.
We report on the development and characterization of the first radioactive boron beams produced by the isotope mass separation online (ISOL) technique at CERN-ISOLDE. Despite the long history of ...the ISOL technique which exploits thick targets, boron beams have up to now not been available. This is due to the low volatility of elemental boron and its high chemical reactivity which make the definition of an appropriate production target unit difficult. In addition, the short half-lives of all boron radioisotopes complicate tracer release studies. We report here on dedicated offline release studies by neutron capture and alpha detection done with implanted
10
B in prospective target materials, as well as molecule formation and ionization tests, which suggested the use of multiwalled carbon nanotubes (CNT) as target material and injection of sulfur hexafluoride SF
6
to promote volatile boron fluoride formation. Two target units equipped with an arc discharge electron impact ion source VADIS coupled to a water cooled transfer line to retain non-volatile elements and molecules were subsequently tested online. The measured yield of these first
8
B ISOL beams increases in the series
8
BF
3
<
8
BF
<
8
B
<
8
BF
2
, reaching a maximum yield of
6
.
4
×
10
4
8
BF
2
+
ions per μC of protons.
Neutron energy measurements can be achieved using time-of-flight (ToF) techniques. A digital data acquisition system was developed for reliable ToF measurements with subnanosecond timing resolution ...based on digitizers with 10ns and 4ns sampling periods using pulse shape analysis algorithms. A validation procedure was developed to confirm the reliability. The response of the algorithm to photomultiplier signals was studied using a specially designed experimental system based on fast plastic scintillators. The presented developments enabled digital data acquisition systems to instrument the recently developed Versatile Array of Neutron Detectors at Low-Energy (VANDLE).
Excited-state spectroscopy from the first experiment at the Facility for Rare Isotope Beams (FRIB) is reported. A 24(2)-μs isomer was observed with the FRIB Decay Station initiator (FDSi) through a ...cascade of 224- and 401-keV γ rays in coincidence with ^{32}Na nuclei. This is the only known microsecond isomer (1 μs≤T_{1/2}<1 ms) in the region. This nucleus is at the heart of the N=20 island of shape inversion and is at the crossroads of the spherical shell-model, deformed shell-model, and ab initio theories. It can be represented as the coupling of a proton hole and neutron particle to ^{32}Mg, ^{32}Mg+π^{-1}+ν^{+1}. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of ^{32}Mg, where the onset of spherical-to-deformed shape inversion begins with a low-lying deformed 2^{+} state at 885 keV and a low-lying shape-coexisting 0_{2}^{+} state at 1058 keV. We suggest two possible explanations for the 625-keV isomer in ^{32}Na: a 6^{-} spherical shape isomer that decays by E2 or a 0^{+} deformed spin isomer that decays by M2. The present results and calculations are most consistent with the latter, indicating that the low-lying states are dominated by deformation.
Abstract
The
β
-delayed neutron-emission probabilities of 28 exotic neutron-rich isotopes of Pm, Sm, Eu, and Gd were measured for the first time at RIKEN Nishina Center using the Advanced ...Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The existing
β
-decay half-life (
T
1/2
) database was significantly increased toward more neutron-rich isotopes, and uncertainties for previously measured values were decreased. The new data not only constrain the theoretical predictions of half-lives and
β
-delayed neutron-emission probabilities, but also allow for probing the mechanisms of formation of the high-mass wing of the rare-earth peak located at
A
≈ 160 in the
r
-process abundance distribution through astrophysical reaction network calculations. An uncertainty quantification of the calculated abundance patterns with the new data shows a reduction of the uncertainty in the rare-earth peak region. The newly introduced variance-based sensitivity analysis method offers valuable insight into the influence of important nuclear physics inputs on the calculated abundance patterns. The analysis has identified the half-lives of
168
Sm and of several gadolinium isotopes as some of the key variables among the current experimental data to understand the remaining abundance uncertainty at
A
= 167–172.
The first complete measurement of the β-decay strength distribution of _{17}^{45}Cl_{28} was performed at the Facility for Rare Isotope Beams (FRIB) with the FRIB Decay Station Initiator during the ...second FRIB experiment. The measurement involved the detection of neutrons and γ rays in two focal planes of the FRIB Decay Station Initiator in a single experiment for the first time. This enabled an analytical consistency in extracting the β-decay strength distribution over the large range of excitation energies, including neutron unbound states. We observe a rapid increase in the β-decay strength distribution above the neutron separation energy in _{18}^{45}Ar_{27}. This was interpreted to be caused by the transitioning of neutrons into protons excited across the Z=20 shell gap. The SDPF-MU interaction with reduced shell gap best reproduced the data. The measurement demonstrates a new approach that is sensitive to the proton shell gap in neutron rich nuclei according to SDPF-MU calculations.
We investigated decays of K 51 , 52 , 53 at the ISOLDE Decay Station at CERN in order to understand the mechanism of the β -delayed neutron-emission ( β n ) process. The experiment quantified neutron ...and γ -ray emission paths for each precursor. We used this information to test the hypothesis, first formulated by Bohr in 1939, that neutrons in the β n process originate from the structureless “compound nucleus.” The data are consistent with this postulate for most of the observed decay paths. The agreement, however, is surprising because the compound-nucleus stage should not be achieved in the studied β decay due to insufficient excitation energy and level densities in the neutron emitter. In the K 53 β n decay, we found a preferential population of the first excited state in Ca 52 that contradicted Bohr’s hypothesis. The latter was interpreted as evidence for direct neutron emission sensitive to the structure of the neutron-unbound state. We propose that the observed nonstatistical neutron emission proceeds through the coupling with nearby doorway states that have large neutron-emission probabilities. The appearance of “compound-nucleus” decay is caused by the aggregated small contributions of multiple doorway states at higher excitation energy. Published by the American Physical Society 2024
Detailed study of the decay of 21Mg Jensen, E. A. M.; Nielsen, S. T.; Andreyev, A. ...
The European physical journal. A, Hadrons and nuclei,
07/2024, Letnik:
60, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Beta-delayed proton and gamma emission in the decay of
21
Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what ...concerns proton transitions to excited states in
20
Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in
21
Na. The previously reported
β
p
α
branch is confirmed. A half-life of 120.5(4) ms is extracted for
21
Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of
21
Mg that is compared with theory.
Aims To provide quantitative information about the absolute and relative risks of acute and clinically relevant drug‐induced liver injury.
Methods We performed a population‐based case‐control study ...using the UK‐based General Practice Research Database as the source of information. A total of 1636792 persons subjects aged 5–75 years old registered in the database from 1 January, 1994 to 31 December, 1999 were followed‐up for a total of 5404705 person‐years. Cases were identified by an exhaustive computer search, then reviewed manually and finally validated against the clinical records. Only idiopathic cases serious enough to be referred to hospital or a consultant were selected. A total of 5000 controls were randomly sampled from the person‐time of study cohort. Current users were defined if a prescription ended within 15 days of the index date, and nonusers if there was no prescription before the index date.
Results One hundred and twenty‐eight patients were considered as valid cases, being the crude incidence rate of 2.4 (95% confidence interval: 2.0, 2.8) per 100 000 person‐years. The strongest associations were found with chlorpromazine (adjusted odds ratio (AOR); 95% CI = 416; 45, 3840), amoxicillin/clavulanic acid (AOR = 94.8; 27.8, 323), flucloxacillin (AOR = 17.7; 4.4, 71.0), macrolides (AOR = 6.9; 2.3, 21.0), tetracyclines (AOR = 6.2; 2.4, 15.8); metoclopramide (AOR = 6.2; 1.8, 21.3); chlorpheniramine (AOR = 9.6; 1.9, 49.7); betahistine (AOR = 15.3; 2.9, 80.7); sulphasalazine (AOR = 25.5; 6.0, 109); azathioprine (AOR = 10.5; 1.4, 76.4), diclofenac (AOR = 4.1; 1.9, 8.8) and antiepileptics (AOR = 5.1; 1.9, 13.7). A dose‐effect was apparent for diclofenac, amoxicillin/clavulanic acid and flucloxacillin. The combination of two or more hepatotoxic drugs increased the risk by a factor of 6. The highest crude incidence rates were found for chlorpromazine, azathioprine, and sulfasalazine (about 1 per 1000 users).
Conclusions Idiopathic, acute and clinically relevant liver injury, which has the use of drugs as the most probable aetiology, is a rare event in the general population. The relative risks of 40 drugs/therapeutic classes are provided, along with the crude incidence rates for 15 of them where a statistical association was found.
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