lleOe percent in 80 years. of the rooting zone will Removing 30 cm of topsoil a fall by some 85 will reduce the level by fall in direct. propartion some 66 percent (Table 2). It should be noted that dose does not to the depth of such excavation. Since dose is proportional to rooting- zone specific-activity, it falls exponentially with depth like the rooting- zone activity (Figure 4). mare: lhlUrlUlUmrecEElUlU The strontium-90 level I00062b 27