Pygmy resonance and low-energy enhancement in the γ\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

Nivåtetthet og _g-styrkefunksjon for kjernene %1%1%1,%1%1%2Cd

Nivåtetthet og gammastyrkefunksjon for atomkjernene 111,112Cd har blitt målt ved hjelp av Oslometoden, basert på data fra Oslo Syklotronlaboratorium. Motivasjonen for dette forsøket var å kartlegge disse to størrelsene i et eksitasjonsområde der lite var kjent fra tidligere eksperimenter. Man ville også undersøke om noen av disse kadmiumisotopene ville ha en økning i gammastyrkefunksjonen ved lave gammaenergier. En slik økning har vært sett i Mo-isotoper, men ikke i Sn-isotoper. Det er derfor av stor interesse å forsøke og finne nøyaktig hvilke kjerner som har denne økningen. Man fant for nivåtettheten i 112Cd tydelige topper ved lave eksitasjonsenergier. Disse toppene skyldes vibrasjonstilstander i kjernen. Det ble ikke funnet en økning i gammahenfallssannsynlighet for lave gammaenergier i disse kjernene. Dermed er det fortsatt et åpent spørsmål for hvilket masseområde denne økningen dukker opp

Analisis pengaruh nilai pelanggan, kualitas pelayanan dan kedekatan emosional terhadap loyalitas nasabah : studi kasus pada BANK CIMB NIAGA Universitas Sanata Dharma

The level densities and γ-ray strength functions of 105,106,111,112Cd have been extracted from particle-γ coincidence data using the Oslo method. The level densities are in very good agreement with known levels at low excitation energy. The γ-ray strength functions display no strong enhancement for low γ energies. However, more low-energy strength is apparent for 105,106Cd than for 111,112Cd. For γ energies above ≈4 MeV, there is evidence for some extra strength, similar to what has been previously observed for the Sn isotopes. The origin of this extra strength is unclear; it might be due to E1 and M1 transitions originating from neutron skin oscillations or the spin-flip resonance, respectively. © 2013 American Physical Societ

Evidence for the dipole nature of the low-energy γ enhancement in 56Fe

The γ-ray strength function of 56Fe has been measured from proton-γ coincidences for excitation energies up to ≈11  MeV. The low-energy enhancement in the γ-ray strength function, which was first discovered in the (3He,αγ)56Fe reaction, is confirmed with the (p,p′γ)56Fe experiment reported here. Angular distributions of the γ rays give for the first time evidence that the enhancement is dominated by dipole transitions. © 2013 American Physical Societ

Low-energy enhancement and fluctuations of γ-ray strength functions in 56,57Fe: test of the Brink–Axel hypothesis

Nuclear level densities and γ-ray strength functions of 56,57Fe have been extracted from proton-γ coincidences. A low-energy enhancement in the γ-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in 57Fe indicate its dipole nature, in agreement with findings for 56Fe. The high statistics and the excellent energy resolution of the large-volume LaBr3(Ce) detectors allowed for a thorough analysis of γ strength as function of excitation energy. Taking into account the presence of strong Porter–Thomas fluctuations, there is no indication of any significant excitation energy dependence in the γ-ray strength function, in support of the generalized Brink–Axel hypothesis. This research was first published in Journal of Physics G: Nuclear and Particle Physics. © IOP Publishing

Low-energy enhancement in the γ-ray strength functions of Ge73,74

The γ -ray strength functions and level densities of 73,74Ge have been extracted up to the neutron-separation energy Sn from particle-γ coincidence data using the Oslo method. Moreover, the γ -ray strength function of 74Ge above Sn has been determined from photoneutron measurements; hence these two experiments cover the range of Eγ ≈ 1–13 MeV for 74Ge. The obtained data show that both 73,74Ge display an increase in strength at low γ energies. The experimental γ -ray strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74Ge are adopted in the calculations of the 72,73Ge(n,γ ) cross sections, where there are no direct experimental data. Calculated reaction rates for more neutron-rich germanium isotopes are shown to be strongly dependent on the presence of the low-energy enhancement

First evidence of low energy enhancement in Ge isotopes

The γ-strength functions and level densities of 73,74Ge have been extracted from particle-γ coincidence data using the Oslo method. In addition the γ-strength function of 74Ge above the neutron separation threshold, Sn = 10.196 MeV has been extracted from photoneutron measurements. When combined, these two experiments give a γ-strength function covering the energy range of ∼1-13 MeV for 74Ge. This thorough investigation of 74Ge is a part of an international campaign to study the previously reported low energy enhancement in this mass region in the γ-strength function from ∼3 MeV towards lower γ energies. The obtained data show that both 73,74Ge display an increase in strength at low γ energies