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Customer Publications

2015

Title: Characterization of neutron fields from bare and heavy water moderated Cf-252 spontaneous fission source using Bonner Sphere Spectrometer

Date: 26-Feb-15
Publication type: Peer Reviewed Publication
Publication: Applied Radiation and Isotopes,Volume 99, May 2015, Pages 122–132
Authors: Jovica Atanackovic, Andre Yonkeu, Jacques Dubeau, Sampath Hakmana Witharana, Nicholas Priest
Abstract: In this work a calibrated Bonner Sphere Spectrometer (BSS), together with ISO shadow cones, was used to quantify the total and scattered components of bare and heavy water moderated 252Cf neutron fields. All measurements were performed with a BSS that was calibrated at the National Physical Laboratory (NPL), Teddington, UK, which is a global primary standard laboratory and world-leading facility for neutron metrology and neutron instruments calibration. The fields were characterized for source-spectrometer distances of 80, 100, 150 and 200 cm; and at heights of 103 and 200 cm from the facility floor. As expected, the scattered contribution was greatest at the farthest distance from the source and closer to the floor. Hence, at a distance of 200 cm and a height of 103 cm, the scatter added to the direct field up to 162% of the total neutron fluence and up to 61% of the ambient dose equivalent, while at the same distance and height of 200 cm above the floor, these values were up to 146% and 52%, respectively. In the case of heavy water moderated 252Cf neutron fields, a shadow cone subtraction technique could not be implemented, however Monte Carlo simulations were utilized in order to differentiate between the direct and scatter components of the neutron fields. In this case, at a source–detector distance of 200 cm and a height of 103 cm, the scatter added to the direct field up to 148% of the total neutron fluence and up to 45% of the ambient dose equivalent, while at the same distance and a height of 200 cm above the floor, these values were up to 134% and 42%, respectively.
Keywords: Cf-252 neutron source; Heavy water moderated neutrons; Bonner Sphere Spectrometer; Shadow cone subtraction methods; Neutron spectral unfolding; MAXED; STAY'SL; ISO-8529; Characterization of neutron fields

 

2014

Title: Pulse-shape discrimination and energy resolution of a liquid-argon scintillator with xenon doping
Date: June 2014
Publication type: Peer reviewed publication
Publication: Journal of Instrumentation, Volume 9, p06013
Authors: C G Wahl, E P Bernard, W H Lippincott, J A Nikkel, Y Shin and D N McKinsey
Abstract: Liquid-argon scintillation detectors are used in fundamental physics experiments and are being considered for security applications. Previous studies have suggested that the addition of small amounts of xenon dopant improves performance in light or signal yield, energy resolution, and particle discrimination. In this study, we investigate the detector response for xenon dopant concentrations from 9 ± 5 ppm to 1100 ± 500 ppm xenon (by weight) in 6 steps. The 3.14-liter detector uses tetraphenyl butadiene (TPB) wavelength shifter with dual photomultiplier tubes and is operated in single-phase mode. Gamma-ray-interaction signal yield of 4.0 ± 0.1 photoelectrons/keV improved to 5.0 ± 0.1 photoelectrons/keV with dopant. Energy resolution at 662 keV improved from (4.4 ± 0.2)% (σ) to (3.5 ± 0.2)% (σ) with dopant. Pulse-shape discrimination performance degraded greatly at the first addition of dopant, slightly improved with additional additions, then rapidly improved near the end of our dopant range, with performance becoming slightly better than pure argon at the highest tested dopant concentration. Some evidence of reduced neutron scintillation efficiency with increasing dopant concentration was observed. Finally, the waveform shape outside the TPB region is discussed, suggesting that the contribution to the waveform from xenon-produced light is primarily in the last portion of the slow component..
Keywords: Noble-liquid detectors (scintillation, ionization two-phase), Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators), Particle detectors, Spectrometers.

Title: Verification and Validation of Monte Carlo n-Particle Code 6 (MCNP6) with Neutron Protection Factor Measurements of an Iron Box
Date: 27th March 2014
Publication type: Thesis, Masters
Publication: AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
Authors: Decker, Andrew W
Abstract: Using a 1984 benchmark experiment, MCNP6 replicated the neutron flux and neutron protection factor (NPF) measurements of an iron box, which simulated a basic military vehicle, resulting in less than 5% difference from the published results. Additionally, the neutron flux spectrum of a 239 PuBe source was characterized using a Bonner Sphere Spectrometer (BSS) and the solution unfolded using the Maximum Entropy Deconvolution (MAXED) program, producing a X2/df of 0.97. Utilizing a steel box provided by the DTRA, measurements of neutron flux from a D-D neutron accelerator were recorded via BSS inside and outside of the box. Both flux spectra were unfolded through MAXED using MCNP6 computations as a priori, which resulted in X2/df values of 0.86 and 0.91, respectively. NPF assessments of the steel box were then conducted using experimental and MCNP6 flux spectra for the box, as well as H*(10) scaling, with final results differing by less than 1%. MAXED software was leveraged for all flux spectrum unfolding, incorporating updated BSS response functions generated within this research from MCNP6. This experiment and its conclusions strongly support the verification and validation of MCNP6 for modeling NPF assessments of military vehicles.
Keywords: EXPOSURE(GENERAL), MILITARY PERSONNEL, PROTECTIVE CLOTHING, RADIATION SHIELDING, ENTROPY, MILITARY VEHICLES, MONTE CARLO METHOD, NEUTRON FLUX, NEUTRON SPECTRUM, SPECTROMETERS, THESES, VALIDATION, VERIFICATION

Patent: US8648314
Title: Fast neutron imaging device and method
Date: Feb 11, 2014
Authors: Vladimir Popov, Pavel Degtiarenko, Igor V. Musatov
Assignee: Jefferson Science Associates, Llc
Abstract: A fast neutron imaging apparatus and method of constructing fast neutron radiography images, the apparatus including a neutron source and a detector that provides event-by-event acquisition of position and energy deposition, and optionally timing and pulse shape for each individual neutron event detected by the detector. The method for constructing fast neutron radiography images utilizes the apparatus of the invention.

Title: MCNP modeling of a neutron generator and its shielding at Missouri University of Science and Technology
Date: 11-Dec-2014
Publication type: Peer Reviewed paper
Publication: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 767, 11 December 2014, Pages 126–134, doi:10.1016/j.nima.2014.08.011
Authors: Manish K. Sharma, Ayodeji B. Alajo, Xin Liu
Abstract: The shielding of a neutron generator producing fast neutrons should be sufficient to limit the dose rates to the prescribed values. A deuterium-deuterium neutron generator has been installed in the Nuclear Engineering Department at Missouri University of Science and Technology (Missouri S&T). The generator produces fast neutrons with an approximate energy of 2.5 MeV. The generator is currently shielded with different materials like lead, high-density polyethylene, and borated polyethylene. An MCNP transport simulation has been performed to estimate the dose rates at various places in and around the facility. The simulations incorporated the geometric and composition information of these shielding materials to determine neutron and photon dose rates at three central planes passing through the neutron source. Neutron and photon dose rate contour plots at these planes were provided using a MATLAB program. Furthermore, the maximum dose rates in the vicinity of the facility were used to estimate the annual limit for the generator׳s hours of operation. A successful operation of this generator will provide a convenient neutron source for basic and applied research at the Nuclear Engineering Department of Missouri S&T.
Keywords: Neutron generator shielding; D-D neutron generator; MCNP; Dose

Title: A compact DD neutron generator–based NAA system to quantify manganese (Mn) in bone in vivo
Date: December 2014
Publication: Yingzi Liu et al 2014 Physiol. Meas. 35 1899 doi:10.1088/0967-3334/35/9/1899
Authors: Yingzi Liu, Patrick Byrne, Haoyu Wang, David Koltick, Wei Zheng and Linda H Nie
Abstract: A deuterium-deuterium (DD) neutron generator–based neutron activation analysis (NAA) system has been developed to quantify metals, including manganese (Mn), in bone in vivo. A DD neutron generator with a flux of up to 3*109 neutrons s−1 was set up in our lab for this purpose. Optimized settings, including moderator, reflector, and shielding material and thickness, were selected based on Monte Carlo (MC) simulations conducted in our previous work. Hand phantoms doped with different Mn concentrations were irradiated using the optimized DD neutron generator irradiation system. The Mn characteristic γ-rays were collected by an HPGe detector system with 100% relative efficiency. The calibration line of the Mn/calcium (Ca) count ratio versus bone Mn concentration was obtained (R2 = 0.99) using the hand phantoms. The detection limit (DL) was calculated to be about 1.05 μg g−1 dry bone (ppm) with an equivalent dose of 85.4 mSv to the hand. The DL can be reduced to 0.74 ppm by using two 100% HPGe detectors. The whole body effective dose delivered to the irradiated subject was calculated to be about 17 μSv. Given the average normal bone Mn concentration of 1 ppm in the general population, this system is promising for in vivo bone Mn quantification in humans.

2013

Title: Development of a transportable neutron activation analysis system to quantify manganese in bone in vivo: feasibility and methodology
Date: December, 2013
Publication: Physiol Meas. 2013 Dec; 34(12): 1593–1609, 2013 Oct 28. doi: 10.1088/0967-3334/34/12/1593
Authors: Yingzi Liu, David Koltick, Patrick Byrne, Haoyu Wang, Wei Zheng, and Linda H Nie
Abstract: This study was conducted to investigate the methodology and feasibility of developing a transportable neutron activation analysis (NAA) system to quantify manganese (Mn) in bone using a portable deuterium–deuterium (DD) neutron generator as the neutron source. Since a DD neutron generator was not available in our laboratory, a deuterium–tritium (DT) neutron generator was used to obtain experimental data and validate the results from Monte Carlo (MC) simulations. After validation, MC simulations using a DD generator as the neutron source were then conducted. Different types of moderators and reflectors were simulated, and the optimal thicknesses for the moderator and reflector were determined. To estimate the detection limit (DL) of the system, and to observe the interference of the magnesium (Mg) γ line at 844 keV to the Mn γ line at 847 keV, three hand phantoms with Mn concentrations of 30 parts per million (ppm), 150 ppm, and 500 ppm were made and irradiated by the DT generator system. The Mn signals in these phantoms were then measured using a 50% high-efficiency high-purity germanium (HPGe) detector. The DL was calculated to be about 4.4 ppm for the chosen irradiation, decay, and measurement time. This was calculated to be equivalent to a DL of about 3.3 ppm for the DD generator system. To achieve this DL with one 50% high-efficiency HPGe detector, the dose to the hand was simulated to be about 37 mSv, with the total body equivalent dose being about 23μSv. In conclusion, it is feasible to develop a transportable NAA system to quantify Mn in bone in vivo with an acceptable radiation exposure to the subject.
Keywords: IVNAA, DD neutron generator, Mn, hand bone

2012

Title: Energy resolution and gamma/neutron discrimination in xenon-doped liquid argon
Date: 3-Nov-12
Publication type: Conference publication
Publication: Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE,, pp339-342, ISSN 1082-3654,INSPEC no: 13647499, doi: 10.1109/NSSMIC.2012.6551121
Authors: Wahl, C.G. Bernard, E.P.; McKinsey, D.N. Nikkel, J.
Abstract: Liquid argon scintillation detectors offer the possibility for large volumes, good pulse-shape discrimination between particles with different ionization densities, and energy resolution comparable with standard inorganic scintillators. Their fast timing and radiation-damage insensitivity also makes it possible to use them in high-count-rate environments. This study investigates the effect of doping liquid argon with small amounts of xenon, which is known to increase light yield and decrease the slow component decay time. These effects were observed. Energy resolution changed little with dopant concentration. Gamma/neutron pulse-shape discrimination, contrary to a previous study, degraded with each addition of xenon.

2010

Title: New detector for use in fast neutron radiography
Date: JULY 11th–15th 2010,
Publication: 12th International Workshop on Radiation Imaging Detectors (IWORID), V Popov et al 2011 JINST 6 C01029 doi:10.1088/1748-0221/6/01/C01029
Authors: V Popov, P Degtiarenko and I Musatov
Abstract: ABSTRACT: We have developed and tested a new detector for use in the fast neutron (FN) imaging radiography applications, which is distinct from other presently known FN imagers. Our device implements a neutron-sensitive scintillator attached to a position-sensitive photomultiplier tube, and operates in the event-by-event readout mode, acquiring energy, timing, and pulse shape information for all detected radiation events. This information is used to help separate events of FN interactions in the scintillator from the background events, caused by the electronics noise and by other types of background radiation. The detector performance for FN imaging application was tested using the D-D neutron generator, designed and manufactured by Adelphi Technology, Inc. This essentially point-like neutron source operates in continuous mode, producing up to 109 of 2.5MeV neutrons per second. Samples made of metals, plastic, and other materials were used to measure the detector resolution, efficiency and uniformity. Results of these tests are presented and discussed. Both X and Y position resolutions of the FN imaging detector are estimated to be less than 0.5 mm (sigma). Because this detector shows the fraction-of-a-millimeter resolution desirable for most of FN applications, is capable of good neutron-background separation, and is built using radiation hard materials, we believe that it could be a good alternative to other FN imaging systems based on CCD or solid state detectors. In addition, because of its sub-nanosecond timing resolution, it is suitable for the time-of-flight energy-resolved FN imaging.
Keywords: Inspection with neutrons; Neutron detectors (cold, thermal, fast neutrons); Neutron radiography

Title: DESIGN STUDIES FOR STAND OFF BOMB DETECTION
Date: 2010
Publication type: Thesis
Publication: Thesis, Department of Mechanical and Nuclear Engineering, College of Engineering, KANSAS STATE UNIVERSITY, Manhattan, Kansas
Authors: CHRISTOPHER P. MATTHEW
Abstract: A prototype system for detecting explosives at standoff distances, using a signature based radiation scanning approach, is being developed at Kansas State University. The prototype will incorporate both a machine x-ray source and a machine neutron source to generate signatures from unknown samples of material. These signatures can be compared to templates measured or calculated from known explosive samples using a figure-of-merit. The machine neutron source uses the fusion of deuterium and tritium to create 14.1 MeV neutrons. Due to its radioactivity, the tritium must be sealed within the system. A new method of controlling the gas pressure with the DT generator was developed using a Zr-V-Fe gettersupplied by a commercial firm. The shielding and collimation of the 14.1 MeV neutron source is accomplished using layers of steel, high-density polyethylene and borated high-density polyethylene. This thesis describes the development of the gas control method for the sealed neutron source, design studies for the shielding and collimation of the neutron source and modifications made to the building in which the prototype is being housed

2009

Title: MCNP SIMULATIONS FOR STANDOFF BOMB DETECTION USING NEUTRON INTERROGATION
Date: 2009
Publication type: Thesis, Master of Science
Publication: Thesis, Department of Mechanical and Nuclear Engineering, College of Engineering, KANSAS STATE UNIVERSITY, Manhattan, Kansas
Authors: MARK JOHLL
Abstract: This report investigates the feasibility of a standoff interrogation method to identify nitrogen-rich explosive samples shielded by other materials (“clutter”) using neutron beams from 252Cf and deuterium-tritium (D-T) generator sources. Neutrons from the beams interact with materials in the target to produce inelastic-scatter gamma rays, and, after slowing down to thermal energies, prompt-capture gamma rays. By detection of these gamma rays, a response vector is formed that is used to calculate a figure-of-merit, whose value is dependent upon the contents of the target. Various target configurations, which include an inert-material shield and a sample that may or may not be explosive, were simulated using the MCNP5 code. Both shielding and collimation of 14.1-MeV neutron beams were simulated to produce effective neutron beams for target interrogation purposes and to minimize dose levels. Templates corresponding to particular target scenarios were generated, and their effectiveness at nitrogen-rich explosive identification was explored. Furthermore, methods were proposed yielding more effective templates including grouping target responses by density and composition. The results indicate that neutron-based interrogation has potential to detect shielded nitrogen-rich explosives. The research found that using a tiered filter approach, in which a sample must satisfy several template requirements, achieved the best results for identifying the explosive cyclonite (RDX). A study in which a 14.1-MeV neutron beam irradiated a target containing a shielded sample, which could either be explosive (RDX) or inert, yielded no false negatives and only 2 false positives over a large parameter space of clutter-sample combinations.