yttrium carrier for at least 14 days and the yttrium precipitated as the hydroxide, converted to oxalate, mounted and counted in a suitable low background counter. The Y°° decay curveis followed and the activity of the Sr*® deduced. Strontium is also precipitated as carbonate, mounted and the ¥°° allowed to re-equilibrate. The sample is counted and as the activity is then due to Sr+ sr? + y*, the Sr® activity can be deduced by difference. The count may be repeated at weekly intervals and the 54-day decay of the Sr®® observed. SP? IN AIR -y- INHALATION DRINKING WATER FALLOUT IN RAIN HUMAN CEREALS AND VEGETABLES SOIL » GRASS = COW w= MILK Fig. 1—Entry of Sr®° to human bone. Typical decay curves from a sample of vegetation ash are shown in Fig. 2. In this instance the count rate of both Y°° and Sr®* was reasonably high, and an end window counter with back- ground of 7 counts/min was used. When the specific activity only a limited weight is available, very much lower counting counters with a background of 0.5 counts/min (Bryant et al., sample of human bone gives a maximum Sr®™ activity of only of the original sample is low, or rates are found. End window 1956) are then used, but a 20-gram a few disintegrations per minute and the ¥°? measurementis often impracticable. The total strontium count is therefore reported for human bone. In instances wherethe activity has been sufficient for the Y°° determination, the Sr*° and total strontium counts have been compared and the Sr®/Sr*’ has been found to be low, as would be expected from the slow turnover of strontium in human bone. (Appendix 3). The analytical methods used at AERE are generally similar to those developed at the Uni- versity of Chicago by Libby and his associates (Libby, 1956; Martell, 1956) and at the Health and Safety Laboratory, USAEC, New York by Harley et al., (1956). Several intercomparison samples have been exchanged between different laboratories (Harley, 1956) and have shown good agreement. There is a variation of practice in the treatment of soils, which is partly due to different objectives. The amount of calcium in the soil, which is removed by ion-exchange processes such aS ammonium acetate leaching or the electrodialysis method used in the U-S., is variable as between one soil and another and depends also on the conditions of the extraction. The Sr* in the soil appears to be mostly exchangeable. Consequently the Sr®*’/Ca ratios or S.U. values in soils are usually higher when determined by ion exchange methods than when more complete extraction is made by hydrochloric acid leaching or fusion with sodium carbonate. The difference is most marked with calcareous soils. The Sr*’/Ca ratio in the roots of plants growing in the soil is more nearly represented by the exchangeable than by the total strontium and calcium analysis, but it is very difficult to reproduce the extraction by the plant by any simple chemical procedure (Bowen & Dymond, 1955, 1956). Since the “exchangeable calcium”in the soil is an imprecise conception it was decided to make extraction with 6 M hydrochloric acid the standard procedure. Previous work (Bryant 210 Sew gees