Coulomb excitation studies of 160Dy, 162Dy and 164Dy

Coulomb excitation measurements with ¹⁶O and ⁴He projectiles have been performed on ¹⁶⁰Dy, ¹⁶²Dy, and ¹⁶⁴Dy. The ground-state rotational bands up through the 8⁺ member were observed in the ¹⁶O experiments. The measured excitation probabilities yield B(E2; I → I ?2) values which are generally in agreement with the rotational predictions except for the 6⁺ → 4⁺ values. In each nucleus, probabilities for exciting the 2⁺, 4⁺, and 6⁺ members of the γ-vibrational band were measured and compared with calculated results. The B (E2; 0⁺ → 2⁺γ) values were measured in experiments involving ⁴He ions. The K^π = 2^? octupole band was observed in each nucleus in addition to 1^? bands in ¹⁶⁰Dy and ¹⁶²Dy. Excitation probabilities were analyzed in an attempt to extract B(E3) values.     

Polarization and polarization transfer in the 2H(d,n)3He reaction at 10 MeV

Angular distributions of six polarization transfer coefficients $\text{K}{}_{\mathrm{x}}{}^{\mathrm{x\prime }}\text{(θ), k}{}_{\mathrm{x}}{}^{\mathrm{z\prime }}\text{(θ), K}{}_{\mathrm{z}}{}^{\mathrm{<mtext>x</mtext><mtext>?</mtext>}}\text{(θ), K}{}_{\mathrm{z}}{}^{\mathrm{<mtext>z</mtext><mtext>?</mtext>}}\text{(θ),}\text{and}\text{K}{}_{\mathrm{yy}}{}^{\mathrm{<mtext>y</mtext><mtext>?</mtext>}}\text{(θ)}$; of the four analyzing powers A_y(θ), A_xx(θ), A_yy(θ), and A_zz(θ); and of the polarization function P^ý(θ), have been measured atE_d = 10.00 MeV for the reaction ²H(d, n)³He. Measurements were made for neutron lab angles between 0° and 80° in 10° steps. Additionally the y-axis associated quantities were measured at θ_1ab = 99°. Most of the measured coefficients are large at some angles and all show considerable variation with angle.     

The 16O(d, 3He)15N reaction at 29 MeV: Reaction mechanism and nuclear structure

The reaction ¹⁶O(d, ³He)¹⁵N has been investigated using 29 MeV deuterons, and angular distributions were obtained for levels in ¹⁵N up to 10 MeV excitation energy. The measured distributions were subjected to distorted-wave (DWBA), compound nucleus (Hauser-Feshbach) and coupled-channel (CCBA) analyses. Only the strong transitions to the $\text{1}\text{2}$^? ground state and the $\text{3}\text{2}$^? state at 6324 keV exhibit distributions which are well described by DWBA. The spectroscopic factors are in agreement with shell-model estimates. The weak transitions generally show little structure and the spectroscopic factors extracted for these transitions tend to be unreasonably large. Contributions from compound nucleus formation were estimated and found to vary between about 10 % and 100 % of the observed cross sections with an average of the order of 30 %. The CCBA analysis for the transitions to the $\text{5}\text{21}{}^{\mathrm{+}}$, $\text{5}\text{22}$⁺ and $\text{7}\text{2}$⁺ states at 5271, 7155 and 7566 keV, respectively, was performed using the spectroscopic amplitudes from weak coupling shell-model wave functions. Inelastic excitations to one-phonon states in the target and residual nuclei were included. The agreement between calculated and experimental distributions is good for both shape and magnitude, a conclusion which is not disturbed by the addition of small compound nucleus contributions. It is evident that spectroscopic factors extracted for the weak transitions on the basis of a direct one-step reaction mechanism alone are unreliable.     

A survey of the (3He, 7Be) reaction at 70 MeV

A study of the (³He, ⁷Be) reaction has been undertaken using a 70 MeV ³He beam. By surveying a wide range of target nuclides, namely ^{12, 13}C, ¹⁶O, ^{24, 26}Mg, ^{40, 42, 44}Ca, ^{58, 60, 62, 64}Ni, ⁹⁰Zr, ^{120, 124}Sn, ¹⁴⁴Sm and ²⁰⁶Pb, systematics of the α-clustering phenomenon were investigated. In addition, masses and energy levels of ⁶⁰Fe and ¹²⁰Cd were measured. The ⁷Be particles were detected in a single wire proportional counter backed by a plastic scintillator in the focal plane of an Enge spectrometer to ensure adequate particle identification. Total energy resolution as small as 140 keV full width at half maximum was obtained, although in most cases the target thickness limited the energy resolution to larger values. Differential cross sections as low as 20 nb/sr were measured. The finite range programs LOLA and LOLITA were used to calculate differential cross sections for comparison to data, assuming the reaction to proceed by a direct α-transfer. The spectroscopic factors which were extracted show a marked decrease with increasing atomic mass number, implying a decrease in surface α-clustering for heavier nuclei.     

Nucleon-nucleon final-state interactions in the reactions He(p, d)2p, He(p, t)2p and He(p, He)pn

The energy spectra of deuterons, tritons and ³He particles from the reactions ³He(p, d)2p, ⁴He(p, t)2p and ⁴He(p, ³He)pn have been measured at angles between 6° and 60° lab. The ³He(p, d)2p reaction was studied at both 30.5 and 49.5 MeV incident proton energies, while the other two reactions were studied at 49.5 MeV only. The energy spectra are compared with calculations based on the Watson-Migdal model of final-state interactions.     

Spectroscopy of low-lying positive parity states in 30P from the study of the reaction (3He,d) at 14.0 MeV

The reaction ²⁹Si(³He, d)³⁰P was studied at an incident energy of 14.0 MeV. Spectroscopic strengths for 14 positive parity states up to an excitation of 4.50 MeV have been obtained using DWBA analysis. The incident channel optical-model parameters for the DWBA calculations were extracted from elastic scattering cross sections measured also at 14.0 MeV.     

A comparison of the He(p, 2p)d and He(p, pd)p reactions

The ³He(p, 2p)d and ³He(p, pd)p reactions have been compared at three bombarding energies from 65 to 100 MeV. A comparison of plane wave impulse approximation calculations to the experimental data indicates that multiple scattering effects are large and energy dependent but that they primarily produce a uniform reduction in cross section. Although multiple scattering effects are large the ratio of the cross sections for the two reactions is in agreement with that predicted by the impulse approximation.     

DWBA analysis of (3He,d) reactions at 90MeV and contributions from the nuclear interior

Differential cross sections of ³He elastic scatterings and (³He, d) reactions have been measured at 90 MeV for ²⁸Si, ⁵⁴Fe, ⁵⁸Ni, ⁹⁰Zr and ¹²⁴Sn. From the optical-model analysis of the elastic scattering, both shallow ($\text{V ? 105}\text{MeV}$) and deep ($\text{V ? 150}\text{MeV}$) potentials of ³He were obtained. The shallow potentials correspond to the ones which were determined uniquely from other measurements extended to more backward angles. The (³He, d) reactions have been analyzed with the DWBA using the shallow and deep potentials for ³He. The calculations using the deep potentials reproduced the data well, but those using the shallow ones did not. The contributions from the nuclear interior were investigated through the radial cutoff in the DWBA. The calculations using the shallow potentials reproduced the data well when the radial cutoffs were introduced. The effects of the radial cutoff were very small when the deep potentials were used. It was found that a much greater reduction of the contributions from the nuclear interior was needed when the shallow potentials were used in the DWBA calculations.     

The 208Pb(α, 3He)209Pb reaction at 58 MeV

The ²⁰⁸Pb(α, ³He)²⁰⁹Pb reaction at 58 MeV has been used to search for high-spin states in ²⁰⁹Pb. Only three levels are excited with appreciable intensity: the ground state $\text{(2}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}$ and levels at $\text{0.781 (}\text{li}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{)}\text{and}\text{1.426}\text{MeV}\text{(}\text{lj}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}\text{)}$. The angular distributions for these levels have been measured and analyzed using standard DWBA calculations to obtain spectroscopic strengths. The ²⁰⁸Pb(α, α) elastic scattering was measured and optical parameters deduced from the data. A normalization value N = 50 yields spectroscopic values which are close to the values measured in the (d, p) reaction. The (α, ³He) reaction should easily pick out any appreciable components of the $\text{j}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ shell model state, which weak-coupling calculations predict should be fragmented. However only three weak transitions previously seen in a (d, p) experiment are observed.     

The study of (d,t) and (d, 3He) reactions in several 1p shell nuclei using vector-polarized beams

Cross-section and vector analyzing power angular distributions using 15 MeV deuterons were taken over an angular range of θ_1ab = 20–100° for the ¹⁰B(d, t)⁹B_{g.s.and 2.36 Mev state}, ¹⁰B(d, ³He)⁹Be_{g.s. and 2.43 Mev state}, ¹³C(d, t)¹²C_g.s., ¹⁴N(d, t)¹³N_g.s., and¹⁴N(d, ³He)¹³C_g.s. reactions, and vector analyzing power data alone were taken for the ¹⁶O(d, t)¹⁵O_g.s. and ¹⁶O(d, ³He)¹⁵N_g.s. reactions. Beams of vector-polarized deuterons were used for the vector analyzing power determinations. A comparison is made of the results for (d, t) and (d, ³He) reactions leading to mirror states when the self-conjugate targets ¹⁰B and ¹⁴N are used. The reactions provide evidence for a j-dependence of the vector analyzing power for l = 1 transfers in 1p shell nuclei. When the reactions involve a j-value admixture, the vector analyzing powers are used to attempt to determine percentage admixtures involved in the population of several final states.     

Study of 71, 73, 75, 77As with Ge(3He,d) reactions

Studies of ^{71, 73, 75, 77}As isotopes using Ge(³He, d) reactions have enabled the identification of many previously unreported levels together with new spin-parity assignments. A comparison of the results with the predictions of the model of Scholz and Malik shows good agreement for both positive- and negative-parity states.     

A systematic study of (n,d), (n,n' p) and (n,pn) reactions at 14.7 MeV

Cross sections for [(n, d) + (n, n′p) + (n, pn)] reactions induced by 14.7 ± 0.3 MeV neutrons on ⁴⁴Ca, ⁴⁹Ti, ⁵⁰Cr, ^{67, 68}Zn, ⁹²Zr and ^{97, 98}Mo have been measured by the activation technique using enriched isotopes as target materials, modern radiochemical separations and high-resolution counting methods. A brief summary of the literature data and our own earlier measurements is given. Our activation data are generally in agreement with those deduced from emitted charged particle characterisation. Some systematic trends in the activation cross-section data were analysed. Similar to other (n, charged particle) reactions, the [(n, d) + (n, n′p) + (n, pn)] reaction cross section decreases as a function of (N?Z)/A; the data, however, fall on two curves, one for nuclei with neutron separation energies (S_n higher than the proton separation energies (S_p) and the other for nuclei with S_n < S_p. For nuclei with S_n ? S_p the (n, n′p) process is very important. Detailed Hauser-Feshbach calculations show that in general contributions of statistical processes to the (n, d) reaction cross section are very small.     

Inelastic processes in the 19F(3He,d)20Ne reaction

We have examined the role of inelastic processes in the ¹⁹F(³He, d)²⁰Ne reaction. By coupling three levels in both the entrance and exit channels it was found that the inelastic processes were able to account for both the magnitude and rather flat shape of the angular distribution for the 4.25 MeV 4⁺ level observed in the ¹⁹F(³He, d)²⁰Ne reaction at 16 MeV bombarding energy. In contrast the DWBA could not account for the data. The magnitude of the inelastic processes was found to be quite sensitive to some of the optical model parameters involved. The DWBA predictions for the 0⁺ and 2⁺ cross sections were modified by the inelastic processes requiring some adjustment of the spectroscopic amplitudes to account for the data.     

On electron screening effects in the low-energy 3He(d,p)4He data

We have calculated the screening effects of the two electrons in the atomic ³He gas target on the low-energy³He(d, p)⁴He data. The nuclear degrees of freedom have been described within the microscopic multi-channel Resonating Group Method, while the two electrons have been treated in Born-Oppenheimer approximation deriving the exact screening potential within the Path Integral Monte Carlo method. Our model underestimates the observed screening effects implying the need to consider the coupling of nuclear and electronic degrees of freedom.     

A study of the C(p, p′) reactions at 135 MeV

A relativistic mean field approach is used to determine and compare the single-particle Dirac potentials for nuclei and hypernuclei (Λ, Σ, Ξ). A simple model is used and the Dirac-Hartree-Fock equations are reduced to a Schrödinger-like equation. The subsequent central and spin-orbit shell-model potentials are compared to those of phenomenological approach and other recent microscopic approaches. In the case of hypernuclei the Hartree approximation works already quite well without any need of taking into account the strangeness exchange part coming from strange mesons. The influence of the anomalous magnetic moment of the baryon on the spin-orbit term is found to be rather important for both Λ- and Σ-hyperons.     

Proton polarization and differential cross section for the (3He,p) reaction on 6Li and 9Be at 14 MeV

Angular distributions of the proton polarization and the differential cross section have been measured for the reaction (³He, p) initiated by 14 MeV incident ³He particles and proceeding to the ground and the first excited states of the final nuclei ⁸Be and ¹¹B. Large polarization values were observed, especially for the ⁹Be(³He, p)¹¹B reaction leading to both the ground and the first excited states in ¹¹B. The experimental results have been analysed in terms of a two-nucleon transfer spindependent distorted-waves theory using finite-range formalism and including corrections due to the non-locality of the optical potentials. A proper coherent summation over L and S, whenever necessary was included in the DWBA calculations of the polarization and the differential cross section as implied by the presence of the spin-orbit terms in the optical-model potentials used to generate the distorted waves.     

The 48Ca(3He,t)48Sc reaction at 66 and 70 MeV: Reaction mechanism and Gamow-Teller strength

The ⁴⁸Ca(³He, t)⁴⁸Sc reaction has been studied at E_3He = 66 MeV and 70 MeV. Angular distributions are given from θ = 8° to 35°. The 0⁺–7⁺ multiplet in ⁴⁸Sc is strongly excited at these energies and the spectra are further characterized by some broad structures on a continuous background. Broad peaks at E_ex = 7.8, 10.6 and 13.3 MeV have an angular distribution similar to the low-lying 1⁺ state. The broad peaks are interpreted as envelopes of groups of 1⁺ states carrying a significant part of the Gamow-Teller strength. The strength distribution is consistent with a shell-model calculation. The reaction mechanism has been examined at 66 MeV. The cross section is calculated for the 0⁺–7⁺ multiplet in ⁴⁸Sc as a coherent sum of one-step and two-step processes. The two-step contribution is calculated in a full finite-range 2nd-order DWBA. The result is similar contributions from (³He, α, t) and (³He, d, t). The calculations account reasonably well for the data with the exception of the transition to 0⁺, IAS.     

Compound nucleus contribution and even-odd effect for (3He,p) reactions in the Ni region

The compound nucleus contributions to the proton spectra from 8 MeV and 10 MeV ³He induced (³He, p) reactions on even-A Ni isotopes were obtained. The relative cross sections for ⁵⁸Ni/⁶⁰Ni/⁶²Ni in the high excitation region are in fair agreement with predictions of statistical theory, but the absolute cross sections in the same region are smaller than the prediction by a factor of 3 to 8, and the shapes of the measured spectra for heavier isotopes do not agree with the prediction. These discrepancies between experiment and theory are in sharp contrast to the situation in (p, p′), (p, α), (α, p) and (α, α′), where good agreement was found.The proton spectra from (³He, p) reactions on nuclei in the A = 54–68 mass range have a systematic difference in slope between even-A targets and odd-A targets; it is similar to the systematic difference found previously in (p, p′) and (α, p) reactions, but none of these is readily explainable by theory.