Personal dosimetry and area monitoring for neutrons and radon in workplaces

The first successful applications of damage track detectors in radiation protection have been made in the early 1970s in personal dosimetry of neutrons, radon and its progenies. Most of the scientists actively engaged in the solution of the complex problem of personal neutron dosimetry by damage track detectors—SSNTD, have attempted to develop individual radon monitoring for exposure in mines by using the same SSNTDs. In late 1970s and the early 1980s, new radon monitoring devices based on SSNTDs have been developed to measure radon in soil, mainly for applications in uranium prospecting or more generally in earth sciences. Most of the radon monitors, developed since then for completely different applications in mind, have been used later for large scale survey of indoor radon. With the current implementation within Europe of the European Union Directive 96/29, applications of damage track detectors will increase drastically, specially for the assessment of the exposure of the workers to natural sources of radiation. In this case, the early work on personal neutron/radon dosimetry, is highly valuable to tackle these new problems of individual monitoring.     

Iridium-catalyzed alternative of the Meinwald rearrangement

A novel and easy to handle procedure for the regioselective rearrangement of epoxides has been developed, based on an iridium catalyst.     

Solvent Effects on the Electrochemical Behavior of Iron(III) Schiff Base Complex

Electrochemical reduction of Fe^IIILCl where L is a Schiff base has been investigated in various aprotic solvents. From a plot of the half wave potential E _1/2 for the reduction of these complexes vs. E _1/2 for the oxidation of ferrocene, the solvent–solute interactions were studied: the E _1/2 variation is found to be a function of Lewis-type acceptor–donor interactions. The diffusion coefficients D in the different solvents were also been determined by linear sweep voltammetry. The variation of D is discussed in terms of viscosity and dielectric constant.     

Damage track detectors in radioprotection dosimetry: a novel approach

Limited sensitivity and unpredictable background are the major drawbacks of damage track detectors in the assessment of low neutron doses and low concentrations of alpha emitters in biological and environmental samples. The simplest way to increase the sensitivity of the damage track detectors is to increase both the exposure time and the detector area. However, the strong variability of the background may make this task often impossible. This background problem has been finally solved by a new registration method based on counting coincidence spots in geometrically matched pair of detectors. By using spark counting and electrochemical etching, both of which produce spots visible at low magnification, coincidences induced in two matched detector-surfaces by a few-microns-long tracks can be easily seen. This novel counting approach can be considered just the converse of those used in the past with Bi-fission detectors and cosmic ray stacks.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Existence and Uniqueness of Fixed Points for Markov Operators and Markov Processes

This paper concerns a Markov operator T on a space L₁, and aMarkov process P which defines a Markov operator on a spaceM of finite signed measures. For T, the paper presents necessaryand sufficient conditions for:

a the existence of invariant probabilitydensities (IPDs)

b the existence of strictly positive IPDs,and

c the existence and uniqueness of IPDs.

Similar resultson invariant probability measures for P are presented. The basicapproach is to pose a fixed-point problem as the problem ofsolving a certain linear equation in a suitable Banach space,and then obtain necessary and sufficient conditions for thisequation to have a solution. 1991 Mathematics Subject Classification:60J05, 47B65, 47N30.     

A better understanding of the background of CR-39 detectors

The background of CR-39 detectors varies from batch to batch, from foil to foil in the same batch, from one side to another of the same foil and within the same foil surface. In spite of many efforts made in the past, little success has been achieved in producing detectors with a consistently low background. For this reason, new investigations have been undertaken with the specific scope in mind to improve the background of these detectors. The key strategy of these studies was to investigate whether the background tracks originate from the detector surface or from detector bulk, if not from both. From these systematic investigations it was possible to demonstrate that most of the background is due to defects present on the detector surface. For this reason, the simplest way to reduce the background is to carry out a heavy pre-etching prior to the use of the CR-39 detector. This procedure has been successfully exploited not only to increase the signal-to-noise ratio of CR-39-based radon dosimeters but also to carry out different radon measurements with the same CR-39 foil.