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Measurement of ortho-Positronium Properties in Liquid Scintillators  [PDF]
S. Perasso,G. Consolati,D. Franco,S. Hans,C. Jollet,A. Meregaglia,A. Tonazzo,M. Yeh
Physics , 2013, DOI: 10.1088/1748-0221/9/03/C03028
Abstract: Pulse shape discrimination in liquid scintillator detectors is a well-established technique for the discrimination of heavy particles from light particles. Nonetheless, it is not efficient in the separation of electrons and positrons, as they give rise to indistinguishable scintillator responses. This inefficiency can be overtaken through the exploitation of the formation of ortho-Positronium (o-Ps), which alters the time profile of light pulses induced by positrons. We characterized the o-Ps properties in the most commonly used liquid scintillators, i.e. PC, PXE, LAB, OIL and PC + PPO. In addition, we studied the effects of scintillator doping on the o-Ps properties for dopants currently used in neutrino experiments, Gd and Nd. Further measurements for Li-loaded and Tl-loaded liquid scintillators are foreseen. We found that the o-Ps properties are suitable for enhancing the electron-positron discrimination.
Positronium signature in organic liquid scintillators for neutrino experiments  [PDF]
D. Franco,G. Consolati,D. Trezzi
Physics , 2010, DOI: 10.1103/PhysRevC.83.015504
Abstract: Electron anti-neutrinos are commonly detected in liquid scintillator experiments via inverse beta decay, by looking at the coincidence between the reaction products, neutron and positron. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in anti-neutrino experiments. Reversing the problem, the o-Ps induced time distortion represents a new signature for tagging anti-neutrinos in liquid scintillator. In this paper, we report the results of measurements of the o-Ps formation probability and lifetime, for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane). We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter. In the second part of the paper, we demonstrate that the o-Ps induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the anti-neutrino detection.
Optical Properties of Quantum-Dot-Doped Liquid Scintillators  [PDF]
C. Aberle,J. J. Li,S. Weiss,L. Winslow
Physics , 2013, DOI: 10.1088/1748-0221/8/10/P10015
Abstract: Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.
Characterization and performances of new indium loaded organic liquid scintillators, based on novel indium carboxilate compounds  [PDF]
I. Barabanov,L. Bezrukov,C. Cattadori,N. Danilov,A. Di Vacri,N. Ferrari,V. Kornoukhov,Y. S. Krylov,N. Nesterova,S. Nisi,E. Yanovich
Physics , 2007,
Abstract: A novel formulation to dope organic liquid scintillators (OLS) with indium at concentrations up to 10% is presented: it is based on specific indium carboxylate compounds adequately synthesized. The produced In-OLS has been characterized: it has light yield 8500 ph/MeV at indium concentration 5.5% and light attenuation length of 2,5 m at wavelength of 430 nm. The scintillator properties were stable during all time of investigation (~ 1 years). The produced In-OLS is compared to other In-OLS formulations and shows superior performances. The developed methodic to metal dope OLS can be easily extended to other metals as Gd, Nd, Cd.
Light propagation and fluorescence quantum yields in liquid scintillators  [PDF]
C. Buck,B. Gramlich,S. Wagner
Physics , 2015, DOI: 10.1088/1748-0221/10/09/P09007
Abstract: For the simulation of the scintillation and Cherenkov light propagation in large liquid scintillator detectors a detailed knowledge about the absorption and emission spectra of the scintillator molecules is mandatory. Furthermore reemission probabilities and quantum yields of the scintillator components influence the light propagation inside the liquid. Absorption and emission properties are presented for liquid scintillators using 2,5-Diphenyloxazole (PPO) and 4-bis-(2-Methylstyryl)benzene (bis-MSB) as primary and secondary wavelength shifter. New measurements of the quantum yields for various aromatic molecules are shown.
A new anti-neutrino detection technique based on positronium tagging with plastic scintillators  [PDF]
G. Consolati,D. Franco,C. Jollet,A. Meregaglia,A. Minotti,S. Perasso,A. Tonazzo
Physics , 2015, DOI: 10.1016/j.nima.2015.06.021
Abstract: The main signature for anti-neutrino detection in reactor and geo-neutrino experiments based on scintillators is provided by the space-time coincidence of positron and neutron produced in the Inverse Beta Decay reaction. Such a signature strongly suppresses backgrounds and allows for measurements performed underground with a relatively high signal-to-background ratio. In an aboveground environment, however, the twofold coincidence technique is not sufficient to efficiently reject the high background rate induced by cosmogenic events. Enhancing the positron-neutron twofold coincidence efficiency has the potential to pave the way future aboveground detectors for reactor monitoring. We propose a new detection scheme based on a threefold coincidence, between the positron ionization, the ortho-positronium (o-Ps) decay, and the neutron capture, in a sandwich detector with alternated layers of plastic scintillator and aerogel powder. We present the results of a set of dedicated measurements on the achievable light yield and on the o-Ps formation and lifetime. The efficiencies for signal detection and background rejection of a preliminary detector design are also discussed.
First-Principles Studies of Luminescence in Ce doped Inorganic Scintillators  [PDF]
A. Canning,A. Chaudhry,R. Boutchko,N. Gr?nbech-Jensen
Physics , 2010, DOI: 10.1103/PhysRevB.83.125115
Abstract: Luminescence in Ce doped materials corresponds to a transition from an excited state where the lowest Ce 5d level is filled to the ground state where a single 4f level is filled. We have performed theoretical calculations based on Density Functional Theory to calculate the ground state band structure of Ce-doped materials as well as the Ce3+ excited state. The excited state calculations used a constrained occupancy approach by setting the occupation of the Ce 4f states to zero and allowing the first excited state above them to be filled. These calculations were performed on a set of Ce doped materials that are known from experiment to be scintillators or non-scintillators to relate theoretically calculable parameters to measured scintillator performance. From these studies we developed a set of criteria based on calculated parameters that are necessary characteristics for bright Ce activated scintillators. Applying these criteria to about a hundred new materials we developed a list of candidate materials for new bright Ce activated scintillators. After synthesis in powder form one of these new materials (Ba2YCl7:Ce) was found to be a bright scintillator. This approach, involving first-principles calculations of modest computing requirements was designed as a systematic, high-throughput method to aid in the discovery of new bright scintillator materials by prioritization and down-selection on the large number of potential new materials.
First-principles study of luminescence in Eu$^{2+}$-doped inorganic scintillators  [PDF]
A. Chaudhry,R. Boutchko,S. Chourou,G. Zhang,N. Gr?nbech-Jensen,A. Canning
Physics , 2014, DOI: 10.1103/PhysRevB.89.155105
Abstract: Luminescence in Eu$^{2+}$ activated materials corresponds to a transition from an excited state where the lowest Eu 5$d$ level is filled with one electron (often called the (Eu$^{2+}$)$^*$ state) to the ground state with half-filled 4$f$ shell with seven electrons of the same spin. We have performed theoretical calculations based on Density Functional Theory to determine the ground state band structure of Eu-doped materials as well as study the (Eu$^{2+}$)$^*$ excited state. Calculations were performed on Eu doped materials, experimentally known to be either scintillators or non-scintillators, in order to relate theoretically calculable parameters to experimentally observed properties. Applying criteria previously developed for Ce-doped systems (A.Canning, A. Chaudhry, R. Boutchko and N. Gr\o{}nbech-Jensen, Phys. Rev. B Vol.83, 125115 (2011)) to new Eu-doped materials we developed a list of candidate materials for new bright Eu activated scintillators. Ba$_2$CsBr$_5$:Eu is an example of a new bright scintillator from our candidate list that has been synthesized in microcrystalline powder form. As discussed in our previous paper on Ce-doped materials this approach was designed as a systematic high-throughput method to aid in the discovery of new bright scintillator materials by prioritization and down-selection on the large number of potential new materials.
Low-Afterglow, High-Refractive-Index Liquid Scintillators for Fast-Neutron Spectrometry and Imaging Applications  [PDF]
Ronald Lauck,Michal Brandis,Benjamin Bromberger,Volker Dangendorf,Mark B. Goldberg,Ilan Mor,Kai Tittelmeier,David Vartsky
Physics , 2009, DOI: 10.1109/TNS.2008.2009449
Abstract: For ion and neutron spectrometry and imaging applications at a high intensity pulsed laser facility, fast liquid scintillators with very low afterglow are required. Furthermore, neutron imaging with fiber (or liquid-core) capillary arrays calls for scintillation materials with high refractive index. To this end, we have examined various combinations of established mixtures of fluors and solvents, that were enriched alternatively with nitrogen or oxygen. Dissolved molecular oxygen is known to be a highly effective quenching agent, that efficiently suppresses the population of the triplet states in the fluor, which are primarily responsible for the afterglow. For measuring the glow curves of scintillators, we have employed the time-correlated single photon counting (TCSPC) technique, characterized by high dynamic range of several orders of magnitude in light intensity. In this paper we outline the application for the fast scintillators, briefly present the scintillation mechanism in liquids, describe our specific TCSPC method and discuss the results.
Temperature dependence of the light yield of the LAB-based and mesitylene-based liquid scintillators  [PDF]
Xia DongMei,Yu BoXiang,Li XiaoBo,Sun XiLei,Ding YaYun,Zhou Li,Cao Jun,Hu Wei,Ye XingCheng,Chen HaiTao,Ding XueFeng,Du Bing
Physics , 2014,
Abstract: We studied the temperature dependence of the light yield of the linear alkyl benzene (LAB)-based and mesitylene-based liquid scintillators. The light yield increases by 23% for both liquid scintillators when the temperature is lowered from $26\;^{\circ}$C to $-40\;^{\circ }$C, correcting for the temperature response of the photomultiplier tube. The measurements help to understand the energy response of the liquid scintillator detectors. Especially, the next generation reactor neutrino experiments for neutrino mass hierarchy, such as the Jiangmen Underground Neutrino Observatory (JUNO), require very high energy resolution. As no apparent degradation on the liquid scintillator transparency was observed, lowering the operation temperature of the detector to $\sim4\;^\circ$C will increase the photoelectron yield of the detector by 13%, combining the light yield increase of the liquid scintillator and the quantum efficiency increase of the photomultiplier tubes.
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