Bimodal fission in binary and ternary spontaneous fission of 252Cf

The hot bimodal fission of ²⁵²Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode. The text was submitted by the authors in English.     

New data on the ternary fission of 252Cf from the Gammasphere facility

Ternary fission of ²⁵²Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2⁺ excited state in ¹⁰Be was found and the population probability ratio N(2⁺)/N(0⁺) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs.     

High-spin 52 117 Te: Rotational bands? Noncollective oblate

¹¹⁷Te has been studied via⁸²Se(⁴⁰Ar,5n)¹¹⁷Te, and a new, substantially extended level scheme is proposed to I53/2. Our TRS calculations suggest rotational bands, but with an experimental sensitivity of 2%, we see none. Our results differ from those of Sharma, et al, who report two isolated E2 bands. We find them less band-like, being joined at the top and changed in content and order. We suggest a noncollective oblate shape for a new 39/2^– level.This work is supported in part by the Department of Energy under Contract No.DE-AC03-76SF0098(LBL).     

Collective bands in 104,106,108Mo

We have used our analysis of γ-γ-γ data (5.7 × 10¹¹ triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of ²⁵²Cf to study the collective bands in ^104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich ^104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in ^104,106Mo, along with the first β-type vibrational band in ¹⁰⁶Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in ¹⁰⁶Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus. The text was submitted by the authors in English.     

Separation of group five elements by reversed-phase chromatography

A chemical separation method based on reversed-phase chromatography has been developed to separate the group five elements from the reaction products produced in the bombardment of ²⁴³Am with ⁴⁸Ca ions. Decontamination factors on the order of 10⁶ were achieved for group-three elements such as americium, and 10⁷ or more for selected reaction products as measured by gamma-ray spectrometry pre-and post-chemistry. Details of the chemical separation scheme are discussed and compared to previously reported results.     

Intense high-energy proton beams from Petawatt-laser irradiation of solids

An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.