Answer to Question #7178 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Cosmic Radiation

The following question was answered by an expert in the appropriate field:

Are there seasonal variations in background radiation levels, in particular cosmic radiation? I have always understood cosmic radiation to be dependent on many factors but largely independent of the time of year.

There are seasonal changes in background radiation levels. For radionuclides in the soil the radiation exposure depends on soil moisture. The more moisture, the more the radiation exposure is attenuated (reduced). In winter there may be snow cover, which essentially interposes a water shield between the radionuclides in the soil and persons above it. These factors are the largest variations in background radiation exposure that are normally encountered.

Cosmic radiation varies over a well-known 11-year solar cycle, but this would not be noticed from season to season. An increase in atmospheric pressure will cause the cosmic radiation exposure to be reduced somewhat. This can happen on a timescale as short as a few hours or days. It is not a very large effect at any particular location. The largest effect on cosmic-ray exposure is altitude. The higher you go the less shielding there is from the air and, therefore, the higher the exposure.

Solar flares can cause brief increases of cosmic radiation that can be quite large. However these are somewhat rare and relatively brief events that would not depend on season.

Carl V. Gogolak, PhD

Answer posted on 21 February 2008. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, 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. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.