# [ RadSafe ] formula and its derivation for rectangular extended radioactive sources exposure rate

Cary Renquist cary.renquist at ezag.com
Fri Jul 12 16:54:01 CDT 2013

```If you can simplify the geometry to a disc, then the flux at a given
distance above the center of the disc is:
(no attenuation)

Gamma/s/cm2 = Sa/4 * ln{(Ro^2+h^2)/h^2}
Where Sa is the source strength (gamma/cm2) [activity of the source
divided by its area]
Ro=radius of the disc (cm)
h=distance from the disc (cm)

To get the dose rate,

D[rad/h]=5.76e-5 * flux[gamma/s/cm2] * Eg[MeV] * (uen/p)[cm2/g]
Eg = energy of the gamma in MeV
uen/p = energy absorption coefficient of your target (e.g. tissue/water)
for the given gamma energy

Once you include attenuation, then you need to either use numerical
methods or tables of Sievert Integrals (or other computational means:
monte carlo, commercial software, etc)

---
Cary Renquist
cary.renquist at ezag.com

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Danak, Subhash
M CTR DOD CAPMED FBCH
Sent: Thursday, 11 July 2013 7:28 AM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] formula and its derivation for rectangular extended
radioactive sources exposure rate

I like to review formula for rectangular radioactive sources exposure
rate. Please provide one.
I thank you.

Subhash
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