Low-energy Detector Research Articles

Matrix-assisted Laser/Desorption Ionization Time-of-flight Mass Spectrometer with Orthogonal Acceleration Geometry: Preliminary Results

An orthogonal acceleration time-of-flight mass spectrometer has been constructed with a matrix-assisted laser desorption/ionization source. The instrument has been set up in a preliminary configuration for an assessment of the viability of the orthogonal acceleration geometry. Measurements of resolving power and statistical evaluation of the mass accuracy/precision are reported here for ions in the range m/z 614 to 1351. The preliminary results indicate that resolving powers in the range of 2800 to 3600 (full width at half maximum) are readily achievable without the use of an ion mirror. A two-point external calibration of the mass scale was found to be stable over several days. The precision of the mass measurement has been estimated statistically in an error analysis involving about 40 measurements in the mass range specified above. The distribution of errors was found to be normal (linear normal probability plot) with a mass accuracy of about 0.1 to 70 ppm (average error) depending on how the calibration was performed, while the precision is found to be 90 ppm (standard deviation) irrespective of calibration method. The observed errors are consistent with calculations based on the resolving power and the 2.5 ns digitizer frequency used in this work. Measurements are restricted in mass range with the current instrument because it has a low ion energy (3 kV) accelerator and detector configuration that is linked to the accelerator by a long narrow drift-tube (1.5 m×20 mm). A new large-detector configuration with a 20 kV accelerator and a wider drift region is briefly described.

X-ray detectors with digitized preamplifiers

With direct digitization of detector pulses, software algorithms are used to calculate the energy of incident photons. Fast high resolution sampling adc's and digital signal processors replace shaping amplifiers and spectroscopy adc's. The difference between the classical analog approach for pulse processing and direct digitization can be summerized as follows. In analog systems, a preamplifier output is filtered by analog means and then digitized to be acquired in a multichannel analyzer, whereas the full digital system will digitize first and then filter by application of algorithms. According to the sampling theorem, both approaches are equivalent. However, using digital signal processing for filtering allows the use of filter functions that cannot be practically realized with analog means. Those digital filter functions promise resolution and throughput close to the theoretical limit. The first commercially available ADSP (Analog to Digital Signal Processor) uses a moving window deconvolution to deconvolve the preamplifier characteristic. All algorithms are calculated in real time, thus there is no dead time added through the computation of an event. A filter function with a trapezoidal impulse response calculates the energy in real time. An adaptive digital trigger allows excellent low energy detection. Another benefit for X-ray applications are very long shaping constants, resulting in 125 eV resolution at 5.9 keV with SiLi detectors. The ADSP consists of an analog linear amplification stage, a 20 MHz sampling adc, circuits for digital signal preprocessing, and four floating point DSPs, performing 240 MFLOP/s. It has been built into a 2-wide NIM module to replace virtually any adc/shaping amplifier combination.

Spin-dependent scattering of polarized protons from a polarized 3He internal gas target

We describe the first experiment to use a polarized internal gas target and polarized beam in a storage ring. A laser optically pumped polarized 3He internal gas target has been used with circulating beams of 197–414 MeV polarized protons to carry out an extensive set of measurements of spin dependent scattering. A large acceptance non-magnetic detector system consisting of wire-chambers, scintillators and microstrip detectors was used to detect protons, neutrons, deuterons, and 3He nuclei from the beam-target interaction. It is demonstrated that these techniques result in low backgrounds (< 1%) due to scattering from species other than the polarized target gas and allow detection of low energy recoiling nuclei. Specific issues such as interfacing the experiment to the storage ring and monitoring the luminosity and polarizations are discussed in detail.

True-coincidence correction when using an LEPD for the determination of the lanthanides in the environment via k0-based INAA.

As part of a recent study on the environmental effects caused by the operation of a coal-fired power station at Sines, Portugal, k0-based instrumental neutron activation analysis (INAA) was used for the determination of the lanthanides (and also of tantalum and uranium) in plant leaves and lichens. In view of the accuracy and sensitivity of the determinations, it was advantageous to make use of a low-energy photon detector (LEPD). To begin with, in the present article, a survey is given of the former developments leading to user-friendly procedures for detection efficiency calibration of the LEPD and for correction for true-coincidence (cascade summing) effects. As a continuation of this, computer coincidence correction factors are now tabulated for the relevant low-energetic gamma-rays of the analytically interesting lanthanide, tantalum, and uranium radionuclides. Also the 140.5-keV line of 99Mo/99mTc is included, molybdenum being the comparator chosen when counting using an LEPD.

High pressure Xe + CF 4 TPC in a low radioactivity acrylic structure

A prototype time projection chamber, constructed in acrylic in order to be used as a low radioactivity, low energy detector, is described. A similar detector, of larger size, can be used in an experiment to search for rare events such as neutrinoless double beta decay. The behaviour of the chamber, filled with 280 g of Xe + CF 4 (5%) at 5 bar, is discussed together with the results obtained on the electron drift length and on the energy resolution. The measurements on the scintillation light of the gas are also presented.

Procedure for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry

A procedure is described for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry of the 46.5 keV gamma ray of 210Pb. The procedure involves microwave dissolution, removal of interfering Fe by extraction with thiocyanate in isobutyl methyl ketone and extraction of Pb as the diethyldithiocarbamate (DDTC) complex into CHCl3. After evaporation of the CHCl3, the DDTC complex is decomposed and Pb is precipitated as PbCrO4. The chemical yield is determined gravimetrically and the precipitate is counted on a low-energy gamma-ray detector. Experiments proved the linearity between the 210Pb counting result for PbCrO4 masses in the range 15–100 mg. For materials with levels of approximately 500 Bq kg–1, 10 g of material are processed and the PbCrO4 preparate is counted for 24 h. Materials with a 210Pb content lower than 75 Bq kg–1 demand larger sample masses and/or longer counting times. The limit of determination is 75 Bq kg–1. A relative standard deviation of 2.5–5.0% at the 500 Bq kg–1 level for replicate 210Pb determinations in phosphate ore and gypsum was achieved. An inaccuracy of the method of less than 10% was derived from results for selected materials, that were also analysed by direct gamma-ray spectrometry.

A low radioactivity acrylic TPC filled with CF 4 at high pressure

A prototype time projection chamber, the first of this kind constructed in acrylic in order to be used as a low radioactivity, low energy detector, is

Possibilities for determination of 241Am in environmental samples by gamma counting, with and without radiochemistry

241Am emits 59.5 keV gamma rays with an abundance of 36%. The lower limits of detection achievable using efficient low energy gamma detectors, namely a low energy HP Ge detector of active area 20 cm2 and an HP Ge well-type detector (active volume 120 cm3) were studied. The low energy detector is more favourable for bulk samples, with an absolute counting efficiency for 100 cm3 samples of about 2%. For small samples (up to 5 cm3) the high efficiency of the well-type detector (20–30% absolute) is more advantageous. Limits of detection of 0.5 or 1 Bq kg−1 for soil or 0.1 Bq kg−1 (dry weight) for ashed biota were obtained. The concept of a simple concentration step to separate 241Am from the bulk of the sample by co-precipitation followed by high sensitivity gamma counting in the well-type detector was investigated, thus avoiding the lengthy radiochemical separation, electro-plating and alpha spectrometry of traditional procedures. A number of real (Cumbrian area) and spiked samples were examined and tracer experiments performed. The two techniques, non-destructive and with simple radiochemistry, show particular promise when rapid assays are required, e.g. in accidental releases.

The soft X-ray diffuse background observed with the HEAO 1 low-energy detectors

Results of a study of the diffuse soft-X-ray background as observed by the low-energy detectors of the A-2 experiment aboard the HEAO 1 satellite are reported. The observed sky intensities are presented as maps of the diffuse X-ray background sky in several energy bands covering the energy range 0.15-2.8 keV. It is found that the soft X-ray diffuse background (SXDB) between 1.5 and 2.8 keV, assuming a power law form with photon number index 1.4, has a normalization constant of 10.5 +/- 1.0 photons/sq cm s sr keV. Below 1.5 keV the spectrum of the SXDB exceeds the extrapolation of this power law. The low-energy excess for the NEP can be fitted with emission from a two-temperature equilibrium plasma model with the temperatures given by log I1 = 6.16 and log T2 = 6.33. It is found that this model is able to account for the spectrum below 1 keV, but fails to yield the observed Galactic latitude variation.

The conversion coefficients of the 48.85 keVM3 transition in80mBr

The conversion coefficientsαT andαK the 48.85 keVM3 isomeric transition in the decay of80mBr were measured to be 297.8±10.6 and 209.9±21.2, respectively employing a low-energy high-resolution photon detector. These results are in agreement with the theory and the experimental values due to the earlier authors.

Double beta decay prototype detector with multiwire drift tubes in the Geiger mode

Abstract A 64 cell low-energy electron tracking detector with multiwire drift tubes operating in the Geiger mode and filled with helium is described. Low radioactive materials have been used to build the detector. Data corresponding to 5619 hours in the Frejus Underground Laboratory are presented. Conclusions are drawn for the possibility of using such a detector for a double beta decay experiment.

X-ray spectrum (0.1-10 keV) of the broad line radio galaxy - 3C 390.3

Broad line radio galaxy, 3C 390.3, was observed with EXOSAT on several occassions between 1984 and 1986 using the low (LE) and medium (ME) energy detectors. Detailed results of the spectral analysis of the LE (0.1-2 keV) and ME (2-10 keV) spectra which were obtained from the EXOSAT archives, of this source are presented. Simple power law and uniform absorption model provided good fit to the combined LE and ME spectra but the hydrogen column density (N H ) values are much smaller than the galactic N H value. However, the above model with the fixed N H value also provides good fit to the datasets.

HEAO 1 A-2 low-energy detector X-ray spectra of the Lupus Loop and SN 1006

The Lupus Loop and SN 1006 were observed by the A-2 low-energy detector proportional counters on the HEAO 1 satellite as part of the all-sky survey. As a result of a major advance in understanding of detector response and background accurate analysis of the data has become possible. Soft X-ray spectra for both supernova remnants were constructed from the PHA data taken during the scanning observations. Single-temperature and two-temperature Raymond-Smith models were fitted to the observed spectra. In addition, power-law and power-law plus one-temperature models were fitted to the spectrum of SN 1006. Only two-component models provide an adequate description for both Lupus Loop and SN 1006 spectra. The temperatures, column densities, and emission measures are significantly more accurate than previous results.

A large, low-energy neutrino detector for neutrino oscillations and supernovae watch

Abstract We describe a large, low-energy and low background Gd-loaded liquid scintillation detector with a fiducial mass of 1000 ton to be installed 200 m underground at a distance of 10–15 km from a power reactor. The detector will serve to explore neutrino oscillations down to mass parameters Δm2 of 10−4 eV2 and mixing angles sin22θ larger than 0.1 and also as a low-energy neutrino observatory for supernovae and other astrophysical events. The detector reaction νep → e+n provides a correlated e+, n signature with the neutron yielding an 8 MeV gamma cascade following capture in Gd. Some of the optimized parameters are: light transmission length 6.1 m, Gd concentration 0.05%, mean neutron capture time 46 μs. With thresholds for the positron kinetic energy and capture gamma rays of 1 and 3.5 MeV, respectively, we expect a detector efficiency of 50% and a signal rate of 16 neutrino events per day per 7.5 GW reactor power with a background rate of 2 per day. A 20 t prototype detector will serve for feasibility studies. Installed 1 km from a reactor it will be sensitive to mass parameters down to 10−3 eV2.

Detection and quantification of low energy, low level electron energy loss edges

Detection and quantification of low energy, low level electron energy loss edges

HEAO 1 A-2 low-energy detector X-ray spectra of the Cygnus Loop

The Cygnus Loop supernova remnant was observed by the A-2 low-energy detector (LED) proportional counters on the HEAO 1 satellite. Recent improvements to the non-X-ray background rejection and detector response simulation have allowed production of the most accurate spectra of the Cygnus Loop to date. Three separate regions of the Cygnus Loop were observed. Single-temperature, Raymond-Smith models are inadequate to describe the spectra, but two component model fits are good. Temperature, column density, and emission measure variations across the Cygnus Loop are found. These results are interpreted and compared with previous work.

Pure state Ne*(*)[| J, M⪢]-preparation in a magnetic field: Polarization effects in ionizing collisions

A compact device (lengh 175 mm) has been built for the energy resolved detection of low energy (1–5 eV) Penning electrons with a 2π solid angle collection efficiency, based on the principle of adiabatic parallelisation of electron motion in a diverging magnetic field. A retarding field analysis is then used as a high pass filter to discriminate between Penning electrons released in collisions of rare gas atoms in metastable and shortlived, laser excited states. The overall detection efficiency is 0.13. The Zeeman-splitting of the atomic levels in the scattering center (maximum B = 222 G) allows the preparation of single magnetic substates | J, M⪢ B . By rotating the detector in the collision plane, well defined | J, M⪢ g states can be produced with respect to the relative velocity g, the quantization axis relevant for the collisions. The system has been tested by measuring the collision energy dependence of polarized-atom cross sections J Q | M| for the Ne* [ 3P 2]-Ar and Ne** [ 3D 3]-Ar systems. For the Ne* [ 3P 2] metastable atoms we find 2 Q 0/ 2 Q 2 = 1.55 ± 0.06 and 1.05 ± 0.06 in the thermal and superthermal energy range, respectively, which should be compared to 1.30 of Bregel et al. at thermal energies. For the Ne** [ 3D 3] state we find 3 Q 0,1/ 3 Q 2,3 = 1.65 ± 0.06 and 1.00 ± 0.10 for the same energy ranges.

Evaluating 30mm2 Si(Li) detectors for light-element x-ray analysis

Light element x-ray microanalysis with the Si(Li) detecor is dependent on two detector crystal characteristics. The first is resolution, which has been traditionally standardized to be FWHM at Mn Kα. The second factor is efficiency, which is primarily but not entirely established by the detector area. These two factors effect light element sensitivity in an inverse manner. A premium resolution detector can be produced by minimizing the area, but the efficiency, as previously discussed , is directly proportional to the detector area.A special effect of efficiency degradation exists in the very low energy end of the spectrum where the x-ray energy pulses are approximately equal to the electronic noise level. The detector dead layer plays an important role in the low energy detection efficiency, since good, low energy efficiency is much more important than good manganese resolution or good electronic noise resolution.In a common 10mm2 Kevex detector, ~135 eV resolution at Mn is obtainable and the electronic noise resolution is 65 eV.

Temporal behavior of Hercules X-1 - The long-term variability of its pulse profile and the 35 day X-ray intensity modulation

view Abstract Citations (23) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Temporal Behavior of Hercules X-1: The Long-Term Variability of Its Pulse Profile and the 35 Day X-Ray Intensity Modulation Soong, Y. ; Gruber, D. E. ; Peterson, L. E. ; Rothschild, R. E. Abstract Data collected by the low-energy detectors of the Hard X-Ray and Low Energy Gamma-Ray Experiment on HEAO 1 were analyzed to study the variability in the temporal behavior of Hercules X-1. Data obtained during thirteen pointed observations distributed in 35-day phase provided details on the time and the energy dependence of the pulse shape and the spectra. It was found that a structural change at the inner edge of the accretion disk, but not at the large radii, was likely to cause the 35-day as well as the observed short-term rapid variations of the pulse profile, which had a considerably more pronounced time dependence than energy dependence. It is suggested that the variable mass-channeling scheme and an intervening effect at the inner accretion disk are directly responsible for the 35-day X-ray modulation. Publication: The Astrophysical Journal Pub Date: January 1990 DOI: 10.1086/168271 Bibcode: 1990ApJ...348..634S Keywords: Light Curve; Neutron Stars; Pulsars; Stellar Spectra; X Ray Binaries; Accretion Disks; Cyclotron Radiation; Heao 1; Periodic Variations; Power Spectra; Spectral Energy Distribution; Astrophysics; STARS: INDIVIDUAL CONSTELLATION NAME: HERCULES X-1; STARS: NEUTRON; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (1)

PIN-diodes for electron detection

The counting and spectroscopy of conversion electrons and β-rays was tested with PIN-diodes. The diodes were used in air at normal pressure and at different operational temperatures. The energy resolution and low-energy detection thresholds as well as the time resolution for coincidence counting were measured.