Γ-ray Excitation Functions Research Articles

Neutron scattering differential cross sections for 23Na from 1.5 to 4.5 MeV

Measurements of neutron elastic and inelastic scattering cross sections from 23Na have been performed for sixteen incident neutron energies between 1.5 and 4.5 MeV. These measurements were complemented by γ-ray excitation functions using the (n,n′γ) reaction to include excited levels not resolved in the neutron detection measurements. The time-of-flight (TOF) technique was employed for background reduction in both neutron and γ-ray measurements and for energy determination in neutron detection measurements. Previous reaction model evaluations relied primarily on neutron total cross sections and four (n, n0) and (n, n1) angular distributions in the 5 to 9 MeV range. The inclusion of more inelastic channels and measurements at lower incident neutron energies provide additional information on direct couplings between elastic and inelastic scattering as a function of angular momentum transfer. Reaction model calculations examining collective direct-coupling and compound absorption components were performed.

Differential Cross Sections for Neutron Elastic and Inelastic Scattering on23Na

Measurements of neutron elastic and inelastic scattering from 23Na have been performed for sixteen incident neutron energies above 1.5 MeV with the 7-MV University of Kentucky Accelerator using the 3H(p,n) reaction as the neutron source. These measurements were complemented by γ-ray excitation functions using the (n,n'γ) reaction. The time-of-flight technique is employed for background reduction in both neutron and γ- ray measurements and for determining the energy of the scattered neutrons. Cross section determinations support fuel cycle and structural materials research and development. Previous reaction model evaluations [1] relied primarily on total cross sections and four (n,n0) and (n,n1) angular distributions in the En = 5 to 9 MeV range. The inclusion of more inelastic channels at lower neutron energies provides additional information on direct couplings between elastic and inelastic scattering as a function of angular momentum transfer. Reaction model calculations examining direct collective and statistical properties were performed.

Gamma-Ray Production Cross Sections in Multiple Channels for Neutron-Induced Reaction on 48Ti for En = 1 to 200 MeV

Prompt γ-ray production cross sections were measured on a 48Ti sample for incident neutron energies from 1 to 200 MeV. Partial γ-ray cross sections for transitions in 45-48Ti, 45-48Sc, and 43-45Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial γ-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center/Weapons Neutron Research facility. The prompt-reaction γ rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, preequilibrium emission, and direct reaction mechanisms are included. Overall, the model calculations of the partial γ-ray cross sections are in good agreement with measured values.

Neutron induced inelastic cross-sections of 150Sm for En = 1–35 MeV

Cross-section measurements were made of prompt γ-ray production as a function of incident neutron energy (En=1–35MeV) on an enriched (95.6%) l50Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction γ-rays were detected with the large-scale Compton-suppressed germanium array for neutron induced excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross-sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Partial γ-ray cross-sections were predicted using the Hauser–Feshbach statistical reaction code GNASH. Above En∼8MeV, the pre-equilibrium reaction process dominates the inelastic reaction. The spin-distribution transferred in pre-equilibrium neutron induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman and Koonin (FKK). These pre-equilibrium spin distributions were incorporated into a new version of GNASH and the γ-ray production cross-sections were calculated and compared with experimental data. The difference in the partial γ-ray cross-sections using spin-distributions with and without pre-equilibrium effects is discussed.

Lifetime measurements and low-lying structure in 112Sn

The low-lying structure of 112Sn has been studied. γ-ray excitation functions, ranging from 2.5 to 4.0MeV, and angular distributions at 2.9 and 3.8MeV have been measured following the (n; n′γ) reaction to characterize the decays of the excited levels. Level lifetimes have been measured with the Doppler-shift attenuation method. Low-lying 1−, (2−), 3− and, 5− states have been identified as members of the heterogeneous quadrupole-octupole quintuplet. Decay properties and excitation energies are consistent with the structure formed by the coupling of the lowest quadrupole, 2 1 + , and octupole, 3 1 − , excitations.

Decay of the 67-μs Isomer in 142Pm

Excited states in 142Pm are investigated via the128Te(19F, 5n)142Pm reaction at beamenergies from 75 to 95 MeV by using techniques of in-beam γ-rayspectroscopy. Measurements of γ-ray excitation function, X–γ andγ–γ–t coincidences are performed with 10 BGO(AC)HPGe detectors.Decay of the previously known 67-μs isomer in 142Pm is observedand added into the new level scheme. This isomer is definitely placedat the excitation energy of 2828.5 keV. The spin of this isomer issuggested to be 13 ℏ according to the measured γ-ray anisotropies.

Excited States in 207Rn

Excited states in 207Rn are investigated via the196Pt(16O,Sn)207Rn reaction at beam energies from85 to 95 MeV using techniques of in-beam γ-ray spectroscopy.Measurements of γ-ray excitation function, x-γ and γ-γ-tcoincidences are performed with ten BGO(AC)HPGe detectors. Based onthese measurements, a level scheme of 207Rn, including 17 γ-raysand 18 levels, is established. Spins for most of the levels areproposed according to the measured DCO ratios. The level structure iscompared with a weak-coupling calculation using the interactionenergies extracted from neighbouring nuclei.

In-beam study of 145Tb

The high-spin states of 145Tb have been studied in the 118Sn(32S, 1p4n) reaction at 32S energies from 161 to 175 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, a level scheme for 145Tb was established for the first time. The observed excited states show typical irregular pattern in a spherical nucleus, and the low-lying levels have been interpreted qualitatively with a particle-core coupling.

Level sructure in 206At

The high-spin states of 206At have been studied in the reaction 197Au (12C,3n) 206At at 12C energies from 60 to 80 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences, and γ-ray angular distributions were carried out with seven BGO(AC)HPGe detectors and one intrinsic Ge planar detector. A level scheme for 206At with 25 γ rays was established for the first time, including a 10− isomer with a measured half-life of 410 ± 80 ns. The level scheme of 206At consists of two disconnected cascades, probably corresponding to the proton excitations and the neutron-hole excitations, respectively.

High-spin states in198Bi

The high-spin states of198Bi have been studied in the reaction187Re(16O, 5n)198Bi at16O energies from 85 to 105 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences and γ-ray angular distributions were carried out with six BGO(AC)HPGe detectors and one intrinsic Ge planar detector. A level scheme for198Bi- with 26 γ rays was established for the first time, including a 15+ isomer with a measured half-life of 8.0±3.6 ns.

New Isomeric States in 197Bi

The high-spin states in 197Bi have been studied with the 187Re(16O,6n) reaction at 16O energies from 85 to 105 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences and γ-ray angular distributions were carried out with six BGO(AC)HPGe detectors and one intrinsic Ge planar detector. Eleven new transitions and three new isomers were observed, and a level scheme for 197Bi was established. Some differences between the present work and the previous results were found.

Level and decay scheme of141Pr by means of the (n, n′γ) and (n, n′γ-γ) reactions

Excited states of141Pr have been studied via the (n,n′γ) and (n,n′γ-γ) reactions, for incident neutron energies from 1.0 MeV to 2.8 MeV. From the analysis of the single and coincident γ-ray spectra a detailed level and decay scheme was constructed up to the excitation energy of 2499 keV. Level spins and parities were deduced on the basis of extensive comparison between the measured γ-ray excitation functions and the theoretical predictions based on the statistical model of the compound nucleus.

On the resonant behavior of the16O+15N reaction

The16O+15N reaction products have been studied by the γ-ray detection method in the CM energy range 15.5 to 36.1 MeV and by the kinematical coincidence method at energies ranging from ECM=20.6 to 33.5MeV. The γ-ray yield excitation function of the16O 3−inelastic channel shows the existence of resonant structures. Two structures with ∼ 1.6 MeV width are observed in the large angle elastic scattering excitation function, they are correlated with the resonances seen in the inelastic channel. Angular momentum assignments were made from the elastic backward angular distributions.

Level scheme and mixed-symmetry states of 134Ba from in-beam (n, n′γ) measurements

The decay properties of the existed states of 134Ba below 3 MeV have been studied with the (n, n′γ) reaction. From γ-ray excitation function and angular distribution measurements, several new levels, spin-parity values and multipole mixing ratios were obtained. Lifetimes were measured by the Doppler-shift attenuation method, and reduced transition probabilities were calculated for a number of levels using the proton-neutron interacting boson model. The 2029 and 2088 keV states appear to share the properties of the lowest mixed-symmetry 2 + state.

Neutron-core excitations in the N=50 nucleus 89Y

High-spin states of the N=50 nucleus 89Y up to 312h̷ at 8.7 MeV have been investigated in the (α,2n) reaction by using in-beam γ-ray spectroscopy. Besides singles γ-ray spectra, excitation functions and γγ-coincidences, the angular distribution and linear polarization of the γ-rays have been measured. For 23 of the observed 28 levels, mean lifetimes or limits have been determined by means of the Doppler-shift attenuation of γ-r.f. methods. In order to calculate the stopping of recoils in the two-component RbCl target a new procedure had to be developed. On the basis of all these experiments several new levels as well as many spin/parity values could be uniquely assigned. The most surprising results are the observed high level density at spin 232and252 and the identification of several fast M1-transitions at high spin. Both results may be explained by the inclusion of neutron particle-hole excitations across the closed N=50 shell. No collective E2 transitions have been found. The experimental results are compared with shell model calculations.

Energy levels and γ-decay scheme of141Pr via the (n, n′ γ) reaction

The γ-radiation following the inelastic scattering of neutrons in141Pr was studied for incident-neutron energies ranging from 600 keV to 2800 keV. From the analysis of the measured spectra and experimental excitation functions of the emitted γ-rays, the level and decay scheme of141Pr nucleus was determined and 8 levels and 28 γ-decays have been observed for the first time in the present work.

Excited states in93Nb

Excited states of93Nb have been studied by means of the γ-ray spectroscopy via the93Nb(n,n′-γ) reaction for incident neutron energies from 870 keV to 2700 keV. From the analysis of the γ-ray single and γ-γ coincidence spectra, a detailed decay scheme of the nucleus was constructed up to the excitation energy of 2584 keV. Level spins and parities were deduced on the basis of extensive comparisons between the measured γ-ray excitation functions and the theoretical prediction based on the statistical model of the compound nucleus.

A study of the level and decay scheme of97Mo via the (n, n′γ) reaction

The results of a measurement of the97Mo (n,n′γ)97Mo reaction are presented for incident-neutron energies ranging from 1200 to 3200 keV. From the examination of the experimental excitation functions of the emitted γ-rays, the level and decay scheme of the97Mo nucleus was determined. Seven levels and 33 γ-decays have been observed for the first time in the present work.

High-spin states in 143Nd produced in the 130Te( 18O, 5n) heavy ion reaction

High-spin states in 143Nd have been produced by the 130Te( 18O, 5n), reaction. The level scheme has been constructed with the aid of excitation functions of the singles γ-rays and γγ-coincidence measurements. Lifetime results or upper limits have been deduced by the recoil-distance Doppler-shift technique for almost all the observed levels. Spins up to 45 2 have been assigned to the states by utilizing the angular distribution measurements combined with the DCO method and transition probability considerations. Configuration assignments to the levels have been discussed on the basis of energy and lifetime comparison with the shell model calculated yrast states and their deduced mode of de-excitation. All the states decay with a 33(4)% long component of τ = 3.05(10) nsec indicating that the levels are populated partially through a side band originating at an unobserved 3 nsec isomer reminiscent of the T 1 2 = 550 nsec isomer in 147Gd.

Stellar reaction rate of 14N(p, γ) 15O and hydrogen burning in massive stars

The capture reaction 14N(p, γ) 15O has been investigated in the energy range E p = 0.2 to 3.6 MeV with the use of windowless gas targets as well as implanted 14N solid targets of high isotopic purity. The measurement of absolute cross sections, γ-ray angular distributions and excitation functions is reported. The data provide information on the capture amplitudes involved in the transitions to all bound states of 15O. The astrophysical S-factor at stellar energies has been determined by means of theoretical fits. The result of S(0) = 3.20 keV · b is in good agreement with the value incorporated in the compilations. Also discussed are the nuclear physics aspects of the data.