in liquid scintillators, and development of plastic scintillators based on novel polymer hosts or novel fluorescent molecules are introduced. Additionally, development of loaded liquid or plastic scintillators is reviewed on the basis of two approaches of loading: molecules or nanoparticles. A disadvantage of organic scintillators has been their low scintillation light yields. Hence, materials design for improving scintillation light yields is introduced in detail with description on related excited state dynamics. Finally, future prospect for the improvement of scintillation light yield is briefly given.
... They are generally classified as organic and inorganic scintillators, and the scintillator type used in a radiation detector is selected according to the radiation particles to be measured and the purpose of radiation detection. Organic scintillators are widely used in applications such as high-energy physics, environmental radiation monitoring, and nuclear security because of their relatively short decay time, low material cost, and ability to be easily manufactured in large sizes and various shapes [3,4]. In particular, some organic scintillators, such as stilbene and liquid scintillators, have excellent pulse-shape discrimination (PSD) capabilities to distinguish neutrons from gamma rays while having high sensitivity to both. ...
A method for calibrating the energy scale and detection efficiency of stilbene scintillators is presented herein. This method can be used to quantitatively analyze the Compton continuum of gamma-ray spectra obtained using such scintillators. First, channel–energy calibration was conducted by fitting a semiempirical equation for the Compton continuum to the acquired energy spectrum and a new method to evaluate the intrinsic detection efficiency, called intrinsic Compton efficiency, of stilbene scintillators was proposed. The validity of this method was verified by changing experimental conditions such as the number of sources being measured simultaneously and the detector–source distance. According to the energy calibration, the standard error for the estimated Compton edge position was ±1.56 keV. The comparison of the intrinsic Compton efficiencies calculated from the single- and two-source spectra showed that the mean absolute difference and the mean absolute percentage difference are 0.031 %p and 0.557%, respectively, demonstrating reasonable accuracy of this method. The feasibility of the method was confirmed for an energy range of 0.5–1.5 MeV, showing that stilbene scintillators can be used to quantitatively analyze gamma rays in mixed-radiation fields.
Liquid scintillation (LS) counting is a common way to detect and measure radioactivity because it has a better time resolution and can discriminate between neutrons and gamma rays. We show how to make a promising liquid scintillator with a light-emitting conjugated oligomer: 9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene (ADS038FO or 9HOTF). A container with a LS blend coupled with a photomultiplier detector setup showed enhanced scintillation for different radioactive sources. The gamma and beta radiation responses of LS were studied under various radiation sources: ¹³⁷Cs, ⁶⁰Co, and ²²Na as gamma rays and ⁹⁰Sr as a beta source. We observed a scintillation count increase with an increase in the percentage of 9HOTF. Further studies were performed to evaluate the characteristics of the fabricated liquid scintillator, such as emission wavelength, absorption, Compton edge (CE), and count rate. CE spectra were used to calibrate the energy, and the pulse height spectra were measured for the prepared LSs. The energy linearity was investigated, and the fabricated LSs showed more than 99% energy linearity. According to the results, the CE determined was more than 90% of the theoretical values for the ¹³⁷Cs, ⁶⁰Co, and ²²Na sources. For the ⁹⁰Sr/⁹⁰Y beta source, the pulse height spectrum's lower energy (⁹⁰Sr) and the higher energy (⁹⁰Y) were distinguishable. The comparison between POPOP and 9HOTF-based LS proved that the performance of 9HOTF was marginally better than that of POPOP.
Organometallic chemistry has recently gained a lot of attention in the domain of plastic scintillators. Homogenously dispersed metal complexes in a polymer matrix can afford plastic scintillators with unseen abilities. Heavy atom loading is very attractive as it gives access to plastics with increased sensitivity towards elusive radiations such as gamma and neutron. But this comes with a drawback, as heavy atoms tend to quench fluorescence, hence decreasing the scintillation yield. We present here a comprehensive study of this phenomenon with bismuth and gadolinium complexes. We investigate the influence of the ligand nature by varying organometallic and fluorophore concentration to probe their interaction. We also propose an explanation of the difference in behavior between these two metals. These results were applied to the fabrication of large volume loaded plastic scintillators (>100 cm3). Bismuth loaded scintillators displayed characteristics equivalent to lead loaded commercial materials, and gadolinium samples proved to be able to capture thermal neutrons and release gamma rays.
This article presents the synthesis and the blend of bismuth complexes in polystyrene based plastic scintillators. Specific design has enabled the fabrication of scintillator loaded with up to 17 wt% of bismuth . Tri-aromatic bismuth compounds were used to explore and understand the influence of bismuth loading towards the two main criteria of plastic scintillation: light yield and detection efficiency of γ-rays. For gamma radiation with energy < 200 keV, bismuth loaded scintillators demonstrate the ability to produce photoelectric peak (total absorption peak) on a pulse height spectra. The increase of interactions due to bismuth doping was quantified and fitted with standard models . Finally performances of our bismuth loaded scintillators were evaluated better than commercial lead loaded counterpart.
Polyvinylcarbazole polymer scintillators with high loading of a bismuth organometallic exhibit good light yields, and are found to be capable of gamma-ray spectroscopy. When activated by a standard fluor, diphenylanthracene, a bismuth-loaded polymer produces ~12000 photons/MeV, exhibits an emission maximum at 420 nm, a ~15 ns decay, and energy resolution of 9% at 662 keV is measured. The same bismuth-loaded polymer doped with an iridium complex fluor has an emission maximum of 500 nm, a decay time of 1.2 μs, a light yield of ~30000 photons/MeV, and energy resolution better than 7% FWHM at 662 keV.
Transparent plastic scintillators based on polyvinyltoluene (PVT) have been fabricated with high loading of bismuth carboxylates for gamma spectroscopy, and with lithium carboxylates for neutron detection. When activated with a combination of standard fluors, 2,5-diphenyloxazole (PPO) and tetraphenylbutadiene (TPB), gamma light yields with 15 wt% bismuth tripivalate of 5000 Ph/MeV are measured. A PVT plastic formulation including 30 wt% lithium pivalate and 30 wt% PPO offers both pulse shape discrimination, and a neutron capture peak at ~400 keVee. In another configuration, a bismuth-loaded PVT plastic is coated with ZnS(6Li) paint, permitting simultaneous gamma and neutron detection via pulse shape discrimination with a figure-of-merit of 3.8, while offering gamma spectroscopy with energy resolution of R(662 keV)=15%.
A search for the neutrinoless double-beta decay of 124Sn124Sn was carried out using the tin-loaded liquid scintillator for an active source-detector technique. Tin (32.6%) in weight was successfully loaded into the liquid scintillator, and light output was as high as 57% of the unloaded liquid scintillator. A tin-loaded liquid scintillator with 1.1 ℓℓ volume was installed at the 700 m underground laboratory in YangYang, and data were taken for 5285 h. No evidence for the 0νββ0νββ decay was found and a lower limit on the 124Sn124Sn half-life was obtained to be 2.0×10192.0×1019 year with 90% C.L. The new limit represents a significant improvement with respect to those previously available for 124Sn124Sn.
Pulse shape discrimination capability based on the charge integration has been investigated for liquid scintillator EJ-309. The effectiveness of neutron–γγ discrimination in 4-in. diameter and 3-in. thick EJ-309 cells coupled with 3-in. photomultiplier tubes has been carefully studied in the laboratory environment and compared to the commonly used EJ-301 liquid scintillator formulation. Influences of distortions in pulse shape caused by 13.7-m long cables necessary for some remote operations have been examined. The parameter space for an effective neutron–γγ discrimination for these assays, such as position and width of a gate used for integration of the delayed light, has been explored.
To the aim of development of a spatially resolved x-ray imaging system intended for Inertial Confinement Fusion (ICF) experiments at the Laser Méga Joule (LMJ) facility, new plastic scintillators have been designed. The main characteristics are the following: fast decay time, red emission and good x-rays photoelectric absorption in the range 10–40 keV. These scintillators are synthesized by copolymerization of different monomers with an organometallic compound. In this matrix two fluorescent compounds are embedded, allowing to shift the energy from the UV to the near IR spectrum. Several parameters were studied: fluorophores concentration, nature of the secondary fluorophore and lead concentration. An outstanding effective atomic number of 53 has been reached, for a loading of lead corresponding to 29 wt%. Thus, small cylinders were prepared and their performances under x-ray beam studied and compared with those of inorganic Cerium-doped Yttrium Aluminum Garnet reference scintillator (Y3Al5O12:Ce3+). Eventually, such new scintillators or their next generation could replace expensive and brittle inorganic scintillators, inducing a strong industrial potential.
A charge-integrating ADC has been used to sample the intensity in two different time regions of a pulse and thus to sense the shape of the pulse. This idea has been applied to produce neutron/gamma-ray discrimination from pulses in a liquid scintillation detector. Optimization of available parameters yields good pulse-shape discrimination for pulses greater than those produced by 100 keV electrons. The method uses only general purpose electronics.
In the past few years, efforts to develop new measurement systems to support nuclear nonproliferation and homeland security have increased substantially. Monte Carlo radiation transport is one of the simulation methods of choice for the analysis of data from existing systems and for the design of new measurement systems; it allows for accurate description of geometries, detailed modeling of particle-nucleus interactions, and event-by-event detection analysis. This paper describes the use of the Monte Carlo code MCNPX-PoliMi for nuclear-nonproliferation applications, with particular emphasis on the simulation of spontaneous and neutron-induced nuclear fission. In fact, of all possible neutron-nucleus interactions, neutron-induced fission is the most defining characteristic of special nuclear material (such as U-235 and Pu-239), which is the material of interest in nuclear-nonproliferation applications. The MCNP-PoliMi code was originally released from the Radiation Safety Shielding Center (RSSIC) at Oak Ridge National Laboratory in 2003 [1]; the MCNPX-PoliMi code contains many enhancements and is based on MCNPX ver. 2.7.0. MCNPX-PoliMi ver. 2.0 was released through RSICC in 2012 as a patch to MCNPX ver. 2.7.0 and as an executable [2].
A full characterization of neutron detector properties was achieved by means of a 252Cf source with timing of fission events.The input neutron energies were separated with the time-of-flight technique. The pulse height, the pulse shape and the time-of-flight spectra were measured incoincidence mode as three-dimensional distributions. On the basis of these data, the following characteristics were determined for each detector: response function, light output versus proton (neutron) energy, energy resolution function for neutron energies from 1 to 7 MeV ,time shift correction, and finally the detector efficiency from threshold up to 12 MeV. The experimental results were compared with Monte-Carlo simulations. Two new analytical dependencies are suggested for the light output calculation for electrons and protons.
Tin-loaded liquid scintillator offers some advantages as a detector for double beta decay experiment. A research program was carried out with the objective of developing such scintillators. Several organometals were loaded into pseudocumene-based liquid scintillator (LS) and light output variation was studied. Up to 50% of tetramethyltin (32.6% w of tin) was successfully loaded into LS and light output was as high as 57% of unloaded LS. We have studied the characteristics and stability of the one liter tin-loaded LS contained in a Teflon vessel. Several g-ray radioactive sources were used for energy calibration and calibration data were compared with Monte Carlo simulation. Data-taking at the 700 m underground laboratory in Yangyang is ongoing for the search of 0 nbb decay of 124 Sn.