Radiation Concerns

2015-01-13

azim58 - Radiation Concerns

Radiation Concerns.one

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

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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-radiati
on/
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.

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Radiation Safety Manual at Caltech in California
http://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&a
mp;cd=7&amp;ved=0CGYQFjAG&amp;url=http%3A%2F%2Fwww.safety.caltech.edu%2Fdoc
uments%2F78-radiation_safety_training_manual.pdf&amp;ei=UFsDUIqbOuLE2gXrn5m
zCw&amp;usg=AFQjCNEqJ6K2PlEewVAPsVs0S8guHah1vQ&amp;sig2=ggzcgZWSTychGna3QYx
ADA

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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

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