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21 November 2009

Answer to Question #2313 Submitted to "Ask the Experts"

Category: Radiation Basics — Alpha Radiation

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

If alpha particles cannot penetrate a piece of paper, what happens to them? Do they get absorbed? Or deflected? Will the paper become radioactive? Why?

An alpha particle is physically identical to the nucleus of a helium atom. It carries two units of positive charge. An alpha particle, initially travelling fast, slows down by having thousands of collisions with atoms in the paper until it is essentially stopped. One describes this by saying that the alpha particle is absorbed by the paper. Once slowed almost to rest, the the alpha particle rapidly captures two negatively charged electrons from the surrounding matter and forms a neutral atom of helium. Helium is a harmless, inert, chemically inactive gas, and the helium atom is free to migrate by thermal motion and escape from the paper. The paper does not become radioactive in any way.

James E. Turner, CHP, PhD

Answer posted on 9 April 2003. 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.