104 research outputs found
Pygmy resonance and low-energy enhancement in the -ray strength functions of Pd~isotopes
An unexpected enhancement in the -ray strength function, as compared
to the low energy tail of the Giant Dipole Resonance (GDR), has been observed
for Sc, Ti, V, Fe and Mo isotopes for MeV. This enhancement was
not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole
Resonance (PDR) centered at MeV was however detected. The
-ray strength functions measured for Cd isotopes exhibit both features
over the range of isotopes, with the low-energy enhancement decreasing- and PDR
strength increasing as a function of neutron number. This suggests a
transitional region for the onset of low-energy enhancement, and also that the
PDR strength depends on the number of neutrons. The -ray strength
functions of Pd have been measured in order to further explore the
proposed transitional region. Experimental data were obtained at the Oslo
Cyclotron Laboratory by using the charged particle reactions (He,
He) and (He, ) on Pd
target foils. Particle coincidence measurements provided information
on initial excitation energies and the corresponding -ray spectra,
which were used to extract the level densities and -ray strength
functions according to the Oslo method. The -ray strength functions
indicate a sudden increase in magnitude for MeV, which is
interpreted as a PDR centered at MeV. An enhanced
-ray strength at low energies is also observed for Pd, which is
the lightest isotope measured in this work. Further, the results correspond and
agree very well with the observations from the Cd isotopes, and support the
suggested transitional region for the onset of low-energy enhancement with
decreasing mass number. The neutron number dependency of the PDR strength is
also evident
La(, ) cross sections constrained with statistical decay properties of La nuclei
The nuclear level densities and -ray strength functions of
La were measured using the La(He, ),
La(He, He) and La(d, p) reactions. The
particle- coincidences were recorded with the silicon particle
telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these
experimental results, the low-energy enhancement in the A140 region is
discussed. The La( cross sections were calculated
at - and -process temperatures using the experimentally measured nuclear
level densities and -ray strength functions. Good agreement is found
between La( calculated cross sections and previous
measurements
Nuclear Level Density and -ray Strength Function of
The nuclear level density (NLD) and -ray strength function
(SF) of have been investigated using the Oslo
method. The extracted NLD is compared with previous measurements using particle
evaporation and those found from neutron resonance spacing. The SF was
found to feature a strong low energy enhancement that could be explained as M1
strength based on large scale shell model calculations. Comparison of
SFs measured with the Oslo method for various isotopes
reveals systematic changes to the strength below MeV with increasing mass.Comment: Submitted to Phys. Rev.
Study of oblate nuclear shapes and shape coexistence in neutron-deficient rare earth isotopes
The little hagedorn that could
The Hagedorn exponential mass spectrum with slope 1/TH was erroneously interpreted as fixing an upper limiting temperature TH that the system can achieve. To the contrary, such spectrum indicates a 1st order phase transition at a fixed temperature TH. A much lower energy example is the log linear level nuclear density below the neutron binding energy that prevails throughout the nuclear chart. We show that, for non-magic nuclei, such linearity implies a 1st order phase transition from the pairing superfluid to an ideal gas of quasi particles
Experimental first order pairing phase transition in atomic nuclei
The natural log of experimental nuclear level densities at low energy is linear with energy. This can be interpreted in terms of a nearly 1st order phase transition from a superfluid to an ideal gas of quasi particles. The transition temperature coincides with the BCS critical temperature and yields gap parameters in good agreement with the values extracted from even- odd mass differences from rotational states. This converging evidence supports the relevance of the BCS theory to atomic nuclei
Extreme nonstatistical effects in γ decay of 95Mo neutron resonances
We demonstrate that high-quality total radiation width (Γγ) data are a virtually untapped resource for testing and improving nuclear models. To this end, we obtained unprecedentedly large sets of Γγ values for all six s- and p-wave Jπ values for 95Mo neutron resonances. We show that Γγ distributions simulated in the framework of the nuclear statistical model are in sharp disagreement with the data. Simulations modified to include doorway effects resulted in much better agreement. These results call into question the reliability of the nuclear statistical model.
© 2013 American Physical Societ
Updated Photonuclear Data Library and Database for Photon Strength Functions
Photonuclear cross sections and gamma-ray data used to extract Photon Strength Functions are important for a large range of applications including basic sciences. The recommendations of an IAEA Consultant’s Meeting to update the IAEA Photonuclear Data Library and create a Reference Database for Photon Strength Functions are presented
Updated Photonuclear Data Library and Database for Photon Strength Functions
Photonuclear cross sections and gamma-ray data used to extract Photon Strength Functions are important for a large range of applications including basic sciences. The recommendations of an IAEA Consultant’s Meeting to update the IAEA Photonuclear Data Library and create a Reference Database for Photon Strength Functions are presented
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