Appl. Radiat. /[sot. Vol. 43, No, 1/2, pp. Int. J. Radiat. Appl. Instrum. Part A
0883-2889/92 $5.00+ 0.00 Pergamon Press plc
83 85, 1992
Printed in Great Britain
The G a m m a Contamination Food Factor A.H. KUKOC, I.V. ANICIN AND P.R. ADZIC The "Boris Kidri~" Institute of Nuclear Sciences-Vinda, P.O. Box 522, 11001 Belgrade, Yugoslavia
We suggest that radioactive food contamination, as determined solely by a quantitative gamma-ray spectroscopic measurement, may, apart from the total activity per unit mass, be for quick reference conveniently characterized by another single figure which we call the "Gamma Contamination Food Factor" (GCFF). This factor may be defined as the ratio of the total specific activity of gamma-ray-emitting radionuclides in the food sample (except that of 40K) to the specific activity of 40K either in the sample itself or in an "average man". We discuss briefly the meaning and advantages of these definitions.
The Chernobyl accident followed by the unprecedented increase of fission-product concentrations in environment brought new concern about the radionuclide contamination limits in food. Probably the most widespread and at the same time most informative and least ambiguous in this respect are the results of the low-background gamma-ray spectroscopic measurements with germanium detectors. The total specific activity of the gamma-ray emitting radionuclides obtained from such a measurement is then the commonly used single figure which characterizes the degree of radioactive contamination ~f the particular product. With this in mind we propose here, on the basis of such measurements, that the "adioactive contamination of food could be conveniently and meaningfully additionally tescribed by another single figure which we call the "Gamma Contamination Food =actor" (GCFF). This factor would be equal to the ratio of the total activity of .gamma-ray-emitting radionuclides in the sample, except that of 4°K, to the activity of 4°K n the same sample. In other words, it's the total activity of gamma-ray emitting :adionuclides in the sample, except 4°K, expressed in units of its o w n 4°K activity. The idea of taking potassium as a reference is justified by a number of its convenient t,roperties. Firstly, it is contained in almost all kinds of human and animal food in a rather well-defined range of concentrations and thus represents a convenient natural unit of ~ctivity akin to every food product. The value of GCFF defined in this way would serve cs a clear single-figure indicator of excessive radioactivity in the sample since the activity ¢ f 4°K in a given food product practically does not cffange with contamination° In the case when GCFF is close to zero, it would mean that there is no superfluous radioactivity in the sample. If GCFF is of the order of one, it would mean that the activity of contaminating gamma-ray emitters in the sample is of the order of its natural activity. If it is of the order of two, then the contaminating activity is twice its natural activity, etc. 83
84
General low level techniques
From the gamma-ray spectroscopic point of view, the single and unmistakable high-energy gamma-ray of 4°K (of 1460.83 keV) with its low alternation and quantum yield, with sufficient accuracy, of I0.7% (Gorbachev, 1976; Reus, 1983; Browne, 1986; Lederer, 1987), is especially convenient for measurements from samples of different compositions and sizes. Its long and accurately determined half life (1.277 x 109y, Tuly, 1990) is another quality recommending it as the permanent reference standard of activity. The only potential interfering gamma ray from the natural series is the 1459.2-keV gamma ray from the decay of 228Ac with quantum yield of 1%. If necessary, its spectral intensity can be deduced from the spectral intensity of the 1495.9 keV gamma ray which also occurs in the decay of 228Ac, and has the same quantum yield of 1% (the difference in detection efficiency being negligible) and then subtracted from the intensity of the 1460.83-keV peak. It is assumed that 228Ac (T1/2 = 6.2h) is in equilibrium with 228Th (TI/2 = 1.93y). Also, corrections due to the contribution of background spectral intensities to all the peaks is assumed to have been made. According to the spectroscopic data available (Gorbachev, 1976; Reus, 1983; Lederer, 1987) there are no gamma rays of fission-born radionuclides in the close neighborhood of 1460.8 keV with half lives longer than one day. When no, or too little, potassium is present in the particular food product, an alternative way to characterize the level of contamination by a single-figure might be more appropriate. If we apply to the case in question the well-known ancient saying: "Man is the measure of all things", then the total activity of gamma-ray-emitting radionuclides per unit mass in a particular food product may be expressed in units of the activity of 4°K per unit mass in an average man. According to the group of authors (Snyder, 1975) "Reference man" who is 1.70-m tall and whose mass is 70 kg, contains 0.140 kg of potassium (Belair, 1980 gives 0.160 kg) which yields about 62 Bq/kg as the specific activity of 4°K in an average man. This figure may be used now as a convenient and meaningful unit for the specific gamma-ray activity of food. Food with (GCFF) m of the order of one, where subscript "m" stands for "man", would now be as active as its potential consumer himself. Also, it should be mentioned that one could define the Partial Gamma Contamination Food Factor (PGCFF) taking the specific activity of each particular contaminating radionuclide instead of the total specific activity of all radionuclides present in the food sample and then dividing either by the specific activity of 4°K in the sample itself or in the "Reference man". This way of presenting the GCFF maybe of some advantage when dealing with food where many radionuclides are found, but only some of them need to be presented. To conclude, we think that even if the non-standard units suggested here were not officially recognized and adopted, those who wish to systemize on the radioactivity of food would find the usually quoted absolute specific activity much more instructive if supplemented by the relative GCFF figure, the more so since it is produced with no additional spectroscopic effort. Relative figures, however, should not be used alone since one should always have in mind those who may try to profit from the business in accidental conditions by adding potassium without control.
General low level techniques
85
References A.B. Belair, B.M. de Fossey, M. Fourestier, (!985) Dictionaire des Constantes Biologique et Physique, 5-eme ed., Maloine S.A. ed., Paris. E. Browne and R.B. Firestone, (1986) Table of Radioactive Isotopes, V. Shirley ed., John Wiley & Sons, Inc. V.M. Gorbachev, Yu.C. Zamyatin, A.A. Lbov, (1976) Vzaimodeistvie Izlucenij s Yadrami Tyazholih Elementov i Delenie Yader, Atomizdat, Moskva. ®
M. Lederer and V. Shirley, (! 987) Table of Isotopes, 8-th ed., John Wiley & Sons, Inc. U. Reus and W. Wesuneier, (1983) Atomic Data and Nuclear Dam Tables, 29, I & 2. W.S. Snyder, M.G. Cook, E.S. NasseL L.R. Karbausen, G Parry Howells, I.H. Tipton, (1975) Reference Man, Pergamon Press, New York J.K. Tuli, (1990) Nuclear Wallet Cards, National Nuclear Data Center, BNL, New York.
A:II 43:1/2-G
0883-2889/92 $5.00+ 0.00 Pergamon Press plc
83 85, 1992
Printed in Great Britain
The G a m m a Contamination Food Factor A.H. KUKOC, I.V. ANICIN AND P.R. ADZIC The "Boris Kidri~" Institute of Nuclear Sciences-Vinda, P.O. Box 522, 11001 Belgrade, Yugoslavia
We suggest that radioactive food contamination, as determined solely by a quantitative gamma-ray spectroscopic measurement, may, apart from the total activity per unit mass, be for quick reference conveniently characterized by another single figure which we call the "Gamma Contamination Food Factor" (GCFF). This factor may be defined as the ratio of the total specific activity of gamma-ray-emitting radionuclides in the food sample (except that of 40K) to the specific activity of 40K either in the sample itself or in an "average man". We discuss briefly the meaning and advantages of these definitions.
The Chernobyl accident followed by the unprecedented increase of fission-product concentrations in environment brought new concern about the radionuclide contamination limits in food. Probably the most widespread and at the same time most informative and least ambiguous in this respect are the results of the low-background gamma-ray spectroscopic measurements with germanium detectors. The total specific activity of the gamma-ray emitting radionuclides obtained from such a measurement is then the commonly used single figure which characterizes the degree of radioactive contamination ~f the particular product. With this in mind we propose here, on the basis of such measurements, that the "adioactive contamination of food could be conveniently and meaningfully additionally tescribed by another single figure which we call the "Gamma Contamination Food =actor" (GCFF). This factor would be equal to the ratio of the total activity of .gamma-ray-emitting radionuclides in the sample, except that of 4°K, to the activity of 4°K n the same sample. In other words, it's the total activity of gamma-ray emitting :adionuclides in the sample, except 4°K, expressed in units of its o w n 4°K activity. The idea of taking potassium as a reference is justified by a number of its convenient t,roperties. Firstly, it is contained in almost all kinds of human and animal food in a rather well-defined range of concentrations and thus represents a convenient natural unit of ~ctivity akin to every food product. The value of GCFF defined in this way would serve cs a clear single-figure indicator of excessive radioactivity in the sample since the activity ¢ f 4°K in a given food product practically does not cffange with contamination° In the case when GCFF is close to zero, it would mean that there is no superfluous radioactivity in the sample. If GCFF is of the order of one, it would mean that the activity of contaminating gamma-ray emitters in the sample is of the order of its natural activity. If it is of the order of two, then the contaminating activity is twice its natural activity, etc. 83
84
General low level techniques
From the gamma-ray spectroscopic point of view, the single and unmistakable high-energy gamma-ray of 4°K (of 1460.83 keV) with its low alternation and quantum yield, with sufficient accuracy, of I0.7% (Gorbachev, 1976; Reus, 1983; Browne, 1986; Lederer, 1987), is especially convenient for measurements from samples of different compositions and sizes. Its long and accurately determined half life (1.277 x 109y, Tuly, 1990) is another quality recommending it as the permanent reference standard of activity. The only potential interfering gamma ray from the natural series is the 1459.2-keV gamma ray from the decay of 228Ac with quantum yield of 1%. If necessary, its spectral intensity can be deduced from the spectral intensity of the 1495.9 keV gamma ray which also occurs in the decay of 228Ac, and has the same quantum yield of 1% (the difference in detection efficiency being negligible) and then subtracted from the intensity of the 1460.83-keV peak. It is assumed that 228Ac (T1/2 = 6.2h) is in equilibrium with 228Th (TI/2 = 1.93y). Also, corrections due to the contribution of background spectral intensities to all the peaks is assumed to have been made. According to the spectroscopic data available (Gorbachev, 1976; Reus, 1983; Lederer, 1987) there are no gamma rays of fission-born radionuclides in the close neighborhood of 1460.8 keV with half lives longer than one day. When no, or too little, potassium is present in the particular food product, an alternative way to characterize the level of contamination by a single-figure might be more appropriate. If we apply to the case in question the well-known ancient saying: "Man is the measure of all things", then the total activity of gamma-ray-emitting radionuclides per unit mass in a particular food product may be expressed in units of the activity of 4°K per unit mass in an average man. According to the group of authors (Snyder, 1975) "Reference man" who is 1.70-m tall and whose mass is 70 kg, contains 0.140 kg of potassium (Belair, 1980 gives 0.160 kg) which yields about 62 Bq/kg as the specific activity of 4°K in an average man. This figure may be used now as a convenient and meaningful unit for the specific gamma-ray activity of food. Food with (GCFF) m of the order of one, where subscript "m" stands for "man", would now be as active as its potential consumer himself. Also, it should be mentioned that one could define the Partial Gamma Contamination Food Factor (PGCFF) taking the specific activity of each particular contaminating radionuclide instead of the total specific activity of all radionuclides present in the food sample and then dividing either by the specific activity of 4°K in the sample itself or in the "Reference man". This way of presenting the GCFF maybe of some advantage when dealing with food where many radionuclides are found, but only some of them need to be presented. To conclude, we think that even if the non-standard units suggested here were not officially recognized and adopted, those who wish to systemize on the radioactivity of food would find the usually quoted absolute specific activity much more instructive if supplemented by the relative GCFF figure, the more so since it is produced with no additional spectroscopic effort. Relative figures, however, should not be used alone since one should always have in mind those who may try to profit from the business in accidental conditions by adding potassium without control.
General low level techniques
85
References A.B. Belair, B.M. de Fossey, M. Fourestier, (!985) Dictionaire des Constantes Biologique et Physique, 5-eme ed., Maloine S.A. ed., Paris. E. Browne and R.B. Firestone, (1986) Table of Radioactive Isotopes, V. Shirley ed., John Wiley & Sons, Inc. V.M. Gorbachev, Yu.C. Zamyatin, A.A. Lbov, (1976) Vzaimodeistvie Izlucenij s Yadrami Tyazholih Elementov i Delenie Yader, Atomizdat, Moskva. ®
M. Lederer and V. Shirley, (! 987) Table of Isotopes, 8-th ed., John Wiley & Sons, Inc. U. Reus and W. Wesuneier, (1983) Atomic Data and Nuclear Dam Tables, 29, I & 2. W.S. Snyder, M.G. Cook, E.S. NasseL L.R. Karbausen, G Parry Howells, I.H. Tipton, (1975) Reference Man, Pergamon Press, New York J.K. Tuli, (1990) Nuclear Wallet Cards, National Nuclear Data Center, BNL, New York.
A:II 43:1/2-G
