Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pygmy resonance and low-energy enhancement in the $\gamma$-ray strength
  functions of Pd~isotopes   An unexpected enhancement in the $\gamma$-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 $E_\gamma<4$ MeV. This enhancement was
not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole
Resonance (PDR) centered at $E_\gamma\approx8$ MeV was however detected. The
$\gamma$-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 $\gamma$-ray strength
functions of $^{105-108}$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 ($^{3}$He,
$^{3}$He$^{\prime}\gamma$) and ($^{3}$He, $\alpha$$\gamma$) on $^{106,108}$Pd
target foils. Particle$-\gamma$ coincidence measurements provided information
on initial excitation energies and the corresponding $\gamma$-ray spectra,
which were used to extract the level densities and $\gamma$-ray strength
functions according to the Oslo method. The $\gamma$-ray strength functions
indicate a sudden increase in magnitude for $E_{\gamma}>4$ MeV, which is
interpreted as a PDR centered at $E_{\gamma}\approx8$ MeV. An enhanced
$\gamma$-ray strength at low energies is also observed for $^{105}$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.

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The categories of this paper are: acc-phys
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: physics
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The categories of this paper are: bayes-an
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci