133 research outputs found
Second T = 3/2 state in B and the isobaric multiplet mass equation
Recent high-precision mass measurements and shell model calculations~[Phys.
Rev. Lett. {\bf 108}, 212501 (2012)] have challenged a longstanding explanation
for the requirement of a cubic isobaric multiplet mass equation for the lowest
isospin quartet. The conclusions relied upon the choice of the
excitation energy for the second state in B, which had two
conflicting measurements prior to this work. We remeasured the energy of the
state using the reaction and significantly disagree
with the most recent measurement. Our result supports the contention that
continuum coupling in the most proton-rich member of the quartet is not the
predominant reason for the large cubic term required for nuclei
Study of proton-unbound states in relevant for the reaction in novae
Background: The nucleosynthesis of several proton-rich nuclei is determined
by radiative proton-capture reactions on unstable nuclei in nova explosions.
One such reaction is , which links the
NeNa and MgAl cycles in oxygen-neon (ONe) novae.
Purpose: To extract resonance
strengths from a study of proton-unbound states in , produced
via the Mg(He,) reaction.
Methods: A beam of ions at 50.7 MeV was used to produce
the states of interest in Al. Proton-triton angular correlations were
measured with a QDD magnetic spectrometer and a silicon detector array,
located at iThemba LABS, South Africa.
Results: We measured the excitation energies of the four lowest
proton-unbound states in Al and place lower-limits on
values for these four states. Together with USD-C shell-model calculations of
partial gamma widths, the experimental data are also used to determine
resonance strengths for the three lowest
resonances.
Conclusions: The energy of the dominant first
resonance is determined to be keV, with a resonance
strength meV
α Clustering in Si 28 probed through the identification of high-lying 0+ states
Background: Aspects of the nuclear structure of light α-conjugate nuclei have long been associated with nuclear clustering based on α particles and heavier α-conjugate systems such as C12 and O16. Such structures are associated with strong deformation corresponding to superdeformed or even hyperdeformed bands. Superdeformed bands have been identified in Ca40 and neighboring nuclei and find good description within shell model, mean-field, and α-cluster models. The utility of the α-cluster description may be probed further by extending such studies to more challenging cases comprising lighter α-conjugate nuclei such as Mg24, Si28, and S32. Purpose: The purpose of this study is to look for the number and energy of isoscalar 0+ states in Si28. These states are the potential bandheads for superdeformed bands in Si28 corresponding to the exotic structures of Si28. Of particular interest is locating the 0+ bandhead of the previously identified superdeformed band in Si28. Methods: α-particle inelastic scattering from a Sinat target at very forward angles including 0 has been performed at the iThemba Laboratory for Accelerator-Based Sciences in South Africa. Scattered particles corresponding to the excitation energy region of 6 to 14 MeV were momentum-analysed in the K600 magnetic spectrometer and detected at the focal plane using two multiwire drift chambers and two plastic scintillators. Results: Several 0+ states have been identified above 9 MeV in Si28. A newly identified 9.71 MeV 0+ state is a strong candidate for the bandhead of the previously discussed superdeformed band. The multichannel dynamical symmetry of the semimicroscopic algebraic model predicts the spectrum of the excited 0+ states. The theoretical prediction is in good agreement with the experimental finding, supporting the assignment of the 9.71-MeV state as the bandhead of a superdeformed band. Conclusion: Excited isoscalar 0+ states in Si28 have been identified. The number of states observed in the present experiment shows good agreement with the prediction of the multichannel dynamical symmetry
Statistical properties of the well deformed Sm nuclei and the scissors resonance
The Nuclear Level Densities (NLDs) and the -ray Strength Functions
(SFs) of Sm have been extracted from (d,p)
coincidences using the Oslo method. The experimental NLD of Sm is
higher than the NLD of Sm, in accordance with microscopic calculations.
The SFs of Sm are in fair agreement with QRPA calculations
based on the D1M Gogny interaction. An enhancement is observed in the
SF for both Sm nuclei around 3 MeV in excitation energy and
is attributed to the M1 Scissors Resonance (SR). Their integrated strengths
were found to be in the range 1.3 - 2.1 and 4.4 - 6.4 for
Sm and Sm, respectively. The strength of the SR for Sm
is comparable to those for deformed even-even Sm isotopes from nuclear
resonance fluorescence measurements, while that of Sm is lower than
expected
Isospin mixing and the cubic isobaric multiplet mass equation in the lowest <i>T</i>=2, <i>A</i>=32 quintet
The isobaric multiplet mass equation (IMME) is known to break down in the
first T = 2, A = 32 isospin quintet. In this work we combine high-resolution
experimental data with state-of-the-art shell-model calculations to investigate
isospin mixing as a possible cause for this violation. The experimental data
are used to validate isospin-mixing matrix elements calculated with newly
developed shell-model Hamiltonians. Our analysis shows that isospin mixing with
nonanalog T = 1 states contributes to the IMME breakdown, making the
requirement of an anomalous cubic term inevitable for the multiplet
Народная культура и традиции
CITATION: Donaldson, L. M., et al. 2018. Deformation dependence of the isovector giant dipole resonance : theneodymium isotopic chain revisited. Physics Letters B, 776:133-138, doi:10.1016/j.physletb.2017.11.025.The original publication is available at https://www.sciencedirect.comProton inelastic scattering experiments at energy Ep=200MeV and a spectrometer scattering angle of 0° were performed on 144,146,148,150Nd and 152Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150Nd and 152Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data.https://www.sciencedirect.com/science/article/pii/S0370269317309176Publisher's versio
g-factor measurements of isomeric states in 174W
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.ISBN: 978-88-7438-101-2; International audience; The experimental setup GAMIPE used for gyromagnetic factormeasurements at Laboratori Nazionali di Legnaro and a recent experimentalwork regarding K-isomers in 174W are described. Aim ofthe experiment is to study the detailed structure of the isomeric stateswave functions, by the measurement of the magnetic dipole moments.This piece of information can provide interesting hints for theoreticalmodels. Preliminary results concerning the population of the isomersof interest and half-lives are presented
Study of the γ decay of high-lying states in 208Pb via inelastic scattering of 17O ions
High-lying states in 208Pb nucleus were populated via inelastic scattering of a 17O beam at bombarding energy of 20 MeV/u. Their subsequent gamma decay was measured with the detector system AGATA Demonstrator based on HPGe detectors, coupled to an array of large volume LaBr3:Ce scintillators. Preliminary results in comparison with (γ,γ′) data, for states in the 5–8 MeV energy interval, seem to indicate that in that region the states belong to two different groups one with a isoscalar character and the other with a isovector nature. This is similar to what was observed in other stable nuclei with (α,α′γ) experiments. The multipolarity of the observed gamma transitions is determined with remarkable sensitivity thanks to angular distribution measurements. Data aiming at studying the neutron decay of the Giant Quadrupole Resonance in the 208Pb by the high resolution measurement of the following gamma decay are also presented in their preliminary form
A focus on selected perspectives of the NUMEN project
The use of double charge exchange reactions is discussed in view of their application to extract information that may be helpful to determinate the nuclear matrix elements entering in the expression of neutrinoless double beta decay half-life. The strategy adopted in the experimental campaigns performed at INFN - Laboratori Nazionali del Sud and in the analysis methods within the NUMEN project is briefly described, emphasizing the advantages of the multi-channel approach to nuclear reaction data analysis. An overview on the research and development activities on the MAGNEX magnetic spectrometer is also given, with a focus on the chosen technological solutions for the focal plane detector which will guarantee the performances at high-rate conditions
Recent results on heavy-ion direct reactions of interest for 0νββ decay at INFN LNS
Neutrinoless double beta decay of nuclei, if observed, would have important implications on fundamental physics. In particular it would give access to the effective neutrino mass. In order to extract such information from 0νββ decay half-life measurements, the knowledge of the Nuclear Matrix Elements (NME) is of utmost importance. In this context the NUMEN and the NURE projects aim to extract information on the NME by measuring cross sections of Double Charge Exchange reactions in selected systems which are expected to spontaneously decay via 0νββ. In this work an overview of the experimental challenges that NUMEN is facing in order to perform the experiments with accelerated beams and the research and development activity for the planned upgrade of the INFN-LNS facilities is reported
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