7/31/2019 Simple screening method for radioactively contaminated food using ashing method with Geiger-M ller counter

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RIKEN Accel. Prog. Rep. 45 (2012)

Simple screening method for radioactively contaminated food using

ashing method with Geiger-Muller counter

M. Wada and H. Haba

After the accident of the Fukushima Daiichi nuclearpower plant in the middle of March, 2011, radioactivecontamination of food has become a serious concern,especially for those who live in the area where the soilis highly contaminated. It is worth developing a simplescreening method, which can be used at home.

In general, -rays can be detected with a muchhigher efficiency than -rays, and the shielding of -rays is considerably easier than that of -rays. How-ever, -rays can be shielded by the sample itself.Only surface contamination can be detected by a thin-window Gaiger-Muller (GM) counter. If the radioac-

tivity could be concentrated into a thin sample, thetotal radiation detection method would be a signifi-cantly sensitive method for contamination surveys.

Most foods consist of water, carbohydrates, proteins,lipids and ash. The concerned radionuclides, such asCs or Sr, belong to the ash that can be extracted fromthe sample by an ashing process. The content of ashin food is on the order of 1%, which implies 100 timesconcentration can be achieved.

First, we tested this method at home using a kitchengrill for fish in order to ash the food samples withoutcontamination. This required approximately 20 minunder a medium flame, and the temperature of the

samples was less than 500 C. The weight of ash wasless than 1 g. The ashes were flattened and coveredwith a 10 m kitchen film (polyvinylidene chloride).The -rays from the ash were detected using a 5 cmaperture GM survey meter (TCS146B). The amount ofpotassium (K) in foods was noted from an ingredientstable and the specific activity of them could be cal-culated from the natural abundance of 40K (0.0117%)and the half-life (1.28109 y). The calculated count-ing rate Ical from the table, with a branching ratio of90% and a detection efficiency of 25%, was comparedwith the measured counting rate Iexp after subtract-

ing the background (Tab. 1). They agreed well withinthe limits of a statistical error.

Next, samples that were radioactively contaminated

Table 1. Specific activities of 40K in foods and the count-

ing rates (Ical and Iexp) obtained with a GM counter.

spices ash K S.A. m Ical Iexp% % Bq/kg g cpm cpm

Spinach 1.7 0.69 219 59 174 169(19)Soy bean 1.4 0.49 155 33 70 72(14)W. mellon 0.2 0.12 38 100 51 67(11)

Onion 0.4 0.15 48 114 73 70(9)Milk 0.7 0.11 35 76 36 34(19)

Table 2. Measurements of contaminated samples.

sample Cs K40 mass ash Ical IexpBq/kg Bq/kg g g cpm cpm

Berry1 135 76.7 21.1 0.53 33 38(4)Berry2 135 76.7 22.6 2.1 36 22(3)Urine1 1727 532 23.9 4.0 378 217(5)Urine2 549 377 21.0 0.9 149 158(5)Milk1 145 48.8 20.2 0.2 28 24(3)Milk2 268 47 20.0