9"/3" neutron monitoring - summary of responses

[Lester Slaback <Lester.Slaback@NIST.GOV>]

Some weeks ago I posed a query to those using the 9"/3" ratio technique for
neutron monitoring.  Here is a brief summary of the responses I received
(unattributed - I was severely criticized by one of the respondents in my
last summary who rightly presumed it was a private email.  A good etiquette
point is not to pass on direct email without the originators permission,
even if you have already said you will!)

The last response first.... it was noted that the 3" detector is no longer
available from Eberline so those possessing 3" detectors and using the
method had better take care of them.  The problem seems to be related to
getting the surface Cd layer.

Several folks use the method as described by Hankins, i.e., for spectral
correction of dosimetry response, and also just as a general tool to check
the neutron spectrum.  One dosimetry provider does not use the technique at
all, but instead performs a complete dosimetry response evaluation any time
conditions change or a new spectrum is encountered.

Another facility for poor agreement between the 9"/3" method and several
other techniques, albeit for a high energy accelerator environment (but of
the type included in Hankins' original research).

One respondent said that he used a 9"/0" (i.e., bare) ratio instead.
Obviously this is very sensitive to room backscatter conditions and would
be limited usefulness.

A response from the medical arena indicated they have not used the 9"/3"
method for a long time, but instead find foil and other techniques such as
the use of the Si/P technique and the bubble detection systems for
spectrometry simpler and less expensive to use.

One respondent referenced the Dineutron (a French instrument incorporating
3 detectors with an algorithm to derive the dose rate).  [Note that there
are a multitude of papers that determine the dose rate based on a limited
set of moderated detectors, 2, 3, etc.  But if you are interested in
correcting the response of another device, e.g., a dosimeter, then you will
need to establish the relationship between both systems.  Oh, for an energy
independent ED device, and independent of the committees that keep changing
the definition! - LAS]

 
A couple of references that might be of interest sent in the responses ....

Swaja R.E., Yeh S.H.: "Potential Problems With Using Sphere Ratios
to Determine Neutron Albedo Dosimetry Correction Factors"
Radiation Protection Management, Vol. 4.,No. 3 (May/June 1987)

Vylet V., Swaja R.E., Pr
être S., Valley J.-F., Lerch P.: " On the
use of the 9-to-3 Sphere Ratio with albedo and track-etch neutron
personnel dosemeters", Radiation Protection Dosimetry , Vol. 27
No. 1 pp. 29-33 (1989)

several papers dealing with the spectral hardness issue -  The most
complete review of these as of recent is by A. Aroua (Institute for Applied
Radiophysics, Switzerland).  For examples see:
On the use of some spectrum hardness quantifiers for operational neutron
fields,  Radiation Protection Dosimetry, Vol. 54 No. 2, p. 99 (1994)
Use of passive detectors to characterize neutron field hardness, Health
Physics, Vol 72, Number 5, May 1997. 

Note also that a search of QUEST for NEUTRON AND MONITOR will get you about
1400 references (thru 1997).  Bill Schadt does not get enough thanks for
this great product/service, and from what he tells me about the cost of
producing it this does not constitute a commercial advertisement.   :-)

The original question ......
> Dale Hankins (many eons ago) originated the 9"/3" ratio technique as a method
> for estimating the neutron spectrum hardness (softness?).  The Navy
(i.e., the
> largest dosimetry processor in the U.S.) uses this method to provide
> corrections for their neutron badge calibration factor.
> 
> Question:  How common is the use of the technique, for either dosimetry or
> field quality estimates, used in the world?
> This is of interest to a current working committee of the ICRU, so this
is your
> chance to contribute to posterity.

Disclaimer:  Only my opinions .....
Lester Slaback, Jr.  C.H.P.  [Lester.Slaback@NIST.GOV] 
NBSR Health Physics 
Center for Neutron Research 
NIST 
100 Bureau Dr.  STOP 3543
Gaithersburg, MD  20899-3543 
301 975-5810 voice
301 921-9847 fax
"A little risk adds a bit of spice to life." 
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