|
||||||||||||||
Answer to Question #4731 Submitted to "Ask the Experts"Category: Medical and Dental Equipment/Shielding — Shielding The following question was answered by an expert in the appropriate field: Q
I subscribe to a National Aeronautics and Space Administration newsletter. Today they sent out an interesting article
on polyethylene as an alternative material for manned Mars spaceships.
Secondary radiation from shielding materials was discussed, including
lead shielding for dental and medical x rays. My question is, what is the
extent of secondary radiation that is emitted from the lead aprons
placed over folks receiving x rays and whether that radiation is a
possible health risk. Also, has polyethylene been considered for such
applications? Do I need to bring a garbage bag with me the next time I
go to the dentist?
A
This is a very interesting article and you pose a very
good question. Different types of radiation require different types of
shielding. Alpha particles (helium nuclei) are relatively heavy and are
shielded with paper. Beta particles (electrons) are lighter particles and are
best shielded with a material with a low atomic number, such as plastic or
aluminum. Gamma rays and x rays (or photons—they are the same thing, each just
originates in a different place) are bundles of energy instead of a particle
and are best shielded by a material with a high atomic number, such as lead. In
general, particles interact with nuclei, while photons interact with electrons
in the shielding material.
As the article mentions, aluminum and plastic are good
shielding materials for the heavy charged particles encountered in space
flight. The two most important issues are having enough shielding to stop
secondary radiation (you can’t have a very large amount of shielding—this will
stop the radiation, but will be too heavy and/or bulky for space flight), and
to have structural integrity (as discussed in the article).
Since medical and dental radiation primarily consists
of gamma rays and x rays, the best shielding to use is something with a high
atomic number that is economical and practical. In most cases, lead is the best
option. There is secondary radiation produced; however, the amount that gets
through a lead apron is very small (a typical lead apron will scatter 92%-97%
of the x rays that strike it). Since your plastic garbage bags are not good
shielding for x rays, you may want to leave them at home until you can take
your spaceflight to Mars!
Ken “Duke” Lovins, CHP
Answer posted on 2 September 2005. 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.
|
||||||||||||||
| Ask a Question • Search ATE & ATE Categories • If you have Web-related problems, contact our Webmaster. If you are lost, see our site map. This page last updated 02 July 2008. | ||||||||||||||
