THE VERTICAL DISTRIBUTION OF BERYLLIUM-7 ACTIVITY IN SOIL PROFILES DETERMINED BY A DESIGNED DEVICE

Beryllium-7 (Be-7) is an environmental radionuclide that is continuously deposited onto the surface of the earth as fallout. After depositing onto the earth, Be-7 is rapidly and strongly adsorbed by soil particles. Beryllium-7 has a short half-life (53.3 days) and thus is primarily distributed in the upper 10 mm of the soil profile; it is therefore considered a useful tracer for documenting soil interrill erosion. The use of Be-7 to document erosion is based on a comparison of the Be-7 inventory at a sampling point with a reference value determined for a nearby reference site. The reference site is often very difficult to find; as a result, determining the reference value is usually the bottleneck for successfully using Be-7 to document soil erosion. The objective of this study was to develop a device that can easily measure a Be-7 reference inventory. A raingauge-like device was designed and used to determine the reference Be-7 inventory and its vertical distribution with depth in three types of soil. The results show that the vertical distribution of Be-7 in soil can be described by an exponentially decreasing function. The majority of Be-7 was distributed in the first 10 mm of the soil surface. These results indicated that the device is valid to determine Be-7 inventory as a reference, as well as its vertical distribution. According to the vertical distribution of Be-7, samples from the upper 4 mm of the soil surface should be less than 2 mm thick, while samples 2 to 3 mm thick can be used in the soil profile below 4 mm. The Be-7 collector can be used to determine both the total Be-7 inventory as a reference value and the distribution of Be-7 at depths in a disturbed soil profile, which is important for estimating short-term interrill soil erosion.