An comparison of absorbed dose rates,). (D 07 0 t & , in tissue at radiation protection levels for beta dosimetry was performed between two national laboratories, the D. I. Mendeleyev Institute for Metrology (VNIIM) in St. Petersburg (Russia) and the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig (Germany), in 1999 and 2001 using flat ionisation chambers as transfer standards. The dose rates were determined at the calibration distances by measurements with the primary standard measuring devices of VNIIM and PTB with extrapolation chambers to realise the unit of absorbed dose rate to tissue for beta radiation. In the two steps reported on here, transfer chambers of VNIIM and PTB were calibrated in beta radiation reference fields at VNIIM and at PTB. The values of the calibration factors for the flat ionisation chambers agreed within ± 2 % for 90 Sr/ 90 Y, 85 Kr and 204 Tl and ± 4 % for 147 Pm beta radiation.
The Russian (VNIIM) and French (BNM-LNHB) national primary laboratories organized in 1997 a bilateral comparison in beta dosimetry. This comparison of national standards, EUROMET.RI(I)-S2.B2, was carried out through a transfer ionization chamber manufactured by the VNIIM. The calibration factors of this chamber were determined by both laboratories in terms of absorbed dose rate at 7 mg.cm-² of tissue depth, for the beta radiation fields of 90 Sr-90 Y, 204 Tl and 147 Pm.
A high-precision multichannel instrument for measuring linear and lateral strains has been developed on the basis of a method suggested for determining the elastic parameters of anisotropic rock samples.The difficulties encountered when using familiar methods to determine the elastic constants of various materials are well known [1][2][3]. They stem from the need to make a large number of measurements simultaneously with the best possible accuracy of measurement for tensiometer stations.It is of practical interest to determine the anisotropy of rocks by comparing small strains (-10 -5 m), measured on various parts of cylindrical core samples, taken from a prospecting hole. The differences of the strains are the main input data for computation when determining the principal directions that characterize an anisotropic elastic state.The relation between the stressed state and the strain of an elastic body is given by Hooke's law, which for uniaxial compression has the formwhere Ah/h = ~l is the relative linear compression or elongation (longitudinal strain), ~ = P/S is the normal stress (not exceeding the elastic limit), P is the force, S is the cross-sectional area of the middle portion of the sample, and E is Young's modulus.The transverse strain e at any point of the lateral surface of a cylinder of radius r o and height h can be written in polar coordinates r, cp aswhere ~p is the azimuthal angle reckoned from an arbitrary datum point A on the surface of the sample (the coordinates of A are r = r 0, ~p = 0) along the circular arc to the point of intersection of the X axis passing through the center of the sample in the direction -+q~l of the maximum value of Poisson's ratio ~rnax" with the surface of the cylinder. By definition, Poisson's ratio is equal to the ratio of the elastic components of the transverse and longitudinal strains of the sample, ~t = e 2/~1" Instruments measuring the longitudinal and transverse strains of core samples determine the angle (Pl by measuring, in the loaded state, the length of the radii of the ellipse (IPPD-1 meter) or the chord that rests on the arc joining the points on the surface of the ellipse (IPPD-2 meter). In the IPPD-I the strains ei(cp) are measured at points separated by an angle of n/4. The IPPD-2, in which strains are determined on six chords resting on others with a divergence angle c~ = ~3, was developed to enhance the operating reliability of the instrument.As a rule, in experiments physical quantities are measured many times and then methods of mathematical statistics are used when the results are processed. The maximum likelihood method gives better results than do other methods of estimating the parameters determined experimentally [6]. 700
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