E2 Multipolarity Research Articles

The astrophysical S-factor of proton radiative capture on triton

The proton capture on 3H is important to understand various physical and astrophysical processes. In this study, the cross section and astrophysical S-factor of the proton radiative capture on triton were taken into account at low energies. The 3H(p,γ)4He reaction was studied using the E1 transition. The gamma-ray transition is dominated by the E1 multipolarity and by incoming p-waves. The non-resonant astrophysical S-factors for the E1 transition were calculated using the potential model. The results were satisfactorily in good agreement with the corresponding experimental data.

Beta decay of 94Pd and of the 71 s isomer of 94Rh

The β decay of 94Pd and of the 71s isomer of 94Rh was investigated by using total γ-ray absorption techniques. Several levels in 94Rh are established, including a new low-lying isomer characterized by a half-life of 0.48(3)μs and a de-exciting transition of 55keV. E2 multipolarity is determined for this transition by measuring the intensities of its γ-rays and the characteristic X-rays from its electron conversion. On the basis of the measured reduced β-decay transition rates to known 94Ru levels and shell model considerations, the spin-parity of the 71s and the 0.48μs isomers of 94Rh is assigned to be (4+) and (2+), respectively. The β-decay strength distributions measured for 94Pd and the 71s isomer of 94Rh yield Q EC values of 6700(320) and 9750(320)keV for these decays and give evidence for the population of those states below and above the magic N = 50 gap that belong to both components of the 0g spin-orbit doublet.

Calculation of the nuclear vertex constant (asymptotic normalization coefficient) for the virtual decay 6Li → α + d on the basis of the three-body model and application of the result in describing the astrophysical nuclear reaction d(α, γ)6Li at ultralow energies

Within the (α, n, p) three-body model, the s-wave 6Li → α + d vertex constant G01 and the asymptotic normalization coefficient C01 (these two quantities are proportional to each other) for the wave function describing the 6Li nucleus in the α + d channel are calculated by solving Faddeev equations for various sets of nucleon-nucleon and αN potentials. The resulting values of G01 and C01 are used to calculate the astrophysical factor S(E) for the radiative-capture reaction d(α, γ)6Li at energies in the range E = 0–600 keV. The calculated values of G01 and C01 appear to be sensitive to the form of the pair potentials used. It is shown that, upon correctly taking into account the contributions of the E2 and E1 multipolarities, the values of S(E) in the region E < 150 keV are determined primarily by the values of C01 and of the 6Li binding energy in the α + d channel.

Re-evaluation of the low-energy Coulomb-dissociation cross section of 8B and the astrophysical S17 factor

An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254 AMeV was used to infer the low-energy 7Be(p,γ)8B cross section. Particular emphasis was placed on the angular correlations of the breakup particles which demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct 7Be(p,γ)8B measurements.

Low-energy cross section of theBe7(p,γ)B8solar fusion reaction from the Coulomb dissociation ofB8

An exclusive measurement of the Coulomb breakup of {sup 8}B into {sup 7}Be+p at 254A MeV was used to infer the low-energy {sup 7}Be(p,{gamma}){sup 8}B cross section. The radioactive {sup 8}B beam was produced by projectile fragmentation of 350A MeV {sup 12}C and separated with the FRagment Separator (FRS) at Gesellschaft fuer Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S{sub 17} factors exhibit good agreement with the most recent direct {sup 7}Be(p,{gamma}){sup 8}B measurements. By using the energy dependence of S{sub 17} according to the recently refined cluster model for {sup 8}B of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S{sub 17}(0)=20.6{+-}0.8(stat){+-}1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.

Precision electron-gamma spectroscopic measurements in 75As

The decay of 75Se to levels of 75As has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 18 gamma rays and 16 conversion electron lines reported for the first time. New results also include E2 multipolarity assignment for the 81 keV transition, M1 assignment to three newly observed transitions and M1 + E2 for the 617 keV transition. A revised 75As level scheme is constructed using the Ritz combination principle through the computer code GTOL. While confirming the existence of 10 well-established levels, two levels at 587 and 859 keV are newly placed into the decay scheme of 75Se. The interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly placed 586.8 keV 1/2- and 859.9 keV 1/2+ levels are studied in the light of the Interacting Boson-Fermion Model.

Coulomb dissociation of 8B and the low-energy cross section of the 7Be(p,gamma)8B solar fusion reaction.

An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254A MeV allowed the study of the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates and that E2 multipolarity can be neglected. By using a simple single-particle model for 8B and treating the breakup in first-order perturbation theory, we extract a zero-energy S factor of S17(0)=18.6+/-1.2+/-1.0 eV b, where the first error is experimental and the second one reflects the theoretical uncertainty in the extrapolation.

A computer program for nuclear scattering at intermediate and high energies

A computer program is presented which calculates the elastic and inelastic scattering in intermediate and high energy nuclear collisions. A coupled-channels method is used for Coulomb and nuclear excitations of E1, E2, E3, M1, and M2 multipolarities, respectively. The program applies to an arbitrary nucleus, specified by the spins and energies of the levels and by reduced matrix elements. For given bombarding conditions, the angular distribution of elastic and inelastic scattered particles and angular distributions of gamma-rays from the excited nucleus are computed.

New features of the IC(4) code and comparison of internal conversion coefficient calculations

The IC(4) software developed to compare calculated internal conversion coefficients (ICC) has been enhanced by adding new features through the use of Borland Delphi and TeeChart. Particularly, the 3D-graph option enhances the possibilities of analyzing calculated ICC values. For example, the comparison between the results given by three sets of theoretical ICC tables for any arbitrary pair of calculated ICC can be presented in a much clearer manner. Their differences can be displayed as energy vs. atomic number surfaces. Results from the analyses of K-shell and total ICCs for E2, E3, M2, M3, and M4 multipolarity are discussed.

Evidence for octupole vibration in superdeformed 196Pb

Abstract Evidence for a low-lying octupole vibrational excitation in the superdeformed energy minimum of 196 Pb is presented. High-spin states in this nucleus have been populated in the 170 Er( 30 Si, 4n) 196 Pb reaction. The in-beam γ -ray decay has been investigated using the EUROBALL IV Ge-detector array. The linear polarization of γ -ray transitions connecting an excited superdeformed band with the yrast superdeformed band has been measured from which E1 multipolarity is determined. These E1 transitions, which compete with the highly collective in-band E2 transitions, are strongly enhanced. This is an important step towards establishing that low-lying octupole vibrations are a wide spread phenomenon in the A =190 region of superdeformation.

Precise determination of the intensity of 226Ra alpha decay to the 186 keV excited state

There is a significant discrepancy in the reported values for the emission probability of the 186 keV gamma-ray resulting from the alpha decay of 226 Ra to 186 keV excited state of 222 Rn. Published values fall in the range of 3.28 to 3.59 gamma-rays per 100 alpha-decays. An interesting observation is that the lower value, 3.28, is based on measuring the 186 keV gamma-ray intensity relative to the 226 Ra alpha-branch to the 186 keV level. The higher values, which are close to 3.59, are based on measuring the gamma-ray intensity from mass standards of 226 Ra that are traceable to the mass standards prepared by HONIGSCHMID in the early 1930's. This discrepancy was resolved in this work by carefully measuring the 226 Ra alpha-branch intensities, then applying the theoretical E2 multipolarity internal conversion coefficient of 0.692±0.007 to calculate the 186 keV gamma-ray emission probability. The measured value for the alpha branch to the 186 keV excited state was (6.16±0.03)%, which gives a 186 keV gamma-ray emission probability of (3.64±0.04)%. This value is in excellent agreement with the most recently reported 186 keV gamma-ray emission probabilities determined using 226 Ra mass standards.

Structure effects on the Coulomb dissociation of [formula omitted]B at relativistic energies

We investigate the Coulomb dissociation of 8B on a 208Pb target at the beam energy of 250 MeV/nucleon, employing the cross sections for the radiative capture reaction 7Be(p,γ)8B calculated within the Shell Model Embedded in the Continuum (SMEC) approach. In contrast to the situation at lower beam energies, the Coulomb breakup cross sections are found to be sensitive to the M1 transitions. Comparisons of SMEC and single-particle potential model predictions show that the Coulomb breakup cross sections at these high energies are sensitive to the structure model of 8B. Comparison with the preliminary data on the angle integrated spectra reported recently by the GSI group shows that the theory is able to reproduce the absolute magnitude as well as the shape of this data well. The contributions of the E2 component strongly depends on the range of the angles of the p–7Be center of mass with respect to the beam direction, included in the angular integrations of the double differential cross section. If integrations are done over the angular range of 0°–1.87°, the E2 multipolarity contributes up to 25 % to the cross sections even for the relative energies of [p–7Be] below 0.25 MeV. However, these contributions are reduced by an order of magnitude at lower relative energies if the maximum of the angle integration is ∼ 1°.

Parity of the band head at 3710 keV in 99Rh using clover detector as compton polarimeter

Clover detector has been used as a Compton polarimeter to measure the linear polarization of γ-rays produced in heavy ion fusion reaction. The polarization sensitivity of the clover detector has been measured over γ-ray energies ranging from 386 to 1368 ke V. The E1 multipolarity of the 1117 keV transition in 99Rh has been established using this polarimeter. This has resulted in the assignment of negative parity to the band head at 3710 keV in 99Rh.

Beta decay of 125Sb and level structures in 125Te

The decay of 2.76y 125Sb to levels of 125Te has been studied using an HPGe detector for gamma-ray and a mini orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 13 gamma rays and 4 conversion electron lines being reported for the first time. New results also include E1 multipolarity assignments to 3 newly observed transitions and M-shell conversion coefficient for the 109 keV M4 transition. A revised 125Te level scheme is constructed using Ritz combination principle. While confirming the existence of 10 well established levels below 700 keV excitation, we introduce 3 other levels at 402.0, 538.6 and 652.9 keV. Interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly introduced 538.6 keV (1/2+) and 652.9 keV (3/2+) levels are seen as the two missing members of the (s 1/2 ⊗ 2+) and (d 3/2 ⊗ 2+) sextuplet in the quasiparticle-phonon coupling scheme.

Excitation of continuum states in 7Li and their decay by quantum tunneling

Strong forward-backward asymmetries were found in the recent α — t coincidence measurement of Coulomb breakup of 42 MeV- 7 Li via continuum states. The competition between E1 and E2 multipolarities and higher order effects in Coulomb excitation were investigated by solving the time-dependent Schrodinger equation. It is shown that higher order effects are an essential ingredient to the observed large asymmetries. The relevant reaction mechanism is discussed.

Conversion--electron gamma--ray coincidence spectroscopy of superdeformed 135Nd

Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e- coincidence spectroscopy of superdeformed 135Nd. Transitions within the superdeformed band are shown to have the expected E2 multipolarity. The 766.5–keV transition which links the band to a positive-parity state has a conversion coefficient consistent with M1 multipolarity. Consequently, positive parity is deduced for the superdeformed band. No evidence for E0 transitions was found.

E2 component in subcoulomb breakup of 8B

We calculate the angular distribution and total cross section of the ^{7}Be fragment emitted in the break up reaction of ^{8}B on ^{58}Ni and ^{208}Pb targets at the subCoulomb beam energy of 25.8 MeV, within the non-relativistic theory of Coulomb excitation with proper three-body kinematics. The relative contributions of the E1, E2 and M1 multipolarities to the cross sections are determined. The E2 component makes up about 65% and 40% of the ^{7}Be total cross section for the ^{58}Ni and ^{208}Pb targets respectively. We find that the extraction of the astrophysical S-factor, S_{17}(0), for the ^{7}Be(p,\gamma)^8B reaction at solar energies from the measurements of the cross sections of the ^{7}Be fragment in the Coulomb dissociation of ^{8}B at sub-Coulomb energies is still not free from the uncertainties of the E2 component.

Conversion-electron spectroscopy in the decay of superdeformed 135Nd

We have investigated the structure of the superdeformed band in 135Nd using conversion-electron spectroscopy. The transitions within the superdeformed band show conversion coefficients which are consistent with an E2 multipolarity. From the conversion coefficients of transitions linking this band with known low-lying states its positive parity was established. Hence, a direct determination of the parity of a high-spin superdeformed band could be performed for the first time.

The photodissociation of 8B and the solar neutrino problem

The extraction of the photodissociation cross sections of $^8B$ from Coulomb dissociation experiments is investigated. A careful study is done on the contributions of the E1, E2 and M1 multipolarities to the breakup. A comparison with the data of a recent experiment is performed. It is shown that the extraction of the radiative capture cross sections $^7Be(p,\ \gamma)^8B$ which are relevant for the solar neutrino problem is not affected appreciably by Coulomb reacceleration. A non-perturbative model is used for the purpose. Emphasis is put on the perspectives for future experiments which are planned at the University of Notre Dame, RIKEN (Japan), and GSI (Germany). An analysis of the total yields of ``photon-point" processes in inelastic electron scattering is also done.

Conversion coefficients and yrast state spins in 180Os

Internal conversion coefficients of transitions in 180Os have been measured using a superconducting, solenoidal electron spectrometer, operated in the lens mode. The high energy resolution and efficiency allow a precise measurement of the conversion coefficients of the 528 keV yrast transition. The values obtained, α K = 0.015(2), α L = 0.004(1) define pure E2 multipolarity. Taken with the measured γ-ray angular distribution, the conversion coefficient leads to an unambiguous assignment of 16 + → 14 + for the 528 keV transition.