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The cross sections of the 89Y(p, γ)90Zr and the 121,123Sb(p, γ)122,124Te reactions were determined from γ-angular distribution measurements at beam energies from 1.6 to 3.4 MeV. In addition, angle-integrated cross sections were also measured at Ep = 2, 3, 4, and 4.8 MeV for the 89Y(p, γ)90Zr reaction using the 4π γ-summing method. Astrophysical S factors and reaction rates were deduced from the measured cross sections. Statistical model calculations were performed using the nuclear-reaction code TALYS. The results from the comparison between theory and experiment are discussed in detail. [ABSTRACT FROM AUTHOR]

Cross sections of proton capture reactions on 74Se, 78Se, and 80Se have been measured at incident beam energies from 2 to 6 MeV, 1.7 to 3 MeV, and 1.5 to 3.5 MeV, respectively. In the case of 78,80Se, cross sections were obtained from in-beam γ-angular distribution measurements, whereas for the 74Se isotope they were derived from off-beam activity measurements. The measured cross sections were compared with calculations performed with the nuclear reaction code talys (version 1.6). A good agreement between theory and experiment was found. Astrophysical S factors and reaction rates deduced from the experimental and calculated cross sections were also compared and the impact of different nuclear ingredients in the calculations on the reaction rates was investigated. It was found that, for certain combinations of nuclear input models, the reaction rates obtained at temperatures relevant to p-process nucleosynthesis differ by a factor 2 at the most, differences that are well within the acceptable deviations of calculated p-nuclei abundances and observations. [ABSTRACT FROM AUTHOR]

The cross sections of the 103Rh(p,γ)104Pd and the 113,115In(p,γ)114,116Sn reactions have been determined from γ angular distribution measurements carried out at beam energies from 2 to 3.5 MeV. An array of four highly efficient HPGe detectors all shielded with BGO crystals for Compton background suppression was used. Astrophysical S factors and reaction rates were deduced from the measured cross sections. Statistical model calculations were performed using the Hauser-Feshbach (HF) code TALYS and were compared with the new data. A good agreement between theory and experiment was found. In addition, the effect of different combinations of the nuclear input parameters entering the HF calculations on the ground-state reaction rates was investigated. It was found that these rates differ by a factor 3 at the most, being thus within the average discrepancies observed between calculated p-nuclei abundances and observations, if certain combinations of optical model potentials, nuclear level densities, and γ-ray strength functions are used. [ABSTRACT FROM AUTHOR]

Lifetimes of yrast and nonyrast states of 102Pd populated via the 92Zr( 13C, 3n) reaction are measured by means of the recoil distance Doppler-shift technique with a Cologne plunger coupled to a GASP spectrometer. The event-by-event data accumulated at 24 plunger distances in the range of 0.1 μm to 9 mm are analyzed using the differential decay curve method. The resulting B(E2) values of the γ transitions depopulating yrast-band members up to the I π = 8+ state are found to deviate significantly from the corresponding predictions of the E(5) critical-point symmetry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Astrophysical models studying the origin of the neutron-deficient ρ nuclides require knowledge of proton capture cross sections at low energy. The production site of the ρ nuclei is still under discussion but a firm basis of nuclear reaction rates is required to address the astrophysical uncertainties. Data at astrophysically relevant interaction energies are scarce. Problems with the prediction of charged particle capture cross sections at low energy were found in the comparisons between previous data and calculations in the Hauser-Feshbach statistical model of compound reactions. Purpose: A measurement of 74Ge(p, y)75As at low proton energies, inside the astrophysically relevant energy region, is important in several respects. The reaction is directly important because it is a bottleneck in the reaction flow which produces the lightest ρ nucleus 74Se. It is also an important addition to the data set required to test reaction-rate predictions and to allow an improvement in the global ρ + nucleus optical potential required in such calculations. Method: An in-beam experiment was performed, making it possible to measure in the range 2.1 ≤ Ep ≤3.7 MeV, which is for the most part inside the astrophysically relevant energy window. Angular distributions of the )/-ray transitions were measured with high-purity germanium detectors at eight angles relative to the beam axis. In addition to the total cross sections, partial cross sections for the direct population of 12 levels were determined. Results: The resulting cross sections were compared to Hauser-Feshbach calculations using the code SMARAGD. Only a constant renormalization factor of the calculated proton widths allowed a good reproduction of both total and partial cross sections. The accuracy of the calculation made it possible to check the spin assignment of some states in75 As. In the case of the 1075-keV state, a double state with spins and parities of 3/2- and 5/2- is needed to explain the experimental partial cross sections. A change in parity from 5/2+ to 5/2- is required for the state at 401 keV. Furthermore, in the case of 74Ge, studying the combination of total and partial cross sections made it possible to test the γ width, which is essential in the calculation of the astrophysical 74As(n,?)75As rate. Conclusions: Between data and statistical model prediction a factor of about two was found. Nevertheless, the improved astrophysical reaction rate of 74Ge(/?, γ) (and its reverse reaction) is only 28% larger than the previous standard rate. The prediction of the 74As(n,y)75As rate (and its reverse) was confirmed, the newly calculated rate differs only by a few percent from the previous prediction. The in-beam method with high-efficiency detectors proved to be a powerful tool for studies in nuclear astrophysics and nuclear structure. [ABSTRACT FROM AUTHOR]

The nuclear level density and the &ggr;-ray strength function have been determined for 43Sc in the energy range up to 2 MeV below the neutron separation energy using the Oslo method with the 46Ti(p, &agr;)43Sc reaction. A comparison to 45Sc shows that the level density of 43Sc is smaller by an approximately constant factor of two. This behavior is well reproduced in a microscopic, combinatorial model calculation. The &ggr;-ray strength function increases at low &ggr;-ray energies, a feature which has been observed in several nuclei but which still awaits theoretical explanation. [ABSTRACT FROM AUTHOR]

Background: In atomic nuclei, a concentration of electric dipole strength around the particle threshold, commonly denoted as pygmy dipole resonance, may have a significant impact on nuclear structure properties and astrophysical scenarios. A clear identification of these states and the structure of this resonance is still under discussion. Purpose: We present an experimental and theoretical study of the isospin character of the pygmy dipole resonance and investigation of a splitting of the electric dipole strength previously observed in experiments on N -- 82 nuclei. Method: The pygmy dipole resonance has been studied in the semi-magic Z = 50 nucleus 124Sn by means of the (α, α′;γ) coincidence method at Ea = 136 MeV using the Big-Bite Spectrometer at the Kernfysisch Versneller Instituut in Groningen, The Netherlands. Results: A splitting of the low-energy part of the electric dipole strength was identified in 124Sn by comparing the differential cross sections measured in (α, α′γ) to results stemming from (γ, γ′) photon-scattering experiments. While an energetically lower-lying group of states is observed in both kinds of experiments, a higher-lying group of states is only excited in the (γ, γ′) reaction. In addition, theoretical calculations using the self-consistent relativistic quasiparticle time-blocking approximation and the quasiparticle-phonon model have been performed. Both calculations show a qualitative agreement with the experimental data and predict a low-lying isoscalar component that is dominated by neutron-skin oscillations as expected for the pygmy dipole resonance. Furthermore, the states at higher energies show a pronounced isovector component and a different radial dependence of the corresponding transition densities as expected for the tail of the giant dipole resonance. Conclusions: An experimental signature of the neutron-skin oscillation of the pygmy dipole resonance has been corroborated. The combination of the presented reactions might make it possible to identify states of this resonance. [ABSTRACT FROM AUTHOR]

Primary &ggr;-ray spectra for a wide excitation-energy range have been extracted for 44Ti from particle-y coincidence data of the 46Ti(p,t&ggr;)44Ti reaction. These spectra reveal information on the &ggr;-decay pattern of the nucleus and may be used to extract the level density and radiative strength function applying the Oslo method. Models of the level density and radiative strength function are used as input for cross-section calculations of the 40Ca(&agr;,&ggr;)44Ti reaction. Acceptable models should reproduce data on the 40Ca(&agr;,&ggr;)44Ti reaction cross section as well as the measured primary &ggr;-ray spectra. This is only achieved when a coherent normalization of the slope of the level density and radiative strength function is performed. Thus, the overall shape of the experimental primary &ggr;-ray spectra puts a constraint on the input models for the rate calculations. [ABSTRACT FROM AUTHOR]

Particle-γ coincidences from the 46Ti(p,p'γ)46Ti inelastic scattering reaction with 15-MeV protons are utilized to obtain γ-ray spectra as a function of excitation energy. The rich data set allows analyzsis of the coincidence data with various gates on excitation energy. For many independent data sets, this enables a simultaneous extraction of level density and radiative strength function (RSF). The results are consistent with one common level density. The data seem to exhibit a universal RSF as the deduced RSFs from different excitation energies show only small fluctuations provided that only excitation energies above 3 MeV are taken into account. If transitions to well-separated low-energy levels are included, the deduced RSF may change by a factor of 2-3, which might be expected because of the involved Porter-Thomas fluctuations. [ABSTRACT FROM AUTHOR]

The cross sections of the 191 Ir (n, 2 n) 190 Ir and 191 Ir (n, 3 n) 189 Ir reactions have been determined by means of the activation technique, relative to the 27 Al (n, a) 24 Na reaction, at neutron beam energies higher than 15 MeV. The quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" by implementing the 3 H (d, n) 4 He reaction. The induced γ -ray activity of the irradiated target and reference foils was measured with high resolution, high purity germanium (HPGe) detectors. The cross section for the high-spin isomeric state (11 -) of the 190 Ir nucleus was determined along with the sum of the ground (4 -), the first (1 -), and the second (11 -) isomeric states. Moreover, the cross section for the production of the ground state of the residual nucleus of (n, 3 n) reaction, 189 Ir, was also estimated. Additionally, cross section theoretical calculations were carried out using the empire 3.2.2 and talys 1.8 codes, in which the input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the (n, 2 n), (n, 3 n), (n, p), (n, a), and (n, total) ones. Similar combination of theoretical model parameters had also been successfully used in the case of the neighboring 197 Au nucleus, and this constitutes an encouraging confirmation of how accurately the theoretical models can reproduce the experimental results in this mass region. [ABSTRACT FROM AUTHOR]

The 162Er(n,2n)161Er reaction cross section (Eth=9.26MeV) was measured at six incident neutron beam energies by means of the activation technique. Two energy regions were covered in the present work: the near-threshold energies between 10.7 and 11.3 MeV, as well as the higher energies from 17.1 up to 19.0 MeV. In this way, the energy range from the reaction threshold up to 19 MeV was experimentally mapped, considering also the existing experimental information around 14 MeV. The quasi-monoenergetic neutron beam at near-threshold energies was produced via the ²H(d,n)³He reaction, while the higher neutron beam energies were achieved by using the ³H(d,n)4He reaction. The primary deuteron beam was delivered in both cases by the 5.5 MV Tandem Van de Graaff accelerator of NSCR "Demokritos." Statistical model calculations were performed and compared with all the available experimental data. [ABSTRACT FROM AUTHOR]

The cross section of the 197Au(n,2n)196Au reaction has been determined at six energies ranging from 15.3-20.9 MeV by means of the activation technique, relative to the 27Al(n,α)24Na reaction. Quasimonoenergetic neutron beams were produced via the ³H(d,n)4He reaction at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR "Demokritos". After the irradiations, the induced γ-ray activity of the target and reference foils was measured with high-resolution HPGe detectors. The cross section for the high spin isomeric state (12-) was determined along with the sum of the ground (2-), the first (5+), and second (12-) isomeric states. Theoretical calculations were carried out with the codes empire 3.2.2 and talys 1.8. Optimum input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the (n,elastic), (n,2n), (n,3n), (n,p), (n,α), and (n,total) ones. [ABSTRACT FROM AUTHOR]

The nuclear level density and the γ-ray strength function have been extracted for 89Y by using the Oslo method on 89Y(p,p'γ)89Y coincidence data. The γ-ray strength function displays a low-energy enhancement consistent with previous observations in this mass region (93-98Mo). Shell-model calculations support the conclusion that the observed enhancement is due to strong, low-energy M1 transitions at high excitation energies. The data were further used as input for calculations of the 88Sr(p,γ)89Y and 88Y(n,γ)89Y cross sections with the talys reaction code. Comparison with cross-section data, where available, as well as with values from the BRUSLIB library, shows a satisfying agreement. [ABSTRACT FROM AUTHOR]

The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn with the (α, α'γ) coincidence method at Eα=136 MeV. The comparison with results of photon-scattering experiments reveals a splitting into two components with different structure: one group of states which is excited in (α, α'γ) as well as in (γ, γ') reactions and a group of states at higher energies which is only excited in (γ, γ') reactions. Calculations with the self-consistent relativistic quasiparticle time-blocking approximation and the quasiparticle phonon model are in qualitative agreement with the experimental results and predict a low-lying isoscalar component dominated by neutron-skin oscillations and a higher-lying more isovector component on the tail of the giant dipole resonance.

The angular distributions of gamma rays from the 12C(alpha,gamma)16O reaction have been measured at 20 energy points in the energy range E(cm) = 0.95 to 2.8 MeV. The sensitivity of the present experiment compared to previous direct investigations was raised by 1-2 orders of magnitude, by using an array of highly efficient ( 100%) Ge detectors shielded actively with BGOs, as well as high beam currents of up to 500 microA that were provided by the Stuttgart Dynamitron accelerator. The S(E1) and S(E2) factors deduced from the gamma angular distributions have been extrapolated to the range of helium burning temperatures applying the R-matrix method, which yielded S(300)(E1) = (76+/-20) keV b and S(300)(E2) = (85+/-30) keV b.