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At least 649 records · Page 36Linked to original sources

arXiv2013

Spatial resolution of a μPIC-based neutron imaging detector

We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100μm-level spatial and sub-μs time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48 +/- 0.77 μm (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334 +/- 13 μm), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60 μm may be possible with optimization of the gas characteristics and μPIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.

physics.ins-det↗

arXiv2013

First demonstration of a sub-keV electron recoil energy threshold in a liquid argon ionization chamber

We describe the first demonstration of a sub-keV electron recoil energy threshold in a dual-phase liquid argon time projection chamber. This is an important step in an effort to develop a detector capable of identifying the ionization signal resulting from nuclear recoils with energies of order a few keV and below. We obtained this result by observing the peaks in the energy spectrum at 2.82 keV and 0.27 keV, following the K- and L-shell electron capture decay of Ar-37, respectively. The Ar-37 source preparation is described in detail, since it enables calibration that may also prove useful in dark matter direct detection experiments. An internally placed Fe-55 x-ray source simultaneously provided another calibration point at 5.9 keV. We discuss the ionization yield and electron recombination in liquid argon at those three calibration energies.

astro-ph.IM↗

arXiv2013

Thermomechanical design of a static gas target for electron accelerators

Gas targets are often used at accelerator facilities. A design of high-pressure gas cells that are suitable for hydrogen and helium isotopes at relatively high electron beam currents is presented. In particular, we consider rare gas targets, $^3$H$_2$ and $^3$He. In the design, heat transfer and mechanical integrity of the target cell are emphasized. ANSYS 12 was used for the thermo-mechanical studies of the target cell. Since the ultimate goal in this study was to design a gas target for use at the Jefferson Laboratory (JLab), particular attention is given to the typical operating conditions found there. It is demonstrated that an aluminum alloy cell can meet the required design goals.

physics.ins-det↗

arXiv2013

Monte Carlo Simulation of the Photon-Tagger Focal-Plane Electronics at the MAX IV Laboratory

Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.

physics.ins-det↗

arXiv2013

The OLYMPUS Experiment

The OLYMPUS experiment was designed to measure the ratio between the positron-proton and electron-proton elastic scattering cross sections, with the goal of determining the contribution of two-photon exchange to the elastic cross section. Two-photon exchange might resolve the discrepancy between measurements of the proton form factor ratio, $μ_p G^p_E/G^p_M$, made using polarization techniques and those made in unpolarized experiments. OLYMPUS operated on the DORIS storage ring at DESY, alternating between 2.01~GeV electron and positron beams incident on an internal hydrogen gas target. The experiment used a toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight detectors to measure rates for elastic scattering over the polar angular range of approximately $25^\circ$--$75^\circ$. Symmetric Møller/Bhabha calorimeters at $1.29^\circ$ and telescopes of GEM and MWPC detectors at $12^\circ$ served as luminosity monitors. A total luminosity of approximately 4.5~fb$^{-1}$ was collected over two running periods in 2012. This paper provides details on the accelerator, target, detectors, and operation of the experiment.

physics.ins-det↗

arXiv2014

Optimization of light collection from crystal scintillators for cryogenic experiments

High light collection efficiency is an important requirement in any application of scintillation detectors. The purpose of this study is to investigate the possibility for improving this parameter in cryogenic scintillation bolometers, which can be considered as a promising detectors in experiments investigating neutrinoless double beta decay and dark matter. Energy resolutions and relative pulse amplitudes of scintillation detectors using ZnWO4 scintillation crystals of different shapes (cylinder 20 mm in dimater by 20 mm and hexagonal prism with diagonal 20 mm and height 20 mm), reflector materials and shapes, optical contact and surface properties (polished and diffused) were measured at room temperature. Propagation of optical photons in these experimental conditions was simulated using Geant4 and ZEMAX codes. The results of the simulations are found to be in good agreement with each other and with direct measurements of the crystals. This could be applied to optimize the geometry of scintillation detectors used in the cryogenic experiments.

physics.ins-det↗

arXiv2014

Characterization and modeling of a low background HPGe detector

A high efficiency, low background counting setup has been made at TIFR consisting of a special HPGe detector ($\sim$ 70%) surrounded by a low activity copper+lead shield. Detailed measurements are performed with point and extended geometry sources to obtain a complete response of the detector. An effective model of the detector has been made with GEANT4 based Monte Carlo simulations which agrees with experimental data within 5%. This setup will be used for qualification and selection of radio-pure materials to be used in a cryogenic bolometer for the study of Neutrinoless Double Beta Decay in $^{124}$Sn as well as for other rare event studies. Using this setup, radio-impurities in the rock sample from India-based Neutrino Observatory (INO) site have been estimated.

physics.ins-det↗

arXiv2014

Concept for a Time-of-Flight Small Angle Neutron Scattering Instrument at the European Spallation Source

A new Small Angle Neutron Scattering instrument is proposed for the European Spallation Source. The pulsed source requires a time-of-flight analysis of the gathered neutrons at the detector. The optimal instrument length is found to be rather large, which allows for a polarizer and a versatile collimation. The polarizer allows for studying magnetic samples and incoherent background subtraction. The wide collimation will host VSANS and SESANS options that increase the resolution of the instrument towards um and tens of um, respectively. Two 1m2 area detectors will cover a large solid angle simultaneously. The expected gains for this new instrument will lie in the range between 20 and 36, depending on the assessment criteria, when compared to up-to-date reactor based instruments. This will open new perspectives for fast kinetics, weakly scattering samples, and multi-dimensional contrast variation studies.

physics.ins-det↗

arXiv2014

The gamma-ray spectrometer HORUS and its applications for nuclear astrophysics

A dedicated setup for the in-beam measurement of absolute cross sections of astrophysically relevant charged-particle induced reactions is presented. These, usually very low, cross sections at energies of astrophysical interest are important to improve the modeling of the nucleosynthesis processes of heavy nuclei. Particular emphasis is put on the production of the $p$ nuclei during the astrophysical $γ$ process. The recently developed setup utilizes the high-efficiency $γ$-ray spectrometer HORUS, which is located at the 10 MV FN tandem ion accelerator of the Institute for Nuclear Physics in Cologne. The design of this setup will be presented and results of the recently measured $^{89}$Y(p,$γ$)$^{90}$Zr reaction will be discussed. The excellent agreement with existing data shows, that the HORUS spectrometer is a powerful tool to determine total and partial cross sections using the in-beam method with high-purity germanium detectors.

nucl-ex↗

arXiv2014

Silica aerogel radiator for use in the A-RICH system utilized in the Belle II experiment

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4$σ$ at momenta up to 4 GeV/$c$. Large-area aerogel tiles (over 18 $\times $ 18 $\times $ 2 cm$^3$) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5 m$^2$) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the $K$/$π$ separation capability of a prototype A-RICH counter exceeded 4$σ$ at 4 GeV/$c$.

physics.ins-det↗

arXiv2014

GEANT4 simulation of the neutron background of the C$_6$D$_6$ set-up for capture studies at n_TOF

The neutron sensitivity of the C$_6$D$_6$ detector setup used at n_TOF for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a $^\mathrm{nat}$C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured $^\mathrm{nat}$C yield has been discovered, which prevents the use of $^\mathrm{nat}$C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross section measurements.

physics.ins-det↗

arXiv2014

DALI2: A NaI(Tl) detector array for measurements of $γ$ rays from fast nuclei

A NaI(Tl) detector array called DALI2 (Detector Array for Low Intensity radiation 2) has been constructed for in-beam $γ$-ray spectroscopy experiments with fast radioactive isotope (RI) beams. It consists typically of 186 NaI(Tl) scintillators covering polar angles from $\sim$15$^{\circ}$ to $\sim$160$^{\circ}$ with an average angular resolution of 6$^{\circ}$ in full width at half maximum. Its high granularity (good angular resolution) enables Doppler-shift corrections that result in, for example, 10% energy resolution and 20% full-energy photopeak efficiency for 1-MeV $γ$ rays emitted from fast-moving nuclei (velocities of $v/c \simeq 0.6$). DALI2 has been employed successfully in numerous experiments using fast RI beams with velocities of $v/c = 0.3 - 0.6$ provided by the RIKEN RI Beam Factory.

nucl-ex↗

arXiv2014

Test and characterization of a prototype silicon-tungsten electromagnetic calorimeter

New generation high-energy physics experiments demand high precision tracking and accurate measurements of a large number of particles produced in the collisions of lementary particles and heavy-ions. Silicon-tungsten (Si-W) calorimeters provide the most viable technological option to meet the requirements of particle detection in high multiplicity environments. We report a novel Si-W calorimeter design, which is optimized for $γ/π^0$ discrimination up to high momenta. In order to test the feasibility of the calorimeter, a prototype mini-tower was constructed using silicon pad detector arrays and tungsten layers. The performance of the mini-tower was tested using pion and electron beams at the CERN Proton Synchrotron (PS). The experimental results are compared with the results from a detailed GEANT-4 simulation. A linear relationship between the observed energy deposition and simulated response of the mini-tower has been obtained, in line with our expectations.

physics.ins-det↗

arXiv2014

Test of a single module of the J-PET scanner based on plastic scintillators

Time of Flight Positron Emission Tomography scanner based on plastic scintillators is being developed at the Jagiellonian University by the J-PET collaboration. The main challenge of the conducted research lies in the elaboration of a method allowing application of plastic scintillators for the detection of low energy gamma quanta. In this article we report on tests of a single detection module built out from BC-420 plastic scintillator strip (with dimensions of 5x19x300mm^3) read out at two ends by Hamamatsu R5320 photomultipliers. The measurements were performed using collimated beam of annihilation quanta from the 68Ge isotope and applying the Serial Data Analyzer (Lecroy SDA6000A) which enabled sampling of signals with 50ps intervals. The time resolution of the prototype module was established to be better than 80ps (sigma) for a single level discrimination. The spatial resolution of the determination of the hit position along the strip was determined to be about 0.93cm (sigma) for the annihilation quanta. The fractional energy resolution for the energy E deposited by the annihilation quanta via the Compton scattering amounts to sigma(E)/E = 0.044/sqrt(E[MeV]) and corresponds to the sigma(E)/E of 7.5% at the Compton edge.

physics.ins-det↗

arXiv2017

A novel technique for determining luminosity in electron-scattering/positron-scattering experiments from multi-interaction events

The OLYMPUS experiment measured the cross-section ratio of positron-proton elastic scattering relative to electron-proton elastic scattering to look for evidence of hard two-photon exchange. To make this measurement, the experiment alternated between electron beam and positron beam running modes, with the relative integrated luminosities of the two running modes providing the crucial normalization. For this reason, OLYMPUS had several redundant luminosity monitoring systems, including a pair of electromagnetic calorimeters positioned downstream from the target to detect symmetric Mø ller and Bhabha scattering from atomic electrons in the hydrogen gas target. Though this system was designed to monitor the rate of events with single Mø ller/Bhabha interactions, we found that a more accurate determination of relative luminosity could be made by additionally considering the rate of events with both a Mø ller/Bhabha interaction and a concurrent elastic $ep$ interaction. This method was improved by small corrections for the variance of the current within bunches in the storage ring and for the probability of three interactions occurring within a bunch. After accounting for systematic effects, we estimate that the method is accurate in determining the relative luminosity to within 0.36\%. This precise technique can be employed in future electron-proton and positron-proton scattering experiments to monitor relative luminosity between different running modes.

physics.ins-det↗

arXiv2018

A large area detector for thermal neutron flux measurements at the KamLAND site

A large area (0.5~m $\times$ 0.5~m) thermal neutron detector was developed based on 0.32~mm-thick $^{6}$LiF:ZnS(Ag) scintillator sheets. The detector was constructed for measurements of seasonal variations in low intensity thermal neutron flux at deep underground sites. The detector response to neutrons was studied using a low intensity $^{241}$Am/$^{9}$Be($α$,n) neutron source. The digital pulse shape discrimination technique was applied to separate neutron capture events from the background caused by traces of $α$-emitters from Uranium and Thorium decay chains in scintillator components. The thermal neutron detection efficiency was 0.368$\pm$0.018 (0.155$\pm$0.009) before (after) event selection based on the digital pulse shape discrimination method. The measured $α$-particle background event rate in the $^{6}$LiF:ZnS(Ag) scintillator was (4.88$\pm$0.06(stat))$\times$10$^{-6}$ $α$ cm$^{-2}$sec$^{-1}$. As a test of detector performance we measured the thermal neutron flux at the KamLAND area of the Kamioka neutrino observatory and compared it with result of the neutron flux measurement carried out at the Super-Kamiokande site. The thermal neutron flux at KamLAND was (6.43$\pm$0.50)$\times$10$^{-6}$ n cm$^{-2}$sec$^{-1}$ that included $\sim$10~\% contribution from neutrons with energies above 1~eV. During the detector construction we identified a source of high amplitude noise pulses generated by 5-inch R1250 photomultipliers manufactured by Hamamatsu Photonics K. K..

physics.ins-det↗

arXiv2022

Simulation of the spatial shift in detector response for polarized protons within a calorimeter

Measurement of the helicity dependent elastic electron-proton scattering cross section provides a key means of investigating parity violation within the proton. However, such measurements exhibit potential instrumental effects associated with the detection of polarized recoiled protons. In particular, spin-orbit interactions within a massive detector induce a systematic spatial shift in the detector signal. In this study, we determine the size of this shift using the Geant4 simulation toolkit. For a typical hadron calorimeter, we found a polarization dependent shift on the order of 0.01-0.1 mm, multiple orders of magnitude smaller than the typical spatial resolution seen in hadronic calorimeters. Additionally, we provide the custom modifications required of the Geant4 source code to implement the quasi-elastic scattering of polarized protons incident on nuclei in the detector. The modifications are readily extendable to generic matter sources, and can be used for the study of additional spin dependent observables in Geant4.

nucl-ex↗

arXiv2013

Activation cross-sections of longer lived products of proton induced nuclear reactions on manganese up to 70 MeV

In the frame of a systematic study of the activation cross-sections of the proton induced nuclear reactions, excitation functions of the 55Mn(p,x)154,152gMn,51Cr and 48V were measured up to 70 MeV. Cross-sections were measured with the activation method using a stacked foil irradiation technique and high resolution gamma-ray spectrometry. The experimental data are analyzed and compared to the earlier results and to the prediction of the EMPIRE-3 as well as the TALYS theoretical model code in the TENDL-2012 library. From the measured cross-section data integral production yields were calculated. Practical applications of the cross-sections are discussed.

nucl-ex↗