[ RadSafe ] Radon progeny in CNG vehicles gas tanks

Brad Keck bradkeck at mac.com
Wed Apr 16 18:47:18 CDT 2014

This is coming up a lot today! 

When you capture the radon with the hydrocarbons, you are capturing principally Rn-222 and perhaps some parent radium as well.  Rn-222 has a 3.8 day half life and has many daughters - many of which contribute some gamma emissions thus are in part responsible for the excitation of the radiation monitors now common at landfills and recyclers.  When you look at the gamma spectrum of such a mix, the most prominent emissions are those of Bi-214 and Pb-214.   Presuming that radium is also captured in the gas, the decay of the 226Ra will be next if equilibrium has been achieved - which would be true I suppose in propane other than that very freshly isolated.  These are part of the 238U natural decay series and you see these gamma lines often as part of the natural background in  most any gamma detector. 

I do not know how much 226Ra is captured with the fuel, but there  must be some, otherwise the radon would fairly quickly decay out along with the progeny.   Does anybody know how much radium is captured in hydrocarbons of interest? 

Bradly D. Keck, PhD, CHP  

Sent from my iPad

> On Apr 16, 2014, at 4:58 PM, John Hultquist <jhultquist at utah.gov> wrote:
> I could use help in exploring a question with fellow radsafers in knowing
> if bi-fuel or CNG vehicles are triggering radiation alarms because of radon
> and its decay products as a natural contaminant of the natural gas.
> I understand that hydrocarbons from the Dakotas and Pennsylvania are being
> produced with radon as a natural contaminant.
> I am going to speculate that as vehicles with CNG tanks age, the lead-210
> from any natural gas with radon is going to build up (Pb-210 half-life is
> 22.26 years)in the inside wall of the tank.   Maybe the radiations from
> Pb-210 or Bi-210 will cause radiation detectors across the country to
> alarm.
> Any insight to this issue would be appreciated.
> John Hultquist,
> Utah Division of Radiation Control
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