
Mohini W Rawool-SullivanLos Alamos National Laboratory | LANL · X Computational Physics Division (XCP)
Mohini W Rawool-Sullivan
Ph. D.
About
115
Publications
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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
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)
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...
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...
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)....
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...
Wavelet shrinkage denoising may provide a way of doing robust feature identification in a low statistics gamma-ray spectra
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...
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.
This presentation is to educate trainees on basics of gamma-ray spectroscopy. This presentation focuses on technical aspects of gamma spectroscopy.
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...
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...
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...
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.
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...
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...
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...
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...
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...
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.
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...
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...
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...
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...
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...
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).
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.
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...
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...
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)
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...
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...
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...
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...
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,...
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...
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...
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...
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...
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...
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...
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...
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 Ïâ»p at 15 energies from 80.0 to 283.9 MeV....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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.
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...
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...
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...