A number of national and international monitoring programs were established to collect the long-term fallout from the atmosphere. Many monitoring techniques and methods have been established for collecting samples at the surface and/or in the troposphere and stratosphere. The simple and robust method for collecting fallout at the surface was using an ion-exchange column collector. The column collector consists of a funnel, an ion-exchange column, and a leveling device constructed of polyethylene. The ion-exchange column is packed with a paper pulp filter and an anion-exchange resin. At the end of sampling, the column is shipped to a central laboratory for analysis. Other sampler for collecting wet or dry fallout was to automatically expose a 'wet collector' during rainfall and a 'dry collector' during dry days. The unit for measuring the activity of fallout deposited on the ground or other surface is becquerels (Bq), defined as the number of radioactive disintegrations per second. The activity of each radionuclide per square meter of ground is important for calculating both external and internal doses. The unit for deposition is usually becquerels per square meter per month or year.
The common technique for sampling in the troposphere/stratosphere was to use high-altitude balloons equipped with large-volume filter samplers. The balloons were made of polyethylene sheet and helium was used as the buoyant gas. The size of the balloon and the amount of helium varied depending on the float altitude needed for sampling. The balloon can be floated up to 40 km height and beyond. Another sampling platforms used were aircraft. The direct-flow impactors were mounted in the front probe of the aircraft. The flow rate was governed by the altitude and aircraft air speed. Aircraft sampling provides useful information because the aircraft flies at various locations and altitudes to collect samples, unlike balloon sampling, which is fixed at a specific location.
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