Harshaw TLD Self-Annealing?

[John_Sukosky@DOM.COM]

While performing a study to determine the neutron factor for power entries into

containment (PWR), Harshaw TLDs showed a significant under-response during a 3

days exposure in the containment basement.  Based on the ambient temperature

(110 deg F) and length of exposure, I suspect self annealing as the cause of the

under-response.



Has anyone observed this under-response of TLDs under the same or similar (e.g.,

desert) conditions?

Is self-annealing the most probable cause of this anomaly or can anyone offer

another explanation?

Does anyone know of a formula to correct for self-annealing at a specific

temperature and temperature exposure time?



Data for this exposure is as follows:



Harshaw Type 16 TLD (three Li-7 elements and one Li-6 element)

six TLDs mounted in center of neutron phantom, 3 feet off the floor

two REM-500 TEPCs attached to sides of phantom

PWR at 100% power

neutron dose rate was approximated equal to gamma dose rate

Location:  Containment Basement (-27 foot level)

Temperature:  110 degrees F

Exposure Time:  3 days

#1 REM-500 integrated reading:  73.3 mrem

#2 REM-500 integrated reading:  76.5 mrem

TLD# 1 = 0 counts neutron (net)

TLD# 2 = 360 counts neutron (net)

TLD# 3 = 72 counts neutron (net)

TLD# 4 = 743 counts neutron (net)

TLD# 5 = 588 counts neutron (net)

TLD# 6 = 759 counts neutron (net)

(around 3000 to 4000 gross counts on each TLD element)



Neutron Factor = Average TLD counts neutron / Average REM-500 integrated reading



Even when eliminating the obvious TLD outliers, the neutron factor for this

location is about 10.  Similar locations at shorter exposure times indicate a

neutron factor of about 40.   Compared to these other locations, TLDs at this

location are under-responding by a factor of about 4.  The TLDs at other

locations show a much more consistent response (< 10% error at 95% confidence

level) at lower delivered doses (typically 25 mrem).



This might seem like a Part II question for the CHP exam but it is a real life

situation.  Thanks for any help.





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