1,959 Matching Results

Search Results

Advanced search parameters have been applied.

Fission properties of the heaviest elements

Description: The authors discuss fission properties of the heaviest elements. In particular they focus on stability with respect to spontaneous fission and on the prospects of extending the region of known nuclei beyond the peninsula of currently known nuclides.
Date: March 1, 1995
Creator: Moller, P. & Nix, R.
Partner: UNT Libraries Government Documents Department

Nuclear Thermodynamics of the Heaviest Elements

Description: The phenomenon of alpha particle emission, a general observable property for the nuclides above lead, makes it possible to relate these nuclides energetically. The radioactive decay energy along a radioactive series can be summed so that the total decay energy for each nuclide in the series is known with respect to its position above teh bottom of the series, that is, with respect to its terminal lead (or bismuth) isotope. This can be done for each of the four mass types and, as shown, one can obtain this information for all the collateral members as well as the members in the main line of decay. Thus it is possible, using the relation between mass and energy and the known mass of the alpha particle, to convert this radioactive decay energy ine ach case to a relative mass value based on the mass of one of the four end products, Pb{sup 208}, Pb{sup 207}, Pb{sup 206}, or Bi{sup 209}. If the absolute mass of each of these is known, it is then possible to calculate the absolute mass for all the heavy nuclides above lead for which decay energy data are known or can be estimated. The absolute mass of only one of this group of four need actually be known since the neutron binding energies related them can be measured. it is also possible to measure the absolute masses of other nuclei in each of the four series, for example, such nuclides as U{sup 238}, Th{sup 232}, U{sup 235}, or Np{sup 237} which are available in sufficient quantity for mass spectrographic measurements, and the aboslute masses of the other members of each of the series may then be calculated from these through proper use of the decay data. if the absolute masses of more than one member of the same ...
Date: March 1, 1952
Creator: Seaborg, Glenn T.
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

MEASUREMENT OF THE SIGMA- POLARIZATION IN THE REACTION pi- + p-->SIGMA- + K+

Description: The average polarization of the {Sigma}{sup -} produced in the reaction {pi}{sup -} + p {yields} {Sigma}{sup -} + K{sup +} has been measured between center-of-mass angles 134{sup o} and 166{sup o} for an incident {pi}{sup -} momentum of 1145 MeV/c. A polarized proton target was used, and the {Sigma}{sup -} polarization was found by measuring the difference in the production-rate of K{sup +} mesons for protons polarized along the production-plane normal and against it. Spark chambers were used to record the {pi}{sup -} and K{sup +} trajectories, and the {pi}{sup -} momentum was obtained from a magnetic spectrometer while the K{sup +} momentum was obtained from a range telescope. Each event was kinematically reconstructed in a one constraint fit to help eliminate events produced from protons bound in heavy nuclei of the target. The {Sigma}{sup -} polarization was found to be -0.36 {+-} 0.46.
Date: October 1, 1967
Creator: Weldon, D.; Steiner, H.; Shapiro, G.; Schultz, C; Johnson, C.H.; Holloway, L. et al.
Partner: UNT Libraries Government Documents Department

Patterns in ultra-high energy cosmic ray arrival directions: a possible footprint of large scale cosmic structures

Description: The public available data of cosmic ray arrival directions with energies above 4 x 10{sup 19} eV present a broad maximum in the cumulative two-point autocorrelation function around 25 degrees. This has been interpreted as the first imprint of the filamentary pattern of large scale structures (LSS) of matter in the near universe. We analyze this suggestion in light of the clustering properties expected from a catalogue of galaxies of the local universe (redshift z {approx}< 0:06). The data reproduce particularly well the clustering properties of the nearby universe within z {approx}< 0:02. There is no statistically significant cross-correlation between data and structures, although intriguingly the nominal cross-correlation chance probability for displacements within {approx}50 degree drops from O(50%) to O(10%) using the catalogue with a smaller horizon. Our results suggest a relevant role of magnetic fields (possibly extragalactic ones, too) and/or possibly some heavy nuclei fraction in the ultra-high energy cosmic rays.
Date: July 1, 2007
Creator: Serpico, Pasquale Dario
Partner: UNT Libraries Government Documents Department

Spontaneous fission half-lives and their systematics

Description: Spontaneous fission is a phenomenon exhibited by heavy nuclei, which can be a major mode of decay of nuclei of elements heavier than thorium and can be a determining factor in their stability. For purposes of this paper, spontaneous fission will be considered a process in which a nucleus breaks up into two approximately equal parts. The emission of light nuclei or heavy ions such as {sup 12}C, {sup 16}O, or {sup 32}S will not be considered. This radioactive decay mode is often much smaller than the spontaneous fission decay mode, although this is not true in all cases. Barwick noted that this might indicate that the assumed half-life for spontaneous fission of some older experiments might be partially due to heavy fragment radioactivity. Other than taking note of this potential correction to spontaneous fission half-lives, this decay mode of heavy fragment radioactivity will be ignored. Excited states of some heavy nuclei may decay via spontaneous fission. These so-called fission isomers will not be discussed here. Electron capture (EC) or beta-delayed fission is a process in which prompt fission of a sufficiently excited daughter state occurs following population by EC or beta decay. The fission activity will appear to decay with the half-life of the parent and was earlier confused in some cases with SF. This process has been discussed in detail in a review and will not be considered in this paper.
Date: March 1, 1998
Creator: Holden, N.E.
Partner: UNT Libraries Government Documents Department

Photofission of Heavy Nuclei at Energies up to 4 GeV

Description: Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80%, implying the presence of important processes that compete with fission. We also observe that the relative photofission cross sections do not depend strongly on the incident photon energy over this entire energy range. If we assume that for 237Np the photofission probability is equal to unity, we observe a significant shadowing effect starting below 1.5 GeV.
Date: April 1, 2000
Creator: Cetina, Catalina; Berman, Barry L.; Briscoe, William; Cole, Philip L.; Feldman, Gerald; Heimberg, Peter et al.
Partner: UNT Libraries Government Documents Department

Gross shell structure at high spin in heavy nuclei

Description: Experimental nuclear moments of inertia at high spins along the yrast line have been determined systematically and found to differ from the rigid-body values. The difference is attributed to shell effect and these have been calculated microscopically. The data and quantal calculations are interpreted by means of the semiclassical Periodic Orbit Theory. From this new perspective, features in the moments of inertia as a function of neutron number and spin, as well as their relation to the shell energies can be understood. Gross shell effects persist up to the highest angular momenta observed.
Date: October 7, 2003
Creator: Deleplanque, Marie-Agnes; Frauendorf, Stefan; Pashkevich, Vitaly V.; Chu, S.Y. & Unzhakova, Anja
Partner: UNT Libraries Government Documents Department

NUCLEAR HOLE STATES AS A PROBE OF THE NUCLEAR MANY BODY SYSTEM

Description: Nuclear hole states studied in proton and neutron pick-up reactions on light and heavy target nuclei exhibit -- for deeply-bound shell model orbits -- properties, which are strongly affected by target nucleus collectivities. Quasiparticle-like holes in nuclei are formed showing features very similar to those of other highly excited modes e.g. giant quadrupole resonances. The similarity between these two complicated modes of excitation in light and heavy nuclei asks for a detailed theoretical interpretation. Both modes are built up by a bulk of levels with fixed spin and parity in the continuum region of nuclei. Deeply bound hole states may, like giant multipole resonances, be interpreted as collective phenomena and, therefore, can represent a new tool for investigating the nuclear many body system. {gamma}-decay measurements of these complicated modes, or nuclear photoeffect measurements of quasiholes, would provide the most direct access to their collective structure. However, such experiments are difficult to perform. On the other hand, light Particle decay studies for the systems discussed here, will surely help to clarify their common microscopic features.
Date: August 1, 1978
Creator: Doll, P.
Partner: UNT Libraries Government Documents Department

Population of Nuclei Via 7Li-Induced Binary Reactions

Description: The authors have investigated the population of nuclei formed in binary reactions involving {sup 7}Li beams on targets of {sup 160}Gd and {sup 184}W. The {sup 7}Li + {sup 184}W data were taken in the first experiment using the LIBERACE Ge-array in combination with the STARS Si {Delta}E-E telescope system at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. By using the Wilczynski binary transfer model, in combination with a standard evaporation model, they are able to reproduce the experimental results. This is a useful method for predicting the population of neutron-rich heavy nuclei formed in binary reactions involving beams of weakly bound nuclei and will be of use in future spectroscopic studies.
Date: August 9, 2005
Creator: Clark, R M; Phair, L W; Descovich, M; Cromaz, M; Deleplanque, M A; Fallon, P et al.
Partner: UNT Libraries Government Documents Department

NUCLEAR INTERACTIONS OF HIGH ENERGY PROTONS IN NUCLEAR EMULSION

Description: Inelastic nuclear interactions in nuclear emulsions exposed to 200, 300 and 400 GeV proton beams are investigated. Dependence of inelastic cross sections on A is discussed. It seems to have been generally accepted that N{sub h}-distribution has little dependence on incident energies, but it is shown that the fraction of events without heavily ionizing tracks (N{sub h}=0) increases appreciably with increasing primary energies. Classifying events by number of heavily ionizing particles, the pseudo-rapidity distributions are studied, and the number of shower particles at higher rapidity region is less in central collisions with heavy nuclei compared to that in collisions with small N{sub h}.
Date: January 1, 1977
Creator: Fujioka, G.; Fukushima, H.; Hayashino, T.; Homma, Y.; Horiguchi, T.; Igarashi, M. et al.
Partner: UNT Libraries Government Documents Department

Model-space approach to parity violation in heavy nuclei

Description: The model-space approach is the basis of both shell model and statistical spectroscopy analyses of nuclear phenomena. The goal of this session is to bring out the main theoretical issues involved in its application to parity violation in the compound nucleus. Section 1 of the current paper sets the stage for the session, and Sect. 2 introduces and explores the model-space formulation as it underlies quantitative connections that are being made between the mean-square matrix element M{sup 2} measured in polarized neutron scattering from compound nuclei and the underlying parity violating interaction. This is followed in the paper by Tomsovic by a description of how statistical spectroscopy is applied to this problem, and in the paper by Hayes by a discussion of shell-model aspects of parity violation in the compound nucleus.
Date: June 1, 1996
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Workshop on the origin of the heavy elements: Astrophysical models and experimental challenges, Santa Fe, New Mexico, September 3-4, 1999

Description: This Workshop was held on September 3--4, 1999, following the 10th International Symposium on Capture Gamma-Ray Spectroscopy. Presentations were made by 14 speakers, 6 from the US and 8 from other countries on topics relevant to s-, r- and rp-process nucleosynthesis. Laboratory experiments, both present and planned, and astrophysical observations were represented as were astrophysical models. Approximately 50 scientists participated in this Workshop. These Proceedings consist of copies of vu-graphs presented at the Workshop. For further information, the interested readers are referred to the authors.
Date: January 1, 2000
Creator: Haight, Robert C.; Ullmann, John L.; Strottman, Daniel D.; Koehler, Paul E. & Kaeppeler, Franz
Partner: UNT Libraries Government Documents Department

Recent Results from RHIC&Some Lessons for Cosmic-RayPhysicists

Description: The Relativistic Heavy Ion Collider (RHIC) studies nuclear matter under a variety of conditions. Cold nuclear matter is probed with deuteron-gold collisions, while hot nuclear matter (possibly a quark-gluon plasma (QGP)) is created in heavy-ion collisions. The distribution of spin in polarized nucleons is measured with polarized proton collisions, and photoproduction is studied using the photons that accompany heavy nuclei. The deuteron-gold data shows less forward particle production than would be expected from a superposition of pp collisions, as expected due to saturation/shadowing. Particle production in AA collisions is well described by a model of an expanding fireball in thermal equilibrium. Strong hydrodynamic flow and jet quenching shows that the produced matter interacts very strongly. These phenomena are consistent with new non-perturbative interactions near the transition temperature to the QGP. This report discusses these results, and their implications for cosmic-ray physicists.
Date: October 1, 2006
Creator: Klein, Spencer R.
Partner: UNT Libraries Government Documents Department

Population of Nuclei Via 7Li-Induced Binary Reactions

Description: The authors have investigated the population of nuclei formed in binary reactions involving {sup 7}Li beams on targets of {sup 160}Gd and {sup 184}W. The {sup 7}Li + {sup 184}W data were taken in the first experiment using the LIBERACE Ge-array in combination with the STARS Si {Delta}E-E telescope system at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. By using the Wilczynski binary transfer model, in combination with a standard evaporation model, they are able to reproduce the experimental results. This is a useful method for predicting the population of neutron-rich heavy nuclei formed in binary reactions involving beams of weakly bound nuclei formed in binary reactions involving beams of weakly bound nuclei and will be of use in future spectroscopic studies.
Date: August 8, 2005
Creator: Clark, Rodney M.; Phair, Larry W.; Descovich, M.; Cromaz, Mario; Deleplanque, M.A.; Fall on, Paul et al.
Partner: UNT Libraries Government Documents Department

Azimuthal HBT and Transverse Momentum Fluctuations from CERES.

Description: CERES is a dilepton experiment at the CERN SPS, known for its observation of enhanced production of low mass efe- pairs in collisions between heavy nuclei [1]. The upgrade of CERES in 1997-1998 by a radial Time Projection Chamber (TPC) [2] allowed to improve the momentum resolution and the particle identification capability while retaining the cylindrical symmetry. The upgraded experiment is shown in Fig. 1. The upgrade also extended the sensitivity of CERES to hadrons and made possible results like those described below. The measurement of central Pb+Au collisions at the maximum SPS energy of 158 GeV per nucleon in the fall of 2000 was the first run of the fully upgraded CERES and at the same time the last run of this experiment. About 30 million Pb+Au collision events at 158 GeV per nucleon were collected, most of them with centrality within the top 7% of the geometrical cross section {sigma}{sub G} = 6.94 b. Small samples of the 20% and the minimum bias collisions, as well as a short run at 80 AGeV, were recorded in addition. The dilepton mass spectra from this experiment were published in [3]. In this talk I present two particular results of hadron analysis, the azimuthal dependence of two-pion correlations and a differential p{sub t} fluctuation study.
Date: July 9, 2007
Creator: Miskowiec,D.; Rehak, P. & al., et
Partner: UNT Libraries Government Documents Department

Nuclear Resonance Fluorescence Excitations Near 2 MeV in 235U and 239Pu

Description: A search for nuclear resonance fluorescence excitations in {sup 235}U and {sup 239}Pu within the energy range of 1.0- to 2.5-MeV was performed using a 4-MeV continuous bremsstrahlung source at the High Voltage Research Laboratory at the Massachusetts Institute of Technology. Measurements utilizing high purity Ge detectors at backward angles identified 9 photopeaks in {sup 235}U and 12 photopeaks in {sup 239}Pu in this energy range. These resonances provide unique signatures that allow the materials to be non-intrusively detected in a variety of environments including fuel cells, waste drums, vehicles and containers. The presence and properties of these states may prove useful in understanding the mechanisms for mixing low-lying collective dipole excitations with other states at low excitations in heavy nuclei.
Date: December 27, 2006
Creator: Bertozzi, W; Caggiano, J A; Hensley, W K; Johnson, M S; Korbly, S E; Ledoux, R J et al.
Partner: UNT Libraries Government Documents Department

Search for Mossbauer type nuclear collisions with the high energy protons

Description: The collision of a high energy projectile with a massive target (nucleon cluster) can considerably increase the center of mass energy available at NAL. In some cases such as neutrino interactions, the increased center mass energy might conceivably be ''traded'' for higher neutrino energies. Thus determination of the characteristics and the fraction of collisions with nuclei that involve large target masses is of interest. We propose to attempt such a determination using sever (A, Z) targets placed directly in front of the 30 inch hydrogen bubble chamber exposed to a 400 or 500 GeV/c proton beam. We will also search for new particles produced in heavy nuclei near the target and survey the K-Short spectrum produced in complex nuclei. We require no additional equipment but the bubble chamber and the beam. 60,000 photographs are requested.
Date: April 1, 1971
Creator: Benvenutti, A.; Cline, D.; Reeder, D.D. & /Wisconsin U., Madison
Partner: UNT Libraries Government Documents Department

Recent results from the microscopic Schrodinger optical model.

Description: Recent developments in nucleon-nucleus scattering at intermediate energies led to a model which is entirely predictive and could produce good to excellent agreement with scattering data. Such a model is required by a number of applications: nuclear astrophysics, structure of exotic nuclei, (e,e{prime}N) studies, applied physics, to name a few. In some cases, the necessity stems from lack of relevant data, in others a need to understand the mechanism in order to study other facets of experiment. The model of nucleon-nucleus scattering developed by the Melbourne Group (recently published as a review article in Advances in Nuclear Physics) is discussed as well as results obtained pertaining to the structure of exotic nuclei, and also to neutron-nucleus scattering and the structure of heavy nuclei.
Date: January 1, 2001
Creator: Karataglidis, S. (Steven)
Partner: UNT Libraries Government Documents Department

Casimir dependence of transverse distribution of pairs produced from a strong constant chromo-electric background field

Description: Recently the transverse distribution of particle production from strong constant chromo-electric fields has been explicitly calculated in Ref. 1 for soft-gluon production and in Ref. 2 for quark (antiquark) production. This particle production method, originally discussed by Heisenberg and Euler, Schwinger and Weisskopf, has a long history as a model of the production of the quark gluon plasma following a relativistic heavy ion collision. The physical picture considered here is that of two relativistic heavy nuclei colliding and leaving behind a semi-classical gluon field which then non-perturbatively produces gluon and quark-antiquark pairs via the Schwinger mechanism. At high energy large hadron colliders, such as RHIC (Au-Au collisions at {radical}{ovr s} = 200 GeV) and LHC (Pb-Pb collisions at {radical}{ovr s} = 5.5 TeV), about half the total center-of-mass energy, E{sub cm}, goes into the production of a semi-classical gluon field, which can be thought to be initially in a Lorentz contracted disc. The gluon field in SU(3) is described by two Casimir invariants, the first one, C{sub 1} = E{sup a}E{sup a}, being related to the energy density of the initial field, where the second one, C{sub 2} = [d{sub abc}E{sup a}E{sup b}E{sup c}]{sup 2}, is related to the SU(3) color hypercharge left behind by the leading particles. So the question we want to study in this short note is how sensitive the transverse distribution is to this second Casimir invariant C{sub 2}. We have considered the dependence of the pair production rate of quarks and gluons from a strong chromo-electric field and have discovered that the effect of the second Casimir invariant of SU(3), which was not present in the electric field problem, effects the distribution by less than 15%. This event by event dependence of the transverse momentum distribution of jets on C{sub 2} may be something of ...
Date: January 1, 2008
Creator: Cooper, Fred M; Mihaila, Bogdan & Dawson, John F
Partner: UNT Libraries Government Documents Department

Nuclear structure research. Annual progress report

Description: The most significant development this year has been the outcome of a survey of EO transition strength, {rho}{sup 2}(EO), in heavy nuclei. The systematics of {rho}{sup 2}(EO) reveals that the strongest EO`s are between pairs of excited states with the same spin and parity. This is observed in the regions Z,N = 38,60; 48,66; 64,88; and 80,106. Unlike other multipoles it is rare that nuclear ground states are strongly connected to excited states by monopole transitions. Another significant finding is in the results of the experimental study of levels in {sup 187}Au. Two bands of states are observed with identical spin sequences, very similar excitation energies, and EO transitions between the favored band members but not between the unfavored band members. This is interpreted in terms of nearly identical diabatic structures. Experimental data sets for the radioactive decays of {sup 183}Pt and {sup 186}Au to {sup 183}Ir and {sup 186}Pt, respectively, have been under analysis. The studies are aimed at elucidating shape coexistence and triaxiality in the A = 185 region. An extensive program of systematics for nuclei at and near N = Z has been continued in preparation for the planned nuclear structure research program using the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge. A considerable effort has been devoted to HRIBF target development.
Date: October 31, 1994
Creator: Wood, J.L.
Partner: UNT Libraries Government Documents Department