45 research outputs found
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
Statistical -decay from highly excited states is determined by the
nuclear level density (NLD) and the -ray strength function
(SF). These average quantities have been measured for several nuclei
using the Oslo method. For the first time, we exploit the NLD and SF to
evaluate the -width in the energy region below the neutron binding
energy, often called the quasi-continuum region. The lifetimes of states in the
quasi-continuum are important benchmarks for a theoretical description of
nuclear structure and dynamics at high temperature. The lifetimes may also have
impact on reaction rates for the rapid neutron-capture process, now
demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure
Level densities and -strength functions in Sm
The level densities and -strength functions of the weakly deformed
Sm and Sm nuclei have been extracted. The temperature versus
excitation energy curve, derived within the framework of the micro canonical
ensemble, shows structures, which we associate with the break up of Cooper
pairs. The nuclear heat capacity is deduced within the framework of both the
micro canonical and the canonical ensemble. We observe negative heat capacity
in the micro canonical ensemble whereas the canonical heat capacity exhibits an
S-shape as function of temperature, both signals of a phase transition. The
structures in the -strength functions are discussed in terms of the
pygmy resonance and the scissors mode built on exited states. The samarium
results are compared with data for the well deformed Dy,
Er and Yb isotopes and with data from
(n,)-experiments and giant dipole resonance studies.Comment: 12 figure
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
New experimental constraint on the W()W cross section
In this work, we present new data on the W() cross
sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU
synchrotron radiation facility. Further, we have extracted the nuclear level
density and -ray strength function of W from data on the
W()W reaction measured at the Oslo
Cyclotron Laboratory. Combining previous measurements on the
W() cross section with our new W()
and ()W data sets, we have deduced the
W -ray strength function in the range of MeV
and MeV.
Our data are used to extract the level density and -ray strength
functions needed as input to the nuclear-reaction code \textsf{TALYS},
providing an indirect, experimental constraint for the
W()W cross section and reaction rate. Compared to the
recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 data
base, our results are on average lower for the relevant energy range keV, and we provide a smaller uncertainty for the MACS. The
theoretical values of Bao \textit{et al.} and the cross section experimentally
constrained on photoneutron data of Sonnabend \textit{et al.} are significantly
higher than our result. The lower value by Mohr \textit{et al.} is in very good
agreement with our deduced MACS. Our new results could have implications for
the -process and in particular the predicted -process production of
Os nuclei.Comment: 17 pages, 15 figures; to be submitted to Phys. Rev.
Nuclear Level Density and -ray Strength Function of and the impact on the i-process
Proton- coincidences from reactions between
a beam and a deuterated polyethylene target have been
analyzed with the inverse Oslo method to find the nuclear level density (NLD)
and -ray strength function (SF) of . The
capture cross section has been calculated
using the Hauser-Feshbach model in TALYS using the measured NLD and SF
as constraints. We confirm that acts as a
bottleneck when relying on one-zone nucleosynthesis calculations. However, we
find that the impact of this reaction is strongly damped in multi-zone
low-metallicity AGB stellar models experiencing i-process nucleosynthesis.Comment: Submitted to Phys. Rev.
Evolution of the -ray strength function in neodymium isotopes
The experimental gamma-ray strength functions (gamma-SFs) of 142,144-151Nd
have been studied for gamma-ray energies up to the neutron separation energy.
The results represent a unique set of gamma-SFs for an isotopic chain with
increasing nuclear deformation. The data reveal how the low-energy enhancement,
the scissors mode and the pygmy dipole resonance evolve with nuclear
deformation and mass number. The data indicate that the mechanisms behind the
low-energy enhancement and the scissors mode are decoupled from each other.Comment: 14 pages and 10 figure
Nuclear level densities and γ -ray strength functions of 180,181Ta and neutron capture cross sections
Abstract: Please refer to full text to view abstract