Re: NUMEC Pu-Be sources

[Philip Hypes <phypes@lanl.gov>]

If you have access to a good germanium detector, the FRAM program can give
you plutonium isotopics with the following typical precisions:

	238	1-10%
	239	0.1-0.5%
	240	0.5-4%
	241	0.2-0.8%
	Am241	0.2-10%

	Pu 242 is calculated by isotopic correlation because of the lack of useful
gamma rays.

The precisions will vary depending on factors such as count rate/time,
filtering, and sample characteristics, but with good statistics (sufficient
counts in the important peaks), the effects should be small.  Under the
best conditions, precisions can approach those possible with destructive
analysis.  The program can also handle spectra from heavily lead shielded
sources.

If you can get a good Ge spectrum from the source, send it to me and I'll
analyze it for you.  We can adapt the program for just about any energy
calibration, provided the spectrum shows all the peaks, but our standard
(for a coax detector) is 8k channels, 0.125 keV/channel.  When I'm
researching with the program, I try to stick close to 10kHz input and 1
hour counts.  Multiple measurements let us get an even better handle on
precision, of course.  I have gotten good results with shorter counts and
lower input rates as well.  I should be able to get some results to you on
a same-day basis (in minutes if all goes well).

Phil

At 10:51 PM 2/20/00 -0600, you wrote:
>Looking for information on the plutonium isotope composition of NUMEC Pu-Be
>neutron sources.  The documentation I've found (including copies of old
>reports to the AEC) lists the Pu-239 fraction, but says nothing about the
>rest of the Pu mass.  I need to know the Pu-241 fraction in order to
>calculate the increase in neutron production due to Am-241 ingrowth (see
>note below).
>
>I know that Babcock and Wilcox bought out NUMEC back in the 1970's, but I'm
>not getting anywhere trying to contact them directly.  Their 800 number
>referred me to the Lynchburg? Virginia facility, whose engineering
>department forwarded me to their legal office, which hasn't called back.
>
>I would appreciate any assistance you folks can give me in locating a
>source for this information.  Thanks!
>
>Eric
>
>Note for those who haven't played with a Pu-Be source (lately):
>Pu-241 beta decays with 14.4-yr half life to Am-241, and Am-241 alpha
>decays with a half-life of 432 years and energies in the same range as
>Pu-239.  Be captures alphas and emits neutrons, regardless of whether the
>alphas come from Pu-239 or somewhere else.  Since Am-241 is longer-lived
>than Pu-241, it builds to an equilibrium level, and since Am-241's decay
>constant is 55 times greater than Pu-239's, the strength of the source
>grows over time in proportion to the original Pu-241 fraction.  If all of
>the "non-239" Pu in our source is Pu-241, the neutron output will be 4
>times greater than if we have no Pu-241 at all.  Makes one hell of a
>difference in my dose rate calculations!
>
>
>J. Eric Denison
>Nuclear Engineering Program
>The Ohio State University
>2030 Robinson Laboratory
>206 West 18th Avenue
>Columbus OH 43210
>(614) 292-3681 or -1074
>denison.8@osu.edu
>
>
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___________________________________________________________
Philip Hypes
Los Alamos National Laboratory
Safeguards Science and Technology Group (NIS 5)
(505) 667-1556  phypes@lanl.gov

Opinions expressed are purely my own unless otherwise noted

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