Mohini W Rawool-Sullivan

Mohini W Rawool-Sullivan
Los Alamos National Laboratory | LANL · X Computational Physics Division (XCP)

Ph. D.

About

115
Publications
19,664
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Citations
Introduction
Mohini W Rawool-Sullivan currently works at the X Computational Physics Division (XCP), Los Alamos National Laboratory. Mohini does research in Nuclear Engineering and Experimental Physics. Currently doing research into application of MCNP to various radiation related issues.
Additional affiliations
February 2015 - March 2019
Los Alamos National Laboratory
Position
  • Researcher
October 1990 - December 1991
New Mexico State University
Position
  • Research Associate
Description
  • Worked on the neutral meson spectrometer construction at LANL.
January 1991 - present
Education
May 1984 - July 1988
New Mexico State University
Field of study
  • Physics
September 1983 - May 1984
New Mexico State University
Field of study
  • Physics

Publications

Publications (115)
Conference Paper
Full-text available
The ability to accurately simulate gamma spectra from materials that emit both neutrons and gammas is very important to the analysis of special nuclear materials (SNM), e.g., uranium and plutonium. The approach presented in this paper uses MCNP neutron/photon transport simulations coupled to GADRAS detector response calculations to produce realisti...
Data
Full-text available
The ability to accurately simulate high-resolution gamma spectra from materials that emit both neutrons and gammas is very important to the analysis of special nuclear materials (SNM), e.g., uranium and plutonium.  One approach under consideration has been to combine MCNP and GADRAS • This approach is expected to generate more accurate gamma ray s...
Article
This is the final report of the project titled, 'Isotope Identification Algorithm for Rapid and Accurate Determination of Radioisotopes,' PMIS project number LA10-HUMANID-PD03. The goal of the work was to demonstrate principles of emulating a human analysis approach towards the data collected using radiation isotope identification devices (RIIDs)....
Data
Full-text available
It is desired to know the fission fraction of many fission product isotopes. This parameter can be used to estimate the number of fissions that occur in irradiations (or burnup). To accomplish this, a SCALE model was produced by Robert Kimpland. The ORIGEN module of SCALE was then used to simulate the production of 622 different isotopes as a funct...
Data
Full-text available
Wavelet shrinkage denoising may provide a way of doing robust feature identification in a low statistics gamma-ray spectra
Conference Paper
Full-text available
Radiation Isotope Identification Devices (RIID) are used in homeland security and other applications to identify radioactive materials. RIIDs have trouble automatically identifying radioisotopes accurately and robustly, which leads to both false positive and false negative alarms. Expert spectroscopists are often called to resolve difficult-to-reso...
Article
Full-text available
Introduction: Customs and other officials who use commercial detectors to survey materials for the presence of radioactive materials are not expert spectroscopists, and therefore sometimes are not able to conclusively identify the sources generating the signals their radiation detectors capture.
Article
Full-text available
This presentation is to educate trainees on basics of gamma-ray spectroscopy. This presentation focuses on technical aspects of gamma spectroscopy.
Article
This paper reports results from a prototype Compton imager (PCI) which consists of three planes of silicon pixel detectors as a scattering detector followed by an array of CsI(Tl) crystals as an absorbing detector. The CsI(Tl) array is mounted directly behind the silicon detectors. Simple back-projection algorithms are not sufficient to resolve ext...
Data
Full-text available
Three silicon scattering planes 16 x 20 array 3 mm x 3 mm x 0.27 mm pads Centered in X and Y 2.7 cm spacing • CsI absorbing plane 6 x 7 array Pixilated into 12 mm x 14mm x 10mm crystals 5 cm behind last silicon plane Data was collected using a coincidence trigger between a single silicon pixel and a single CsI crystal. Abstract -Compton imaging is...
Article
Compton imaging is used to predict the location of gamma-emitting radiation sources. The X and Y coordinates of the source can be obtained using a back-projected image and a two-dimensional peak-finding algorithm. The emphasis of this work is to estimate the source-to-detector distance (Z). The algorithm presented uses the solid angle subtended by...
Article
Full-text available
This report assesses the utility of lanthanum-halide detectors for isotope identification and total mass measurements for uranium and plutonium isotopes. Comparisons to similar measurements with NaI detectors are made.
Data
Full-text available
Currently portable nuclear instruments are being developed that utilize compact high sensitivity detectors operated at room temperature. It is desirable that these detectors have large absolute efficiency and reasonably good energy resolution in the 50 to 3,000 keV energy range. In order to provide high efficiency, large volumes are needed. For sem...
Data
Full-text available
We have constructed a prototype Compton imager (PCI) which consists of three planes of silicon pixel detectors as a scattering detector followed by an array of CsI(Tl) crystals as an absorbing detector. The CsI(Tl) array is mounted directly behind the silicon detectors. The relative alignment and spacing of the silicon detectors and CsI array is ad...
Article
We present results from Compton imaging of gamma-ray sources using an instrument constructed from thin silicon scattering detectors and CsI(Tl) absorbing detectors. We have successfully imaged single and double point sources for several common radioactive isotopes ((137)Cs, (60)Co, (22)Na, (54)Mn). The measured angular resolution is 11.6( composite...
Data
Full-text available
Many applications in nuclear physics, astrophysics, homeland security, and medicine require simultaneous measure-ments of more than one quantity like energy, time and position. Several new materials have been developed that may provide simultaneous high-resolution energy, time and position measure-ments. In this paper, we report on measurements of...
Article
Full-text available
In this report, we present the results of simulation studies performed using the Los Alamos National Laboratory Prototype Compton imager. This report presents the effects of detection thresholds and detector energy resolution on the angular resolution measure (ARM). This study shows that the thresholds in both the scatterer and the absorber can hav...
Data
Full-text available
This report describes experimental work performed for the "three-dimensional imaging using Compton backscatter" project. In the fourth quarter, studies were conducted on various hardware components to determine what hardware and detection equipment would be necessary for conducting the prototype experiment.
Data
Full-text available
This report presents gamma-ray spectra taken with two 1-cm diameter × 1-cm thick PreLude ® 420 scintillators with photomultipliers attached. They were purchased from Saint Gobain. This scintillator has internal contamination from Lu-176—a naturally abundant radioactive isotope of lutetium. The measured background rate was 228 ± 1 decays per sec. Th...
Article
Full-text available
Today we face serious threats from radiological dispersion devices, improvised nuclear devices, and unsecured nuclear materials. Detectors which are currently used to detect and characterize these radioactive materials (or the radioactive materials within larger assemblies) suffer from large background rates. In addition, these detectors have only...
Article
Full-text available
Gamma-ray spectra were collected using lanthanum halide detectors, specifically LaCl 3 (Ce) and LaBr 3 (Ce) detectors that were 2.54 cm in diameter × 2.54 cm in length. LaCl 3 (Ce) and LaBr 3 (Ce) usually contain radioactive contaminants that raise the background levels in detectors from 1400 keV to 2700 keV. In this study, we measured polyethylene...
Conference Paper
Radiation handheld instruments perform an integral role in first responder programs to detect illicit radioactive materials and reduce terrorist attacks. A comprehensive understanding of each commercial instrument's performance facilitates rapid and accurate data interpretation and threat assessment. RadAssessor was developed as a radiation detecto...
Data
Full-text available
Lo E s Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U.S. Department of nergy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the publ...
Article
Full-text available
This report describes tests performed on Silicon Pixel Detectors (SPDs) in the fiscal year 2002-2003 time period. The SPDs were purchased from Brookhaven National Laboratory. These detectors are being used in a prototype Compton imager currently being constructed currently at Los Alamos National Laboratory (LANL).
Data
Full-text available
This report describes performance comparisons between three commercial charge sensitive preamplifiers. The selected preamplifier will be used in the readout electronics that will be used to read out the individual elements of the CsI(Tl)/PIN array. This array is used for the back plane of the Los Alamos Compton gamma-ray imager.
Article
Full-text available
Commercially available hand-held spectrometers are widely used to interdict both smuggling and dispersal (accidental or intentional) of radioactive materials. Such instruments are also used in the non-proliferation and safeguards communities. Currently most of the commercial instruments contain NaI(Tl) and/or CdZnTe detectors. NaI(Tl) detectors hav...
Data
Full-text available
This report presents data taken with four 2.54-cm diameter and 2.54-cm thick LaBr3(Ce) scintillators. For 662 keV gamma-rays these LaBr3(Ce) detectors have efficiencies superior to NaI(Tl) and LaCl3(Ce) detectors of the same size and resolution better than CdZnTe and LaCl3(Ce). Therefore, gamma-ray spectrometers with LaBr3(Ce) scintillators are pot...
Article
Full-text available
Laboratory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. FORM 836 (10/96)
Article
The most serious terrorist threat we face today may come from radiological dispersion devices and unsecured nuclear weapons. It is imperative for national security that we develop and implement radiation detection technology capable of locating and tracking nuclear material moving across and within our borders. Many radionuclides emit gamma rays in...
Article
Full-text available
We, three members of the secondary reachback program at the Los Alamos National Laboratory (LANL), have evaluated handheld detectors that may be used by the Department of Homeland Security (DHS) customers to assist in the detection of illicit radioactive materials. Understanding the neutron response is essential for distinguishing the illicit radio...
Conference Paper
Full-text available
Compton imaging, which reconstructs the direction of incident photons based on the kinematics of Compton scattering, is of interest in the fields of astrophysics, medical imaging, and homeland defense. We are attempting to build a device in which the Compton scatter takes place in one of several layers of thin Silicon detectors and the secondary ph...
Article
Full-text available
As monitoring for radioactive materials has been routinely carried out at various borders, ports, airports, and other check points, it is becoming essential that we understand the sources of radiation signals from routinely used consumer products and materials. The main reasons for innocent alarms of border monitoring systems are shipments of medic...
Article
Full-text available
At Los Alamos National Laboratory, Los Alamos, NM, we are constructing a multilayer prototype camera using silicon pixel detectors. Each pixel detector is 5.80 cm×6.30 cm×200 μm. The pixels are 3 mm×3 mm in size. With this prototype, we intend to study electron-tracking techniques along with the three-plane Compton-imaging technique. In this paper,...
Article
Full-text available
The result of measurements of plutonium mass and metal attributes relevant to the Inventory Sampling Measurement System (ISMS) are reported. These measurements, using methods based on both neutrons and gamma rays, were performed with the special facilities and nuclear materials at Los Alamos National Laboratory. In this report we specifically focus...
Article
Full-text available
The report begins by discussing the development of the Russian naval propulsion program, including the origins of the liquid metal cooled reactor program. It then discusses the design, development, production, and operation of the Alfa-class submarines that were powered by LMC reactors. The LMC reactor fuel cycle and its proliferation and safety im...
Conference Paper
Gamma imaging based on Compton scattering was first proposed approximately 25 years ago as a replacement for mechanically collimated imaging systems. The advantages of such instruments over mechanically collimated systems are a wider field of view, higher efficiency (more source photons are used in the image construction), source localization, use...
Article
A method is described for the extraction of isotopic information from attenuated gamma-ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in...
Conference Paper
A comparison study of pulse-shape analysis techniques was conducted for a BC501A scintillator using digital signal processing (DSP). In this study, output signals from a preamplifier were input directly into a 1 GHz analog-to-digital converter. The digitized data obtained with this method was post-processed for both pulse-height and pulse-shape inf...
Article
The gross-count material basis set model (GC-MBS) for response-function fitting is applied to CdZnTe spectra. This method has been developed to solve for the isotopic composition of an unknown mixture of radionuclides attenuated through absorbers of unknown material. Results are presented for source strength and isotopic composition measurements of...
Article
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 (π+,2p), (π+,3p), and total absorption cross sections for multiproton final st...
Article
Integral cross sections for the scattering of pions by protons into angles greater than 30° (lab) have been measured at a wide range of energies spanning the delta resonance using liquid hydrogen targets. Cross sections were measured for Ï{sup +}p scattering at 40 energies from 39.8 to 283.9 MeV and for Ï⁻p at 15 energies from 80.0 to 283.9 MeV....
Article
Full-text available
The authors examined the accuracy and sensitivity levels for three variations on the TGS method: the original TGS method using a high-purity germanium (HPGe) detector to measure net areas of full-energy gamma-ray peaks; a modified HPGe-detector method that uses net areas for the transmission analysis and the gross count TGS (GC-TGS) method for the...
Article
In this paper we present the gross-count material basis set (GC-MBS) method for estimating transmission losses in measurements of radionuclides using low-resolution gamma-ray detectors such as NaI or CdZnTe. The application to continuum-subtracted peaks measured with high-purity Ge detectors is also discussed. To illustrate the method, we apply it...
Article
This work investigates the use of annihilation photons from gamma-ray-induced electron-positron pair production to inspect objects when only one side is accessible. The Z<sup>2</sup>-dependence of the pair-production cross section and the high penetration of 511-keV photons allow this method to differentiate high-Z materials in low-Z matrices. The...
Article
Differential cross sections for ${$\pi${}}^{+}{+}^{12}\mathrm{C}$ elastic scattering in the energy range of 18\char21{}44 MeV for six scattering angles have been measured with an increment in the incident energy of 2 MeV. The measured cross sections are compared to calculations within the framework of a unitary scattering theory of the pion-nucleus...
Conference Paper
Full-text available
CdZnTe detectors are potential replacements for traditional room temperature detectors such as NaI in many applications. One particularly suitable application could be their use in portable field instruments for isotopic identification. To fully exploit them for this purpose, however, their behavior in conditions likely to be encountered in the fie...
Conference Paper
It was recently shown that a logarithmic response-function technique based on the material basis set (MBS) formalism used in the tomographic gamma scanner (TGS) method allows gross spectra from NaI detectors to be used in both measuring MBS transmission corrections using external transmission sources and in applying the corrections to emission spec...
Article
The goals of this project were (1) to develop a capability to study the scattered components in the NaI spectra of attenuated sources and (2) to evaluate the effectiveness of the gross count material basis set (GC-MBS) method in quantifying transmission losses from the shapes of measured NaI spectra. These goals are related, as the GC-MBS method in...
Article
A physics-based approach to gamma-ray response-function generation is presented in which the response of CdZnTe detectors is modeled from first principles. Computer modeling is used to generate response functions needed for spectrum analysis for general detector configurations (e.g., electrode design, detector materials and geometry, and operating...
Article
Full-text available
Pion-nucleus elastic scattering at energies above the Δ(1232) resonance is studied using both π+ and π- beams on 12C, 40Ca, 90Zr, and 208Pb. The present data provide an opportunity to study the interaction of pions with nuclei at energies where second-order corrections to impulse approximation calculations should be small. The results are compared...
Article
Full-text available
A study of the reaction π++d→p+p has been performed in the energy range of 18–44 MeV. Total cross sections and differential cross sections at six angles have been measured at 15 energies with an energy increment of 1–2 MeV. This is the most systematic data set in this energy range. No structure in the energy dependence of the cross section has been...
Preprint
A study of the reaction pi+ + d --> p + p has been performed in the energy range of 18 - 44 MeV. Total cross sections and differential cross sections at six angles have been measured at 15 energies with an energy increment of 1 - 2 MeV. This is the most systematic data set in this energy range. No structure in the energy dependence of the cross sec...
Article
This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The collection of ions created by alpha particles in air is a powerful technique for detecting the presence of alpha-emitting radioactive contamination. These ions have a relatively long lifetime (greater...
Article
Full-text available
This is the final report for a one year Laboratory Directed Research and Development project at the Los Alamos National Laboratory. This systems analysis study provided a framework for evaluating the technology developments needed to support an emerging nonproliferation regime that provides for global fissile materials control. The project produced...
Conference Paper
The sensitivity and application of traditional alpha monitors is limited by the short range of alpha particles in air and in solid materials. Detecting small amounts of alpha-emitting contamination inside pipes presents particular problems. The alpha particle cannot penetrate the walls of the pipe. Associated gamma-ray detection and active neutron...
Article
We describe a technique for etching electrically isolated strips onto metalized Mylar surfaces suitable for strip cathode readout multiwire chambers. Cathode planes created using this technique are much thinner than those made using previously described techniques.
Conference Paper
Key problems in detecting alpha contamination for site characterization and decontamination and decommissioning that remain to be solved include measurement of airborne contamination, material holdup within pipes, and leakage of material containers. These problems are very difficult using traditional alpha detectors and systems. The ionization dete...
Article
An alpha detector for application in areas of high velocity gas flows, such as smokestacks and air vents. A plurality of spaced apart signal collectors are placed inside an enclosure, which would include smokestacks and air vents, in sufficient numbers to substantially span said enclosure so that gas ions generated within the gas flow are electrost...
Article
Angular distributions for π+ and π- elastic and inelastic scattering from the Z=28 closed-proton-shell nuclei 58,60,62,64Ni have been measured at an incident pion kinetic energy of 180 MeV. Values for the neutron and proton matrix elements for the transition to the Jπ=21+ state have been extracted using the distorted wave impulse approximation in w...
Article
Measurements are presented for several mixtures of the spin observables CSS,CSL=CLS, CLL, and CNN for neutron-proton elastic scattering. These data were obtained with a free polarized neutron beam, a polarized proton target, and a large magnetic spectrometer for the outgoing proton. The neutron beam kinetic energies were 484, 567, 634, 720, and 788...
Article
Measurements are presented for several mixtures of the spin observables CSS, CLS= CLS, CLL, and CNN for neutron-proton elastic scattering. These data were obtained with a free polarized neutron beam, a polarized proton target, and a large magnetic spectrometer for the outgoing proton. The neutron beam kinetic energies were 484, 567, 634, 720, and 7...
Article
Full-text available
We have developed a prototype instrument capable of assessing alpha-emitting contamination on interior surfaces of ducts, pipes, tanks, and other enclosed volumes without inserting a probe. Air is drawn through the potentially contaminated volume and then through a detection grid, where ions created in the air by alpha particles are collected and t...
Article
The process of decontaminating and decomissioning former nuclear facilities sometimes requires that large areas of concrete and other materials be scanned to verify they are not contaminated. A specially developed concrete surface monitor (CSM) can greatly expedite that process. The CSM is basically an aluminum box, open on the bottom, that uses an...
Article
We have developed a new approach to glove box monitoring that involves drawing air out of one glove port through a detection grid that collects ions created in the air inside the glove box by ionizing radiation, especially alpha radiation. The charge deposited on the detection grid by the ions is measured with a sensitive electrometer. The air can...
Article
Instruments based on the principle of Long-Range Alpha Detection (LRAD) detect the ions created in ambient air by Ionizing radiation, particularly alpha radiation, interacting with air molecules. Using either an electrostatic field or forced convection, these ions can be transported to a detection grid where the ions produce a small current that is...
Article
We present results of measurements of the forward-angle cross sections for pion double charge exchange on 40,44Ca to the nonanalog ground states of 40,44Ti at incident pion energies from 35 to 80 MeV. The data indicate that a substantial contribution to these cross sections arises from core polarization and/or cross-shell transitions.
Conference Paper
Many DOE facilities have several miles of waste pipe systems that are internally contaminated with various and often undetermined radio nuclides. Unfortunately, currently acceptable alpha detection technologies are inefficient, time consuming, and do not address the problems presented by small diameter or curved pipes. In general, the problem of de...
Conference Paper
Full-text available
A real-time monitor for radioactive liquid waste is being developed at Los Alamos National Laboratory (LANL). This detector system is designed to monitor for large changes in alpha activity in a liquid waste stream. The detector is unique in that it monitors the ionization created by alpha interactions with air, using long-range alpha detector (LRA...
Conference Paper
Waste minimization and worker protection at D&D sites requires continual and extensive characterization for radioactive contamination. Contamination detectors that are sensitive, rugged, fast, and capable of covering large areas are needed. The concrete surface monitor (CSM) developed at LANL supports both characterization and waste minimization ef...
Article
We present results of measurements of the forward-angle cross sections for pion double charge exchange on [sup 40,44]Ca to the nonanalog ground states of [sup 40,44]Ti at incident pion energies from 35 to 80 MeV. The data indicate that a substantial contribution to these cross sections arises from core polarization and/or cross-shell transitions.
Article
Decontamination and decommissioning (D&D) procedures consist of an assessment phase and a remediation phase. The primary problem during assessment is the location and identification of the contaminants. Identification is difficult in buildings because contaminants may be hiding in difficult-to-sample areas and systems. Detectors based on long-range...
Conference Paper
Characterization of radioactive contaminants is required during D&D operations at any facility where radioactivity is suspected or known to exist. Alpha radiation is an excellent indicator of the presence of many isotopes (such as Pu{sup 239}) which are otherwise difficult to observe. However, traditional fieldable alpha detectors have been hampere...
Article
Studies of the production of the Δ resonance in hadronic charge exchange reactions show a shift in the Δ peak position. Measurements looking also at the Δ decay products give some evidence for coherent pion production. We have recently completed a new measurement of the 12C(p,n) reaction leading to the Δ resonance, including a higher resolution coi...
Article
Experimental differential cross sections for π+ and π- elastic scattering on 28Si at an incident pion energy of 400 meV are reported. The data fall above the predictions of a calculation using a momentum-space first-order optical potential. The behavior is similar to earlier results for pion scattering at Tπ=672 meV and to K+ nucleus scattering in...
Article
Measurements of small-angle cross sections for the pion double-charge-exchange (DCX) reaction 16O(π+,π-)16Ne (g.s.) at incident energies of 300-500 MeV are reported. These are the first measurements of DCX cross sections on a T=0 nucleus in this energy region. The behavior of the cross sections is similar to that of analog transitions, but they are...
Article
Measurements of small-angle cross sections for the pion double-charge-exchange (DCX) reaction $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${)}^{16}$Ne (g.s.) at incident energies of 300\char21{}500 MeV are reported. These are the first measurements of DCX cross sections on a T=0 nucleus...
Article
The search for an eta bound state in the double charge exchange (DCX) reaction 18O(pi+,pi-)18Ne(DIAS) has been carried out at LAMPF using the P3 channel and the LAS spectrometer. An excitation function for this reaction was measured for energies ranging from 350 to 440 MeV and for momentum transfers of 0, 105, and 210 MeV/c. The measured cross sect...
Article
Double charge exchange cross sections for 50 MeV pions to double isobaric analog states in 44Ca, 56Fe, and 93Nb were measured. The results indicate that the effective double charge exchange operator at this energy has a strong short-range component. In addition, evidence is presented tending to implicate isospin mixing as the mechanism for excitati...
Article
Results are presented for the spin-spin correlation parameters CSS and CLS for free np elastic scattering at neutron beam kinetic energies of 484, 634, 720, and 788 MeV and c.m. angles between 25° and 80°. The measurements were performed with a polarized neutron beam and a polarized proton target. These are the first measurements of this type to be...
Article
Measurements of the response of the participant calorimeter to 250-400 MeV/c pi+, mu-, and e+ are described. The participant calorimeter is a Pb/Fe/scintillator sampling calorimeter with a novel wavelength shifting fiber optic readout which is used in experiment 814 at Brookhaven National Laboratory. The e+/pi+ response ratio at 250-400 MeV/c is la...