Position Sensitive Proportional Counter Research Articles

Measurement of the Cross Section for the Neutron-Induced Fission of 238U Nuclei in the Energy Range of 0.3–500 MeV

The cross section for the neutron-induced fission of 238U nuclei has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, in the neutron energy range of 0.3–500 MeV. Fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The cross section for 238U(n, f) fission has been measured with respect to the cross section for 235U(n, f) fission, which is an accepted international standard. Data on the energy dependence of the anisotropy of the angular distribution of fragments of neutron-induced 238U nuclei are also presented. The data obtained have been compared to previous experiments carried out using both similar and significantly different methods.

Development of THGEM-based Detectors for Nuclear Fission Studies

To optimize the exploration of Super Heavy Elements (SHE), the key challenge is to understand the dynamics of the fusion-fission through the measurements of mass and angular distribution of the fission fragments. For the detection of fission fragments, position sensitive Multi-Wire Proportional Counters are generally used due to their high gain, good temporal and position resolution. However, these detectors use fragile anode wires having a diameter of only 10 μm and therefore they are vulnerable. In the present work, a detector based on robust Thick Gaseous Electron Multiplier (THGEM) has been proposed. A numerical demonstration of THGEM-Multi Wire hybrid detector technology as a possible candidate for the new generation low-energy fission studies and their evaluation as a function of different possible geometric and electric configuration in low-pressure gas is discussed here.

Position and gain non-uniformities in Helium-3 filled position sensitive proportional counters

Helium-3-filled position sensitive detectors (PSDs) comprise the neutron sensing component of many neutron imaging arrays at scattering laboratories around the world, including SNS, NIST, CSNS, ACNS and others. This basic detector technology is decades old, but gradual improvement in detector electronics, increases in detector length, and tighter position resolution requirements have driven a need for improvements in detector performance. As an experienced manufacturer of PSDs, Reuter-Stokes has collaborated with neutron scientists and end users from around the world to drive improvements to PSD manufacture and testing procedures over the last decade. Here, we describe our work to understand detector defects, and detail detector testing methods which we have developed to ensure and improve PSD quality.

A two-dimensional neutron detector assembly at the China Mianyang Research Reactor

A two-dimensional neutron detector consisting of 96 3He position-sensitive proportional counters was assembled at the China Mianyang Research Reactor. With a count rate limit that is higher than that of the initial multi-wire proportional chamber detector at CMRR, it will be used for the small-angle neutron scattering spectrometer Suanni. The problems caused by low air pressure and γ radiation in the working environment are pretreated, and detector performance is evaluated and compared with that of the initial proportional chamber. Now the new detector is ready to be used for Suanni.

Development of a time of flight spectrometer based on position sensitive multi-wire proportional counters for fission fragment mass distribution studies.

Characteristics and performance of a time of flight (TOF) spectrometer developed for performing fission mass distribution studies are presented. The spectrometer contains two TOF arms based on multi-wire proportional counters (MWPCs). Each arm has two MWPCs to form a start-stop detection system for TOF measurements. The start detector has an active area of 4 × 4cm2. The stop detector is a two-dimensional position sensitive MWPC with an active area of 16 × 11cm2. Salient features of the MWPCs are the use of reduced sub-millimeter wire pitches of 0.635 and 0.317mm in the electrodes along with the use of gold plated tungsten wires of diameters 10 and 20 µm. A delay line for position electrodes is prepared using chip inductors and capacitors. Ten different configurations of MWPC were investigated for the start detector, which involved the use of three and four electrode geometries, use of different wire pitches, and use of aluminized mylar for timing electrodes. Performance results close to micro-channel plate detectors have been observed with some designs of MWPC, displaying rise times better than 2ns with an estimated inherent time resolution of ∼100ps FWHM. A position resolution of ∼1mm (FWHM) has been observed. Design features of the MWPCs and their test performance results are described in this article.

Measurement of fragment-mass distributions from fission of At214 following the Be9+Tl205 reaction

Background: The recent surprising experimental discovery of asymmetric fission in the nucleus $^{180}\mathrm{Hg}$ at low excitation energy has renewed interest concerning our understanding of the role of nuclear shell effects in the dynamics of the fission process. New theoretical models have been developed that claim to successfully explain the observed asymmetric fission of $^{180}\mathrm{Hg}$ and also predict the nature of mass distributions of several other preactinide nuclei for which experimental data are scarce.Purpose: We investigated fragment-mass distributions in the fission of the preactinide nucleus $^{214}\mathrm{At}$ at different excitation energies near the Coulomb barrier. The present results were compared with the predictions from a recent state-of-the-art theoretical calculation, as well as with our previous measurement for the nearby nucleus $^{210}\mathrm{Po}$.Methods: A pulsed heavy-ion beam was used in the experiment. Fission fragments were detected with two large-area position-sensitive multiwire proportional counters placed at the folding angle. Mass distributions were extracted from time-of-flight differences and position information ($\ensuremath{\theta},\ensuremath{\phi}$) for the fission fragments.Results: An asymmetry in fragment-mass distribution in the fission of $^{214}\mathrm{At}$ was observed at an excitation energy of $\ensuremath{\approx}31$ MeV, where a shell effect is found to influence the potential energy surface. At higher excitation energies, mass distributions are predominantly symmetric indicating the absence of shell effects.Conclusion: This finding is consistent with the prediction of a recent macroscopic-microscopic dynamical model. However, for the preactinides, static models with nascent fragment shell structure are likely to produce similar results.

Measurement of mass and total kinetic energy distribution of fission fragments using newly developed compact MWPC detectors

Two large area (12.5 cm × 7.5 cm) position sensitive compact multiwire proportional counter detectors have been developed for the study of fission reactions for bombarding energies near the Coulomb barrier. Each detector provides one negative fast signal (anode signal) which is used for the time of flight measurement, in addition to four position signals. The timing signal from anode and delayed timing signal from position frames are processed through non-inverting and inverting fast preamplifiers developed in-house. These preamplifiers are based on monolithic microwave integrated circuits. The position resolutions were measured using a mask made of aluminium. The X and Y-position resolutions were found to be ≈ 1.3 and 1.4 mm respectively. The time spread obtained from the sum spectra of position signals extracted from both the ends of the same position frame, was ≈ 1.6 ns. The detectors were used successfully in an in-beam experiment to detect the fission fragments in the 19F+238U reaction. The time correlation spectra between two anode signals provide clean identification of fission events. Difference of those recorded time was used to measure the mass distribution and hence the total kinetic energy distribution of the fission fragments.

A Neutron Testing Facility to Study the Radiation Hardness of the Electronic Components at the SC-1000 Synchrocyclotron of National Research Center Kurchatov Institute—Petersburg Nuclear Physics Institute

The article presents a description of the ISNP/GNEIS testing facility with a neutron spectrum that reproduces the spectrum of atmospheric neutron radiation. The facility was developed at the Petersburg Nuclear Physics Institute (PNPI) of the National Research Center Kurchatov Institute in collaboration with the Institute of Space Device Engineering, a branch of JSC (Joint Stock Company) United Rocket and Space Corporation. The spallation neutron source of the facility is based on the 1-GeV SC-1000 proton synchrocyclotron at the PNPI. The internal neutron-production lead target produces 10-ns pulses of neutrons with a repetition rate of 45–50 Hz and an average neutron intensity of 3 × 1014 n/s (in the 4σ solid angle). In the irradiation area located at a distance of 36 m from the neutron source, a high-quality collimated neutron beam with a broad energy spectrum of 1–1000 MeV and a neutron flux of 4 × 105 n/(cm2 s) allows conducting accelerated single-event soft error testing of electronic components. In the course of the irradiation, the neutron energy spectrum and intensity and the spatial profile of the beam are controlled using a fission ionization chamber (beam monitor) and a position-sensitive multiwire proportional counter (beam profile meter). The data acquisition system of the ISNP/GNEIS facility utilizes 250 MS/s 12 bit CAEN waveform digitizers for the processing of signals from the monitor and profile meter by the neutron time-of-flight technique. In the report, parameters of the ISNP/GNEIS testing facility are discussed in comparison with analogous world-class facilities, as well as requirements and recommendations of the standards used in this field.

Simulations and systematic neutron beam characterisations on two-dimensional position-sensitive neutron detector multi-wire proportional counter with delay-line readout

A two-dimensional position-sensitive neutron detector multi-wire proportional counter (MWPC) was systematically characterised on dedicated detector test station V17 at reactor BER2 of HZB. Performances including characteristic anode curve, characteristic drift curve, detection efficiency, efficiency homogeneity, horizontal position resolution, vertical position resolution, counting rate capability, and gamma sensitivity were measured. In addition, systematic simulations were conducted based on the detector configurations. These systematic studies are presented here for the first time. They assist in obtaining a greater understanding of detector performances, form the methodology for detector characterisations by reactor neutron beams, and can be used as references for neutron detector research and applications.

Fission fragment velocity distribution measurement using time of flight technique

Two large area position sensitive Multi Wire Proportional Counters (MWPCs) have been developed for the detection of Fission Fragments (FFs). The detectors were characterized using FFs from 252Cf source to obtain position information by employing delay-line read out method and the resolution is about 1 mm in both X and Y directions. Velocity distribution of the FFs produced from spontaneous fission of 252Cf has been measured employing a time-of-flight (TOF) technique, using a barium fluoride (BaF2) detector and a MWPC. The most probable velocities obtained for the heavy and light fragment groups are 1.035 ± 0.003 and 1.378 ± 0.004 cm/ns, respectively. The energy dependence of fragment velocity distribution was also studied after degrading the energy of the fragments by using Mylar foils. It is observed that the width of the distribution for the heavy fission fragments decreases with the reduction in the energies, but for light fragments it does not show any significant dependence on the energy.

Angular Distributions and Anisotropy of the Fragments from Neutron-Induced Fission of 239Pu and natPb in the Energy Range of 1–200 MeV

The angular distributions of fragments from the neutron-induced fission of natPb and 239Pu nuclei have been measured in the energy of range 1–200 MeV using the neutron time-of-flight spectrometer GNEIS. Fission fragments have been detected by position sensitive multiwire proportional counters. The results for the anisotropy of fission fragments deduced from the measured angular distributions have been presented. The results have been compared with the experimental data of other authors.

Calibrating SANS data for instrument geometry and pixel sensitivity effects: access to an extended Q range.

An improved data-reduction procedure is proposed and demonstrated for small-angle neutron scattering (SANS) measurements. Its main feature is the correction of geometry- and wavelength-dependent intensity variations on the detector in a separate step from the different pixel sensitivities: the geometric and wavelength effects can be corrected analytically, while pixel sensitivities have to be calibrated to a reference measurement. The geometric effects are treated for position-sensitive 3He proportional counter tubes, where they are anisotropic owing to the cylindrical geometry of the gas tubes. For the calibration of pixel sensitivities, a procedure is developed that is valid for isotropic and anisotropic signals. The proposed procedure can save a significant amount of beamtime which has hitherto been used for calibration measurements.

Scanning sky monitor (SSM) onboard AstroSat

Scanning Sky Monitor (SSM) onboard AstroSat is an Xray sky monitor in the soft X-ray band designed with a large field of view to detect and locate transient X-ray sources and alert the astronomical community about interesting phenomena in the X-ray sky. SSM comprises position sensitive proportional counters with 1D coded mask for imaging. There are three detector units mounted on a platform capable of rotation which helps covering about 50% of the sky in one full rotation. This paper discusses the elaborate details of the instrument and few immediate results from the instrument after launch.

Development of An Epi-thermal Neutron Field for Fundamental Researches for BNCT with A DT Neutron Source

Boron Neutron Capture Therapy (BNCT) is known to be a new promising cancer therapy suppressing influence against normal cells. In Japan, Accelerator Based Neutron Sources (ABNS) are being developed for BNCT. For the spread of ABNS based BNCT, we should characterize the neutron field beforehand. For this purpose, we have been developing a low-energy neutron spectrometer based on 3He position sensitive proportional counter. In this study, a new intense epi-thermal neutron field was developed with a DT neutron source for verification of validity of the spectrometer. After the development, the neutron field characteristics were experimentally evaluated by using activation foils. As a result, we confirmed that an epi-thermal neutron field was successfully developed suppressing fast neutrons substantially. Thereafter, the neutron spectrometer was verified experimentally. In the verification, although a measured detection depth distribution agreed well with the calculated distribution by MCNP, the unfolded spectrum was significantly different from the calculated neutron spectrum due to contribution of the side neutron incidence. Therefore, we designed a new neutron collimator consisting of a polyethylene pre-collimator and boron carbide neutron absorber and confirmed numerically that it could suppress the side incident neutrons and shape the neutron flux to be like a pencil beam.

Angular distributions and anisotropy of the fragments from neutron-induced fission of 233U and 209Bi in the intermediate energy range of 1–200 MeV

New results of the neutron-induced fission experiments carried out at the neutron time-of-flight spectrometer GNEIS of the PNPI are given. Angular distributions of fission fragments from the neutron-induced fission of 233U and 209Bi nuclei have been measured in the energy range 1–200 MeV using position sensitive multiwire proportional counters as fission fragment detector. The recent improvements of the measurement and data processing procedures are described. The data on anisotropy of fission fragments deduced from the measured angular distributions are presented in comparison with the experimental data of other authors.

LOW X-RAY LUMINOSITY GALAXY CLUSTERS: MAIN GOALS, SAMPLE SELECTION, PHOTOMETRIC AND SPECTROSCOPIC OBSERVATIONS

ABSTRACT We present our study of 19 low X-ray luminosity galaxy clusters (L X ∼ 0.5–45 × 1043 erg s−1), selected from the ROSAT Position Sensitive Proportional Counters Pointed Observations and the revised version of Mullis et al. in the redshift range of 0.16–0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations, and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. Using the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogs contain the point-spread function and aperture magnitudes of galaxies within the 90% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km s−1 for [VMF98]022 to 775 km s−1 for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray emission peak and with clustercentric velocities smaller than the cluster velocity dispersion or 6000 km s−1, respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations, the galaxy luminosity function, and cluster dynamics.

Dual Position Sensitive MWPC for tracking reaction products at VAMOS++

The characteristics and performance of a Dual Position Sensitive Multi-Wire Proportional Counter (DPS-MWPC) used to measure the scattering angle, the interaction position on the target and the velocity of reaction products detected in the VAMOS++ magnetic spectrometer, are reported. The detector consists of a pair of position sensitive low pressure MWPCs and provides both fast timing signals, along with the two-dimensional position coordinates required to define the trajectory of the reaction products. A time-of-flight resolution of 305(11)ps (FWHM) was measured. The measured resolutions (FWHM) were 2.5(3)mrad and 560(70)μm for the scattering angle and the interaction point at the target respectively. The subsequent improvement of the Doppler correction of the energy of the γ-rays, detected in the γ-ray tracking array AGATA in coincidence with isotopically identified ions in VAMOS++, is also discussed.

Optical discovery and multiwavelength investigation of supernova remnant MCSNR J0512– 6707 in the Large Magellanic Cloud

We present optical, radio and X-ray data that confirm a new supernova remnant (SNR) in the Large Magellanic Cloud (LMC) discovered using our deep H-alpha imagery. Optically, the new SNR has a somewhat filamentary morphology and a diameter of 56 x 64 arcsec (13.5 x 15.5 pc at the 49.9 kpc distance of the LMC). Spectroscopic follow-up of multiple regions show high [SII]/H-alpha emission-line ratios ranging from 0.66+/-0.02 to 0.93+/-0.01, all of which are typical of an SNR. We found radio counterparts for this object using our new Australia Telescope Compact Array (ATCA) 6cm pointed observations as well as a number of available radio surveys at 8 640 MHz, 4 850 MHz, 1 377 MHz and 843 MHz. With these combined data we provide a spectral index (alpha) = -0.5 between 843 and 8640 MHz. Both spectral line analysis and the magnetic field strength, ranging from 124 - 184 mG, suggest a dynamical age between 2,200 and 4,700 yrs. The SNR has a previously catalogued X-ray counterpart listed as HP 483 in the ROSAT Position Sensitive Proportional Counter (PSPC) catalogue.

Anisotropy of the fission fragments from neutron-induced fission in the intermediate energy range of 1–200 MeV

Angular distributions of fission fragments from the neutron-induced fission of 232Th, 235U, and 238U have been measured in the energy range 1–200 MeV at the neutron time-of-flight (TOF) spectrometer GNEIS using position sensitive multiwire proportional counters as fission fragment detector. A short description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors.

X-ray photometry

Abstract I describe a method for synthesizing photometric passbands for use with current and future X-ray instruments. The method permits the standardization of X-ray passbands and thus X-ray photometry between different instruments and missions. The method is illustrated by synthesizing a passband in the XMM–Newton European Photon Imaging Camera pn which is similar to the ROSAT Position Sensitive Proportional Counter 0.5–2 keV band.