We report on a new measurement of the half-life of
42
Ar by following its decay over a time period of more than 13 years using γ-ray spectrometry. The obtained value of (39.5 ± 3.6) y confirms the ...only other, previously measured value of (33 ± 2) y. However, since partial outgassing of the accumulated Ar from the sample cannot be excluded, this value should be understood as a lower limit. The sample has now been stored in a gas-tight quartz ampoule to enable further measurements excluding the outgas effect in order to confirm our finding.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Background: The neutron-deficient lead region provides a range of nuclear phenomena, including isomerism at low energies. This phenomenon can be studied by α decay because the degree of hindrance of ...α decay provides information on the change in nuclear structure of connected states. Purpose: The aim of this work was to investigate the α-decay properties of $^{200,202}$FR and daughter products. Method: Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Surface ionization and mass-separation techniques were employed to provide a pure radioactive ion beam at a radiation-detection setup. Results: Due to the very high statistics and the high beam purity, improved decay data for $^{202}$FR and its daughters were obtained. In particular, this data set allowed us to identify many fine-structure α lines with a relative reduced α-decay width up to five orders of magnitude lower as the strongest ground-to-ground state or isomeric-to-isomeric state α-decay transition. In addition, several half-life values were extracted with similar or better precision as compared with the literature. Conclusions: The observation of crossover transitions positioned the isomeric high-spin level of $^{198}$At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of $^{198}$At and 52(3) ms for the ground-state decay of $^{200}$FR. Furthermore, α-decay schemes for Fr202 and its daughter $^{198}$At could be constructed.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The CEA in collaboration with ILL and LPSC has developed a measurement program on symmetric and heavy mass fission product distributions. The combination of measurements with ionisation chamber and ...Ge detectors is necessary to describe precisely the heavy fission product region in mass and charge. Recently, new measurements of fission yields and kinetic energy distributions, for different fissioning systems (
233,235
U(
n
th
, f
),
241
Am(2
n
th
, f
) and
239,241
Pu(
n
th
, f
), were performed with recoil spectrometer LOHENGRIN. The focus has been done on the self-normalization of the data to provide new absolute measurements, independently of any libraries along with the experimental covariance matrix. To reach precise measurements, a new experimental procedure was developed along with a new analysis method.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We review major experiments and results obtained by the on-line low temperature nuclear orientation method at the NICOLE facility at ISOLDE, CERN since the year 2000 and highlight their general ...physical impact. This versatile facility, providing a large degree of controlled nuclear polarization, was used for a long-standing study of magnetic moments at shell closures in the region Z = 28, N = 28-50 but also for dedicated studies in the deformed region around A ∼ 180. Another physics program was conducted to test symmetry in the weak sector and constrain weak coupling beyond V-A. Those two programs were supported by careful measurements of the involved solid state physics parameters to attain the full sensitivity of the technique and provide interesting interdisciplinary results. Future plans for this facility include the challenging idea of measuring the beta-gamma-neutron angular distributions from polarized beta delayed neutron emitters, further test of fundamental symmetries and obtaining nuclear structure data used in medical applications. The facility will also continue to contribute to both the nuclear structure and fundamental symmetry test programs.
The first accurate measurements of the α-decay branching ratio and half-life of the Iπ=1/2+ ground state in 181Tl have been made, along with the first determination of the magnetic moments and I=1/2 ...spin assignments of the ground states in 177,179Au. The results are discussed within the complementary systematics of the reduced α-decay widths and nuclear g factors of low-lying, Iπ=1/2+ states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the 1/2+→1/2+, 181Tl→g177Augα decay, which is explained by a mixing of π3s1/2 and π2d3/2 configurations in 177Aug, whilst 181Tlg remains a near-pure π3s1/2. This conclusion is inferred from the g factor of 177Aug which has an intermediate value between those of π3s1/2 and π2d3/2 states. A similar mixed configuration is proposed for the Iπ=1/2+ ground state of 179Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The assessment of the neutrino absolute mass scale is still a crucial challenge in today particle physics and cosmology. Beta or electron capture spectrum end-point study is currently the only ...experimental method which can provide a model independent measurement of the absolute scale of neutrino mass. HOLMES is an experiment to directly measure the neutrino mass by performing a calorimetric measurement of the energy released in the electron capture decay of the artificial isotope 163Ho. In a calorimetric measurement the energy released in the decay process is entirely contained into the detector, except for the fraction taken away by the neutrino. This approach eliminates both the issues related to the use of an external source and the systematic uncertainties arising from decays on excited final states. HOLMES will deploy a large array of low temperature microcalorimeters implanted with 163Ho nuclei. The achievable neutrino mass statistical sensitivity is expected in the eV range, thereby making HOLMES an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. HOLMES will also establish the potential of this approach to achieve a sub-eV sensitivity. HOLMES is designed to collect about 3 × 1013 decays with an instrumental energy resolution around 1 eV FWHM and a time resolution around 1 µs. To achieve this in three years of measuring time, HOLMES is going to deploy 16 sub-arrays of TES microcalorimeters. Each sub-array has 64 pixels ion implanted with 163Ho nuclei to give a pixel activity of 300 Bq per pixel. The TES arrays are read out using microwave multiplexed rf-SQUIDs in combination with a Software Designed Radio data acquisition system. The commissioning of the first implanted sub-array is scheduled for 2018 and it will provide first high statistics data about the EC decay of 163Ho together with a preliminary limit on the neutrino mass. In this contribution we outline the HOLMES project with its physics reach and technical challenges, along with its status and perspectives. In particular we will present the status of the HOLMES activities concerning the 163Ho isotope production by neutron irradiation and purification, the TES pixel design and optimization, the multiplexed array read-out characterization, the cryogenic set-up installation, and the setting up of the mass separation and ion implantation system for the isotope embedding in the TES absorbers.
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