Lars Westerberg

Multiphonon vibrational states in 106,108Pd

Abstract The nuclei 106 Pd and 108 Pd have been Coulomb excited using beams of 16 O, 58 Ni and 208 Pb. The data determined 25 and 31 E2 matrix elements in 106 Pd and 108 Pd, respectively. The experimental data are qualitatively in agreement with the spherical-harmonic quadrupole vibrational model, but quantitatively there are large discrepancies, even for the states generally accepted to be the two-phonon vibrational states. A sum-rule method was applied to the data, the result of which implies that the vibrational quadrupole strengths of the 0 + and 4 + two-phonon states are fragmented and shared between several E2 matrix elements. The E2 matrix elements imply appreciable quadrupole triaxiality with a γ-centroid of about 20°. A systematic comparison is made with neighbouring Pd-isotopes and with 114 Cd.

Heavy-ion Coulomb excitation of 72Ge

Abstract The nucleus 72Ge has been Coulomb excited using 16O, 58Ni and 208Pb. Seventeen E2 matrix elements coupling the low-lying states have been determined. Based on these data, an interpretation of the structure of 72Ge has been proposed that includes an “intruder” 0+ state perturbing what the present work shows to be a triaxial quadrupole-deformed collective rotational structure.

Fabrication of an integrated ΔE-E-silicon detector by wafer bonding using cobalt disilicide

Abstract The problem concerning mechanical stability of thin self-supporting ΔE detector in a ΔE-E semiconductor detector telescope, has been solved by integrating both detectors into one unit. We show here a low-cost method to integrate the detectors by wafer bonding using cobalt disilicide. The ΔE-detector has a thickness of 6.5 μm and the E detector 290 μm with an area of 24.8 mm2. The system was characterized with secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), electrical measurement, particle measurement and two-dimensional electrical simulation.

Stable absolute calibration standards for hydrogen profile analysis using nuclear resonance techniques

Abstract Samples of pyrolytic carbon, CH x ( x ≈ 0.03) from pyrolysis of methane, and amorphous silicon, SiH x ( x ≈ 0.2) from plasma deposition of silane, are shown to be stable during ion bombardment and vacuum storage. They are therefore well suited as calibration standards for hydrogen profile analysis using nuclear resonance reactions such as 1 H( 15 N, αγ) 12 C. Due to its high hydrogen content and the possibility of absolute calibration by vacuum extraction, tantalum hydride, TaH x ( x ≈ 0.5) has been used for the absolute calibration of these standards.

E0 transitions in 114,116,118Sn

Abstract Low-lying 0 + states have been excited in the (p, p′) reaction via the s 1 2 isobaric analog resonance in 114,116 Sn and in radioactive decay in 118 Sn. From conversion electron measurements, values of X = B( EO ;0 + → 0 1 + ) B( E 2; 0 + →2 1 + ) are obtained from the 1953 keV state in 114 Sn, 1757 and 2027 keV states in 116 Sn and 1758 and 2056 keV states in 118 Sn.

Stroke Asymmetry of Tilted Superhydrophobic Ion Track Textures

The stroke asymmetry of contact angles of water drops on tilted hydrophobic textures is demonstrated, obtained by ion track etching followed by a hydrophobic treatment. Preliminary trends concerning the advancing and receding contact angles are established, each with and against stroke direction. In rough agreement with Cassie-Baxter theory, the cosines of these four contact angles depend linearly on the wetted area fraction. The etched tracks are randomly distributed on the surface of polycarbonate disks and inclined by 30 degrees with respect to the surface, whereby the aspect ratio of individual etched cones is larger than 10. The morphology of the resulting surface is characterized by randomly shaped flat tops overhanging on one side and gradually falling off on the other side. The area fraction of the supporting tops can be calculated from the number of impinging ions per unit area and the cross section of the etched ion tracks. The top layer of the texture consists of flat, horizontal, irregularly shaped tops supporting water drops in the Cassie-Baxter state. With increasing etching time, the texture becomes increasingly clefted. To fabricate the textures, we irradiated polycarbonate with 5 x 10(7) (80)Br(7+) ions/cm(2) of 30 MeV total energy (having a range of about 20 microm in polycarbonate) at a tilt angle of 30 degrees with respect to the sample surface and etched the latent ion tracks selectively. The textured surface is made hydrophobic by carbondifluoride radicals (CF(2)) resulting from the decay of octafluorocyclobutane, C(4)F(8), in a plasma reactor. The goal of the report is to show that the tilt orientation of a superhydrophobic surface leads to advancing and receding contact angles depending on the orientation with and against the stroke direction. In addition, a rotating movement is demonstrated qualitatively by floating a rotationally asymmetric disk on an ultrasonic bath, similarly treated after an irradiation with (1.2 +/- 0.4) x 10(7) (129)Xe(27+) ions/cm(2) of 8.3 MeV/nucleon at an angle of 45 degrees, whereby the superhydrophobic side of the disk points downward to the water of the ultrasonic bath.

EO transitions from A K = 0+ band in 162Dy

Abstract The decay of 162Ho has been studied by means of γ-ray, conversion electron and γ-electron coincidence spectroscopy. A K = 0+ bandhead is established at 1400.3 keV, and the ratio of EO to E2 transition probabilities is measured. Comparison is made with various models.

The 371 keV 2+-2+ transition in 190Os investigated by electron-electron and gamma-electron directional correlations

Abstract Electron-electron directional correlation measurements have been made on the 2 + (371 keV) 2 + (187 keV)0 + cascade in 190 Os and the magnitude of electric monopole to quadrupole mixing ratio for the 371 keV transition was determined to be q K (E0/E2) = −0.08(17) for λ = 1. To obtain this result it was necessary to use the following information: (i) The gamma-ray spectrum following the electron capture decay of 190 Ir obtained using a Ge(Li) solid-state detector. (ii) The mixing ratio δ (E2/M1, 371 keV) = 6.5(13) calculated from a γ-e directional correlation measurement. (iii) The conversion coefficient α K (371 keV) = 0.0375(17) measured by a coincidence method. (iv) The K/L III (371 keV) = 15.8(5) measured in an iron-free double focusing spectrometer. (v) The half-life of the decay of iridium T 1 2 = 12.1(2) d .

Charged particle production in peripheral reactions induced by 118 MeV 12C ions on 118Sn

Abstract The multiplicities of γ -cascades observed in coincidence with fast charged ejectiles from 118 Sn + 118 MeV 12 C collisions are measured. The analysis gives evidence for a peripheral nature of these reactions and supports the sum-rule model for incomplete (and complete) fusion.

Vibrational transitions in 182W

Abstract Directional correlation measurements (e-e, e-γ) have been performed on 182W. The multipole mixing ratios have been measured for the 2γ+2−2g+0 and 4γ+2−4g+0 transitions and a 6+6-6g+0 transition in the decay of 182Ta and 182Re. The mixing ratio of the 2β+0-2g+0 transition is discussed. A strong mixing of the 4β+ and 4γ+ states is suggested.