Absolute Detection Efficiency Research Articles

Performance of a micro-channel plates position sensitive detector

The absolute detection efficiency of large area micro-channel plates (MCPs) detectors has been measured with 6Li + and 23Na + ions in the 0.5–7.5 keV energy range. Two detectors of 47 mm and 83 mm active diameter have been tested. They consist in a pair of MCPs mounted in a chevron configuration with delay line anodes for position readout. The efficiency saturates above 3000 eV, reaching a value of 52.3(3)%, consistent with the MCPs geometry. The behaviour of the efficiency with respect to the ion kinetic energy is ascribed to the electronic threshold, through a detailed analysis of the collected charge distribution. The efficiency dependence on the ions impact position and incidence angle has also been studied. A loss of efficiency has been observed in the vicinity of the MCPs bias angle, which can be avoided if a large post-acceleration field is created in front of the MCPs. Finally the study of a position calibration is presented. A position resolution of 110(26) μm has been achieved.

Establishment of HPGe detector efficiency for point source including true coincidence correction

Due to the variation of the activity levels of various samples in γ-ray spectroscopy, the source-to-detector distance is not fixed at a constant value. This means that the measurements of the absolute detector efficiency must be carried out for each geometrical arrangement used in γ-ray measurements, which is difficult and non-feasible. This work established a method to calibrate an HPGe detector using only one precise efficiency curve obtained experimentally at a reference source-to-detector distance and a simple computer program to extract the resulting efficiency curves at other distances. The validity of the computed efficiencies for various detector geometries was checked against published calculation and simulation results. The disagreements were <1% for the calculations and <2.7% in the case of simulation results except for one case with a 9% discrepancy. The results obtained with this method were also checked against efficiency curves measured experimentally at different source-to-detector distances using 10% and 50% p-type HPGe detectors with single and multi γ-ray emitters. The results of this method are in good agreement with that carried out by single γ-ray emitters. The disagreement was <2.2% and 4.7% for the 50% and 10% HPGe, respectively. The experimental results with multi γ-ray radionuclides were found to disagree with those obtained using the established method at small source-to-detector distances. A computer program was used to estimate the γ–γ true coincidence correction factor to eliminate this disagreement. For multi γ-ray emitters the disagreement after true coincidence correction was found to be <10% and <6% at small source-to-detector distances for the 50% and 10% HPGe, respectively. The maximum values were <3% and <5% at large distances (⩾11.5 cm) in the case of the 50% and 10% HPGe, respectively.

Absolute detection efficiency of space-based ion mass spectrometers and neutral atom imagers

Space-based ion mass spectrometers and neutral atom imagers often utilize a thin foil for generation of secondary electrons and employ a coincidence measurement between detection of the secondary electrons and detection of the primary ion or neutral atom, allowing unambiguous detection of the particle in a large noise background and determination of properties of the particle using time-of-flight measurement. We demonstrate a simple and straightforward method for laboratory calibration and in situ quantification and monitoring of the absolute detection probabilities of the detectors and the absolute detection efficiency of the detector subsystem without knowledge of the incident particle flux.

Prompt gamma neutron activation analysis of boron with a 241Am-Be neutron source

A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq 241Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36. 104 n. m-2 . s-1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120-1500 keV was determined using 152Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt.

Development of a Neutron Mu1tiplicity Counter System for the Nuc1ear Material Accounting and Safeguards in KAERl

A well-type neutron multiplicity counter(WNMC) system was installed in a hot cell for the purpose of nuclear material control, accounting (NMC&A) and safeguards. The WNMC system determined the nuclear material amount on the basis of the Cm-monitoring method by measuring the neutron multiplicity and the number of coincidence events. The developed system consisted of 20 He-3 tubes with a 2.54 cm diameter and 50 cm length to cover a 25 cm long uniform neutron efficiency region along the tube length direction. As a neutron moderator in order to increase the neutron absorption rate at the He-3 tube, a well type high density polyethylene(HDPE) with a 50cm diameter was used. The efficiently optimized cylindrical Cd-plate was used in order to satisfy the uniformity along the tube direction. The absolute neutron detection efficiency of the HDPE system was measured about 14.0 % and the die-away time was 51.6µs. This system will be used not only for NMC8A but also the process for material quality control, for example, decladding performance of rod-cuts and the homogeneity of a mixing powder, waste and ingot.

Potential of a Compton camera for high performance scintimammography

In this paper, we present a novel approach to scintimammography that is based on the Compton camera principle. We analyse the performance of our scheme using Monte Carlo simulations. In particular, we evaluate the detection efficiency, spatial resolution and lesion visibility of the system at several gamma photon energies. The simulation results show that the proposed technique achieves an absolute detection efficiency of 0.03 and a full width at half maximum resolution of 3.8 mm at 141 keV photon energy for point sources 2.5 cm deep in a 5 cm thick breast phantom using 5 mm thick silicon detectors. Furthermore, our approach shows good performance in lesion detection, especially at high gamma photon energies, where mechanically collimated systems perform poorly due to severe septal penetration. With total collected counts of 1.35 million, equivalent to a 30 s acquisition time for an activity concentration level of 3.7 kBq ml−1 (100 nCi cm−3) in normal breast tissue, and a tumour-to-background ratio of 8:1, our system can clearly reveal an 8 mm diameter tumour that is located 2.5 cm deep in a 500 ml breast phantom. We also present a simulation-based quantitative performance comparison between the proposed scintimammographic system and the compact collimated scintimammographic system in the task of lesion detection under a clinical imaging situation using a non-prewhitening matched filter observer model. Our comparison demonstrates that for the same imaging time, the two systems have a comparable performance in detecting an 8 mm tumour at 141 keV, with the proposed system performing marginally better. However, the proposed scintimammographic system clearly outperforms the compact collimated counterpart in the detection of a 5 mm tumour. We also investigate the contribution of scatter and direct radiation from adjacent organs. We find that the background contribution of liver to the right breast is 30% at 141 keV, which can be reduced to 4.8% with shielding.

Monte Carlo modeling of heterogeneous scintillation flow-cell detectors

Heterogeneous flow-cell detectors packed with scintillator granules were simulated with the Monte Carlo code, PENetration and Energy LOss of Positrons and Electrons (PENELOPE) (Version 2000), for the detection of beta particles in aqueous media. The simulations were run for monoenergetic electrons at the average and endpoint energies of common beta-emitting radionuclides. PENELOPE was used to simulate the electron interactions as a means of investigating the effects of: packing geometry of scintillator granules, scintillator granule size, and the energy and initial location of electrons within the flow-cell on the fraction of energy deposited in the scintillator and the geometrical detection efficiency. The simulation results showed that higher packing density (lower porosity) and smaller scintillator granule size would result in a higher fraction of energy deposited in the scintillator, but the effect is more pronounced for low-energy electrons (180keV or lower) than for higher-energy ones (550keV or higher). The simulation results also showed that the initial location of electrons within the flow-cell has a significant effect on the fraction of energy deposited in the scintillator for low-energy electrons (180keV or lower), but gradually diminishes as the electron energy increases (above 550keV). The geometrical detection efficiency as simulated using PENELOPE was compared to experimental absolute detection efficiency found in the literature. The former was generally higher than the latter as expected and their ratio was used to estimate the light collection efficiency, whereas the reasons for the difference at electron energy of 53keV and lower were discussed.

Spatial Profile Measurement Method of Absolute Detection Efficiency of an Infrared Heterodyne Receiver for the CO2 Laser Collective Thomson Scattering System in JT-60U

A collective Thomson scattering (CTS) system based on CO2 laser is being developed in JT-60U to demonstrate the feasibility of ion temperature and alpha particle measurement in international thermonuclear experimental reactor (ITER). A new and effective method of measuring the spatial profile of absolute detection efficiency of an infrared heterodyne receiver has been developed for the CTS system. The viewing area and divergence of the field of view were first investigated with this method. Consequently, the spot size of the field of view could be narrowed to 0.74 mrad by adjusting the focal length of the local oscillator. The effective sample volume length determined by the injection beam waist and divergence of the field of view was also investigated.

Simultaneous separation and detection of actinides in acidic solutions using an extractive scintillating resin.

An extractive scintillating resin was evaluated for the simultaneous separation and detection of actinides in acidic solutions. The transuranic extractive scintillating (TRU-ES) resin is composed of an inert macroporous polystyrene core impregnated with organic fluors (diphenyloxazole and 1,4-bis-(4-methyl-5-phenyl-2-oxazolyl)benzene) and an extractant (octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide in tributyl phosphate). The TRU-ES resin was packed into FEP Teflon tubing to produce a flow cell (0.2-mL free column volume), which is placed into a scintillation detection system to obtain pulse height spectra and time series data during loading and elution of actinides onto/from the resin. The alpha-particle absolute detection efficiencies ranged from 77% to 96.5%, depending on the alpha energy and quench. In addition to the on-line analyses, off-line analyses of the effluent can be conducted using conventional detection methods. The TRU-ES resin was applied to the quantification of a mixed radionuclide solution and two actual waste samples. The on-line characterization of the mixed radionuclide solution was within 10% of the reported activities whereas the agreement with the waste samples was not as good due to sorption onto the sample container walls and the oxidation state of plutonium. Agreement between the on-line and off-line analyses was within 35% of one another for both waste samples.

Characterization of superconducting tunnel junction X-ray detectors by means of monochromatized undulator radiation

A superconducting tunnel junction X-ray detector system was designed to match current energy resolution, count rate and UHV requirements in soft X-ray spectroscopy. It employs a two-stage adiabatic demagnetization refrigerator with a 23 cm long cold finger to operate the detector inside a sample chamber for X-ray fluorescence measurements. This cryogenic detector system was characterized in the energy range from 100 eV to 900 eV with respect to its energy resolution ranging from 12 eV to 25 eV FWHM, count rate capability up to 80 kcps and absolute detection efficiency using undulator radiation monochromatized by means of a plane grating monochromator beamline. Collimating the beam to the detector area improves the energy resolution by about 10%. The potential of this novel detector for beamline characterization was investigated.

Nuclear recoil detection with microchannel plates

Measurements of particle-recoil coincidences in low-energy (p,α) reactions on 6,7 Li, 15 N, 19 F and 23 Na target nuclei are described. Reaction α-particles were detected using a silicon surface-barrier detector, while the corresponding recoil nuclei were measured with a microchannel plate detector. Absolute microchannel plate detection efficiencies for a range of recoil energies (0.3– 8.3 MeV ) and masses ( A=3–20) are presented. The dependence of the microchannel plate detection efficiency on increasing background count rates is investigated. The usefulness of the present experimental technique for investigations of interest to nuclear astrophysics is discussed.

Continuous bioaerosol monitoring using UV excitation fluorescence: Outdoor test results*

AbstractThis report describes procedures and results of recent outdoor tests in evaluating a prototype single particle fluorescence analyzer (SPFA), an instrument that is being developed to simultaneously monitor ambient concentrations of both biological and nonbiological aerosols using optical techniques. Recent modifications to the SPFA are also noted and discussed. During recent outdoor tests, aerosols were generated containing four different types of biological material: ova albumin, MS‐2 phage, Erwinia herbicola vegetative cells and Bacillus subtilis spores. Analysis of the SPFA results indicates that a probability of detection of at least 87% was achieved for target aerosol concentrations as low as a few (1–5) particles/liter. Moreover, comparison with different reference instruments indicate that the SPFA can achieve absolute quantitative detection efficiencies for individual biological aerosols of at least 70% (assuming appropriate alignment and threshold settings are made). During some of the outdoor tests different nonbiological aerosols were also released that generally did not generate any significant fluorescent signals. Although official test scores have not yet been distributed, we provide here the SPFA results for each of the aerosol releases made during the test. Analysis of the relative fluorescent intensities in the visible and UV spectral bands suggests that these data can be used in the future to provide an indication of the type of biological aerosol being released as well. © 2001 John Wiley &amp; Sons, Inc. Field Analyt Chem Technol 5: 205–212, 2001

Imaging of laser–plasma x-ray emission with charge-injection devices

This work details the method of obtaining time-integrated images of laser–plasma x-ray emission using charge-injection devices (CIDs), as has been demonstrated on the University of Rochester’s 60-beam UV OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The CID has an architecture similar to a charge-coupled device. The differences make them more resistant to radiation damage and, therefore, more appropriate for some application in laser–plasma x-ray imaging. CID-recorded images have been obtained with x-ray pinhole cameras, x-ray microscopes, x-ray spectrometers, and monochromatic x-ray imaging systems. Simultaneous images obtained on these systems with calibrated x-ray film have enabled determination of the absolute detection efficiency of the CIDs in the energy range from 2 to 8 keV.

Measurement of k0-Factors in Prompt Gamma-Ray Neutron Activation Analysis

The guided thermal neutron beam at 100 MW Dhruva research reactor facility of Bhabha Atomic Research Centre (BARC) was used to carry out prompt gamma-ray neutron activation analysis (PGNAA). The prompt k0-factors have been determined for the isotopes of the elements H, B, K, Co, Cu, Ca, Ti, Cr, Cd, Ba, Hg and Gd with respect to 1951 keV gamma-line of 36Cl. The prompt k0-factors for H, Cl and Cu were also measured with respect to the 1381 keV gamma-line of 49Ti. Different samples like NH4Cl, Ti metal, cobalt chloride and other stoichiometric compounds and pure metals were used for this purpose. Prompt gamma-rays were accumulated using a 22% HPGe detector connected to a PC based 8k MCA in single mode counting. The energy calibration in the range of 100–8500 keV was carried out using gamma-rays from 152Eu and 60Co, and the prompt gamma-rays from 36Cl whereas the absolute detection efficiency for this energy range was determined using 152Eu and prompt gamma-rays from 36Cl and 49Ti.

Absolute detection efficiencies of low energy H, H −, H +, H 2+ and H 3+ incident on a multichannel plate detector

Measured absolute detection efficiencies are presented for H, H − and H n + ( n=1,2,3) impacting a commercially available, dual multichannel plate (MCP) electron multiplier at kinetic energies ranging from 30 to 1000 eV. Measurements involving isotopic substitutions (D, D −, D n +) and Ar + are also presented. In addition, atomic hydrogen detection efficiencies relative to those of H + and H − are given, as they may have a more universal application. For the three charge states, H, H + and H −, the absolute detection efficiencies are markedly different at low energies and converge to a nearly uniform value of ∼70% with increasing projectile energy. The energy dependence is strongest for H +, varying nearly three orders of magnitude over the energy range studied, and weakest for H −, varying by less than one order of magnitude. In general, for the low energy positive ions at a given energy, the lighter the incident particle mass, the greater the probability of its detection.

Detection efficiency of a channel electron multiplier for low energy incident noble gas ions

The absolute detection efficiency of a continuous channel electron multiplier (DeTech 407-EIC) has been measured for the noble gas ions He+, Ar+, and Xe+, with energies up to 4.9 keV. For all ions, the detection efficiency initially rises linearly as a function of velocity. Our results and a reanalysis of literature data show that the threshold velocity below which a multiplier does not respond to impinging ions cannot be regarded as independent of the ion’s atomic number, Z, as previously reported. Instead, the threshold velocity is proportional to Z−c. The experimentally obtained efficiency-versus-velocity curves for our detector have been analyzed in the region of linear increase. The resulting expression for the detector efficiency, ε, is a function of the ion’s atomic number and velocity, v, and can be written as ε(v,Z)=a(v−b/Zc)Zn, with a, b, c, and n being constants.

The performance of a CCD digital autoradiography imaging system

Autoradiography is a widely used technique for imaging trace quantities ofradioactivity within biological samples, conventionally using photographicfilm. This method produces images with high spatial resolution, but it suffersfrom very low sensitivity and poor dynamic range. Digital autoradiographysystems with greatly improved sensitivity and linearity are commerciallyavailable, but the spatial resolution is usually much less than that achievedusing film. We report here the design, construction and characterization of anovel digital autoradiography system based on scientific-grade charged coupleddevices (CCDs). Images of x-ray and β emissions from radionuclidescommonly used in autoradiography show that the system can perform high-speedquantitative imaging with a spatial resolution of ~30 µm. Usinga frame by frame acquisition method the dynamic range is shown to be at leastthree orders of magnitude. The absolute detection efficiency is comparable tothe best of the currently available digital systems. CCD images of 125Iand 14C radioisotope distributions in tissue samples are superior tothe equivalent film images and have been acquired in 1-10% of the time.

Absolute detection efficiency of a microchannel plate detector for neutral atoms

The absolute detection efficiency (ADE) of microchannel plates for neutral sodium and potassium atoms is measured in the low keV energy range. It is shown that ADE is primarily a function of the particle energy. This result is compared to measurements made by other authors for ionic particles.

Fluorescence photobleaching‐based image standardization for fluorescence microscopy

A method is presented for the standardization of images acquired with fluorescence microscopy, based on the knowledge of spatial distributions proportional to the microscope's absolute excitation intensity and fluorescence detection efficiency distributions over the image field. These distributions are determined using a thin fluorescent test layer, employed under practically mono-exponential photobleaching conditions. It is demonstrated that these distributions can be used for (i) the quantitative evaluation of differences between both the excitation intensity and the fluorescence detection efficiency of different fluorescence microscopes and (ii) the standardization of images acquired with different microscopes, permitting the deduction of quantitative relationships between images obtained under different imaging conditions.

Absolute calibration of a multichannel plate detector for low energy O, O−, and O+

Absolute detection efficiencies of a commercial multichannel plate detector have been measured for O, O+, and O−, impacting at normal incidence for energies ranging from 30–1000 eV. In addition, the detection efficiencies for O relative to its ions are presented, as they may have a more universal application. The absolute detection efficiencies are strongly energy dependent and significant differences are observed for the various charge states at lower energies. The detection efficiencies for the different charge states appear to converge at higher energies. The strongest energy dependence is for O+; the detection efficiency varies by three orders of magnitude across the energy range studied. The weakest dependence is for O−, which varies less than one order of magnitude.