Instability of Gravitating Sphalerons

We prove the instability of the gravitating regular sphaleron solutions of the $SU(2)$ Einstein-Yang-Mills-Higgs system with a Higgs doublet, by studying the frequency spectrum of a class of radial perturbations. With the help of a variational principle we show that there exist always unstable modes. Our method has the advantage that no detailed knowledge of the equilibrium solution is required. It does, however, not directly apply to black holes.Comment: replaced mainly due to LaTex problems', 11p, Latex, ZU-TH 7-9

Present status of the personal neutron dosemeter based on direct ion storage

In this paper the present status of the Direct Ion Storage Neutron (DIS-N) prototype dosemeter (RADOS) is described. The separation of neutron from photon dose equivalent has been improved by adding tin shieldings. The neutron energy response has been changed by additional plastic covers containing 40% B4C in order to reduce the over-response to thermal neutrons. The responses of the dosemeters were determined for standard photon and neutron fields (monoenergetic neutrons, neutron sources and simulated workplace fields). Irradiations in real workplaces were also performed. The dependence of the neutron response on the angle of incidence was measured for different neutron source

Comparison of different PADC materials for neutron dosimetry

Investigations on track density and track size distributions of different PADC (poly allyl diglycol carbonate) materials have been performed. The PADC used for the tests has been produced by Thermo Electron (USA), Track Analysis System Limited (UK), Chiyoda Technol Corporation (Japan) and Intercast srl (Italy). For each PADC material 120 detectors were randomly selected out of 2 sheets: 60 detectors from one sheet have been irradiated with a personal dose equivalent of 3 mSv in the field of a 241Am-Be source at the calibration laboratory of PSI, whilst the other 60 detectors from the other sheet have been used as background samples. All detectors have been processed according to an identical etching procedure and have been analysed with TASLImage scanning system. For each set of detectors the value of the average background signal, the average neutron sensitivity and the detection limit with respect to a personal dose equivalent measured with a dosemeter based on PADC have been determined. The results of the investigations allowed a comparison of the neutron sensitivity and background signal behaviours of PADC materials from different manufacturers and the assessment of the variation of neutron sensitivity and background signal over a single shee

Determination of the response function for two personal neutron dosemeter designs based on PADC

Since 1998 neutron dosimetry based on PADC (poly allyl diglycol carbonate) is done with a so-called original Paul Scherrer Institute (PSI) design at PSI. The original design (i.e. holder) was later changed. Both designs are optimised for use in workplaces around high-energy accelerators, where the neutron energy spectra are dominated by fast neutrons ranging up to some 100 MeV. In addition to the change of the dosemeter design a new evaluation method based on a microscope scanning technique has been introduced and the etching conditions have been optimised. In the present work, the responses obtained with the original and the new dosemeter designs are compared for fields of radionuclide sources and monoenergetic reference fields using the new evaluation method. The response curves in terms of the personal dose equivalent for normally incident neutrons were built as functions of the incident neutron energ

Progress report of the CR-39 neutron personal monitoring service at PSI

At the Paul Scherrer Institute a personal neutron dosimetry system based on chemically etched CR-39 detectors and automatic track counting is in routine use since the beginning of 1998. The quality of the CR-39 detectors has always been a crucial aspect to maintain a trustable personal neutron dosimetry system. This paper summarises the 7 y experience in routine use. The effect of detector material defects which could lead to false positive neutron doses is described. The potentiality of improving the background statistics by extending the pre-etch time is investigated and involves as a drawback a quite lower sensitivity to thermal neutrons. Furthermore, the impact of small changes in the production process of the detectors on the response to fast and thermal neutrons is shown. For the personal dosimetry at CERN, a new dosimetry concept was launched by combining a CR-39 neutron dosemeter with a Direct-Ion Storage (DIS) dosemeter for photon and beta radiation. The usage period of the CR-39 dosemeters is prolonged now from 3 months up to 12 months. In this context, the long-term behaviour over 1 y of the background track density and the response to Am-Be are describe

Performance of a personal neutron dosemeter based on direct ion storage at workplace fields in the nuclear industry

In the framework of the EVIDOS project, funded by the EC, measurements were carried out using dosemeters, based on ionisation chambers with direct ion storage (DIS-N), at several workplace fields, namely, at a fuel processing plant, a boiling and a pressurised water reactor, and near transport and storage casks. The measurements and results obtained with the DIS-N in these workplaces, which are representative for the nuclear industry, are described in this study. Different dosemeter configurations of converter and shielding materials were considered. The results are compared with values for personal dose equivalent which were assessed within the EVIDOS project by other partners. The advantages and limitations of the DIS-N dosemeter are discusse

Unsupervised identification of topological order using predictive models

Machine-learning driven models have proven to be powerful tools for the identification of phases of matter. In particular, unsupervised methods hold the promise to help discover new phases of matter without the need for any prior theoretical knowledge. While for phases characterized by a broken symmetry, the use of unsupervised methods has proven to be successful, topological phases without a local order parameter seem to be much harder to identify without supervision. Here, we use an unsupervised approach to identify topological phases and transitions out of them. We train artificial neural nets to relate configurational data or measurement outcomes to quantities like temperature or tuning parameters in the Hamiltonian. The accuracy of these predictive models can then serve as an indicator for phase transitions. We successfully illustrate this approach on both the classical Ising gauge theory as well as on the quantum ground state of a generalized toric code.Comment: 12 pages, 13 figure