RE: Skin Dose from Tc-99m

["Muldoon, Patrick" <patrick.muldoon@med.va.gov>]

Just a quick calculation (which I didn't check the math well due to time
- sorry) gave me a dose of about 10 microgray per microcurie - if left
on the skin to decay.  I used .0278 cm2/g for a mass energy absorption
coefficient (for 0.15 MeV gammas - a little high) and .89 for the
frequency of gamma emmision.  The formula I used was:

Dose rate (Gy/s) = (photons/cm2/sec) X E MeV/photon X 1.6E-13 J/MeV X
mass energy absorption coefficient X clean-up units factor  then

Dose = dose rate/decay factor

This is a gamma dose to the hand.  Whole body gamma will be lower due to
distance.  I don't think you would really consider this a "skin dose"
per say.

Now you just have to figure your counts per minute versus decays per
minute to determine your microcurie content.

So, guys, check my work  :-)!

Patrick Muldoon, CHP
Patrick.Muldoon@med.va.gov <mailto:Patrick.Muldoon@med.va.gov> 
Assistant Radiation Safety Officer
VA Medical Center, San Francisco