224 research outputs found
Identification of a millisecond isomeric state in 129Cd81 via the detection of internal conversion and Compton electrons
published_or_final_versio
In-beam γ-ray spectroscopy of 136Te at relativistic energies
The reduced transition probability B(E2; 0+ 1 →2+ 1 ) to the first excited 2+ state of the neutron-rich nucleus 136Te, with two protons and two neutrons outside the doubly magic 132Sn core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. A value of B(E2)= 0.191(26) e2b2 was extracted from the measured inelastic scattering cross section on an Au target taking into account the contributions from both Coulomb and nuclear excitations. In addition, an upper limit for the transition strength to a 2+ state of mixed-symmetry character in the excitation energy range of 1.5–2.2 MeV was determined and compared to the predictions of various theoretical calculations. Because of the high statistics gathered in the present experiment the error of the deduced B(E2) value is dominated by the systematic uncertainties involved in the analysis of Coulomb excitation experiments at beam energies around 150 MeV/u. Therefore, the latter are for the first time assessed in detail in the present work.Spanish Ministerio de Economía y Competitividad (FPA2014-57196-C5-4-P, FPA2017-84756-C4-2-P, FIS2014-53448-C2-1-P
rp-Process weak-interaction mediated rates of waiting-point nuclei
Electron capture and positron decay rates are calculated for
neutron-deficient Kr and Sr waiting point nuclei in stellar matter. The
calculation is performed within the framework of pn-QRPA model for rp-process
conditions. Fine tuning of particle-particle, particle-hole interaction
parameters and a proper choice of the deformation parameter resulted in an
accurate reproduction of the measured half-lives. The same model parameters
were used to calculate stellar rates. Inclusion of measured Gamow-Teller
strength distributions finally led to a reliable calculation of weak rates that
reproduced the measured half-lives well under limiting conditions. For the
rp-process conditions, electron capture and positron decay rates on Kr
and Sr are of comparable magnitude whereas electron capture rates on
Sr and Kr are 1--2 orders of magnitude bigger than the
corresponding positron decay rates. The pn-QRPA calculated electron capture
rates on Kr are bigger than previously calculated. The present
calculation strongly suggests that, under rp-process conditions, electron
capture rates form an integral part of weak-interaction mediated rates and
should not be neglected in nuclear reaction network calculations as done
previously.Comment: 13 pages, 4 figures, 4 tables; Astrophysics and Space Science (2012
Deformation of the N=Z nucleus 76Sr using beta-decay studies
A novel method of deducing the deformation of the N=Z nucleus 76Sr is
presented. It is based on the comparison of the experimental Gamow-Teller
strength distribution B(GT) from its beta decay with the results of QRPA
calculations. This method confirms previous indications of the strong prolate
deformation of this nucleus in a totally independent way. The measurement has
been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia",
newly installed at CERN-ISOLDE.Comment: Accepted in Phys. Rev. Letter
Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector
We study the S-wave interaction of mesons with baryons in the strangeness S=0
sector in a coupled channel unitary approach. The basic dynamics is drawn from
the lowest order meson baryon chiral Lagrangians. Small modifications inspired
by models with explicit vector meson exchange in the t-channel are also
considered. In addition the pi pi N channel is included and shown to have an
important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure
Characterization of a novel proton-CT scanner based on Silicon and LaBr(Ce) detectors
Treatment planning systems at proton-therapy centres generally use X-ray
computed tomography (CT) as primary imaging technique to infer the proton
treatment doses to tumour and healthy tissues. However, proton stopping powers
in the body, as derived from X-ray images, suffer from important proton-range
uncertainties. In order to reduce this uncertainty in range, one could use
proton-CT images instead. The main goal of this work is to test the
capabilities of a newly-developed proton-CT scanner, based on the use of a set
of tracking detectors and a high energy resolution scintillator for the
residual energy of the protons. Different custom-made phantoms were positioned
at the field of view of the scanner and were irradiated with protons at the CCB
proton-therapy center in Krakow. We measured with the phantoms at different
angles and produced sinograms that were used to obtain reconstructed images by
Filtered Back-Projection (FBP). The obtained images were used to determine the
capabilities of our scanner in terms of spatial resolution and proton Relative
Stopping Power mapping and validate its use as proton-CT scanner. The results
show that the scanner can produce medium-high quality images, with spatial
resolution better than 2 mm in radiography, below 3 mm in tomography and
resolving power in the RSP comparable to other state of the art pCT cameras
The Neurogenesis Actuator and NR2B/NMDA Receptor Antagonist Ro25-6981 Consistently Improves Spatial Memory Retraining Via Brain Region-Specific Gene Expression
NR2B-containing NMDA (NR2B/NMDA) receptors are important in controlling neurogenesis and are involved in generating spatial memory. Ro25-6981 is a selective antagonist at these receptors and actuates neurogenesis and spatial memory. Inter-structural neuroanatomical profiles of gene expression regulating adult neurogenesis and neuroapoptosis require examination in the context of memory retrieval and reversal learning. The aim was to investigate spatial memory retrieval and reversal learning in relation to gene expression-linked neurogenetic processes following blockade of NR2B/NMDA receptors by Ro25-6981. Rats were trained in Morris water maze (MWM) platform location for 5 days. Ro25-6981 was administered (protocol days 6–7) followed by retraining (days 15–18 or 29–32). Platform location was tested (on days 19 or 33) then post-mortem brain tissue sampling (on days 20 or 34). The expression of three genes known to regulate cell proliferation (S100a6), differentiation (Ascl1), and apoptosis (Casp-3) were concomitantly evaluated in the hippocampus, prefrontal cortex, and cerebellum in relation to the MWM performance protocol. Following initial training, Ro25-6981 enhanced visuospatial memory retrieval performance during further retraining (protocol days 29–32) but did not influence visuospatial reversal learning (day 33). Hippocampal Ascl1 and Casp-3 expressions were correspondingly increased and decreased while cerebellar S100a6 and Casp-3 activities were decreased and increased respectively 27 days after Ro25-6981 treatment. Chronological analysis indicated a possible involvement of new mature neurons in the reconfiguration of memory processes. This was attended by behavioral/gene correlations which revealed direct links between spatial memory retrieval enhancement and modified gene activity induced by NR2B/NMDA receptor blockade and upregulation
Scattering of the Halo Nucleus 11Be on 197Au at Energies around the Coulomb Barrier
Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus 11Be on197 Au were measured at energies below (Elab =31.9 MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of 11Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the β (E1) distribution in 11Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in 11Be.Ministerio de Economía y Competitividad FPA2015-64969-P, FIS2014-53448-C2-1-P, FPA2013-47327-c02-01-R, FPA2012-32443, FIS2013-41994-PCentro Nacional de Física de Partículas, Astropartículas y Nuclear CSD2007- 00042European Collaborative Research EUI-2009-04162European Unions 654002Nuclear Astrophysics Virtual Institute VH-VI-417European Commission, Seventh Framework Program 60037
Proton radiographs using position-sensitive silicon detectors and high-resolution scintillators
Proton therapy is a cancer treatment technique currently in growth worldwide.
It offers advantages with respect to conventional X-ray and -ray
radiotherapy, in particular, a better control of the dose deposition allowing
to reach a higher conformity in the treatments. Therefore, it causes less
damage to the surrounding healthy tissue and less secondary effects. However,
in order to take full advantage of its potential, improvements in treatment
planning and dose verification are required. A new prototype of proton Computed
Tomography scanner is proposed to design more accurate and precise treatment
plans for proton therapy. Here, results obtained from an experiment performed
using a 100-MeV proton beam at the CCB facility in Krakow (Poland) are
presented. Proton radiographs of PMMA samples of 50-mm thickness with spatial
patterns in aluminum were taken. Their properties were studied, including
reproduction of the dimensions, spatial resolution and sensitivity to different
materials. They demonstrate the capabilities of the system to produce images
with protons. Structures of up to 2 mm are nicely resolved and the sensitivity
of the system was enough to distinguish thicknesses of 10 mm of aluminum or
PMMA. This constitutes a first step to validate the device as a proton
radiography scanner previous to the future tests as a proton CT scanner.Comment: 7 pages, 11 figures, submitted to IEEE TNS ANIMMA 2021 Conference
Proceeding
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