K.L. Narasimham

Photoelectric cross-sections of light elements and compounds at low photon energies

Total photon mass attenuation coefficients in C, Al, S, Ti, B2O3, LiF, ZnO, Y2O3 and H8O2C5 (perspex) are measured on a good geometry set-up using proportional counter, Si(Li) and Ge(Li) detecting systems in the energy region from 6.47 to 52.014 keV employing x-rays and gamma rays from radioactive sources. The deduced photoelectric cross-sections are found to agree with the theoretical values of Storm and Israel, Scofield and semiexperimental values of Veigele wherever available within a few percent. The photo-electric cross-sections in elements, S, Ti and Y at their respectiveK-edges obtained by extrapolation technique agree with the theoretical values of Storm and Israel and Scofield at the respectiveK-edges except in S. In the case of S both the theoretical values atK-edges are found to be underestimations, more in the case of Scofield evaluations.

Measurement of K-shell photoelectric cross sections using a direct method

Abstract K-shell photoelectric cross sections are determined by the direct method at 661.65 keV in Au at 30° and 40° and in Yb, Ta and U at 40°. A high resolution HPGe detector is used to detect both the X-ray and incoherently scattered gamma ray intensities simultaneously. The superiority of the direct method over the indirect method at higher energies is discussed. The results are showing a good agreement with the available theoretical and other experimental values. A close observation shows that the measured values are in a better agreement with the accurate and recently reported data of Scofield.

Photoelectric effect around K-edges in the elements Ce, Sm, Dy and Yb

SummaryPhotoelectric cross-sections are determined in the elements Ce, Sm, Dy and Yb in the photon energy range from 24 to 122 KeV employing Si(Li) and Ge(Li) detecting systems and using subtraction technique. The deduced photoelectric cross-sections and theK-shell photoelectric cross-sections atK-edges are found to be in satisfactory agreement with the theoretical values of Storm and Israel and Scofleld.

Anomalous conversion in the decay of197mHg

The total andK-shell conversion coefficients of the 165 keV transition in the decay of197mHg are determined from intensity balance considerations and a coincidence technique using a Ge(Li)—NaI (Tl) system respectively. The resultant values areaT=274.8±19.2 andaK=47±12, whil the corresponding theoretical values are 344 and 77 respectively, indicating anomalous conversion. The gamma ray transition probability however, shows a hindrance of only about 6 and cannot be correlated with the present anomalous conversion data. TheK/L ratio of the 130 keV transition, determined using a summing method with a Ge(Li) detector, yielded 0.090±0.012, while the corresponding theoretical value is 0.048, indicating anomalous conversion. The corresponding gamma transition probability shows a hindrance of about 3000, in correlation with anomalous conversion.

Conversion of the 42 keV transition in the decay of191Os

SummaryThe total as well as theL-conversion coefficient of the 42 keV transition in the decay of191Os are determined from intensity balance considerations and XPG technique, respectively, using a 3 mm Si(Li) detector system. The resultant values are αT = 13709 (1900), αL = 11700 (2100). The present total conversion coefficient shows good agreement within the uncertainty limits, with the value αT = 13.500−5200+21100 reported by Lange, whereas theL-conversion coefficient is reported for the first time. Our present values are also compared with the theoretical values interpolated from the tables of Hager and Seltzer and of Roselet al.RiassuntoSi determinano il coefficiente totale e quello di conversioneL della transizione a 42 keV nel decadimento di191Os considerando il bilancio d’intensità e la tecnica XPG, rispettivamente, usando un sistema di rivelatori a 3 mm Si(Li). I valori risultanti sono αT = 13709 (1900), αL = 11700 (2100). Il coefficinete di conversione totale è in buon accordo, entro i limiti di incertezza, con il valore αT = 13.500−5200+21100 riportato da Lange, mentre il coefficiente di conversioneL è riportato per la prima volta. I nostri valori attuali sono anche confrontati con i valori teorici interpolati dalle tavole di Hager e Seltzer e di Roselet al.

Incoherent scattering functions of 145 keV gamma rays by K-shell electrons in Y, Ag and Au

The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.

Simultaneous K plus L shell ionized atoms during heavy-ion collision process

The fraction of simultaneous K plus L shell ionized atoms is estimated in Fe, Co and Cu elements using carbon ions at different projectile energies. The present results indicate that the fraction of simultaneous K plus L shell ionization probability decreases with increase in projectile energy as well as with increase in the atomic number of the targets atoms.

Precision measurements of total gamma ray cross sections with a high resolution detector

Abstract Total gamma ray cross sections are obtained experimentally in Cd, Er and Pt at 122.061 and 136.474 keV and in Pd at 93.613 keV. A transmission experiment is conducted carefully using a high resolution hyperpure germanium (HPGe) detector and a good geometry setup to measure these cross sections with an accuracy close to 1%. In a transmission experiment there generally is a chance of underestimation of these cross sections due to small angle scattering. Photopeak areas that are evaluated must be free from scattering contributions as well as from background. Measures are taken to account correctly for the included small angle scattering. The experimental values are compared with theoretical and semiexperimental data and are found to be in good agreement.