EPA 520/5-73-007
AN INTEGRATING DEVICE FOR USE WITH
PRESSURIZED IONIZATION CHAMBERS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Offici of Ridiition Progtimi
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EPA 520/5-73-007
AN INTEGRATING DEVICE FOR USE WITH
PRESSURIZED IONIZATION CHAMBERS
S. T. Windham
J. E. Partridge
Eastern Environmental Radiation Facility
P. 0. Box 3009
Montgomery, Alabama 36109
K. L. Kelley
National Environmental Research Center
P. 0. Box 15027
Las Vegas, Nevada 89114
December 1973
ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
Waterside Mall East
401 M Street, S. W.
Washington, D. C. 20460
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The mention of commercial products, their source,
or their use in connection with material reported
herein is not to be construed as either an actual
or implied endorsement of such products by the
U. S. Environmental Protection Agency.
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PREFACE
The Eastern Environmental Radiation Facility participates in the identification
of solutions to problem areas as defined by the Office of Radiation Programs. The
Facility provides laboratory capability for evaluation and assessment of radiation
sources through environmental studies and surveillance and analysis. The EERF
provides technical assistance to the State and local health departments in their
radiological health programs and provides special laboratory support for EPA
Regional Offices and other federal governmen^ageiicies as requested.
Charles R. Porter
Acting Director
Eastern Environmental Radiation Facility
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An Integrating Device for Use with Pressurized
lonization Chambers
Introduction
The proposed AEC Regulation 10CFR50 Appendix I limits radiation dose
equivalent at the site boundary of light water power reactors to a maximum of 5
millirem per year (mrem/yr) above natural background. A dose equivalent of 5
mrem/yr added to a natural background dose equivalent of 100-120 mrem/yr is
virtually impossible to measure using monitoring devices such as film badges or
thermoluminescent dosimeters. The Health and Safety Laboratory (HASL) of the U.
S. Atomic Energy Commission describes in HASL-260 a high pressure ionization
chamber designed to accurately measure ambient environmental radiation exposure
rates. A commercial instrument similar to the HASL chamber is now available from
Reuter Stokes (Model RSS-111). This instrument has gained rather widespread
acceptance in the nuclear power field. Several of the instruments have been used by
the EERF for over a year with very satisfactory results.
The basic RSS-111 pressurized ionization chamber (PIC) as marketed by Reuter
Stokes is equipped with a panel meter readout and a strip chart recorder. For short-
term or real time measurements these forms of data presentation are entirely
satisfactory. However, for long-term field monitoring which we routinely perform for
periods from 1-3 months duration, visual reduction of the voluminous strip chart data
using a planimeter is quite time consuming. An optional magnetic tape recorder is
to be offered by Reuter Stokes. After storing data the magnetic tape is read into a
computer for data processing. This system of data handling, however, is rather
expensive (~ $4,000) and it requires the user to have a computer available for data
retrieval.
As an option to the readout methods described above, the EERF has adapted
a low cost, commercially available integrator module to work in conjunction with the
recorder and panel meter which are standard on the RSS-111, making a very versatile
arrangement. The integrator may be disengaged when real-time or short-term
measurements only are necessary. When using the integrator in conjunction with the
strip chart recorder for long-term measurements, the readouts provide total exposure,
and the time and exposure rates of intermittent exposures. This report describes the
integrator and provides details for its use in conjunction with RSS-111.
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2
General Description
The integrator adapted for use with the RSS-111 is manufactured by Curtis
Instruments, Inc. Integration of current is performed with a mercury microcoulometer.
The microcoulometer consists of a glass capillary tube containing two columns
of mercury separated by an electrolyte. Wire electrodes are inserted into the mercury
columns through the ends of the capillary for electrical connection (Figure 1).
When a direct current is passed through the coulometer, mercury is deposited across
the electrolyte gap which causes the gap to move toward the anode. The movement
of the electrolyte is directly proportional to the current/time integral.*
A metal sheath is positioned around the exterior of the capillary such that the
length of either mercury columns can be determined electronically by measuring the
capacitance between the sheath and the column of mercury, which varies in length
as the gap moves.
Unlike electronic integration which depends upon the state-of-charge of a
capacitor, the mercury microcoulometer does not undergo leakage and loss of data
over a long storage period. This characteristic is very important since long-term
integration with maximum stability is essential in this application.
It was desired to obtain an integrator which would require no electronic
modifications to the RSS-111. After learning of our specific requirements, Curtis
mstruments was able to produce a unit which was compatible with the RSS-111.
Ranges of current to be integrated, type of data readout, and characteristics of the
RSS-111 were taken into account when adapting the integrator for our application.
Data from the integrator are presented on two devices, a panel meter and a
mechanical register. As current flows and the electrolyte gap moves in the capillary
its position is indicated on the panel meter. Total range movement of the gap
corresponds to full scale deflection of the meter and to an integrated exposure of 50
microroentgens, depending on the calibration. When the electrolyte gap reaches the
end of its travel the polarity of the electrodes is automatically reversed, the panel
meter is reset to zero, and one count is registered on the mechanical register. For each
50 microroentgens exposure integrated, one count will be recorded. Thus, with a
mechanical register having five decades, it is possible to integrate large exposures
over a long period of time with no data overflow and at the same time very small
exposures are easily and accurately recorded.
* C.C. Beusman, "Electrochemical Devices for Timing and Switching Applications,"
IEEE International Convention Record, March 1964.
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Figure 1. Mercury Microcoulometer
MERCURY COLUMNS
METAL SHEATH
ELECTROLYTE GAP
ELECTRODE
Installation
In keeping with our desire to perform no electronic modifications to the RSS-
111, the integrator derives its input signal from the output jacks which are present
on the front panel of the RSS-111. Power to operate the integrator ± 12 volts DC,
is obtained from the RSS-111, however, to obtain (+) 12 volts with respect to ground
it is necessary to ground the negative side of the recorder motor supply. This is the
only modification necessary to the RSS-111, and it does not detract from the
instrument's independent performance in any way.
The RSS-111 is designed to operate from 110 volts AC or from an internal,
rechargeable battery pack for up to 200 hours. The integrator, however, requires too
much current to operate from this battery pack for extended periods, and for this
reason the integrator is designed to operate from 110 volts AC only. The RSS-111,
when operating from 110 volts AC, will automatically switch to the battery pack
power supply should the AC source be interrupted. During field testing of the
integrator it was found that when this automatic changeover occurs and the integrator
is no longer receiving its ±12 volt DC supply voltage (due to excess battery drain)
damage will occur-to the integrator. This damage occurs since the signal from the
RSS-111 is still present and driving the coulometer, however the polarity reversing
circuitry is inoperative thus driving the coulometer beyond its capacity. This may be
prevented by using a three pole relay as shown in (Figure 2). When 110 volts AC is
not present, the supply voltages and signal are disconnected from the integrator.
Two versions of the integrator have been obtained from Curtis Instruments.
In the first version which cost $425, the integrator circuitry and readout units are all
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mounted within a metal case (Figure 3). Signal and power connections to the RSS-111
are made using appropriate cables from a terminal strip on the back of the integrator
case. This version is quite easy to put into operation and requires no major
modifications to the RSS-1 1 1. Also, this arrangement allows the integrator to be used
alternately with several PIC's since it is easily connected and disconnected through
the use of jacks on the front panel of the PIC.
In the second version of the integrator, which cost $380, the components are
supplied without a case. These components include a printed circuit board, a panel
meter, and a mechanical register (Figure 4). These components can be installed
directly in the case of the PIC, (Figure 5). This arrangement produces a very compact
and rugged arrangement. Both versions work equally well.
110 VOLT AC RELAY
110 VAC
ENERGIZED
-+12 VDC SOURCE
-+12 VDC TO INTEGRATOR
--12 VDC SOURCE
-12 VDC TO INTEGRATOR
SIGNAL FROM FRONT PANEL JACKS
- SIGNAL TO INTEGRATOR
Figure 2.
Protective
Circuit for
Integrator
Figure 3.
Integrator Mounted
in External Case
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Figure 4.
Components
of Integrator
Figure 5. Components
Installed in PIC Case
Laboratory Calibration
Prior to use of the integrator it is necessary to establish the exposure
relationship between the recorder and the integrator. It is assumed that the recorder
has been previously calibrated either by Reuter Stokes or by the user. A high
resolution potentiometer is provided on the integrator so that it can be adjusted to
minimize the scaling error between the recorder and the integrator proper adjustment
5 the potentiometer, following the instructions provided by Curt.s Instruments,
should result in errors less than ± It%.
Having made this adjustment the error may be determined in the laboratory
by using a small radioactive source to expose the ionizati^n chamber at a cor
rate wUh both the recorder and the integrator operating. The total exposure should
be a least several hundred microroentgens. At the end of the exposure penod the
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6
"true" exposure is determined by integrating the area under the curve produced by'
the recorder. This may then be compared to the integrator readout which should be
the same if the scaling adjustment is correctly set.
Field Testing
Testing in the field has provided comparative results between the recorder and
the integrator. Tests were run at exposure rates ranging from 6 microroentgens/hour
up to 165 microroentgens/hour and for both short and long integration periods.
Results of these tests are presented in Table 1.
Table 1. Comparison of Total Exposures as Determined
by the Recorder and by the Integrator
in Field Tests
Integration of Integrator Percent
Test Recorder Tape Reading Difference
(microroentgens) (microroentgens)
1 1271 1295 1.9%
2 1465 1411 2.7%
3 3048 3035 0.4%
4 1645 1655 0.6%
5 1236 1250 1.1%
6 1226 1237 0.9%
Differences between the recorder and the integrator are seen to be quite small.
A likely source of these differences arises from the inaccuracy of using a planimeter
on a long recorder tape.
Summary
The integrator described has been used with good results and no malfunctions.
The low cost makes the integrator particularly appealing compared to other methods
of data integration which are available. No major modifications to the RSS-111
ionization chamber are required for use of the integrator.
Field and laboratory testing of the integrator have shown the unit to produce
good results at both high and low exposure rates for extended periods of time.
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. REPORT NO.
EPA-520/5-73-007
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
\2.
3. RECIPIENT'S ACCESSION-NO.
. TITLE AND SUBTITLE
AN INTEGRATING DEVICE FOR USE WITH PRESSURIZED
IONIZATION CHAMBERS
5. REPORT DATE^
December 1973
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
S. T. Windham, J. E. Partridge, H. L. Kelley
. PERFORMING ORG \NIZATION NAME AND ADDRESS
Office of Radiation Programs
Eastern Environmental Radiation Facility
P. 0. Box 3009
Montgomery, AL 36109
2. SPONSORING AGENCY NAME AND ADDRESS
Same as #9
10. PROGRAM ELEMENT NO,
2F6120
11. CONTRACT/GRANT NO.
13 TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
integrating th^area under a lengthy strip chart curve.
Use of the integrator with the RSS-111 is quite simple and requires
•5! mLJfiration of the ionization chamber. Field and laboratory tests
Sf Se0in?egrIlSr ave"shown t to produce consistent results over both short
and long integration times, and at both high and low exposure rates.
17.
KEY WORDS AND DOCUMENT ANALYSIS
- electronic circuit
- exposure integrator
18. DISTRIBUTION STATEMEN I
Release Unlimited
.——.«•—
EPA Form 2220-1 (9-73)
- PIC integrator . . .
- integrating environ-
mental radiation
levels . . .
19. SECURITY CLASS (ThisReport)
unclassified
20. SECURITY CLASS (TMS page)
unclassified
b.lDENTIFIERS/OPEN ENDED TERMS
18. Nuclear
Science &
Technology
D. Nuclear
Instrumenta
:ion
21. NO, OF PAGES
14
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EPA Form 2220-1 (9-73) (Reverse)
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