[en] A gamma-ray tracking detector is a new concept for a detector array composed of highly segmented Ge detector elements. The detector would give the energy and the position of all the interaction points and by using the angle-energy relation of the Compton scattering, the scattering sequence of the gamma rays can be reconstructed. Such a detector will have a high efficiency and a good peak-to-background ratio. Research and development are being carried out in the production of highly segmented Ge detectors, understanding the signal, and development of tracking algorithms. Recent progress indicated that this type of detector system appears to be feasible and would have a large impact on a wide variety of physics

[en] Gamma-ray tracking detectors using highly segmented germanium detectors will give higher efficiency, better peak-to-total ratio and much higher position resolution than current generation of detectors. Particularly, the capability of reconstructing the position of the interaction with millimeters resolution is needed to fully exploit the physics opportunities provided by the next generation radioactive beam facilities. This paper presents the basic concepts of tracking, examples of physics opportunities, and the status of the project GRETA/GRETINA.

[en] A gamma-ray tracking detector is a new concept for a detector array composed of highly segmented Ge detector elements. The detector would give the energy and the position of all the interaction points and by using the angle-energy relation of the Compton scattering, the scattering sequence of the gamma rays can be reconstructed. Such a detector will have a high efficiency and a good peak-to-background ratio. Research and development are being carried out in the production of highly segmented Ge detectors, understanding the signal, and development of tracking algorithms. Recent progress indicated that this type of detector system appears to be feasible and would have a large impact on a wide variety of physics. (c) 1999 American Institute of Physics

[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)

[en] The cerebral palsy(CP) encephalopathies are often of uncertain etiology and various functional image findings comparing with anatomical image findings have been reported. However, only a few have mentioned its clinical implications. The purpose of our report is to compare clinical severity and functional SPECT abnormalities of thalami and cerebellum in CP patients with normal MRI. Thirty six CP patients with bilateral spastic palsy who had normal MRI and brain SPECT were studied from July 1996 to September 1997. The patients' age at the time of SPECT was 22.84±17.69 months. The patients were divided into two groups according to motor quotient(MQ); moderate defect (>50MQ : n=27 MQ=22.78±10.36), mild defect (<50MQ : n=9, MQ=66.11±13.87). The degree of rCBF decrease between the two groups was evaluated by χ² test. Brain SPECT was performed following IV administration of 0.05-0.1 mCi/kg (minimum 2.0 mCi) of Tc-99m ECD and chloral hydrate sedation (50-80 mg/kg p.o) using a triple head system (MS 3, Siemens). Interpretation of brain SPECT was visual analysis: severe decrease is defined when the defect is moderate to marked and mild decrease in rCBF as mild. Seven of 36 (19.4%) showed unilateral or bilateral moderate decrease in rCBF in thalami, 20(55.6%) showed mild decrease, and 9(25.0%) showed no decreased rCBF. All 7 who had moderate thalamic defect reveled moderate motor defect clinically. Ten of 36(27.9%) revealed unilateral or bilateral moderate rCBF defect, 23 (63.9%) depicted mild defect, and 3(8.3%) showed no defect. Sixteen with moderate thalamic rCBF defect showed moderate motor defect in 15 patients. There was statistically significant (p=0.02605) relationship between rCBF defect and motor defect in our CP patients. In conclusion, brain SPECT appears sensitive, non-invasive tool in the evaluation as well as in the prognostication of bilateral spastic cerebral palsy patients and deserves further study using larger number of patients

[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

[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, Γ_μ, the spreading (compound-damping) width, and Γ_rot, the rotational damping width, together with P_nar, the probability that the population enters and leaves a given state via the same component of the wave function. Our results for Γ_μ and Γ_rot are in good agreement with theoretical expectations, as well as with those of other groups using different methods. Our results for P_nar 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 Γ_rot in nuclei. The basic physics occurring in this region is level mixing, which our simulation technique reproduces surprisingly well

[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

[en] We measured the ratio of the fission probabilities of ²³⁴U* relative to ²³⁶U* formed via an (α,α(prime)) direct reactions using the STARS array at the 88-inch cyclotron at the Lawrence Berkeley National Laboratory. This ratio has a shape similar to the ratio of neutron capture probabilities from ²³³U(n; f) and ²³⁵U(n; f), indicating the alpha reactions likely formed a compound nucleus. This result indicates that the ratios of fission exit channel probabilities for two actinide nuclei populated via (α, α(prime)) can be used to determine an unknown fission cross section relative to a known one. The validity of the External Surrogate Ratio Method (ESRM) is tested and the results support the conclusions of Burke et al. [1]

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