Volume form of coupling interaction in semi-direct (n, γ) and (p, γ) reactions

A coupling interaction between the nucleon and the nuclear E1 mode having a volume radial form instead of the usual surface one is used in the semi-direct nucleon radiative-capture theory. The calculated cross sections for the ²⁰⁸Pb(n,γ) and ¹⁴²Ce(p,γ) reactions in the giantresonance region reproduce the measured ones both in shape and magnitude. Satisfactory agreement is achieved in comparing the predicted and detected γ-ray spectra following neutron capture by ²⁰⁸Pb. A detailed analysis of the energy and angular-momentum dependence of the matrix elements when the volume and surface form factors are used, is performed.     

Thermonuclear reaction rates from (p,n) reactions

Thermonuclear reaction rates for the temperature range 1≤T ₉≤5 have been extracted from experimentally measured (p, n) cross sections for⁴⁵Sc⁵⁰Ti,⁵¹V,⁵⁴Cr,⁵⁵Mn and⁵⁹Co nuclides below 5 MeV bombarding energy. These reaction rates are important in the build-up of medium and heavy nuclides in the stellar evolution process and nucleosynthesis. To enhance the usefulness of these reaction rates in astrophysical calculations, they have been fitted to an analytic function of temperature, valid throughout the temperature range considered here.     

Forward (p,n) reactions and nucleon-nucleon scattering

Forward (p, n) reaction cross sections are expressed in terms of nucleon-nucleon phase shifts. The ratio of the probabilities for triggering Gamow-Teller or Fermi transitions is found to be in quite good agreement with experiment. New np scattering experiments are also suggested in order to improve the interpretation of (p, n) reactions.     

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.     

Measurement of (p,n) and (n,p) reactions on 6Li and 7Li at 800 MeV

The measured ⁷Li(p,n), and ⁶Li(n,p) cross sections at 0° show a high-energy peak (≈25 MeV/c FWHM) which we attribute primarily to nuclear charge exchange leading to final states in ⁷Be, ⁶Be, and ⁶He, respectively. By contrast, the ⁷Li(n,p) cross section at O° shows a broad weak high-energy peak believed due mostly to break-up processes. At 16°, the ^6,7Li(n,p) cross sections are dominated by quasi-elastic scattering.     

The (γ, p n) and (γ, 3p3n) reactions in40Ca at intermediate energies

The yields of the reactions⁴⁰Ca(γ, p n)^38g K and⁴⁰Ca(γ, 3p 3n)^34m Cl have been measured by the activation method in the energy range 80–800 MeV. From the measured yields the cross sections are deduced. The experimental cross sections are compared to calculations with a cascade-evaporation model for photo-induced reactions.     

Analysis of (n,n) and (d,p) reactions on the same target using phase-equivalent potentials

The difference between (d, p) “Stripping into Continuum” and (n, n) Elastic Scattering on the same target has been investigated and discussed in terms of a non-local force and its local equivalent. In general our results indicate an influence of non local effects. In particular with the inclusion of the non locality a possible spin assignment for the levels at the excitation energiesE _x =3.359 MeV and 3.519 MeV in the reaction¹⁵N(d, p)N¹⁶ (unbound) has been indicated.     

Cross-sections of a few (n,α) and (n,p) reactions induced at 14.7 MeV neutrons

Cross-sections of the nuclear reactions²⁷Al(n, p)²⁷Mg,³⁰Si(n, α)²⁷Mg,⁵²Cr(n, p)⁵²V,⁵³Cr(n, p)⁵³V,⁵⁴Cr(n, p)⁵⁴V,⁵⁴Cr(n, α)⁵¹Ti and¹²⁰Sn(n, α)¹¹⁷Cd at 14.7 Mev neutrons were measured using⁵⁶Fe(n, p)⁵⁶Mn and²⁷Al(n, α)²⁴Na as monitor reactions. For comparison, theoretical values of the cross-section for these reactions were also obtained through different approaches of compound nucleus theory and computer code Alice. Accuracies achieved in the present measured values of the cross-sections are better than those available in literature.     

Energy levels of80,82Br from (p,nγ) reactions

The levels of odd-odd^{80, 82}Br nuclei have been investigated via^{80, 82}Se(p, nγ)^{80, 82}Br reactions. Excitation functions and angular distributions were analysed with the Hauser-Feshbach compound nucleus theory. 27 and 29 levels have been identified. The transitions connecting the first 1⁺ and 2^?levels have been studied by the delayed coincidence method and their half-lives are 7.8±0.5 ns and 7.2±0.8 ns for⁸⁰Br and⁸²Br respectively. The experimental results are discussed in the framework of thej- j coupling.     

Preequilibrium emission in (p,x n) reactions on palladium isotopes

Energy spectra of neutrons from the^{104, 105, 106, 108, 110}pd(p, xn) reactions atE _p=26.1 MeV have been measured using the time-of-flight technique with good overall energy resolution (< 250=" kev).=" the=" hard=" part=" of=" angle-integrated=" spectra=" corresponding=" to=" low=" residual=" excitations=">U6MeV) exhibits pronounced structure varying from isotope to isotope. The observed structure can be reasonably well described by preequilibrium-model calculations with two-quasiparticle state densities for proton-particle neutron-hole configurations based on Nilsson-model single-particle levels instead of equidistant ones. The influence of nuclear deformation and pairing on preequilibrium particle emission is explored.Supported in part by the exchange program of the Universities of Hamburg and Zagreb, Internationales Büro — KFA Jülich, and by the BMFT (Contract 06 HH 142)     

Total cross sections for some (α, n) and (α, p) reactions in medium-weight nuclei

Total cross sections have been measured for the ⁴⁵Sc(α, n), ⁴⁶Ti(α, n), ⁵⁰Cr(α, n), ⁵¹V(α, n), ⁵⁴Fe(α, n) and ⁵⁸Ni(α, p) reactions, and stellar reaction rates have been calculated from them. These have been compared to recent theoretical calculations which used compound nuclear theory. The calculated values are generally higher than the experimental values by factors ranging from 2 to 10.     

A systematic study of (n,d), (n,n' p) and (n,pn) reactions at 14.7 MeV

Cross sections for [(n, d) + (n, n′p) + (n, pn)] reactions induced by 14.7 ± 0.3 MeV neutrons on ⁴⁴Ca, ⁴⁹Ti, ⁵⁰Cr, ^{67, 68}Zn, ⁹²Zr and ^{97, 98}Mo have been measured by the activation technique using enriched isotopes as target materials, modern radiochemical separations and high-resolution counting methods. A brief summary of the literature data and our own earlier measurements is given. Our activation data are generally in agreement with those deduced from emitted charged particle characterisation. Some systematic trends in the activation cross-section data were analysed. Similar to other (n, charged particle) reactions, the [(n, d) + (n, n′p) + (n, pn)] reaction cross section decreases as a function of (N?Z)/A; the data, however, fall on two curves, one for nuclei with neutron separation energies (S_n higher than the proton separation energies (S_p) and the other for nuclei with S_n < S_p. For nuclei with S_n ? S_p the (n, n′p) process is very important. Detailed Hauser-Feshbach calculations show that in general contributions of statistical processes to the (n, d) reaction cross section are very small.     

An investigation of 73As energy levels by means of (p,n) and (p,nγ) reactions

The energy levels of ⁷³As were studied by means of the ⁷³Ge(p, n)⁷³As reaction at proton energies between 2.1 and 3.3 MeV. Neutron energies were measured by time of flight, and γ-ray energies with Ge(Li) detectors. The γ-decay of levels was studied by means of γ-n coincidences. Angular distributions were measured for the strongest de-excitation γ-rays, and relative excitation strengths of levels were derived from the neutron spectra. These are compared with predictions of the statistical theory to derive spins for a number of levels. A level and decay scheme for ⁷³As up to 1.98 MeV excitation is presented.     

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.     

A microscopic multi-channel calculation for the reactions 7Li(p,p)7Li and7Li(p,n)7Be

Based on a refined resonating group method a microscopic multi-channel calculation for the reactions ⁷Li(p, p)⁷Li and ⁷Li(p, n)⁷Be has been performed. Diagonal S-matrix elements and differential cross sections are presented from the ⁷Li-p threshold up to E = 2.5 MeV c.m. and compared with experimental data.     

A microscopic model analysis of the 90Zr(p,n) IAS transition

Direct reaction (p, n) data to the isobaric analogue of the ground state of ⁹⁰Zr is analysed within a DWA using a complex effective two-nucleon transition interaction, the real part of which has been used in many previous inelastic scattering analyses. Using collective model form factors in the ansatz for the imaginary part of the transition interaction and allowing for virtual resonance excitation, the differential cross sections from the scattering of 18.5–45 MeV protons are well reproduced. The parameters of the required complex interaction have a smooth energy variation similar to that required by a microscopic model analysis of proton inelastic scattering to collective states in nuclei.     

Study of the excitation functions of27Al(n, α)24Na,27Al(n,p)27Mg and28Si(n,p)28Al reactions

Cross sections for the reactions²⁷Al(n, p)²⁷Mg and²⁸Si(n,p)²⁸Al were measured by activation method between 13.40 and 14.83 MeV neutron energy. An accuracy of about 4% was achieved using the²⁷Al(n, α)²⁴Na reaction as a reference at 14.1 MeV where the relative excitation function has also been measured. Results obtained were compared to a recent compilation and that calculated by the Hauser-Feshbach model. Using the back-shifted level density formula and taking into account the contribution of the separated levels, the calculations were extended to the energy range from the threshold to 18 MeV. A structure was observed in the²⁷Al(n, α)²⁴Na reaction cross section curve around 14 MeV neutron energy.