No abstract available

[en] Monte Carlo calculations are described which confirm that the response of a spherical thermal-neutron detector at the centre of a spherical moderating assembly in a neutron beam diverging from a point source is simply related to its response in a parallel neutron beam. (orig.)

[en] In neutron spectrometry and dosimetry where Bonner spheres are used, certain questions arise, such as: which of these spheres should be employed in a particular neutron field or energy region, and in a given measuring time, to obtain the neutron spectrum, fluence, or dose equivalent with a minimum uncertainty? These and similar questions in spectrometer optimisation can be answered by means of a general measure of the quality of an experiment, established from basic requirements. The most suitable measure turns out to be the trace of the squared, reduced covariance matrix of the measurands of the experiment, whereby this matrix expresses the individual and mutual uncertainties of the measurement results. (author)

[en] To reduce the error of measurement that the sphere-sphere disturbance caused when the on-line Bonner sphere spectrometers use many slow-sphere in the measurement, this thesis uses MCNP to simulate the impact on sphere-sphere disturbance of three factors of disturb-sphere radius, detect-sphere radius, distance of sphere-sphere, and make a synthesis of simulation and actual measurement results and design a plan of placing slow-sphere. The results show that this plan can reduce the sphere-sphere disturbance to an acceptable level and also can provide the design of on-line Bonner sphere spectrometers with theoretical support and data reference. (authors)

[en] This paper compares the use of both standard unfolding and Bayesian methods to analyze data extracted from neutron spectrometric measurements with a view to deriving some integral quantities characterizing a neutron field. We consider, as an example, the determination of the total neutron fluence and dose in the vicinity of an Am–Be source from Bonner spheres measurements. It is shown that the Bayesian analysis provides a rigorous estimation of these quantities and their correlated uncertainties and overcomes difficulties encountered in the standard unfolding methods.

[en] The adhesive contact between spheres for a small Tabor parameter is investigated. It is found that the DMT model cannot describe the adhesive contact for a small Tabor parameter. By assuming a new contact distance, the modified Hertzian contact is proposed. For a small Tabor parameter, the rigid-sphere model can describe the adhesive contact behaviour for a small load and the modified Hertzian model can describe the adhesive contact behaviour for a large load

[en] Collision probabilities in spherical geometry are decomposed into a sum of Meijer's G functions, which are subsequently identified as the product of an exponential and a polynomial of finite degree and are hence easily computed. The series is then summed analytically, and the usual transport kernel for spherical geometry--the exponential integral--appears. A new form of the integral transport equation for the scalar flux is thus found

[en] The most widely used system in neutrons measurements for radiological protection is the Bonner Sphere Spectrometer (BSS). The BSS is applied to characterise neutron fields from thermal to hundreds of MeVs. The Nuclear Regulatory Authority of Argentina has developed and calibrated its own BSS system, which has been used in many Argentine facilities during the last eleven years when the regulatory activities have been carried out. Following this line of work, the present development has been done in the framework of the International Intercomparison 'Uncertainty Assessment in Computational Dosimetry: A Comparison of Approaches', organised by the CONRAD project (Coordinated Network for Radiation Dosimetry). The aim of intercomparison was to study the response of a proposed widespread neutron spectrometer exposed to arbitrary neutron sources. With this goal in mind, the experimental system has been modelled in detail according to the provided layout. The modelled neutron spectrometer consists of 8 Bonner spheres made of high-density polyethylene (δ=0.95gc/m³). The spheres diameter range between 2' and 12' in addition to a 12' diameter lead-loaded sphere. The defined active thermal neutron detector, a ⁶LiI(Eu) scintillation crystal, was according to provided dimensions (4 mm (diameter) by 4 mm (height)), and located at each sphere centre. Irradiation geometry has been according to measurements carried out during the experimental part of the intercomparison. The theoretical neutron response has been calculated applying the well-known MCNPX code. The complete response matrix of the system has been obtained in the energy range between thermal neutron and 17.77 MeV. The obtained system theoretical response to ISO standard ²⁴¹Am-Be and ²⁵²Cf sources shows an excellent agreement with experimental results provided by EURADOS. This response can be used to calibrate the system. The obtained matrix response can be coupled to any unfolding code to complete the BSS system used in the intercomparison or similar. (authors)

[en] The Bonner spheres spectrometer is utilized to estimate the neutron spectrum of neutrons from thermal up to several MeV neutrons. Its response is increased to few GeV neutrons by introducing large Z materials as inner shells. To use the spectrometer a matrix response and an unfolding method are required; these are crucial to assure the quality of spectrometer output. The response matrix of a Bonner sphere spectrometer was calculated by use of the MCNP code. As thermal neutron counter the spectrometer has a 0.4 θ x 0.4 cm2 ⁶LiI(Eu) scintillator which is located at the centre of a set of polyethylene spheres. The response functions were calculated for 0, 2, 3, 5, 8, 10, and 12 inches-diameter polyethylene spheres for neutrons whose energy goes from 10^-8 to 100 MeV. For energies from 10^-8 to 20 MeV the MCNP4C code was utilized while for neutrons from 20 to 100 MeV calculations were carried out with MCNPX code. The response functions were compared with those reported in the literature. (author)

[en] For plurisubharmonic functions Cⁿ of lower order λ<+∞ estimates of the growth of their maximum value on the sphere of radius r with centre at the origin in terms of the growth of the Nevanlinna characteristics T(r,u) are obtained. These estimates are best possible for λ≤1. The results are new even in the case of functions of the form u= log |f|, where f is an entire function in Cⁿ, n>1