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SAFETY HANDLING
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ME RADIOISOTOPE SOURCE SAFETY TESTING PROGRAM
OF THE UNTTED STATES ATOMIC ENERGY COMMISSION*
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NOV 1 3 1984
CONF800-2
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Eugene Lamb and R. A. Robinson
Oak Ridge National Laboratory
Oak Ridge, Tennessee
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The radiation from radioisotopes servis man waily in such diverse
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ways as determining the action of his complex biological system, the
tracing of water flows in rivers, the treatment and diagnosis of
*
diseases, and the preservation of food. One of the most useful
radioisotope forms is the sealed source of radiation which emits
alpha, beta, gamma, neutron, or bremsstrahlung radiation. However,
the properties of these radiations, which make radioisotopes so
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erly used. For this reason safety in the utilization of radioactive
materials is of concern to the United States Atomic Energy Commission,
as evidenced by its establishment of federal regulations governing
radiation protection requirements and its assumption of the respon-
sibility of licensing and regulating the use of radioactive materials.
The regulation of sealed sources by the United States Atomic
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inergy Commission is administered under the provisions of federal
regulations published in Title 10, Code of Federal Regulations,
Chapter 1, Parts 20, 30, and 31. Individual states can also assume
responsibility for regulating sources and establish regulations which
can differ from Sederal regulations and those of other states. The
need for a system of source rating and testing to assist in licensing
*Research sponsored by the U. S. Atomic Energy Commission under
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contract with the Union Carbide Corporation.
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and regulating the use of sources became apparent because of the
increasing diversity of source designs and applications, the growing
number of source fabricators, and the differing requirements of the
various regulatory agencies. The United States Atomic Energy Commis-
sion established the Source Safety Testing Program in the Isotopes
Development Center at Oak Ridge National Laboratory in 1960 with the
objective of developing consistent source and application rating
systems as guides in assessing the ability of a source capsule to
withstand the anticipated environmental stresses of its proposed
application.
The individual tasks of the Source Safety Testing Program and
the status of each at the present time are listed below.
1. Surveys of the existing safety criteria and environmental con-
ditions of sealed sources in the United States. These surveys
were accomplished by Battelle Memorial Institute under contract
with the AEC Division of Isotopes Development. (+12)
2. The development of a Source Capsule Classification System based
on the ability of the source capsule to maintain containment of
the radioactive material under various physical stresses and
environmental conditions.
This task has been accompl.ished at
the Oak Ridge National Laboratory Isotopes Development Center.
3.
The development of a Source and Application Rating System.
This system, now under development by the ORNL Isotopes Develop-
ment Center, will be used with the Source Capsule Classification
System as a guide in considering the advisability of using a
source in a proposed application environment.
The development of standardized tests for use in determining
the classification of prototype sources.
This work is in progress
in the ORNL Isotopes Development Center.
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5. The establishment at ORNL of a continuing program of examination
of sources after extended use.
Environmental Survey
Although the number of sealed sources in industrial appl.ications
is large, literature and data defining the environmental conditions
of use were practically non-existent at the beginning of the Source
Safety Testing Program. In 1963 Battelle Memorial Institute completed
a survey of industrial application environments in order to define
the ranges of normal environmental conditions under which sources
are used, to evaluate abnormal conditions to which they may be ex-
posed, and to establish parameters for development of appropriate
testing and environmental rating systems for sources.(2)
After establishing 25 industrial categories, BMI selected 400
licensees as a representative sample of industrial users of sources
in the major categories of applications. Information relating to
environmental conditions and source failures was obtained by examina-
tion of the files of these licensees; however, the incompleteness of
such information indicated the necessity of a field survey to obtain
definitive data.
In order to obtain the required coverage in a reasonable time,
the on-site surveys were concentrated in industries involving the
bulk of source applications and only the must critical one-of-a-kind
applications were considered. Also, the major attention was focused
on applications where more than minimum environments were anticipated.
The t'ield Investigation involved on-site visits to 57 plants, repre-
senting 18 industrial categories, where approximately 1200 sealed
sources were located. At the same time, pertinent information was
!
obtained on another 1100 sources used in other plants of the companies
which were visited.
Sealed source applications were surveyed in industrial radiog-
raphy organizations, medical institutions, research laboratories,
and in industrial sites concerned with chemicals and pharmaceuticals,
glass, cement and allied products, petroleum, electric power, steel,
non-ferrous metals, waste treatment, roods and beverages, rubber,
plastics, tobacco, paper and allied industries, aeronautics, and
electronics. Most of the devices utilizing sources were gages which
measure thicknesl, density, and level. Since this technique of
radioisotope utilization is found in a wide variety of industries,
the sources used in gages are subjected to the greatest range of
environmental conditions of all those surveyed. Although corrosive
atmospheres, high temperature, and vibration were observed at some
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gaging source locations, the shielding and the structure in which
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the source was held furnished almost complete isolation from these
conditions. This finding is not surprising because the ability to
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gage remotely allows the source to be located external to equipment
which may contain a harmful environment.
Conclusions which can be drawn as a result of the survey are
*W5RZEC
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as follows:
1. The present safety status of sealed source applications is
very good on the basis of observed stresses and the excellent
record of containment reliability of sealed sources.
2. Normal environmental stresses are well within the design
capabilities of sealed sources.
3. Possible abnormal environmental stresses would present the
greatest possibility of source failure and should be considered
in evaluating sources in the safety testing program.
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4. A highly reliable quality control system is needed to insure that
& source has integrity at the time of its manufacture.
Source Capsule Classification System
The essential features of a sealed source are the radioactive
material and the containment capsule. The radioactive material may
be in the form of a compound, a metal, a ceramic, a glass, a matrix
containing the radioisotope, or a gas. The containment capsule is
usually metallic, and the design is dependent both on the environmental
conditions to which it will be subject and the operational require-
ments of the source application.
Radio.sotopes emitting gamma, bremsstrahlung, or neutron radia-
tion are usually contained in metal capsules having walls of suffi-
cient thickness to provide structural strength while permitting
efficient utilization of the radiation. Although some gamma sources
are sealed by threaded plugs or solder, the great majority consist
of two concentric capsules, each of which is sealed by welding a cap
or plug to the capsule body in an inert gas atmosphere." A typical
framma source design 18 shown in Figure 1. The form of the radioactive
material is selected on the basis of radionuclide concentration,
compatibility with capsule material, and resistance to the effects
of radiation.
The covering for alpha- and beta-emitting sources must be much
thinner than that of gamma sources to permit utilization of the
easily absorbed radiation. This requirement presents difficult
design problems in balancing effective containment of radioactive
material against efficient utilization of the emitted particles. A
typical design of a low activity level beta source (curie quantities
27
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or less), shown in Figure 2, provides thick side walls for strength
and a single thin covering over the active area. Many alpha sources
constitute a special case in that a metallic cover is not provided
and containment of the active material is dependent on the source
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material itself or a very thin glaze or electroplated coating. Both
beta and alpha sources are usuully provided additional protection in
the device where they are used. In addition, considerable attention
18 paid to the selection of a source form which is resistant to the
environment or use. Examples of such source forms are small, sintered
ceramic spheros, glasses, enamels, and glazes of inorganic ion exchange
material containing the radioisotope.
The typical source designs described above are simplified repre-
WE
sentatives of many different types of sources, differing in design
features from one another. In order to provide the maximum assistance
to agencies concerned with licensing and regulating the use of sources,
it is desirable to group the wide variety of source designs into a
minimum number of classes according to resistance to well-defined
stresses. This grouping can be accomplished by use of the Source
Capsule Classification System, which is concerned only with the ability
of the source capsule to maintain its integrity on exposure to normal
and abnormal environmental stresses and not with the intended use of
the source. A companion system now under development, the Source
**
and Applications Rating System, will permit the ussessment of a
proposed utilization environment and the assignment of a relative
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numerical rating; a range of values will also be assigned to each
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category in the Source Capsule Classification System. These integrated
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systems can then be used as a guide in approval of a particular type
of source for use in a specified location.
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The excellent safety experience with commercial sources in
existing applications provides a good basis for defining the range
of stresses that each source class must resist. Therefore, the
determination of the resistance characteristics of existing commer-
cially manufactured sealed sources was the first phase of the source
classification work to be performed. To date, mechanical and thermal
stress tests have been conducted on over 500 sources, including
internal and external medical sources, beta and garma gages, gamma
radiography sources, alpha particle fire detection sources, oil
well logging sources, and many other specialized types. As a result
of these tests, five structural and five thertilal stress resistance
classes and their associated stress values were defined as shown in
Tables I and II. Under this system a source capsule must meet the
standards of all tests defining the class to be admitted to that
class. For exanple, if a source capsule withstands all of the
conditing listed under Class IV except the 4540 ig shear force test,
but it does withstand a 454 kg shear force test, it is a Class III
'capsule. Similarly, it is subjected to the temperature tests and
is given a temperature rating. These ratings are combined to give
a composite olassification, for example, Class IIIB, which clearly
defines the limits of stress resistance of that capsule.
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Source Capsule Classification Tests
The tests for classifying source capsules listed in Tables I
and II are described in more detail below. The prototype capsule
18 subjected to a detailed visual examination and leak test before
and after each test.
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Table I. Thermal Stress Resistance Classes
CLASS
CLASS
LAS
B.
B
400 for 1h
Maximum temperature
resistance, °C
200 for 1 h
930 for 1h
3.400 for 1 h
2500 for 1 h
Operating temperature,
°C
0 to 100
-40 to 100
-200 to 260
-60 to 930
0 to 1650
....-. .
Thermal shock,
100 to 0 then
to -60
160 to -18
then to -60
260 to 0 then
to -60
930 to -60
1650 to -200
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Same as A
Temperature-humidity
cycling
No requirement
No requirement
No requirement
.
93°C-100% RH
to 2°C~5% RH
2 h cycle time
for 48 h
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Table II. Structural Stress Resistance Classes
CLASS
IDE
I
II
IV
2.1
7.0
Internal pressure,
kg/cm2 (gage)
70
210
2100
Puncture
resistance
700 cm/sec onto
3 mm d pin
1340 cm/sec onto
3 mom d pin
1890 cm/sec onto
3 mm d pin
430 cm/sec onto
3 mm d pin
90.7 kg for 15 min
18.1 kg for 30 min
945 cm/sec onto
3 mm d pin
907 kg for 1 h
454 kg for 1h
2.
Crishing force
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90.7 kg for 1h
45.4 kg for 1h
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9070 kg for 1 h
4540 kg for 1 h
22 700 kg for 1 h
11 340 kg for 1 h
Shear strength
Impact
Source weight 900g
Source weight >900 g
Vibration
2.77 kg-m
3.1 m free fall
4.15 kg-m
4.6 m free fall
8.3 kg-m
9.1 m free fall
16.6 kg-m
18.3 m free fall
No requirement
33.2 kg-m
36.6 m free fall
10 cycles/sec at
10 g for 12 h
10 c
10 g for 12 h
4 h at resonance
between 5 and 500
cycles/sec and
0.025 to 2.5 cm
double amplitude
Abrasion
No requirement
No requirement
No requirement
50 M A1203
abrasive for 250
rev. of 25 cm
grinding lap
50 u Al2O3
abrasive for 250
rev. of 25 cm
grinding lap
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1. Internal Pressure Test-The prototype capsule, equipped with
a pressure connection, is pressurized with water or oil and
held at the test pressure for 15 minutes. An alternative test
involves subjecting the source to a uniform external hydraulic
pressure that will produce stresses equivalent to those that
would be produced at the required internal test pressure.
2. Puncture Test-The capsule is propelled at the specified test
velocity against a 3 mm diameter pin having the impact end
rounded on a 1.5 mm radius. The source and pin are oriented
80 that maximum damage will occur; in the event of uncertainty
about the proper orientation, the source is tested at several
different orientations. The source is dropped or driven by a
pneumatic ram to give the proper velocity on impact with the
pin.
3. Crushing Strength-The source is placed under a 25 mm diameter
ram and the specified force is applied for a period of one hour.
4. Shear Strength-The source is mounted in a pair of shear blocks
and the test force is applied for one hour.
5.
Impact Strength-The source is placed under a 25 mm diameter
ram, and the ram 18 allowed to fall against the source from a
height which represents the amount of work specified by the
test. Additional weight may be added to the ram in order to
reduce the distance through which it must fall to produce the
required amount of work. Instead of a free fall, the ram may
be moved by a pneumatic cylinder which is pressurized with an
amount of air calculated to accomplish the specified amount of
work on the ram. The free fall of the source from the required
height onto an essentially unyielding surface may be used as an
alternative test, provided that the orientation can be deter-
mined at the time of impact.
6. Vibration and Abrasion-Commercially available vibration and
abrasion test machines are used for these tests. In the case
of vibration testing, the axis of vibration 18 randomly chosen
unle88 inspection of the source indicates that a particular
mounting may produce this worst effects.
7. Maximum Temperature Test-The source is placed in a furnace
in an air atmosphere and raised to the test temperature. The
test temperature is ma.lntained for one hour, and then the source
18 removed from the rurnace and allowed to cool by natural
convection to room temperature.
8. Operating Temperature Test-The source is maintained at the
low test temperature for 24 hours and then at the high test
temperature for 24 hours. The source may be immersed in the
cooling medium during the low temperature test, but must be
kept in air during the high temperature test.
Thermal Shock Test-The source is raised to the highest specified
temperature and held there for at least 15 minutes. Then,
within a period of one second, the source is removed from the
high temperature environment, placed in an environment at the
lower specified temperature, and allowed to cool to the lower
temperature. The source is then allowed to warm raturally to
room temperature. In the case of Classes A, B, and C, the source
18 further cooled, over a period not exceeding 15 minutes, to -60°C
after the initial thermal shock.
10. Temperature-Humidity Testing-Standard commercial environmental
chambers are used to duplicate the specified test conditions.
The classification tests are generally performed on prototype
capsules containing a non-radioactive material which accurately
duplicates the actual radioactive material to be used in the source
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from the standpoint of quantity, density, and physical propert168.
Thore 18 no specific order in which the tests have to be performed
however, an initial review of the capsule design will usually
indicate the test to which the capsule will have the least resistance,
and this test can be carried out first because it will probably
establish the highest possible class of the capsule. Usually a
complete classification can be made with four capsules.
The only criterion determining failure of a classification
test is the presence of a leak in the source capsule at the conclu-
sion of the test that was not evident prior to the test. A simple
leak test has been developed(") for use with the classification
tests and for potential use as a quality control procedure in source
manufacture. The source to be leak tested is immersed in ethylene
glycol or isopropyl alcohol and the pressure above the liquid reduced
ito about 125 mm of Hg absolute; a leak 18 indicated by a stream of
bubbles rising through the liquid. The sensitivity of the test
was determined by preparing a number of calibrated leaks, measuring
the hole sizes microscopically, and measuring the leak rates. Under
the test conditions described above, leaks as small as 3 x 10-8 sta
cm sec-t can be readily detected and leaks of 1 x 10-7 std cm sec-2
have been detected by subjecting the capsule to a higher gas pressure
Inmediately before the test. The relationship between the leak diameter
(D), surface tension of the immersion liquid (T), and pressure differ-
ential required to initiate bubbling (AP) can be expressed by the
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glycol can be used as the immersion liquid because of their
relatively low vapor pressures and surface tensions.
The racuum leak test can be used only if there 18 a free'
volume in the capsule adequate to support a stream of air bubbles
in the event of leak. The test has been used successfully on samples
having free volumes as small as 0.1 cm®, however, this is considered
the minimum volume at which it should be used. In cases where there
is not sufficient free space in the capsule for the vacuum leak test,
an alternative test can be used. This test involves adding a small
amount of an easily soluble cesium or lithium salt (cesium or
lithium chloride) to the non-radioactive source compound in the
prototype capsule being tested and submerging the source in water
in a vessel which is alternately evacuated and vented to atmospheric
pressure for a period of 20 minutes. The water is then analyzed by
a photometric technique capable of detecting cesium concentrations
as low as .003 ug cm-3. A soluble radioactive tracer (137C8c1, 24Naci)
can be substituted for the non-radioactive tracer and standard counting
methods used for analysis.
In addition to the above tests, four other simple leak tests
have been investigated.
1. Smear Test-The source is wiped on all accessible surfaces with
LAN
an absorbent paper disk 25 mm in diameter. No attempt is made
to "scrub" the source vigorously, but it is thoroughly wiped,
using moderate pressure on the paper. Although both wet and
dry smear papers are used, the wet sme ars consistently pick up
a higher count than the dry smears. In all cases in which a
wet smear shows a leak, however, the corresponding dry smear
also shows a leak.
2. Hot-Water Bubble Test-The source at room temperature is quickly
immersed in water that is just below the boiling point (n90°c).
If a stream of bubbles emanates from the source due to the
Bitivity of this test is estimated to be ~10-4 std cm® secºl,
3. Air-Pressure Bubble Test-This test is a variation of Test 2
above. The source is placed in a pressure vessel at 540 cm Hg
air pressure for 15 minutes and then 18 quickly transferred to
the hot water. A leak 18 present if a stream of bubbles is
observed.
4. Weight-Lain Test-The source is first weighed to an accuracy of
at least 0.18 and 18 then placed in a water-filled pressure
from the pressure vessel and reweighed. A gain in weight indicates
that water has entered the capsule through a leak.
The following conclusions can be made from experience with these
: 1. The smear test does not always give indication of a leaking
source capsule.
2. The weight-gain test is inreliable, particularly when there are
small leaks or when there may be extraneous material on the
capsule that can be dislodged.
3. The air-pressure bubble tesi 18 only slightly more effective
than the hot-water bubble test. The sensitivity of the air
pressure test could probably be improved by increasing the
pressure and performing the entire test in a single vessel.
The vacuum leak test is the most sensitive and reliable of the
tests and detected leaks when all other methods failed. The
4.
test is not effective, however, when the free volume inside
the source is too small to support a stream of bubbles, e.g.,
Interstitial therapy needles. This test may not be satistactory
in the case of a large leak which permits the air to escape .n
one or two large bubbles that might not be seen by the observer.
5. The value of a thorough visual examination should not be dis-
counted, for, in many instances, examination of seal areas
under moderate magnification (5x-20x) clearly revealed porosity.
Other means of leak detection which are known to be very sen-
sitive, such as the 85Kr or helium leak tests, have not been used
because the development of methods that require simple inexpensive
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equipment has been emphasized.
After the initial testing of commercial sources was completed
to determine the values used in the Source Capsule Classification
System, 120 sources representing 37 commercial designs were tested
to determine their classification. The results of this trial
classification are arranged in Table III according to the intended
applications of the 37 designs.
The trial classification results in Table III show that 70%
of the tested source designs intended for use with multicurie quan-
tities of activity (teletherapy, radiography, and neutron sources)
are in the Class III structural category while the remaining 30%
are in the 1988 demanding Class II. However, 85% of the gaging
sources, which normally use less than one curie of activity, are
in the Class II structural category while 15% are in Class III.
These results indicate that the ranges of strese values chosen for
co
the structural classes are sufficiently narrow to distinguish between
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Table III.
Trial Classification of Representative
Commercial sources
Application
Clas 8
Nuniber of Designs
Teletherapy
IIIB
No
Teletherapy
t
IIIC
IIIB
Gage 8
Gages
IIC
F
Gages
IIB
--
Gages
IIA
-
N
-
--
-
Radiography
IIIC
Radiography
IIIB
N
Radiography
IIC
N
Radiography
IIB
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IIIC
now
Neutron
IIA
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applications on the basis of quantity of radioactivity but are not
too narrow to allow a wide variety of classes within one applica-
tion category. The fact that all of these sources are in Clase "II
or III Indicates that manufacturers are providing more than minimum
Bafety standards in their products.
The temperature classes of the source designs in Table III are
more varied and do not show definite relationships either to quantity
of isotope or source application. This result was not entirely un-
expected because the testing program during the development of the
Source Capsule Classification System had shown a rather wide varia-
tion of temperature resistance. The four source designs falling
within Class A, which has the lowest temperature requirements, were
sealed by solder. Since the temperature classification ranges were
chosen to restrict solder sealed sources to Class A, the system is
effective in this regard.
Examination of Sources After Use
An important function of the Source Safety Testing Program
is the examination of sources that have been in use for varying
periods of time and sources that have developed leaks in service.
Eighteen lead "O" ring sealed 60Co teletherapy sources that had been
in use for periods up to 8 years were examined') and in all cases
the lead "0" ring seal was found to be broken. Some of these sources
contained unplated cobalt metal and others contained nickel-plated
cobalt, but both types contained approximately equal amounts of finely
divided corrosion products. This design of teletherapy source has
beer, replaced by the superior all-welded design and is no longer
manufactured in the United States. One of the most interesting
sources examined was a 1370801 teletherapy source that had been in
use for 9 years. (6) Examination of the sectioned capsule showed no
evidence of corrosion. A complete metallographic examination 'of the
0.5 mm end window of the source did not reveal any reaction between
the source compound and metal.
Most of the sources that have been examined because of leakage
have been small gaging or calibration sources containing millicurie
quantities of activity. A typical example of this type of source
is a solder-sealed calibration source containing about 5 millicuries
or Pogr. Seven of these sources (out of many hundreds in use) were
examined because a standard wipe test by the users had indicated
that they were leaking. In all seven cases it was found that the
soldered seal had been improperly made and probably could have been
detected at the time of manufacture by a simple quality control
and inspection program.
some types of unsealed sources such as plated alpha sources,
· radiation activated phosphors, and foil-type sources have also been
i tested. Luminous watch dials having radiation activated phosphors
using tritium have been subjected to soaking, aging, and bending
tests and have been found to meet safety requirements. Foil sources
used in static electricity eliminators and fire detection devices
maintained containment of the activity when cut, bent, and soaked
for prolonged periods, but were quite susceptible to 1088 of
activity when exposed to a fire. Plated alpha sources have been
found to require special care in use because of the ease with which
activity can be wiped from the active surfaces--particularly as
the sources age. However, this type of source usually contains only
very small quantities of activity and is used under carefully controlled
laboratory conditions.
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Summary
Th3 Source Capsule Classification System has been submitted to
the United States Atomic Energy Commission and to interested source
manufacturers for comments which will be considered in further re-
visions. A trial classification of 120 sources, representing 37
different designs, indicated that the proposed classification system
can accomplish its intended purpose of classifying a large number of
different source capsule designs within a few categories.
A companion system, the source and Application Rating System,
is now under development. Under this system, relative numerical
ratings will be assigned to (1) utilization environments; (2) the
degree of protection afforded by the source housing; (3) possible
abnormal conditions; and (4) the consequences of a release of radio-
active material. The use of this system with the Source Capsule
Classification System will permit a reliable assessment of the ability
of a source capsule to withstand the expected environmental stresses
of its proposed application.
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20
1. TOWNIEY, Charles W., et al, "The Development and Evaluation
of Safety Performance Criteria for Sealed Radiation Sources,"
USAEC Rpt BMI-1559, December 5, 1961.
2. EWING, Robert A., et al, "Industrial Environmental Conditions
of Sealed Radiation Sources," USAEC Rpt BMI-1648, September 10,
1963.
3. PIERCE, E. E., "Remote Welding of Stainless Steel Containers,"
Hot Lab. Operations and Equip. Proc. 5th Conf., Philadelphia
(Ed. J. R. Dunning and B. R. Prentice), Pergamon, New York
(1957), Vol. 3, pp 147-50.
4. KING, C. R., "Vacuum Leak Testing of Radioactive Source Capsules,"
USAEC Rpt ORNL-3664, to be published.
5. HAFF, K. W., "Leak and Strength Tests of Old Cobalt-60 Tele-
therapy Source Capsules Sealed with Lead O-Rings," USAEC Rpt
ORNL-TM-712, December 1963.
6. HAFF, K. W., "Examination of Nine-Year Old 137CsC1 Source
Capsule," USAEC Rpt ORNL-IM-584, August 1963.
FIGURE LIST
Figure 1.
Typical Gamma Source Design.
Figure 2. Typical Beta Source Design.
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22

DATE FILMED
(12/29164
LEGAL NOTICE
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with the Commission, or his employment with such contractor.
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