The grouping of isotopes adopted in this paper is based on Rosholt's subdivision and is shown in Table 1. They have been successfully used in recent years to mea- sure the concentration of radioisotopes in rocks. Until recently, quantitative analysis of radioiso- topes in rocks required chemical separation and mass-spectrographic measurements of the key radiogenic elements. D ow nl oa de d fr om w w w .n rc re se ar ch pr es s. A study on the methodology of high-resolution y-ray spectrometry is given by Smith and Wollen- berg (1972). The sam- ples were from a 2 ft thick surface layer of the outcrop. De- pending on the activity of the sample, the duration of the runs varied from 1 h for 100 ppm uranium content to 2 d for uranium concentration of 4 ppm in order to obtain statistical errors below 5%. Geological Survey of Canada, Paper 75-38, Part 2, pp.
The disequilibrium charac- teristics of individual radioactive districts are not the subject of this paper and will be discussed elsewhere. Method of Measurement and Data Analysis I Natural y-ray and X-ray activities of radioactive rock samples were measured with a 5-mm thick, 130-mmz surface, planar Ge(Li) detector and con- ventional electronics. Natural radioactive disequilibrium of the uranium series. 1-30, United States Government Printing Office, Washing- ton, D. Une methode est presentee pour determiner l'equilibre radioactif de la sene de l'uranium et de I'actiniurn dans les roches auivant les photons emis de faible tnergie. L'iqui Iibre dans les series est indique parl'abondance relative de5 isotopes n8U. La prcpara- tion des 6chanti Hons est simple et les mesnres peuvent effectuies sur le t m i n . He found "considerable degree of dis- equilibrium . The handling of a limited number of intense lines makes a field application possible.
Our mea- surements were performed with AC (alternating current) operated laboratory equipment, about 120 kg in weight. Precision measurement of gamma ray energies from 238U daughters.
A portable detector and analyzer, such as an intrinsic, temperature cycled Ge(Li) detector, coupled with Omega- 1 analyzer from Canberra Industries, weighs about 40 kg.
The aim of this paper is to familiarize the field geologist with a physical method of determining radio-disequilibrium.
The samples were placed at a distance of about 1 mm from the beryllium window of the detector.
The spectra were accumulated below 250 ke V photon energy in a 1024 channel analyzer and were stored on magnetic tape.
In routine exploration work such equilibrium is generally assumed.