S. KONDO and H. ISHIWA
National Institute of Genetics, Misima, Japan
We have already confirmed that the coast of wheat seeds soaked in 32P or 131I aqueous solutions prevent strongly radioactive isotopes from penetrating into the interior of the seeds at least for one to two days1). Therefore the dosimetry of seeds soaked for one or two days can be made with a good accuracy by taking account of the contribution of the isotopes assumed to be homogeneously distributed outside the seeds. Roughly speaking, the dry seeds of Triticum monococcum flavescens have an ellipsoidal shape with the three axes 2, 3 and 6 mm long. In this report, however, we will calculate the average embryo dose based on simplified models.
(1) Average embryo dose : Assume that the dose to the embryo of thickness h(g/cm2) can be approximated by that to surface layer of thickness h of an infinite plane slab made of a tissue-like material with infinite thickness whose plane surface is in contact with an infinite aqueous solution with homogeneously distributed Beta-emitting isotopes. Then, integrating LOEVINGER'S empirical formula2), the average dose has been calculated.
(2) Comparison with experimental data : Comparing with MATSUMURA's3) data for soaking the seeds in 32P and 131I aqueous solutions for two days and two day exposure of soaked seeds to 60Co gamma-rays, we obtain the following table.
Considering the partial shielding of Beta-rays by the proximity of seeds touching each other when they are soaked in the isotope solution in batches of 20 seeds per a gauze puch, from Table 1 we may conclude that the present calculation gives a fairly good estimation of the average embryo dose, because the RBE values of these Beta-rays relative to 60Co gamma-rays will be close to unity.