Frisking question

[coshaun]

As we all know, standard frisking rate is 1-2 inches per second. Can someone explain the necessity of slowing the scan rate to 1.5 inches if Sr90 is present?   Thanks for you help! 

[SloGlo]

i'm at  a loss on yer question.... iffen yer acknowledged frisk rate is 1-2 inches/second, how much velocity are you losing by slowing to 1.5 inches/second?

the mostest prime rule of thumb for using a probe to measure any radiation emitting item is to not exceed 1/2 the width of the probe per second.  this'll keep ya safe whether it's a gm pancake or a half a meter gas proportional.  its the probe size to speed ratio.

[Melrose]

I'm with SloGo, you haven't really slowed much.
Really don't need.  You're not going to see Sr90 anyway.  What you will see that is indicative of Sr90 is decay getting into the itrium (?)  which is about 2.2- 2.4 Kev, you'll see that across the street, through clothing, eye protection ...... yada yadayada.

Don't know if this helps you.... just insight for you

[makua13]

Frisk rate based on certain isotopes and type of GM.  Lowerenergy will require slower rate in order to gaurantee that magical 95% certainty or MDA.  Maybe you want the probe closer too.?  There is always a diference between gemeric and spcific.  And by the way do youknow the efficiency of a "typical" pancake probe?  It isn't 10%, but more like 12-13%.  Then there is the thin window Alpha GM detector.  However in the end it is all not very accuate, just too many variables and too mch difference in isotopic energies.  Just do what the procedure tells you and write down the numbers "they" are looking for.

[RDTroja]

What you will see that is indicative of Sr90 is decay getting into the itrium (?)  which is about 2.2- 2.4 Kev, you'll see that across the street, through clothing, eye protection ...... yada yadayada.

Hi -- your friendly neighborhood proofreading PITA here...

Melrose, I think you meant MeV, not KeV. Won't see 2.2 KeV through much of anything... but 2.2 MeV will penetrate much more than you want it to. Yttrium-90 is indeed a pain to deal with. Not sure why you would need to slow down to see it. The 2.2 MeV beta may be hard to detect with a standard frisker probe designed for beta because it penetrates too well. But there are other, softer betas too. If you want some fun-with-firskers go to a plant with isotopes that decay by electron capture. They emit a soft (usually) x-ray that friskers are only 2% efficient for. Frisk a smear, its clean, put it in a SAM and it is screaming.

And by the way do youknow the efficiency of a "typical" pancake probe?  It isn't 10%, but more like 12-13%.

I used to calibrate HP-210 probes on scalers and regularly get a realistic 18% efficiency. Gotta love conservative numbers and Rad-Con math. Easier to add a zero than multiply by 6 or 8.

[Melrose]

Hi -- your friendly neighborhood proofreading PITA here...

Melrose, I think you meant MeV, not KeV. Won't see 2.2 KeV through much of anything... but 2.2 MeV will penetrate much more than you want it to. Yttrium-90 is indeed a pain to deal with. Not sure why you would need to slow down to see it. The 2.2 MeV beta may be hard to detect with a standard frisker probe designed for beta because it penetrates too well. But there are other, softer betas too. If you want some fun-with-firskers go to a plant with isotopes that decay by electron capture. They emit a soft (usually) x-ray that friskers are only 2% efficient for. Frisk a smear, its clean, put it in a SAM and it is screaming.

I used to calibrate HP-210 probes on scalers and regularly get a realistic 18% efficiency. Gotta love conservative numbers and Rad-Con math. Easier to add a zero than multiply by 6 or 8.

Thanks.... boy, what a goof   

[makua13]

I used to calibrate HP-210 probes on scalers and regularly get a realistic 18% efficiency.

I been calibratin them things for years and never saw 18%, not with Tc99 anyways.  Funny how numbers get larger when you get older.. 

[870xprs]

NRC issued a generic letter way back in the early '80s on the requirements for free-release monitoring using hand held detectors.  I would have sworn that it was Generic Letter 83-06, but looking through the listing at the NRC web site, I don't see it.

Do any of you remember that generic letter?  If someone finds it, please let us know.

I know it existed because I used to keep a copy of it on file.  I used it as a reference to explain to my supervisors that, even though our sophisticated contamination monitors "can" see activity at much lower levels, we don't want to do that because to do so would exceed the standard set by the NRC in the generic letter.  We would be shooting ourselves in the foot to look for radioactivity at levels lower than the NRC's standard.  That's why we dont use a GeLi to release everything.

The generic letter specified that the HP-210 detector was the standard for monitoring for free-release (<100 cpm), when held at a distance of no more than 1/2 inch from the article being monitored, and when moved no faster than 2 inches per second.  The generic letter was based on a study done by some college prof. who published his findings in some journal, which was later cited by the NRC in the generic letter as the basis for setting the standard of "how hard you have to look".

Anyway, either the generic letter or the college prof's paper may also discuss contamination monitoring for pure beta emitters like Sr-90.  Maybe that's where your 1.5 inches per second comes from.

[870xprs]

Found it. 

IE Circular No. 81-07: CONTROL OF RADIOACTIVELY CONTAMINATED MATERIAL


http://www.nrc.gov/reading-rm/doc-collections/gen-comm/circulars/1981/cr81007.html


It doesn't say anything specifically about beta emitters, but it references the study by Sommers, et.al.

[coshaun]

Thanks for all the input!  I guess it might have helped if I had explained that this reduction in scanning rate is a recommendation being used at a DOE site and I was trying to understand why.  I guess my simple mind just doesn't understand why it has to be complicated.

[RDTroja]

I been calibratin them things for years and never saw 18%, not with Tc99 anyways.  Funny how numbers get larger when you get older.. 

Interesting... just the other day I was thinking that some numbers get smaller as you get older...

And I never referenced Tc-99. Not sure I ever used that as a calibration source myself, but that was 100 years ago or so.

[RDTroja]

... even though our sophisticated contamination monitors "can" see activity at much lower levels, we don't want to do that because to do so would exceed the standard set by the NRC in the generic letter.  We would be shooting ourselves in the foot to look for radioactivity at levels lower than the NRC's standard.  That's why we dont use a GeLi to release everything.

I wonder what happened to that concept. If I ever get my hands on the idiot that came up with 'no detectable activity' as a limit I think I may strangle him.

And the first time someone in the position of authority recommends using a GeLi to free release something, I am coming after you, 870xprs, just for putting it in print! 

[Shonkatoys]

The  limit  for  Strontim  is  only 1000 dpm  100 cm2 where  the  limit for  uranium is 5000 dpm  100 cm 2  therefore  I  would  slow  down even more than 1.5  inches  a   second  to  realistically  check for strontium per 10cfr 835  to  detect  the  lower  limit.
  For  transuranics  I  was  told  you  should  frisk at 1  inch  every 11 seconds  with  a  43-5 ZnS probe to  meet  the  limits,  However  no  one  does  this.  Transuranics  should  only  be  surveyed  with  a   large  surface  Contamination  monitor  if  surveying  buildings in  my  opinion.  Surveying  for  transuranics  is  a  joke  on  everysite  I  have  been in  my  opinion.  20 clicks  different  from  background  give  or  take a  few  clicks in  a  minute.  You  must  be  crazy  if  you  think  that  anyone  can  survey  to  this.   Too  easy  to miss 500 dpm  100 cm 2. 

[stownsend]

There are a couple of limits for Sr90,either pure or in a mixed fission product.When you take into consideration of the energy,eff,and probe size your only looking for ~30 counts so you need to stress the turbo frisk doesn't work or as an HP help frisk them.As far as transuranics go you can't see  20 dpm/100cm2 in the field,only on lab equip.ie.tennelec or protean and frisking to the 500dpm/100cm2 total takes a trained eye .That's why we seniors make the big bucks!!!

[870xprs]

I wonder what happened to that concept. If I ever get my hands on the idiot that came up with 'no detectable activity' as a limit I think I may strangle him.

And the first time someone in the position of authority recommends using a GeLi to free release something, I am coming after you, 870xprs, just for putting it in print! 

That's ok, but I should point out that it's considered one of the rites of passage for Sr. HPs that they have to 'splain things to someone in a position of authority.  That's another reason they pay us the big bucks.     

[SloGlo]

I wonder what happened to that concept. If I ever get my hands on the idiot that came up with 'no detectable activity' as a limit I think I may strangle him.

yinz kin start wit da werldz smartest man at da beav.

[ageoldtech]

I haven't heard anyone mention response time.  The response time on the average Ludlum 177 or RM-14 is approximately 20 seconds. At 2 inches per second at one half inch, contamination can be missed and often is, as proven when Oconee released tons of red iron used in containment for their SGR. I prefer to travel at 1 inch per second.

[wrecked_edsel]

Hey bone how the heck have you been? Man I really like you new Avatar, well not as well as I liked your other one but I guess somebody was offended by it, but anyway where are you working and what have you been doing? Not much been going on with us down here at MNS but give us a call sometime. Now about the frisking I seem to think that they had at Oconee was not frisking to fast but just kind of you know not frisking ANYTHING. Which is evident by what those hard working guys that had to go to TEXAS and frisk (all of that red steel you know it may have been painted red for a reason) found. I think even the worlds crappiest RP sould be able to find 10,000 ccpm fixed and 3-4K smearable but who am I to judge because even a tater has eyes to see that would you not think

[ageoldtech]

Edsel, good to here from ya, were doing the N-1 outage at Watts bar. I've been to better outages. Op's dosen't have everything in one sock!! They have lost containment 6 times. Im wondering if they will find it before the outage is over. The boys that went to Texas did a great job finding the hot stuff, and I think your right, any tech worth his or her salt would have been able to find 10K with a standard frisker probe. see ya later tater.