Pulse Shape Discrimination Capability Research Articles

Polystyrene-based scintillator with pulse-shape discrimination capability

Polystyrene-based scintillators with 2-phenyl-5-(4-tert-butylephenyl)-1,3,4-oxadiazole (tert-BuPPD) or 2,5-di-(3-methylphenyl)-1,3,4 oxadiazole (m-DMePPD) are proposed for pulse-shape n/γ-discrimination. These scintillators have improved mechanical properties, long operational time and high n/γ discrimination parameter – figure of merit (1.49 and 1.81 in a wide energy region), so they can be used as detectors of fast neutrons in the presence of gamma radiation background.

Neutron response characterization for an EJ299-33 plastic scintillation detector

Organic scintillation detectors have shown promise as neutron detectors for characterizing special nuclear materials in various arms-control and homeland-security applications. Recent advances have yielded a new plastic scintillator – EJ299-33 – with pulse-shape-discrimination (PSD) capability. Plastic scintillators would have a much-expanded range of deployment relative to liquids and crystals. Here, we present a full characterization of pulse-height response to fission-energy neutrons for an EJ299-33 detector with 7.62-by-7.62-cm cylindrical active volume, and compare with an EJ309 liquid scintillator in the same assembly. Scintillation light-output relations, energy resolutions, and response matrices are presented for both detectors. A continuous-spectrum neutron source, obtained via the bombardment of 27Al with 7.44-MeV deuterons at the Edwards Accelerator Facility at Ohio University, was used for the measurement. A new procedure for evaluating and comparing PSD performance is presented which accounts for the effect of the light-output relation on the ability to detect low-energy neutrons. The EJ299-33 is shown to have considerable deficit in matrix condition, and in PSD figure of merit when compared to EJ309, especially when neutron energy is taken into account. Nevertheless the EJ299 is likely to bring a modest PSD capability into a array of field applications that are not accessible to liquids or crystals.

Boron-loaded plastic scintillator with neutron-γ pulse shape discrimination capability

Development of the plastic scintillator with neutron sensitivity from thermal to multi-MeV and pulse shape discrimination (PSD) has been demonstrated. Incorporation of 10B-containing compounds into the plastic scintillator with PSD capability leads to detector improvement in regard to neutron detection efficiency while preserving the discrimination between neutrons and γ-rays. Effects of boron loading on scintillation and pulse shape discrimination properties are discussed. A PSD figure-of-merit value of 1.4±0.03 has been achieved for events in a thermal neutron energy domain, 50–100keVee, for PSD plastic loaded with 5wt.% of m-carborane.

Neutron/gamma pulse shape discrimination in plastic scintillators: Preparation and characterization of various compositions

This work deals with the preparation and evaluation of plastic scintillators for neutron/gamma pulse shape discrimination (PSD). We succeeded in developing a plastic scintillator with good neutron/gamma discrimination properties in the range of what is already being commercialized. Several combinations of primary and secondary fluorophores were implemented in chemically modified polymers. These scintillators were fully characterized by fluorescence spectroscopy and under neutron irradiation. The materials proved to be stable for up to 5 years without any degradation of PSD properties. They were then classified in terms of their PSD capabilities and light yield. Our best candidate, 28.6wt% of primary fluorophore with a small amount of secondary fluorophore, shows promising PSD results and is particularly suited to industrial development, because its preparation does not involve the use of expensive or exotic compounds. Furthermore, even at the highest prepared concentration, high stability over time was observed. As a proof of concept, one sample with dimensions 109mm ∅×114mm height (≈1L) was prepared.

Pulse shape discrimination with fast digitizers

The pulse shape discrimination (PSD) between neutrons and gamma rays in liquid scintillators is studied by using the charge integration method with fast digitizers having different technical characteristics. The use of the Figure of Merit (FoM) to verify the PSD capability is discussed. The dependence of the FoM on the digitizer sampling rate and resolution is experimentally determined. The effects due to the type of source and the irradiation geometry are also evidenced and discussed.

Scintillation properties of composite ceramic YAG and its capability on pulse shape descrimination

Transparent ceramic composite of non-doped and Ce-doped YAG was prepared by Konoshima Chemical with the vacuum sintering technique and investigated on pulse shape discrimination capability for functional collimator. Scintillation responses such as X-ray induced radioluminescence and decay time profiles of non-doped and Ce-doped YAG were evaluated. Pulse shape discrimination capability of the composite ceramic was evaluated by 137Cs 662 keV γ-ray irradiation. As a result, clear separation of γ-ray events at non-doped or Ce-doped YAG layers was observed in two dimensional histogram by using signal processing with two different shaping times.

Experimental tests of the new plastic scintillator with pulse shape discrimination capabilities EJ-299-33

We have studied the prototype of a new plastic scintillator material (EJ-299-33) engineered for gamma-neutron discrimination. Energy and time resolutions as well as pulse shape discrimination capability have been compared with those of standard plastic and liquid scintillators. EJ-299-33 characteristics are somewhat poorer compared to standard scintillators. However, results obtained with the new plastic material suggest its possible use in basic research (time-of-flight measurements) as well as in Homeland Security applications (neutron/gamma monitoring device).

Comparison of deuterated and normal liquid scintillators for fast-neutron detection

Liquid organic scintillators have long been used for fast-neutron detection due to their fast response and the ability to use pulse-shape discrimination (PSD) to distinguish between neutron and γ-ray interactions. Deuterated liquid organic scintillators have, in addition to the aforementioned properties, structure on their pulse-height spectra due to the different characteristics of n–d vs. n–p scattering.We report on the direct comparison of two small-volume liquid scintillator detectors with exactly the same geometries (11.43cm diameter and 2.54cm thickness); the first based on NE213 produced by Nuclear Enterprise, and the second based on EJ-315 produced by Eljen Technologies, the latter being a deuterated scintillator. A variety of photomultiplier tubes (PMTs) were used, but the quality of the data was determined to be independent of the PMT type.It is shown that, while the light output of the deuterated detector is lower than for the conventional non-deuterated detector, it is possible to detect 60keV neutrons. The PSD capabilities of the deuterated detector match and surpass those of the NE213 detector. Its efficiency is comparable to that of the NE213 detector at neutron energies above 2MeV; below that energy its relative efficiency suffers from the significantly lower n–d scattering cross-section. For very low neutron energies (<200keV), the relative efficiency of the deuterated detector increases again, due to the lower noise level for our particular detectors, showing the importance of low photomultiplier tube noise for the detection of low-energy neutrons.

Studies of neutron–[formula omitted] pulse shape discrimination in EJ-309 liquid scintillator using charge integration method

Pulse shape discrimination capability based on the charge integration has been investigated for liquid scintillator EJ-309. The effectiveness of neutron–γ 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–γ discrimination for these assays, such as position and width of a gate used for integration of the delayed light, has been explored.

Characteristics of a stilbene scintillation crystal in a neutron spectrometer

Various organic scintillators are commonly used as the detecting material for neutrons, but these detectors are less sensitive to gamma rays. In particular, stilbene crystals and BC501A (NE213, EJ301) have good pulse-shape discrimination (PSD) between neutron and gamma-ray events, and have been selected as the media for fast-neutron detection among the organic, inorganic and plastic materials in a mixed radiation field. Although some of the scintillation characteristics of stilbene crystals have been studied, the detailed scintillation characteristics of the crystal are not completely understood. In this study, the light yield, decay time and pulse shape discrimination capability of a stilbene crystal were measured because this crystal is an optimized detector in a large flux of neutrons such as those might be found in cyclotron and charged particle accelerator facilities. The pulse-shape discrimination of neutrons and gamma rays with a stilbene crystal was measured using a 252Cf neutron source at room temperature. A neutron tagger module was used for the neutron and gamma separation using the charge comparison method in real time. The total pulse width for the charge integration and the delay from the peak-to tail start time were optimized for a better neutron and gamma separation. The relative light yield and decay time of the stilbene crystal scintillator were also measured.

Neutron-induced235U fission spectrum measurements using liquid organic scintillation detectors

Measurements have been performed at Los Alamos Neutron Science Center to acquire neutron fission spectra of ${}^{235}$U in the energy range between 0.5 and 10 MeV. These new data complement the currently available experimental data, which are not well known in the energy range below 1 and above 5 MeV. Organic liquid scintillation detectors (EJ-309s) were used together with a digital data-acquisition system. The EJ-309 detectors show excellent pulse shape discrimination capabilities and this is vital for identifying only neutron pulses and rejecting $\ensuremath{\gamma}$-ray pulses. The measurement data show the dependence of average fission neutron energy as a function of the inducing neutron energy. The data agree well with previously published measurements and Watt spectra fits for energies up to tens of MeV. At high fission-inducing neutron energies the spectrum deviates from Watt-spectra fits. The increased energy deposited in higher energy neutron-induced fissions does not significantly increase emitted fission neutron energies for up to 10 MeV. A significant decrease in neutron energy around second-chance fission cannot be observed beyond the current measurement uncertainties.

Pulse shape analysis with scintillating bolometers

Rare event searches impose strict requirements to the detectors such as an excellent energy resolution, a high detection efficiency and a very low background level. The bolometric technique has already proven to be very promising in this field. Among the features on which it is possible to further act to improve the detection sensitivity, the radioactive background reduction covers a primary role. This request can be satisfied through the possibility to identify the nature of the interacting particle. However, up to now, this opportunity can be fulfilled only with a double readout (e.g. heat and scintillation light). This double readout could greatly complicate the assembly of a huge, multi-detector array. The possibility to recognize the interacting particle through the shape of the thermal pulse is therefore a very interesting opportunity.Detailed analysis of the signal time development in macro-bolometers composed by scintillating crystals showed that it is possible to distinguish between β/γ and α particle interaction (i.e. the main source of background for 0νDBD experiments based on the bolometric technique). Results of pulse shape analysis of signals from several bolometers with absorbers of different compositions (CaMoO4, ZnMoO4, ZnSe) are presented and the pulse shape discrimination capability of such detectors is discussed. An explanation of this behavior, based on the energy partition in the heat and scintillation channels, is also presented.

Characterization of a liquid scintillator based on linear alkyl benzene for neutron detection

A liquid scintillator (LS) based on linear alkyl benzene (LAB) solvent has been characterized using multiple radiation sources. The results confirm that boron-loaded LAB is suitable for neutron detection in a gamma ray environment. To study indirectly the LAB pulse shape discrimination (PSD) capability between neutrons and gamma rays, a dissolved 212Pb source emitting alpha and beta particles was used to emulate the conditions in a mixed radiation field for detecting neutrons in the presence of a high gamma ray background. The quenching factor depends on the alpha energy and increases from 10 to 25 as the alpha energy decreases from 10 to 1MeV. 10B loaded LAB-based LS has been tested in a neutron beam of energy which is equal to 14.56meV. The observed peak at 60keVee is attributed to the absorption of neutrons. Our results show that a boron-loaded LAB-based scintillator is a sensitive medium for neutron detection in a relatively large background of gamma rays. A neutron detector could be achieved with a figure of merit (FOM) of 1.75.

Decay time and pulse shape discrimination of liquid scintillators based on novel solvents

Over the past few years the liquid scintillation technique employed for particle detection applications has undergone a significant technological breakthrough with the introduction of novel solvents tailored to address the concerns about toxicity, flammability and disposal problems associated with the scintillators of traditional formulation.The increasing popularity of the new solvents in the realization of experimental set-ups of various degrees of size and complexity implies the need of a thorough study and characterization of the features of the corresponding scintillation mixtures, with the aim to approach eventually a level of understanding similar to that, very accurate, achieved throughout many years of research for the scintillators realized with conventional solvents.In this general context, aim of this work is to illustrate the results of the fluorescence decay time and pulse shape discrimination measurements carried out on a set of scintillation mixtures realized using two of such novel solvents, i.e., linear alkylbenzene (LAB) and di-isopropylnaphthalene (DIN). The measurements have been performed either under particle or UV excitation of the scintillating solutions, which permitted to unravel the features both of the fast component and of the long tail forming the entire scintillation pulse.Moreover, the particle characterization via β or α excitation allows also predicting the α⧸β pulse shape discrimination capability of the mixtures, a property of paramount significance for applications focused on the increasingly important field of low background detectors.

Optimisation of nasal swab analysis by liquid scintillation counting

When responding to an emergency radiological incident, rapid methods are needed toprovide the physicians and radiation protection personnel with an early estimation ofpossible internal dose resulting from the inhalation of radionuclides. This information isneeded so that appropriate medical treatment and radiological protection controlprocedures can be implemented. Nasal swab analysis, which employs swabs swiped inside anostril followed by liquid scintillation counting of alpha and beta activity on theswab, could provide valuable information to quickly identify contamination ofthe affected population. In this study, various parameters (such as alpha/betadiscrimination, swab materials, counting time and volume of scintillation cocktail etc) wereevaluated in order to optimise the effectiveness of the nasal swab analysis method. Animproved nasal swab procedure was developed by replacing cotton swabs withpolyurethane-tipped swabs. Liquid scintillation counting was performed using a Hidex300SL counter with alpha/beta pulse shape discrimination capability. Results show thatthe new method is more reliable than existing methods using cotton swabs andeffectively meets the analysis requirements for screening personnel in an emergencysituation. This swab analysis procedure is also applicable to wipe tests of surfacecontamination to minimise the source self-absorption effect on liquid scintillation counting.

Characterization and development of an active scintillating target for nuclear reaction studies on actinides

This article presents the development of a new kind of active actinide target, based on organic liquid scintillators containing the dissolved isotope. Amongst many advantages one can mention the very high detection efficiency, the Pulse Shape Discrimination capability, the fast response allowing high count rates and good time resolution and the ease of fabrication. The response of this target to fission fragments has been studied. The discrimination of alpha, fission and proton recoil events is demonstrated. The alpha decay and fission detection efficiencies are simulated and compared to measurements. Finally the use of such a target in the context of fast neutron induced reactions is discussed.

Characterization of a Mixed Multiplicity Counter Based on Liquid Organic Scintillators

A measurement system capable of multiplicity measurements for both neutrons and gamma rays has been developed. The benefit of such an approach is in the increased number of available observables. A pure neutron assay results in three observables for third-order multiples, while a combined neutron/gamma-ray assay results in nine observables for the same order of multiples. The idea is to use the additional observables to achieve greater accuracy when determining unknown parameters of the sample such as the fissile mass. The measurement system is based on liquid scintillation detectors (EJ-309s) which feed detected pulses to a digital data-acquisition system. The excellent pulse shape discrimination capabilities of the EJ-309s allow for accurate differentiation between gamma-ray pulses and neutron pulses. The PSD is vital to correctly identify the different multiples up to the third order: n, γ , nn, nγ , γγ , nnn, nnγ , nγγ and γγγ . Previous investigation of the measurement system showed that good counting statistics can be achieved within minutes for spontaneous-fission sources such as <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf. In this paper, we present new measurement results and corresponding Monte Carlo simulations aimed at characterizing the measurement system. Comparison of the measured and simulated multiples is discussed in detail and a relatively good agreement is found.

A novel technique of particle identification with bolometric detectors

We report in this paper the proofs that the pulse shape analysis can be used in some bolometers to identify the nature of the interacting particle. Indeed, while detailed analyses of the signal time development in purely thermal detectors have not produced so far interesting results, similar analyses on bolometers built with scintillating crystals seem to show that it is possible to distinguish between an electron or gamma-ray and an alpha particle interaction. This information can be used to eliminate background events from the recorded data in many rare process studies, especially Neutrinoless Double Beta decay search. Results of pulse shape analysis of signals from a number of bolometers with absorbers of different composition (CaMoO4, ZnMoO4, MgMoO4 and ZnSe) are presented and the pulse shape discrimination capability of such detectors is discussed.

Fast Neutron and Gamma induced Radiation Dose Monitoring during Nano-particle Production by Proton beam Irradiation

We report a fast neutron and gamma induced radiation dose and flux monitoring study during the nano-particle production at the proton beam irradiation facility. The monitoring results will be used for understanding of the activation of irradiated samples and the effect to the nano-particle production. A cylindrical shape of BC523A liquid scintillator was used for the fast neutron and gamma monitoring purpose. A neutron tagger module was used for the signal digitization and it has a function of pulse shape discrimination capability by using a charge comparison method. Samples for the nano-particle production were irradiated with 45-MeV proton beam from the MC-50 cyclotron at the Korea Institute of Radiological and Medical Sciences. The fast neutron detector was located just behind of the sample. Proton beam current from 20 nA to 500 nA was used for the test. The measured neutron and gamma flux, energy spectra, and neutron and gamma induced radiation dose in the liquid scintillator were evaluated and compared with different sample setup. This study showed that the developed detection system is useful for the absorbed dose and flux monitoring of neutron and gamma in the proton beam line.

Development of Low Background CsI(Tl) Crystals and Search for WIMP

The response of CsI(Tl) crystals to nuclear recoils and gammas down to 3 keV has been studied, and it has been demonstrated that the pulse shape discrimination capability for CsI(Tl) is better than that for NaI(Tl). Extensive study of internal background of CsI powder was performed and a lot of efforts have been made to reduce the internal background sources such as <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb. The <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs concentration of 2 mBq/kg was achieved successfully in the CsI powder using ultra-pure water for whole extraction process. The Rb concentration was successfully reduced to be less than 1 ppb by the recrystallization method. The CsI(Tl) crystal used for the experiment was grown with the ultra-low background CsI powder and a dimension of the CsI(Tl) crystal is 8times8times30 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> which corresponds to weight of 8.7 kg. The number of photoelectrons is measured to be about 4-6/keV with a RbCs photocathode PMT. The background of CsI(Tl) crystals were measured in the shielding of 30 cm thick mineral oil, 15 cm thick lead, 5 cm thick polyethylene and 10 cm copper at the 700 m minimum depth of underground laboratory at YangYang Pumped Storage Power Plant in Korea. The WIMP search with low background CsI(Tl) crystals has been carried out by the Korean Invisible Mass Search (KIMS) Collaboration and the lower limit on WIMP-nucleon cross section are reported.