228 Matching Results

Search Results

Advanced search parameters have been applied.

The influence of projectile neutron number in the 208Pb(48Ti, n)255Rf and 208Pb(50Ti, n)257Rf reactions

Description: Four isotopes of rutherfordium,254-257Rf, were produced by the 208Pb(48Ti, xn)256-xRf and 208Pb(50Ti, xn)258-xRf reactions (x = 1, 2) at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Excitation functions were measured for the 1n and 2n exit channels. A maximum likelihood technique, which correctly accounts for the changing cross section at all energies subtended by the targets, was used to fit the 1n data to allow a more direct comparison between excitation functions obtained under different experimental conditions. The maximum 1n crosssections of the 208Pb(48Ti, n)255Rf and 208Pb(50Ti, n)257Rf reactions obtained from fits to the experimental data are 0.38 +/- 0.07 nb and 40 +/-5 nb, respectively. Excitation functions for the 2n exit channel were also measured, with maximum cross sections of nb for the 48Ti induced reaction, and 15.7 +/- 0.2 nb for the 50Ti induced reaction. The impact of the two neutron difference in the projectile on the 1n cross section is discussed. The results are compared to the Fusion by Diffusion model developed by Swiatecki, Wilczynska, and Wilczynski.
Date: July 11, 2008
Creator: Dragojevic, Irena; Dragojevic, I.; Gregorich, K.E.; Dullmann, Ch.E.; Garcia, M.A.; Gates, J.M. et al.
Partner: UNT Libraries Government Documents Department

HIGH ENERGY EXCITATION FUNCTIONS IN THE HEAVY REGION

Description: The electrostatically deflected beam of the 184-inch cyclotron has been used with the stacked foil and absorber technique to determine the excitation functions for the following reactions: Th{sup 232}(p,6n)Pa{sup 227}, Th{sup 232}(p,3n)Pa{sup 230}, Th{sup 232}(d,7n)Pa{sup 227}, Th{sup 232}({alpha},p8n)Pa{sup 227}, Th{sup 232}({alpha},p5n)Pa{sup 230}, and U{sup 238}(p,{alpha}8n)Pa{sup 227}. The data are presented graphically and discussed individually for each of the reactions. Some rough excitation function data have also been determined for the reactions Th{sup 232}(d,4n)Pa{sup 230}, U{sup 238}(p,{alpha}5n)Pa{sup 230}, Th{sup 232}({alpha},7n)U{sup 229}, and Th{sup 232}({alpha},6n)U{sup 230}. The results are discussed in terms of compound nucleus formation, transparency effects, and other factors in order to arrive at a qualitative picture for the mechanism of high energy nuclear reactions with heavy nuclei.
Date: September 26, 1950
Creator: Meinke, W.W.; Wick, G.C. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Excitation Function of the Reaction C12(n,2n)C11 at High Energies

Description: The excitation curve for the reaction C{sup 12}(n,2n)C{sup 11} has been calculated for energies up to 100 Mev. The calculations were done as described in the preceding letter for the similar reaction of C{sup 12} under proton bombardment. The results of the calculations for 50% charge exchange are shown in Figure 1. The calculated cross section for the reaction at 90 Mev is: .011 barns for 100% charge exchange and .013 barns for 50% charge exchange. The experimental value is 0.025 {+-} .004 barns. The ratio of the cross section of the reaction C{sup 12}(pnpn)C{sup 11} to the cross section of the above reaction at 90 Mev is 5.8 for 100% charge exchange and 3.8 for 50% charge exchange. The experimental ratio is 2.7 at 90 Mev. This difference in cross sections between the two reactions is established by two factors. Firstly, there is the part played by charge exchange in the C{sup 12}(pnpn)C{sup 11} reaction which leads to excited N{sup 12} with the subsequent boiling off of a proton, while a similar exchange process cannot take place for the C{sup 12}(n2n)C{sup 11} reaction. Secondly, there is the difference between the contributions of the knock out process as a result of the difference in the n - p and the n - n cross sections, which favors the p + C{sup 12} knock out reaction. It will be noted that the parts of the reactions which go through excited C{sup 12}, while practically equal, are so small that they do not greatly affect either reaction. Although the results of these calculations do not agree too closely with the experimental results, the results are probably as good as are to be expected because of the crudity of the assumed model. The results do, though, seem to give a good qualitative picture ...
Date: November 1, 1947
Creator: Heckrotte, Wolff & Wolff, Peter
Partner: UNT Libraries Government Documents Department

Excitation Function of the Reaction C12(p,pn)C11 at High Energies

Description: Chupp and McMillan have recently measured the excitation curve for the reaction C{sup 12}(pnpn)C{sup 11} at high energies. Using the model of the nucleus described by Serber, the excitation curve of the above reaction has been calculated for energies up to 100 Mev. The excitation of the nucleus is determined on the basis that the incident proton makes individual collisions with the nucleons, the transferred energy exciting the nucleus. n-p collisions are taken to be three times more probable than n-n or p-p collisions. Charge exchange is assumed. The calculations were made for both 50% and 100% charge exchange. The decay of the excited nucleus is treated by the usual evaporation mode.
Date: November 1, 1947
Creator: Heckrotte, W. & Wolff, Peter
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

The Structure of 12N using 11C + p resonance scattering

Description: The level structure of {sup 12}N has been investigated from 2.2 to 11.0 MeV in excitation energy using a {sup 11}C + p resonance interaction with thick targets and inverse kinematics. Excitation functions were fitted using an R-matrix approach. Sixteen levels in {sup 12}N were included in the analysis, several of them are new. Spin-parity assignments, excitation energies and widths are proposed for these levels. To fit the high energy part of the excitation function, imaginary phase shifts had to be added to the phase shifts generated by the hard sphere scattering.
Date: March 2, 2006
Creator: Perajarvi, K.; Chang, Bo Fu; Rogachev, G.V.; Chubarian, G.; Goldberg, V.Z.; Guo, Q. et al.
Partner: UNT Libraries Government Documents Department

Study of low-lying resonant states in 16F using an 15O radioactiveion beam

Description: A 120 MeV {sup 15}O radioactive ion beam with an intensity on target of 4.5 x 10{sup 4} pps has been developed at the 88-inch cyclotron at the Lawrence Berkeley National Laboratory. This beam has been used to study the level structure of {sup 16}F at low energies via the p({sup 15}O,p) reaction using the thick target inverse kinematics method on a polyethylene target. The experimental excitation function was analyzed using R-matrix calculations. Significantly improved values for the level widths of the four low-lying states in 16F are reported. Good agreement with the theoretical spectroscopic factors is also obtained.
Date: January 22, 2007
Creator: Lee, D.W.; Perajarvi, K.; Powell, J.; O'Neil, J.P.; Moltz, D.M.; Goldberg, V.Z. et al.
Partner: UNT Libraries Government Documents Department

Neutron capture and (n,2n) measurements on 241Am

Description: We report on a set of neutron-induced reaction measurements on {sup 241}Am which are important for nuclear forensics and advanced nuclear reactor design. Neutron capture measurements have been performed on the DANCE detector array at the Los Alamos Neutron Scattering CEnter (LANSCE). In general, good agreement is found with the most recent data evaluations up to an incident neutron energy of {approx} 300 keV where background limits the measurement. Using mono-energetic neutrons produced in the {sup 2}H(d,n){sup 3}He reaction at Triangle University Nuclear Laboratory (TUNL), we have measured the {sup 241}Am(n,2n) excitation function from threshold (6.7 MeV) to 14.5 MeV using the activation method. Good agreement is found with previous measurements, with the exception of the three data points reported by Perdikakis et al. around 11 MeV, where we obtain a much lower cross section that is more consistent with theoretical estimates.
Date: July 18, 2007
Creator: Vieira, D; Jandel, M; Bredeweg, T; Bond, E; Clement, R; Couture, A et al.
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

Semiempirical Studies of Atomic Structure. Final Report for July 1, 2000 - June 30, 2003

Description: This project has developed a comprehensive and reliable base of accurate atomic structure data for complex many-electron systems. This has been achieved through the use of sensitive data-based parametric systematizations, precise experimental measurements, and supporting theoretical computations. The atomic properties studies involved primary data (wavelengths, frequency intervals, lifetimes, relative intensities, production rates, etc.) and derived structural parameters (energy levels, ionization potentials, line strengths, electric polarizabilities, branching fractions, excitation functions, etc).
Date: May 1, 2004
Creator: Curtis, L. J.
Partner: UNT Libraries Government Documents Department

A model of the AGS based on stepwise ray-tracing through the measured field maps of the main magnets

Description: Two-dimensional mid-plane magnetic field maps of two of the main AGS magnets were produced, from Hall probe measurements, for a series of different current settings. The analysis of these data yielded the excitation functions [1] and the harmonic coefficients [2] of the main magnets which have been used so far in all the models of the AGS. The constant increase of the computation power makes it possible today to directly use a stepwise raytracing through these measured field maps with a reasonable computation time. We describe in detail how these field maps have allowed the generation of models of the 6 different types of AGS main magnets, and how they are being handled with the Zgoubi ray-tracing code [3]. We give and discuss a number of results obtained regarding both beam and spin dynamics in the AGS, and we provide comparisons with other numerical and analytical modelling methods.
Date: May 20, 2012
Creator: Y., Dutheil; Meot, F. & Tsoupas, N.
Partner: UNT Libraries Government Documents Department

Influence of projectile neutron number on cross section in cold fusion reactions

Description: Elements 107-112 [1,2] have been discovered in reactions between {sup 208}Pb or {sup 209}Bi targets and projectiles ranging from {sup 54}Cr through {sup 70}Zn. In such reactions, the compound nucleus can be formed at excitation energies as low as {approx}12 MeV, thus this type of reaction has been referred to as 'cold fusion'. The study of cold fusion reactions is an indispensable approach to gaining a better understanding of heavy element formation and decay. A theoretical model that successfully predicts not only the magnitudes of cold fusion cross sections, but also the shapes of excitation functions and the cross section ratios between various reaction pairs was recently developed by Swiatecki, Siwek-Wilczynska, and Wilczynski [3,4]. This theoretical model, also referred to as Fusion by Diffusion, has been the guide in all of our cold fusion studies. One particularly interesting aspect of this model is the large predicted difference in cross sections between projectiles differing by two neutrons. The projectile pair where this difference is predicted to be largest is {sup 48}Ti and {sup 50}Ti. To test and extend this model, {sup 208}Pb({sup 48}Ti,n){sup 255}Rf and {sup 208}Pb({sup 50}Ti,n){sup 257}Rf excitation functions were recently measured at the Lawrence Berkeley National Laboratory's (LBNL) 88-Inch Cyclotron utilizing the Berkeley Gas-filled Separator (BGS). The {sup 50}Ti reaction was carried out with thin lead targets ({approx}100 {micro}g/cm{sup 2}), and the {sup 48}Ti reaction with both thin and thick targets ({approx}470 {micro}g/cm{sup 2}). In addition to this reaction pair, reactions with projectile pairs {sup 52}Cr and {sup 54}Cr [5], {sup 56}Fe and {sup 58}Fe [6], and {sup 62}Ni [7] and {sup 64}Ni [8] will be discussed and compared to the Fusion by Diffusion predictions. The model predictions show a very good agreement with the data.
Date: September 1, 2007
Creator: Dragojevic, Irena; Dragojevic, I.; Gregorich, K.E.; Dullmann, Ch.E.; Folden III, C.M.; Garcia, M.A. et al.
Partner: UNT Libraries Government Documents Department

Phase transitions in nuclear physics

Description: A critical overview of the low energy phase transitions in nuclei is presented with particular attention to the 2nd (1st) order pairing phase transitions, and to the 1st order liquid-vapor phase transition. The role of fluctuations in washing out these transitions is discussed and illustrated with examples. A robust indicator of phase coexistence in multifragmentation is presented.
Date: August 1, 1997
Creator: Moretto, L.G.; Phair, L. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department

Development of an odd-Z-projectile reaction for heavy element synthesis: 208Pb(64Ni, n)271Ds and 208Pb(65Cu, n)272111

Description: Seven {sup 271}Ds decay chains were identified in the bombardment of {sup 208}Pb targets with 311.5- and 314.3-MeV {sup 64}Ni projectiles using the Berkeley Gas-filled Separator. These data, combined with previous results, provide an excitation function for this reaction. From these results, an optimum energy of 321 MeV was estimated for the production of {sup 272}111 in the reaction {sup 208}Pb({sup 65}Cu, n). One decay chain was observed, resulting in a cross section of 1.7{sub -1.4}{sup +3.9} pb. This experiment confirms the discovery of element 111 by the Darmstadt group who used the {sup 209}Bi({sup 64}Ni, n){sup 272}111 reaction.
Date: August 16, 2004
Creator: Folden III, C.M.; Gregorich, K.E.; Dullmann, Ch.E.; Mahmud, H.; Pang, G.K.; Schwantes, J.M. et al.
Partner: UNT Libraries Government Documents Department

Comparison of reactions for the production of 258,257Db: 208Pb(51V,xn) and 209Bi(50Ti,xn)

Description: Excitation functions for the 1n and 2n exit channels of the 208Pb(51V,xn)259-xDb reaction were measured. A maximum cross section of the 1n exit channel of 2070+1100/-760 pb was measured at an excitation energy of 16.0 +- 1.8 MeV. For the 2n exit channel, a maximum cross section of 1660+450/-370 pb was measured at 22.0 +- 1.8 MeV excitation energy. The 1n excitation function for the 209Bi(50Ti,n)258Db reaction was remeasured, resulting in a cross section of 5480+1750/-1370 pb at an excitation energy of 16.0 +- 1.6 MeV, in agreement with previous values [F. P. Hebberger, et al., Eur. Phys. J. A 12, 57 (2001)]. Differences in cross section maxima are discussed in terms of the fusion probability below the barrier.
Date: September 29, 2008
Creator: Gates, Jacklyn M.; Nelson, Sarah L.; Gregorich, Kenneth E.; Dragojevic, Irena; Dullmann, Christoph E.; Ellison, Paul A. et al.
Partner: UNT Libraries Government Documents Department

Spallation-Fission Competition in Heaviest Elements; Helium IonInduced Reactions in Plutonium Isotopes

Description: Excitation functions have been determined for the spallation and fission reactions induced in plutonium isotopes by 20 to 50 Mev helium ions. The method employed consisted of cyclotron bombardments of plutonium oxide followed by the chemical isolation and alpha or beta counting of radioactive reaction products. Formation cross sections are given where possible for the curium and americium spallation products corresponding to ({alpha},n), ({alpha},2n), ({alpha},3n), ({alpha},4n), ({alpha}5n), ({alpha},p), ({alpha},pn or d), ({alpha},p2n or t), and ({alpha},p3n) reactions in Pu{sup 238} , Pu{sup 239}, and Pu{sup 242}. Fission yield curves and fission cross sections for Pu{sup 238} and Pu{sup 239} serve to define the characteristics of the ({alpha},f) reaction for plutonium isotopes. Chemical procedures are outlined for the separation of both spallation and fission product elements in a sequence of operations performed on the entire dissolved target.
Date: June 1, 1956
Creator: Glass, Richard A.; Carr, Robert J.; Cobble, James W. & Seaborg,Glenn T.
Partner: UNT Libraries Government Documents Department

Some Excitation Functions of Bismuth

Description: Excitation functions have been measured, using a 38-Mev alpha-beam and a 19-Mev deuteron beam for the following reactions: Bi({alpha},2n)At{sup 211}, Bi({alpha},3n)At{sup 210}, Bi(d,p)Ra E, Bi(d,n)Po{sup 210}, and Bi(d,3n)Po{sup 209}. The results are summarized in Figs. 4 and 5 and Tables I and II. A new isotope of astatine, At{sup 210}, has been identified; this isotope has a half life of 8.3 hr., decaying by K-capture to Po{sup 210} with the emission of a 1.0-Mev gamma-ray and a few conversion electrons.
Date: October 10, 1948
Creator: Kelly, E.L. & Segre, E.
Partner: UNT Libraries Government Documents Department

Gamma-ray production cross sections in multiple channels for neutron induced reaction on 48Ti for En=1 to 200 MeV

Description: Prompt {gamma}-ray production cross sections were measured on a {sup 48}Ti sample for incident neutron energies from 1 MeV to 200 MeV. Partial {gamma}-ray cross sections for transitions in {sup 45-48}Ti, {sup 45-48}Sc, and {sup 43-45}Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial {gamma}-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the LANSCE/WNR facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, pre-equilibrium emission and direct reaction mechanisms are included. Overall the model calculations of the partial {gamma}-ray cross sections are in good agreement with measured values.
Date: July 6, 2006
Creator: Dashdorj, D; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A et al.
Partner: UNT Libraries Government Documents Department

Neutron induced inelastic cross sections of 150Sm for En = 1 to 35 MeV

Description: Cross-section measurements were made of prompt gamma-ray production as a function of incident neutron energy (E{sub n} = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction gamma rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Partial {gamma}-ray cross sections were predicted using the Hauser-Feshbach statistical reaction code GNASH. Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These pre-equilibrium spin distributions were incorporated into a new version of GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without pre-equilibrium effects is discussed.
Date: August 16, 2006
Creator: Dashdorj, D; Mitchell, G E; Kawano, T; Becker, J A; Agvaanluvsan, U; Chadwick, M B et al.
Partner: UNT Libraries Government Documents Department

Progress on the Europium Neutron-Capture Study using DANCE

Description: The accurate measurement of neutron-capture cross sections of the Eu isotopes is important for many reasons including nuclear astrophysics and nuclear diagnostics. Neutron capture excitation functions of {sup 151,153}Eu targets were measured recently using a 4{pi} {gamma}-ray calorimeter array DANCE located at the Los Alamos Neutron Science Center for E{sub n} = 0.1-100 keV. The progress on the data analysis efforts is given in the present paper. The {gamma}-ray multiplicity distributions for the Eu targets and Be backing are significantly different. The {gamma}-ray multiplicity distribution is found to be the same for different neutron energies for both {sup 151}Eu and {sup 153}Eu. The statistical simulation to model the {gamma}-ray decay cascade is summarized.
Date: September 5, 2006
Creator: Agvaanluvsan, U; Becker, J A; Macri, R A; Parker, W; Wilk, P; Wu, C Y et al.
Partner: UNT Libraries Government Documents Department

Bevatron Operation and Development, VI

Description: A large fraction of the effort on high-energy physics this quarter was devoted to the study of K particles. Ten of the fourteen external laboratory groups, as well as seven of the internal laboratory groups, used the K{sup {+-}}-beam facilities. These experiments included measurements of lifetimes, modes of decay; and excitation functions. Counters and cloud-chamber techniques were used in addition to nuclear emulsions. Measurements of total and differential cross-sections for {pi}{sup -} mesons continued. Work on proton-proton scattering was extended to 4.8 Bev. Radiochemical investigations of spallation products in light and heavy elements were extended. A new target plunger, a 4-inch quadrupole magnet, and two new steel collimators were added to the experimental facilities. Accelerator development this quarter included experiments on increasing the acceptance time of the Bevatron, self-tracking of the radiofrequency equipment, and the substitution of an analogue computer for the 3D-point curve corrector.
Date: November 18, 1955
Partner: UNT Libraries Government Documents Department