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Answer to Question #1640 Submitted to "Ask the Experts"Category: Environmental and Background Radiation — General The following question was answered by an expert in the appropriate field: Q
How far into the body does background radiation penetrate? Is it capable of passing through the body (as x rays do)?
A
The background radiation to which we are exposed can be considered to consist of two types:
1. Important External Sources. We are continually exposed to the cosmic radiation produced in the upper levels of the atmosphere and to the gamma rays emitted by radioactive material in the ground. The major component of the cosmic radiation to which we are exposed consists of muons (somewhat similar to electrons). These cosmic muons are of such high energy that they pass completely through our body. However, as they do so, they transfer a fraction of their energy to our body. The result is an annual dose of approximately 30 millirem. Many of the gamma rays emitted by radioactive material in the ground pass through our body without interacting—that is, they transfer no energy to it. Some gamma rays scatter off the atoms in our body and transfer some fraction of their energy. Other gamma rays are completely stopped, that is, they transfer all their energy to our body. The result is an annual exposure similar to that delivered by cosmic radiation: approximately 30 millirem per year. 2. Sources inside our body. Various kinds of radiation are emitted by the radioactive material naturally found inside the body: alpha particles, beta particles, gamma rays, etc. The dose delivered by the alpha particles and beta particles is larger than that delivered by the gamma rays because alpha and beta particles produced inside the body deposit almost all their energy, whereas only a fraction of the gamma-ray energy is deposited. Another way to say this is that these alpha and beta particles do not escape the body, whereas many of these gamma rays do escape. Examples of the radioactive materials inside the body include: the radon decay products deposited in the lungs, the 40K distributed throughout the soft tissues of the body, and the 210Pb and 210Po mostly found in the skeleton. The dose from these sources is approximately 240 millirem per year. Paul Frame, CHP, PhD
Answer posted on 5 February 2002. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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