74 research outputs found
Concentration of electric dipole strength below the neutron separation energy in N = 82 nuclei
The semi-magic nuclei Ba-138, Ce-140, and Sm-144 have been investigated in
photon scattering experiments up to an excitation energy of about 10 MeV. The
distribution of the electric dipole strength shows a resonance like structure
at energies between 5.5 and 8 MeV exhausting up to 1% of the isovector E1
Energy Weighted Sum Rule.Comment: 10 pages, 3 figure
Parity assignments in 172,174Yb using polarized photons and the K quantum number in rare earth nuclei
The 100 % polarized photon beam at the High Intensity gamma-ray Source (HIgS)
at Duke University has been used to determine the parity of six dipole
excitations between 2.9 and 3.6 MeV in the deformed nuclei 172,174 Yb in photon
scattering (g,g') experiments. The measured parities are compared with previous
assignments based on the K quantum number that had been assigned in Nuclear
Resonance Fluorescence (NRF) experiments by using the Alaga rules. A systematic
survey of the relation between gamma-decay branching ratios and parity quantum
numbers is given for the rare earth nuclei.Comment: 5 pages, 6 figures, to be published in Phys. Rev.
Kabul Times (November 9, 1967, vol. 6, no. 184)
Recent experimental findings and theoretical approaches to the electric dipole (El) strength distribution below the particle emission threshold at shell closures are revisited. Results from photon scattering experiments are discussed and compared to predictions within the quasiparticle-phonon nuclear model. An analysis of the fine structure of the El strength is presented. Recent studies of the E1 response of light exotic nuclei are also discussed
Experimental simulation of a stellar photon bath by bremsstrahlung: the astrophysical -process
The nucleosynthesis of heavy proton-rich nuclei in a stellar photon bath at
temperatures of the astrophysical -process was investigated where the
photon bath was simulated by the superposition of bremsstrahlung spectra with
different endpoint energies. The method was applied to derive (,n)
cross sections and reaction rates for several platinum isotopes.Comment: 3 pages, 3 figures, Phys. Lett. B, in prin
Direct determination of photodisintegration cross sections and the p-process
Photon-induced reactions play a key role in the nucleosynthesis of heavy
neutron-deficient nuclei, the so-called p-nuclei. In this paper we review the
present status of experiments on photon-induced reactions at energies of
astrophysical importance and their relevance to p-process modeling.Comment: Nucl. Phys. A, in pres
Isomeric Decay of \u3csup\u3e208\u3c/sup\u3eRa
Low-energy excited states of 208Ra were investigated using the 182W(30Si, 4n) reaction at the Wright Nuclear Structure Laboratory of Yale University. Fusion evaporation recoils were selected using the gas-filled spectrometer SASSYER. Delayed γ rays, following isomeric decays, were detected at the focal plane of SASSYER with a small array of three clover Ge detectors. Transitions following a proposed J π = 8+ isomer were observed, and the half-life was measured
Measuring Reaction Probability Ratios to Simulate Neutron-Induced Cross-sections of Short-Lived Nuclei
Measuring the neutron-induced fission cross-sections of short-lived nuclei represents an experimental challenge due to target activity and the low intensity of neutron beams. One way to alleviate the problems inherent in the direct measurement is to use the surrogate method, where one measures the decay probability of the same compound nucleus formed using a charged beam and a stable target. The decay probability of the compound nucleus is then used to estimate the neutron-induced cross-section. As an extension to the surrogate method, we introduce a new method of reporting the fission probabilities of two compound nuclei as a ratio, which has the advantage of removing most of the systematic uncertainties. The ratio method was checked in a known case, the 236U (n, f) /238U (n, f) cross-section ratio, which turned out to be the same as the probability ratio of P (236U (d, pf))/P (238U (d, pf)). As an application, the 237U(n, f )/235U(n, f ) cross-section ratio was inferred, on the basis of the measured P(238U(d, d f ))/P (236U(d, d f )) probability ratio
Isomers and Seniority in the Trans-Pb Nuclei
Low-energy excited states of 210Ra and 208Ra were investigated at the Wright Nuclear Structure Laboratory of Yale University. Fusion evaporation recoils were selected using the gas-filled spectrometer, SASSYER. Delayed γ -rays, following isomeric decays, were detected at the focal plane of SASSYER with a small array of HPGe detectors. Transitions following the proposed J π = 8+ isomers were observed, and the half-lives measured. The experiments are discussed and results compared to expectations from the seniority scheme
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