Radiological Safety Traning for Uranium Facilities
Module 104 - Internal Dose Control
Alpha particles are highly charged and will only travel about 2 inches in
air. Alpha particles are also stopped by the dead layer of skin. This
means that alpha particles external to the body are not a health concern.
It also means that alpha particles are hard to detect because the detector
must be close to the source of the material emitting the alpha particle.
There are many detector types available for detecting alpha
contamination. Two of the most commonly used types are scintillation
detectors and gas proportional counters. A thin window Geiger-Mueller
(GM) detector, such as a pancake probe, will also detect a small portion
of the alpha radiation emitted.
Proportional counters and GM detectors are well suited for detecting
beta-gamma radiation emitted by radioactive decay products in the
uranium chain. Beta-gamma radiation travels further than alpha
radiation and is easier to detect. For natural, depleted, and lower levels
of enriched uranium, the ability to measure uranium by detecting the
beta-gamma radiation from the uranium and its radioactive decay
products is about five times more sensitive than by alpha monitoring
Many surfaces that could be contaminated are porous. If the uranium
contamination is in the pores of the material or the surface of the
material is wet, the alpha radiation will be blocked. Under these
circumstances, beta-gamma monitoring is the only means of detecting