Structure of 14C from 12C(t,p)

The reaction ¹²C(t, p)¹⁴C has been investigated with an 18 MeV triton beam. Twenty energy levels of ¹⁴C were identified up to 13 MeV excitation. Angular distributions were measured and compared with DWBA calculations. A previously unreported 0⁺ level at 9.75 MeV was observed; it undoubtedly corresponds to the second predominantly sd shell 0⁺ state in ¹⁴C. Additional spin and parity assignments have been made in the present work: 9.81 MeV, (1^?); 10.43 MeV, 2⁺; 10.50 MeV, (3^?); 10.74 MeV, 4⁺; 11.40 MeV, 1^?; 11.67 MeV, (1^?); 11.73 MeV, (5^?); 12.58 MeV, (2⁺, 3^?); 12.87 MeV. 2⁺, 3^?; and 12.96 MeV, (1^?); none of which had a definite spin and parity assignment previously. Our results confirm the previous information on the level structure of ¹⁴C below 8.5 MeV. The cross section for the unnatural parity state at 7.34 MeV, J^π = 2^?, is well reproduced by a two-step reaction calculation. The results are compared with the predictions of a weak coupling model.     

Measurements of the radiative widths of the first T = 1, 2+ state of 20Ne and their relationship to analog β-decays

The radiative widths for decays of the ²⁰Ne T = 1, 2⁺ (10.27 MeV) state were measured by resonance α-capture in the reaction ¹⁶O(α, γ)²⁰Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2⁺(7.83 MeV), 2⁺(7.42 MeV), 3^?(5.62 MeV), 2^?(4.97 MeV), 2⁺(1.63 MeV) and 0⁺(g.s.). The branching ratios and radiative widths Γ_γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.     

States in Be studied through the reaction B(p, α)Be with 40 MeV protons

Spectroscopy of the α- and τ-particles from 40 MeV proton bombardment of ¹¹B reveals transitions to ⁸Be states up to 19 MeV. The ratio of excitation of the 16.6 MeV state to the 16.9 MeV state is 2.3 ± 0.4. The ⁸Be(4⁺) state is found at 12.5 MeV with a width of 4.0 ± 0.5 MeV.     

Study of even-mass Ba nuclei by the (p,t) reaction

The (p, t) reaction on the nuclei ^{134, 136, 138}Ba has been studied at a bombarding energy of 52 MeV. Angular distributions of emitted tritons were obtained between 6° and 60°. The following six negative-parity states were strongly excited by the (p, t) reaction: 5^?(2.121 MeV) and 7^?(2.482 MeV) in ¹³²Ba, 5^?(1.998 MeV) and 7^?(2.274 MeV) in ¹³⁴Ba, and 5^?(2.139 MeV) and 7^?(2.031 MeV) in ¹³⁶Ba. DWBA calculations using the code DWUCK successfully reproduce these angular distributions. The 0⁺ assignment to the 1.761 MeV level in ¹³⁴Ba is confirmed. Intensities of the (p, t) reaction for low-lying states are discussed.     

Observation of the proton-pairing vibration in 48Ca

The two-proton transfer reaction (¹⁴C, ¹⁶O) has been investigated at 96 MeV on targets of ⁵⁰Ti and ⁴⁸Ca. The ⁴⁸Ca states at 0 MeV (0⁺), 3.83 MeV (2⁺), 4.28 MeV (0⁺) and 4.50 MeV (3⁻) and the ⁴⁶Ar ground state were excited. The 4.28 MeV 0⁺state has a transfer strength comparable to the g.s. transition to ⁴⁶Ar and a predominant proton vibrational character. The interpretation of the state as the proton-pairing vibrational state is supported by estimates of the excitation energy based on experimental binding energies.     

Der Zerfall des In109m (0,21 sec)

In^109m(0,21±0,01 sec) was produced from natural Ag and enriched Ag¹⁰⁷ byα irradiation and investigated using scintillation spectrometers and coincidence techniques. The mass assignment follows from the excitation function for the (α, 2n) reaction on Ag¹⁰⁷. The following results were obtained: energy of the isomeric level (2,11±0,02) MeV, determined directly by summing up the cascade transitions in a well-type scintillator; four gamma transitions with energies (0,680±0,015) MeV, (0,405±0,015) MeV, (1,035±0,030) MeV and (1,435±0,020) MeV, respectively. The proposed decay scheme contains the isomeric level (19/2⁺) at 2,11 MeV and a further level (13/2⁺) at 1,435 MeV which decays either by the 1,435 MeV transition (80±3)% or by a 0,405–1,035 MeV cascade (20±3)% via an (11/2⁺) level at 1,035 MeV to the 9/2⁺-ground state of In¹⁰⁹.     

Unnatural parity levels populated in the 16O(6Li,d)20Ne reaction

The ¹⁶O(⁶Li, d)²⁰Ne reaction to the 2^?, 4.97 MeV, 3^?, 5.63 MeV, and 4^?, 7.01 MeV members of the K^π = 2^? band has been studied. Angular distributions were measured at 32 MeV from 7.5° to 145° (lab). Excitation functions were measured at 15° (lab) and 145° (lab) from 31 to 33 MeV and 31.75 to 32.5 MeV, respectively. Results of multi-step and compound nuclear calculations are compared to the data. At this incident energy, both mechanisms appear to contribute to the population of the unnatural parity levels.     

Investigation of the structure of lower excited states of the 28Si nucleus in α scattering at Eα = 30.3 MeV

The differential cross sections of the ²⁸Si(α, αγ)²⁸Si reaction at E _α = 30.3 MeV, calculated according to the coupled channel method (CCM) with the FRESCO program, are presented for a wide α-particle scattering region with the excitation of the lower ²⁸Si states (0⁺, ground; 2⁺, 1.78 MeV; 4⁺, 4.62 MeV; 0⁺, 4.96 MeV; 3⁻ + 4⁺, 6.88 MeV + 6.89 MeV). The coupling factors are calculated in the Nilsson model.     

Polarization and phase shifts in Be(p, p)Be from 0.8 TO 2.7 MeV and the structure of B

Angular distributions of the analyzing power in Be have been measured to an accuracy of about ±0.03 at 21 energies from 0.9 to 2.7 MeV with a target thickness of 20 keV at 1 MeV. These data and the cross section measurements of others are reproduced well in the region from 0.8 to 1.6 MeV by a set of phase shifts that vary reasonably with energy. The ³S₁, ⁵S₂, ⁵P₁, and ⁵P₂ phases suffice to describe the data, although channel spin and s-d mixing are required. Three levels satisfy the data: at 0.980±0.010 MeV are two levels, a 1⁺ of width 0.10 MeV and a 2⁻ of width 0.11 MeV; at 1.37±0.02 MeV is a 1⁻ level of width 0.30 MeV. The 1⁺ and 1⁻ states do not agree with earlier assignments. Outside of the energy region from 0.8 to 1.6 MeV a satisfactory set of phases could not be obtained, owing to inadequate data. These regions were studied in the analysis, however, and the results are discussed.     

Cluster states in the neutron excess nucleus 22Ne

High-spin states of the ²²Ne nucleus in the excitation energy range of 15–30 MeV have been studied. The angular correlation method has been used to determine the spins of excited states. A number of new states with high angular momenta—20.0 MeV (9^?), 20.7 MeV (11^?), 21.6 MeV (9^?), 22.2 MeV (12⁺), and 25.0 MeV (9^?)—have been revealed. They are intensely populated in the reaction ¹⁴C(¹²C, α₁)²²Ne* → α₂ + ¹⁸O and correspond to the rotational bands of various structures.     

Investigation of the mechanism of inelastic alpha-particle scattering on 28Si nuclei by the method of angular αγ correlations at E α = 30.3 MeV

The angular dependence of the differential cross sections for alpha-particle scattering on ²⁸Si nuclei and double-differential cross sections for the reaction ²⁸Si(α, αγ)²⁸Si at E _α = 30.3 MeV is measured for the case of alpha-particle emission angle between 20° and 160° and the excitation of low-lying states of the ²⁸Si nucleus (0⁺, ground state; 2⁺ state at 1.78 MeV; 4⁺ state at 4.62 MeV; 0⁺ state at 4.96 MeV; and 3^? + 4⁺, 6.88 MeV + 6.89 MeV). The spin-tensor components of the density matrix for the 2⁺ state at 1.78 MeV and the 4⁺ state at 4.62 MeV in the ²⁸Si* nucleus are reconstructed in a modelindependent way. Seven rank-6 components are reconstructed for the 3^? state at 6.88 MeV. Orientation features of ²⁸Si* are determined. The experimental data in question are compared with the results of the calculations performed under the assumption of the collective-excitation mechanism and by the coupled-channel method.     

Spin assignment to the 9.026 MeV resonance level of36Ar using35Cl(p, γ)36Ar triple angular correlation measurements forE p = 533 keV

Triple correlation experiments have been performed to study the³⁵Cl(p, γ)³⁶Ar resonance for a proton energyE _p = 533 keV. From the analysis of the measured gamma ray angular distributions, due to the gamma decay of the 9.026 MeV resonance level in³⁶Ar via the 9.026 MeV→1.97 MeV→0 MeV double cascade, a spin value ofJ ₁ =2⁺ for the 9.026 MeV level and a mixing ratio of ?1.97 MeV∥L′₁ = 2∥9.026 MeV?/?1.97 MeV∥ L₁ = 1∥9.026 MeV? = ?0.055 + 0.022 for the 9.026 MeV→ 1.97 MeV transition could be derived.     

Spin-dependent effects in inelastic scattering

The differential cross sections for the inelastic scattering of 10 MeV, 19.6 MeV, 30.4 MeV, 40 MeV and 49.35 MeV protons to the 2⁺ state (1.409 MeV) in ⁵⁴Fe and of 19.6 MeV protons to the 2⁺ state (0.846 MeV) in ⁵⁶Fe are analyzed in conjunction with the available data on the asymmetries and spin-flip probability amplitudes. The scattering amplitudes for both one step (valence plus core polarization) and two step (intermediate resonance) processes are evaluated using an antisymmetrized distorted wave approximation. Collective model representations for both the one step (core polarization) and two step (intermediate resonance) processes are used, and included are the effects of deforming the full Thomas spin-orbit potentials. The one step processes are fixed by the analyses of the scattering of 30.4, 40 and 49.35 MeV protons, with the core polarization contributions being constrained by the B(E2) values for the γ-ray deexcitation of the 2⁺ states. The analyses of the 19.6 MeV data demonstrates the need for an extra (two step) contribution to the reaction process and are consistent with the virtual formation of an L = 3 giant resonance. The 10 MeV data most certainly demonstrate compound nucleus effects but could also have some strength due to the virtual formation of an intermediate L = 2 giant resonance. The resonance parameters are consistent with recent information concerning the mass variation of giant resonances.     

Analysis of inelastic scattering of 3He on 13C at 37.9 MeV

The differential cross section of elastic and inelastic scattering of ³He ions on the ¹³C nucleus has been measured at an energy of 37.9 MeV. By fitting the shape of the measured angular distribution of the elastic scattering the parameters of the optical model have been found. These parameters have been used for the DWBA calculations of angular distributions corresponding to excitations of the ¹³C levels 3.09(1/2⁺) MeV, 3.68(3/2^–) MeV, 3.85(5/2⁺) MeV, 7.55(5/2^–) MeV, 8.84(1/2^–) MeV and 11.85(7/2⁺) MeV. Several sets of transition densities calculated with different effective nucleon-nucleon interactions and six different M3Y interactions between a projectile and target nucleon have been tested. Analysis of the inelastic scattering of 135 MeV protons on ¹³C is also presented, which enabled us to obtain additional information about the tested structure models.     

Charge exchange reaction 14C(6Li, 6He)14N

Angular distributions of the charge exchange reaction ¹⁴C(⁶Li, ⁶He)¹⁴N leading to the 1⁺ ground state and 3.95 MeV 1⁺, and 5.20 MeV 2^? excited states at the 34 MeV incident beam energy were analyzed and measured. The 62 MeV data of Goodman et al. were also reanalyzed. The direct one-step charge exchange caused by the spin-isospin dependent term in the two-body interaction can account well for the observed data. The strength of spin-isospin dependent effective interaction (gaussian form with a range parameter of 1.8 fm) was extracted to be 18.5 MeV.     

Folding-model analysis of the inelastic scattering of 32S on 40Ca at 100, 120 and 151.5 MeV

The angular distributions for the 2⁺ level of ³²S at 2.24 MeV and 3⁻ level of ⁴⁰Ca at 3.74 MeV have been measured at 100, 120 and 151.5 MeV ³²S bombarding energies and the 3⁻ level of ³²S at 5.01 MeV at 120 and 151.5 MeV. The levels have been analysed by the coupled-channel approximation using real potentials and form factors deduced from the folding model. It has been found that the energy dependence of the folding-model renormalization coefficient decreases in comparison with that found in the elastic-channel analysis and that an overall energy-independent renormalization coefficient seems to be needed.     

A study of the 12N 2.43 MeV level

We have measured the differential cross sections for the reactions ¹²C(τ, τ′)¹²C(17.77 MeV 0⁺T=1) and ¹²C(τ, t)¹²N(2.43 MeV) at E_τ=44 MeV. The similar shapes of the angular distributions and the relative magnitudes of the cross sections suggest that the ¹²N 2.43 MeV level is the 0⁺T=1 analog to the ^q12C 17.77 MeV level. We have also studied the reaction ¹⁴N(p,t) ¹²N(2.43 MeV) at E_p=52 MeV. The strength with which this level is excited in this reaction is consistent with reasonable two-step calculations assuming the 2.43 MeV level to have J^π=0⁺.     

Fluctuations in12C+24Mg elastic and inelastic scattering

The data on the ϑ_c.m.=180° excitation functions of¹²C+²⁴Mg,¹²C* (4.43 MeV)+²⁴Mg and¹²C+²⁴Mg*(1.36 MeV) from 12.27 to 22.80 MeV, 16.53 to 27.47 MeV, and 11.33 to 26.40 MeV(c.m.) respectively have been subjected to statistical analysis. The effect of averaging interval, employed for data reduction, on the coherence widths as obtained from the autocorrelation function has been studied. The fluctuating features of the cross-sections turn out to be consistent with the statistical model expectations.     

Concerning high-spin negative parity states in 20Ne

Unambiguous spin and parity assignment have been made from angular correlation measurements to states in ²⁰Ne at 15.18 MeV (6⁺) and 17.40 MeV (9^?). Our results are in disagreement with an earlier 9^? assignment to the 15.18 MeV state. The 17.40 MeV state is assigned to the K = 2^? rotational band based on the 2^? state at 4.97 meV.     

On the identification of the nuclear forward glory in heavy-ion scattering

We present a simple method which enables us to identify the occurence of a forward glory in heavy ion scattering data. The method is successfully applied to the elastic scattering data of ¹²C (65 MeV), ¹³C (60 MeV), ¹⁵N (85 MeV) and ¹⁶O (75 MeV) on ²⁸Si. Received: 2 July 1999 / Revised version: 3 December 1999