Towards commissioning the new IGISOL-4 facility Moore, I.D.; Eronen, T.; Gorelov, D. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2013, Letnik:
317
Journal Article
Recenzirano
•The commissioning of the new IGISOL-4 facility.•First successful implantation of neutron-deficient Pd.•In-jet laser ionization of copper demonstrated.
The Ion Guide Isotope Separator On-Line ...facility at the Accelerator Laboratory of the University of Jyväskylä is currently being re-commissioned as IGISOL-4 in a new experimental hall. Access to intense beams of protons and deuterons from a new MCC30/15 cyclotron, with continued possibility to deliver heavy-ion beams from the K=130MeV cyclotron, offers extensive opportunities for long periods of fundamental experimental research, developments and applications. A new layout of beam lines with a considerable increase in floor space offers new modes of operation at the facility, as well as a possibility to incorporate more complex detector setups. We present a general overview of IGISOL-4 and the current status of several projects, including the collinear laser spectroscopy station and the future of neutron-induced fission. Recent milestones from the first commissioning experiments are presented.
Obtaining reliable data for nuclear reactions on unstable isotopes remains an extremely important task and a formidable challenge. Neutron capture cross sections-crucial ingredients for models of ...astrophysical processes, national security applications, and simulations of nuclear energy generation-are particularly elusive, as both projectile and target in the reaction are unstable. We demonstrate a new method for determining cross sections for neutron capture on unstable isotopes, using ^{87}Y(n,γ) as a prototype. To validate the method, a benchmark experiment is carried out to obtain the known ^{90}Zr(n,γ) cross section analogously. Our approach, which employs an indirect ("surrogate") measurement combined with theory, can be generalized to a larger class of nuclear reactions. It can be used both with traditional stable-beam experiments and in inverse kinematics at rare-isotope facilities.
Background: Dexmedetomidine, a selective α2‐adrenoceptor agonist, induces a unique, sleep‐like state of sedation. The objective of the present work was to study human electroencephalogram (EEG) sleep ...spindles during dexmedetomidine sedation and compare them with spindles during normal physiological sleep, to test the hypothesis that dexmedetomidine exerts its effects via normal sleep‐promoting pathways.
Methods: EEG was continuously recorded from a bipolar frontopolar–laterofrontal derivation with Entropy Module (GE Healthcare) during light and deep dexmedetomidine sedation (target‐controlled infusions set at 0.5 and 3.2 ng/ml) in 11 healthy subjects, and during physiological sleep in 10 healthy control subjects. Sleep spindles were visually scored and quantitatively analyzed for density, duration, amplitude (band‐pass filtering) and frequency content (matching pursuit approach), and compared between the two groups.
Results: In visual analysis, EEG activity during dexmedetomidine sedation was similar to physiological stage 2 (S2) sleep with slight to moderate amount of slow‐wave activity and abundant sleep spindle activity. In quantitative EEG analyses, sleep spindles were similar during dexmedetomidine sedation and normal sleep. No statistically significant differences were found in spindle density, amplitude or frequency content, but the spindles during dexmedetomidine sedation had longer duration (mean 1.11 s, SD 0.14 s) than spindles in normal sleep (mean 0.88 s, SD 0.14 s; P=0.0014).
Conclusions: Analysis of sleep spindles shows that dexmedetomidine produces a state closely resembling physiological S2 sleep in humans, which gives further support to earlier experimental evidence for activation of normal non‐rapid eye movement sleep‐promoting pathways by this sedative agent.
The γ -strength functions and level densities in the quasicontinuum of 147 , 149 Sm isotopes have been extracted from particle- γ coincidences using the Oslo method. The nuclei of interest were ...populated via (p,d) reactions on pure 148 , 150 Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the γ SF has been observed. The systematic analysis of the γ SF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental γ SFs and confirm the correspondence between the upbend and scissors mode.
Direct measurements of the total fusion cross section for B8+40Ar were achieved with the active target technique. The fusion excitation function was extracted at energies near the Coulomb barrier. ...The cross section is well described by a coupled reaction channels calculation. The data were compared with previous B8 fusion experiments on Si28 and Ni58 targets. No evidence of striking enhancement of the total fusion cross section at near the Coulomb barrier, that was previously reported for the B8+58Ni system, was observed in these direct measurements. The present data are systematically consistent with the results for B8+28Si at higher energies and with other weakly-bound systems at near-barrier energies.
In this article a comprehensive description and performance of the double Penning-trap setup JYFLTRAP will be detailed. The setup is designed for atomic mass measurements of both radioactive and ...stable ions and additionally serves as a very high-resolution mass separator. The setup is coupled to the IGISOL facility at the accelerator laboratory of the University of Jyväskylä. The trap has been online since 2003 and it was shut down in the summer of 2010 for relocation to the upgraded IGISOL facility. Numerous atomic mass and decay energy measurements have been performed using the time-of-flight ion-cyclotron resonance technique. The trap has also been used in several decay spectroscopy experiments as a high-resolution mass filter.
The nuclear structure of 66 Se, nucleus beyond the N=Z line on the proton-rich side of the valley of stability, was investigated by the neutron knock-out reaction 67 Se( 12 C,X) 66 Se using a 12 C ...target. The analysis of the singles spectrum of the γ-rays emitted during the de-excitation of the populated low-lying excited states revealed two previously detected (927(4) keV, 1460(32) keV) and three new (744(6) keV, 1210(17) keV, 1661(23) keV) transitions. The 744-keV, the 1210-keV, and the 1460-keV transitions were found to be in coincidence with the one at 927 keV. The spectrum coincident with the 927-keV transition showed a further possible transition at 299(35) keV, which was obscured by significant atomic background in the singles spectrum. This transition might correspond to a peak previously reported at 273(5) keV that could not be assigned to 66 Se unambiguously. Based on a comparison of the experimental data to theoretical calculations, four new excited states are proposed which suggest that 66 Se exhibits shape coexistence.
The nuclear structure of 66Se, nucleus beyond the N=Z line on the proton-rich side of the valley of stability, was investigated by the neutron knock-out reaction 67Se(12C,X)66Se using a 12C target. ...The analysis of the singles spectrum of the γ-rays emitted during the de-excitation of the populated low-lying excited states revealed two previously detected (927(4) keV, 1460(32) keV) and three new (744(6) keV, 1210(17) keV, 1661(23) keV) transitions. The 744-keV, the 1210-keV, and the 1460-keV transitions were found to be in coincidence with the one at 927 keV. The spectrum coincident with the 927-keV transition showed a further possible transition at 299(35) keV, which was obscured by significant atomic background in the singles spectrum. This transition might correspond to a peak previously reported at 273(5) keV that could not be assigned to 66Se unambiguously. Based on a comparison of the experimental data to theoretical calculations, four new excited states are proposed which suggest that 66Se exhibits shape coexistence.
A MICROMEGAS detection amplifier has been incorporated into the design of the TAMU-MDM focal plane detector with the purpose of improving the energy resolution and thus, the particle identification. ...Beam tests showed a factor of 2 improvement over the original design, from 10%–12% to 4%–6%, for ions with A≤40 at E/A ∼ 10–20 MeV.
The 22Ne(α,γ)26Mg and 22Ne(α,n)25Mg reactions play an important role in astrophysics because they have significant influence on the neutron flux during the weak branch of the s-process. We constrain ...the astrophysical rates for these reactions by measuring partial α-widths of resonances in 26Mg located in the Gamow window for the Ne22+α capture. These resonances were populated using 22Ne(6Li,d)26Mg and 22Ne(7Li,t)26Mg reactions at energies near the Coulomb barrier. At these low energies α-transfer reactions favor population of low spin states and the extracted partial α-widths for the observed resonances exhibit only minor dependence on the model parameters. The astrophysical rates for both the 22Ne(α,γ)26Mg and the 22Ne(α,n)25Mg reactions are shown to be significantly different than the previously suggested values.
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