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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
MASTER S
ORN-P21910
Conf-660207-1
RADIOISOTOPE SOURCES AND SOURCE TESTING*
R. G. Niemeyer
RELEASED FOR AX91."VEST
Isotopes Development Center
Oak Ridge National Laborator IN NUCLEAR SCI“.CE ABSTRACTS
Oak Ridge, Tennessee

FEB 4 . 1966
ARSTRACT
The Isotopes Development Center at Oak Ridge National Laboratory
has been engaged in a Source Testing Program since 1962. The overall
objective of this program is to obtain information that can be used by
source manufacturers, standards groups, and regulatory agencies to
design and specify radioactive sources and shipping containers that
will be consistent with the safety requirements involved. In the course
of this study, several hundred sources have been tested to determine
their structural and environmental limitations.
The excellent safety record of domestically manufactured sealed.
sources together with the ini'ormation acquired in the Source Testing
Program serves as the basis for the proposed ORNL Source Capsule Classi-
fication System. This system permits classification of source capsules
according to structural and temperature characteristics as these relate
to the overall objective of ensuring containment of the radioisotope.
The information obtained in developing the proposed Source Capsule .
Classification System and in the Source Testing Program has been made
available to the American Standards Association Committee to aid in
the formulation of source design standards.
A large number of sources have been fabricated, loaded, and sealed
at ORNL. Sources are loaded and sealed in hot cells using remote handling
and welding equipment. Source sizes range from very small (millicurie)
radiation sources to large (kilocurie) heat sources. Materials of
construction range from relatively low-melting materials such as
aluminum to the high-melting refractory metals.
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*Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
SEALED RADIOISOTOPE SOURCES
Sealed radioisotope sources containing isotopes that emit alpha,
beta, gamma, bremsstrahlung, or neutron radiation have many useful
applications in science and industry. Radioisotope gaging devices are
used in the cigarette industry to control the uniformity of the tobacco
rod during manufacture. Thickness gages are used in the manufacture of
paper, textiles, plastics, adhesives, floor coverings, roofing materi.als,
metal plates, and castings. Radioisotope density gages are used in the
manufacture of chemicals, food, petroleum, plastics, rubber, and glass
products. Many level sages are used to control the levels of liquids
such as molten 'metal, gasoline, and paper-pulp slurries.
Sealed radioisotope sources are used by many Industries for radiographic
inspection of welds, forgings, and castings. Many sealed sources are
used in hospitals for radiation therapy. These include teletherapy
sources, medical applicators, and needles. Neutron sources are used in
oil-well logging devices to detect oil-bearing strata and for detecting
water. They are also used to start up nuclear reactors and for activa-
tion analysis. Large gamma irradiation sources are used in both public
and private research laboratories to study the effects of gamma radiation
on materials and processes, including the sterilization of food, drugs,
and medical supplies. Irradiation sources are also used in the produc-
tion of wood-plastic products and in the production of ethyl bromide.
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capsule for the sources are made on the basis of the requirements for :
safe efficient utilization of the radiation. The form of the radio-
active material is based on radionuclide concentration, compatibility :
with the source capsule, and resistance to the effects of radiation. .
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The form may be a simple compound, a glass, a metal, a ceramic, a gas,
or a matrix containing the radioisotope. Ideally the source form would
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be one with high resistance to the environment in which it is to be used
80 that dispersion of the radioactive material would be prevented,
although the containment capsule were to fail. The capsule is usually
metal with the design dependent both on the environmental conditions
to which it will be subjected and on the operational requirements of
the source application. Provision is often made for double enclosure
of the radioactive material, each of the enclosures being sealed by
heliarc welding. Additional safety is provided in many cases by the
· devices in which the sources are used.
Alpha sources are used principally for instrument calibration and
research applications. A few are used industrially, mostly as static
electricity eliminators. Due to the low penetrating power of alpha
radiation, the containment covering of this type of source must be very
thin in order to permit efficient use of the radiation. These coverings,
called windows, are made of extreme ly thin metal or mica, usually less
than 0.3 mil thick. The sidewalls of these sources may be made of much
thicker material to provide optimum strength. Some alpha sources do
not have a cover to contain the radioactive material but rely on'the
properties of the source material itself for containment, considerable
attention is therefore given to the selection of a source form which
is resistant to the use environment. Some alpha emitters are electrolyti-
cally deposited on metal backings and may or may not be protected by a
very thin glaze or electroplated coating.
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LEGAL NOTICE
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The report was prepared na mocount of Covenammet spoorond work. Malther the United
Hate, nor the Communalan, nor a pornoa acting on behalf of the Commission:
A. Make my warranty or reprouentation, proceed or implied, with respect to the sou-
rney, completeness, or wofalnow of the information contained ha dulo report, or that the we
of way toormation, appunto, methods or prooon dincloned la the report may not infringe
privately owned suhtes of
B. And any liabidea with repeat to the wool, or for damages routes from the
um of my tutoration, apparatus, method, or proon dieclound in the report.
. As wood tam the above, peranca notte a ball of the Commission" lnoludna u m .
ployee or contractor of the Constanton, or mployee of much contractor, to the attent that
moh omployee or contractor of the Commission, or employee of much contractor propers,
dienominated, or provides nous to, w information per muant to do employment or contriot
... ORNL - AEC - OFFICIAL :
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Beta sources find their most important industrial applications in
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thickness, density, and level gaging. The design problem with beta
sources is much the same as with alpha sources in that thin windows
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radiation, her.ce considerable attention is given to the source form.
Examples of such source forms are chemical compounds contained in glasses,
ceramics, compressed pellets, enamels, or inorganic ion-exchange materials
containing the radioisotope.
Gamma sources are used primarily for gaging, radiography, tele-
therapy, and irradiation. Due to the great penetrating power of samma
radiation, these sources can generally be designed for considerably
greater structural strength than either alpha or beta sources. Most gamma
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sources are doubly encapsulated in cylindrical stainless steel containers,
each of which is sealed by welding an end cap to the capsule body. Many
of the low-energy ganma sources still require thin windows to permit
efficient use of the radiation, but these windows are usually from
10-20 mils thick. The source forms are usually pressed pellets of a
source compound or the metallic form of the isotope.
Small isotopic heat sources have been used as heat standards and
larger ones as isotopic power sources for terrestrial, marine, and
space applications.
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RADIOISOTOPE SOURCE FABRICATION AT ORNL
A large number of sealed sources have been designed and fabricated
at ORNL. Sources are loaded and sealed in manipulator cells using remote
handling and welding equipment. Source sizes range from very small
(millicurie) radiation sources to large (kilocurie) heat or power sources.
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Materials of construction range from relatively low-melting materials
such as aluminum to the high-melting refractory metals.
The fabrication of 1970s sources provides a typical example of the
techniques used. Since 1958 more than 600,000 curies of 137Cs have
been fabricated as sealed sources at ORNL for use in a great variety of
applications by medical industrial, and research organizations. The
radioactive cesium, chemically recovered from processing reactor fuel
waste, is converted to dry 137C8C1 powder. The powder is heated at
400°C for 2 hr to bake out any remaining water or free acid and is than
maintained at a temperature of 80 to 100°C during storage to preserve
its anhydrous condition.
The desired amount of powder for a particular source is weighed
and transferred to a tool-steel die and compressed at pressures up to
50,000 psi to form a pellet having the required dimensions for encap-
sulation. Nearly all pellets are right cylinders; however, square wafers
have been made for encapsulation in flat plates. The equipment is
shown in Fig. 1. The pellets are doubly encapsulated in cylindrical
capsules of Type 316 stainless steel, machined from stainless steel
rods, one end being left open to permit loading the pellet. After
the pellet has been loaded in the inner capsule, a custom-fit stainless ::
steel spacer is inserted to take up any free space and thus limit move-
ment of the pellet within the capsule. An end plug which has been
machined to a slight interference fit with the capsule is inserted
and the capsule is sealed by remote heliarc welding. The completed
inner capsule is tested for leaks, decontaminated, and placed inside
the outer capsule. The outer capsule is then sealed by welding the ..
outer end plug to the outer capsule.
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Most capsules are sealed using the tungsten-inert gas method. The
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remote welders developed at ORNL utilize a standard commercial power
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supply and are designed to occupy a minimum of space ins:.de the manipu-
lator cells. Manual rather than automatic controls are used because
of the wide diversity in source designs. In one of the ORNL welder
designs, the source capsule is held in an upright position either by
a fitted massive heat zink or by an adjustable drill chuck. The heat
sink and sourcè capsule rotate on the vertical centerline of the capsule
so that the weld area is always under the stationary tungsten electrode.
Rotation 18 provided by a remotely operated variable-speed drive. The
tungsten electrode holder can be positioned by moving it vertically or
horizontally by vorm gears driven by remotely operated electric motors.
The power supply and controls for operation are placed in the celi'
operating area near the viewing window to permit ease of operation. The
welder is designed so that parts can be readily replaced by remote .
manipulation. One type of remotely operated welder 18 shown in Fig. 2.
In some cases the refractory metal capsules of radioisotope power sources :
have been welded by means of a remotely controlled electron-beam welder:
After welding, the source. capsule is cooled to room temperature
and tested for leaks by subjecting it to the hot-water bubble test, which
involves immersing the source in hot water just below the boiling point.
A leak is indicated by a stream of bubbles caused by expansion of air
in the source capsule. If no bubbles appear within 2 min, the capsule
is considered to be leak tight. In the more sensitive frequently used
vacuum leak test, the source capsule is imersed in ethylene glycol and
the pressure over the liquid is reduced to 23-25 in. Hg vacuum; any bubbles
indicate a leak. This method is discussed in detail in a later section :
on the classification of source capsules. .
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After leak testing, the source capsule is decontaminated by washing
with a detergent solution. When the source is found to be free of leaks
and has surface contamination below the prescribed limits, it is placed
in storage for a period of seven days, at which time the tests for leaks
and contamination are repeated as an additional safeguard. After pass-
ing these tests the source is ready for shipment.
The procedure of double encapsulation not only provides for safer
containment of the radioisotope, but it also makes the cost of source
capsule decontamination much less demanding. By use of this procedure,
the outer source capsule can be kept relatively free of contamination
since it does not have to be placed inside the manipulator cell until
after the inner capsule is decontaminated. The sectioned teletherapy
source in Fig. 3 provides an illustration of a typical doubly encapsulated
source.
The facilities of ORNL have been used in joint efforts with several
commercial organizations in fueling electric generators. Among the sources
encapsulated are 124,000 curies of SOSrT10g used for fueling one of the
SNAP-7 thermoelectric generators designed by the Martin Company for the
USAEC; 83,400 curies of pºsrTi0g used for fueling a thermoelectric genera-
tor designed by RCA; 70,000 curies of 60Co used in powering a hydrogen
thruster designed by the Marquardt Corporation; and 25,500 curies of
187C8. glass for fueling an underwater thermoelectric generator designed
by Royal Research Corporation.
CLASSIFICATION OF SOURCE CAPSULES
The Isotopes Development Center at Oak Ridge National Laboratory has
developed a system for the classification of sealed source capsules as
a part of the Source Testing Program established by the USAEC.
ORNL - AEC - OFFICIAL
A system such as this, which groups source capsules according to struc-
ORNI-AIC - Drill
tural and temperature characteristics relating to the overall objective
of ensuring containment of the radioisotope during normal and abnormal
use situations, is needed in order to simp).ify regulation of the use and
fabrication of these devices as well as to minimize hazards to the
general public.
The classification system is composed of two sections. Temperature
Classes A through E are shown in Table 1; Structural Classes I through V
are shown in Table 2. Each source capsule design under consideration
will be classified in both of these sections to give a composite classi-
fication, such as IC or IIIA, which describes both the temperature and
structural limitations of the capsule. Under this system a source.
capsule must meet the requirements of all of the tests which define a
class in order to be admitted to that class.
The rationale behind the selection of individual values in the
ORNL Source Capsule Classification System is based largely on the
excellent safety record of domestically manufactured sealed sources.
The early work in the ORNL Source Testing Program was designed to
define those characteristics of commercial source capsules which brought ·
about this safety record. The results of these tests strongly influenced
the selection of the values in the source capsule classification tables,
thus ensuring that the classification tests would reflect current safe
practice in sealed source capsule design.
For the purpose of classification, a source capsule is defined as
the totally assembled, sealed enclosure which provides the containment :
of the radioactive material. It includes both single enclosure and
multiple enclosure but does not include housings, shields, or other
devices external to the sealed containment enclosure.
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Table 2. Proposed ORNL Source Capsule Classification System
Temperature Characteristics
Maximum tomperature Operating
resistance, 'F ' temperature,
Thermal
Temperature-
humidity cycling
Class
I
n
A
400 for 1 hr
.
32 to 212
212 to 32
then to -70
200°F - 95% RH
to 35°F - 5% RH
8-hr cycle time
t'or 48-hr period
B
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750 for 1 hr
-40 to 212
Same as A
212 to 0
then to -70
500 to 32
then to -70
1700 for 1 hr
-320 to 500
No requirement
D
2400 for 1 hr
4500 for 30 min,
2400 for 1 hr
-70 to 1700
32 to 2400
1700 to -70 No requirement
2400 to -320 No requirement
Table 2. Proposed ORNL Source Capsule Classification System
Structural Characteristics

Impact
force
External pressure,
Puncture resistance,
ft/sec onto
1/8-in. dia pin
.
Crushing force,
lb for 1 hr
Shear strength,
| 1b for 1 hr.
{ Class
2 lb,
ft-lb
lb, ft
free fall
>
Vibration
100
200 for 40 for 10 10 cps at 10 g's
15 min 30 min
(longest axis): for 12 hr
23 | 200 100
Same as I
12,000 1,000
No requirement
IV 3,000 44 20,000 10,000 60 No requirement
v20,000 62 50,000 25,000 240 120 4 hr at each resonance*
to 500 cps and 0.001 to 0.1-in. double amplitude applied along each
of three perpendicular axes; when no resonant frequencies are found,
vibrate for 12 hr at 0:018-in. double amplitude and 150 cps on each axis.
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ORNL - AEC - 0!FICIAL
The classification of a source capsule is made using dummies in
which nearly equel volumes of the nonradioactive source compound are
substituted for the radioactive material. A chemical analog may be used
in cases where a nonradioactive compound is excessively expensive or
does not exist. The dummy source capsules are made of the same mate-
rials of construction and manufactured in the same manner as the
radioactive ones.
The only criterion for determining failure of a classification test
is the presence of a new leak in the source capsule at the conclusion
of the test. A simple test has been developed in which the source
capsuie to be leak tested is immersed in either ethylene glycol or
isopropyl alcohol (used because of their relatively low vapor pressures
and surface tensions) and the pressure above the liquid is reduced to
23-25 in. Hg Vacuum. A leak is indicated by a stream of bubbles rising
through the liquid. The sensivitity 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 condi- .
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tions described above, leaks as small as 3 x 10-8 std cm®/sec can be
readily detected and smaller leaks have been detected by pressurizing
the capsule with air immediately before the leak test.
The vacuum leak test can be used only if there is a free volume in
the capsule adequate to support a stream of air bubbles in the event of
a 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 for testing. For the purpose of classifying source capsules,
an arbitrary value of 0.25 cm was selected for the minimum volume..
Source capsules with a free volume equal to or greater than 0.25 cm
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are vacuum leak tested. In cases where there is less than 0.25 cmø free
volume in the capsules, an alternate test is used which involves adding a
small amount of lithium chloride to the nonradioactive source compound in
the dummy source capsule being tested and submerging the source in water in
a vessel which is alternately evacuated and vented to atmospheric pressure
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for a period of 20 min. The water is then analyzed by a photometric tech-
nique capable of detecting lithium concentrations as low as 0.001 ug/cmº.
This test, unlike the vacuum leak test, is not used for routine leak test-
ing of production sources.
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• SOURCE APPLICATIONS GUIDE
The Source Applications Guide, currently under study, will
establish the classification test requirements of a source capsule to .
be used in a specific location. Under this system, relative numerical
ratings will be assigned to each of the following:
1. Radiotoxicity
8. Operating temperature
2. Quantity of activity 9. Operating pressure
:3. Source location
10. Corrosive atmosphere
Source compound
11. Fire and explosion hazards:
5. Radiation effects
12. Personnel experience
6. Population density
3. Design experience
7. Source housings
The numerical ratings will then be summed and related to the class
requirements of the classification tables in a manner that reflects
existing safe practice in commercial source capsule design.
The information obtained in developing the proposed ORNL Source
Capsule Classification System, together with that obtained in the Source
Testing Program, has been made available to the American Standards
Association Committee to aid in the formulation of source design standards.
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After the initial testing of commercial sources was completed to help
determine the values used in the Source Capsule Classification System, 120
sources representing 37 commercial designs were tested to determine their
classifications. The results are arranged in Table 3 according to the
intended applications of the 37 designs. The results show that 70% of the
tested source designs intended for use with multicurie quantities of activity
(teletherapy, radiography, and neutron sources) are in the Class III ;
structural category while the remaining 30% are in the less 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 the Class III. These results indicate that the ranges of stress values
chosen for the structural classes are sufficiently narrow to distinguish
between applications on the basis of quantity of radioactivity but are not
too narrow to allow a wide variety of classes within one application
category. The fact that all of these sources are in Class II or III indicates
that manufacturers are providing more than minimum safety standards in their
products.
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Table 3. Trial Classification
of Representative Commercial Sour ces
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Application
Class
Number of designs
· Teletherapy
Teletherapy
IIIB
IIIC
Gages
Gages
IIIB
IIC
IIB
IIA
Gages
Gages
Radiography
Radiography
Radiography
Radiography
Neutron.
Neutron
IIIC
IIIB
IIC
IIB
..:: .. 1790
ow wio
IIIC
IIA
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The temperature classes of the source designs in Table 3 are more
varied and do not show definite relationships either to quantity of isoto pe
or source application. This result was expected because the testing
program during the development of the Source Capsule Classification System
had shown a rather wide variation of temperature resistance. The four
source designs falling in Class A, which has the lowest temperature require-
ments, were sealed by solder.' Since the temperature classification ranges
were selected to restrict solder-sealed sources to Class A, the system is
effective in this regard."
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A second follow-up program of testing commercial sources is now in
progress. These sources were selected from the 37 commercial designs listed
in Table 3. The results of the current tests will be compared with results
of the previous tests made on identical source capsules in order to ensure
that the classification testing procedures are reproducible over an extended
period of time. Of the ten source capsule designs tested thus far, two have
failed to pass all of the structural tests required by their original classi-
fication. One of these, a cesium radiography source, did not contain an
inactive substitute for the radioactive material, which may account for its
failure to pass one test, the impact test. The failure of the other, a
krypton gage source, has not as yet been explained.
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REFERENCES
1. J. A. Jones, "Fabrication of Cesium-137. Sources," USAEC Rpt. ORNL- :
3675, Oak Ridge National Laboratory (September 1964).
2. E. E. Pierce, "Remote Welding of Stainless Steel Capsules," USAEC
Rpt. ORNL-2280, Oak Ridge National Laboratory (March 1957).
3. C. R. King, "Vacuum Leak Testing of Radioactive Source Capsules,".
USAEC Rpt. ORNL-3664, Oak Ridge National Laboratory (January 1965).
TABLE LIST
Table 1. Proposed ORNL Source Capsule Classification System
Temperature Characteristics
Table 2. Proposed ORNL Source Capsule Classification System
Structural Characteristics
Table 3. Trial Classification of Representative Commercial Sources
FIGURE LIST
Figure 1. Equipment for forming and encapsulating pellets.
Figure 2. Pemotely operated source capsule welder.
Figure 3. Section of a dummy international standard teletherapy source..
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DATE FILMED
3/ 7 / 66