Re: Contamination Dispersion Cs 137

[DSnowder@aol.com]

Mike, 

You did not specify the make or model of the density gauge or whether the 
Cs-137 source is actually installed in the Nuclear density gauge or in a 
source rod attached to the gauge which is then inserted into the material 
being tested.  The vast majority of Nuclear density gauges manufactured in 
the U.S. contain 30-50 milliCurie Cs-137 sources compressed inside a series 
of stainless steel capsules, one within the other, and both are welded shut.  
It would appear that both internal capsules have ruptured and released 
contamination into the outer aluminum capsule. This is caused by one or more 
situations, either internal pressure which ruputured the weld, a faulty weld, 
and/or other physical damage to the double capsule itself. Since you did not 
indicate the latter (which would be obvious since the gauge itself would be 
severely damaged) the first two should be considered.  

On the issue of an inadequate weld,  Troxler Corp. which manufactures a large 
number of Nuclear gauges, issued a notification to all of its gauge owners in 
the recent past which provided a list of Gauge serial numbers that they 
requested to be leak tested and inspected for faulty welds. Other gauge 
manufacturers may have done the same. I would check with them to see if your 
gauge source is one of those. 

On the issue of the source capsule rupture, and exclusive of a faulty weld,  
the U.S. NRC, U.S. DOT, and IAEA  require rigid compliance to ANSI 
specifications in order for the sources to meet the "Special Form" criteria. 
That compliance includes testing to high temperatures, pressures, drop & 
impact testing, as well as several other environmental stresses not normally 
encountered in routine use. Since the capsules are likely stainless steel and 
the Cs-137 source is a ceramic material I do not believe that corrosion is 
the issue. The NRC also requires in NUREG 1556 that all Nuclear gauges be 
leak tested at least every six months in order to detect  any contamination 
problems.   While most Nuclear gauges used in construction and 
soil/aggregrate testing receive some rough treatment at times including 
vibration, shock, and sitting on hot asphalt (150-230 F) for extended periods 
of time, it is doubtful that would be the cause of the source capsule rupture 
(again, assuming that the initial weld is OK). 

My guess is that the capsule had a faulty weld, and/or the source rod and 
capsule were damaged.  


Dale Snowder
Alpha-Idaho 
(208) 523-5557 
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