Re: Dose equivalent rates at the surface of a 10 Ci (239)PuBe?

[tdc@ehssun.lbl.gov]

>Can anyone tell me measured dose (equivalent) rates (both gamma and
>neutron) at the surface of a 10 Ci (239)PuBe source (Monsanto corp)?  I
>am looking for ballpark figures for dose planning purposes.

Hmmmm - didn't know the 239's came in 10 Ci!

Anyhow our 5 Ci 239 Be sources have a 4 pi neutron emmission of about
7x10^6 neutrons/sec and a neutron dose rate at a meter of about 10 mREM/hr.

We haven't paid much detailed attention to the gamma dose rate - but it is
about the same as the neutron.

Note - the 239 sources have a considerable anisotropy so the rate at a
meter depends on what angle you look at it from.  Right now I am
characterizing the anisotropy of ALL of our 239, 238 and AmBe sources.

If your source was made after the MID 60's - I wouldn't worry much about
the swelling folklore.  That was a problem of early 60's sources and due to
incomplete oxidation of the Pu and NOT He evolution!

He was the early knee-jerk guess as to the problem but later found not to
be so.

Most early 60's sources were recanned in the middle to late 60's - as were
ours.

Realize however that for DOE people ANY sources made before 1972 and the
ANSI sealed source standard cannot have the ANSI specified pedigree and are
therefore defined as unsealed and according to DOE that makes the facility
using them a Non Reactor Nuclear Facility!  Also they must ship as
unsealed!  Since yours has been in a barrel since 1971 - it no doubt falls
into the unsealed sealed source catagory!

Ted de Castro
tdc@ehssun.lbl.gov
University of California Lawrence Berkeley Laboratory
Bldg 90 Rm 0026B
Berkeley, CA 94720
(510) 486-5256
(510) 486-6939 - FAX