553 Matching Results

Search Results

Advanced search parameters have been applied.

Measurement of Tritium in Gas Phase Soil Moisture and Helium-3 in Soil Gas at the Hanford Townsite and 100 K Area

Description: In 1999, eight soil gas sampling points ranging in depth from 4.9 ft to 32 ft below ground surface (bgs) in two clusters were installed adjacent to well 699-41-1, south of the Hanford Townsite. Fifteen soil gas sampling points, ranging in depth from 7.0 ft to 10.4 ft bgs, were installed to the north and east of the 100-K East Reactor facility. Gas phase soil moisture samples were collected using silica gel traps from all eight sampling locations adjacent to well 699-41-1 and eight locations at the 100-K Area. Soil gas samples for helium-3 measurements were collected at all sampling points. No detectable tritium (<240 pCi/L) was found in the soil moisture samples from either the Hanford Townsite or 100-K Area sampling points. This behavior suggests that tritiated moisture from groundwater is not migrating upward to the sampling points and there are no large vadose zone sources of tritium at either location. Helium-3 analyses of the soil gas samples showed significant enrichments relative to ambient air helium-3 concentrations with a depth dependence consistent with a groundwater source from decay of tritium. Helium-3/helium-4 ratios (normalized to the abundances in ambient air) at the Hanford Townsite ranged from 1.012 at 5 feet below ground surface (bgs) to 2.157 at 32 feet bgs. Helium-3/helium-4 ratios at the 100-K area ranged from 0.972 to 1.131. Based on results from the 100-K area, we believe that a major tritium plume does not lie within that study area. The data also suggest there may be a tritium groundwater plume or a source of helium-3 to the southeast of the study area. We recommend that the study be continued by the placement of additional soil gas sampling points along the perimeter road to the west and to the south of the initial study area.
Date: July 5, 2000
Creator: Olsen, Khris B.; Patton, Gregory W.; Poreda, R.; Dresel, P Evan & Evans, John C.
Partner: UNT Libraries Government Documents Department

Measurement of Helium-3/Helium-4 Ratios in Soil Gas at the 618-11 Burial Ground

Description: Seventy soil gas-sampling points were installed around the perimeter of the 618-11 Burial Ground, approximately 400 feet downgradient of well 699-13-3A, and in four transects downgradient of the burial ground to a maximum distance of 3,100 feet. Soil gas samples were collected and analyzed for helium-3/helium-4 ratios from these 70 points. Helium-3/helium-4 ratios determined from the soil gas sampling points showed significant enrichments, relative to ambient air helium-3 concentrations. The highest concentrations were located along the northern perimeter of the burial ground. Helium-3/helium-4 ratios (normalized to the abundances in ambient air) ranged from 1.0 to 62 around the burial ground. The helium-3/helium-4 ratios from the 4 transect downgradient of the burial ground ranged from 0.988 to 1.68. The helium-3/helium-4 ratios from around the burial ground suggest there is a vadose zone source of tritium along the north side of the burial ground. This vadose zone source is likely the source of tritium in the groundwater. The helium-3/helium-4 ratios also suggest the groundwater plume is traveling east-northeast from the burial ground and the highest groundwater tritium value may be to the north of well 699-13-3A. Finally, there appears to be no immediately upgradient sources of tritium impacting the burial ground since all the upgradient helium-3/helium-4 ratios are approximately 1.0.
Date: October 31, 2001
Creator: Olsen, Khris B.; Dresel, P Evan & Evans, John C.
Partner: UNT Libraries Government Documents Department

Duoplasmatron source modifications for {sup 3}He{sup +} Operation

Description: A duoplasmatron ion source is used to produce 25 mA of {sup 3}He+ with a pulse width of {approximately}80 ms at 360 Hz for acceleration to 10.5 MeV. At this energy, {sup 3}He striking water or carbon targets can produce short lived isotopes of {sup 11}C, {sup 13}N, {sup 15}O and {sup 18}F for medical positron emission tomography (PET). A duoplasmatron ion source was chosen originally since it is capable of a sufficient singly-charged helium beam with an acceptable gas consumption. Stable long-term operation of the source required a change in the filament material to molybdenum, and a careful understanding of the oxide filament conditioning, operation and geometry. Other improvements, particularly in the electronics, were helpful to increasing the reliability. The source has operated for many months at {approximately}2.5% duty factor without significant problems and with good stability. We report here the effort that was done to make this source understandable and reliable.
Date: November 1, 1997
Creator: Schmidt, C.W. & Popovic, M.
Partner: UNT Libraries Government Documents Department

Scaling laws, transient times and shell effects in helium induced nuclear fission

Description: Fission excitation functions are analyzed and discussed according to a method which allows one to check the validity of the transition state rate predictions over a large range of excitation energies and a regime of compound nuclei masses characterized by strong shell effects. Once these shell effects are accounted for, no deviation from transition state rates can be observed. Furthermore, shell effects can be determined directly from the experiment by using the above described procedure. In contrast to the standard method, there is no need to include liquid drop model calculations. Finally, plotting the quantity R{sub f} allows one to search for evidence of transition times (discussed in a series of papers): our results set an upper limit of 10{sup {minus}20} seconds.
Date: February 1, 1996
Creator: Rubehn, T.; Jing, Kexing; Moretto, L.G.; Phair, L.; Tso, Kin & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department

Helium bubble linkage and the transition to rapid He release in aging Pd tritide.

Description: A model is presented for the linking of helium bubbles growing in aging metal tritides. Stresses created by neighboring bubbles are found to produce bubble growth toward coalescence. This process is interrupted by the fracture of ligaments between bubble arrays. The condition for ligament fracture percolates through the material to reach external surfaces, leading to material micro-cracking and the release of helium within the linked-bubble cluster. A comparison of pure coalescence and pure fracture mechanisms shows the critical HeM concentration for bubble linkage is not strongly dependent on details of the linkage process. The combined stress-directed growth and fracture process produces predictions for the onset of rapid He release and the He emission rate. Transition to this rapid release state is determined from the physical size of the linked-bubble clusters, which is calculated from dimensional invariants in classical percolation theory. The result is a transition that depends on material dimensions. The onset of bubble linkage and rapid He release are found to be quite sensitive to the bubble spacing distribution, which is log-normal for bubbles nucleated by self-trapping.
Date: February 1, 2006
Creator: Cowgill, Donald F.
Partner: UNT Libraries Government Documents Department

Nucleon spin structure functions from HERMES: The first year

Description: HERMES, {und HE}RA {und Me}asurement of {und S}pin, is a second generation exper to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 28 GeV electron storage ring. Scattered positrons and coincident hadrons are detected in an open geometry spectrometer which includes particle identification. Inclusive data with polarized {sup 3}He give the spin structure function {ital g{sup n}{sub 1}(x)} and the Ellis-Jaffe integral RR{Lambda} = {integral}{sub 0}{sup 1} {ital g{sup n}{sub 1}(x)dx} for the neutron. The semi-inclusive spin asymmetries are a unique and sensitive probe of the flavor dependence of quark helicity distributions and properties of the quark sea. Data taken in 1995 with unpolarized hydrogen and deuterium targets provide measurements of the flavor distributions of sea and valence quarks. In a preliminary analysis, {Lambda}{sup {ital n}}{sub 1} = -0.032{+-}0. 013{sub {ital stat.}} {+-} O.017{sub {ital syst.}} is obtained at Q{sup 2} = 3(GeV/c){sup 2} for the Ellis-Jaffe integral.
Date: December 31, 1996
Creator: Jackson, H.E. & Collaboration, HERMES
Partner: UNT Libraries Government Documents Department

Nuclear physics input for solar models

Description: The authors discuss microscopic cluster model descriptions of two solar nuclear reactions, {sup 7}Be(p,{gamma}){sup 8}B, and {sup 3}He({sup 3}He, 2p){sup 4}He. The low-energy reaction cross section of {sup 7}Be(p,{gamma}){sup 8}B, which determines the high-energy solar neutrino flux, is constrained by {sup 7}Be and {sup 8}Be observables. The results show that a small value of the zero-energy cross section is rather unlikely. In {sup 3}He({sup 3}He, 2p){sup 4}He the authors study the effects of a possible virtual state on the cross section. Although, they have found no indication for such a state so far, its existence cannot be ruled out yet. They calculated the {sup 3}He({sup 3}He, 2p){sup 4}He and {sup 3}H({sup 3}H, 2n){sup 4}He cross sections in a continuum-discretized coupled channel approximation, and found a good general agreement with the data.
Date: March 1, 1998
Creator: Csoto, A.
Partner: UNT Libraries Government Documents Department


Description: J-Integral fracture toughness tests were conducted on tritium-exposed-and-aged Types 304L and 21-6-9 stainless steel weldments in order to measure the combined effects of tritium and its decay product, helium-3 on the fracture toughness properties. Initially, weldments have fracture toughness values about three times higher than base-metal values. Delta-ferrite phase in the weld microstructure improved toughness provided no tritium was present in the microstructure. After a tritium-exposure-and-aging treatment that resulted in {approx}1400 atomic parts per million (appm) dissolved tritium, both weldments and base metals had their fracture toughness values reduced to about the same level. The tritium effect was greater in weldments (67 % reduction vs. 37% reduction) largely because the ductile discontinuous delta-ferrite interfaces were embrittled by tritium and decay helium. Fracture toughness values decreased for both base metals and weldments with increasing decay helium content in the range tested (50-200 appm).
Date: August 31, 2007
Creator: Morgan, M; Scott West, S & Michael Tosten, M
Partner: UNT Libraries Government Documents Department


Description: The burst test is used to assess the material performance of tritium reservoirs in the surveillance program in which reservoirs have been in service for extended periods of time. A materials system model and finite element procedure were developed under a Savannah River Site Plant-Directed Research and Development (PDRD) program to predict the structural response under a full range of loading and aged material conditions of the reservoir. The results show that the predicted burst pressure and volume ductility are in good agreement with the actual burst test results for the unexposed units. The material tensile properties used in the calculations were obtained from a curved tensile specimen harvested from a companion reservoir by Electric Discharge Machining (EDM). In the absence of exposed and aged material tensile data, literature data were used for demonstrating the methodology in terms of the helium-3 concentration in the metal and the depth of penetration in the reservoir sidewall. It can be shown that the volume ductility decreases significantly with the presence of tritium and its decay product, helium-3, in the metal, as was observed in the laboratory-controlled burst tests. The model and analytical procedure provides a predictive tool for reservoir structural integrity under aging conditions. It is recommended that benchmark tests and analysis for aged materials be performed. The methodology can be augmented to predict performance for reservoir with flaws.
Date: November 10, 2005
Creator: Lam, P.S. & Morgan, M.J
Partner: UNT Libraries Government Documents Department

[sup 3]He neutron detector performance in mixed neutron gamma environments

Description: A test program of the performance of 3He neutron proportional detectors with varying gas pressures, and their response to lligh level gamma-ray exposure in a mixed neutrodgamma environment, ha$ been performed Our intent was to identie the optimal gas pressure to reduce the gamma-ray sensitivity of these detectors. These detectors were manufxtured using materials to minimize their gamma response. Earlier work focused on 3He fill pressures of four atmospheres and above, whereas the present work focuses on a wider range of pressures. Tests have shown that reducing the .filling pressure will M e r increase the gamma-ray dose range in which the detectors can be operated.
Date: January 1, 2002
Creator: Johnson, N. H. (Nathan H.) & Beddingfield, D. H. (David H.)
Partner: UNT Libraries Government Documents Department

Calculations of the ground state energy and exchange integrals of crystalline $sup 3$He

Description: Thesis. The variational equation is derived and discussed using Jastrowtype wave functions, which are a product of pair wave functions, as the trail wave function. The various approximations used in simplifying the variational equations so as to obtain a form that is possible to solve numerically are discussed also. A Monte Carlo calculation is described using the wave function obtained. Exchange in /sup 3/He is discussed. (MHR)
Date: July 1, 1973
Creator: Lim, W L
Partner: UNT Libraries Government Documents Department

A 3He{sup +}{sup +} RFQ accelerator for the production of PET isotopes

Description: Project status of the 3He{sup +}{sup +} 10.5 MeV RFQ Linear Accelerator for the production of PET isotopes will be presented. The accelerator design was begun in September of 1995 with a goal of completion and delivery of the accelerator to BRF in Shreveport, Louisiana by the summer of 1997. The design effort and construction is concentrated in Lab G on the Fermilab campus. Some of the high lights include a 25 mA peak current 3He` ion source, four RFQ accelerating stages that are powered by surplus Fermilab linac RF stations, a gas jet charge doubler, and a novel 540 degree bending Medium Energy Beam Transport (MEBT). The machine is designed to operate at 360 Hz repetition rate with a 2.5% duty cycle. The average beam current is expected to be 150-300 micro amperes electrical, 75- 150 micro amperes particle current.
Date: May 1, 1997
Creator: Pasquinelli, R.J. & Collaboration, E887
Partner: UNT Libraries Government Documents Department

{sup 3}He- and {sup 4}He-induced nuclear fission -- A test of the transition state method

Description: Fission in {sup 3}H and {sup 4}He induced reactions at excitation energies between the fission barrier and 140 MeV has been investigated. Twenty-three fission excitation functions of various compound nuclei in different mass regions are shown to scale exactly according to the transition state prediction once the shell effects are accounted for. New precise measurements of excitation functions in a mass region where shell effects are very strong, allow one to test the predictions with an even higher accuracy. The fact that no deviations from the transition state method have been observed within the experimentally investigated excitation energy regime allows one to assign limits for the fission transient time. The precise measurement of fission excitation functions of neighboring isotopes enables one to experimentally estimate the first chance fission probability. Even if only first chance fission is investigated, no evidence for fission transient times larger than 30 zs can be found.
Date: January 1, 1997
Creator: Rubehn, T.; Jing, K.X.; Moretto, L.G.; Phair, L.; Tso, K. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department

Determination of the nuclear induced electrical conductivity of {sup 3}He for magnetohydrodynamic energy conversion

Description: This is the final report for a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The continual need for more efficient, high-output energy conversion techniques has renewed interest in nuclear-driven magnetohydrodynamic (MHD) energy conversion. To provide the fundamental knowledge required to evaluate the potential value of this concept, a one-year project aimed at measuring the nuclear-induced electrical conductivity of a {sup 3}He/{sup 4}He gas mixture under thermodynamic conditions consistent with the MHD flow conditions was carried out. The range of bulk gas conditions to be considered were: pressure = 0.1 to 3800 Torr and temperature = 300 to 1500 K. The maximum neutron flux to be considered was 10{sup 16}/cm{sup 2}sec. The range of parameters considered surpassed previous experiments in all aspects.
Date: November 1996
Creator: Bitteker, L.; Scheuer, J. & Howe, S.
Partner: UNT Libraries Government Documents Department

A program in medium energy nuclear physics. Progress report, January 1, 1992--March 31, 1995

Description: This progress report and continuation proposal summarizes our achievements for the period from July 1, 1994 to September 30, 1995 and requests continued funding for our program in experimental medium-energy nuclear physics. The focus of our program remains the understanding of the short-range part of the strong interaction in the nuclear medium. In the past year we have focused our attention ever more sharply on experiments with real tagged photons, and we have successfully defended two new experimental proposals: Photofission of Actinide and Preactinide Nuclei at SAL and Photoproduction of the {rho} Meson from the Proton with Linearly Polarized Photons at CEBAF. (We are co-spokespersons on two previously approved Hall-B experiments at CEBAF, Photoreactions on {sup 3}He and Photoabsorption and Photofission of Nuclei.) As part of the team that is instrumenting the Photon Tagger for Hall B; we report excellent progress on the focal-plane detector array that is being built at our Nuclear Detector Laboratory, as well as progress on our plans for instrumentation of a tagged polarized-photon beam using coherent bremsstrahlung. Also, we shall soon receive a large computer system (from the SSC) which will form the basis for our new Data Analysis Center, which, like the Nuclear Detector Laboratory, will be operated under the auspices of The George Washington University Center for Nuclear Studies. Finally, during the past year we have published six more papers on the results of our measurements of pion scattering at LAMPF and of electron scattering at NIKHEF and Bates, and we can report that nearly all of the remaining papers documenting this long series of measurements are in the pipeline.
Date: October 1, 1995
Creator: Berman, B.L. & Dhuga, K.S.
Partner: UNT Libraries Government Documents Department

Polarized neutrons in RHIC

Description: There does not appear to be any obvious way to accelerate neutrons, polarized or otherwise, to high energies by themselves. To investigate the behavior of polarized neutrons the authors therefore have to obtain them by accelerating them as components of heavier nuclei, and then sorting out the contribution of the neutrons in the analysis of the reactions produced by the heavy ion beams. The best neutron carriers for this purpose are probably {sup 3}He nuclei and deuterons. A polarized deuteron is primarily a combination of a proton and a neutron with their spins pointing in the same direction; in the {sup 3}He nucleus the spins of the two protons are opposite and the net spin (and magnetic moment) is almost the same as that of a free neutron. Polarized ions other than protons may be accelerated, stored and collided in a ring such as RHIC provided the techniques proposed for polarized proton operation can be adapted (or replaced by other strategies) for these ions. This paper discusses techniques for accelerating polarized {sup 3}He nuclei and deuterons.
Date: April 20, 1998
Creator: Courant, E.D.
Partner: UNT Libraries Government Documents Department