Competition cusps in (α, γ) reactions

Absolute cross sections are presented for the reactions ³⁷Cl(α, γ)⁴¹K for 2.90 MeV ≦ E^lab_α ≦ 5.23 MeV, ${}^{62}\text{Ni}\text{(α, γ)}{}^{66}\text{Zn}\text{for}\text{5.07}\text{MeV}\text{≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{?2}}\text{lab}\text{≦ 8.64}\text{MeV}\text{,}{}^{62}\text{Ni}\text{(α,}\text{n}\text{)}{}^{65}\text{Zn}$ for energies near the (α, n₀) threshold at $\text{E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{= 6.90}\text{MeV up to}\text{8.76}\text{MeV}\text{,}{}^{64}\text{Ni}\text{(α, γ)}{}^{68}\text{Zn for}\text{4.50 ≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{≦ 7.45}\text{MeV}$, and for ⁶⁴Ni(α, n)⁶⁷N from E_α^lab = 5.30 MeV up to E_α = 7.45 MeV. Substantial competition cusps were observed in the excitation function for all three (α, γ) reactions. The data were found to be in reasonable agreement with the predictions of the current versions of global Hauser-Feshbach models used in nucleosynthesis calculations. Including width fluctuation corrections and realistic neutron strength functions generally improves the ability of the models to predict the depth of the (α, γ) competition cusps; the depths of the predicted (α,γ) cusps are insensitive to the degree of isospin mixing. Taken together with studies of competition effects in proton-induced reactions, the present data confirm the importance of width fluctuation and strength function effects, and indicate essentially complete isospin mixing between T^< and T^> states in the compound nucleus.     

The 12C(13C, α)21Ne reaction: High-spin states,resonances and coherence widths

Excitation functions were measured for states of ²¹Ne populated by the ${}^{12}\text{C}\text{(}{}^{13}\text{C}\text{, α)}$ reaction over the bombarding energy range E_lab = 18.2–32.0 MeV (18.4–27.0 MeV) at θ_lab = 7°(25°) in in 200 keV steps, and average coherence widths of states and the moment of inertia of the compound nucleus ²⁵Mg were obtained from these excitation functions. A statistical analysis of these data was performed. Angular distributions for states in ²¹Ne to 10 MeV in excitation energy were measured at θ_lab = 7°, 18°, 28° and 43° at bombarding energies from 29.0 to 31.0 MeV in 400 keV steps. These data along with Hauser-Feshbach predictions allow us to suggest spins for some states as well as to suggest possible candidates for rotational bands in ²¹Ne.     

Proton spectra from the 6,7Li(γ,p) 5,6He reactions at Eγ = 60 MeV

The ${}^{\mathrm{6,7}}\text{Li}\text{(γ,}\text{p}\text{)}$ reactions have been investigated for E_γ = 60 MeV. Excitation of residual (1p)^?1 and (1s)^?1 hole states is evident from the proton spectra measured at ?_p = 45°. The data are compared with a theoretical calculation which includes short-range correlations.     

Search for highly excited states in 8Be

Excitation functions and angular distributions of the reactions ${}^7\text{Li}\text{(}\text{p}\text{, α)α}{}^1$ and ${}^6\text{(}\text{Li}\text{(}\text{d}\text{, α)α}{}^1$ have b investigated for the excitation-energy region E_X = 21?28 MeV in ⁸Be ($\text{α}{}^1$ denotes the first excited state of the α-particle). pronounced resonant structure has been observed in both channels around E_X = 24 MeV. It is excited simultaneously by odd and even angular momenta. The experimental results are discussed in the light of two models, the αα¹ cluster model and the symplectic model which take into account the configuration interaction (core excitation) in different manners.     

Investigation of the level schemes of 73,75,77As via the (3He,d) reaction

The reactions ^{72, 74, 76}Ge(³He, d) were investigated at E_lab = 23 MeV with a multigap and a Q3D magnetic spectrograph. Some 30 new levels up to $\text{E}{}^1\text{≈ 4}\text{MeV}$ have been found. The level schemes of the odd As isotopes ^{73, 75, 77}As up to $\text{E}{}^1\text{≈ 4}\text{MeV}$ seem to be rather independent of the neutron number. The good agreement of the low-lying level structure with the Coriolis-coupling model including a pairing force was verified and the vacancies of low-lying shell model states were extracted and compared with the simple pairing theory.     

Elastic scattering of vector polarized 6Li

Vector polarized ⁶Li nuclei have been elastically scattered on ${}^{12}\text{C(E = 20, 22.8}\text{MeV}\text{)}$ and on ¹⁶O, ²⁸Si, ⁵⁸Ni (E = 22.8 MeV). For the lighter nuclei surprisingly large asymmetries have been observed. The order of magnitude of the polarization effects observed can be understood within a folding model for the ⁶Li spin-orbit potential.     

On the 18O positive-parity rotational band

Deuteron-alpha angular correlations have been measured for the reaction ${}^{14}\text{C}\text{(}{}^6\text{Li,d}\text{)}{}^{18}\text{O}{}^1\text{→α}{}_0\text{+}{}^{14}\text{C at}\text{E(}{}^6\text{Li}\text{)=34}\text{MeV}$ and θ_d^lab=10°. Transitions involving the 11.69 MeV (6⁺) and the 17.6±0.2 MeV ¹⁸O states have been analyzed. Spin and parity are confirmed for the known 11.69 MeV (6⁺) state and assigned to be 8⁺ for the 17.6 MeV level. This last is suggested to be the fifth member of the positive-parity ¹⁸O rotational band built on the 3.63 MeV (0⁺) level.     

Remeasurement of the low-energy cross section for the 15N(p, α0)12C reaction

The cross section for the ${}^{15}\text{N(p}\text{, α}{}_0\text{)}{}^{12}\text{C}$ reaction has been measured at θ_lab = 135° over the proton energy range 93 ≦ E_p ≦ 418 keV. The results are in good agreement with the less precise but much earlier measurements of Schardt, Fowler and Lauritsen (1952). An analysis of the present data in terms of a two-level calculation including the 338 keV (1^?) and 1028 keV (1^?) resonances determines a zero-energy intercept for the astrophysical S-factor of S(0) = 78 ± 6 MeV · b.     

Semiclassical description of analyzing powers in one-nucleon transfer reactions induced by 44MeV polarized 7Li ions on 120Sn

Analyzing powers of various ranks for the reaction ${}^{120}\text{Sn(}{}^7\text{L}$, ⁶Li) at E_lab = 44 MeV have been measured as functions of scattering angle and Q-value. The reaction is understood semiclassically as transfer of the neutron from one reaction partner to the other during their relative motion on classical trajectories. An approximate evaluation of transfer amplitudes is presented which takes care of the relative magnitude of amplitudes for various spin quantum numbers and also of the discontinuity of the trajectory angular momentum in the interaction point. Thus simple formulae for analyzing powers are derived. All the characteristic features of the data are reproduced within this model.     

Strong coupled-channels effects in the 9Be(α, t)10B reaction

Differential cross sections were measured for the reactions ${}^9\text{Be}\text{(α, α')}{}^9\text{Be}\text{,}{}^9\text{Be}\text{(α,}\text{t}\text{)}{}^{10}\text{B and}{}^9\text{Be}\text{(α,}{}^3\text{He}\text{)}{}^{10}\text{B at}\text{E}{}_{\mathrm{\alpha }}\text{= 65}\text{MeV}$ for angles ranging from θ_lab = 6° to 48°. Optical-model analysis was performed for elastic α-scattering from ⁹Be at E_α = 48, 65 and 104 MeV, and DWBA and CC calculations were done for the inelastic α-scattering at E_α = 65 MeV. DWBA calculations for the ⁹Be(α, ³He) reactions do not fit the transfer data so well and extracted spectroscopic factors are in disagreement with those of Cohen and Kurath and with values obtained from other reactions. Full CRC calculations assuming a band structure for the low-lying states of ¹⁰B and employing a modified set of Cohen and Kurath spectroscopic factors yield globally better fits both in shape and in absolute cross section for differential cross sections to low-lying states in ¹⁰B obtained in ⁹Be(α, t)¹⁰B at $\text{E}{}_{\mathrm{\alpha }}\text{= 65}\text{MeV and}{}^9\text{Be}\text{(}{}^3\text{He, d}\text{)}{}^{10}\text{B at}\text{E}{}_{\mathrm{<mtext>d</mtext>}}\text{= 17}\text{MeV}$. In general, strong coupled-channel effects mainly affecting the distorted waves are observed both in entrance and exit channels.     

An experimental investigation of the radiative structure decay K+ → e+υγ

The decay K⁺ → e⁺υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD₊) the branching ratio $\text{Γ(}\text{SD}{}_{\mathrm{+}}\text{)}\text{Γ(}\text{K}{}_{\mathrm{\mu 2}}\text{) = (2.33 ± 0.42) × 10}{}^{\mathrm{?5}}$ is obtained from 51 ± 3 events observed in the kinematical region E_e ? 235 MeV, E_γ > 48 MeV and θ_eγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD_?)/Γ(SD₊) < 11 (90% CL) from the sample of electrons with energies 220 MeV ? E_e < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region $\text{?1.8 < a}{}_{\mathrm{<mtext>K</mtext>}}\text{υ}{}_{\mathrm{<mtext>K</mtext>}}\text{< ?0.54}$.For the decay $\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}$ the limit $\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}\text{)/Γ(}\text{K}{}_{\mathrm{e2}}\text{) < 3.8}$ 90% confidence level) was found.     

The five-nucleon system above the three-particle threshold

Compound nucleus states in ${}^5\text{Li}$ and ${}^5\text{He}$ have been investigated with the ${}^3\text{He(d,p)pt}$ and ${}^3\text{H(d,n)pt}$ three-particle reactions. The observed $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$ states (E_X≈20 MeV) can be understood, in analogy to the ground states of the A=5 system, by coupling a $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ nucleon to the first 0⁺ excited state of ${}^4\text{He}$.     

Anomalous gamma-ray multiplicity distributions-evidence for pre-equilibrium neutron emission

Multiplicity distributions and 〈E_γ〉 have been measured for the ${}^{124}\text{Sn}\text{(}{}^{40}\text{Ar}\text{, x}\text{n}\text{)}{}^{\mathrm{164?x}}\text{Er}$ reaction at E(Ar) = 161, 182, 189, 209, and 236 MeV. The data at E(Ar) = 236 MeV indicate that pre-equilibrium neutrons are emitted. These data, together with other reactions leading to Er final systems, are discussed in terms of pre-equilibrium mechanisms.     

The excited states of 27Al

The γ-decay of 60 and the strengths of 51 ²⁶Mg(p, γ)²⁷Al resonances were studied for E_p < 2.20 MeV. The energies of 32 and the γ-decay of 54 bound levels were determined. Spin and parity assignments $\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{+}}\text{,}\text{5}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{and}\text{3}\text{2}{}^{\mathrm{+}}$ were made to the bound states at E_x = 4.81, 5.44, 6.61, 6.78, 7.68 and 7.86 MeV, respectively. Spin assignments $\text{J =}\text{5}\text{2}$and $\text{3}\text{2}$ were made to the bound levels at Einx = 5.55 and 6.08 MeV, respectively. For other levels spin and parity limitations were set. Lifetimes or lifetime upper limits of 19 bound levels were measured by means of the DSA technique. The spins and/or parities of 15 resonances were unambiguously determined from γ-ray angular distributions and strengths.     

Exact finite range CCBA results for the reaction 24Mg(d,p)25Mg at 14 and 15 MeV

The differential cross-sections for the ${}^{24}\text{Mg(d, p)}{}^{25}\text{Mg}\text{5}\text{2}{}^{\mathrm{+}}\text{(}\text{g.s.}\text{)}$ reactions at E_d = 15 Mev and $\text{7}\text{2}{}^{\mathrm{+}}\text{(1.61}\text{MeV state}\text{)}$ reaction at E_d = 14 and 15 MeV have been calculated using the full finite range CCBA code OUKID. It is shown that finite range effects are very important for these light ion reactions and that the deuteron D-state makes a negligible contribution at these energies.     

Measurement of vector and tensor analyzing powers in the d + 3He three-body break-up

The vector analyzing power A_y and the two tensor analyzing powers A_yy and A_xx have been measured for the three-body break-up reactions $\text{d}\text{+}{}^3\text{He}\text{→}\text{p}\text{+}{}^3\text{He}\text{+}\text{n}$ and $\text{d}\text{+}{}^3\text{He}\text{→}\text{p}\text{+}\text{t}\text{+}\text{p}$. Two of the outgoing particles were identified and detected in coincidence at θ_lab = ±30°. The deuteron bombarding energy was E_d = 15 MeV. The measurements are backed up by a series of tests in order to prove the absence of false asymmetries.