SAFEGUARDS PERSONNEL
MONITOR
J»
L.
Martines,
G. J.
Cunningham
" and C. R.
Forrey
THE
DOW
CHEMICAL COMPAM"
Rocky Plats Division
Paper
To Be
Presented
At The
TWELFTH ANNUAL MEETING
OF THE
"INSTITUTE
OP
NUCLEAR
MATERIALS MANAGEMENT
;'••
Palm Beach, Florida
•-
June 30,
1971
Work Performed Under
U.
S,.
^•Atomic Energy Commission
. •
Contract AT(2^-l)-ilO6
.
Thia report was prepared at an account of work
aponaored by the United Statei Government. Neither
tht United Statec nor the United Statei Atomic Energy
Commluion, nor any of thtftr employees, nor any of
their contractor*, aubcontractore, or their employeos,
nakei any warranty, expreia or implied, or mumei any
l*f*l liability or reipomibility for the accuracy, com-
pieUneK or UMfuInex of any Information, apparatui,
product or
1
proc«M disclosed, or represents that Us use
would not Infringe privately owned rights.
ABSTRACT
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The purpose of a safeguards monitor is to prevent the acci-
dental or intentional diversion of special nuclear materials.
The monitor must have high sensitivity for the radiometric
scanning of items passing through it, and must have a fast
response time. The personnel monitor designed at Rocky Flats
meets these requirements by using two 24-inches by
6-inches
by
2-inches
plastic scintillators which are sensitive to both
gamma and neutron radiation. The,electronics used with these
plastic scintillators consist* of the standard photomultiplier,
preamplifier, amplifier, and single channel analyzer combina-
tion.
The output pulses are.fed to an averaging integrator
which compares the immediate count rate observed while a person
is walking past the monitoring station to a current history of
the time averaged background count rate. Statistical differences
between the two rates cause, an alarm to be sounded. Batemeters,
sealers,
or graphical plotters may be incorporated if desired
to give a visual presentation of the count data. Experimentally,
the monitor will respond to Vieth inch brass shielded source
of less than 0.5 gram plutonium-239 when carried by a person
punning between the detectors.
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Rocky Flats Plant
is an
Atomic Energy Commission facility
-operated
by the Dow
Chemical Company.
As
part
of the
opera-
tions,
large amounts
of
plutonium
in
various chemical forms
are handled,
or
stored routinely.
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Within
the
past
few
years, increasing "emphasis
by the AEC and
the various contractors, such
as
Dow>
has
been placed
on the
safeguarding
of
special.nuclear materials
to
insure their
not
eing diverted
for
unauthorized
uses.
One
potential diversion
3 oute from
the
Rocky Plats facility obviously concerns personnel
cjarrying plutonium from
a
process area past
the
guard checking
station.
It is
next
to
impossible
for
complete checks
to be
wade upon personnel
by the
security force, particularly
at
shift change times when several hundred
men and
women pass
the guard station
in
a
few
minutes.
The consideration
of
these factors
led to the
development
of
the Rocky Flats Personnel Safeguards Monitor, several
of
which
are scheduled
to be
installed
at the
guard stations associated
with
the
plutonium process areas.
;^
To perform
its
function properly,
the
Personnel Safeguards
Monitor must meet certain design criteria.
It
must have fast
response,
or be
able
to
detect rapid changes
in the
radiation
observed
by the
detectors.
It
must have high geometrical
efficiency
for the
human body
to
prevent blind spots.
It
must
be
able
to
handle large numbers
of
people
in
a
short
period
of
time.
It
.should have high sensitivity which means
that
a
person intent
en
plutonium diversion
is
restricted
to
sub-gram quantities.
It
should
be
both gamma
and
neutron
sensitive, which makes
the
shielding
of
plutonium more diffi-
cult than
the
simple
use of
high
Z
materials.
It
should
be
able
to
compensate
for
variations
in the
normal background
radiation,
and it
should
be low in
cost.
;
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r+
:
-'"*
•
' "',
. Ths
sya-tr.c-
developsd
at
Rocky Flats meets these
requirements.
DESCRIPTION
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The Rocky Plats Safeguards Personnel Monitor consists of four
major items (See Slide 1.): the nuclear detectors, a floor,
switchmat, the electronics, and the audible alarm.
The nuclear detectors consist of two slabs of plastic seintil-
- iator with dimensions
of.
24x5x2 inches (See Slide 2). The
slabs have been machine-polished on all 3ides, and light pipes
have been permanently attached at both ends so that two-inch
diameter photcmultiplier tubes may be optically coupled to the
scintillator slabs. To increase the reflection coefficient
on the plastic scintillator slabs, aluminized mylar was placed
on their surfaces. Black electrical tape was then wrapped on
top of the mylar coating to insure a light-tight assembly of
the plastic scintillator and the photomultiplier tubes.
Mechanical protection to both units (photomultiplier and plastic
scintillator) was afforded by enclosing the assembly in a metal
box.
This box was fabricated with
1
A-inch aluminum sheet .and
steel angles to support the slabs. The ends of the metallic box
which support the necks of the photomultiplier tubes were fabri-
cated with
s
/e-inch thick aluminum sheet to provide additional
rigidity to the entire structure. The radiation sensitive
surface of the plastic slab was covered with 202^ aluminum
sheet,
Vas-'inch thick. Minimum attenuation of low energy
gamma from plutonium-239 "was encountered from this arrangement.
Notice the collar which supports the neck of the photbmulti-
plier tube within the enclosure. This collar was spring-loaded
against the ends of the metallic box so that pressure could be
obtained at the point of optical coupling between the light pipe
end the photomultiplier tube surface.. It was found that even
though the detector assembly was exposed to a certain degree of
vibration, good contact between the light pipe and the photo-
multiplier tube was maintained, • • •
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SLUES 1.
IKE LABORATORY MODEL OP THE ROCKY PLATS
EERSONNEL SAFEGUARDS MONITOR