400 Matching Results

Search Results

Advanced search parameters have been applied.

An Isotope Effect in Photosynthesis

Description: In the course of some kinetic studies on photosynthesis of barley seedlings, it has been found that plants utilize C{sup 12}O{sub 2} faster than C{sup 14}O{sub 2}. The plants were placed in a closed system containing an infra-red absorption-cell for the analysis of total CO{sub 2} and an ionization chamber for the determination of C{sup 14}O{sub 2} in the gas phase, both instruments recording continuously. Carbon dioxide, containing about 2% C{sup 14}O{sub 2}, was introduced in the dark and the specific activity at this point taken as unity. After a short dark period, the lights were turned on and photosynthesis was allowed to take place. A figure shows the result of a typical experiment. During the initial dark period the specific activity fell because of dilution by inactive respired CO{sub 2}. However, as photosynthesis proceeded, the specific activity of the residual CO{sub 2} rose until, when only 1/6 of it remained, the specific activity reached a peak some 20% higher than it had been at the start of photosynthesis. At this point the steady respiratory dilution became an appreciable fraction of the total remaining CO{sub 2}, and the specific activity dropped rapidly.
Date: November 23, 1948
Creator: Weigl, J.W. & Calvin, M.
Partner: UNT Libraries Government Documents Department


Description: The four-nucleon transfer reaction {sup 12}C({sup 10}B, {sup 6}Li*(2.18 MeV)) {sup 16}O has been studied at 68 MeV by coincidence measurement of the d + {alpha} breakup particles. The reaction is quite selective as is observed in other established {alpha}-transfer reactions.
Date: July 1, 1980
Creator: Bice, A.N.; Shotter, A.C.; Stahel, D.P. & Cerny, J.
Partner: UNT Libraries Government Documents Department

The Inclusive Muon Neutrino Reaction In 12C

Description: We calculate the charged current inclusive cross section for the reaction, v(sub)u +12C ->u^- + X, from the threshold to 300 MeV.In addition we obtain the average cross section over the spectrum currently being produced at LAMPF.We discuss our results with respect to the current experimental work and consider the possible contributions from higher l states.
Date: November 1, 1995
Creator: Pourkaviani, M. & Mintz, S.
Partner: UNT Libraries Government Documents Department

Heavy Residue Spectra in the Interaction of 85 A MeV 12C with197Au

Description: We have measured the heavy residue differential range distributions in the interaction of 85 MeV/nucleon {sup 12}C with {sup 197}Au. The range distributions were converted to energy spectra using known range-energy relationships. The mean residue energies range from 15 keV/nucleon (A = 189) to 314 keV/nucleon (A = 131). Longitudinal momenta of the heavy residues have been deduced (<p{sub {parallel}} > /p{sub cn} = 0.27). The mean spectral energies and the shapes of the residue spectra are shown to be in agreement with the predictions of the VUU model.
Date: December 1, 1988
Creator: Aleklett, K.; Johansson, M.; Lihver, L.; Loveland, W.; Groening,H.; McGaughey, P.L. et al.
Partner: UNT Libraries Government Documents Department

Ion Beam Induced Charge Collection (IBICC) from Integrated Circuit Test Structures Using a 10 MeV Carbon Microbeam

Description: As future sizes of Integrated Circuits (ICs) continue to shrink the sensitivity of these devices, particularly SRAMs and DRAMs, to natural radiation is increasing. In this paper, the Ion Beam Induced Charge Collection (IBICC) technique is utilized to simulate neutron-induced Si recoil effects in ICS. The IBICC measurements, conducted at the Sandia National Laboratories employed a 10 MeV carbon microbeam with 1pm diameter spot to scan test structures on specifically designed ICS. With the aid of layout information, an analysis of the charge collection efficiency from different test areas is presented. In the present work a 10 MeV Carbon high-resolution microbeam was used to demonstrate the differential charge collection efficiency in ICS with the aid of the IC design Information. When ions strike outside the FET, the charge was only measured on the outer ring, and decreased with strike distance from this diode. When ions directly strike the inner and ring diodes, the collected charge was localized to these diodes. The charge for ions striking the gate region was shared between the inner and ring diodes. I The IBICC measurements directly confirmed the interpretations made in the earlier work.
Date: November 18, 1998
Creator: Aton, T.J.; Doyle, B.L.; Duggan, J.L.; El Bouanani, M.; Guo, B.N.; McDaniel, F.D. et al.
Partner: UNT Libraries Government Documents Department

Possible measurement of the vacuum polarization in heavy ion scattering

Description: A measurement of vacuum polarization effects in nonrelativistic elastic heavy ion scattering is suggested. It is found that in a typical subcoulomb barrier event enough momentum is transferred from the projectile to the target nucleus to make the high q/sup 2/ behavior of the photon propagator observable. The elastic cross section is increased in a typical case by 2.5% above the Rutherford value. Only relative measurements are needed. (auth)
Date: January 1, 1973
Creator: Rafelski, J. & Klein, A.
Partner: UNT Libraries Government Documents Department

Entrance channel dependent light-charged particle emission of the {sup 156}Er compound

Description: Light-charged particle decay from the {sup 156}Er compound nucleus, populated by {sup 12}C+{sup 144}Sm and {sup 60}Ni+{sup 96}Zr at the same excitation energy, were measured in coincidence with the evaporation residues. The high energy slope of charged particle spectra for the {sup 60}Ni-induced reaction is steeper than for the {sup 12}C-induced reaction. Model calculations including particle evaporation during compound nucleus formation result in good agreement with the data. This suggests that the difference in the charged particle spectra between the two entrance channels is due to a longer formation time in the {sup 60}Ni-induced reaction. 14 refs., 3 figs.
Date: September 1, 1996
Creator: Liang, J.F.; Bierman, J.D.; Kelly, M.P.; Sonzogni, A.A.; Vandenbosch, R. & van Schagen, J.P.S.
Partner: UNT Libraries Government Documents Department

Evidence for alpha-particle chain configurations in {sup 24}Mg

Description: Many theoretical models have been employed to described the structure of the nucleus {sup 24}Mg. Among these are the Cranked Shell model (CSM), the Cranked Cluster Model (CCM), and calculations have also been performed using the Hartree-Fock formalism. One very striking prediction of these calculations is that in this nucleus there exist very unusual configurations, with structures reminiscent of linear chains of alpha particles. In the CSM, for instance, such a configuration is identified with a pronounced minimum in the potential energy energy at very large prolate deformation. In the CCM, several very different alpha-particle duster configurations are identified, many having rather large deformations. These cluster configurations can be associated with the different potential-energy minima obtained in the CSM results. In the case of the CCM, a 6{alpha} chain-like configuration is predicted to occur at excitation energies between 40 and 50 MeV, with predicted rotational spacing given by {Dirac_h}{sup 2}/2I=22 keV. At this excitation energy, such a chain configuration would lie well above the threshold for the decay of {sup 24}Mg into 6 alpha particles, and its identification poses a difficult experimental challenge. This report discusses this challenge.
Date: September 1, 1992
Creator: Wuosmaa, A. H.; Back, B. B.; Betts, R. R.; Ferre, M.; Gehring, J.; Glagola, P. G. et al.
Partner: UNT Libraries Government Documents Department


Description: Thirteen hadron beam therapy facilities began operation between 1990 and 2001 - 5 in Europe, 4 in North America, 3 in Japan, and 1 in South Africa [l]. Ten of them irradiate tumors with protons, 2 with Carbon- 12 ions, and 1 with both protons and Carbon-12. The facility with the highest patient throughput - a total of 6 174 patients in 11 years and as many as 150 patient treatments per day -is the Loma Linda University Medical Center, which uses a weak focusing slow cycling synchrotron to accelerate beam for delivery to passive scattering nozzles at the end of rotatable gantries [2, 3,4]. The Rapid Cycling Medical Synchrotron (RCMS) is a second generation synchrotron that, by contrast with the Loma Linda synchrotron, is strong focusing and rapid cycling, with a repetition rate of 30 Hz. Primary parameters for the RCMS are listed in Table 1.
Date: June 2, 2002
Partner: UNT Libraries Government Documents Department

Research Studies on Analysis of Ionized Gases. Final Report

Description: The appearance of a large mass 12 peak in pure helium afterglows prompted further investigations, from which it is believed that the maas 12 peak is carbon from a CO impurity, probably a result of outgassing of the walls of the discharge chamber, Mixtures of oxygen with helium and neon have been examined in an attempt to measure the O/sup +/ to O/sub 2/ charge transfer rate. Afterglows in hydrogen, water vapor, and nitrogen-- hydrogen mixtures have also been studied. (auth)
Date: July 31, 1962
Creator: Snow, W. R.
Partner: UNT Libraries Government Documents Department

Human radiation studies: Remembering the early years. Oral history of physiologist Nello Pace, Ph.D., August 16, 1994

Description: Dr. Nello Pace was interviewed by representatives of the US DOE Office of Human Radiation Experiments (OHRE). Dr. Pace was selected fro the interview because of the positions he held with the US Navy, at the University of California, Berkeley, and as Director of the White Mountain Research Station near Bishop, California. Following a brief biographical sketch, Dr. Pace related his remembrances concerning tritium injections experiments in animals and humans during World War II, the development of Medical Physics Degree Programs at UC Berkeley, conducting the first radiation survey at Nagasaki after the bomb, and the establishment of a research laboratory at White Mountain. He also offers reflections on Shields Warren and comments on the public`s attitudes towards radiation both then and now.
Date: June 1, 1995
Partner: UNT Libraries Government Documents Department

Determining properties of baryon resonances in nuclei

Description: Meson-nucleus and photon-nucleus interactions are important sources of information about the medium modifications of baryon resonances in nuclei. Indications of how large the medium effects are for resonances above the {Delta}{sub 33}(1232) are provided by it combined analysis of photonuclear and pion cross sections in the GeV range of energies. Tile existing data indicate a possible 10-20% renormalization of the pion coupling to higher-lying resonances in nuclei.
Date: October 1, 1996
Creator: Johnson, M.B.; Chen, C.M.; Ernst, D.J. & Jiang, M.F.
Partner: UNT Libraries Government Documents Department

Inductively coupled plasma mass spectrometry for stable isotope metabolic tracer studies of living systems

Description: This dissertation focuses on the development of methods for stable isotope metabolic tracer studies in living systems using inductively coupled plasma single and dual quadrupole mass spectrometers. Sub-nanogram per gram levels of molybdenum (Mo) from human blood plasma are isolated by the use of anion exchange alumina microcolumns. Million-fold more concentrated spectral and matrix interferences such as sodium, chloride, sulfate, phosphate, etc. in the blood constituents are removed from the analyte. The recovery of Mo from the alumina column is 82 {+-} 5% (n = 5). Isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) is utilized for the quantitative ultra-trace concentration determination of Mo in bovine and human blood samples. The average Mo concentration in reference bovine serum determined by this method is 10.2 {+-} 0.4 ng/g, while the certified value is 11.5 {+-} 1.1 ng/g (95% confidence interval). The Mo concentration of one pool of human blood plasma from two healthy male donors is 0.5 {+-} 0.1 ng/g. The inductively coupled plasma twin quadrupole mass spectrometer (ICP-TQMS) is used to measure the carbon isotope ratio from non-volatile organic compounds and bio-organic molecules to assess the ability as an alternative analytical method to gas chromatography combustion isotope ratio mass spectrometry (GC-combustion-IRMS). Trytophan, myoglobin, and {beta}-cyclodextrin are chosen for the study, initial observation of spectral interference of {sup 13}C{sup +} with {sup 12}C{sup 1}H{sup +} comes from the incomplete dissociation of myoglobin and/or {beta}-cyclodextrin.
Date: May 10, 1999
Creator: Luong, E.
Partner: UNT Libraries Government Documents Department

A study of the abundance and {sup 13}C/{sup 12}C ratio of atmospheric carbon dioxide and oceanic carbon in relation to the global carbon cycle. Final technical report, February 15, 1990--July 31, 1995

Description: Knowledge can be gained about the fluxes and storage of carbon in natural systems and their relation to climate by detecting temporal and spatial patterns in atmospheric CO{sub 2}. When patterns in its {sup 13}C/{sup 12}C isotopic ratio are included in the analysis, there is also a basis for distinguishing organic and inorganic processes. The authors systematically measured the concentration and {sup 13}C/{sup 12}C ratio of atmospheric CO{sub 2} to produce time series data essential to reveal these temporal and spatial patterns. To pursue the significance of these patterns further, the result also involved measurements of inorganic carbon in sea water and of CO{sub 2} in air near growing land plants. The study was coordinated with a study of the same title concurrently funded by the National Science Foundation (NSF). The study called for continued atmospheric measurements at an array of ten stations from the Arctic Basin to the South Pole. Air was collected in flasks brought back to the laboratory for analysis, except at Mauna Loa. Observatory, Hawaii, where continuous measurements were also carried out.
Date: December 31, 1995
Creator: Keeling, C.D.
Partner: UNT Libraries Government Documents Department

Helium-induced reactions in astrophysics

Description: Helium-induced reactions play a crucial role in stellar nucleosynthesis. Carbon and oxygen are produced mainly during the helium-burning phase by the chain of reactions {sup 8}Be({alpha}, {gamma} + e{sup +}e{sup {minus}}){sup 12}C({alpha}, {gamma}){sup 16}O. The first step, often called triple-{alpha} capture, was proposed by Hoyle to bypass the mass stability gap at {sup 8}Be. The second step gives rise to the largest uncertainty in most of the calculated stellar abundances. Later {alpha}-captures on {sup 13}C are believed to be a major source of s-process neutrons. The status of each of these important reactions is reviewed here.
Date: November 1, 1997
Creator: Hale, G.M.
Partner: UNT Libraries Government Documents Department

A-dependence of nuclear transparency in quasielastic A(e,e{prime}p) at high Q{sup 2}

Description: The A-dependence of the quasielastic A(e,e{prime}p) reaction has been studied with {sup 3}H, C, Fe, and Au nuclei at momentum transfers Q{sup 2} = 1, 3, 5, and 6.8(GeV/c){sup 2}. The authors extract the nuclear transparency T(A,Q{sup 2}), a measure of the average probability of escape of a proton from a nucleus A. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as color transparency. No statistically significant rise is seen for any of the nuclei studied.
Date: May 1, 1994
Creator: O`Neill, T.G.; Lorenzon, W. & Arrington, J.
Partner: UNT Libraries Government Documents Department

Proton propagation through nuclei and the quasi-free reaction mechanism studied with (e,e{prime}p) reactions

Description: Jefferson Lab experiment E91-013 measured the energy dependence of proton propagation in nuclei, using the quasi-free (e, e{prime}p) reaction. The ratios of the experimental (e, e{prime}p) cross-sections integrated over the quasi-free region to PWIA calculations are presented as a function of momentum transfer, (0.6 < Q{sup 2} < 3.3 GeV{sup 2}) and target nucleus (C, Fe and Au). As a first step towards a longitudinal and transverse separation of the quasi-free cross-section, a super ratio of the measured to the calculated cross-sections at forward and backward angles is presented.
Date: September 1, 1997
Creator: Dutta, D.; Abbott, D. & Amatuni, T.A.
Partner: UNT Libraries Government Documents Department