The excitation functions for quasielastic scattering of ^{22}Ne+^{248}Cm, ^{26}Mg+^{248}Cm, and ^{48}Ca+^{238}U are measured using a gas-filled recoil ion separator. The quasielastic barrier ...distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg (Z=106), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.
Beams of short-lived radioactive nuclei are needed for frontier experimental research in nuclear structure, reactions, and astrophysics. Negatively charged radioactive ion beams have unique ...advantages and allow for the use of a tandem accelerator for post-acceleration, which can provide the highest beam quality and continuously variable energies. Negative ion beams can be obtained with high intensity and some unique beam purification techniques based on differences in electronegativity and chemical reactivity can be used to provide beams with high purity. This article describes the production of negative radioactive ion beams at the former holifield radioactive ion beam facility at Oak Ridge National Laboratory and at the CERN ISOLDE facility with emphasis on the development of the negative ion sources employed at these two facilities.
Here, we report the results of a β-decay study of fission products 86Br, 89Kr, 89Rb, 90gsRb, 90mRb, 90Kr, 92Rb, 139Xe, and 142Cs performed with the Modular Total Absorption Spectrometer (MTAS) and ...on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10 000 s after fission of 235U and 239Pu by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor ¯νe flux used to analyze reactor ¯νe interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, 235U, 238U, 239Pu, and 241Pu, amounts to 0.976, 0.986, 0.983, and 0.984, respectively.
A resonant ionization laser ion source at ORNL Liu, Y.; Stracener, D.W.
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
06/2016, Letnik:
376, Številka:
C
Journal Article
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Multi-step resonance laser ionization has become an essential tool for the production of isobarically pure radioactive ion beams at the isotope separator on-line (ISOL) facilities around the world. A ...resonant ionization laser ion source (RILIS) has been developed for the former Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory. The RILIS employs a hot-cavity ion source and a laser system featuring three grating-tuned and individually pumped Ti:Sapphire lasers, especially designed for stable and simple operation. The RILIS has been installed at the second ISOL production platform of former HRIBF and has successfully provided beams of exotic neutron-rich Ga isotopes for beta decay studies. This paper reports the features, advantages, limitations, and on-line and off-line performance of the RILIS.
The Holi eld Radioactive Ion Beam Facility, located in Oak Ridge, Tennessee, is operated as a National User Facility for the U.S. Department of Energy, producing high quality ISOL beams of ...short-lived, radioactive nuclei for studies of exotic nuclei, astrophysics research, and various societal applications. The primary driver, the Oak Ridge Isochronous Cyclotron, produces rare isotopes by bombarding highly refractory targets with light ions. The radioactive isotopes are ionized, formed into a beam, mass selected, injected into the 25-MV Tandem, accelerated, and used in experiments. This article reviews HRIBF and its science.
The β-delayed neutron emission of 83,84Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high ...above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to 78Ni core-excited states in 83,84Ge favored by shell effects. We developed shell model calculations in the proton fpg9/2 and neutron extended fpg9/2 + d5/2 valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. Furthermore, this leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.
Resonance laser ionization spectroscopy of tellurium Kieck, T.; Liu, Y.; Stracener, D.W. ...
Spectrochimica acta. Part B: Atomic spectroscopy,
September 2019, 2019-09-00, 20190901, 2019-09-01, Letnik:
159, Številka:
C
Journal Article
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Resonance ionization schemes for tellurium are investigated with a resonance ionization laser ion source and Ti:Sapphire lasers for fundamental research applications. We present the first three-step ...resonance ionization spectra of atomic Te. Several autoionizing Rydberg series converging to the first excited state of Te+ are observed and assigned to 5p3 (2Do3/2) ns and nd configurations. Our results include confirmation and significant expansion of the Rydberg series previously reported as well as observation of three new series. From the series convergence limits the ionization potential of tellurium is revised to be 72,669.006(42)stat(20)sys cm−1.
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•First three-step resonance ionization of tellurium with Ti:Sapphire lasers.•Three new autoionizing Rydberg series of odd parity observed.•Revised value for the ionization potential (IP) of tellurium.
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