Beobachtung der inneren Paarbildung an200Hg nach Neutroneneinfang

Absolute excitation functions and angular distributions have been measured for the reactions⁹Be(d, p₀),⁹Be(d, p₁),⁹Be(d, t₀),⁹Be(d, α₀) and⁹Be(d, α₁) at energies between 0.6 and 2.7 MeV. Attempts to fit some of the data with DWBA calculations are discussed.     

Identification of a 3+ state in16O and evidence for a (1f 7/2 1p 1 2/−1 ) component in its wave function

Excitation functions and angular distributions for the elastic scattering of protons on¹⁵N and the reactions¹⁵N(p, α ₀)¹²C and¹⁵N(p,α ₁)¹²C^* were measured in the proton energy range of 2.50?5.14 MeV (E _x (¹⁶O)=14.47?16.94 MeV). Besides known resonances two new ones were found at 16.46 and 16.82MeV. For the latterJ ^?=3⁺ is assigned using the compound nucleus theory. The wave function of this state contains a (1f _7/2 1p ₁ ^2/?1 )₃-particle-hole-component. Earlier spin parity assignments of other resonances are discussed.     

Excitation of high-spin unnatural parity states in 208Pb from the (p,p′) reaction at 135 MeV

Differential cross sections for the excitation of states at 6.42, 6.73 and 7.04 MeV in ²⁰⁸Pb by 135 MeV protons are reported. Both the excitation energies and the backward peaked angular distributions observed in this experiment and in a recent (e, e′) experiment strongly suggest that these states are predominantly one-particle-one-hole excitations with J^π = 12^?, 14^? and 12^?, respectively. The present (p, p′) data are interpreted using a distorted wave impluse approximation and the effect of configuration mixing between the two 12^? states is investigated.     

Isospin mixing observed in the reaction 12C(6Li, α)14N

The reaction ¹²C(¹²Li, α)¹⁴N was studied to investigate the isospin mixing of high-lying levels in ¹⁸F. Excitation functions and angular distributions of the α-transitions to the ground, first and second excited states in ¹⁴N were measured for bombarding energies from 3.2 to 8.0 MeV. The isospin-forbidden cross section for the excitation of the lowest T = 1 state in ¹⁴N at 2.31 MeV was found to lie between 1–2 % of that of the allowed transitions. A partial wave analysis of the α₁ angular distribution data revealed a strong resonance with J^π = 2⁺ at E_x = 15.99 MeV. Arguments are presented which tentatively identify this resonance as being due to two close-lying 2⁺ levels with different isospin.     

Application of the Abrikosov pseudofermion technique to a homogeneous spin system

The angular distributions of the α₀ and α₁ groups for the (n,α) reactions on¹¹B,¹⁴N,¹⁶O have been measured atE _n=14.1 MeV. In the¹¹B(n, α₀)⁸Li reaction the compound mechanism seems to be favoured as can be demonstrated with Hauser-Feshbach calculations. In the other reactions direct mechanisms dominate.     

Two-nucleon T = 0 transfer reactions in the 0p shell

The ¹⁶O(d, α)¹⁴N, ¹⁴N(d, α)¹²C and ¹²C(d, α)¹⁰B reactions at E_d = 40MeV and the ¹²C(α d)1¹⁴N at E_α = 55 MeV were investigated. A total of seventeen transitions are analysed in terms of one-step, zero-range DWBA calculations, using the two-particle coefficients of fractional parentage obtained from the Cohen-Kurath Op shell wave functions. For most transitions, fair agreement is obtained between experiment and calculation, possible exceptions being the transition to the E_x = 4.43 MeV, J^π = 2⁺ state in ¹²C and to the E_x = 2.15 MeV, J^π = 1⁺ state in ¹⁰B, for which the calculations predict too much L = 0 strength. Where possible, a comparison with previous (p, ³He) results is made. In ¹⁴N a state at E_x = 11.04 MeV was observed for which the values (J_π; T) = (3⁺; 0) are suggested. In ¹²C we found, in addition to the well known T = 0 states, two relatively sharp T = 0 states at E_x = 19.50 ± 0.10 and 20.55 ± 0.10 MeV. The shape and strength of the angular distribution for the transitions to these states can be approximately accounted for by the calculations, although no one-to-one correspondence between observed and predicted levels could be established.     

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⁺.     

Structures in the excitation functions for compound reactions in the12C+14C system

Excitation functions for the elastic scattering of¹²C on¹⁴C and the reactions¹⁴C(¹²C, α)²²Ne,¹⁴C(¹²C,t)²³Na and¹⁴C(¹²C,d)²⁴Na have been measured in the vicinity of the Coulombbarrier. Strong fluctuations of the differential cross sections as a function of incident energy are observed in the α-particle, triton and deuteron channels. The total yield in the three different channels shows correlated structures at energiesE _c.m.=6.8, 7.2 and 8.3 MeV. This phenomenon is similar to the structures observed in the¹²C+¹²C reactions and indicates the possible presence of resonances in the entrance channel.     

Size and shape of the nuclear density distributions of20Ne and28Si from 104 MeV alpha particle scattering

Measured differential cross sections for the scattering of 104 MeV α particles from²⁰Ne and²⁸Si are analyzed on the basis of a deformed folding model. Rms-radii and values of the deformation parameters for the nuclear density distributions are extracted, and the effect of the size of the α particle is demonstrated. Previous discrepancies between (p,p′) and (α, α′) results are partly removed.     

Investigation of quasimolecular states in 24Mg* through the analysis of the angular dα correlations in the 12C(14N, d)24Mg(α)20Ne reaction

Theoretical analysis of the differential cross sections and angular correlation functions in the ¹²C(¹⁴N, d)²⁴Mg*(α)²⁰Ne reaction at the energy of the incident nitrogen ions E _lab=29–42 MeV is performed in the models of the direct transfer of ¹²C cluster and the compound nucleus. Amplitudes of the reduced widths for the excited quasimolecular states like ¹²C ? ¹²C* in the ²⁴Mg nucleus are obtained. The effect of various states of the relative motion of nuclei in the ¹²C + ¹²C* configuration on the angular dα-correlation functions is studied.     

Spin assignments by a high spin selective heavy ion reaction

The reaction¹²C(¹⁴N,d)²⁴Mg is investigated atE _Lab=52 MeV by means or a multigap magnetic spectrograph. Angular distributions of levels between 6.00 and 20.21 MeV are measured using nuclear track emulsions. By quantitative analysis of the angular distributions (FRDWBA- and Hauser-Feshbach calculations), the reaction is shown to proceed almost completely via compound mechanism. The reaction is applied for selective excitation of high spin states in²⁴Mg. Evidence is given by this example that under suitably chosen conditions a complex heavy ion reaction can be a powerful means for spin assignments at high excitation energies.     

A study of the (d, α) reaction in 56Fe at 12 MeV

The (d, α) reaction in ⁵⁶Fe is studied at E_d = 12 MeV and angular distributions of the α-particles are obtained over the angular range 13°–83° (c.m.s.); the results are analysed in terms of the DWBA theory of direct reactions using the two-nucleon pick-up mechanism of Glendenning. Spectroscopic information on ⁵⁴Mn levels up to 4.3 MeV excitation is obtained.     

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, ¹²C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E_α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A_t^{?5 ± 1}. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ_T < 10^?34 cm² consistent with present experimental limits. The data for ²⁴Mg(α, ¹²C)¹⁶O has been studied in more detail and indicates a selective population of final states including ¹⁶O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct ⁸Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2⁺, E_x ≈ 7 MeV; 4⁺, E_x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated ⁸Be cluster overlaps and the calculated and measured (α, ¹²C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.     

Measurement of a 4π angular pattern for α-decay of 12C excited by inelastic deuteron scattering

The reaction ¹²C(d, d′)¹²C(3^?,9.6MeV) → α + ⁸Be(g.s.), was studied experimentally at 26 MeV deuteron energy with the multi-detector system BOL. The grid of angular coordinates at which data were taken is evenly spread over the available phase space. The angular correlation function of the inelastically scattered deuteron and the α-particle emitted by the excited ¹²C nucleus was obtained. Experimental results are presented as the coefficients of an expansion in spherical harmonics. A DWBA analysis can explain the measured angular correlation pattern in a qualitative way only.     

Elastic scattering of deuterons by 14C from Ed = 4 to 10 MeV

Angular distributions for the elastic scattering of deuterons by ¹⁴C were measured at nine energies between E_d = 4.2 and 10 MeV. Excitation functions were taken in 50 keV steps from E_d = 4 to 10 MeV. A resonance was observed at E_d = 4.5 MeV, which corresponds to an excitation energy of 14.41 MeV in ¹⁶N. An analysis using an optical model plus a single-level formula derived from the R-matrix formalism yields an l-value assignment of l = 4 for this resonance. Of the three J^π values allowed for l = 4 (J^π = 3⁺, 4⁺, 5⁺), the value of J_π = 3⁺ is found to be slightly preferred. Possible identification of this resonance with an analog in ¹⁶O is discussed. The angular distributions measured at off-resonance energies were analyzed with an optical-model potential which has a surface-peaked imaginary well. The energy dependence of the real and imaginary well depths are explicitly determined in the present work for E_d = 4 to 10 MeV. The best-fit optical-model parameters obtained from the present study are compared to those from the ¹⁴N(d, d)¹⁴N work.     

Level density parameters of47Ti and50V

The energy distribution of the protons andα-particles from the reactions⁴⁷Ti(α, α′),⁴⁷Ti(α, p) and⁵⁰V(p, α) was measured in the angular range from 60° to 150°. The energies of the incoming particles were 15.35 MeV forα-particles and 13.85 MeV for protons. The results can be described in the frame of the statistical model of the nuclear reactions. The level density parameters could be determined by comparing the experimental data with the theoretical results. The values for the backshifted Fermi gas model are⁴⁷Ti:a=6.6±0.6MeV^?1,Δ=?0.5±0.3 MeV⁵⁰V:a=6.3±0.6 MeV^?1,Δ=?1.0±0.3 MeV.     

Winkelverteilung der Polarisation der Neutronen aus der Reaktion14C(d,n 0)15N bei Deuteronenenergien zwischen 1,3 und 1,9 MeV

Polarization distributions of ground state neutrons emitted from the¹⁴C(d,n ₀)¹⁵N reaction were investigated over the angular range from 15 ° (lab) to 150 ° (lab) at bombarding energies of 1.28, 1.55 and 1.88 MeV. Scattering of neutrons from helium served as polarization analyzer. The experimental results show a large variation with energy of the polarization ranging betweenP(Θ_lab=130 °)=?21% andP(Θ_lab=130 °)=+50% at 1.28 and 1.88 MeV respectively.     

The reaction12C(α,p 0)15N around 18 mev excitation energy of16O

Proton angular distributions of the reaction¹²C(α, p ₀)¹⁵N have been measured at excitation energies from 17.5 to 18.7 MeV. The shape of the angular distributions changes strongly betweenθ _cm = 26°–162°. The integrated cross section shows a smooth behaviour in contrast to the (α, n) mirror reaction. The results can be explained by an interference of the known 18.18 MeV, 2⁺ state with a strong isospin mixed 18.1, 3^? state in the¹⁶O compound nucleus.     

Angular distributions of neutron polarization from the 14C(p,n)14N and 11B(α, n)14N reactions and R-matrix analysis oF 15N in the excitation-energy range between 11.5 and 12.5 MeV

Angular distributions of neutron polarization from the ¹⁴C(p, n)¹⁴N and ¹¹B(α, n)¹⁴N reactions have been studied for the particle energies E_p = 1.788, 2.025, 2.272 and 2.450 MeV, and E_α = 2.049 MeV. The polarization was derived from the left-right asymmetry induced by elastic scattering from ⁴He. Together with existing measurements of angular distributions and total cross sections for several reaction channels leading to ¹⁵N with an excitation energy between 11.5 and 12.5 MeV, these data were used to deduce from R-matrix analysis a set of resonance parameters for the ¹⁵N levels in this energy range.     

Exact finite-range DWBA description of the60Ni(160,12C)64Zn reaction at 60 MeV incident energy

Cross section angular distributions of⁶⁰Ni(¹⁶O,¹²C)⁶⁴Zn reactions leading to three strongly excited states at 60 MeV incident energy and the¹⁶O+⁶⁰Ni and¹²C+⁶⁴Zn elastic scattering at 60 MeV respectively 45 MeV and 54 MeV have been measured using aQ3D magnetic spectrograph. EFR-DWBA calculations assuming the transfer of anα-cluster in its 0s ground state are able to describe the general features of the strongly oscillating experimental angular distributions using a surface transparent optical model potential. The optical model parameters used in the DWBA calculations are obtained from fits of the elastic scattering data of incident and exit channels. The importance of “correct” optical model parameters in the exit channels for relative spectroscopic factors will be discussed and the extracted relative spectroscopic factors will be compared to previous (⁶Li,d) results.