Nuclear Chemistry

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.