K. Venkata Reddy

Effective atomic numbers for materials of dosimetric interest

Abstract Effective atomic numbers ( Z eff ) for different materials of dosimetric interest have been calculated for total photon interaction in the energy region 1 keV–20 MeV. The calculations are made using the mass attenuation coefficients data from Tables of X-ray Mass Attenuation Coefficients and Mass Energy-absorption Coefficients 1 keV to 20 MeV for elements Z = 1 to 92 and 48 Additional Substances of Dosimetric Interest , J. H. Hubbell and S. M. Seltzer (Hubbell and Seltzer, 1995), NISTIR-5632. The variation of Z eff value with energy is discussed.

Effective atomic number studies in clay minerals for total photon interaction in the energy region 10 keV–10 MeV

Effective atomic numbers (Zeff) of different clay minerals are calculated for total photon interaction in the energy region 10 keV–10 MeV. The variation of Zeff with energy is discussed by comparing with the similar studies made for alloys and compounds from our laboratory.

An intermediate-image spectrometer for precision analysis of beta spectra

Abstract Eventual distortion of beta spectra due to instrumental components of a spectrometer is discussed. Simple relations for backscattering correction and maximum permissible discriminator bias-setting for any primary energy are suggested. A limit of 0.5% for any changes in the transmission of the Intermediate-image spectrometer due to baffle-scattering is prescribed. An exact but easy method of resolution correction due to Hinman 26 ) without involving any assumptions regarding line-shapes and the true beta spectra is also discussed.

Negaton spectrum of 76As

Abstract A FK analysis with proper shapes for the outer beta groups yielded beta groups with endpoints 2970±2 (50 %), 2410±4 (31 %), 1785±7 (7 %), 1184±20 (3 %) and 320±30 (1.8 %) keV, which fit very well in the level scheme of 76 Se. A large ∝ B ij contribution is expected for the 2.41 MeV beta group because its log /tf t value is comparable to that of the outer unique group and also the condition ξ ⪢ W 0 is not well fulfilled. No precise data are available on its shape, and the contribution of the 1852 keV beta group is ignored in a previous work. The present measurement ( a = − 0.007 ±0.01) yields a surprisingly statistical character for this transition which therefore cannot be analysed under the “modified B ij approximation”. However an earlier analysis by Fischbeck and Newsome under the latter formalism indicated two possibilities for the configuration of the 2 + first excited level of 76 Se for which the shapes were nearly statistical. A further distinction between these two possibilities will require an analysis employing exact formulae and data on angular and energy dependence of circular polarization. Incidentally, it was found that the outer first-forbidden unique transition requires an additional small-order shape factor ( a = −0.027±0.008) for its complete description.

IMPROVED METHODS IN THE ANALYSIS OF NON-STATISTICAL BETA SPECTRA.

Abstract With a view to eliminating all possible uncertainties in the method of analysis of linear and curvilinear shape deviations, the correlation between the endpoint energy and the shape factor coefficients including the modified B ij shape parameter D is thoroughly discussed. In contrast to the earlier methods which are either insensitive or unreliable, an ordered sequence of analysis which is physically very significant is developed. The method is highly sensitive and the effects on the shape factor of the unknown parameters can be individually studied.

Beta Spectrum of 124Sb

Abstract The repeated measurements of Langer et al. and Canty et al. do not agree on the magnitude of D in the modified B ij shape. A recent analysis including circular polarization and the formers value of D yielded the matrix element set compatible with CVC theory, whereas the value of D by Canty et al. yielded matrix elements incompatible with CVC theory. The present work gives D = 7.3 ± 1 in good agreement with Canty et al. The statistical accuracy of the present measurement is good enough to distinguish between the different predictions of matrix element sets. A correlation is shown between D and W 0 and the calibration constant. The discrepancy in the results of Langer et al. can be understood on this basis. The existence of beta groups with endpoint energies 1579 and 1656 keV is inferred from the FK analysis.

Comments on theoretical limitations for experimental values of photoeffect cross sections at low energies

Experimental photoeffect cross section data of Wang et al. [Nucl. Instr. and Meth. B 71 (1992) 241, 71 (1992) 249, 86 (1994) 231 and 86 (1994) 236] are compared with unrenormalised and renomialised theoretical photoeffect cross sections calculated by Scofield [Lawrence Livermoore Nat. Lab. UCRL-51326 (1973)) to test the inequality condition suggested by Gerward [Nucl. Instr. and Meth. B 69 (1992) 407, J. Phys. B 22 (1939) 1963]. It is found that these recently measured experimental cross sections are higher than both unrenormalised and renormalised values of Scofield. Hence the suggestion made by Gerward that the Scofield values with and without Hartree-Fock renormalisation can be used as lower and upper limits to the experimental photoeffect cross sections requires further rethinking of theoretical limits.

Shape factor analysis of beta transitions in Pm-149

Shape factor analysis of the beta transitions in149Pm is carried out for the first time, employing an intermediate image beta ray spectrometer. The ambigous situation arising from the disagreement between reported values in end point energies and intensities of the beta transitions is clarified. An attempt was made to evaluate the NME, for the 780 keV beta transition, using Simms formalism.

Shape of the 935 keV beta transition of143Pr

The beta spectrum shape of the 7/2+ → 7/2− beta transition in the decay of143Pr is measured employing a thoroughly tested intermediate image beta ray spectrometer of the Siegbahn-Slatis type and using the source produced by irradiation of highly enriched stable142Ce sample. The spectrum exhibits a definite energy dependence and is well fitted with shape factorC(W) = 1 − (0·057 ± 0·006)W whereW is in m0c2 units for an end point energy of 935 ± 2 keV agreeing well with the results of Hamiltonet al and Spejweskiet al and disagreeing with the results of Persson and Reynolds. The single particle configurations for the low lying levels of143Pr could not give quantitative results.

Spectral shape studies in the beta decay of 192Ir

The spectral shapes of the beta groups feeding the 3+ and 4+ levels of 192Pt in the decay of 192Ir are analysed employing a Siegbahn-Slatis beta ray spectrometer in the coincidence mode of operation. These two beta transitions with end-point energies 535+or-2 keV and 666+or-2 keV are found to exhibit similar characteristics of statistical shapes within the experimental uncertainties. The shapes are in accordance with the xi approximation, thus confirming the first forbidden nature of the beta transition feeding the 3+ and 4+ levels of 162Pt and in turn favouring a negative parity for the ground state of 192Ir. The results seem to support the description of the 4+ and 3+ levels in 192Pt as the two-phonon and three-phonon quadrupole vibrational levels.