26 research outputs found
VME Readout at and Below the Conversion Time Limit
The achievable acquisition rates of modern triggered nuclear physics experiments are heavily dependent on the readout software, in addition to the limits given by the utilized hardware. This paper presents an asynchronous readout scheme that significantly improves the livetime of an otherwise synchronous triggered Versa Module Eurocard Bus-based data acquisition system. A detailed performance analysis of this and other readout schemes, in terms of the basic data transfer operations, is described. The performance of the newly developed scheme as well as synchronous schemes on two systems has been measured. The measurements show excellent agreement with the detailed description. For the second system, which previously used a synchronous readout, the deadtime ratio is at a 20-kHz trigger request frequency reduced by 30% compared to the nearest contender, allowing 10% more events to be recorded in the same time. The interaction between the network and readout tasks for single-core processors is also investigated. A livetime ratio loss of a few percents can be observed, depending on the size of the data chunks given to the operating system kernel for network transfer. With appropriately chosen chunk size, the effect can be mitigated
Study of bound states in Be-10 by one neutron removal reactions of Be-11
The bound states of Be-10 have been studied by removing single neutrons from Be-11 nuclei. A 2.8 MeV u(-1) beam of Be-11 was produced at ISOLDE, CERN and directed on to both proton and deuteron targets inducing one-neutron removal reactions. Charged particles were detected to identify the two reaction channels (d, t) and (p, d), and the individual states in Be-10 were identified by gamma detection. All bound states but one were populated and identified in the (d, t) reaction. The combination of REX-ISOLDE and MINIBALL allowed for a clean separation of the high-lying states in Be-10. This is the first time these states have been separated in a reaction experiment. Differential cross sections have been calculated for all the reaction channels and compared to DWBA calculations. Spectroscopic factors are derived and compared to values from the litterature. While the overall agreement between the spectrocopic factors is poor, the ratio between the ground state and the first excited state is in agreement with the previous measured ones. Furthermore, a significant population of the 2(2)(+) state is observed, which which may indicate the presence of multi-step processes at our beam energy.Peer reviewe
Rb-37(97)60 : The Cornerstone of the Region of Deformation around A similar to 100
Excited states of the neutron-rich nuclei Rb-97,Rb- 99 were populated for the first time using the multistep Coulomb excitation of radioactive beams. Comparisons of the results with particle-rotor model calculations provide clear identification for the ground-state rotational band of Rb-97 as being built on the pi g(9/2) [431] 3/2(+) Nilsson-model configuration. The ground-state excitation spectra of the Rb isotopes show a marked distinction between single-particle-like structures below N = 60 and rotational bands above. The present study defines the limits of the deformed region around A similar to 100 and indicates that the deformation of Rb-97 is essentially the same as that observed well inside the deformed region. It further highlights the power of the Coulomb-excitation technique for obtaining spectroscopic information far from stability. The Rb-99 case demonstrates the challenges of studies with very short-lived postaccelerated radioactive beams.Peer reviewe
First Accurate Normalization of the beta-delayed alpha Decay of N-16 and Implications for the C-12(alpha,gamma)O-16 Astrophysical Reaction Rate
The C-12(alpha,gamma)O-16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced a width, gamma(11), of the bound 1(-) level in O-16 is particularly important to determine the cross section. The magnitude of gamma(11) is determined via sub-Coulomb a-transfer reactions or the beta-delayed a decay of N-16, but the latter approach is presently hampered by the lack of sufficiently precise data on the beta-decay branching ratios. Here we report improved branching ratios for the bound 1(-) level [b(beta,11) = (5.02 +/- 0.10) x 10(-2)] and for beta-delayed alpha emission [b(beta alpha) = (1.59 +/- 0.06) x 10(-5)]. Our value for b(beta alpha) is 33% larger than previously held, leading to a substantial increase in gamma(11). Our revised value for gamma(11) is in good agreement with the value obtained in a-transfer studies and the weighted average of the two gives a robust and precise determination of gamma(11), which provides significantly improved constraints on the C-12(alpha,gamma) cross section in the energy range relevant to hydrostatic He burning.Peer reviewe
Three Ways of Combining Genotyping and Resequencing in Case-Control Association Studies
We describe three statistical results that we have found to be useful in case-control genetic association testing. All three involve combining the discovery of novel genetic variants, usually by sequencing, with genotyping methods that recognize previously discovered variants. We first consider expanding the list of known variants by concentrating variant-discovery in cases. Although the naive inclusion of cases-only sequencing data would create a bias, we show that some sequencing data may be retained, even if controls are not sequenced. Furthermore, for alleles of intermediate frequency, cases-only sequencing with bias-correction entails little if any loss of power, compared to dividing the same sequencing effort among cases and controls. Secondly, we investigate more strongly focused variant discovery to obtain a greater enrichment for disease-related variants. We show how case status, family history, and marker sharing enrich the discovery set by increments that are multiplicative with penetrance, enabling the preferential discovery of high-penetrance variants. A third result applies when sequencing is the primary means of counting alleles in both cases and controls, but a supplementary pooled genotyping sample is used to identify the variants that are very rare. We show that this raises no validity issues, and we evaluate a less expensive and more adaptive approach to judging rarity, based on group-specific variants. We demonstrate the important and unusual caveat that this method requires equal sample sizes for validity. These three results can be used to more efficiently detect the association of rare genetic variants with disease
Observation of a correlated free four-neutron system
A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades(1), with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far(2-4), leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy He-8 beam was key
Shell evolution of N = 40 isotones towards 60Ca: First spectroscopy of 62Ti
Excited states in the N=40 isotone 62Ti were populated via the 63V(p,2p)62Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ-ray spectroscopy. The energies of the 21+→0gs+ and 41+→21+ transitions, observed here for the first time, indicate a deformed 62Ti ground state. These energies are increased compared to the neighboring 64Cr and 66Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for 62Ti show a dominant configuration with four neutrons excited across the N=40 gap. Likewise, they indicate that the N=40 island of inversion extends down to Z=20, disfavoring a possible doubly magic character of the elusive 60Ca
First coupling of the FRS particle identification and the FRS-Ion Catcher data acquisition systems: The case of 109In
6 pags. 5 figs.For the first time, the FRagment Separator (FRS) and the Multiple-Reflection Time-Of-Flight Mass-Spectrometer (MR-TOF-MS) particle identification (PID) systems at GSI have been coupled. This new approach adds to the standard FRS PID an additional unambiguous identification of the fragments and the possibility to identify and count long-lived isomeric states (>ms). For this purpose, single-event timestamp information given by a common clock was used to correlate both systems. Two methods were implemented to improve the signal-to-background ratio by more than a factor 2 in the high resolution mass spectrum obtained with the MR-TOF-MS for the 109In isotope. Moreover, the coupling of the systems allows an improvement in the on-line monitoring of the FRS-Ion Catcher (IC) efficiency and extraction time. In addition, range calculations were implemented in the on-line monitoring; a powerful tool for real-time optimization of stopped beam experiments.The ELI-NP group was supported by Extreme Light Infrastructure Nuclear Physics (ELI-NP), Germany Phase II, a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund the Competitiveness Operational Programme (1/07.07.2016, COP,ID 1334) and by the Romanian Ministry of Research and Innovation under contract PN 19 06 01 05.
This work was supported by the German Federal Ministry for Education and Research (BMBF) under contracts No. 05P19RGFN1, 05P12RGFN8 and 05P15RGFN1, by Justus Liebig University Gießen, Germany and GSI, Germany under the JLU-GSI strategic Helmholtz partnership agreement, by HGS-HIRe, and by theHessian Ministry for Science and Art (HMWK), Germany.
O. Hall was supported by UKRI STFC, United Kingdom grant ST/P004008/1.Peer reviewe
Mesoporous zeolite single crystal catalysts: Diffusion and catalysis in hierarchical zeolites
Rb-97(37)60: The Cornerstone of the Region of Deformation around A similar to 100 (vol 115, 172501, 2015)
Excited states of the neutron-rich nuclei 97,99Rb were populated for the first time using the multistep Coulomb excitation of radioactive beams. Comparisons of the results with particle-rotor model calculations provide clear identification for the ground-state rotational band of 97Rb as being built on the πg9/2 [431] 3/2+ Nilsson-model configuration. The ground-state excitation spectra of the Rb isotopes show a marked distinction between single-particle-like structures below N=60 and rotational bands above. The present study defines the limits of the deformed region around A∼100 and indicates that the deformation of 97Rb is essentially the same as that observed well inside the deformed region. It further highlights the power of the Coulomb-excitation technique for obtaining spectroscopic information far from stability. The 99Rb case demonstrates the challenges of studies with very short-lived postaccelerated radioactive beams.nrpages: 172501status: publishe