[en] Cross section measurements were made of prompt γ-ray production as a function of incident neutron energy on a ⁴⁸Ti sample. Partial γ-ray cross sections for transitions in ^45-48Ti, ^44-48Sc, and ^42-45Ca have been determined. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the LANSCE/WNR 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). The data are presented for neutron energies E_n between 1 to 200 MeV. These results are compared with model calculations which include compound nuclear and pre-equilibrium emission. The model calculations are performed using the STAPRE reaction code for E_n up to 20 MeV and the GNASH reaction code for E_n up to 120 MeV. Using the GNASH reaction code the effect of the spin distribution in preequilibrium reactions has been investigated. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). The multistep direct (MSD) part of the FKK theory was calculated for a one-step process. The contribution from higher steps is estimated to be small. The spin distribution of the multistep compound (MSC) part of FKK theory is assumed to be the same as in the compound nucleus. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations 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 preequilibrium effects is found to be significant. Specifically, the probability of γ transitions from a high spin state is strongly suppressed because of the preequilibrium spin distribution. Preequilibrium reactions are found to be important for neutron energies above 10 MeV

[en] Cross-section measurements were made of prompt discrete γ-ray production as a function of incident neutron energy (E_n = 1 to 35 MeV) on a ¹⁵⁰Sm sample fo 1550 mg/cm² of Sm₂O₃ enriched to 95.6% in ¹⁵⁰Sm. Results are compared with enhanced Hauser-Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ rays were detected with the Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ-rays up to E_x = 0.8 MeV in ¹⁴⁹Sm and one γ-ray transition between the first excited and ground state in ¹⁴⁸Sm were measured. Partial γ-ray cross sections were calculated using GNASH, an enhanced Hauser-Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic 'global' optical model potential parameters. The coupled-channel optical model based on the soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin distribution in ¹⁵⁰Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. the partial cross sections for discrete γ-ray cascade paths leading to the ground state in ¹⁴⁹Sm and ¹⁴⁸Sm have been summed (without double counting) to estimate lower limits for reaction cross sections. These lower limits are combined with Hauser-Feshbach model calculations to deduce the reaction channel cross sections. These reaction channel cross sections agree with previously measured experimental and ENDF/B-VII evaluations.

[en] Absolute partial γ-ray cross sections for the production of discrete γ-rays from the reaction ¹⁵⁰Sm(n,2nγ_i)¹⁴⁹Sm were measured using the GEANIE γ-ray spectrometer coupled with the intense white neutron source at WNR/LANSCE. The measurements were made for incident neutron energies between threshold (8.04 MeV) and 20 MeV. The partial cross sections for 21 γ-rays were extracted from the data. Of these, 17 were compared to calculations performed using the enhanced Hauser-Feshbach code STAPRE. The partial γ-ray cross sections of the observed parallel decay paths to the ground state were summed, forming a lower bound for the (n,2n) reaction channel. A combination of theory and experiment was then used to deduce the (n,2n) reaction channel cross section

[en] Cross section measurements were made of prompt γ-ray production as a function of incident neutron energy on a ⁴⁸Ti sample. Partial γ-ray cross sections for transitions in ^45--48Ti, ^44--48Sc, ^42--45Ca, ^41--44K, and ^41--42Ar have been determined. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the LANSCE/WNR 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). The data will be presented for neutron energies between 1 to 250 MeV. These results are compared with model calculations which include compound nuclear and pre-equilibrium emission

[en] The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E_n ∼ 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through γ-ray spectroscopy. Cross-section measurements were made of prompt γ-ray production as a function of incident neutron energy (E_n = 1 to 250 MeV) on a ⁴⁸Ti sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center 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). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations 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 preequilibrium effects is significant

[en] Prompt γ-ray production cross sections were measured on a ⁴⁸Ti sample for incident neutron energies from 1 MeV 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 LANSCE/WNR 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, pre-equilibrium 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

[en] γ-ray excitation functions have been measured for the interaction of fast neutrons with ⁴⁸Ti (neutron energy from 1 MeV to 250 MeV). The Los Alamos National Laboratory spallation neutron source, at the LANSCE/WNR facility, provided a ''white'' neutron beam which is produced by bombarding a natural W target with a pulsed proton beam. The prompt-reaction γ rays were measured with the large-scale Compton-suppressed Ge spectrometer, GEANIE. Neutron energies were determined by the time-of-flight technique. Excitation functions were converted to partial γ-ray cross sections, taking into account the dead-time correction, the target thickness, the detector efficiency, and neutron flux (monitored with an in-line fission chamber). The data analysis is presented here for neutron energies between 1 to 20 MeV. Partial γ-ray cross sections for transitions in ^47,48Ti, ⁴⁸Sc, and ⁴⁵Ca have been determined. These results are compared to Hauser-Feshbach predictions calculated using the STAPRE code, which includes compound nuclear and pre-equilibrium emission. The partial cross sections for γ rays, whose discrete γ-ray cascade path leads to the ground state in ⁴⁸Ti, ⁴⁷Ti, ⁴⁸Sc, and ⁴⁵Ca have been summed to obtain estimates of the lower limits for reaction cross sections. Partial cross sections for unobserved γ-rays are predicted from the STAPRE code. These lower limits are combined with Hauser-Feshbach calculations to deduce ⁴⁸Ti(n,n')⁴⁸Ti, ⁴⁸Ti(n,2n)⁴⁷Ti, ⁴⁸Ti(n,p)⁴⁸Sc, and ⁴⁸Ti(n,α)⁴⁵Ca reaction channel cross sections

[en] Cross-section measurements were made of prompt gamma-ray production as a function of incident neutron energy (E_n = 1 to 35 MeV) on an enriched (95.6%) ¹⁵⁰Sm 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 gamma 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 E_n ∼ 8 MeV 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

[en] We evaluated the nuclear data on titanium isotopes, ^46-50Ti. We used GNASH, a Hauser-Feshbach reaction model code, for the threshold reactions and CoH for the total and capture cross sections. While we calculated the transmission coefficients using well-known optical potentials for the GNASH calculation, we adjusted the level density and the pre-equilibrium parameters by taking into account the LANSCE/GEANIE experiment on ⁴⁸Ti reaction cross sections as well as other experiments available for (n,p), (n,α), etc. The direct inelastic scattering was also included by using the coupled-channel calculation and the DWBA method. The coupled-channels potential was assumed to be similar to the spherical potential of Koning and Delaroche with proper deformation parameters. Meanwhile we investigated the resolved resonance parameters in the energy region below several hundred keV. In essence, we adopted the parameters from the Mughabghab's 2006 compilation, making some adjustments to mainly reproduce the reference thermal cross sections. This new evaluation was validated with the MCNP calculations of k-eff's on seven hard-spectrum criticality experiments that involve Ti as a reflector or moderator

[en] Prompt γ-ray production cross section measurements were made as a function of incident neutron energy (En = 1 to 35 MeV) on an enriched (95.6%) ¹⁵⁰Sm 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). Above E_n ∼ 8 MeV 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 preequilibrium spin distributions were incorporated into the Hauser-Feshbach statistical reaction code GNASH and the γ-ray production cross sections were calculated and compared with experimental data. Neutron inelastic scattering populates 150Sm excited states either by (1) forming the compound nucleus ¹⁵¹Sm* and decaying by neutron emission, or (2) by the incoming neutron transferring energy to create a particle-hole pair, and thus initiating the pre-equilibrium process. These two processes produce rather different spin distributions: the momentum transfer via the pre-equilibrium process tends to be smaller than in the compound reaction. This difference in the spin population has a significant impact on the γ-ray de-excitation cascade and therefore in the partial γ-ray cross sections. The difference in the partial γ-ray cross sections using spin distributions with and without preequilibrium effects was significant, e.g., for the 558-keV transition between 8⁺ and 6⁺ states the calculated partial γ-ray production cross sections changed by 70% at E_n = 20 MeV with inclusion of the spin distribution of pre-equilibrium process