The (n,p) reaction as a probe of Gamow-Teller strength

The ground state differential cross sections for the (n, p) reaction at 0° on ⁶Li, ¹²C and ¹³C have been measured for 198 MeV neutrons with a precision of about 4% relative to the corresponding value for the H(n, p) reaction. These data, together with the accurately known ft values for the β- decay of ⁶He, ¹²B and ¹³B provide three calibrations of the (n, p) reaction as a probe of Gamow-Teller strength for isospin raising transitions.     

Gamow-Teller and dipole strength in the 208Pb(n,p) reaction

Earlier data on the ²⁰⁸Pb(n,p)²⁰⁸Ti reaction at 198 MeV has been analysed using the multipole decomposition technique, and the contributions to the spectra from L = 0 and 1 transitions determined. The L = 0 cross section has been found to be smaller than values given by the calculations of MacFarlane [3] for Gamow-Teller transitions, using three different forms for the population of single particle states about the Fermi energy. Comparison is made with GT-strength values obtained from a more recent mean field calculation of these populations, and with an older nuclear structure calculation of properties of the lead nuclei. The L = 1 strength distribution is also reported.     

The (p,nγ) reaction on Al and Si

The reactions ²⁷Al(p, n γ) ²⁷Si and ²⁸Si(p, n γ)²⁸P have been studied at E_p = 16 and 23 MeV, respectively, with a Ge(Li) detector in coincidence with a neutron detector. In ²⁷Si, two new γ-tran- sitions were detected and accurate excitation energies were determined. In ²⁸P, the γ-decay scheme was studied for the first time and new levels were located at 879 and 1602 keV excitation energy. For both nuclei the γ-ray spectra were supplemented by neutron time-of-flight spectra. The excitation energies are compared with those of the analogue nuclei and with the predictions from Coulomb displacement calculations.     

On a quasi-elastic mechanism of the reaction d(p, 2p)n

The problem on validity of quasi-elastic mechanism of the reaction d(p, 2p)n in the range of low energies (20–50 MeV) is studied. While estimating the effect of multiple scattering it is shown that the condition of quasi-elasticity holds sufficiently well in all the considered cases under the assumption on peripheral collision of counted particles (the cutoff method). The dependence of the cutoff radius R₀ on the energy of incident particles E₀ is discussed.     

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.     

The88Sr(d,n∼p)88Sr reaction

The⁸⁸Sr(d, n～p)⁸⁸Sr cross section has been measured at 170 ° for deuteron energies from 7.5 to 10.0 MeV, and the total⁸⁸Sr(d, n～p) cross section obtained. The total cross section is compared with results of coupled-channel Born approximation calculations using both empirical and shell-model-reaction-theory form factors to describe the decaying isobaric analog state. It is shown also that the new data and calculations are consistent with earlier⁸⁸Sr(d, p)⁸⁹Sr data.     

Effects due to Coulomb interaction in the sequential decay reaction2H(α,p α)n

Discrepancies between experimental values for the resonance energy and width of⁵He(g.s.) as reported by various authors may be due to the Coulomb interaction in the final channel. Calculations based on a semi-classical model are in good agreement with a recent experiment.     

Final-state interactions in the reaction H (p, 2p) n

The cross sections for the reaction ²H(p, 2p)n are calculated by taking into account final state interactions including S, P and D waves for all pairs of outgoing nucleons. The D-state wave functions of the deuteron are also included in the calculation. The angular correlation distributions of the cross sections are compared with data at 156 MeV incident protons.     

The Mo(p, n)Tc reaction cross section and its use as a normalization for shuttle-system measurements

The ¹⁰⁰Mo(p, n)¹⁰⁰Tc reaction cross section was determined from 2 to 11 MeV (c.m.), by counting the delayed γ-rays from the ¹⁰⁰Tc decays (half-life = 15.8 s). These yields were measured with Ge(Li) and NaI(Tl) detectors and thick natural Mo targets. The use of this reaction as a normalizing reaction for cross-section measurements with a rapid target-transfer system is discussed. This technique was applied to the measurement of the astrophysically interesting ²³Na(p, n)²³Mg cross section (²³Mg HALF-LIFE = 11.57s). The results agree well with an independent ²³Na(p, n)²³Mg cross-section measurement.     

Theoretical analysis of the d(p, 2p)n reaction by a polar graph

In the scheme of the dispersion approach with Feynman graphs to nuclear reactions, we study the reaction d(p, 2p)n at low energy using a polar graph. For the energy dependence of the scattering peak and for the normalization factor, the results of our calculations are in good agreement with the experimental data.     

Investigation of7Be(n,p)7Li reaction

The⁷Be(n, p)⁷Li nuclear reaction with thermal and 2 keV neutrons was studied. For thermal neutrons the total cross section of (46 800± 4 000) b was obtained and the proton branching ratio to the first excited and ground states of⁷Li was determined to be ₁/₀ = (2±1) %. For 2 keV neutrons the upper limit of the cross section of 540 b was estimated.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The autors thank Mr. A. Dvoák and Mrs. B. Michalcová for their manufacturing the⁶Li standards, Dr. J. Frána for his help in determining the number of⁷Be atoms and Ing. J. Hoffmann, Mr. J. Novotný and Mr. J. Badura for their careful preparation of electronics.     

The γ-ray decay properties of low-lying levels of 65Zn via the 65Cu(p,nγ)65Zn reaction

They γ-ray decay of 13 low-lying levels of ⁶⁵Zn has been studied utilizing the ⁶⁵Cu(p, nγ)⁶⁵Zn reaction. The decay scheme was obtained from θ_γ = 90° yield curve measurements and from a neutron-gamma coincidence measurement. Angular distributions γ-rays were measured for seven angles at E_p = 3.5 and 4.0 MeV. Gamma-ray energies, level energies, and branching ratios obtained are compared with recent measurements. Expected angular correlations for possible spin sequences are calculated utilizing Hauser-Feshbach statistical reaction theory. The results, combined with other available evidence, establish the J^π assignments for the following levels: $\text{768.9 ± 0.1}\text{keV}\text{(}\text{5}\text{2}{}^{\mathrm{?}}\text{), 864.8 ± 0.2 (}\text{7}\text{2}{}^{\mathrm{?}}\text{), 1047.5 ± 0.1 (}\text{5}\text{2}{}^{\mathrm{?}}\text{), 1252.9 ± 0.4 (}\text{7}\text{2}\text{and}\text{1343.9 ± 0.1 (}\text{5}\text{2}{}^{\mathrm{?}}\text{)}$. Previous assignments are confirmed for the levels $\text{909.8 ± 0.1}\text{keV}\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{)}\text{and}\text{1369.5 ± 0.2 (}\text{5}\text{2}{}^{\mathrm{+}}\text{)}$. Limiting ifJ-values are obtained for the levels of $\text{1577.1 ± 0.2}\text{keV}\text{(≦}\text{5}\text{2}\text{)}\text{and}\text{1588.2 ± 0.4 (≦}\text{7}\text{2}\text{)}$. Gamma-ray multipole mixing ratios are extracted for 19 transitions between low-lying levels and transition strengths calculated where the level lifetimes are assumed to be in the range 10^?12 to 10^?13 sec.     

Proton-induced deuteron breakup reaction2H(p,pp)n

The screening and renormalization approach allows for a mathematically correct incorporation, in three-body scattering theory, of the long-ranged Coulomb interaction between charged particles. It is based on first calculating the transition amplitudes using screened Coulomb potentials. Then, after renormalization the zero-screening limit, leading to the amplitudes pertaining to unscreened Coulomb potentials, is performed numerically. Within this formalism the proton-induced breakup of deuterons is investigated, with the Coulomb repulsion between the two protons taken into account. Kinematically complete differential cross sections in various kinematic configurations are calculated and compared with the results of an identical calculation but for the neutron-induced reaction. In this way information on the size of the Coulomb effects in the proton-deuteron reaction can be extracted. Comparison is made with experimental data at 13.0 MeV projectile energy. In addition, the quality of approximate ways of including the Coulomb interaction is studied.Dedicated to Prof. Werner Sandhas on the occasion of his 60th birthday     

51(p,n)51Cr reaction from E p 1.9 to 4.5 MeV

The total cross-section for the reaction⁵¹V(p, n)⁵¹Cr has been measured fromE _p 1.9 to 4.5 MeV by using two different techniques: (i) by detecting the neutron using the 4π neutron counter and (ii) by measuring the activity of the residual nucleus⁵¹Cr. The two measurements are consistent with each other and together they are in good agreement with the data of Zyskindet al. The thermonuclear reaction rates have also been extracted starting from these cross-sections.     

Proton transitions in22Na(n,p)22Ne reaction

The nuclear reactions induced by thermal and 2 keV neutrons on²²Na radioactive nucleus were studied. For the thermal neutrons a more accurate value of²²Na (n,p)²²Ne reaction cross section was obtained. A weak proton transition to the²²Ne ground state was observed. The upper limits of cross sections for thermal neutron induced (n,∞) reaction and (n, p) reaction with 2 keV neut·rons are given.     

The low energy 2H(α, αp)n reaction

An investigation of the breakup reaction ²H(α, αp)n with incident energies of α-particles between 9.847 and 13.991 MeV has been performed. Results from kinematically complete measurements at 21 different kinematical configurations are presented. Final-state interaction enhancements have been experimentally observed. The energy is sufficiently low that the A = 6 system should be reasonably well described as a three-body system. The experimental data were compared with predictions based on Faddeev equations. Taking into account that no adjustable parameter is used, the quality of agreement is in general acceptable.     

The 208Pb(n,p)208Tl reaction at En = 97 MeV

Double-differential cross sections of the ²⁰⁸Pb(n,p) reaction have been measured at 97 MeV in the angular range 0°–30° for excitation energies up to 40 MeV. The experimental proton spectra have been compared with calculated spectra obtained with a statistical multistep direct reaction theory, in which charge exchange and inelastic response functions are described microscopically in the quasiparticle random phase approximation. The direct parts of the spectra have also been distributed on different multipole components by using a decomposition technique, based on sample angular distributions calculated within the distorted-wave Born approximation.     

The14N(n,p)14C reaction cross section for thermal neutrons

The¹⁴N(n,p)¹⁴C reaction cross section has been measured for thermal neutrons, making use of the neutron beam of the IBR-30 pulsed booster of the JINR, Dubna. Thermal neutrons were identified by a time-offlight method. Solid adenin targets were utilized. An ionization chamber was used for detecting the charged particles. The cross section was found to beσ _np ^th =(1.83±0.07)b.