D.C. Kean

Mass dependence of the static quadrupole moments of the first 2+ states in the cadmium isotopes

Abstract The static quadrupole moments Q 2 + and the B (E2; 0 + → 2 + ) values of the first 2 + states m the even-mass Cd isotopes have been determined using the reorientation effect. The Coulomb excitation probabilities were measured by resolving inelastically and elastically backwardscattered 4 He and 16 O projectiles in an annular surface barrier detector. The results, in contrast to theoretical predictions and previous experimental work, indicate no significant variation of Q 2 + with mass number. Assuming constructive interference from higher 2 + states, we find: Q 2 + ( 106 Cd ) = −0.28 ± 0.08, Q 2 + ( 108 Cd ) = −0.45 ± 0.08, Q 2 + ( 110 Cd ) = −0.36 ± 0.08, Q 2 + ( 112 Cd ) = −0.39 ± 0.08, Q 2 + ( 114 Cd ) = −0.36 ± 0.08 and Q 2 + ( 116 Cd ) = −0.42 ± 0.08 e · emb. For 116 Cd , B( E 2; 0 + → 2 + ) = 0.532 ± 0.004 e 2 · b 2 , which is 20% lower than the previously adopted value.

The static quadrupole moment of the first excited state of 198Hg

Abstract The first direct evidence of oblate nuclear deformation in the even-A mercury isotopes has been obtained by measurement of the static quadrupole moment of the first excited state of 198Hg using the reorientation effect in Coulomb excitation.

Energy calibration of the A.N.U. 14UD Pelletron accelerator

Abstract The energy calibration of the 14UD Pelletron accelerator at the Australian National University has been determined, with an accuracy better than 0.1%, up to 64 MeV equivalent proton energy using a simple alpha-particle back-scattering technique. From the observed width of the 14.2 MeV resonance in the 12 C(p, α 0 ) 9 B reaction, the energy spread ΔE / E of the analysed beam was measured as (1.7±0.3)×10 −4 at terminal potential of 7.1 MV.

Electric moments of the first excited state of 18O

Abstract The static quadrupole moment Q 2 + and the B (E2; 0 + → 2 + ) value of the first excited state of 18 O at e x = 1.982 MeV have been determined using the reorientation effect in Coulomb excitation. Surface-barrier detectors at laboratory angles of 90° and 174° were used to detect 18 O ions elastically and inelastically scattered from 208 Pb. At both angles, we determined experimentally the maximum bombarding energies at which nuclear interference effects were negligible. It is found that Q + = −0.023 ± 0.021 e · b (−0.052 ± 0.021 e · b) for destructive (constructive) interference from higher states. This result is in good agreement with theoretical expectation. For the transition moment we find B (E2; 0 + → 2 + ) = 0.00390 ± 0.00018 e 2 · b 2 (0.00371 ± 0.00018 e 2 · b 2 ) for destructive (constructive) interference.

Quadrupole moments of the first excited states of 204,206Pb

Abstract The static quadrupole moments of the first excited states of 204,206 Pb are measured to be +0.23 ± 0.09 and +0.05 ± 0.09 eb, respectively. These results, together with measured B (E2; 0 + → 2 + ) values, are interpreted in terms of the systematics of nuclear deformation in the A ≈ 200 mass region.

Systematics of coulomb-nuclear interference: Implications for reliable measurement of the reorientation effect

Abstract Data are presented which show an inverse correlation between Coulomb excitation probability and the nuclear separation corresponding to onset of Coulomb-nuclear interference. They demonstrate that the safe energy for reorientation effect measurements should always be determined experimentally.

Static quadrupole moments of the first excited states of 200Hg and 202Hg

Abstract The static quadrupole moments Q2+ and B(E2; 0+ → 2+) values of the 2+ first excited states of 200Hg and 202Hg have been determined using the reorientation effect in Coulomb excitation. An annular silicon surface-barrier detector was used to detect backscattered 4He, 12C and 16O projectiles. It is found that for 200Hg, Q2+ = +1.07 ± 0.19 e · b(+0.98 ± 0.19 e · b) for destructive (constructive) interference from the 2+′ state, and B(E2; 0+ → 2+) = 0.853 ± 0.007 e2 · b2. For 202Hg, we find Q2+ = +1.01 ± 0.13 e · b (+0.87 ± 0.13 e · b) and B(E2; 0+ → 2+) = 0.605 ± 0.005 e2 · b2. The Q2+ value obtained for 200Hg is in agreement with previous work, but that for 202Hg is not. The results obtained are compared with the predictions of various nuclear models, and the mass dependence of Q2+ in the region 182 ≦ A ≦ 206 is examined.

Static quadrupole moment of the first excited state of 24Mg

Abstract The static quadrupole moment Q2+ and the B(E2; 0+ → 2+) value for the first excited state of 24Mg have been determined using the reorientation effect in Coulomb excitation. Surface barrier detectors at 90° and 172° were used to detect 24Mg ions scattered from 208Pb. It is found that Q2+ = −17.8 ± 1.3 e · fm2, suggesting that, contrary to most previous experimental evidence, the quadrupole moment is in agreement with theoretical predictions. For B(E2; 0+ → 2+) we obtain the value 445 ± 24 e2 · fm4.

The preparation of mercury targets for high resolution particle spectroscopy

Abstract The preparation and use of uniform, stable HgS targets for high resolution particle spectroscopy are described.

The response of silicon surface-barrier detectors to light and heavy ions

Abstract The spectral response of a number of silicon surface-barrier detectors has been measured for essentially monoenegetic beams of 1 H, 4 He, 6 Li, 7 Li, 12 C, 16 O, 18 O, 24 Mg, 28 Si, 32 S and 58 Ni ions, with particular emphasis on those parts of the lineshape which are important in the measurement of weak inelastic scattering peaks observed in Coulomb-excitation experiments. These weak peaks are usually superimposed on the low-energy tail of an intense elastic scattering peak. This tail has an essentially smooth component which is found, in practice, to be due largely to slit-edge scattering and target effects; the detector appears to make only a minor contribution. With light ions ( 1 H and 4 He) discrete peaks due to inelastic scattering of the incident particles from 28 Si nuclei in the detector are also observed. Such peaks have not been seen with ions heavier than 4 He. This behaviour can be understood in view of the much smaller range of the heavier ions in the detector at the incident energies used. With heavier ions ( A ⩾ 28) incident on certain detectors, significant fractions ofthe incident particles produce pulses with up to 10% greater pulse height than those in the main spectrum peak. This phenomenon appears to be associated with high ionization densities and large electric fields in the detectors.