ORP/EERF 73-3
PORTABLE ANNEALER
FOR THERMOLUMINESCENT DOSIMETERS
U.S ENVIRONMENTAL PROTECTION AGENCY
Office o* Radiation Programs
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OFFICE OF RADIATION PROGRAMS
EASTERN ENVIRONMENTAL RADIATION FACILITY
TECHNICAL REPORTS
Technical reports of the Eastern Environmental
Radiation Facility are available from the National Technical
Information Service, Springfield, Virginia 22151, when
a PB number is indicated after the title. Microfiche
copies are $0.95; prices for paper copies are indicated
after the PB number. Bulk order prices are available
from NTIS. The PB number should be cited when ordering.
Title
Radiological Survey of Major California
Nuclear Ports (April 1967) (PB 178 728
$6.00)
BRH/SERHL 70-1
RO/EERL 71-1
EERL 71-2
ORP/EERF 73-1
ORP/EERF 73-2
ORP/EERF 73-3
Radiological Survey of Hampton Roads,
Virginia (January 1968) (AD 683 208 $6.00)
Laboratory Examination of a Ruptured 50-mg
Radium Source (May 1970) (PB 191 810 $3.00)
Development of Ion Exchange Processes for
the Removal of Radionuclides from Milk
(January 1971) (PB 198 052 $0.50)
Investigation of Tritiated Luminous
Compounds (June 1971)
Suitability of Glass-Encapsulated
Thermoluminescent Dosimeters for Environ-
mental Radiation Surveillance (June 1973)
Construction and Operation of an Ion
Exchange Cartridge for Monitoring Radio-
nuclides in the Environment (June 1973)
Portable Annealer for Thermoluminescent
Dosimeters (June 1973)
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ORP/EERF 73-3
PORTABLE ANNEALER
FOR THERMOLUMINESCENT DOSIMETERS
S. T. Windham
H. L. Kelley
T. K. Plant
Eastern Environmental Radiation Facility
P. 0. Box 61
Montgomery, Alabama 36101
Author's present addresses:
1. Eastern Environmental Radiation Facility
2. Eastern Environmental Radiation Facility
3. University of Illinois
June 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 endorse-
ment of such products by the U. S.
Environmental Protection Agency.
11
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FOREWORD
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 assess-
ment 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 government agencies as requested.
Charles R. Porter
Acting Director
Eastern Environmental Radiation Facility
111
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CONTENTS
Page
Foreword ii
List of Figures iv
Introduction 1
General Description 1
Circuit Description , 2
Performance Characteristics 2
Parts List 5
Summary 6
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FIGURES
Page
1. Portable TLD Annealer 3
2. Schematic of Portable TLD Annealer 4
VI
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PORTABLE ANNEALER FOR THERMOLUMINESCENT DOSIMETERS
ORP/EERF-73-3
S. T. Windham, H. L. Kelley, T. K. Plant
INTRODUCTION
The requirement for low-level environmental radiological
monitoring has led to the development and widespread use
of thermoluminescent dosimeters (TLD's) for this purpose.
TLD's offer a sensitive and accurate means for integrating
exposures over extended periods of time, and are especially
well suited for determining environmental radiation levels
in the vicinity of nuclear facilities. The EERF, as well
as several other organizations, has used the EG&G TL-15
TLD for environmental radiological monitoring.
The TL-15 is "read out" by applying a current to the
heating element within the dosimeter and measuring the
light output from the CaF2:Mn chips. For the magnitude
of exposure normally found in environmental monitoring
for exposure periods of one month and in general for
exposures below 200 mR, the "read out" process is adequate
to anneal or dedose the dosimeter and permit reuse with
no further annealing. Immediately prior to placing
dosimeters in the field for a monitoring period, it is
necessary to anneal dosimeters if they have been shipped
and possibly exposed, or if some time has elapsed since
they were last annealed. To avoid unnecessary shipment
of the reader or an annealing oven into the field for
this purpose, a small, portable annealer was designed and
built by the Electronics Instrumentation Section at the
Eastern Environmental Radiation Facility. This report
describes the design and operation of the annealer.
GENERAL DESCRIPTION
In function the annealer performs similar to the
heating circuit of the EG&G TL-3 reader, but without the
photomultiplier tube and associated recording and control
circuitry. The TL-3 reader uses a heating time of 13 seconds
and a current of 6.5 amperes to "read out" the TL-15
dosimeter. Likewise, the annealer delivers a regulated
current through the heating element of the TLD for a
selected length of time. The heating time is adjustable
from 0-30 seconds and the current is adjustable from 3-7.5
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amperes. A meter is used to aid in adjusting the current
to the desired value. With the current and time easily
adjustable, it is possible to use the instrument to
anneal vacuum tube dosimeters of other manufacturers
simply by changing the socket in which the dosimeter is
inserted for annealing.
A principal consideration in the design of the
annealer was to produce a small, portable instrument.
The final design, as seen in figure 1, will easily fit
into an attache case with room remaining for dosimeters
and other accessories.
CIRCUIT DESCRIPTION
The annealer consists of a timer and a current
regulated power supply (figure 2). The timer is not
necessary to the operation of the circuit, but aids in
obtaining consistent annealing results. The operation
of the current regulator is quite simple. A phase control
circuit consisting of R3, GI, the diac, and the triac
delivers power to the primary winding of T]_, a 110 VAC
transformer with a 6.3 volt, 10 ampere secondary. RS and
GI have been chosen such that the triac is conducting
during most of the cycle. When the anneal circuit is
first energized, essentially full voltage (6.3 VAC) is
produced on the secondary. Unlimited, this surge would
burn out the TLD being annealed, but the drop across Ry
illuminates lamp 13. The normally high resistance of
photocell R4 is quickly lowered which reduces the average
conduction time of the triac. This reduces the current
through the secondary of TI, but maintains a constant
value depending on the setting of Rg. This constant
current value is independent of the resistance of the TLD
heating element due to the negative feedback action obtaine
with the module containing 13 and R4. RS is a thermal
resistor which acts to decrease the initial surge of
current and thereby damps excessive meter movement.
PERFORMANCE CHARACTERISTICS
The manufacturer of the TL-15 dosimeter recommends
a heating current of 6.5 amperes which was used through-
out the performance tests of the annealer. To determine
the minimum time required to dedose a dosimeter using the
annealer, a group of dosimeters was exposed to 11.1 mR,
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0 3456
Front panel of annealer
Inside view
Figure 1. Portable TLD Annealer
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115V
60 Hz A.C.
0-10AA.C. P,
Figure 2. Schematics of Portable TLD Annealer.
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PARTS LIST
Cx - .05 yF
I, , I2 - neon indicator lamps
F - 1 amp slo-blow fuse
I3r £4 ~ Clairex CLM 3006A Photo Mod
Sj_ - SPST Power-On Switch
S2 - SPST Momentary Contact
T>L - 110 VAC Primary 6.3 volt 10 amp secondary
GE ST2 - Diac trigger diode
GE SC 40B - Triac Switch
Rl' R2 ~ 48k ohm, 1/4 watt resistors
RO - 68k ohm, 1/2 watt resistor
Re - Glow-Bar Surge Arrester
Rg - 250 ohm, 2 watt resistor
R7 - 0.5 ohm, 100 watt resistor
P - appropriate socket for TLD being used
M-, - 0-10 ampere AC meter
Timer - 0-30 second instant reset timer
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heated in the annealer, and "read out" using the TL-3
reader. The minimum time required for complete annealing
was found to be 15 seconds. This annealing technique
6.5 amperes for 15 seconds, was accepted as the routine
procedure used with the TL-15 dosimeter.
For dosimeters which have been exposed to greater
than 50 mR, EG&G recommends an oven annealing procedure
instead of depending on the reader to dedose the^dosimeters.
To determine the effectiveness of the annealer in dedosing
exposures greater than 50 mR, several groups of dosimeters
were given known exposures, heated in the annealer, and
"read out" to determine any residual exposure. The following
data were obtained:
Annealing Effectiveness
6.5 amperes 15 seconds
Delivered Residual reading Percent
exposure after annealing annealed
232 mR 0 mR 100%
400 mR 0.14 mR 99.97%
872 mR 0.24 mR 99.97%
1760 mR 0.40 mR 99.97%
From this it is seen that for normal environmental levels,
less than 200 mR, the annealer is totally effective in
dedosing the dosimeters. For exposures greater than this
negligible residual exposure remains after annealing.
For most applications this small residual exposure will
be insignificant. If total annealing is necessary at
these higher levels, an oven annealing procedure may be
used or, possibly, longer heating times.
SUMMARY
The annealer described has been in use for several
months with good results and no malfunctions. Components
used in construction of this compact annealer are readily
available and construction requires no special skills
or equipment. The cost of building the annealer, less
than $75 including the optional timer, represents a
significant savings compared to the repair cost and
down time should damage to the TLD reader occur during
shipment to monitoring sites. Use of the annealer makes
unnecessary a number of these shipments.
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The effectiveness of the annealer in dedosing the
TL-15 dosimeter was demonstrated. For exposures less
than 200 mR, annealing was 100%. Thus the annealer
has proven to be most adequate for environmental measure-
ment work.
US. Government Printing Office: 1973 - 743 - 901/7768 Region No. 4
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