Neutron Inelastic Scattering Cross Section Measurements for 23Na

In March 2011 the final data from measurements for the 23Na(n,n'gamma) reaction were delivered to the CEA - Commissariat à l'Énergie Atomique, Cadarache, France in the context of the EURATOM-CEA collaboration agreement. This report documents that deliverable. The measurement campaign was initiated in response to a request expressed by the CEA at a meeting of the Joint Evaluated Fission and Fusion nuclear data library project in 2007. This meeting took place under the auspices of the Nuclear Energy Agency (Organisation for Economic Co-operation and Development). The CEA supports research for the advanced, Generation-IV type, sodium cooled fast reactor and is engaged in a project to develop a prototype: ASTRID - the advanced sodium test reactor for industrial development. Inelastic scattering cross sections for sodium are of interest to the development of sodium cooled fast reactors. A recent OECD-NEA subgroup analysed the sensitivity of reactor parameters to cross sections and accordingly determined target uncertainties for the nuclear data [1]. Comparing these target uncertainties with the current status of nuclear data uncertainties and covariance data resulted in a list of target priorities. Among these features sodium inelastic scattering for which a target uncertainty of 4% was established for the average cross section in the energy range from threshold to 1.35 MeV. This is approximately seven times as good as the uncertainty for current evaluated data files for this isotope (see OECD-NEA High Priority Request List [2]). At IRMM, the GAINS gamma-array for inelastic neutron scattering was developed with the purpose of measuring cross sections with uncertainties at or below the target uncertainties for nuclides like 23Na using the (n, n'g)-technique [3,4]. In response to the request, a measurement campaign of the 23Na(n,n¿g) reaction was conducted with the GAINS array during 2009-2010, using metallic Na discs of 99.8% purity. The sample and the measurements were made at the Institute for Reference Materials and Measurements in Geel making use of GELINA, the Geel linear electron accelerator that drives a pulsed white neutron source allowing measurements by the neutron time-of-flight technique. A preliminary report of this work was presented earlier [5]. For the experimental work a careful review was made of the gamma-efficiency calibrations and the flux normalization in order to investigate in detail the corrections and the final uncertainties that may realistically be achieved.JRC.DG.D.5-Nuclear physic

Identification of the crossing point at N=21 between normal and intruder configurations

The beta(-) decay of Mg-34 was used to study the Al-34 nucleus through. spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two beta-decaying states in Al-34 having spin-parity assignments J(pi) = 4(-) dominated by the normal configuration pi(d(5/2))(-1)circle times nu(f(7/2)) and J(pi) = 1(+) by the intruder configuration pi(d(5/2))(-1) circle times nu(d(3/2))(-1) (f(7/2))(2). Their unknown ordering and relative energy have been the subject of debate for the placement of Al-34 inside or outside the N = 20 "island of inversion." We report here that the 1(+) intruder lies only 46.6 keV above the 4(-) ground state. In addition, a new half-life of T-1/2 = 44.9(4) ms, that is twice as long as the previously measured 20(10) ms, has been determined for Mg-34. Large-scale shell-model calculations with the recently developed SDPF-U-MIX interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the N = 20 island of inversion.Peer reviewe

Beta-delayed proton emission from 20Mg

Beta-delayed proton emission from 20 Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station (IDS) setup including both charged-particle and gamma-ray detection capabilities. A total of 27 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in 20 Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State (IAS) in 20 Na is observed. This may allow studies of the 4032.9(2.4)keV resonance in 19 Ne through the beta decay of 20 Mg, which is important for the astrophysically relevant reaction 15O( $\alpha$ , $\gamma$ )19Ne . Beta-delayed protons were used to obtain a more precise value for the half-life of 20 Mg, 91.4(1.0)ms

Evolution of deformation in neutron-rich Ba isotopes up to A=150

The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N = 90. To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z = 56 isotopic chain accessible at present, Ba-148,Ba-150, has been studied via beta decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive-and negative-parity low-spin excited states of 150Ba and presents an extension of the beta-decay scheme of Cs-148. Employing the fast timing technique, half-lives for the 2(1)(+) level in both nuclei have been determined, resulting in T-1/2 = 1.51(1) ns for Ba-148 and T-1/2 = 3.4(2) ns for Ba-150. The systematics of low-spin states, together with the experimental determination of the B(E2 : 2(+) -> 0(+)) transition probabilities, indicate an increasing collectivity in Ba148-150, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.Peer reviewe

Search for 22^{22}Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of $^{26}$Al and $^{22}$Na. While gamma rays from the decay of the former radioisotope have been observed throughout the Galaxy, $^{22}$Na remains untraceable. The half-life of $^{22}$Na (2.6 yr) would allow the observation of its 1.275 MeV gamma-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus. The $^{22}$Na($p,\gamma$)$^{23}$Mg reaction remains the only source of large uncertainty about the amount of $^{22}$Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in $^{23}$Mg. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the $^{23}$Mg states, combining magnetic and highly-segmented tracking gamma-ray spectrometers, places strong limits on the amount of $^{22}$Na produced in novae, explains its non-observation to date in gamma rays (flux < 2.5x$10^{-4}$ ph/(cm$^2$s)), and constrains its detectability with future space-borne observatories.Comment: 18 pages, 3 figures, 1 tabl

First beta-decay spectroscopy of In-135 and new beta-decay branches of In-134

The beta decay of the neutron-rich In-134 and In-135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z = 50 above the N = 82 shell. The beta-delayed gamma-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three beta-decay branches of In-134 were established, two of which were observed for the first time. Population of neutron-unbound states decaying via. rays was identified in the two daughter nuclei of In-134, Sn-134 and Sn-133, at excitation energies exceeding the neutron separation energy by 1 MeV. The beta-delayed one- and two-neutron emission branching ratios of In-134 were determined and compared with theoretical calculations. The beta-delayed one-neutron decay was observed to be dominant beta-decay branch of In-134 even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of Sn-134. Transitions following the beta decay of In-135 are reported for the first time, including. rays tentatively attributed to Sn-135. In total, six new levels were identified in Sn-134 on the basis of the beta.. coincidences observed in the In-134 and In-135 beta decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2(+) state in Sn-133 was observed in both beta decays and its assignment is discussed. Experimental level schemes of Sn-134 and Sn-135 are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2(+), 4(+), and 6(+) levels in Sn-134 were determined. From the lifetime of the 4(+) state measured for the first time, an unexpectedly large B(E2; 4(+)-> 2(+)) transition strength was deduced, which is not reproduced by the shell-model calculations.Peer reviewe

Spectroscopie gamma en ligne de noyaux légers riches en neutrons produits par fragmentation de faisceau radioactif et mesures de temps de vie des niveaux excités dans les noyaux proches de 68^{68}Ni

This thesis deals with studies of nuclei far from the valley of stability produced at GANIL by projectile fragmentation at intermediate energies. It consists of two parts. The first one is dedicated to the study of very light exotic nuclei around N=14. This is the first time that online gamma-ray spectroscopy combined with the projectile fragmentation was used with radioactive incident beams at GANIL. The advantages and the limitations of this method were established. 40 different nuclei have been produced and studied at the same time. A strong dependence of the population of excited states on the type of projectile was observed. New information was obtained on the structure of the isotopes 14,15B, 17,18,19,20C, 18,19,20,21,22N, 22,23,24O, 24,25,26F and 29Ne. The level schemes obtained from this study have been compared with shell-model predictions. In particular, the energy of 1588(20) keV found for the first 2+ excited state in 20C, as well as the non-existence of a bound state in 24O, show that the protonneutron interaction plays an important role in the structure of these nuclei. In the second part, an experiment is presented concerning the neutron-rich isomer nuclei around 68Ni produced by the LISE spectrometer. The fast-timing method was applied for the first time for the study of nuclei produced by projectile fragmentation. Subnanosecond half-lives of several levels in 67,69,90Ni and 71,72Cu were measured simultaneously and with high precision. These results have allowed us to test the shell model predictions for several E2 transitions and their associated B(E2) transition probabilities.Cette thèse entre dans le cadre de l'étude des noyaux loin de la vallée de stabilité produits au GANIL par fragmentation du projectile aux énergies intermédiaires. Elle comprend deux parties. La première concerne l'étude des noyaux exotiques très légers ayant des nombres de neutrons proches de 14. C'est la première fois que la méthode spectroscopie gamma en-ligne par fragmentation du projectile est utilisée avec des faisceaux incidents radioactifs au GANIL. Ainsi les performances et les limitations de cette méthode ont pu être établies. 40 noyaux différents ont été produits et étudiés en même temps. Une forte dépendance dans les peuplements des états excités en fonction du type de projectile a été observée. Des informations nouvelles sur la structure ont pu être obtenues pour les isotopes de 14,15B, 17,18,19,20C, 18,19,20,21,22N, 22,23,24O, 24,25,26F, 29Ne. Les schémas de niveaux établis ont été comparés aux prédictions du modèle en couches. En particulier l'énergie de 1588(20) keV trouvée pour le premier état excité 2+ dans 20C ainsi que l'inexistence d'un état lié dans 24O a montré que l'interaction proton-neutron joue un rôle très important dans la structure de ces noyaux. Dans la deuxième partie, une expérience concernant les noyaux isomères riches en neutrons autour de 68Ni produits par le spectromètre LISE est présentée. C'est la première fois que la méthode "fast timing" est appliquée à l'étude des noyaux produits par la fragmentation du projectile. Des temps de vie entre quelques dizaines de picosecondes et quelques nanosecondes ont été mesurés avec une grande précision pour plusieurs niveaux dans les noyaux 67,69,90Ni et 71,72Cu. Ces résultats ont permis de vérifier les prédictions du modèle en couches pour plusieurs transitions de type E2 et leurs probabilités de transitions B(E2) associées

Spectroscopie gamma en ligne de noyaux légers riches en neutrons produits par fragmentation de faisceau radioactif et mesures de temps de vie des niveaux excités dans les noyaux proches du 68Ni

CAEN-BU Sciences et STAPS (141182103) / SudocSTRASBOURG-Bib.Central Recherche (674822133) / SudocSudocFranceF

Neutron Inelastic Cross Section Measurements for Sodium

Inelastic scattering cross sections for sodium are of interest to the development of sodium cooled fast reactors. A recent OECD-NEA subgroup analysed the sensitivity of reactor parameters to cross sections and accordingly determined target uncertainties for the nuclear data. Comparing these target uncertainties with the current status of nuclear data uncertainties and covariance data resulted in a list of target priorities. Among these features sodium inelastic scattering for which a target uncertainty of about 5% was established, approximately two to three times as good as the uncertainty for current evaluated data files for this isotope (see OECD-NEA High Priority Request List, http://www.nea.fr/html/dbdata/hprl/hprlview.pl?ID=448). At IRMM, the GAINS gamma-array for inelastic neutron scattering was developed with the purpose of measuring cross sections with uncertainties at or below the target uncertainties for nuclides like 23Na using the (n,n'gamma)-technique. Measurements were performed at the GELINA facility at a 200 m flight path with eight high purity germanium detectors. The sample was an 80 mm diameter metallic disk prepared at IRMM by cutting, pressing, rolling and punching. For the experimental work, a careful review was made of the gamma-efficiency calibrations and the flux normalization in order to investigate in detail the corrections and the final uncertainties that may realistically be achieved. An elaborate account will be presented of the data analysis and checks that have been made and implications for earlier work by our group will be discussed. First results will be shown for the gamma-production cross sections of the main transitions in the energy range from threshold to 10 MeV.JRC.DG.D.5-Nuclear physic