Juan Manuel Navarrete
Professor
Title: 40K radioactive detection for K quantitative analysis in foodstuff
Biography
Biography: Juan Manuel Navarrete
Abstract
40K radioactive detection in foodstuff is easily performed by filling Marinelli containers with any food sample in order to detect the γ rays emitted (energy 1461 KeV, 11% decaying nucleus to 40Ar by electron capture, EC), and detectd either by one NaI(Tl) scintillation or HPGe semiconductor detector. So, if each one is used during a suitable detection time, for example 12 hours overnigth, counts number with reasonable standard deviation are accumulated, and it is possible to compare and obtain better results, when Bq per gram of sample (Bq/gs) is divided by specific activity of elementary K (31.19 Bq/gK) and multiplied by 100, to get the K concentration in the sample as percentage. In this way, to obtain Bq/gs next equation is used:
Bq/gs = Cs – Cb/Ws.xDet. Eff.x0.11 (where: Cs=counts per second obtained from sample;Cb=counts per second obtained from background; Ws=foodstuff sample weigth in grams;Det. Eff.=Detection Efficiency of each detector for 1461 KeV γ rays/100; 0.11=40K branching ratio decaying to 40Ar by EC). Elementary K specific activity is a constant obtained from next equation:
Bq/gK = λN = 0.693x6.02x1023x0.0118/1.28x109x365x24x3600x39.1x100=31.19 Bq/gK
(where: λ=40K decay constant; N=40K atoms number per K gram; 0.693=ln 2; 6.02x1023= Avogadro’s number; 0.0118/100=40K isotopic abundance;1.28x109x365x24x3600=40K half life in seconds; 39.1=Elementary K atomic weigth).
And finally:
K(o/o)=Bqx100/gs / Bq/gK = gKx100/gs
So, severalvegetables, seeds and grains have been analysed for K concentration, and this paper presents the higher K concentration in peels, related to grains of cacao and coffee, obtained by this non destructive, easy and precise enough procedure.