Gamma Counting Techniques Research Articles

An Ultrasonic Trepanning Technique for Radial Sampling of Ceramic Fuel Pellets

An ultrasonic trepanning technique for use in the radial sampling of small-diameter ceramic fuel pellets takes an initial sample in the form of a small-diameter solid cylinder from the center of the pellet. Subsequent samples are thin-wall concentric hollow cylinders. Radial samples 1.56 to 6.80 mm in diameter and 5.35 to 6.80 mm long have been obtained from 93 percent dense UO$sub 2$ pellets and 91 percent dense mixed-oxide (UO$sub 2$--PuO$sub 2$) fuel pellets. Cylindrical samples with wall thicknesses of 0.25 to 0.44 mm can be obtained without difficulty. Diameters and wall thicknesses of individual samples and concentricity between samples can be held within +--0.01 mm, at a sample cutting rate of 0.02 mm/s. The technique has been adapted to existing ultrasonic grinding equipment located in a shielded glove-box facility, which had been used for less precise ultrasonic drilling operations. The technique is currently being used to obtain radial samples from fresh (unirradiated) mixed-oxide fuel pellets that have been subjected to low-burnup exposure in the transient test reactor (TREAT). The individual samples taken from each pellet undergo burnup analysis using standard gamma-counting techniques. The gamma emitters are the $sup 140$Ba--$sup 140$La daughters formed during the radioactive decay of the activatedmore » fuel pellets. The analytical results, expressed as fiss/(g s), obtained for discrete radial locations provide the necessary information on the radial power distribution within the individual pellet. (auth)« less

Mass Distribution of Fission Products Following Photofission of Uranium-238

The mass-yield distribution of fission products following photofission of /sup 238/U using bremsstrahlung energies of 22, 24, and 28 MeV were measured by radiochemically isolating the fission products belonging to 24 mass chains. The absolute activities of these nuclides were determined by BETA - and gamma counting techniques, and the cumulative fission yields were calculated relative to /sup 140/Ba. The peak-to-valley ratio was found to be effectively constant; thus, the average photon-energy-inducing fission is essentially equal for all three energies studied. The fission yields in the mass region from 130 to 140 were examined for evidence of fine structure around A = 132 or A = 133. Although there were some deviations in this region from a smooth curve,'' it did not yield conclusive evidence for fine structure. Finally, to set the slope of the heavy wing of the mass yield curves, cumulative fission yields of mass chains in the rare-earth region (in addition to others) were measured. (5 figures, 2 tables) (auth)

Neutron activation cross-sections in rare earths and heavier nuclei

Radiative neutron capture cross-sections for the isotopes138Ba,140Ce,142Ce,146Nd,148Nd,160Gd,165Ho,180Hf,181Ta,190Os,197Au and202Hg have been measured at the neutron energy (23±5) keV by means of the activation method and 4π-geometry gamma-counting technique. In 9 cases for each of which there is a single previous report of the cross-section, the present work serves as a check on the previous value. In the remaining cases the present study helps to resolve the existing discrepancies in the reported values. The present results are generally supported by the recent semi-empirical estimates of the cross-section by Musgrove.

Capture Cross Sections of Intermediate Neutrons

Radiative neutron capture cross sections for the isotopes /sup 59/Co, / sup 68/Zn/, /sup 86/Sr, /sup 87/Rb,/sup 976/Ryu, /sup 98/Mo, /sup 100/Mo, /sup 102/Ru, /sup 104/Ru, / sup 113/In, /sup 115/In, /sup 122/Sn and /sup 133/Cs were remeasured at the neutron energy 24 plus or minus 5 keV in view of the wide discrepancies in their values as reported in literature. The activation method and 4 pi geometry absolute gamma counting technique were used to obtain the cross sections. By making a critical comparison of the present results with the earlier experimental values on the one hand and with semi-theoretical estimates on the other, an attempt is made to resolve the discrepancies. (auth)

P wave neutron capture in medium and heavy weight nuclei

A systematic investigation of the average neutron capture cross sections at 25 keV is undertaken to study the structure of giant resonances in the p wave neutron strength functions. As a part of this program and to fill in the gaps in the existing cross section data, radiative capture cross sections for the following isotopes have been measured. 74Se, 78Se, 84Sr, 109Ag, 122Te, 159Tb, 169Tm, 174Yb, 176Yb, 178Hf, 179Hf and 192Os. The activation method and absolute gamma counting technique have been employed. The new results are reported with a discussion of the p wave neutron capture in these nuclei.

Neutron capture cross sections at 25 keV

The radiative capture cross sections for eight even-even nuclei in the mass region 80<A<160 have been investigated using the activation method and gamma counting technique. The cross sections for the three isotopes 84Kr, 110Cd and 146Nd are reported for the first time and in the rest of the cases a comparison is made with previously reported values. The case of 115In(n, gamma )116In is reinvestigated as there is a discrepancy between the values reported using beta and gamma counting methods. The present results are in better agreement with gamma counting values.

A new simple method for accurate measurement of urinary I131 after tracer and therapeutic doses.

WE HAVE recently (1) described a method for quantitative measurement of the amount of I131 in the thyroid gland by external counting. It was apparent that the method was not only applicable to the external counting of I131 in the thyroid but likewise afforded a simple, direct measurement of I131 content in urine, as shown by the experimental data presented here. This new method of measurement is as accurate as the standard gamma counting technique previously reported from this laboratory, is simple, and requires minimum handling and exposure of the urine sample (2) Four platinum cathode Geiger-Mueller tubes were connected in a parallel electrical circuit and arranged in a horizontal plane (Fig. 1). The distance of each tube from the center was 60.0 cm. We have previously shown (3) that within a “circle” of this diameter (120.0 cm.) is a smaller concentric sphere, approximately 40 cm. in diameter, in which a source of I131 may be moved with a change in counting rate of not more than 5 percent, as compared to net counts per minute obtained with the I131 source in the center of the circle. We have termed this central space the “free area” and have shown that its diameter is proportional to the diameter of the Geiger-Mueller tube circle (Fig 2).