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[en] Gamma-ray spectroscopy was revolutionized with the introduction of high energy-resolution semiconductor germanium (Ge) detectors in the early 1960s. This led to the large increase in sensitivity realized by today's arrays of Compton-suppressed Ge detectors. A still larger increase in sensitivity is expected by implementing the new concept of tracking. A tracking array consists of highly segmented Ge detectors (that can cover the full 4π solid-angle) in which γ rays will be identified by measuring and tracking every γ ray interaction. This article reviews the physics motivation for such detectors and the development of the new technologies involved. The concept of tracking is explained using the example of a proposed array called γ-ray energy tracking array (GRETA)
Journal
[en] The nucleus 68Ge has been studied by gamma-ray spectroscopy following its population at high spin in the reaction 40Ca(32S,4p)68Ge. The reaction channel was selected with the Microball array and gamma rays were detected with the Gammasphere array. The level scheme is very complex, reflecting the many different, and presumably mixed, excitation modes in this nucleus. Nevertheless, there appear to be some simplifications in the spin range above 18ℎ where we have identified a superdeformed band and several terminating bands. The results are compared with a cranked Nilsson-Strutinsky model without pairing
Journal
[en] We present a semi-classical analysis of the B(M1) and B(E2) transition probabilities in the shears bands in 193-199Pb as a function of the shears angle. This provides a semi-empirical confirmation of the shears mechanism proposed by S. Frauendorf using the Tilted-Axis-Cranking model. We interpret this as a consequence of a residual interaction between the proton and neutron blades, and it is shown that the main ingredient of this effective force can be described by a P2(θ) term with a strength of 400-600 keV. Such an interaction can be mediated through the core by particle-vibration coupling. The competition between the shears and the rotation of the core is investigated within the framework of a classical solution of two particles-plus-rotor model
Journal
[en] We have studied the unresolved γ-ray spectrum of three ytterbium nuclei produced in heavy-ion fusion reactions and measured the two damping widths, Γμ, the spreading (compound-damping) width, and Γrot, the rotational damping width, together with Pnar, the probability that the population enters and leaves a given state via the same component of the wave function. Our results for Γμ and Γrot are in good agreement with theoretical expectations, as well as with those of other groups using different methods. Our results for Pnar lead to a new method for quantitative evaluation of the full order-to-chaos transition in these Yb nuclei. Finally, we provide the first evidence for the motional narrowing of Γrot in nuclei. The basic physics occurring in this region is level mixing, which our simulation technique reproduces surprisingly well
Journal
[en] We have developed a new method to study the order-to-chaos transition in rotational nuclei. Energy correlations between successive γ-rays are used to determine the average complexity of the levels and thereby the ratio of the interaction between levels to the level spacing. γ-Rays from fusion reactions, leading to 168,169,170Yb nuclei, were measured with Gammasphere, and the measured ratios span the range from nearly fully ordered to nearly fully chaotic
Journal
Physica Scripta (Online); ISSN 1402-4896; 
; v. 2006(T125); p. 142-146
; v. 2006(T125); p. 142-146
[en] In this paper we present the results of an experiment performed at LBNL's 88-Inch Cyclotron using GAMMASPHERE in which we searched for strange matter by applying the heavy ion activation technique to samples of meteorites. Our exploratory experiment improved existing experimental limits by 3 orders of magnitude
Journal
[en] The authors have deduced the cross section for 237U(n,f) over an equivalent neutron energy range from 0 to 20 MeV using the Surrogate Ratio method. A 55 MeV 4He beam from the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory was used to induce fission in the following reactions: 238U(α,α(prime)f) and 236U(α,α(prime)f). The 238U reaction was a surrogate for 237U(n,f) and the 236U reaction was used as a surrogate for 235U(n,f). Scattered alpha particles were detected in a fully depleted segmented silicon telescope array (STARS) over an angle range of 35o to 60o with respect to the beam axis. The fission fragments were detected in a third independent silicon detector located at backward angles between 106o and 131o
Journal
Physical Review. C, Nuclear Physics (Online); ISSN 1089-490X; ; v. 73; vp
; v. 73; vp
[en] The lifetime of the 21+ state in 16C has been measured with the recoil distance method using the 9Be(9Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2; 21+→0+) value of 4.15(73)e2 fm4 [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for ''decoupled'' valence neutrons
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