R.H. Spear

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.

Electric quadrupole moments of the first excited states of 194Pt, 196Pt and 198Pt

Abstract Coulomb excitation of 194, 196, 198 Pt by 4 He, 12 C and 16 O projectiles has been used to determine the static electric quadrupole moments Q (2 1 + ) of the first excited states of 194,196,198 Pt, together with values of B (E2; 0 1 + → 2 1 + ). It is clearly established that Q (2 1 + ) is positive for each nucleus, having values of 0.48 (14) e · b and 0.66 (12) e · b for 194 Pt and 196 Pt, respectively, and 0.42 (12) e · b or 0.54 (12) e · b for 198 Pt, depending on whether the interference term P 4 (2 2 + ) is positive or negative. Results obtained for B (E2; 0 1 + → 2 1 + ) are 1.661 (11) e 2 · b 2 , 1.382 (6) e 2 · b 2 and 1.090 (7) e 2 · b 2 for 194, 196, 198 Pt respectively. The results are compared with the predictions of various nuclear models.

Proton scattering from 27Al in the energy range from 3.5 to 11.3 MeV

Abstract The scattering of protons from 27Al has been studied for proton energies from 3.5 to 11.3 MeV with an energy resolution of approximately 10 keV. Excitation functions have been obtained at laboratory angles of 90° and 140° for groups corresponding to the ground and first six excited states of 27Al. The validity of a fluctuation theory interpretation of the data has been investigated; it is concluded that such an interpretation is valid for the upper part of the range but is questionable for the lower energies. The distortion of auto-correlation functions due to non-statistical variations in the reaction yield has been eliminated by calculating fluctuations with respect to an average cross section defined by using an averaging interval of 400 keV. An auto-correlation analysis indicates that the mean width of 28Si levels participating in the reaction is approximately 34 keV at an excitation energy of 21.5 MeV. Estimates of level width based on the density of maxima in the excitation functions are in satisfactory agreement with this value. The present result is compared with 28Si level widths reported by other authors. The significance of values for the normalized variances of the excitation functions determined from the auto-correlation analysis is discussed. The data show some evidence for the presence of intermediate structure of width and spacing of the order of several hundred keV.

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.

Cross section of the reaction 6Li(p, γ)7Be

Abstract The cross section of the reaction 6 Li(p, γ ) 7 Be has been measured using Ge(Li) γ-ray spectrometers for proton bombarding energies E p from 200 keV to 1200 keV. At E p = 800 keV, the total (p, γ) integrated cross section is found to be 3.1 ± 0.4 μ b. The cross section adopted from consideration of this and previous measurements is in good agreement with that predicted from the known thermal neutron cross section for 6 Li(n, γ ) 7 Li on the assumption that properties of mirror direct capture reactions can be well described by optical potentials that use the same parmeter values for the two reactions.

A measurement of B(E3;0+ → 31−) and some E2 transition probabilities in 132, 134, 136, 138Ba using Coulomb excitation

Abstract Reduced transition probabilities, B (E2) and B (E3), have been measured for low-lying 2 + and 3 − states in 132, 134, 136, 138 Ba using Coulomb excitation by 40 MeV 12 C ions. The B (E2) values are in general consistent with previous measurements and the B (E3;0 + → 3 1 − ) values are 0.176 ± 0.022, 0.148 ± 0.018, 0.155 ± 0.018 and 0.133 ± 0.013 e 2 · b 3 for 132, 134, 136, 138 Ba respectively. These B (E3) values correspond to about 24 to 17 W.u. and such enhancements suggest that these 3 − states have an essentially collective character which may be attributed to octupole vibrations.

Octupole vibrations in the even mercury and lead isotopes

Abstract Prominent groups are observed corresponding to excited states in the region of 2.6 MeV in the scattering of 24 and 27 MeV α-particles from 198, 200, 202, 204 Hg and 204, 206, 208 Pb. For each of the Pb isotopes the state concerned is identified with the known 3 − octupole vibration. Angular distribution measurements for scattering to the Pb and 204 Hg states are in agreement with octupole-vibration coupled-channels predictions, and systematic trends suggest that the states observed in the isotopes 198, 200, 202 Hg can also be attributed to octupole vibrations.

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.