Evolution of E2 transition strength in deformed hafnium isotopes from new measurements on 172^{172}Hf, 174^{174}Hf, and 176^{176}Hf

The available data for E2 transition strengths in the region between neutron-deficient Hf and Pt isotopes are far from complete. More and precise data are needed to enhance the picture of structure evolution in this region and to test state-of-the-art nuclear models. In a simple model, the maximum collectivity is expected at the middle of the major shell. However, for actual nuclei, this picture may no longer be the case, and one should use a more realistic nuclear-structure model. We address this point by studying the spectroscopy of Hf. We remeasure the 2^+_1 half-lives of 172,174,176Hf, for which there is some disagreement in the literature. The main goal is to measure, for the first time, the half-lives of higher-lying states of the rotational band. The new results are compared to a theoretical calculation for absolute transition strengths. The half-lives were measured using \gamma-\gamma and conversion-electron-\gamma delayed coincidences with the fast timing method. For the determination of half-lives in the picosecond region, the generalized centroid difference method was applied. For the theoretical calculation of the spectroscopic properties, the interacting boson model is employed, whose Hamiltonian is determined based on microscopic energy-density functional calculations. The measured 2^+_1 half-lives disagree with results from earlier \gamma-\gamma fast timing measurements, but are in agreement with data from Coulomb excitation experiments and other methods. Half-lives of the 4^+_1 and 6^+_1 states were measured, as well as a lower limit for the 8^+_1 states. We show the importance of the mass-dependence of effective boson charge in the description of E2 transition rates in chains of nuclei. It encourages further studies of the microscopic origin of this mass dependence. New data on transition rates in nuclei from neighboring isotopic chains could support these studies.Comment: 16 pages, 16 figures, 7 tables; Abstract shortened due to character limi

First MATISSE L-band observations of HD 179218: is the inner 10 au region rich in carbon dust particles?

Stars and planetary system

A simple procedure for gamma-gamma lifetime measurements using multi-element fast-timing arrays

The lifetimes of nuclear excited states are important observables in nuclear physics. Their precise measurement is of key importance for developing and testing nuclear models as they are directly linked with the quantum nature of the nuclear system. The gamma-gamma timing technique represents a direct lifetime determination by means of time-difference measurements between the gamma rays which directly feed and decay from a nuclear excited state. Using arrays of very-fast scintillator detectors, picosecond-sensitive time-difference measurements can be performed. We propose to construct a symmetric energy-energy-time cube as is usually done to perform gamma-gamma coincidence analyses and lifetime determination with high-resolution germanium detectors. By construction, a symmetric mean time-walk characteristics is obtained, that can be precisely determined and used as a single time correction for all the data independently of the detectors. We present the results of timing characteristics measurements of an array with six LaBr3(Ce) detectors, as obtained using a(152)Eu point gamma-ray source. Compared with a single detector pair, the time resolution of the symmetrised time-difference spectra of the array is nearly unaffected

On the time response of background obtained in gamma-ray spectroscopy experiments using LaBr3(Ce)detectors with different shielding

Employing the gamma-gamma fast-timing technique with LaBr3(Ce) scintillator detectors allows the direct determination of lifetimes of nuclear excited states with a lower limit of about 5 ps. This limit is increased as soon as background is present in the coincidence spectra underneath the full-energy peaks of the gamma-gamma cascade. Our aim was to identify the components of the gamma-ray background by systematic gamma-gamma fast-timing measurements using different types of gamma shielding within a large gamma-ray spectrometer. The energy dependent physical zero-time response was measured using background-free full-energy peak events from the Eu-152 gamma-ray source. This is compared with the time response of the (Compton-) background distribution as obtained using the prompt Co-60 gamma-ray source. The time response of the typical Compton background is about 15 ps faster than the time response of background-free full-energy peak events. Below about 500 keV, a second type of background contributes by the detection of Compton-scattered gamma rays generated in the materials of the spectrometer around the detector. Due to the additional time-of-flight of the Compton-scattered gamma rays, this low-energy background is largely delayed. Compared with a bare cylindrical 1.5 in. x 1.5 in. LaBr3(Ce) detector, the BGO-shielded detector in the Compton-suppression mode improves the peak-to-total ratio by a factor of 1.66(5), while the Pb-shielded detector only slightly reduces the low-energy background. (C) 2015 Elsevier B.V. All rights reserved

Reduced gamma-gamma time walk to below 50 ps using the multiplexed-start and multiplexed-stop fast-timing technique with LaBr3(Ce) detectors

The electronic gamma-gamma fast-timing technique using arrays consisting of many LaBr3(Ce) detectors is a powerful method to determine lifetimes of nuclear excited states with a lower limit of about 5 ps. This method requires the determination of the energy-dependent time walk of the zero time which is represented by the centroid of a prompt gamma-gamma time distribution. The full-energy peak versus full-energy peak prompt response difference which represents the linearly combined mean gamma-gamma time walk of a fast-timing array consisting of 8 LaBr3(Ce) detectors was measured using a standard Eu-152 gamma-ray source for the energy region of 40-1408 keV. The data were acquired using a multiplexed-start and multiplexed-stop analogue electronics circuitry and analysed by employing the generalized centroid difference method. Concerning the cylindrical 1.5 in. x 1.5 in. LaBr3(Ce) crystals which are coupled to the Hamamatsu R9779 photomultiplier tubes, the best fast-timing array time resolution of 202(3) ps is obtained for the two prompt gamma lines of Co-60 by using the leading-edge timing principle. When using the zero-crossover timing principle the time resolution is degraded by up to 30%, dependent on the energy and the shaping delay time of the constant fraction discriminator model Ortec 935. The smallest gamma-gamma time walk to below 50 ps is obtained by using a shaping delay time of about 17 ns and an optimum time-walk adjustment needed for detector output pulses with amplitudes smaller than 400 mV. (C) 2016 Elsevier B.V. All rights reserved

Lifetime determination in Hg-190,Hg-192,Hg-194,Hg-196 via gamma-gamma fast-timing spectroscopy

Lifetimes of 2(1)(+) and 4(1)(+) states in Hg-190,Hg-192,Hg-194,Hg-196 and of some negative parity band members were measured using the gamma-gamma fast-timing technique with a high-purity germanium and LaBr3(Ce) detector array. The excited states were populated via fusion-evaporation reactions using the Tandem Van de Graaff accelerator of the Institute of Nuclear Physics in Cologne, Germany. The derived reduced transition probabilities of the 2(1)(+)-> 0(1)(+) and 4(1)(+) -> 2(l)(+) transitions are discussed in the framework of the interacting boson approximation with two models using configuration mixing: a phenomenological one and a microscopical one. Both models describe the observed quantities of the nuclei within the experimental uncertainties

Lifetimes in At-211 and their implications for the nuclear structure above Pb-208

Lifetimes of excited states in At-211 were measured using the electronic gamma-gamma fast timing technique. The nucleus of interest was populated in a Pb-208(Li-6, 3n)(211) At fusion-evaporation reaction at the FN Tandem accelerator of the Institute for Nuclear Physics, University of Cologne. The lifetimes of the 17/2(1)(-) and 23/2(1)(-) states were determined, together with an upper limit for the 13/2(1)(-) state. The experimental results are compared to two shell-model calculations, one using a semiempirical interaction for three particles in a single j = 9/2 shell and the other using the modified Kuo-Herling interaction in a multi- j model space

Odontoid Type II fractures in elderly: what are the real management goals and how to best achieve them? A multicenter European study on functional outcome

Odontoid fractures constitute the most common cervical fractures in elderly. External immobilization is the treatment of choice for Type I and III; there is still no wide consensus about the best management of Type II fractures. Observational multicenter study was conducted on a prospectively built database on elderly patients (> 75 years) with Type II odontoid fracture managed conservatively during the last 10 years. All patients underwent CT scan on admission and at 3 months; if indicated, selected patient had CT scan at 6 and 12 months. All patients were clinically evaluated by Neck Disability Index (NDI), Charlson Comorbidity Index (CCI), and American Society of Anaesthesiologists classification (ASA) on admission; NDI was assessed also at 6 weeks, 3, 6, 12, and 24 months; furthermore, a quality of life (QoL) assessment with the SF-12 form was performed at 3 and 12 months. Among the 260 patients enrolled, 177 (68%) were women and 83 (32%) men, with a median age of 83 years. Patients were followed up for a minimum of 24 months: 247 (95%) showed an excellent functional outcome within 6 weeks, among them 117 (45%) showed a good bony healing, whereas 130 (50%) healed in pseudo-arthrosis. The residual 5% were still variably symptomatic at 12 weeks; however, only 5 out of 13 (2% of the total cohort) required delayed surgery. This study showed that a conservative approach to odontoid Type II fracture in elderly is an effective and valid option, resulting in an excellent functional outcome (regardless of bony fusion) in the majority of cases. Failure of conservative treatment can be safely addressed with surgical fixation at a later stage

Evolution of collectivity in the N=100 isotones near Yb-170

An experiment using the electronic gamma - gamma fast-timing technique was performed to measure lifetimes of the yrast states in Yb-170. The lifetime of the yrast 2(+) state was determined using the slope method. The value of t = 2.33(3) ns is in good agreement with the lifetimes measured using other techniques. The lifetimes of the first 4(+) and 6(+) states are determined using the generalized centroid difference method. The derived B(E2) values are compared to calculations done using the confined beta soft model and show good agreement with the experimental values. These calculations were extended to the isotonic chain N = 100 around Yb-170 and show a good quantitative description of the collectivity observed along it

In situ calibration of charged particle spectrometers on the OMEGA Laser Facility using 241Am and 226Ra sources

Charged particle spectrometry is a critical diagnostic to study inertial-confinement-fusion plasmas and high energy density plasmas. The OMEGA Laser Facility has two fixed magnetic charged particle spectrometers (CPSs) to measure MeV-ions. In situ calibration of these spectrometers was carried out using 241Am and 226Ra alpha emitters. The alpha emission spectrum from the sources was measured independently using surface-barrier detectors (SBDs). The energy dispersion and broadening of the CPS systems were determined by comparing the CPS measured alpha spectrum to that of the SBD. The calibration method significantly constrains the energy dispersion, which was previously obtained through the measurement of charged particle fusion products. Overall, a small shift of 100 keV was observed between previous and the calibration done in this work. </jats:p