Comment on `Two-body random ensembles: from nuclear spectra to random polynomials

In PRL 85, 3773 (2000) it was suggested to use random polynomials to analyze and understand the properties of two-body random ensembles. In this comment we point out that for the vibron model the random polynomial is not quadratic, but has a more general form. We make a comparison for the percentage of ground states with L=0 in the vibron model with random interactions.Comment: 2 pages, 1 figure, Phys. Rev. Lett., in pres

Simulation, design and fabrication of large area implanted silicon two-dimensional position sensitive radiation detectors

The fabrication process of a two-dimensional position sensitive radiation detector (2-D PSD) with a 4 cm2 active area is presented. Critical steps in the fabrication are emphasised. Edge effects represent critical problems in producing large area ion implanted silicon radiation detectors with low leakage currents and a high breakdown voltage (BV). Two methods have been used to increase the breakdown voltage of the junction: the use of i) floating field limiting rings (FFLR) and ii) field plates (FP). Several situations have been simulated analytically and numerically. A comparison of the theoretical results with the measurements realised using the detectors is presented. It is shown that a substantial improvement in the BV of the detector can be achieved by these methods

Many-body Systems Interacting via a Two-body Random Ensemble (I): Angular Momentum distribution in the ground states

In this paper, we discuss the angular momentum distribution in the ground states of many-body systems interacting via a two-body random ensemble. Beginning with a few simple examples, a simple approach to predict P(I)'s, angular momenta I ground state (g.s.) probabilities, of a few solvable cases, such as fermions in a small single-j shell and d boson systems, is given. This method is generalized to predict P(I)'s of more complicated cases, such as even or odd number of fermions in a large single-j shell or a many-j shell, d-boson, sd-boson or sdg-boson systems, etc. By this method we are able to tell which interactions are essential to produce a sizable P(I) in a many-body system. The g.s. probability of maximum angular momentum $I_{max}$ is discussed. An argument on the microscopic foundation of our approach, and certain matrix elements which are useful to understand the observed regularities, are also given or addressed in detail. The low seniority chain of 0 g.s. by using the same set of two-body interactions is confirmed but it is noted that contribution to the total 0 g.s. probability beyond this chain may be more important for even fermions in a single-j shell. Preliminary results by taking a displaced two-body random ensemble are presented for the I g.s. probabilities.Comment: 39 pages and 8 figure

Spectroscopy with random and displaced random ensembles

Due to the time reversal invariance of the angular momentum operator J^2, the average energies and variances at fixed J for random two-body Hamiltonians exhibit odd-even-J staggering, that may be especially strong for J=0. It is shown that upon ensemble averaging over random runs, this behaviour is reflected in the yrast states. Displaced (attractive) random ensembles lead to rotational spectra with strongly enhanced BE2 transitions for a certain class of model spaces. It is explained how to generalize these results to other forms of collectivity.Comment: 4 pages, 4 figure