Pulse Height Research Articles

Response Function Simulation of Labr3 (Ce) Scintillation Detector

In Nuclear physics, gamma detection techniques are the most common ones being used for spectroscopy. Scintillation detectors find their applications in a large number of fields. The most commonly used and famous scintillation detector was NaI(Tl) that has been in use since the last 50 years. Recently, several new detectors have also been introduced commercially and they include lanthanum-based detectors. This study focuses on the response function simulation of the LaBr3(Ce) detector crystal. This is accomplished by developing a model that calculates various key properties for the detector crystal. This is done by using the Monte Carlo N-Particle (MCNP) transport code. A complete model for the detector is developed to simulate the lab setup. The simulation is then used to obtain the energy distribution of pluses that are created in the detector. Several gamma sources are used to obtain the pulse height spectra to calculate our properties of interest. The effect of distance on the spectra is also simulated. For Cs137 (662KeV), the energy resolution comes out to be 3.447% and FWHM is 22.12 KeV. An increase in the incident gamma energy results in increased FWHM whereas energy resolution and detection efficiency show a decreasing trend. After simulations, the crystal was also studied experimentally. In this case, both the simulation and experimental coincided. This proves the validity of the model developed.

Contaminant detection in non-destructive testing using a CZT photon-counting detector

With recent advances in the growth of CdZnTe (CZT) sensors, high-flux photon-counting detectors (PCDs) have begun to see more use commercially in non-destructive testing (NDT). One such application is food inspection, where radiography is currently used to detect undesirable contaminants introduced in the production and packaging processes. PCDs can offer better detection than conventional radiography due to the preservation of energy data by analyzing the pulse height of each x-ray detection and sorting the x-ray into one of a number of energy bins. However, there are a number of parameters that must be explored in order to offer efficient and efficacious detection of contaminants. Here, two such parameters were investigated in a phantom study with an 8×24 mm2 CZT detector for a number of common contaminant materials. The detectability of contaminants was evaluated based on their contrast-to-noise ratio (CNR) in 2D transmission images. First, the energy bin demonstrating the highest CNR for each contaminant material was found by adjusting the threshold energies defining the edges of the bin. Second, various pixel binning schemes were utilized to lower noise and investigate the effect on the detectability based on the size of contaminants. CNR was maximized for pixel binning that corresponded to the approximate size of the contaminant objects in x-ray images.

A numerical model to predict pulse height distribution of alpha particles in thin ZnS(Ag) scintillators

The SnowWhite7 numerical model was developed to predict pulse height distribution from multicrystalline ZnS(Ag) scintillators exposed to alpha particles. The model, implemented in LabView, treats the following effects: charged particle energy loss, stopping-power-dependent light yield, and light self absorption in the multicrystalline matrix. SnowWhite7 was validated against experimental data obtained with scintillators manufactured at INFN-LNF and having thickness from 1.6 mg⋅cm−2 up to about 10 mg⋅cm−2. The scintillation light output was collected using a commercial photomultiplier and a digitizer. SnowWhite7 internal parameters were adjusted to satisfactorily match the experimental spectra. SnowWhite7 will be used in a broader project on the design of neutron sensitive scintillators based on ZnS(Ag) combined with 6LiF.

A revised definition of dynamic adsorption coefficient for characterizing activated carbon instead of retention bed

Activated carbon (AC) retention beds are widely used in nuclear facilities, removing radioactive contaminants from exhaust air. Dynamic adsorption coefficient (DAC) is the core parameter to quantify the performance. Its definition has not been unified and it is affected by the geometry of the retention bed, the presence, the flow rate, and the concentration of adsorbate. So, DAC is currently a parameter characterizing the adsorption performance of the retention bed instead of the AC. In this regard, the definition of DAC should be revised, stripping away the influence of other factors. In this study, a 1D model for the AC column, a 2D model for blank piping, and a mathematical model for retention factor is developed. All are validated with simulations and experiments based on the “pulse dynamic method”. They are used to analyze the factors affecting DAC quantitatively in detail, including the direct effect of blank piping, the indirect effect of blank piping by affecting the pulse height into the column, and the effect of krypton concentration distribution in the column. Finally, an improved definition of DAC characterizing AC instead of retention bed is given. This definition can be used as a reference for scholars who formulate relevant standards.

Low power pulsed flip-flop with clock gating and conditional pulse enhancement

A clock system consumes above 25% of the total system power. Flip-flops (FFs) are widely used as the basic storage element in all kinds of digital structures. The use of pulse-triggered flip-flops (P-FFs) in digital design provides better performance than conventional flip-flop designs. This paper presents the design of a new power-efficient implicit pulse-triggered flip-flop suitable for low power applications. Two important features are embedded in this flip-flop architecture. Firstly, the enhancement in width and height of trigger pulses during specific conditions gives a solution for the longest discharging path problem in existing P-FFs. Secondly, the clock gating concept reduces unwanted switching activities at sleep/idle mode of operation and thereby reducing dynamic power consumption. The post-layout simulation results in cadence software based on CMOS 90 nm technology shows that the proposed design features less power dissipation and better power delay performance (PDP) when compared with conventional P-FFs. This paper also presents a comparative study on the performance of implicit and explicit pulse flip-flop designs. The maximum power saving of proposed design against conventional implicit and explicit design is up to 18.45% and 58.49%, respectively.

Optical fiber-based ZnS(Ag) detector for selectively detecting alpha particles

In alpha radionuclide therapy, an optical fiber-based alpha particle detector is a new tool that could possibly be employed for the direct detection of alpha particles in subjects. Thus, in the present study, we developed an optical fiber-based alpha particle detector. The alpha particle detector was made of a 1mm diameter, 10 cm long plastic double clad optical fiber drilled a 0.7 mm diameter, 2 mm depth open space at the one end of the fiber. Silver-doped zinc sulfide (ZnS (Ag)) was painted inside this open space to form a ZnS(Ag) small scintillation chamber. To conduct performance comparisons, we also developed a fiber detector using the same fiber in which a Ce-doped Lu1.8Y0·2SiO5 (LYSO(Ce)) scintillator with dimensions of 0.32 mm × 0.5 mm × 5 mm was inserted. Both fiber detectors were wrapped in aluminized Mylar and optically coupled to a position sensitive photomultiplier tube, before calculating the two-dimensional distributions, energy, and pulse shape spectra. For 5.5-MeV alpha particles, the ZnS(Ag) fiber detector produced ~ 5 times larger pulse heights and the count rate was ~2 times higher compared with those using the LYSO(Ce) fiber detector. For the maximum energy 2.28-MeV beta particles and 0.66-MeV gamma photons, the ZnS(Ag) fiber detector produced no counts, but it yielded small counts from natural alpha particles. Our results confirmed that the ZnS(Ag) fiber detector developed in this study could selectively detect alpha particles and it was insensitive to beta particles and gamma photons.

Study on fast timing MCP-PMT in magnetic fields from simulation and measurement

In recent years, fast timing detectors have attracted more and more attention in the fields of high-energy physics and nuclear medicine due to their advantages in magnetic immunity and time resolution. Through simulation analysis, we discussed in detail the reason why the gain of sensor changes with the magnetic field strength. To improve the test efficiency, we proposed a test scheme to evaluate the magnetic immunity through the shift of the signal pulse height with the magnetic field. The results show that when the sensor axis is parallel and perpendicular to the magnetic field direction, the magnetic field tolerance of the sensor is up to 5 T and 1.85 T, respectively. Besides, the time resolution of the sensor is not affected by the magnetic field strength under fixed conditions.

Validation of neutron emission and neutron energy spectrum calculations on a Mega Ampere Spherical Tokamak with directional relativistic spectrum simulator

The recently developed directional relativistic spectrum simulator (DRESS) code has been validated for the first time against numerical calculations and experimental measurements performed on the Mega Ampere Spherical Tokamak. In this validation, the neutron emissivities and rates computed by DRESS are benchmarked against TRANSP/NUBEAM predictions while the neutron energy spectra provided by DRESS taking as input TRANSP/NUBEAM and ASCOT/BBNBI in Gyro-Orbit mode fast ion distributions are validated against proton pulse height spectra measured by the neutron flux monitor. Excellent agreement was found between DRESS and TRANSP/NUBEAM predictions of local and total neutron emission.

Neutron-gamma separation study for ZnS(Ag)/6LiF scintillator and silicon photomultipliers

Registration of thermal neutrons while simultaneously suppressing or rejecting accompanying gamma-ray background is an important task for many fields. We report on two different experimental neutron-gamma separation studies, utilizing a ZnS(Ag)/6LiF scintillator and pulse height discrimination technique: one is a comparison of the responses of a ZnS(Ag)/6LiF scintillator and a ‘reference’ GAGG(Ce) scintillator when irradiated by gamma sources 137Cs and 241Am; and the second is testing a dual readout, where a photosensor coupled to the ZnS(Ag)/6LiF scintillator screen on each side was irradiated by neutrons (252Cf neutron source). For all measurements the silicon photomultipliers (SiPMs) PM3315-WB-A0 (3x3 mm2 sensitive area, 15 μm cell pitch) manufactured by KETEK were used as a photosensor. High-speed digital oscilloscope LeCroyWR 620zi with a sample rate of 10 GS/s was used as a data acquisition system.

Bench tests of a helium ion source for the neutral particle diagnostic system of the ITER tokamak.

Bench tests of a 15 keV helium ion source, which has been developed for the neutral particle diagnostic system of the International Thermonuclear Experimental Reactor (ITER), are described. Being part of the diagnostic system, the ion source will be used to monitor the intactness of carbon stripping foils as well as to check the detection and dispersion systems of the main diagnostic instruments-neutral particle analyzers (NPAs). The ion source produces a wide 5-cm diameter (FWHM) ion beam at a distance of about 50 cm; the ion beam uniformity at a 2-cm area corresponding to the size of the stripping foil is not worse than 10%. The beam current over the area of the stripping foil can be adjusted in the range of 0.1 pA-1 pA. After initial heating, the temporal stability of the ion beam is better than 10%. Pulse height measurements of registered signals show that 15 keV He+ ions can be reliably registered by the NPA detector system. The obtained results allow us to conclude that the developed ion source can provide a reliable check of the NPA system during the diagnostic performance on the ITER tokamak.

Tl-concentration dependence of scintillation properties in Tl-doped CsBr single crystals

Photoluminescence and scintillation properties of CsBr single crystals with various concentrations of Tl (0.1%, 0.2%, 0.3%, 0.5% and 1%) were examined. Under an excitation at 260–280 nm and X-ray excitation, all the samples exhibited emission peaking around 360 and 510 nm with the decay time constants of μs order. The former emission would be due to 3P1 → 1S0 transitions of Tl+ ion associated with tetragonal structures, and the latter one was due to off-center configurations of self-trapped excitons localized near Tl+ ions at trigonal structures. The pulse height analysis under 137Cs γ-ray (662 keV) irradiation indicated that the 0.3%Tl-doped sample possessed the highest scintillation output among the prepared samples. From the results under various γ-ray irradiation, we confirmed that the scintillation output showed a good proportional response against γ-ray energy up to 1274 keV.

Comparison of light outputs, decay times, and imaging performance of a ZnS(Ag) scintillator for alpha particles, beta particles, and gamma photons

ZnS(Ag) is a scintillator mainly used for alpha particle detection because of the high light output for alpha particles. However, the light output and decay times of ZnS(Ag) for beta particles or gamma photons are not obvious. We therefore measured and compared the light outputs and decay times of ZnS(Ag) for beta particles or gamma photons with that for alpha particles. We measured the pulse height distribution and decay times of ZnS(Ag) for Am-241 alpha particles (5.5 MeV), St-Y-90 beta particles (2.28-MeV maximum energy), and Cs-137 gamma photons (0.66 MeV). The relative light output/MeV for the beta particles and gamma photons was ~2%–~5% of that for alpha particles. Decay time for the beta particles and gamma photons was 2.7 ns–2.8 ns, while that for alpha particles was 61 ns. With the different decay times, pulse shape discrimination of the alpha and beta particles was possible for the ZnS(Ag) radiation-imaging detector. We confirmed that ZnS(Ag) is a suitable scintillator for the detection of alpha particles using energy discrimination as well as pulse shape discrimination.

Neutron background measurement for rare event search experiments in the YangYang underground laboratory

Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double beta decay, which require an extremely low background event rate due to the detector system and the environment. In underground experiments, neutrons have been identified as one of the background sources. The neutron flux in the experimental site needs to be determined to design a proper shielding system and for precise background estimation. We measured the neutron spectrum with a Bonner sphere spectrometer, with Helium-3 (3He) proportional counters. The neutron flux at the underground laboratory was so low that the radioactive decays from the radioisotopes contained in the detector created a significant background interference to the neutron measurement. Using Monte Carlo simulations, the intrinsic α background distribution due to the radioactive isotopes in the detector materials, was estimated. The neutron count rate of each Bonner sphere was measured from the pulse height spectrum of the 3He proportional counter, after subtracting the α particle background. The neutron flux and the energy spectrum were determined using the unfolding technique. The total neutron flux measured was (4.46 ± 0.66) × 10−5 cm−2 s−1, and the thermal and fast neutron flux (in the range 1–10 MeV) were (1.44 ± 0.15) × 10−5 cm−2 s−1 and (0.71 ± 0.10) × 10−5 cm−2 s−1, respectively.

Characterization of Eu-doped Ba2SiO4, a high light yield scintillator

Photoluminescence and scintillation characteristics of Eu-doped Ba2SiO4 were investigated. A broad emission band due to Eu2+ is observed at 500 nm, and the photoluminescence and radioluminescence decay time constants are about 397 and 515 ns, respectively. From the pulse height distribution of 57Co γ-rays, the light yield of Eu:Ba2SiO4 is ∼48 000 ph MeV−1, which is comparable with those of developed oxide scintillators showing a high light yield. The results demonstrate that Eu-doped Ba2SiO4 is a high-performance scintillator for X- and γ-ray measurements and characterized by excellent scintillation output and afterglow.

Low-energy continuous filtered X-ray measurement and dosimetry with a PIPS detector

The true fluence spectra and its conversion coefficients from the air kerma to the ICRU operational quantities for our low-energy X-ray radiation field were determined using spectrometry. The pulse height spectra were measured with a PIPS detector for the ISO reference radiations (N-15 to N-30 and L-20 to L-30). According to the calculated detector response matrices, the measured pulse height spectra were unfolded. Then the average photon energy and the first half-value layer for each radiation quality were calculated and compared with the recommended or measured values. The conversion coefficients from the air kerma to the ICRU operational quantities Hp(10), H*(10), Hp(0.07) and H′ (0.07) and the revised operational quantities ambient dose H*, personal dose Hp and personal absorbed dose in local skin Dp local skin were determined. This work presents the spectrometry and dosimetry for the filtered low-energy X-ray radiations based on a PIPS detector spectrum measurement system in detail. This portable spectrum measurement system can help calibration laborites simplify the experimental setup when performing the dosemeter calibrations according to ISO 4037–4.

Integrated-Photonic Characterization of Single-Photon Detectors for Use in Neuromorphic Synapses

We show several techniques for using integrated-photonic waveguide structures to simultaneously characterize multiple waveguide-integrated superconducting-nanowire detectors with a single fiber input. The first set of structures allows direct comparison of detector performance of waveguide-integrated detectors with various widths and lengths. The second type of demonstrated integrated-photonic structure allows us to achieve detection with a high dynamic range. This device allows a small number of detectors to count photons across many orders of magnitude in count rate. However, we find a stray light floor of -30 dB limits the dynamic range to three orders of magnitude. To assess the utility of the detectors for use in synapses in spiking neural systems, we measured the response with average incident photon numbers ranging from less than $10^{-3}$ to greater than $10$. The detector response is identical across this entire range, indicating that synaptic responses based on these detectors will be independent of the number of incident photons in a communication pulse. Such a binary response is ideal for communication in neural systems. We further demonstrate that the response has a linear dependence of output current pulse height on bias current with up to a factor of 1.7 tunability in pulse height. Throughout the work, we compare room-temperature measurements to cryogenic measurements. The agreement indicates room-temperature measurements can be used to determine important properties of the detectors.

Photoluminescence and scintillation properties of Ce-doped SrLu2O4 single crystals

Undoped and Ce-doped SrLu2O4 single crystals were synthesized by the floating zone method equipped with four Xe lamps, and the photoluminescence (PL) and scintillation properties were investigated. A broad emission band appeared at around 470 nm in PL and scintillation spectra due to the 5d–4f transition of Ce3+. In addition, the PL and scintillation decay time constants were close to typical values of the 5d–4f transition of Ce3+. The pulse height spectra of 137Cs gamma-ray demonstrated that the light yield of undoped and 0.3% Ce-doped SrLu2O4 were 1490 and 570 photons/MeV, respectively. In addition, relationship between gamma-ray energy and photoabsorption peak channel was evaluated.

Sleep-Dependent Memory Consolidation in a Neuromorphic Nanowire Network.

A neuromorphic network composed of silver nanowires coated with TiO2 is found to show certain parallels with neural networks in nature such as biological brains. Owing to the memristive properties emerging at nanowire-to-nanowire contacts, where the Ag/TiO2/Ag interface exists, the network can store information in the form of connectivity between nanowires in the network as electrically measured as an increase in conductance. The observed memory arises from an interplay between the topological constraints imposed by a complex network structure and the plasticity of its constituting memristive Ag/TiO2/Ag junctions. Regarding the long-term decay of the connectivity in the network, we further investigate the controllability of the established connectivity. Inspired by the regulated activity cycles of the human brain during sleep, a learning-sleep-recovery cycle was mimicked by applying voltage pulses, with controlling pulse heights and duty ratios, to the nanowire network. Interestingly, even when the conductance was lost during sleep, the network could quickly recover previous states of conductance in the recovery process after sleep. Comparison between results of experiments and theoretical simulations revealed that such a quick recovery of conductance can be realized by sparse voltage pulse application during sleep; in other words, sleep-dependent memory consolidation occurs and can be controlled. The present results provide clues to new learning designs in neuromorphic networks for achieving longer memory retention for future neuromorphic technology.

Effects of adiabaticity of electrons and negative ions on the modulational instability of ion-acoustic waves in electronegative plasma

In the present work, we investigate modulational instability (MI) in an unmagnetised collisionless electronegative plasma consisting of inertialess adiabatic electrons, inertialess adiabatic negative ions and mobile positive ions. For this purpose, a nonlinear Schrodinger equation (NLSE) is derived to study envelope evolution of the ion-acoustic carrier waves for our system by using reductive perturbation technique. In examining the stability/instability of the ion-acoustic envelope wavepackets, the critical wavenumber kc at which MI sets in is found to be shifted to higher values as adiabaticity γ increases. The effects of electron-to-negative ion temperature ratio σn and negative ion density fraction f on the region for propagation of stable wave pulses are also discussed. Within the instability region, the rational solution of NLSE provides the rogue wave (RW) profiles which is localised in space and time. With the increase of adiabaticity, the possibility for the formation of RW decreases at the lower wavenumber which is in good agreement with experimental observations. The change in adiabaticity significantly influences the rogue wave amplitudes. Maximum pulse height for RW is found to be increasing with the increase of adiabaticity. Our theoretical findings may be helpful for basic characteristic study of rogue waves in the laboratory as well as space plasmas.

Photoluminescence and scintillation properties of Ce-substituted Pr2Si2O7 crystal scintillators

The Ce-substituted (Cex, Pr1-x)2Si2O7 bulk single crystals were synthesized by the floating zone method, and their photoluminescence (PL) and scintillation properties were evaluated. The X-ray diffraction patterns showed that all the synthesized samples were a single-phase of monoclinic Pr2Si2O7. In PL and scintillation, an emission peak was observed at around 370–390 nm due to the 5d–4f transitions of Ce3+. In pulse height spectra, the scintillation light yield was ∼400 ph MeV−1 in the 99% Ce-substituted sample. The 99% Ce-substituted sample showed the highest scintillation light yield among the present samples.