[ RadSafe ] Fwd: Ra-226 Activity in Vintage Compass

[Chris Alston]

Roy et al.

I'll second that, but expand on it a bit, by your leave.  Ra-226 is
very close to a pure alpha-emitter.  There is the 186 keV gamma, at 4%
abundance, and some diddley x-rays at < 1% each, but that is about it.
So, essentially all of the gammas, that make radium such a notorious
photon-emitter, originate with the Rn daughters.

If you put an air-tight seal on the device, it is safe to assume that
the Rn progeny will ingrow with a half-time of ~ 4 d.  It's really
just the inverse of radioactive decay.  After one half-time, you have
50% ingrowth, at 2 x 4 d, you have 75% ingrowth, 3 x 4 d = 87.5%
ingrowth, etc.  (Here, I invite the slings and arrows.)

Please keep us posted.

Best
cja
---------- Forwarded message ----------
From:  <gelsg at aol.com>
Date: Fri, Jul 18, 2014 at 5:06 PM
Subject: Re: [ RadSafe ] Ra-226 Activity in Vintage Compass
To: radsafe at health.phys.iit.edu
Roy, Joe:
I agree.  A reading at one meter should give you pretty good
information with which to calculate the activity of the source.
I would only add that, to get the best number, the compass should be
encased in a leak-tight container for 2 - 3 weeks before making the
measurement.  This would allow the short-lived radon daughters, which
contribute significantly to the gamma activity, to achieve
equilibrium.
Jerry Gels
Cincinnati, OH
On Fri, Jul 18, 2014 at 1:20 PM, Roy Parker <radmail at cox.net> wrote:
> I am trying to move a shipment containing a World War I vintage compass:
> U.S.E.D. Creagh - Osborne Marching Compass Mark VII Model E Sperry
> Gyroscope Brooklyn, N.Y.
> It is radioactive, therefore obviously Ra-226.  I am trying to find the
> activity.
> Regards,
> Roy A. Parker, Ph.D.
> Radiation Physics Consultant
> 225-924-1473 Office