Cross sections for the (n,n') and (n, 2n) reactions on 113In and 204Pb

The cross sections for the (n, n')^m and (n, 2n) reactions on the target nuclei ¹¹³In and ²⁰⁴Pb were measured by the activation method in the neutron energy range 13 to 18 MeV. The results were compared with the predictions of compound nucleus theory. The angular momentum effects and the γ-decay of unbound states were taken into account.     

Cross sections for the (n,n′), (n,p) and (n, 2n) reactions on 107Ag and 109Ag isotopes

The cross sections for (n, n′), (n, p) and (n, 2n) reactions on the target nuclei ¹⁰⁷Ag and ¹⁰⁹Ag were measured by the activation technique in the neutron energy range 13 to 18 MeV. The results are interpreted in terms of the compound nucleus and precompound emission models.     

Cross-sections for the formation of isomeric pair Ge through (n, 2n), (n, p) and (n, α) reactions measured over 13.73 MeV to 14.77 MeV and calculated from near threshold to 20 MeV neutron energies

The cross-sections for formation of isomeric pair, ⁷⁵Ge^m(σ_m) and ⁷⁵Ge^g(σ_g), through ⁷⁶Ge(n, 2n), ⁷⁵As(n, p) and ⁷⁸Se(n, α) reactions were measured at 13.73 MeV, 14.42 MeV and 14.77 MeV neutrons and also estimated using EMPIRE-II and TALYS codes over neutron energies from near threshold to 20 MeV. For each (n, 2n), (n, p) and (n, α) reaction, the cross-section initially increases with neutron energy, but starts decreasing as the neutron energy exceeds the respective threshold of (n, 3n), (n, pn) and (n, αn) reactions. The higher values of σ_m relative to σ_g reveal that the transitions of the excited ⁷⁵Ge from higher energy levels to metastable state (7⁺/2) are favored as compared to unstable ground state (1⁻/2). The present values of cross sections for formation of ⁷⁵Ge^m,g through (n, 2n) and (n, α) reactions are lower, and that of (n, p) reaction are higher compared to most of the corresponding literature cross-sections.     

Measurements of activation cross-sections for 165Ho(n,2n)164gHo and 180W(n,2n)179gW reactions induced by neutrons around 14 MeV

The cross-sections of ¹⁶⁵Ho(n,2n)^164gHo and ¹⁸⁰W(n,2n)^179gW reactions induced by neutrons around 14 MeV were measured using activation technique and calculated by a previously developed formulas, in which the neutron flux was determined using the monitor reaction ⁹³Nb(n,2n)^92mNb. Because both of the excited and ground states were produced in each of the two reactions, one formula was introduced to take out the effect from excited state. Comparison between this work and old data were given.     

A generalized r-matrix interpretation of the 89Y + n total cross section at low incident energies

The resonance structure observed in the ⁸⁹Y(n, n)⁸⁹Y total cross-section measurements in the range of 0.9 to 1.2 MeV neutron energy is investigated using a comprehensive theory of nuclear reactions. A shell-model calculation which formed the initial stage of this study predicts satisfactorily the energies of the negative-parity states that contribute to the observed anomalies. The neutron decay widths for these resonances are evaluated using the model wave functions. The general trends in the energy dependence of the total cross section are satisfactorily reproduced by the theory. The factors that could contribute to the discrepancies between theory and experiment are discussed. The theoretical estimates of the damping widths for the two 1^? anomalies that occur in this region were within 20 to 25% of the experimental values and support the view that these are intermediate-type resonances. Their configurational structure as predicted by the model calculation suggests that they are the parent states of the T_> components of the giant dipole resonance near 21.0 MeV in ⁹⁰Zr. The distribution of E1 widths calculated for a proposed 1^? → 2⁺ (at 0.78 MeV) transition in ⁹⁰Y indicates that an anomaly corresponding to these 1^? states can also be expected in the (n, γ) reaction.     

Direct and compound contributions to (n, γ) cross sections

We have investigated the direct and compound nucleus contributions to the²⁰⁸Pb (n, γ)²⁰⁹Pb reaction in the region 2.25–7.25 MeV. We have used for the compound nucleus cross sections a modified Hauser-Feshbach theory in the presence of direct reactions. The corrections to the traditional Hauser-Feshbach theory are found to be small in this case.     

9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.     

Measurement of neutron polarization from (d,n) reactions on Mg,Si and Ca and comparison to DWBA calculations

Angular distributions of the neutron polarization produced in (d, n) reactions on ²⁴Mg and ²⁸Si were obtained in about 300 keV steps from 3.9 MeV down to 2.2 and 2.9 MeV, respectively. Excitation functions of the polarization were measured at 20° and 40° (lab) over these energy ranges. Polarization angular distributions were also measured for (d, n) reactions on ²⁸Si at 8.1 MeV and ⁴⁰Ca at 3.8 MeV. DWBA calculations are compared to the latter distributions as well as to the (d, n) cross-section data. Fluctuations in the low-energy polarization d ata from the ²⁴Mg and ²⁸Si targets made DWBA comparison of questionable value.     

(n, α) Reactions on light nuclei atE n =13.9 MeV

The reactions¹⁴N (n, α)¹¹B and¹⁰B(n, α)⁷Li were studied with 13.9 MeV neutrons using a counter telescope. Differential cross sections were measured for the transitions to the ground states and to some excited states. The results provide evidence for a strong contribution from a direct reaction mechanism. Systematics of integrated cross sections for the ground state transitions of all known (n, α) reactions on light nuclei with 14 MeV neutrons is also given.     

Study of the excitation of high-spin isomers in <Superscript>190</Superscript>Ir and <Superscript>196,198</Superscript>Au in the near-threshold region

The isomeric ratios of the yields for ^190m,g Ir and ^196m,g Au have been measured in the (γ,n) reaction in the near-threshold region at γ-ray energies of 12 and 12.5 MeV. The isomeric ratios for ^198m,g Au have been measured in the (d,p) and (n,γ) reactions. The statistical nature of the (γ,n) and (n,γ) reactions is shown.     

Cross sections for the (n,p) and (n,n′) reactions on Pd,Cd and Os

The cross sections for the ¹⁰⁵Pd(n, p)¹⁰⁵Rh, ¹¹¹Cd(n, n′)^111mCd, ¹¹²Cd(n, p)¹¹²Ag and ¹⁹⁰Os(n, n′)^190mOs reactions were measured by the activation method in the neutron energy range from 13 to 17 MeV. The results of the measurements are compared with the predictions of the compound and the precompound emission models.     

(n,t) and (n, α) reactions on 9Be

A metallic ⁹Be target was bombarded with 13.99 MeV neutrons; α-particles, tritons and ⁶He recoil nuclei were detected and identified with a telescope consisting of two proportional counters and a solid state detector. Absolute differential cross sections were measured for the (n, t) reactions leading to the ground state and first excited state of ⁷Li and for the (n, α) reactions leading to the ground state and first excited state of ⁶He. No evidence for higher excited states in ⁶He has been found. An attempt has been made to interpret the observed (n, α) angular distributions in terms of the direct reaction model.     

Effects of exchange and final-state interactions in the reactions 2H(3He, 3H p)p and 2H(3He, 3He p)n

Absolute coincidence cross sections for the ²H(³He, ³He p)n and ²H(³He,³H p)p reactions were measured at E_He = 35.9 MeV. Spectra dominated by the nucleon-nucleon final-state interaction (FSI) are fitted by a fully antisymmetrized PWBA theory which includes the effects of FSI in all its matrix elements. Previously reported 26.8 MeV data showing both FSI and quasi-elastic scattering (both with and without charge exchange) are also fitted by the theory, which qualitatively describes the shapes of all these spectra and the ratios of the cross sections for the various processes. Predictions of Watson-Migdal theory are fitted to the FSI spectra and differences between the two theories are analyzed.     

Long-lived isomers in 190Ir

Long-lived isomeric states in ¹⁹⁰Ir have been investigated with the ¹⁹²Os(p,3n) ¹⁹⁰Ir and ¹⁹²Os(d,4n) ¹⁹⁰Ir reactions using beams of 18–31 MeV protons and 27.8 MeV deuterons, respectively. A series of measurements, including excitation functions, half lives, e⁻γ coincidences and e⁻e⁻ coincidences, was performed. Five new transitions were observed, and the results of e⁻γ and e⁻e⁻ coincidences indicate that these transitions are fed by the 148.7 keV M4 transition that depopulates the 11⁻ isomer. The previous decay scheme is shown to be incorrect, and the results allow the ground state parity and mass excess to be determined.     

Initial-state distortion and final-state interactions in the 2H(3He, 3He p)n and 2H(3He, 3H p)p reactions

The predictions of two fully antisymmetrized reaction theories (DWBA and PWBA-FSI) are compared with absolute coincidence cross sections for the ²H(³He, ³He p)n and ²H(³He, ³H p)p reactions exhibiting final-state interactions (FSI) and quasi-elastic scattering (QES) both with and without charge exchange. The DWBA theory takes into account both the initial ³He-d and the final N-N interactions, while the PWBA-FSI theory includes only the latter. New QES data at E_He = 35.9 MeV, as well as previously reported 26.8 and 35.9 MeV data, are fitted. The DWBA theory gives good fits, both in shape and magnitude, to spectra showing N-N final-state interactions but gives somewhat poorer fits to QES spectra whose predicted magnitudes are two to ten times too large. The PWBA-FSI theory always predicts cross sections that are too large; however the predicted shapes are about as good as those from the DWBA. The initial-state interaction is shown to affect both the width and position of QES peaks from these reactions.     

High energy 2H(α, αp)n reaction

The ²H(α, αp)n reactions at 78.3 and 165 MeV lab energy are analysed by the semi-phenomenological method which was introduced in a previous paper. The same parameter set is adopted for both the 78.3 and 165 MeV cases. The agreement with data is excellent, as well as in low energy cases. The results indicate strongly that the even parity (D- and G-waves) reactions are very strong while the odd parity (P- and F-waves) ones are definitely weak.     

The Zr(d,n)Nb and Zr(d,n)Nb reactions

The (d, n) reaction on ⁹⁰Zr and ⁹⁶Zr has been studied at 12 MeV deuteron bombarding energy using the neutron time-of-flight technique with an overall neutron time resolution of 1.9 ns. Angular distributions of neutron groups leading to states in ⁹¹Nb and ⁹⁷Nb were measured in the angular range between 15° and 60°. The measured cross sections were analyzed in the framework of the distorted-wave theory of stripping reactions to deduce l-values and proton spectroscopic factors of states in the residual nuclei. The results are compared with the corresponding data available from (³He, d) studies. The fractionation of the single-particle proton states and their centroid energies are determined.     

The excitation function for the 89Y(n, 2n)88Y reaction

Activation cross sections for the ⁸⁹Y(n, 2n)⁸⁸Y reaction at neutron energies between 12.6 and 17.8 MeV have been measured by using the mixed-powder method and γ-ray detection by a Ge(Li) spectrometer. Using the ²⁷Al(n, α)²⁴Na reaction for monitoring the neutron flux, the measured cross-section values for the ⁸⁹Y(n, 2n)⁸⁸Y reaction were found to be 331±32 mb, 603±58 mb, 820±79 mb, 1040±100 mb, 1072±103 mb, 1172±112 mb, 1221±117 mb and 1218±117 mb at the respective incident neutron energies of 12.6±0.1 MeV, 13.3±0.1 MeV, 14.0±0.4 MeV, 14.9±0.3 MeV, 15.1±0.3 MeV, 16.0±0.4 MeV, 16.7±0.5 MeV and 17.8±0.7 MeV. The measured values are compared with the experimental values of others and with the theoretical values obtained from calculations based on the statistical model for the formation of a compound nucleus and its subsequent emission of neutrons.     

Forward peaking of near Coulomb energy protons in (n,p) reactions at 14.1 MeV

We apply a modified statistical model of compound nucleus reactions to analyse low energy proton angular distributions from the ⁹³Nb(n, p), ^natAg(n, p) and ^natIn(n, p) reactions at E_n=14.1 MeV. The forward peaking at the maximum of the proton evaporation spectrum at E _p = 6–8 MeV is reproduced and interpreted as an indication of the decay of thermalized-nonequilibrated nuclear states.