19 Search Results

Using laser-induced nuclear-orientation and optical-saturation techniques, we have produced sub-Doppler changes in the anisotropy of the angular distribution of the 514-keV {gamma} rays from the 1-{mu}s isomer {sup 85}Rb{sup {ital m}}. This permits high-resolution measurements of {ital D}1 and {ital D}2 hyperfine transitions of atoms of the isomer, which give the isomer's nuclear electric quadrupole moment, {minus}0.73{plus minus}0.17 b, and its nuclear magnetic dipole moment, (6.043{plus minus}0.005){mu}{sub {ital N}}. The isomer shift, {minus}113{plus minus}8 MHz relative to the ground state of {sup 85}Rb, corresponds to a change in the mean-square charge radius of +0.174{plus minus}0.008 fm{sup 2}.

A gas-filled, liquid-nitrogen-cooled cell on-line with an accelerator permits fluorescence spectroscopy of atoms of heavy-ion reaction products generated at rates less than 10{sup 3} s{sup {minus}1}. This low required rate of production allows the optical spectroscopy of radioactive atoms to be extended further from stability. With the cell we have measured isotope shifts of {sup 152,154,156,158,166}Yb, reaching {ital N}=82, four nuclides further than previously reached with other techniques. The change in rms charge radius near the shell closure is surprisingly large.

Frequency-resolved laser-induced gamma-ray anisotropy has been achieved and used to measure the D/sub 1/ hyperfine structure of the 1-..mu..s isomer /sup 85/Rb/sup m/. The magnetic dipole moment obtained is (6.046 +- 0.010)..mu../sub N/ and the isomer shift relative to /sup 85/Rb is -52 +- 9 MHz. The experiment was performed with a sealed cell containing radioactive /sup 85/Kr (3 mCi) and natural Rb (approx.10 mTorr). This method is simple and convenient and promises to be of wide usefulness.

Thin self-supporting Ni, Rh, Ta, and Au foils were bombarded with 5- to 12-Mev protons from a Tandem Van de Graaff accelerator. Neutron energy spectra arising from the (p,n) reactions were obtained by means of a pulsedbeam time-of- flight spectroraeter. Spectra were taken at neutron emission angles from 0 deg to 140 deg at each bombarding energy. Below the threshold of the Ni/sup 58/ (p,n) reaction, bombardment of Ni with protons produced a neutron spectrum containing well deflned structure. The peaks were attributed to the Ni/sup 60/ (p,n) reaction. Reaction energies were determined for the observed peaks. The Rh, Ta, and Au neutron spectra exhibited no structure. These continuous energy distributions were interpreted in terms of Weisskopf's statistical theory, which relates the energy distribution of the emitted particles to the level density of the residual nucleus. A nuclear temperature with an uncertainty between 7 and 15% was determined from each spectrum. These temperatures are constant for all observed neutron energies at a given bombarding energy, but increase with increasing bombarding energy. At some bombarding energies the competing (p,2n) reaction was possible. Neutrons from this reaction could in many cases be distinguished from neutrons from the (p,n) reaction by an analysis of the shape of the spectrum. No effects of direct interactions were observed. Angular distributions were isotropic and no excess of high energy particles was present in the spectra. Total (p,n) cross sections were calculated from the differential cross sections determined in this experiment. The results are consistent with values obtained by other authors. (M.P.G.)

Spectra of neutrons from the bombardment of rhodium with protons were studied at bombarding energies between 5 and 12 Mev and neutron emission angles up to 140 deg . Neutron energies were measured by time-of-flight spectrometry. Data are presented in graphs. (M.C.G.)

Thin targets of Ni, Rh, Ta, and Au were bombarded with protons of energies between 6 and 12 Mev. Neutrons emitted at angles up to 140 deg were observed. The neutron spectra were studied by time-of-flight spectroscopy. Except for Ni, continuous spectra resulted that had a Maxwellian energy distribution. The nuclear temperature showed, however, an anomalous increase with bombarding energy. Results consistent with the statistical theory could be obtained in the case of Rh by taking into account the energy dependence of the inverse reaction cross section. (auth)

Continuous neutron spectra produced by bombarding T and H with deuterons have been measured using time-offlight spectrometry for a wide range of deuteron bombarding energies and neutron emission angles. The observed spectra for the D + T interaction exhibit two maxima, one occurring at a neutron energy slightly below the maximum possible energy of neutrons from deuteron breakup and the other occurring several Mev lower. The high energy peak is interpreted as arising from monoenergetic neutrons which leave He/sup 4/ in an excited state at 20 Mev. For the D + H interaction the observed spectra exhibit no structure. (auth)