Pulse Height Research Articles

Convolution-based frequency domain multiplexing of SiPM readouts using the DRS4 digitizer

We present 4:1 multiplexing of organic scintillators, each coupled to a silicon photomultiplier (SiPM), to reduce the need for a large number of digitizer input channels to readout highly pixelated radiation detection systems. Frequency domain multiplexing (FDM) encodes a detector pulse by assigning it a unique frequency via convolution before combining the encoded signal into a single channel. The combined signal is then read through a digitizer input channel. We have designed an FDM system to multiplex four SiPMs using DRS4 digitizer evaluation board from Paul Scherrer Institute (PSI). We demonstrate 4:1 multiplexing of the SiPM fast output signals and pulse recovery from the digitized multiplexed signal using deconvolution. The noise in the recovered pulse introduces a bias and uncertainty in the estimate of energy and timing that changes with pulse height. The relative uncertainty in the estimated energy from the recovered pulse decreases with pulse height with a maximum uncertainty of 3.1% for the low energy pulses (corresponding to 100 keV); the uncertainty in the estimated time pick-off also decreases with pulse height with a maximum uncertainty of 110 ps for the low energy pulses.

Absolute efficiency of a two-stage microchannel plate for electrons in the 30–900 eV energy range

We report on an apparatus able to measure the absolute detection efficiency of a detector for electrons in the 30–900 eV range. In particular, we discuss the characterisation of a two-stage chevron microchannel plate (MCP). The measurements have been performed in the LASEC laboratory at Roma Tre University, whit a custom-made electron gun. The very good stability of the beam current in the fA range, together with the picoammeter nominal resolution of 0.01 fA, allowed the measurement of the MCP absolute efficiency ε. We found an with no evident energy dependence. We fully characterised the MCP pulse shape distribution, which is quasi-Gaussian with a well visible peak above the noise level. We measured a 68 variation of the average pulse height between 30 and 500 eV. Furthermore, with a deeper analysis of the pulse shape, and in particular of the correlation between pulse height, area and width, we found a method to discriminate single- and multi- electron events occurring within a 10 ns time window.

Mixture model analysis of Transition Edge Sensor pulse height spectra.

To calibrate an optical transition edge sensor (TES), for each pulse of the light source (e.g. pulsed laser), one must determine the ratio of the expected number of photons that deposit energy and the expected number of photons created by the laser. Based on the estimated pulse height generated by each energy deposit, we form a pulse height spectrum with features corresponding to different numbers of deposited photons. We model the number of photons that deposit energy per laser pulse as a realization of a Poisson process, and the observed pulse height spectrum with a mixture model method. For each candidate feature set, we determine the expected number of photons that deposit energy per pulse and its associated uncertainty based on the mixture model weights corresponding to that candidate feature set. From training data, we select the optimal feature set according to an uncertainty minimization criterion. We then determine the expected number of photons that deposit energy per pulse and its associated uncertainty for test data that is independent of the training data. Our uncertainty budget accounts for random measurement errors, systematic effects due to mismodeling feature shapes in our mixture model, and possible imperfections in our feature set selection method.

X-ray characterization of BUSARD chip: A HV-SOI monolithic particle detector with pixel sensors under the buried oxide

This work presents the design of BUSARD, an application specific integrated circuit (ASIC) for the detection of ionizing particles. The ASIC is a monolithic active pixel sensor which has been fabricated in a High-Voltage Silicon-On-Insulator (HV-SOI) process that allows the fabrication of a buried N+ diffusion below the Buried OXide (BOX) as a standard processing step. The first version of the chip, BUSARD-A, takes advantage of this buried diffusion as an ionizing particle sensor. It includes a small array of 13×13 pixels, with a pitch of 80 μm, and each pixel has one buried diffusion with a charge amplifier, discriminator with offset tuning and digital processing. The detector has several operation modes including particle counting and Time-over-Threshold (ToT). An initial X-ray characterization of the detector was carried out, obtaining several pulse height and ToT spectra, which then were used to perform the energy calibration of the device. The Molybdenum \U0001d40aα emission was measured with a standard deviation of 127 e- of ENC by using the analog pulse output, and with 276 e- of ENC by using the ToT digital output. The resolution in ToT mode is dominated by the pixel-to-pixel variation.

Effect of deep level defects on CdZnTe detector internal electric field and device performance

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility (μe), electron transport time (TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

Growth and Characterization of Mixed Halide Scintillators K2LaClxBr5−x:Ce

AbstractIn this paper, it is recently discovered that mixed‐anion Cl‐Br halide scintillator K2LaClxBr5−x:Ce (x = 0, 1, 2, 3, 4, 5) has promising performance. The mixed crystal polycrystalline materials are synthesized by high‐temperature solid‐phase method, and transparent cylindrical crystals of K2LaClxBr5−x:Ce are grown successfully by the vertical Bridgman technique. The crystals are measured by powder X‐ray diffraction, X‐ray‐induced luminescence spectra, optical transmittance, photoluminescence spectrum, photoluminescence decay time, and pulse height spectrum. Under the UV and X‐ray excitation, all of the crystal samples have the typical Ce3+ 5d1→2F5/2 and 5d1→2F7/2 double peaks, emission centered between 350 and 400 nm. The photoluminescence decay time of the K2LaClxBr5−x:Ce crystal is about 30 ns under the UV excitation. The energy resolution of the crystal is generally less than 10%. As the proportion of Br‐ ions increases, the luminescence intensity is enhanced, the photoluminescence decay speed increases, and energy resolution of these crystals is optimized. The simplicity of the growth of small‐sized crystals is promising for expanding the growth process to larger sizes.

Correlation between luminescence of cerium and chemical compositions in lithium silicate-based glasses

In contrast to conventional photoluminescence, the radiation-induced luminescence of glasses is difficult to understand because of the complex energy transfer system. In this study, we examined the optical and luminescent properties of Ce 3+ in lithium silicate-based glasses prepared in air. The Ce 3+ ratio in the glasses decreased with increasing Ce concentration, which is the opposite of the trend previously observed for Al 2 O 3 –P 2 O 5 glasses. The 33.3Li 2 O-66.7SiO 2 (LS) glass, which is the stoichiometric chemical composition of Li 2 Si 2 O 5 crystal, exhibited higher photoluminescence intensity, quantum yield (QY), X-ray-induced scintillation intensity, and storage luminescence than 34Li 2 O–5MgO–10Al 2 O 3 –51SiO 2 (GS10) glass. The pulse height spectra obtained by 252 Cf irradiation also suggested that a higher light yield was observed in the LS glasses compared with GS10 glasses. The 0.5 mol% Ce-doped LS glass exhibited the highest light yield 493.7 ph/n among these glasses despite the low QY value. It is found that additional factors correlate with the light yield by 252 Cf irradiation in addition to the QY and Ce 3+ concentrations. • We have prepared Ce 3+ in lithium silicate-based glasses containing different Ce concentrations. • The quantum yield (QY) depends on both the chemical composition and the Ce 3+ ratio. • 33.3Li 2 O-66.7SiO 2 (LS) glass exhibited photoluminescence intensity and quantum yield higher than MgO–Al 2 O 3 substituted glass. • The 0.5 mol% Ce-doped LS glass exhibited the highest light yield 493.7 ph/n despite the low QY value.

From Sintering to Particle Discrimination: New Opportunities in Metal–Organic Frameworks Scintillators

The characterization of a scintillating metal organic framework (MOF) is not straightforward, mainly due to the small size and low density of the material. In this context, we present herein a generic method to give an easy access to the determination of a key parameter in the scintillation field, namely the light output. To reach this, MOF‐205 was first synthesized as millimetric‐size single crystals then sintered under pressure and temperature conditions to afford a pellet. The density was increased by 300% while maintaining optical properties on par with scintillation application. The as‐prepared scintillator was then characterized in terms of photoluminescence (PL; UV‐excited emission spectrum, time‐correlated single photon counting) and radioluminescence (RL) spectroscopy (beta‐excited emission spectrum, alpha, beta and gamma pulse height spectra, alpha/beta and alpha/gamma discrimination). Results were compared with commercial BC‐404 plastic scintillator performances as well as supported by MCNP6.2 simulation.

Three-phase flow meters based on X-rays and artificial neural network to measure the flow compositions

The methodology presented in this study is based on a 149.5 keV X-ray beam and two planar germanium detectors for X-ray transmission and scattering measurements for prediction of volume fractions in a three-phase system. Fluid volume fractions have been modeled using the MCNP6 code for an annular flow regime. A mathematical algorithm based on an artificial neural network was used to correlate the energy spectra from both detectors with the fluids volume fractions. The pulse height distributions obtained by the detectors are used as input data of the network that outputs the volume fractions of gas and water. The mean relative error, using the procedure presented here, for all data, was below 2.5% for both phases investigated. These results show that the methodology based on an X-ray beam has the potential to be used with flow meters.

Gapless implementation of crosshair light-sharing PET detector

Recently, silicon photomultipliers (SiPMs) have become established as photo-sensors for PET scanners. Commercially available SiPM arrays are typically about 3–4 cm in size. In order to develop larger detectors with an Anger calculation, multiple SiPM arrays need to be combined. This configuration requires the use of a light guide and has inactive areas between SiPM arrays. If not addressed, crystal identification degrades not only for peripheral crystals but also for crystals to bridge the gap between the SiPM arrays. On the other hand, we have developed the crosshair light-sharing (CLS) PET detector, which is based on a single-ended readout scheme with roughly quadrisected crystals comparable in size to a SiPM, with depth-of-interaction (DOI) capability. The CLS PET detector based on the local centroid calculation was expected to mitigate the edge effect similar to what the one-to-one coupling detector is able to do. In this work, we developed the axially long CLS PET detector with two multipixel photon counter (MPPC) arrays. The proposed long CLS PET detector consisted of 30 × 14 gadolinium fine aluminum garnet (GFAG) arrays coupled to two 8 × 8 MPPC arrays without the light guide. From 511-keV uniform irradiation, responses of all crystal elements could be separated clearly on a 2D position histogram after applying the Anger calculation. Pulse heights of additional crystals to bridge the gap were 18% lower than those of crystals at the center of the MPPC array, but similar to that of the peripheral crystals based on non-uniformity of the MPPC array. On the other hand, energy resolutions of additional crystals to bridge the gap were almost the same to those of other crystals. The long CLS PET detector promises improvement of the packing fraction while keeping performance.

Neutron capture and total cross-section measurements and resonance parameter analysis of niobium-93 below 400 eV

ABSTRACT Neutron capture yields and transmission ratios of 93Nb were measured by applying the time-of-flight method using the Accurate Neutron-Nucleus Reaction measurement Instrument of the Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex. Nb metal foils were used as samples. Germanium gamma-ray and Li-glass neutron detectors were used for capture yields and transmission ratio measurements, respectively. The pulse height weighting technique was applied to deduce the capture cross-sections from 0.01 to 400 eV, and the thermal-neutron capture cross-section was determined to be 0.97 ± 0.11 b. The total cross-sections were derived from transmission ratios ranging from 0.2 to 400 eV. The resonance parameters of 93Nb below 400 eV were determined based on the obtained capture cross-sections and transmission ratios using the resonance analysis code, REFIT, and compared with the parameters given by past measurements and the evaluated nuclear data library, JENDL-4.0.

Influence of a short reverse positive HPPMS pulse on the deposition of CrAlN

In conventional high power impulse magnetron sputtering processes (HPPMS) short pulses of a negative voltage are used to maintain the discharge. A new approach to accelerate ionized species towards the substrate position and subsequently improved coating properties is the use of a power supply, which generates a reverse positive pulse immediately after the negative pulse. In the present paper the influence of the frequency f and the pulse on time t on for a CrAlN process on the coating properties is investigated. All experiments were carried out on an industrial scale coating unit. In the present investigations coatings deposited by three different duty cycles are compared. For each duty cycle one coating was deposited using a conventional power supply and one coating using a power supply with a positive pulse. The positive pulse was clearly detected. It was found that the height of the positive pulse depends on the chosen pulse parameters. Furthermore, higher values of the peak power were found when using a power supply with a positive pulse, which should influence the ionization of the sputtered material. Regarding the chemical composition, a decreasing nitrogen content of the coatings was found when using a positive pulse. The investigations of the deposited coatings showed a denser morphology and increased values of the indentation hardness when using a power supply with a positive pulse compared to a conventional power supply. In addition to the higher indentation hardness, even the amount of plastic work showed increasing values for the power supply using a positive pulse compared to the conventional power supply. Furthermore, increased values of the roughness for coatings deposited on cemented carbide were found when using a positive pulse. The coatings deposited on cemented carbide showed a higher adhesion when using a positive pulse. • Higher peak power when using a short reverse positive pulse • Improved mechanical properties when using a positive pulse • Preferred (200) orientation for the use of a short reversed positive pulse and low duty cycles • Improved adhesion when using a positive pulse

Modelling the response of semiconductor based thermal neutron detectors with MCNP 6.2 and PHITS

This paper describes the experimental characterization and Monte Carlo (MC) modelling of developed thermal neutron detectors based on p-i-n silicon diodes covered with micrometric layers of 6LiF, called TNPD (Thermal Neutron Pulse Detector). TNPDs are routinely manufactured at INFN-LNF for a variety of neutron measurement applications. TNPDs with different 6LiF thickness, in the range 10–60 μm, were manufactured and thoroughly modelled using two independent Monte Carlo transport codes: MCNP6.2 and PHITS. The simulations were focussed on determining the pulse height distribution induced in the detectors when exposed to thermal neutrons. A validation experiment was performed in the HOTNES thermal neutron calibration facility (ENEA/INFN Frascati, Italy). The simulated pulse height distributions matched very well the experimental ones in terms of both shape and energy-integrated quantities. No scaling factors were needed. This work is an important milestone for the INFN-LNF detector-manufacturing laboratory. In addition, it provides guidance for others who need to accurately predict the response of similar detectors in a wide range of applications.

252Cf -induced luminescence of cerium-doped lithium silicate glasses

In addition to the total attenuation of ionizing radiation, photoluminescence has been conventionally recognized to affect radiation-induced luminescence. In this study, we examined the optical and luminescence properties of Ce3+ in lithium silicate-based glasses with different optical basicities. The existence of Ce4+ was confirmed based on the optical absorption, Ce L3-edge X-ray absorption near edge structure (XANES), and optical coefficients of the calculated Ce4+ using the optical absorption and XANES data of Ce4+ species from a previous report. Compared to other multicomponent glasses, there was a slight deviation in the decay constant and quantum yield (QY) of the stoichiometric Li2O–2SiO2 glass. In addition, the light yields calculated from the pulse height spectra with 252Cf irradiation depend on the QY of the glasses. Considering the energy conversion process, the dependence of the light yield agreed with that of the conventional energy conversion process of neutron-induced luminescence.

Characterization of Diamond and Silicon Carbide Detectors With Fission Fragments

Experimental fission studies for reaction physics or nuclear spectroscopy can profit from fast, efficient, and radiation-resistant fission fragment (FF) detectors. When such experiments are performed in-beam in intense thermal neutron beams, additional constraints arise in terms of target-detector interface, beam-induced background, etc. Therefore, wide gap semi-conductor detectors were tested with the aim of developing innovative instrumentation for such applications. The detector characterization was performed with mass- and energy-separated fission fragment beams at the ILL (Institut Laue Langevin) LOHENGRIN spectrometer. Two single crystal diamonds, three polycrystalline and one diamond-on-iridium as well as a silicon carbide detector were characterized as solid state ionization chamber for FF detection. Timing measurements were performed with a 500-µm thick single crystal diamond detector read out by a broadband amplifier. A timing resolution of ∼10.2 ps RMS was obtained for FF with mass A = 98 at 90 MeV kinetic energy. Using a spectroscopic preamplifier developed at INFN-Milano, the energy resolution measured for the same FF was found to be slightly better for a ∼50-µm thin single crystal diamond detector (∼1.4% RMS) than for the 500-µm thick one (∼1.6% RMS), while a value of 3.4% RMS was obtained with the 400-µm silicon carbide detector. The Pulse Height Defect (PHD), which is significant in silicon detectors, was also investigated with the two single crystal diamond detectors. The comparison with results from α and triton measurements enabled us to conclude that PHD leads to ∼50% loss of the initial generated charge carriers for FF. In view of these results, a possible detector configuration and integration for in-beam experiments has been discussed.

Flow-rate prediction independent of the regime in a dynamic two-phase flow system using a simple pulse height spectrum of a detector and Artificial Neural Networks

In this work, the air and water flow-rates were accurately predicted within a two-phase flow loop using features extracted from a simple detector spectrum, independently of the changes in the flow regime. In this regard, a new method based on a single beam-single detector using single-energy of gamma-rays was proposed. The gamma-ray attenuation setup combined with Artificial Neural Network (ANN) was used to predict the flow-rates in various regime of gas–liquid two-phase flows such as bubble, plug, slug, annular and dispersed regimes. Moreover, the ANN was developed based on four features extracted from the recorded pulse height spectrum in the dynamic condition of the fluids. The results showed that the air and water flow-rates can be measured with an average of Mean Relative Error (MRE) less than 4.5%. Overall results revealed that using the proposed method, prediction of the flow-rates can be successfully carried out independent of their regimes.

Photoluminescence and scintillation characteristics of organic–inorganic layered perovskite-type compounds with a methoxyphenethylamine

Crystals of organic–inorganic layered perovskite-type compounds with a methoxyphenethylamine (nOCH3-C6H4C2H4NH3)2PbBr4 (n = 2, 3, 4) were synthesized by a temperature gradient method, and their radiation response properties were evaluated for scintillator applications. The perovskite-type compounds with a methoxyphenethylamine exhibited luminescence due to the exciton recombination when excited by ultraviolet light and X-ray. The quantum efficiency (0.12) of the perovskite-type compound with a 4-methoxyphenethylamine was the highest among the fabricated crystals. Furthermore, scintillation light yields of the perovskite-type compounds with a methoxyphenethylamine were evaluated by pulse height spectra using 241Am gamma-ray source. Their obtained yields of (2OCH3–C6H4C2H4NH3)2PbBr4, (3OCH3–C6H4C2H4NH3)2PbBr4, and (4OCH3–C6H4C2H4NH3)2PbBr4 crystals were 3600, 6100 and 11,000 photons/MeV, respectively. In addition, fast decay times on the order of a few nanoseconds under X-ray irradiation were observed in the (2OCH3–C6H4C2H4NH3)2PbBr4 (6.7 ns), (3OCH3–C6H4C2H4NH3)2PbBr4 (4.5 ns), and (4OCH3–C6H4C2H4NH3)2PbBr4 crystals (6.8 ns) owing to the free exciton recombination.

Central-to-peripheral stiffness gradients determine diastolic pressure and flow fluctuation waveforms: time domain analysis of femoral artery pulse.

Blood pressure fluctuates during diastole to create a dicrotic wave but the mechanistic origin remains poorly understood. We sought to investigate the characteristics and determinants of diastolic pressure and flow fluctuations with a focus on stiffness gradients between the central aorta and peripheral arteries. Using applanation tonometry and duplex ultrasound, pulse waveforms were recorded on the femoral artery in 592 patients (age: 55 ± 14 years) to estimate the diastolic pressure fluctuation as a residual wave against the mono-exponential decay and the diastolic flow fluctuation as a bidirectional (forward and reverse) velocity wave. The radial, carotid, and dorsalis pedis pressures were also recorded to measure the peripheral/aortic pulse pressure (PP) and pulse wave velocity (PWV) ratios. There were close resemblances between the femoral pressure and flow fluctuation waveforms. The pressure and flow fluctuations were mutually correlated in relative amplitude as indexed to the total pulse height (r = 0.63), and the former temporally followed the latter. In multivariate-adjusted models, higher peripheral/aortic PP and PWV ratios were independently associated with greater pressure and flow fluctuation indices (P < 0.001). Mediation analysis revealed that the associations of PP and PWV ratios with the pressure fluctuation index were largely mediated by the flow fluctuation index [indirect/total effect ratio: 57 (95% CI 42-80)% and 54 (30-100)%, respectively]. These results suggest that central-to-peripheral pulse amplification and stiffness gradients contribute to triphasic flow fluctuations and dicrotic pressure waves. Diminished or inverted stiffness gradients caused by aortic stiffening may thus reduce diastolic runoff leading to ischemic organ damage.

A Compact Memristor Model for Neuromorphic ReRAM Devices in Flux-Charge Space

In this paper, we present a compact memristor model for bipolar neuromorphic ReRAM devices. The proposed model focuses on the high level description of the device, and it reproduces some of the most important characteristics (i.e. conductance, energy dissipation) without needing a detailed electrical simulation. Its functionality is shown by using it to model the behavior of three different ReRAM devices that were fabricated and measured at the CNR-IMM, MDM Laboratory. The parameters extraction procedure is also discussed. The obtained results clearly show that the model proposed in this paper is able to capture the influence of the programming pulse parameters (i.e. pulse duration and height) changes. This is accomplished by the introduction of a parameter, which is related to the specific device technology.

Monte Carlo Simulations of scintillation detectors for the use as dosemeters

The energy dependent conversion factors from measured photon pulse height spectra to ambient dose equivalent (H*(10)) of three different detectors based on the scintillation materials CeBr_3, LaBr3 and SrI2 were simulated with the three Monte Carlo Codes, GEANT4, MCNP and PENELOPE, respectively. The performance of the detection systems, using the calculated conversion factors (fitted to response functions), is demonstrated for different scenarios ranging from laboratory conditions (i.e. a precisely defined radiation field in a calibration facility) to a free-field irradiation scenario produced by the natural radioactivity at a large lawn. With very simple geometric models of the detector systems, the response function of scintillation based dosemeters can be derived from the aforementioned Monte Carlo simulations with an accuracy of the measured doses in H*(10) of ±10% in an photon energy range from 100 keV to 3000 keV, as being typical for natural environmental gamma radiation.