Radiation+Concerns



Information about shielding e-mail to Andrey on 6-28-11

The other day I made a brief statement that wasn't quite true. I said that I thought I remember from the radiation safety class that it can be dangerous if you try to use plastic with gamma radiation. This is basically true because plastic is not enough to protect against gamma and you need lead. However, the fact I was actually trying to remember was this: you should not use lead to protect against beta radiation. When beta particles hit lead they can generate x-rays. Here's some copied text and links about this.

http://www.furryelephant.com/content/radioactivity/alpha- beta - gamma -radiation/ Beta ’s longer range in air means you have to be a few metres away from the radioactive source in order to be safe. So you can protect yourself from exposure to beta radiation by keeping your distance. You could also use a thin lead shield but sometimes this can produce X -rays, which carry their own risk.

@http://en.wikipedia.org/wiki/Radiation_protection However, in cases where high energy beta particles are emitted shielding must be accomplished with low density materials, e.g. plastic, wood, water or acrylic glass (Plexiglas, Lucite) [1]. This is to reduce generation of Bremsstrahlung X-rays. In the case of beta + radiation (positrons), the gamma radiation from the electron-positron annihilation reaction poses additional concern.

Anyway, for us it looks like it will be fine to put our gamma radioactive samples in plastic boxes which are wrapped in an outer layer of lead foil.

Radiation Safety Manual at Caltech in California http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CGYQFjAG&url=http%3A%2F%2Fwww.safety.caltech.edu%2Fdocuments%2F78-radiation_safety_training_manual.pdf&ei=UFsDUIqbOuLE2gXrn5mzCw&usg=AFQjCNEqJ6K2PlEewVAPsVs0S8guHah1vQ&sig2=ggzcgZWSTychGna3QYxADA

Estimating my exposure

I'm not sure how to estimate my exposure

How do I make a connection between dpm (decays per minute) or Ci (Curies) and REM (radiation equivalent in man)? I know I'll be working with some radioactive chromium with a specific dpm or Ci (don't know the exact number yet), and I know some of the ALARA limits for radiation exposure

Whole Body …………………… 5000 millirem Extremities ……………………. 50000 millirem Lens of the Eye ……………….. 15000 millirem Fetus ……………………………… 500 millirem* Individuals in the General Public …100 millirem (These ALARA limits can be found here: http://www.ncsu.edu/ehs/radiation/forms/alara.pdf)

But I'm not exactly sure how I can determine if I will exceed a specific rem limit given a specific amount of time and distance from a source of radiation with a certain dpm.

The answer about how to estimate exposure seems to lie with gamma ray dose constants. These are listed for certain element and provide the amount of rems received from a certain amount of Ci of the substance from a certain distance. Here is a listing of gamma ray dose constants http://www.iem-inc.com/toolgam.html Here is a chromium 51 radionuclide data sheet http://ehs.missouri.edu/rad/isotopedata/cr-51.pdf

Here's some info from that data sheet Gamma constant: 0.26 mR/hr per 1 mCi at 30 cm

Action Quantities: Bench top quantity must be less than 20000 μCi Containers require labeling when greater than 1000 μCi Rooms require posting when there is greater than 10000 μCi Contamination lasting more than 24 hrs require NRC notification when greater than 10000 μCi