Assessment of the Annual Effective Dose due to Intake of Natural Radionuclides from some Food Samples

Since the main source of ingestion exposure to natural radioactivity originating mainly from foodstuffs, the current study aims to assess the total committed doses from 226 Ra, 232 Th and 40 K from some food products. Thirty food samples such as wheat, beans, meat, chicken, fish, Molokai, coffee, tea and powder milk were randomly collected from some markets in Cairo and dried using an electric oven. Specific activity for the 226 Ra, 232 Th and 40 K concentrations in food samples was measured using


INTRODUCTION
Ingestion dose is mainly due to 40 K and the 238 U and 232 Th series radionuclides present in foods.Ingestion intake of natural radionuclides depends on the consumption rates of food on the radionuclide concentrations [1].Estimates of uranium and thorium series were determined from market basket evaluations.Regular monitoring of food may become a basic requirement for following the internal natural radiation doses.S. Harb and Rafat M et al determined natural radionuclides in tea and spices [2][3].Vahid Since the main source of ingestion exposure to natural radioactivity originating mainly from foodstuffs, the current study aims to assess the total committed doses from 226  Ra, 232 Th and 40 K from some food products.Thirty food samples such as wheat, beans, meat, chicken, fish, Molokai, coffee, tea and powder milk were randomly collected from some markets in Cairo and dried using an electric oven.Specific activity for the 226  Ra, 232 Th and 40 K concentrations in food samples was measured using a high-purity germanium spectrometer.The effective dose from the resulting food was calculated using the dose conversion factors recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation, 2000.The specific activity for the selected food samples varies from 3.5±0.1 to 8.8±0.2,1.0± 0.1 to 4.6±2.2 and 20±1.0 to 718±2.0Bq.kg -1 for 226  Ra, 232 Th and 40 K respectively.The obtained annual ingestion dose was lower than dose constrain and lower than the public dose which gave indication for radiation food safety.that the average activity concentrations of primordial radionuclides in wheat and corn samples were found to be 1,67, 0.5, 91.73, 0.01 Bq/kg respectively [4].S. Harb and Nurul Absar et found that activity concentrations of natural background radiation in some vegetables and fruits samples were within the normal range.[5][6].Sangbok Lee et al assessed the average radioactivity for natural radionuclides in coffee by country origin .They mentioned that the highest concentration of the natural radionuclides was measured in Brazil and the lowest in Ethiopia [7].The current study aims to assess the total committed doses from 226 Ra, 232 Th and 40 K due to ingestion.

MATERIALS AND METHODS
The radioactivity concentrations of food samples were measured using high purity germanium gamma ray spectrometer (HPGe) (Canberra) with 25% relative efficiency.
Thirty food samples of wheat, beans, meat, chicken, fish, Molokai, lantils, coffee, tea, and milk powder which were collected from local markets in Cairo.Each sample was dried in an electric oven at 105 ℃ for 16 h to eliminate any water content.This is in addition to meat, chicken and fish ached at 250 ℃ [8].Then, the samples were stored for a period of 1 four weeks to establish secular equilibrium between radium and radon daughters .Each sample was counted for 86400 seconds (24 hrs.).The concentrations of 226 Ra, 232 Th and 40 K in the three samples for each type was calculated using efficiency energy relation relationship as shown in Figure1.It represents the relationship between energy and efficiency calibration for standard reference material (IAEA-RGU-1).

Figure 1 Counting Efficiency for (HPGe)
The secondary standards were calibrated by the primary standard RGU-I with concentration of 4940 Bqkg -1 .Detector was calibrated to convert channel numbers or spectra into gamma-ray energies.A spectroscopy study was conducted for a source-todetector distance of 2 cm.The concentration of 226 Ra was determined using the 609 keV gamma line of 214 Bi, while 1462 keV for 40 K, and 385 keV and 2614.5 keV of 208 Tl were used for determining the 232 Th activity concentration in the sample.Each sample was analyzed for 24 hours (86400 seconds) to measure the presence of radioactivity in samples.After that, the efficiency term related to detector efficiency (ε) for a particular peak and the energy efficiency curves obtained by the calibration source, by using the following equation (1).
Where N p is the net number of counts in a given peak area obtained from each photo peak, and A c is the activity value of each calibrating source, t is the counting time of a spectrum acquired, y is the emission probability, and K c is the decay factor for the decay of source during counting time.

Mathematical equations
The activity calculated in Bqkg -1 as presented in equation (2).It was used to find out the activity concentration for potassium, radium and thorium ( 40 K, 226

Effective dose due to ingestion
The ingested dose per year for 226

DISCUSSION
The total committed doses from 226 Ra, 232 Th and 40 K have been estimated from dietary intakes for some food samples.The sum of annual ingestion effective dose to 226  Ra ,  232 Th and 40 K due to intake of nine types of Egyptian diet was 0.32 mSv .It is in a good agreement with the typical range of 0.2-1 mSv [10].The highest annual effective doses due to food intake was found in beans and wheat which are considered main breakfast diet.The internal effective dose per year from dietary habit contained 226 Ra decayed to stable lead in approximately 50 minutes and after about 6 hours .In addition to the recommendations of ICRP, Gastrointestinal tract model indicates that within few hours the food is digested by the stomach so the food will absorb by small intestine with low doses.The Annual effective doses for 40 K was 153 µSv which is within the range of the total body burden of 40 K deposited in the total body and the total ingestion doses were within the dose range of internal natural radiation [11].The 226 Ra and 234 Th contents of grains and leaves powder food samples depend on 226 Ra and 234 Th present in nearby soil where they are grown.The plants of molokhia uptake radium isotopes existing in soil throughout their growth by their extensive root system.

CONCLUSION
As a result of our study, we can conclude the followings.In general, radionuclides 226 Ra, , 232 Th and 40 K were measured in seven types of food samples.We noticed that the mean and standard deviation for activity concentrations of 226  Ra, 232 Th and 40 K were 80.1± 6.6, 29.1± 2.5 and 126.1 ± 20 respectively.The obtained results are considered a baseline data for future reference dose levels.The obtained annual ingestion dose was lower than dose constrain and lower than the public dose which gave indication for radiation food safety.
Th, and 232 Th) radioactive elements.Where: Activity in Bq.kg -1 N: Sample Count-Background count ε: Efficiency percentage P: Photon energy probability emission W: Sample weight in kilogram.
Changizi et al found