A feasibility study was made of an important aspect of the Coulomb-dissociation method, which has been proposed for the determination of the rate of the astrophysically important C-12(alpha, gamma)160 reaction. A crucial aspect is the disentanglement of nuclear and Coulomb interactions on one hand and the separation of dipole and quadrupole contributions on the other. As a first step the resonant breakup via two well-known 2(+) states of 160 was measured. The differential cross section of Pb-208(O-16, O-16*)Pb-208 and the angular correlations of the fragments C-12 and alpha in the center of mass were measured and compared to theoretical predictions calculated in DWBA and the coupled-channel method. The best agreement was found for the state at 11.52 MeV associated to a one-step excitation from the ground state, while the 9.84 MeV requires coupling to the first-excited 2(+) state and is not well described. (c) 2005 Elsevier B.V. All rights reserved.

Neutron inner hole responses in Sn-115 and Sn-119 nuclei have been studied via the ((d) over right arrow ,t) reaction at E-d=200 MeV using a polarized beam with both vector and tensor components. One-step pickup observables corresponding to the overlapping 1g(9/2), 1f(5/2), and 1f(7/2) responses were analyzed between 3degrees and 15degrees via a least square fit procedure up to E-X=21.5 MeV and 20 MeV in Sn-115 and Sn-119, respectively. The relative enhancement of transitions with high total angular momentum j and the strongly characteristic angular distributions of j(-)=l-1/2 versus j(+)=l+1/2 vector and tensor analyzing powers allow the extraction for the first time of 1f(5/2) and 1f(7/2) strength distributions and of new 1g(9/2) strength in addition to its previously known main component. The standard DWBA analysis is complemented by a refined analysis taking into account the form factor dependence on excitation energy due to the hole coupling with surface vibrations calculated in the framework of the quasiparticle-phonon coupling model (QPMFF). Residual nucleus spectra were measured, mainly in Sn-115, up to E(X)similar to45 MeV where the underlying background of multistep reactions is dominant and can be calibrated. The background of multistep pickup cross section is calculated for the first time in the forward angle region, assuming a dominant role of collective excitations in inelastic steps. Coupled channel calculations for two-step pickup observables involving low multipole collective excitations are performed for comparison. Integrated strengths deduced in the present work are compared with previous data on the 1g(9/2) structure and tail, and with the very limited previous information existing on the 1f strengths. The 1g(9/2), 1f(5/2), and 1f(7/2) QPMFF and standard strength distributions are compared with available theoretical predictions. In particular, we find that the 1f(5/2) and 1f(7/2) strength distributions are not well reproduced by the QPM model. The QPMFF spreading widths are found much narrower than the standard ones, but nevertheless much wider than predicted by theoretical calculations.

We describe the polarimeter POMME, and give the results of its calibration in the region 200-1200 MeV, using the Saturne polarized proton beam . The high energy part of this domain (800-1200 MeV) was previously unexplored. Parametrizations of the inclusive p-C analyzing power and polarimeter efficiency as a function of scattering angle and incident energy are given, completing the data already available at lower energies. The optimization of proton polarimeters in this energy domain is also discussed .

The Pb-nat(He-3,t) reaction and the subsequent decay of the excited nucleus by proton emission at backward angles were studied at E(He-3) = 177 MeV with the aim to separate the 2 (h) over bar omega isovector monopole strength in Bi isotopes from the continuum background. Since the continuum is largely due to quasifree processes associated with forward-peaked high-energy protons, the observed resonance-to-continuum ratio is drastically improved when coincidences between ejectile tritons and protons emitted at backward angles are required. Furthermore, the cross section for the monopole resonances excited via (He-3,t) is, unlike the cross sections for higher multipolarity excitations, strongly forward peaked. By comparing coincidence spectra at theta (t)approximate to0 degrees and at finite angles. monopole strength was found in the region -45<Q<-30 MeV. The measured monopole cross section is compared with distorted-wave Born approximation calculations for spin-Rip and non-spin-Aip isovector monopole excitations. It is found that 20% of the respective non-energy-weighted sum rules are exhausted in the proton-decay channel.

The Pb-nat(He-3, tp) reaction at E(He-3) = 177 MeV was studied to identify 2hw isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45 < Q < -30 MeV in the coincidence data. The cross section is compared with distorted-wave Born approximation calculations for non-spin-flip and spin-flip isovector monopole resonances. The observed spin-flip and non-spin-flip monopole strengths in the proton-decay channel amount to 20% of the respective non-energy-weighted sum rule.

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in Bi-208 has been investigated in the Pb-208(He-3,tp)Pb-207 reaction at E(He-3) = 450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in Pb-207 were deduced. These are found to be in good agreement with recent theoretical estimates. The (He-3,tp) reaction on Pb at E(He-3) = 177 MeV was also studied in order to locate isovector monopole strength corresponding to 2 (h) over bar w transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

Isoscalar spin-transfer excitations have been measured in Zr-90 and Pb-208 by inelastic scattering of vector and tensor polarized 400 MeV deuterons in an excitation energy range from 2.5 to 43 MeV and 2.3 to 23 MeV, respectively. For Zr-90, spin excitations were found between 7.5 and 10.7 MeV and in a large structure in the continuum (18 to 28 MeV). For (208)pb, spin excitations were found at 3.55 and 5.85 MeV, between 6.5 and 11 MeV, and spread over the continuum. Elastic scattering cross sections and vector and tensor analyzing powers were measured between 3.4 and 24 degrees for Zr and Pb, and optical potential parameters were derived. The experimental results are compared to DWIA/RPA calculations. The transition densities used are generated using the continuum random phase approximation. [S0556-2813(99)06301-3].

The study of the Pb-208((d) over right arrow,t)Pb-207 reaction at E-d=200MeV has been extended up to typically E-x =40 MeV in Pb-207 using a polarized beam with both vector and tensor components. Two-step pickup reactions involving low multipolarity collective transitions have been evaluated for the first time via systematic coupled channel calculations, allowing a new approach of the background determination. The (d,t) observables corresponding to the overlapping 1h(11/2), 1g(7/2), and 1g(9/2) inner hole responses have been analyzed up to E-x = 25 MeV via a least squares fit procedure. Necessary input values were deduced for hole states of interest from finite range distorted wave (DWBA) calculations. The optical parameters and the range function were those successfully used in a previous survey of valence state observables. The highest j transitions are enhanced in the reaction and analyzing powers exhibit strongly characteristic features for j(-) = l - 1/2 versus j(+) = l + 1/2 states. We have calculated for the first time the separation energy dependence of nlj transition observables, taking into account the form factor modifications induced by the hole coupling with surface vibrations. The calculations have been performed in the framework of the quasiparticle-phonon model (QPM). This analysis (QPMFF) predicts a large variation of differential cross sections with excitation energy of the hole fragments, while angular distribution shapes remain quite stable. The strength distributions resulting of the QPMFF analysis and of a standard analysis using DWBA observables calculated at the centroid energies are systematically compared. As a general rule, the QPMFF analysis increases the strength concentration toward lower excitation energy. The corresponding 1h(11/2), 1g(7/2), and the tentative 1g(9/2) strength distributions are compared and discussed with the available theoretical calculations. In particular, the narrower spreading widths deduced via the QPMFF analysis are quite well predicted by the calculation of spectral functions in a modified mean field. The 1 i(13/2) and 1 h(9/2) valence strength distributions are revisited along this new approach and found to be in fair agreement with the fragmentation predicted by the QPM, which is not the case of inner hole strength distributions. [S0556-2813(98)04510-5].

Inelastic scattering of 600 MeV vector and tensor polarized deuterons has been carried out at energy losses corresponding to quasielastic, incoherent scattering from individual nucleons in targets of CH2, CD2, C, Ca, and Pb at fixed momentum transfers of 345 and 500 MeV/c. Vector (A(y)) and tenser (A(yy)) analyzing powers were measured, and the vector polarizations P-y' of the scattered deuterons were determined by the polarimeter POMME. These observables were combined to determine the vector spin transfer coefficients K-y(y') for the deuterons and several signatures for spin transfer probabilities across the quasielastic spectra.

The isoscalar spin‐transfer signature Syd has been used in inelastic scattering of 400 MeV polarized deuterons to search for ΔS=1 ΔT=0 strength in 40Ca and 12C. In 40Ca, spin excitations were found in the 9 MeV region and over a broad range in the continuum with a cluster strength around 15 MeV. In 12C, a previously unknown ΔS=1 ΔT=0 level was observed at 20.5 MeV; ΔS=1 ΔT=0 resonances were also found at 20 MeV and 30 MeV. Microscopic DWIA calculations agree nicely with 12C data.

We have developed a DWIA method to calculate (d,d′) inelastic scattering at intermediate energies. Comparison is made to existing data for 12C(d,d′) at 400 MeV for dσdΩ, Ay, Ayy, Py, Kyy and the spin-flip probability. All observables are correctly reproduced.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation S. Kox, C. Furget, J. S. Réal, L. Bimbot, C. Djalali, G. W. R. Edwards, M. Garçon, C. Glashausser, B. N. R. Johnson, M. Morlet, L. Rosier, E. Tomasi‐Gustafsson, E. Voutier, A. Willis; A new deuteron tensor polarimeter and a measurement of t20 in e‐d scattering at CEBAF. AIP Conf. Proc. 15 July 1995; 339 (1): 545–550. https://doi.org/10.1063/1.48631 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

A cross section enhancement, persisting to high momentum transfer, has been observed around 1HBAR omega in excitation energy in spectra from inelastic proton-, alpha- and electron scattering on Zr-90, Sn-116, Pt-196 and Pb-208. Data are presented for (p,p') at 201 MeV, (alpha,alpha') at 120 MeV and analyzed together with existing data obtained with 133.8 MeV polarized ((p) over right arrow,p') on Sn-116 and electron-scattering data on Sn-116 and Pt-196. Two different interpretations of the observed enhancement are discussed: that of the incoherent sum of all 1HBAR omega cross section and alternatively the sum over the isoscalar normal modes of all multipolarities.