Publications (201)569.81 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: Cross sections for the 90,92,94Zr(p,n) reactions were measured at energies of 79.2 and 119.4 MeV. A phenomenological model was developed to describe the variation with bombarding energy of the position of the L=1 peak observed in these and other (p,n) reactions. The model yields the splitting between the giant dipole and giant spindipole resonances. Values of these splittings are obtained for isotopes of Zr and Sn and for 208Pb. 
Article: Microscopic description of the excitation of some states in the Zr90,Zr92,Zr94,Zr96 isotopes
[Show abstract] [Hide abstract]
ABSTRACT: We describe the application of a realistic selfconsistent theory of finite Fermi systems to the ground and low excited states of the 90,92,94,96Zr isotopes. Results were obtained for the ground, 21+ and 31− states in each nucleus, and for the lowest 4+, 5−, 6+ and 8+ states in 90Zr. Transition densities were generated for the excitation of each of these states and their properties examined. Transition potentials for their excitation by hadronic inelastic scattering were constructed by folding with appropriate interactions between the projectile and each target nucleon. The calculated inelastic scattering cross sections are compared in detail with experimental results, particularly those for alpha particles at 35.4 MeV and 6Li at 70 MeV. The implications of any discrepancies found are discussed. In addition, the theoretical results were used as “experimental” data in order to test the validity of using various simple models for the analysis of data.  [Show abstract] [Hide abstract]
ABSTRACT: We give a comparative review of the use of the deformed potential and folded potential models for the analysis of data from the inelastic scattering of heavy ions and alpha particles. Representative cases are studied. It is shown that use of the deformed potential can very significantly underestimate the corresponding nuclear transition rate by amounts that increase strongly as the multipolarity increases. Some criticism of the implicit folding procedure is also offered.  [Show abstract] [Hide abstract]
ABSTRACT: We have made simultaneous measurements of singles (p→, p→′) spintransfer observables and coincident (p→, p′γ) yields and asymmetries for the 15.11 MeV, 1+, T=1 state in C12, at an incident proton bombarding energy of 200 MeV. Data were taken at four proton scattering angles ranging from θpc.m.=5.5° to 16.5°. Both vertical (normal to the reaction plane) and horizontal (inplane) incident beam polarizations were used, which allowed us to extract 16 different observables for this transition. In particular, using the (p→, p′γ) reaction, we measured the sideways and longitudinal analyzing powers, D0S and D0L, which vanish identically in the (p→, p′) reaction. Detailed comparisons of all observables to calculations done in both relativistic and nonrelativistic formalisms are presented. Surprisingly, a relativistic description in which knockon exchange processes are not explicitly included provides the best overall agreement with the data.  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of the excitation of nuclear giant resonances by heavyion inelastic scattering have previously been analyzed using the deformed optical potential model. Here we reexamine these data using a folded potential model which employs a simple, but effective, nucleonnucleon interaction that was deduced recently from heavyion elastic scattering measurements. The resulting estimates of the sumrule exhaustion by the giant quadrupole resonance increase by amounts ranging from about 20% for the lighter targets to no change for Â²Â°â¸Pb. Applying the same model to data for excitation of the giant monopole resonance, we find that these transitions overexhaust the corresponding sum rule even more than previously indicated.  [Show abstract] [Hide abstract]
ABSTRACT: The extension of singles ({rvec p},{rvec p}{prime}) studies to include coincident ({rvec p},p{prime}{gamma}) measurements can provide new information about the effective nucleonnucleus interaction. We have therefore made simultaneous measurements of ({rvec p},{rvec p}{prime}) and ({rvec p},p{prime}{gamma}) observables for the 15.11 MeV, 1{sup +}, T=1 state in {sup 12}C at an incident beam energy of 200 MeV. Contained in these coincident observables are determinations of the sideways and longitudinal analyzing powers, {ital D}{sub 0S} and {ital D}{sub 0L}, which must vanish in singles measurements due to parity conservation. With this large data set on a transition with a relatively simple spin sequence, we have, in principle, enough information for a complete determination of the scattering amplitude.  [Show abstract] [Hide abstract]
ABSTRACT: Highenergy γray spectra were measured following the reactions 18O+92Mo and 50Ti+60Ni forming the compound nucleus 110Sn at the same excitation energy of 56 MeV. The angular momentum gated γray spectra from both reactions can be described by standard statistical model calculations. The influence of particle and γray decay during the formation time is found to be small in both reactions. This result is consistent with predictions from dissipative dyanmics calculations.  [Show abstract] [Hide abstract]
ABSTRACT: The elastic and inelastic scattering of 35.4 MeV alpha particles by 90,92,94,96Zr have been measured to investigate the isospin mixing of transitions to the 21+ and 31 states. The data have been analyzed using a deformed optical model potential and a folding model assuming transition densities of either the standard collective model type or resulting from randomphase approximation calculations. For the 21+ states of 90,92,94Zr, both models give B(E2)↑ values which are in excellent agreement with those determined from Coulomb excitation or lifetime measurements. Both models of analysis suggest a sharp drop in the B(E2)↑ at 96Zr relative to the value at 90,92,94Zr, in agreement with an earlier measurement of alphaparticle scattering. Deduced Mn/Mp ratios for 92,94,96Zr are considerably larger than their respective ratios of N/Z. General agreement is found between folding model calculations for alphaparticle scattering and 6Li scattering when using the same randomphase approximation (RPA) transition densities. A small shift in phase is observed between the oscillations in the calculated inelastic angular distributions and the measured ones. A possible means to reproduce this shift is presented, but the changes required appear to be too large to be physically meaningful.  [Show abstract] [Hide abstract]
ABSTRACT: It has been reported that the excitation of lowlying 3− states in nuclei by hadronic probes indicate much weaker transition strengths than are implied by the results of electromagnetic measurements. We demonstrate that this is a consequence of using the deformed optical potential model to analyze the hadronic scattering. The apparent hindrance disappears when a folding model is used. The discrepancy between the results of using the two models increases dramatically as the multipolarity of the transition increases, and we recommend the folding approach.  [Show abstract] [Hide abstract]
ABSTRACT: It is customary to extract deformation lengths from inelastic scattering data by using a deformed optical potential. It is then assumed that this deformation length also characterizes the deformation of the underlying density distribution of the excited nucleus. This equivalence is exact for a dipole deformation, but this corresponds simply to a spurious excitation mode, namely a shift of the center of mass of the system. We show that, even when the potential is obtained by folding an effective interaction over the density distribution, the deformed potential model is not exact for other multipoles, except in the limit that the interaction has a zero range. The errors made when the interaction has a realistic finite range can be large.  [Show abstract] [Hide abstract]
ABSTRACT: The halflife of the 1897.2keV, 31 state in 96Zr has been measured as (67.8±4.3) ps using the recoildistance technique following inelastic excitation by 105MeV 32S ions. This is equivalent to a lifetime which is about 40% longer than those reported from two recent centroidshift measurements. Our lifetime implies B(E3)↑=(0.180±0.018) e2b3, i.e., (47.1±4.7) W.u., which is the most enhanced onephonon g.s.→31 transition strength observed in nuclei. A recent quasiparticle randomphase approximation (QRPA) calculation reproduces our result. Serious doubts are raised about an earlier conclusion that the reduced octupole transition probabilities of ‘‘mirror’’ nuclei correspond to the harmonic low for small amplitude vibrations. The enhanced B(E1:31→21+)=(1.71±0.11) 105 e2b deduced from the present work is consistent with appreciable octupole deformation. The measured B(E3)↑ resolves problems in the interpretation of the isospin character of the E3 transition derived from inelastic scattering data.  [Show abstract] [Hide abstract]
ABSTRACT: The assumptions underlying the use of the “implicit folding procedure” are examined and found to be invalid. We advocate that explicit folding calculations be used instead. 
Article: Octupole collectivity in {sup 96}Zr
[Show abstract] [Hide abstract]
ABSTRACT: The halflife of the 3{sup }{sub 1} state in {sup 96}Zr has been measured as (67.8{+} 4.3)ps by means of a Dopplershift technique from which we deduce B(E3){up_arrow} = (0.179 {+} 0.018)e{sup 2}b{sup 3}. Our halflife is about 35% longer than those reported using centroidshift techniques. Comparison of folding model calculations with the inelastic cross section data for exciting the 3{sup }{sub 1} state with {sup 6}Li ions gives M{sub n}/M{sub p} = 1.30 in good agreement with QRPA structure calculations. 
Article: Halflife of the 21+ state of Zr94
[Show abstract] [Hide abstract]
ABSTRACT: The halflife of the 21+ state of 94Zr is measured as T1/2=7.26±0.42 ps, which corresponds to B(E2)↑=0.060±0.004 e2b2.  [Show abstract] [Hide abstract]
ABSTRACT: High energy gamma rays from the decay of the giant dipole resonance built on highly excited states in 164Yb at Eex=49 MeV formed in two different reactions have been measured. While standard statistical model calculations can describe the gammaray spectrum from the 16O + 148Sm reaction they fail to reproduce the gammaray spectra from the more symmetric reaction 64Ni + 100Mo. Simple model calculations which include particle evaporation and gammaray decay during the formation process suggest that the observed differences may be related to a long fusion time in the more symmetric reaction.  [Show abstract] [Hide abstract]
ABSTRACT: Differential cross sections for exciting the 21+ and 31 states of 90,92,94,96Zr with 70MeV 6Li ions have been measured. Calculations of the cross sections have been performed using a deformed optical model potential (DOMP) with OMP deduced from fits to the elastic data, as well as a folding model with an effective nucleonnucleon interaction with a Yukawa form factor obtained from fits to the elastic data and transition densities obtained from openshell random phase approximation (RPA) calculations. The DOMP fits to the data yield values of Mn/Mp which are in good agreement with those predicted using the RPA. For the 21+ states, we find Mn/Mp increases from less than N/Z to greater than N/Z in going from 90Zr to 96Zr. However, for the 31 states Mn/Mp remains less than N/Z for all cases, a result which is in disagreement with previous works. The folding model, with the RPA transition densities, provides good agreement with the 21+ measurements, but underpredicts the cross sections for the 31 states. A reanalysis of the earlier data from excitation of these states by (α,α’) reactions removes much of the apparent discrepancies between those measurements and other measurements, including the ones reported here. The localization of the 6Li interaction is also discussed.  [Show abstract] [Hide abstract]
ABSTRACT: The halflife of the 2[sub 1][sup +] state of [sup 94]Zr is measured as [ital T][sub 1/2]=7.26[plus minus]0.42 ps, which corresponds to [ital B]([ital E]2)[up arrow]=0.060[plus minus]0.004 [ital e][sup 2]b[sup 2].  [Show abstract] [Hide abstract]
ABSTRACT: We have used the 90,92,94,96Zr(6Li, 6Li) reaction at E = 70 MeV to deduce the ratio of Mn/Mp for transitions to the first 2+ and 3 excited states. For the first 2+ state, we find Mn/Mp increases from less than N/Z to greater than N/Z going from 90Zr to 96Zr. However, for the 3 state we find that Mn/Mp is significantly smaller than N/Z for all four isotopes, a result which is in sharp disagreement with previous work. We find that our measured values of Mn/Mp are well reproduced by randomphaseapproximation calculations including pairing. Managed by Martin Marietta Energy Systems, Inc. Under contract DEAC0584OR21400 with the US Department of Energy.  [Show abstract] [Hide abstract]
ABSTRACT: The decay of excited {sup 16}O projectiles into the four alpha particle exit channel has been investigated. The projectiles, with bombarding energies of {ital E}/{ital A}=25 MeV, were excited through peripheral interactions with {sup 159}Tb target nuclei. A 4{pi} counter was used to detect both the projectile alpha particles and the light charged particles evaporated from the target nucleus. Criteria for selecting true {sup 16}O{r arrow}4{alpha} events with the minimum contamination from incorrectly identified events were examined. The distribution of relative angles between the four alpha particles in their center of mass frame was compared to simulations of {sup 16}O decay by sequential decay mechanisms. The relative angles were shown to be consistent with a sequential evaporation mechanism if a nonzero angular momentum is assumed for the excited projectile. The momentum distribution of the alpha particles in the reaction plane was examined and found to be anisotropic for high projectile excitation energies. This anisotropy was shown to be consistent with Coulomb interactions between the first emitted alpha particle and the target nucleus, which would indicate that the lifetime of the projectile is very short, on the order of 10{sup {minus}22} s. 
Article: Isospin character of the transition to the 0.803MeV state in Pb206 from scattering at 180 MeV
[Show abstract] [Hide abstract]
ABSTRACT: Elastic and inelastic pi+/ scattering by 206Pb has been studied to measure the isospin character of transitions to bound states. The data have been interpreted using both distorted wave impulse approximation and optical model potentials. The data for the collective states at 2.647 MeV (3) and 4.111 MeV (2+) are well reproduced with delta+l=deltal=deltapl, i.e., assuming that these transitions are isoscalar. For the 0.803MeV, 2+ level we deduce Mn/Mp=2.6+/0.3 which is in excellent agreement with a value obtained from inelastic heavyion scattering.
Publication Stats
4k  Citations  
569.81  Total Impact Points  
Top Journals
 Physical Review C (75)
 Physics Letters B (22)
 Nuclear Physics A (14)
 Nuclear Data Sheets (11)
 Physical Review Letters (5)
Institutions

19712001

Oak Ridge National Laboratory
 • Physics Division
 • Fusion Energy Division
Oak Ridge, Florida, United States


1996

Joint Institute for Heavy Ion Research
Oak Ridge, Tennessee, United States


1993

Washington University in St. Louis
 Department of Chemistry
San Luis, Missouri, United States


1990

Indiana University Bloomington
 Department of Physics
Bloomington, Indiana, United States


1987

TRIUMF
Vancouver, British Columbia, Canada


1981

University of Colorado at Boulder
 Department of Physics
Boulder, Colorado, United States
