Sains Ma1aysiana 26(3&4): 119-120 (1997)                                                                               Sains Fizis dan Gunaan/

                                                                                                                                               Physical and Applied Sciences

Comparison of Measured and Calculated ⁴⁰K

Activitiy per Gram of K

Supian Bin Samat

Department of Physics

Faculty of Physical and Applied Sciences

Universiti Kebangsaan Malaysia

43600 UKM Bangi Selangor D.E. MALAYSIA

Stuart Green & Alun H. Beddoe

Department of Medical Physics

University Hospital Birmingham NHS Trust

Queen Elizabeth Hospital

Birmingham 815 2TH, U.K.

Measurement of the natural ⁴⁰K body gamma-ray radioactivity via the whole-body counter (WBC) technique may yield the total body potassium (TBK) status, from which for example, the body cell mass can be derived (Moore et al. 1963). The accuracy of the derived TBK is of course critically dependent on the assumed value of the ratio ⁴⁰K:TBK. Potassium chloride (KCI) has been widely used as the ⁴⁰K calibration standard. In reviewing the literature (Burkinshaw 1967; Ross & Morris 1968; Havlik 1970, Young et al 1975; Manocha & Mohindra 1976; Holtzman 1977; Graham 1983; HMSO 1985-1986, Lykken et al 1987; Lan & Weng 1989; Fenwick et al. 1991), it is apparent that inconsistencies occur in the use of ⁴⁰K activity per gram of natural potassium. It varies between 27.33 to 31.31 Bq per gram of potassium. The objectives of this study were to independently measure and calculate the ⁴⁰K activity per gram of natural potassium in an attempt to reduce the uncertainty in the accepted figure. Experimentally the activity of ⁴⁰K from a known amount of K was determined by measuring the ⁴⁰K photon emission of an analar grade KCI sample solution and the absolute efficiency of the detection system at energy 1460 KeV. Both the photopeak count-rate and the absolute efficiency were measured using the gamma-ray spectroscopy technique. The ⁴⁰K activity is also calculated from its half-life (IAEA 1989) and the number of atoms present in the sample. The measured and calculated values obtained were 30.18 ± 0.72 Bq g^-1 and 31.00 ± 0.33 Bq g^-1 respectively. The difference is of the order of 2.6%. The measured value is consistent with the literature values being close to the mean of the values, namely 29.77. In conclusion, it is believed that the experimental values reported in this work is one of the few experimentally determined results and it is reassuring to note that the experimental and theoretical values are in reasonable agreement.

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