[ RadSafe ] Rb-87 Atomic Clocks

Robert Atkinson robert8rpi at yahoo.co.uk
Thu Jul 28 13:10:52 CDT 2011

Hi Elsa,
As well a a radiation detector collector, I'm a "Time Nut" and have several Rubidium oscillators or "Atomic Clocks". The amount of Rb in these units is tiny. The older, larger units such as the Efratom FRK have lamps and cells about 1/2" in diameter. most of the volume is buffer gas. I've never seen any reference to a radiation hazard in any of the manuals or data sheets. There is no detectable radiation from an FRK even with the lamp access covers removed. The "other" atomic clock uses Caesium-133 (stable) which does make them hazardous cargo due to it's reactivity. Agilent (HP) have a dispensation for shipping their designs as it's sealed in a heavy metal vacuum tube inside the instrument.
So in short,
No they are not considered radioactive. I get a higher reading from a package of Lo-Salt (K-40).
Robert Atkinson G8RPI MRAeS
--- On Wed, 27/7/11, Elsa Nimmo <enimmo at berkeley.edu> wrote:

From: Elsa Nimmo <enimmo at berkeley.edu>
Subject: [ RadSafe ] Rb-87 Atomic Clocks
To: radsafe at health.phys.iit.edu
Date: Wednesday, 27 July, 2011, 22:27


I find myself needing some information on atomic clocks.  And even though we
have people on campus who worked on related research, their concerns were
different ones & they're not able to help.

The rubidium version of an atomic clock appears to contain small amounts of
Rb-87 (approx. 49 billion-year half life).   

Does anyone know whether there were rubidium atomic clocks (e.g.versions of
type used by astronomers in past decades) that would contain activities
above 10 microcuries Rb-87?

California regulations set 10 microcuries as the exempt quantity for Rb-87.
I've seen one atomic clock manufacturer's data sheet noting at total Rb-87
activity of less than 0.0002 microcuries in their current products.



Elsa Nimmo, CHP

Alternate Radiation Safety Officer

Environment, Health & Safety

University of California, Berkeley

317 University Hall, Mail Stop 1150

Berkeley, CA 94720-1150

enimmo at berkeley.edu

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