47 Matching Results

Search Results

Advanced search parameters have been applied.

Optimization of the {sup 7}Li(p,n) proton beam energy for BNCT applications

Description: The reaction {sup 7}Li(p,n){sup 7} Be has been proposed as an accelerator-based source of neutrons for Boron Neutron Capture Therapy (BNCT). This reaction has a large steep resonance for proton energies of about 2.3 MeV which ends at about 2.5 MeV. It has generally been accepted that one should use 2.5 MeV protons to get the highest yield of neutrons for BNCT. This paper suggests that for BNCT the optimum proton energy may be about 2.3 MeV and that a proton energy of about 2.2 MeV will provide the same useful neutron fluence outside a thinner moderator as the neutron fluence from a 2.5 MeV proton beam with a thicker moderator.
Date: February 1, 1996
Creator: Bleuel, D.L. & Donahue, R.J.
Partner: UNT Libraries Government Documents Department

On optimizing the {sup 7}Li(p,n) proton beam energy and moderator material for BNCT

Description: The reaction {sup 7}Li(p,n){sup 7}Be has been proposed as an accelerator-based source of neutrons for Boron Neutron Capture Therapy (BNCT). This reaction has a large steep resonance for proton energies around 2.3 MeV which ends at approximately 2.5 MeV. It is generally accepted that the use of 2.5 MeV protons produces the highest yield of neutrons for BNCT. This paper suggests that for BNCT the optimum proton energy may be as low as 2.2-2.3 MeV. The evaluation of the clinical usefulness of the epithermal neutron beams investigated here has been based on depth-dose distributions in a head phantom.
Date: September 1, 1996
Creator: Bleuel, D.L.; Donahue, R.J. & Ludewigt, B.A.
Partner: UNT Libraries Government Documents Department

Design of a new BNCT facility based on an ESQ accelerator

Description: The authors plan to build a BNCT facility based on electrostatic quadrupole (ESQ) accelerator technology. It is an experimentally-proven technology capable of delivering a high proton current for producing a neutron intensity greater than what is required for BNCT clinical trials. They also present a design of a lithium neutron-production target with adequate cooling of the heat generated by the high-current proton beam.
Date: September 1, 1996
Creator: Chu, W.T.; Bleuel, D.L. & Donahue, R.J.
Partner: UNT Libraries Government Documents Department

Neutronics analysis of three beam-filter assemblies for an accelerator-based BNCT facility

Description: Three moderator materials, AlF{sub 3}/Al, D{sub 2}O and LiF, have been analyzed for clinical usefulness using the reaction {sup 7}Li(p,n) as an accelerator driven neutron source. Proton energies between 2.1 MeV and 2.6 MeV have been investigated. Radiation transport in the reflector/moderator assembly is simulated using the MCNP program. Depth-dose distributions in a head phanton are calculated with the BNCT-RTPE patient treatment planning program from INEEL using the MCNP generated neutron and photon spectra as the subsequent source. Clinical efficacy is compared using the current BMRR protocol for all designs. Depth-dose distributions are compared for a fixed normal tissue tolerance dose of 12.5 Gy-Eq. Radiation analyses also include a complete anthropomorphic phantom. Results of organ and whole body dose components are presented for several designs. Results indicate that high quality accelerator beams may produce clinically favorable treatments to deep-seated tumors when compared to the BMRR beam. Also discussed are problems identified in comparing accelerator and reactor based designs using in-air figures of merit as well as some results of spectrum-averaged RBE`s.
Date: August 1, 1997
Creator: Bleuel, D.L.; Costes, S.V.; Donahue, R.J. & Ludewigt, B.A.
Partner: UNT Libraries Government Documents Department

Simulating variable source problems via post processing of individual particle tallies

Description: Monte Carlo is an extremely powerful method of simulating complex, three dimensional environments without excessive problem simplification. However, it is often time consuming to simulate models in which the source can be highly varied. Similarly difficult are optimization studies involving sources in which many input parameters are variable, such as particle energy, angle, and spatial distribution. Such studies are often approached using brute force methods or intelligent guesswork. One field in which these problems are often encountered is accelerator-driven Boron Neutron Capture Therapy (BNCT) for the treatment of cancers. Solving the reverse problem of determining the best neutron source for optimal BNCT treatment can be accomplished by separating the time-consuming particle-tracking process of a full Monte Carlo simulation from the calculation of the source weighting factors which is typically performed at the beginning of a Monte Carlo simulation. By post-processing these weighting factors on a recorded file of individual particle tally information, the effect of changing source variables can be realized in a matter of seconds, instead of requiring hours or days for additional complete simulations. By intelligent source biasing, any number of different source distributions can be calculated quickly from a single Monte Carlo simulation. The source description can be treated as variable and the effect of changing multiple interdependent source variables on the problem's solution can be determined. Though the focus of this study is on BNCT applications, this procedure may be applicable to any problem that involves a variable source.
Date: October 20, 2000
Creator: Bleuel, D.L.; Donahue, R.J.; Ludewigt, B.A. & Vujic, J.
Partner: UNT Libraries Government Documents Department

Post-processing of Monte Carlo simulations for rapid BNCT source optimization studies

Description: A great advantage of some neutron sources, such as accelerator-produced sources, is that they can be tuned to produce different spectra. Unfortunately, optimization studies are often time-consuming and difficult, as they require a lengthy Monte Carlo simulation for each source. When multiple characteristics, such as energy, angle, and spatial distribution of a neutron beam are allowed to vary, an overwhelming number of simulations may be required. Many optimization studies, therefore, suffer from a small number of datapoints, restrictive treatment conditions, or poor statistics. By scoring pertinent information from every particle tally in a Monte Carlo simulation, then applying appropriate source variable weight factors in a post-processing algorithm, a single simulation can be used to model any number of multiple sources. Through this method, the response to a new source can be modeled in minutes or seconds, rather than hours or days, allowing for the analysis of truly variable source conditions of much greater resolution than is normally possible when a new simulation must be run for each datapoint in a study. This method has been benchmarked and used to recreate optimization studies in a small fraction of the time spent in the original studies.
Date: October 1, 2000
Creator: Bleuel, D.L.; Chu, W.T.; Donahue, R.J.; Ludewigt, B.A. & Vujic, J.
Partner: UNT Libraries Government Documents Department

Characterization of a Tunable Quasi-Monoenergetic Neutron Beamfrom Deuteron Breakup

Description: A neutron irradiation facility is being developed at the88-Inch Cyclotron at Lawrence Berkeley National Laboratory for thepurposes of measuring neutron reaction cross sections on radioactivetargets and for radiation effects testing. Applications are of benefit tostockpile stewardship, nuclear astrophysics, next generation advancedfuel reactors, and cosmic radiation biology and electronics in space. Thefacility will supply a tunable, quasi-monoenergetic neutron beam in therange of 10-30 MeV or a white neutron source, produced by deuteronbreakup reactions on thin and thick targets, respectively. Because thedeuteron breakup reaction has not been well studied at intermediateincident deuteron energies, above the target Coulomb barrier and below 56MeV, a detailed characterization was necessary of the neutron spectraproduced by thin targets.Neutron time of flight (TOF) methods have beenused to measure the neutron spectra produced on thin targets of low-Z(titanium) and high-Z (tantalum) materials at incident deuteron energiesof 20 MeV and 29 MeV at 0 deg. Breakup neutrons at both energies fromlow-Z targets appear to peak at roughly half of the available kineticenergy, while neutrons from high-Z interactions peak somewhat lower inenergy, owing to the increased proton energy due to breakup within theCoulomb field. Furthermore, neutron spectra appear narrower for high-Ztargets. These centroids are consistent with recent preliminary protonenergy measurements using silicon telescope detectors conducted at LBNL,though there is a notable discrepancy with spectral widths.
Date: December 14, 2006
Creator: Bleuel, D.L.; McMahan, M.A.; Ahle, L.; Barquest, B.R.; Cerny, J.; Heilbronn, L.H. et al.
Partner: UNT Libraries Government Documents Department

Neutron Beams from Deuteron Breakup at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory

Description: Accelerator-based neutron sources offer many advantages, in particular tunability of the neutron beam in energy and width to match the needs of the application. Using a recently constructed neutron beam line at the 88-Inch Cyclotron at LBNL, tunable high-intensity sources of quasi-monoenergetic and broad spectrum neutrons from deuteron breakup are under development for a variety of applications.
Date: July 31, 2007
Creator: McMahan, M.A.; Ahle, L.; Bleuel, D.L.; Bernstein, L.; Braquest, B.R.; Cerny, J. et al.
Partner: UNT Libraries Government Documents Department

Report on 240Am(n,x) surrogate cross section test measurement

Description: The main goal of the test measurement was to determine the feasibility of the {sup 243}Am(p,t) reaction as a surrogate for {sup 240}Am(n,f). No data cross section data exists for neutron induced reactions on {sup 240}Am; the half-life of this isotope is only 2.1 days making direct measurements difficult, if not impossible. The 48-hour experiment was conducted using the STARS/LIBERACE experimental facility located at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory in August 2011. A description of the experiment and results is given. The beam energy was initially chosen to be 39 MeV in order to measure an equivalent neutron energy range from 0 to 20 MeV. However, the proton beam was not stopped in the farady cup and the beam was deposited in the surrounding shielding material. The shielding material was not conductive, and a beam current, needed for proper tuning of the beam as well as experimental monitoring, could not be read. If the {sup 240}Am(n,f) surrogate experiment is to be run at LBNL, simple modifications to the beam collection site will need to be made. The beam energy was reduced to 29 MeV, which was within an energy regime of prior experiments and tuning conditions at STARS/LIBERACE. At this energy, the beam current was successfully tuned and measured. At 29 MeV, data was collected with both the {sup 243}Am and {sup 238}U targets. An example particle identification plot is shown in Fig. 1. The triton-fission coincidence rate for the {sup 243}Am target and {sup 238}U target were measured. Coincidence rates of 0.0233(1) cps and 0.150(6) cps were observed for the {sup 243}Am and {sup 238}U targets, respectively. The difference in count rate is largely attributed to the available target material - the {sup 238}U target contains approximately 7 times more atoms than the {sup 243}Am. ...
Date: February 1, 2012
Creator: Ressler, J J; Burke, J T; Gostic, J; Bleuel, D; Escher, J E; Henderson, R A et al.
Partner: UNT Libraries Government Documents Department

LDRD Final Report: Surrogate Nuclear Reactions and the Origin of the Heavy Elements (04-ERD-057)

Description: Research carried out in the framework of the LDRD project ''Surrogate Nuclear Reactions and the Origin of the Heavy Elements'' (04-ERD-057) is summarized. The project was designed to address the challenge of determining cross sections for nuclear reactions involving unstable targets, with a particular emphasis on reactions that play a key role in the production of the elements between Iron and Uranium. This report reviews the motivation for the research, introduces the approach employed to address the problem, and summarizes the resulting scientific insights, technical findings, and related accomplishments.
Date: February 23, 2007
Creator: Escher, J E; Bernstein, L A; Bleuel, D; Burke, J; Church, J A; Dietrich, F S et al.
Partner: UNT Libraries Government Documents Department

Development of an accelerator-based BNCT facility at the Berkeley Lab

Description: An accelerator-based BNCT facility is under construction at the Berkeley Lab. An electrostatic-quadrupole (ESQ) accelerator is under development for the production of neutrons via the {sup 7}Li(p,n){sup 7}Be reaction at proton energies between 2.3 and 2.5 MeV. A novel type of power supply, an air-core coupled transformer power supply, is being built for the acceleration of beam currents exceeding 50 mA. A metallic lithium target has been developed for handling such high beam currents. Moderator, reflector and neutron beam delimiter have extensively been modeled and designs have been identified which produce epithermal neutron spectra sharply peaked between 10 and 20 keV. These. neutron beams are predicted to deliver significantly higher doses to deep seated brain tumors, up to 50% more near the midline of the brain than is possible with currently available reactor beams. The accelerator neutron source will be suitable for future installation at hospitals.
Date: March 1, 1998
Creator: Ludewigt, B.A.; Bleuel, D.; Chu, W.T.; Donahue, R.J.; Kwan, J.; Reginato, L.L. et al.
Partner: UNT Libraries Government Documents Department

Accelerator-Driven Neutron Source for Cargo Screening

Description: Advanced neutron interrogation systems for the screening ofsea-land cargo containers for shielded special nuclear materials (SNM)require a high-yield neutron source to achieve the desired detectionprobability, false alarm rate, and throughput. An accelerator-drivenneutron source is described that produces a forward directed beam ofhigh-energy (up to 8.5 MeV) neutrons utilizing the D(d,n)3He reaction atdeuteron beam energies of up to 6 MeV. The key components of the neutronsource are a high-current RFQ accelerator and an innovative neutronproduction target. A microwave-driven deuteron source is coupled to anelectrostatic LEBT that injects a 40 mA D+-beam into a 6 MeV, 5.1meter-long, 200 MHz RFQ. The RFQ is based on an unusual beam dynamicsdesign and is capable of operating at a duty factor that produces morethan 1.2 mA timeaverage beam current. The beam is transported to a2-atmosphere deuterium gas target with a specially-designed, thinentrance window. A high-frequency dipole magnet is used to spread thebeam over the long dimension of the 4 by 35 cm target window. The sourcewill be capable of delivering a neutron flux of ~;2 x 107 n/(cm2 x s) tothe center of a sea-land cargo container and is expected t o satisfy therequirements for full testing and demonstration of advanced neutroninterrogation techniques based on stimulated SNM signatures.
Date: November 15, 2006
Creator: Ludewigt, B. A.; Bleuel, D. L.; Hoff, M. D.; Kwan, J. W.; Li, D.; Ratti, A. et al.
Partner: UNT Libraries Government Documents Department

Relative {sup 235}U(n,{gamma}) and (n,f) cross sections from {sup 235}U(d,p{gamma}) and (d,pf)

Description: The internal surrogate ratio method allows for the determination of an unknown cross section, such as (n,{gamma}), relative to a better-known cross section, such as (n,f), by measuring the relative exit-channel probabilities of a surrogate reaction that proceeds through the same compound nucleus. The validity of the internal surrogate ratio method is tested by comparing the relative gamma and fission exit-channel probabilities of a {sup 236}U* compound nucleus, formed in the {sup 235}U(d,p) reaction, to the known {sup 235}U(n,{gamma}) and (n,f) cross sections. A model-independent method for measuring the gamma-channel yield is presented and used.
Date: January 1, 2009
Creator: Allmond, J.M.; Bernstein, L.A.; Beausang, C.W.; Phair, L.; Bleuel, D.L.; Burke, J.T. et al.
Partner: UNT Libraries Government Documents Department

Indirect Determination of the 230Th(n,f) and 231Th(n,f) Cross Sections for Thorium-Based Nuclear Energy Systems

Description: The Surrogate Ratio Method (SRM) was employed in the first experimental determination of the 231Th(n,f) cross section, relative to the 235U(n,f) cross section, over an equivalent neutron energy range of 360 keV to 10 MeV. The 230Th(n,f) cross section was also deduced using the SRM, relative to the 234U(n,f) cross section, over an equivalent neutron energy range of 220 keV to 25 MeV. The desired compound nuclei were populated using (3He,3He) and (3He) reactions on targets of 232Th and 236U and relative fission decay probabilities were measured. The surrogate 230,231Th(n,f) cross sections were compared to cross section evaluations and directly-measured experimental data, where available.
Date: September 11, 2009
Creator: Stroberg, S.R.; Allmond, J.M.; Angell, C.; Bernstein, L.A.; Bleuel, D.L.; Burke, J.T. et al.
Partner: UNT Libraries Government Documents Department

Gamma-ray multiplicity measurement of the spontaneous fission decay of 252Cf in a segmented HPGe/BGO detector array

Description: Coincident {gamma} rays from a {sup 252}Cf source were measured using an array of six segmented high-purity germanium (HPGe) Clover detectors each enclosed by 16 bismuth-germanate (BGO) detectors. The detectors were arranged in a cubic pattern around a 1 {micro}Ci {sup 252}Cf source to cover a large solid angle for {gamma}-ray measurement with a reasonable reconstruction of the multiplicity. Neutron multiplicity was determined in certain cases by identifying the prompt {gamma} rays from individual fission fragment pairs. Multiplicity distributions from previous experiments and theoretical models were convolved with the response function of the array and compared to the present results. These results suggest a {gamma}-ray multiplicity spectrum broader than previous measurements and models, and provide no evidence of correlation with neutron multiplicity.
Date: April 23, 2008
Creator: Bleuel, D L; Bernstein, L A; Burke, J T; Gibelin, J; Heffner, M D; Mintz, J et al.
Partner: UNT Libraries Government Documents Department

Radiochemistry as a (rho)R Diagnostic with the RAGS Gas Collection System

Description: Radiochemical diagnostic techniques such as gas-phase capsule debris analysis may prove to be successful methods for establishing the success or failure of ignition experiments at the National Ignition Facility (NIF). Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. The target capsules will be prepared with dopants which will produce radioactive noble gas isotopes upon activation with neutrons. We have designed and constructed the Radchem Apparatus for Gas Sampling (RAGS) in order to collect post-shot gaseous samples for NIF capsule diagnostics. The design of RAGS incorporates multiple stages intended to purify, transfer, and count the radioactive decays from gaseous products synthesized in NIF experiments. At the moment the dopant of choice is {sup 124}Xe, which will undergo (n,{gamma}) and (n, 2n) reactions to produce {sup 125}Xe and {sup 123}Xe. The half-lives of each are on the order of multiple hours and are suitable for long-term gamma-counting. These isotopes and the rest of the gases evolved in a NIF shot will be drawn through the NIF turbo pumps, past the temporarily shuttered cryo pumps (to aid our collection efficiency), and towards the first main portion of the RAGS system: the pre-cleaner. The pre-cleaner will consist of a water removal system, a series of heated getter cartridges to remove most other impurities such as N{sub 2}, O{sub 2}, CO{sub 2}, etc., and a residual gas analyzer (RGA) to monitor vacuum quality. The noble gases will flow through the precleaner and into the second stage of the system: the cryo collector. This cryo collector consists of a main cryo head for noble gas collection which will operate for approximately five minutes post-shot. Afterwards a valve will close and isolate the pre-cleaner, while the cryo head warms to release ...
Date: May 21, 2010
Creator: Nelson, S L; Shaughnessy, D A; Schneider, D H; Stoeffl, W; Moody, K J; Cerjan, C et al.
Partner: UNT Libraries Government Documents Department

Report on 241,242Am(n,x) surrogate cross section measurement

Description: The main goal of this measurement is to determine the {sup 242}Am(n,f) and {sup 241}Am(n,f) cross sections via the surrogate {sup 243}Am. Gamma-ray data was also collected for the purpose of measuring the (n,2n) cross-sections. The experiment was conducted using the STARS/LIBERACE experimental facility located at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory the first week of February 2011. A description of the experiment and status of the data analysis follow.
Date: February 16, 2011
Creator: Burke, J. T.; Ressler, J. J.; Gostic, J.; Henderson, R. A.; Bernstein, L. A.; Escher, J. E. et al.
Partner: UNT Libraries Government Documents Department

Gamma Ray Multiplicity of 252Cf Spontaneous Fission using LiBerACE

Description: We are studying the gamma ray and neutron multiplicity of various fission processes, beginning with the spontaneous fission of {sup 252}Cf, for a variety of basic and applied science purposes. The Livermore-Berkeley Array for Collaborative Experiments (LiBerACE) consists of six high-purity germanium Clover detectors (HPGe) each enclosed by an array of 16 bismuth-germanate (BGO) detectors. These detectors were arranged in a cubic pattern around a 1 {micro}Ci {sup 252}Cf source to attempt to cover as much solid angle of gamma ray emission as possible with a high level of segmentation. The single-gamma detector response function is determined at several energies by tagging in a HPGe detector on the photopeak of one of two gamma rays in two-gamma ray calibration sources and observing the multiplicity of the remainder of the array. Summing these single-gamma responses in groups yields the response function of the array to higher multiplicity events, which are convolved with multiplicity distributions from theoretical models and compared to the measured results to test the models validity.
Date: January 15, 2008
Creator: Bleuel, D L; Bernstein, L A; Burke, J T; Heffner, M D; Norman, E B; Scielzo, N D et al.
Partner: UNT Libraries Government Documents Department

Thick target measurement of the 40Ca(alpha,gamma)44Ti reaction rate

Description: The thick-target yield for the {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction has been measured for E{sub beam} = 4.13, 4.54, and 5.36 MeV using both an activation measurement and online {gamma}-ray spectroscopy. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than statistical model calculations. This implies a smaller {sup 44}Ti production in supernova compared to recently measured {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction rates.
Date: February 6, 2009
Creator: Sheets, S A; Burke, J T; Scielzo, N D; Phair, L; Bleuel, D; Norman, E B et al.
Partner: UNT Libraries Government Documents Department

Studying neutron-rich 18 N in fusion-evaporation reactions

Description: Light neutron-rich nuclei provide an excellent opportunity to study the changes in nuclear shell structure that occur with increasing neutron number and are an important testing ground for shell model theories. Probably one of the most striking examples of shell modification is the occurrence of intruder ground states, which signal an inversion of the normal shell ordering. Intruder ground states are observed around {sup 32}Mg (Z=10-12), ''the island of inversion'', and in {sup 11}Be. An analogous situation appears in the Z=2 He isotopes, where the intrusion of sd excitations in p-shell configurations becomes important in the heavy helium isotopes. Finally, for Z=8, recent data on {sup 20}O [1] show a reduction in the p-sd shell gap with increasing neutron number. It remains an open question whether the observed diminishing of the p-sd shell gap is restricted to O and F isotopes or extends also to neighboring nuclei. Here, we report preliminary results on {sup 18}N (Z=7), which is sufficiently far from stability to exhibit modified shell structure and yet still within the reach of stable beam facilities utilizing state-of-the art detector systems. {sup 18}N was produced in the {sup 9}Be({sup 11}B,2p){sup 18}N reaction at the 88'' Cyclotron at LBNL and studied using the LIBERACE-STARS detector array--an array of large area segmented silicon detectors (E-{Delta}E) and six HPGe Clover detectors. This experiment was the first to use a fusion-evaporation reaction to populate {sup 18}N. Previous information on the excited states of 18N came from {sup 18}C beta-decay [2] and charge-exchange reactions [3]. These are highly selective reactions and the fusion-evaporation reaction used here can provide a more comprehensive picture of the excitation spectrum. The beam energy of 50 MeV was chosen to optimize the cross section for the evaporation of 2 protons while simultaneously suppressing the evaporation of additional neutrons in ...
Date: July 28, 2006
Creator: Wiedeking, M; Fallon, P; Bernstein, L; Macchiavelli, A; Phair, L; Burke, J et al.
Partner: UNT Libraries Government Documents Department