Medical Radiology and Radiation Safety. 2013. Vol. 58. No. 5. P. 11-25

RADIATION SAFETY

Yu.I. Gavrilin

Retrospective Estimation of ¹³¹I Integrated Deposition Considering Prolonged Character of Area Contamination

Burnasyan Federal Medical Biophysical Center of FMBA, Moscow, Russia, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Purpose: Development of reliable method for estimation of integrated ¹³¹I deposition considering prolonged fall-out character, first of all, for the areas with density of ¹³⁷Cs deposition less than 3.7×104 Bq m^–2. Those estimates will be used in order to reconstruct the thyroid doses.

Material and methods: We used the results of determination of daily deposition of ¹³¹I on plane-tables placed in 43 reference points which were received by the staff of Scientific Production Association “Taifun” from various regions of former USSR being based on treatment with corresponding materials. In addition, the results of determination of ¹³¹I and ¹³⁷Cs activity in soil samples collected by the staff of the Institute of Nuclear Energy (Belarus) and other researchers in various areas at different times after the Chernobyl accident have been used. A new reliable method for estimation of integrated ¹³¹I deposition using the simplest way is presented.

Results: 1) It has been shown that the value of the ratio of total activity of ¹³¹I (G_ΣΣ(I)) to the integrated deposition of ¹³¹I q_Σ(I) reaches its maximum value on 56th day after the Chernobyl accident. For the areas with deposition of ¹³¹I more than 4500 Bq m^–2 a relationship has been received П =12 while for the areas with deposition of ¹³¹I less than 4500 Bq m^–2 – П = 11.

2) It has been shown that the transfer from accumulated activity of ¹³¹I in soil (G_ΣГ(I)) on day (t) to the integrated activity of ¹³¹I, for example, during 56 days counting from the date of the accident can be taken into account by using the relationship G_ΣГ(I) × Z = G_ΣΣ(I). The values of coefficient of Z have been determined for 10 reference (index «O») cities for each day from 26.04 to 12.07.1986 with the values of the integrated deposition of ¹³¹I q_Σ(I) from 4.3×103 to 2.7×106 Bq m^–2.

The measured values of activity G_ΣГ(I)_jх in soil for any day (t) in the vicinity of the settlement «j» located in territory «x» НП_jх are compared with the values from Table G_ΣГ(I)о for reference cities НПо for the same day (t), selecting the most close to the corresponding values of G_ΣГ(I)о together with corresponding value of Z. The values of integrated deposition for НП_jх are assessed according to the relationship q_Σ(I)_jх = G_ΣГ(I)_jх×Z / П. Clarification of the parameters used is presented in section “Introduction”.

The calculated values of parameter q_Σ(I)_jх together with corresponding values of parameter q_Σ(Cs)_jх are used to derive the relationship of q_Σ(I)_jх versus q_Σ(Cs)_jх for an area of interest, according to which the integrated deposition of ¹³¹I are assessed for НП_jх where only integrated values of ¹³⁷Cs are known.

Conclusion: A simple and reliable method for reconstruction of the integrated deposition of ¹³¹I for areas of interest has been developed.

Key words: Chernobyl accident, retrospective dosimetry, deposition of ¹³¹I and ¹³⁷Cs, thyroid gland