Excited states of 10B from the 6Li(α, γ) and 9Be(p, γ) reactions

Excitation functions for the (α, γ) and (p, γ) reactions leading to ¹⁰B have been measured at θ = 0° in the energy range from E_x = 6.7 to 7.6 MeV. Two resonances corresponding to levels at 6.88 and 7.44 MeV are observed. Branching ratios extracted from γ-ray spectra are the same in both reactions for the 6.88 MeV (1^?, T = 0 + 1) level, but different at 7.44 MeV. The T = 0 + 1 level at 7.44 MeV (Γ = 90±10keV) is assigned 2^? or 2⁺ from its strong branch to the 3⁺ ground state. We find no evidence for a second isospin mixed 1^? state.     

Microscopic study of the 12C + 16O system

An angular momentum projected microscopic calculation is performed for the ¹²C + ¹⁶O system with an effective nuclear force and the exact Coulomb interaction. The ¹²C wave function is projected on a 0⁺ state. Parametrizations of the Coulomb interaction between the nuclei are fitted. The L-projected energy curves present a quite complicated structure especially for the negative parity states. The role played by critical angular momenta is put into evidence. A generator coordinate calculation gives several bands of bound, quasibound and virtual states. Excellent agreement in energy and angular momentum is obtained with the 13.7 MeV (J = 9), 19.7 MeV (J = 14), 22.7 MeV (J = 15) and other resonances.     

Study of the 19F(p, γ)20Ne radiative capture reaction from 0.2–1.2 MeV

The ¹⁹F(p, γ)²⁰Ne radiative capture reaction has been investigated for proton energies of 0.2–1.2 MeV. Excitation functions of γ-rays arising from capture reactions have been measured and the properties of known J^π = J^?J+1 resonances were studied. From the branching ratio and angular distribution measurements, the partial widths for gamma ray and proton emission of the 13.88 MeV level in ²⁰Ne were obtained, and J^π = 2⁺, T = 1 assignments for this resonance at E_P = 1091keV were made. Lower upper limit for the total width Γ = 0.8 keV has been obtained.     

Spin and parity assignments for 35Cl levels from the 31P(α, p)34S reaction

³⁵Cl states at excitation energies between 9.9 and 11.8 MeV have been identified through sharp resonances in the ³¹P(α, p_o)³⁴S excitation functions at 25°, 105° and 155° for E_α = 3.25–5.50 MeV. Forty-eight on-resonance angular distributions, normalized to an absolute cross section scale, have been subjected to single-level and two-level analyses resulting in spin and parity assignments for each resonance. Approximately half the resonances were of the pure single-state type, having unique angular distribution shapes. Data from 12 resonances of an earlier experiment ¹) were analyzed with the same theory, extending the diagnostics down to a ³⁵Cl excitation energy of 9.1 MeV. A set of optical potentials consistent in all four reactions that this experimental program encompasses has been incorporated in the present analysis. Validity of the optical potential is demonstrated for α-particles elastically scattered by ³¹P.     

Two-particle,two-hole Jπ=0+ states in 40Ca

Excited J^π=0⁺ states in ⁴⁰Ca have been identified by the observation of L=0 angular distributions in the ³⁸Ar(τ, n) ⁴⁰Ca reaction. Strong transitions are observed to the ground state, the known 2p–2h at 9.38 (T=1) and 11.98 MeV (T=2), and to states at 8.28 and 10.65 MeV. The strongest excited-state transition is to the 8.28 MeV state, which we identify as the 2p–2h T=0 state. The J^π=0⁺ state at 7.30 MeV which has been suggested as the 2p–2h T=0 state is not observed.     

Intermediate resonance of inelastic 12C + 12C scattering

The intermediate resonances observed in the inelastic ¹²C + ¹²C cross sections to the single and mutual 2₁⁺(4.43 MeV) excitations and the single 3₁^? (9.64 MeV) excitation are studied by the coupled-channel method with the use of the coupling interaction derived by the folding procedure between ¹²C and ¹²C. It is shown that the model is successful in reproducing the gross structures of the inelastic cross sections and especially the correlated resonance energies of the inelastic channels. The inelastic resonances are shown to be due to the molecular resonances in an adiabatic potential between two ¹²C, which reproduces correctly the coupled channel resonances.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.     

A study of 28Si(α, γ)32S resonances below Eα = 3.83 MeV

The γ-decays of eleven resonances in the ²⁸Si(α,γ)³²S reaction below E_α = 3.83 MeV have been studied using a large Ge(Li) detector. Results for branching ratios differ considerably from previous NaI work. The previous discrepancy in radiative strengths for the 2.61 MeV resonance is explained by this data. The strengths of the first five resonances at E_α = 1.77, 1.99, 2.19, 2.37 and 2.42 MeV appear to be (39 ± 13)% lower than previously reported. Spin-parities of l^?, 2⁺ and 2⁺ have been assigned to the levels at 8.50, 8.69 and 8.86 MeV respectively. The radiative width of the E_p = 1.467 MeV, J^π = 3^? resonance in the ³¹P(p,γ)³²S reaction has also been measured.     

The width of the 5.11 MeV state in 10B and isovector parity mixing

We review estimates for effects of parity mixing on the α-capture of vector polarized ⁶Li to the 5.16 MeV, 2⁺, T = 1 state in ¹⁰B. The cross section depends on the ⁶Li polarization direction because of isovector parity mixing with the 5.11 MeV, 2^?, T = 0 state. The effect is enhanced due to isospin conservation. The α-width of the 5.11 MeV state, an important parameter for calculating the enhancement, has been measured to be 0.98 ± 0.07 keV. The consequences of parity mixing are reevaluated using best available values for the relevant parameters.     

12C(12C, 8Be)16O angular distributions and excitation functions between 35 and 69 MeV bombarding energy

An array of eight detectors has been developed for identifying the particle unstable ⁸Be nucleus from nuclear reactions with high detection efficiency. Absolute cross sections have been measured for the reaction ¹²C(¹²C, ⁸Be_g.s.)¹⁶O to the ground state and to several excited states in ¹⁶O. Excitation functions at seven angles from 15° to 45° (lab) in 5° steps have been measured for bombarding energies between E¹²_C(lab) = 35 and 69 MeV. Excitation functions were obtained for the following states in the residual nucleus ¹⁶O which were found to be strongly populated: g.s.(0⁺); 6.1 MeV (0⁺, 3^?); 6.9 MeV (2⁺); 10.4 MeV (4⁺); 11.1 MeV (4⁺); 14.7 MeV (6⁺,…) and 16.3 MeV (6⁺,…). The energy range is covered in 250 keV (c.m.) steps; at certain energy ranges in ¹²⁵ keV or 50keV steps. All excitation functions exhibit a strong energy dependence of the cross section; pronounced gross structures with superimposed fine structures, similar to those observed for ¹²C+¹²C elastic and inelastic scattering at these energies, are observed. At 19.3 MeV, where resonant structures were observed in the reactions ¹²C(¹²C, p)²³Na, ¹²C(¹²C, n)²³Mg and ¹²C(¹²C, d)²²Na, no resonance is found for the reaction studied here. At 60, 61 and 63 MeV angular distributions have been measured in 1° and 2.5°(lab) angular steps. The excitation functions have been analyzed in terms of Ericson fluctuations and cross-correlation functions.     

Precise excitation energy and γ-ray decay of the lowest T = 2 state in 40K

The excitation energy of the lowest T = 2 state in ⁴⁰K has been determined as E_x = 4384.0 ± 0.3 keV from n-γ and γ-γ coincidence experiments. The state was populated with the ⁴Ar(p,n)⁴⁰K reaction at E_p = 8.30 MeV. Gamma-gamma angular correlation measurements yield unambiguous spin assignments J = 0 and 1 for the 1.64 and 2.290 MeV states, respectively. The excitation energy of the T = 2, J^π = 0⁺ state leads to a calculated mass excess of ?9120 ± 150 keV for ⁴⁰Ti.     

Investigation of 28Si levels with the (α, γ) and (p, γ) reactions

Particle energies have been measured for resonances in the ²⁷Al(p, γ)²⁸Si and ²⁴Mg(α, γ)²⁸Si reactions with an accuracy of 0.5 × 10^?4 and 1 × 10^?4, respectively. The E_p = 991.88 ± 0.04 keV²⁷Al(p, γ)²⁸Si resonance served as calibration point. From these data the Q-value of the reaction ²⁷Al(p, α)²⁴Mg has been determined as 1600.14 ± 0.21 keV. Excitation energies of ²⁸Si levels have been measured with the ²⁷Al(p, γ)²⁸Si reaction; the reaction energy is Q = 11584.5 ± 0.4 keV.Of 33 resonances observed in the ²⁴Mg(α, γ)²⁸Si reaction (E_α = 1.5–3.8 MeV), energies, strengths and γ-ray decay have been measured; five of these resonances had not been reported previously. The γ-ray angular distribution measurements at three resonances yield the resonance J^π values and the mixing ratios of the strongest transitions involved in the decay. The 10.38 MeV level has J^π = 3⁺, T = 1. The arguments on which T-assignments can be based are critically reviewed. These arguments are used to assign T = 1 character to ¹⁹ states of ²⁸Si.     

Resonant behaviour of the 16O-12C elastic scattering cross section

Resonances in the elastic scattering of ¹⁶O by ¹²C are reported at E_c.m. = 17.29 and 20.79 MeV, with respective J^π assignments of 11^? and 13^?. A 14⁺ spin assignment is shown to be more probable for the resonance at 22.79 MeV than a previous tentative assignment of 16⁺. A correlation is found between maxima of the total fusion cross section and the position of odd angular momentum resonances.     

Levels of 28Si from the 24Mg(α, α)24Mg and 24Mg(α, γ)28Si reactions

Excitation functions have been measured at six angles for ²⁴Mg(α, α)²⁴Mg up to E_α 4.94 MeV. Multi-level R-matrix analysis was performed for nineteen resonances. More than ha of the determined spin-parities and other resonance parameters are new values. The ²⁴Mg(α, γ)²⁸Si studies of Maas et al. were extended up to E_α = 5.13 MeV. Resonance strengths and branchin ratios were determined. The γ-ray angular distribution measurement at E_α = 3.79 MeV gives J^π = 2⁺ value for the resonance. A comparison of the results obtained in different reaction channel is given and the possibility of clusterisation in some excited states of ²⁸Si is discussed.     

A study of the states of 30Si with the 28Si(t,p)30Si and 29Si(d,p)30Si reactions

The excitation energies of the levels in ³⁰Si have been measured up to an excitation of 9.46 MeV with the ²⁸Si(t, p)³⁰Si reaction at a triton energy of 6.0 MeV. Angular distributions have been measured of proton groups from the ²⁸Si(t, p)³⁰Si and ²⁹Si(d, p)³⁰Si reactions in a multi-angle magnetic spectrograph. Triton bombarding energies of 10.5 and 12.1 MeV were used and the deuteron incident energy was 10.0 MeV. States in ³⁰Si up to an excitation of 8 MeV were observed. Spins and parities of several states have been assigned using an empirical method for the (t, p) results and using a DWBA analysis for the (d, p) distributions. Spectroscopic factors for twelve states were obtained from the latter analysis. Two of these disagree with theoretical predictions. The state previously reported at an excitation of 6.63 MeV in ³⁰Si was observed to be formed by a strong L = 0 transition in the (t, p) reaction and also by a strong l = 1 transition in the (d, p) reaction. We deduce that there are two closely spaced states at about this excitation, one having a spin and parity of 0⁺ and the other 0^?, 1^? or 2^?.     

Configuration of 3.59 MeV 0+ state in 44Ca

Results obtained with the ⁴⁸Ti(d, ⁶Li) reaction, at E_d = 55 MeV, establish the 3.59 MeV 0⁺ level of ⁴⁴Ca as virtually pure 8 p?4h, with T_h = 0.     

A study of isobaric analogue resonances in 71Ga

Differential cross-section and analysing-power excitation functions were measured for elastic proton scattering from E_p = 3.6–6.4 MeV at θ_c.m. = 90°, 115.8°, 129.8° and 155.3°. Differential cross-section angular distributions were measured at 3.56, 3.94, 5.78 and 8.98 MeV and analysing-power angular distributions at 5.78 and 8.98 MeV. Optical-model parameters were deduced from these distributions. Resonance parameters were determined for eight analogue resonances in ⁷¹Ga and neutron spectroscopic factors were calculated. These were compared with the results of previous (p, p) cross-section analyses and the results of (d, p) reactions leading to states in ⁷¹Zn.     

Study of the 208Pb(n, γ0)209Pb reaction between 0.8 and 7.7 MeV

The reaction ²⁰⁸Pb(n, γ₀)²⁰⁹Pb was studied from 0.8 to 7.7 MeV to investigate relative contributions of the compound-nucleus and direct and semidirect processes in this energy range. Compound-nucleus reactions dominate below about 5 MeV and semidirect processes above 6 MeV. The direct-semidirect (DSD) model with a complex particle-vibration coupling describes the experimental data in the giant resonance region. A relatively large imaginary term is necessary to obtain a good fit to the data indicating either that the reactions proceed to a large extent in more complicated ways than the simple two-step semidirect reaction or that the model has a serious defect in its present formulation. A second objective was to search for a possible excitation of the isoscalar E2 and the M1 giant resonances by measuring asymmetries around 90° in the angular distribution of the γ-rays. The results indicate no (or very weak) asymmetry effects.     

Study of proton elastic and inelastic scattering from 74Se at the isobaric analogue resonances

Excitation functions of proton elastic and inelastic scattering from ⁷⁴Se were measured to investigate the isobaric analogue resonances (IAR) in ⁷⁵Br. Observed IAR correspond to the parent states of ⁷⁵Se in excitation energy from 0.29 to 1.8 MeV. For eleven resonances, resonance parameters were determined from the analysis of the elastic scattering. For three of these resonances, inelastic widths to the 2⁺ (0.635 MeV) state in ⁷⁴Se were obtained from the analysis of the angular distributions of inelastically scattered protons. Spectroscopic factors obtained from the elastic scattering were compared with those from the ⁷⁴Se(d, p)⁷⁵Se reaction. There is good agreement between the corresponding Spectroscopic factors except for the states with l_n = 1 where they were much smaller than the (d, p) ones. For the inelastic scattering, it was proved that the compound process via IAR play an important role and the analysis including the compound process explained the experimental results reasonably well.