Large Solid Angle Detector Research Articles

Quantitative Analysis of Energy-Dispersive Spectra Acquired with Large Solid Angle Detectors

Quantitative Analysis of Energy-Dispersive Spectra Acquired with Large Solid Angle Detectors

The retarding Bessel–Box—An electron-spectrometer designed for pump/probe experiments

A new type of electrostatic electron spectrometer is developed, capable of particular sensitive measurements of energy spectra and time-of-flight distributions. This instrument is specifically designed and optimized for laser-pump/X-ray-probe measurements, where photo electrons or Auger electrons from surfaces, clusters, molecular or atomic targets are being measured with high time-resolution at an extremely low detection-noise level. The compact and robust cylinder-symmetrical system is a strongly improved Bessel–Box design, featuring electron retardation, a large detection solid-angle, about 100% electron transmission (gridless design) and excellent time-resolution. In this paper we describe the principle of operation of this type of spectrometer and various tests. We present quantitative results for electron measurements with different solid-state targets and two different electron-detection systems in comparison to electron-trajectory simulations inside the electrostatic spectrometer fields. Picosecond-pump/probe operation has been tested with high laser power and even the ability to work under femtosecond-pump-probe conditions with electron detection at the BESSY II slicing facility has been proven.

Breakup following interactions with light targets: Investigating new methods to probe nuclear physics input to the cosmological lithium problem.

A well known issue with concordance cosmology is the cosmological lithium problem, where models of Big Bang Nucleosynthesis indicate abundances of 7 Li three to four times larger than values inferred via spectroscopic measurements of metal-poor halo stars [1]. Since the source of this discrepancy remains unclear [2], it is vital to fully understand the nuclear reactions that affect the production of 7 Li during the Big Bang [3]. At the Australian National University, experimental equipment and analysis techniques have been developed for nuclear reaction studies at energies near the fusion barrier, exploiting large solid angle detectors to enable the investigation of breakup without a priori assumption of the breakup kinematics. The extension to reactions of astrophysical interest may help shed light on these reactions. Recent experiments, using these new techniques, have provided a complete picture of the breakup mechanisms of light nuclei in collisions with heavy targets [4]. The present work focuses on obtaining a complete picture of breakup mechanisms of 7 Li following interactions with 27 Al. It has been found that breakup is almost exclusively triggered by nucleon transfer between the colliding partners, to a larger extent than was found for heavier targets. The findings of these experiments, as well as progress towards extensions to astrophysically relevant reactions, such as d + 7 Be [5] will be presented.

Quantified, multi-scale X-ray fluorescence element mapping using the Maia detector array: application to mineral deposit studies

The Maia large solid-angle detector array and imaging system is capable of collecting high-resolution images of up to ∼100 M pixels in size with dwell times of less than 0.2 ms per pixel and thus it is possible to document variation in textures associated with trace element chemistry by collecting quantified elemental maps of geological samples on the scale of entire thin sections in a short time frame (6–8 hr). The analysis is nondestructive and allows variation to be recognised on a centimetre scale while also recognising zonations at the micron scale. Studies of ore systems require microanalysis of samples to collect information on mineral chemistry in order to understand physiochemical conditions during ore genesis and alteration. Such studies contribute to the debate on whether precious metals are remobilised or introduced in multiple hydrothermal events. In this study we demonstrate the microanalytical capabilities of the Maia large solid-angle detector array and imaging system on the X-ray fluorescence microscopy beamline at the Australian Synchrotron to provide data for these studies. We present a series of case studies from orogenic gold deposits that illustrate the power of the Maia detector for constraining chemical zonations in sulphides and associated alteration minerals, which can be used to decipher ore-forming processes associated with gold deposition. A series of large-area (<7 cm2) elemental maps were collected with 2 to 4 μm pixel size using the Maia detector array. The data was processed using the GeoPIXE™ software package which allows variation in trace, minor and major element chemistry to be visualised in element maps. These maps are used to target further investigation with bulk spectra extracted and fitted for specific mineral grains and transects drawn through regions of interest. Analysis using the Maia detector offers a complementary method to map element distribution in geological samples that is both relatively fast and has a low detection limit for many elements of interest.

Radioactivity measurement of Sr/Y-90 mixed with Cs-134 and Cs-137 using large solid angle detectors without chemical separation

We proposed a method to measure the radioactivity of Sr/Y-90 in the mixture of Cs-134 and Cs-137 without chemical pretreatment. It was realized by subtracting the electrons produced in Cs-134 and Cs-137 from entire electron emission rate that can be determined by the efficiency tracer technique in the 4πβ–γ coincidence counting method. The radioactivity of Cs-134 and Cs-137 can be determined by gamma ray spectrometry. The measurements were conducted using plastic and NaI(Tl) scintillation detector with a large solid angle. The validity of the measurement method was shown by agreement of the results with the known radioactivities.

Fluence measurement of fast neutron fields with a highly efficient recoil proton telescope using active pixel sensors

The spectrometer ATHENA (Accurate Telescope for High-Energy Neutron metrology Applications) is being developed at the LNE-IRSN and aims at characterising energy and fluence of fast neutron fields. The detector is a recoil proton telescope and measures neutron fields in the range of 5-20 MeV. This telescope is intended to become a primary standard for both energy and fluence measurements. The neutron detection is achieved by a polyethylene radiator for n-p conversion, three 50-µm-thick silicon sensors that use CMOS technology for proton tracking and a 3-mm-thick silicon diode to measure the residual proton energy. The use of CMOS sensors and silicon diode, owing to a large detection solid angle, increases the intrinsic efficiency of the detector by a factor of 10 compared with conventional designs. The ability of the spectrometer to determine the neutron energy was demonstrated and reported elsewhere. This paper focuses on the fluence measurement of monoenergetic neutron fields in the range of 5-20 MeV. Experimental investigations, performed at the AMANDE facility, indicate a good estimation of neutron fluence at various energies. In addition, a complete description of uncertainties budget is presented in this paper and a Monte Carlo propagation of uncertainty sources leads to a fluence measurement with a precision ∼3-5 % depending on the neutron energy.

Vacuum Ultraviolet and Soft X‐ray Photoelectron Spectroscopy of Liquid Beams Using a Hemispherical Photoelectron Spectrometer with a Multistage Differential Pumping System

AbstractWe present photoelectron spectroscopy of liquid beams using a high‐resolution hemispherical photoelectron spectrometer with a multistage differential pumping system developed in our laboratory. Intense soft X‐ray synchrotron radiation (500‐1200 eV) at SPring‐8 and a relatively large detection solid angle (1.5 × 10−2 π sr) of the spectrometer enable highly efficient measurements of X‐ray photoelectron spectra of liquids. Vacuum ultraviolet photoelectron spectroscopy using the same spectrometer provides sufficiently high spectral resolution to resolve rotational isomers of gas‐phase molecules.

A Bragg curve counter with an internal production target for the measurement of the double-differential cross-section of fragment production induced by neutrons at energies of tens of MeV

A Bragg curve counter equipped with an internal production target was developed for the measurements of double-differential cross-sections of fragment production induced by neutrons at energies of tens of MeV. The internal target permitted a large detection solid angle and thus the registration of processes at low production rates. In this specific geometry, the detection solid angle depends on the emission angle and the range of the particle. Therefore the energy, atomic number, and angle of trajectory of the particle have to be taken into account for the determination of the solid angle. For the selection of events with tracks confined within a defined cylindrical volume around the detector axis, a segmented anode was applied. The double-differential cross-sections for neutron-induced production of lithium, beryllium, and boron fragments from a carbon target were measured at 0° for 65 MeV neutrons. The results are in good agreement with theoretical calculation using PHITS code with GEM and ISOBAR model.

Performances of a [formula omitted]-delayed neutron detection array at Peking University

A β-delayed neutron detection array composed of a neutron sphere and two neutron walls was constructed in the State Key Laboratory of Nuclear Physics and Technology at Peking University. Recently the performances of this detection array were largely improved and tested with a Co60 source, cosmic rays and C16 and N17 radioactive beams. The Tyvek 1056D paper and silicone grease were chosen for the reflection and coupling materials, respectively. For the neutron sphere with large detection solid angle (30% of 4π steradian), the intrinsic efficiency is about 14.1% at a neutron energy of 1MeV and the detection threshold is about 350keV; for the neutron walls with flexible setup, these values are 36.5% and 200keV, respectively. The combined array of neutron sphere and neutron walls has successfully been applied to measure the β-delayed neutrons emitted from neutron-rich unstable nuclei.

Large detector array and real-time processing and elemental image projection of X-ray and proton microprobe fluorescence data

A detector concept is described that integrates a large solid-angle detector array developed at Brookhaven National Laboratory and a high speed pipelined parallel processing engine developed at CSIRO for machine vision, with an embedded implementation of the Dynamic Analysis method for fluorescence spectra deconvolution and image projection, to yield a detection system capable of energy-dispersive detection, spectral deconvolution and real-time elemental imaging at ∼10 8 events per second for PIXE elemental imaging using the nuclear microprobe and SXRF elemental imaging using the synchrotron X-ray microprobe.

Measurement of stopping beam distributions in the PIBETA detector

Precise calculation of the geometrical acceptance of a large solid angle detector with an integrated stopping target relies on precise knowledge of the beam geometry. We describe four alternative methods that we used to measure the beam stopping distributions in the PIBETA detector active target: (i) light response of segmented target elements to incident beam particles, (ii) back-tracking of charged particles from π + and μ + decays using multi-wire proportional chambers, (iii) volume distribution of the Dalitz decay ( π 0 → γ e + e - ) event vertices, and (iv) the opening angle distribution of two π 0 photons originating from the beta decay of π + at rest. We demonstrate consistent results obtained by these four independent approaches and show how particular beam stopping distributions affect the detector's geometrical acceptance.

Measurement of the half-life for two 57Fe excited states by a single-crystal scintillation time spectrometer

Half-lives measurements for two excited states of 57Fe located at 14.4 and 136.5 keV, in the 57Fe nucleus have been recently proposed using the Autocorrelation single-crystal scintillation time spectrometer (ASCSTS) .We have proved that ASCSTS has a reasonably high detection efficiency for γ–γ coincidences in the energy range around 5 keV, preserving its main distinctive feature: a large detection solid angle (close to 2 π) in a wide time interval (from ∼4 ns to 100 μs).

Development of three-dimensional medium-energy ion scattering using a large solid angle detector

Three-dimensional medium-energy ion scattering (3D-MEIS) equipped with a large detector has been developed for crystallographic structural and elemental analysis of materials. Backscattering experiments have been made for a Si(001) sample at the geometry that the range of the scattering angle is as large as ±17.5°. Clear blocking shadows were observed together with belt-like shadow aggregations. A low yield spot not relevant to a blocking cone appears, but it can be excluded from the blocking pattern by changing the detection geometry. The results indicate that 3D-MEIS using a large solid angle detector is promising for crystallographic material analysis.

Nitrogen depletion of indium nitride films during Elastic Recoil Detection analysis

Elastic Recoil Detection analysis of different types of indium nitride films has been performed using a 200 MeV Au beam. Recoil ions were detected with a gas ionisation detector featuring a large detection solid angle. Severe and non-linear nitrogen depletion has been observed, with films grown by RF-sputtering losing nitrogen more quickly than MBE-grown films. Assuming the formation of molecular nitrogen as the decisive step leading to nitrogen loss, the nitrogen depletion process has been modelled using the bulk molecular recombination model. The model allows accurate extrapolations of the original nitrogen content of the material. Since the other important elements can also be quantified, the stoichiometry of the film can thus reliably be obtained from Elastic Recoil Detection analysis. All the films analysed have been found to have excess nitrogen.

Pion Absorption and Re-Scattering

Pion absorption is a large fraction of the total pion-nucleus total cross section. Studies of pion absorption with large solid angle detectors have shown that the pion energy is typically distributed among three to four nucleons. The implications for neutrino interaction Monte Carlos is discussed.

Measurement of differential cross sections for evaluation of radiation dose of ten’s of MeV neutrons

Double differential cross sections of several ten’s of MeV neutron induced reactions for elements composing the human tissue were measured using specially designed spectrometers at TIARA 7Li(p,n) neutron source. In spectroscopy of particles from neutron induced reactions, a large solid angle and particle acceptance detector is indespensable. For particles from 5 MeV a to 70 MeV proton, a spectrometer consisting of three counter telescopes and a vacuum chamber was used. For heavier particles, a Bragg curve spectroscopy technique was adopted to neutron field. Double differential cross section of p,d,t,a emission for N and O were obtained using the former spectrometer. In the later method we fabricated a test spectrometer to check applicability and signal to noise ratio in neutron field. Using the spectrometer, energy spectra of heavier particles (Li, Be, B, C) from carbon were observed.

Reliable ERD analysis of group-III nitrides despite severe nitrogen depletion

ERD analysis of different group-III nitride films has been performed using a 200 MeV Au beam. Recoil ions were detected employing a gas ionisation detector with large detection solid angle. The nitrogen depletion in the irradiated film volume has been measured as a function of incident ion fluence. Severe depletion rates have been observed for GaN and InN films, resulting in the eventual loss of all nitrogen, with InN losing nitrogen more than ten times faster than GaN. For GaN a delayed onset of the nitrogen depletion is apparent. A two parameter bulk molecular recombination model describes the nitrogen depletion well and enables reliable extrapolations of the original nitrogen content of GaN and InN films. A refinement of the model may be possible by considering the diffusion of nitrogen radicals.

Measurement of the electric form factor of the neutron at Q2=0.5 and 1.0 GeV2/c2.

The electric form factor of the neutron was determined from measurements of the d-->(e-->,e'n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia (15ND3) target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle detector. We find G(n)(E)=0.0526+/-0.0033(stat)+/-0.0026(sys) and 0.0454+/-0.0054+/-0.0037 at Q(2)=0.5 and 1.0 (GeV/c)(2), respectively.

3D imaging of elemental distributions using multi-angle RBS 2D-data

We developed a novel technique to obtain 3D-imaging of elemental distribution based on multi-angle RBS measurement and micro-beam scanning. Since cross-sections of RBS are too small to obtain 3D-imaging, it is necessary to measure scattered particles with large solid angle detectors. Hence, the RBS profiles from each scattering angle are superposed and a true depth profile cannot be obtained. Recently, a large solid angle X-ray detector array consisting of 45 detector elements was installed at the TIARA facility of Japan Energy Research Institute. Each detector element measures X-rays as well as scattered particles. For this utilization, we introduced a technique to superpose RBS profiles and applied it to the surface analysis of an ant’s head.

Multiproton final states in positive pion absorption below theΔ(1232)resonance

Inclusive cross sections for positive pion absorption leading to final states including two or more protons have been measured with a large solid angle detector for incident pion energies from 30 to 135 MeV for targets with $A=2--208.$ The mass dependences for the inclusive $({\ensuremath{\pi}}^{+},2p),$ $({\ensuremath{\pi}}^{+},3p),$ and total absorption cross sections for multiproton final states were found to be proportional to ${A}^{n}$ with $n\ensuremath{\approx}0.5.$ These cross sections also were observed to have an energy dependence at energies below 150 MeV reflective of the importance of the $\ensuremath{\Delta}(1232)$ resonance, similar to that observed for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The inclusive cross sections for $({\ensuremath{\pi}}^{+},4p)$ were found to be less than 10 mb for all targets at all energies. Estimates were also obtained for cross sections for pion absorption leading to $2p1n$ and $3p1n$ final states. Quasideuteron absorption contributions increase slowly with A, and the energy dependence of those contributions mirrors that for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The data obtained here for multiproton final states indicate that a significant fraction of absorption events, increasing with A, most likely arises from final states containing fewer than two protons.