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Contained Source Radiation
Safety Training
Module 7: Working Safely with Contained
Sources
Types of Contained Sources
Category - A
Category - B
Category - C
Category - D
Characteristics of Contained Sources and Their Radioisotopes
General Guidelines and Requirements for the Safe Use
of Contained Sources
Specific Requirements for Category B & C Sources
Source Modification
Security
Leak Testing and Source Recertification
Radiation Incidents
Types of Contained Sources (top)
Contained sources of radioactive material come in a variety of activities and configurations. To better address the varying hazards, the Radiation Safety Committee has established four categories (A, B, C, D), each with specific requirements governing their use.
Every contained source used at Princeton University has been assigned to one of the following categories.
Contained Source Category-A (top)
These sources contain very small amounts of radioactivity, defined as 'exempt quantities' (as set forth in 10 CFR 30.18). Examples of such sources are the 0.01 µCi Sr-90 sources used for cloud chamber experiments in the Physics Department instructional labs and 1 µCi Cs-137 plastic disk sources often used as instrument check sources.
Contained Source Category-B (top)
These sources contain activity in excess of exempt quantity (see Category A) but contain activity such that leak testing per 10 CFR 39.35(e) is not required. Category B sources do not meet the criteria for registered sealed sources (see Category D).
Contained Source Category-C (top)
These sources contain activity in excess of exempt quantity (see Category A) but contain activity such that leak testing is required. Category C sources do not meet the criteria for registered sealed sources (see Category D).
Contained Source Category-D (top)
These sources meet the US NRC criteria for registered sealed sources. These are sources designed, constructed and rigorously tested such that leakage and source damage is extremely unlikely.
Characteristics of Contained Sources and Their Radioisotopes
(top)
The contained sources referred to in this set of modules consist
of radioactive material that is encased in metal or plastic as in Figure 1 or radioactive material that has been plated as
a thin film onto metal or plastic as in Figure 2. Figure
3 shows various types of contained sources. Because the radioactivity
is encapsulated or plated onto a surface, contained sources do not present
a significant contamination hazard under normal conditions. However,
contained and plated sources may present an external exposure hazard, depending
on the properties of the radioisotope or the amount of activity present. Under certain conditions, contained sources may present contamination hazards as well.
The University's Radiation Safety Committee has introduced Contained Source Categories (A, B, C, D) each with its own set of requirements. The categories are described above.
While most contained sources are stand-alone sources used to calibrate
or check instrumentation, to irradiate materials, or for experiments
in student science labs, sometimes analytical equipment such as gas
chromatographs and liquid scintillation counters contain sources.
The persons responsible for such equipment should be aware of the presence
of contained sources.
Fig.
1
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Fig. 2
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Fig. 3 |
Decay Schemes
The radioisotopes listed in the following tables are among the most
common used in contained sources at Princeton University. Detailed fact
sheets for each of these radioisotopes, as well as many other radioisotopes,
are available upon request from EHS.
Radioisotope |
Half-Life |
Significant Radiations |
Comments |
| Sodium-22 |
2.6 yr |
0.54 MeV positron; 0.51 and 1.27 MeV gammas |
High beta and gamma dose rates |
| Iron-55 |
2.7 yr |
Various low energy x-rays and Auger electrons (<6 keV) |
Does not present a significant external hazard |
| Cobalt-57 |
271.8 days |
Gammas (< 0.13 MeV) |
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| Cobalt-60 |
5.3 yr |
0.31 MeV beta; 1.17 and 1.33 MeV gammas |
High beta and gamma dose rates |
| Nickel-63 |
100 yr |
0.066 MeV |
Beta does not present a significant external hazard |
| Strontium-90 |
29.1 yr |
0.54 MeV beta from Sr-90; 2.26 MeV beta from Y-90 |
Decays to short-lived Y-90; very high dose rates |
| Cesium-137 |
30.1 yr |
0.51 MeV beta; 0.661 gamma from Ba-133m |
Decays to short-lived Ba-133m |
| Polonium-210 |
138.4 days |
5.3 MeV |
Alpha does not present a significant external hazard |
| Radium-226 |
1600 yr |
4.8 MeV alpha; various alphas, betas and gammas from decay products |
Decays to Rn-222, with a long decay chain following |
| Americium-241 |
432.7 yr |
5.6 MeV alpha; various alphas, betas and gammas from decay products |
Decays to long-lived Np-237, decaying in turn to Pa-233 and U-233.
Alpha emissions are the greatest concern. |
Dose Rates
Radioisotope |
Beta dose rate at 30 cm from source*
(millirem/hr per millicurie) |
Gamma dose rate at 30 cm from
source (millirem/hr per millicurie) |
Sodium-22 |
370 |
13.3 |
Cobalt-57 |
0 |
0.94 |
Cobalt-60 |
48 |
14.4 |
Strontium-90 |
740 |
0 |
Cesium-137 |
777 |
4.1 |
Americium-241 |
0 |
0.56 |
General Guidelines and Requirements for the Safe Use of Contained (top)
The following guidelines incorporate the classic techniques of minimizing
time, increasing distance and using shielding to minimize radiation
exposure. Increasing distance from a source is an effective way to minimize
dose because radiation intensity follows the inverse square law:
The Inverse Square Law
The intensity of radiation emitted
by a radioactive point source follows the inverse square law,
i.e., as distance from a point source increases, the intensity
decreases proportionally to the square of the change in distance.
For example, if the dose rate is measured to be 10 millrem/hour
at 10 cm from a point source, the dose rate at 20 cm from the
source will be 2.5 millirem/hour:
Dose rate at 20 cm = 10 mrem/hr x (10 cm/20 cm)2
= 2.5 mrem/hour
Consequently small changes in distance
near a source mean large changes in radiation exposure.
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Handling the Source
- Minimize the time spent handling a source or in the vicinity of
a source.
- Do not touch the active surface of a plated source with your fingers.
- Wash hands after handling a plated source
Eating & Drinking
You are not permitted to eat or drink in rooms where contained sources are
used or stored.
- NJ Department
of Environmental Protection regulations prohibit eating and drinking
in areas where state-licensed radioisotopes are used or stored.
- In 2006 a Sr-90 contained source was breached which resulted in contamination throughout a laboratory and contamination of the user's hands. This incident confirms the necessity for ensuring that food and beverages are not consumed in a lab in which contained sources are used.
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Labeling Sources
- Contained sources must be labeled with a Caution:
Radioactive Material label that lists the radioisotope, the
amount of radioactivity, and the date the source was fabricated.
Shielding and Radiation Surveys
- Use appropriate shielding. Gamma and x-ray emitters should be shielded
with lead. Because bremsstrahlung
production is a concern with beta emitters, beta emitters should be
shielded with a primary shield of plexiglas or similar low Z material.
If sufficient bremsstrahlung is produced in the low-Z primary shield,
a secondary shield of lead should be placed outside the primary shield.
- High activity sources in storage must be shielded appropriately
when is use or in storage.
- Sources should be stored away from normally occupied areas
- If you are uncertain about whether a source should be shielded or
is sufficiently shielded, contact EHS to perform a radiation survey.
Radiation survey meters
Radiation
survey meters are required to be calibrated once a year. EHS performs electronic calibrations of portable Geiger-Muller
and scintillation meters and arranges for off-site calibrations
of exposure rate and dose rate meters. The calibration date
and the date that the next calibration is due is posted on a label
on the side of the meter. Do not use meters that are out
of calibration. If you find a meter that is out of
calibration, contact EHS.
Before you use a survey meter, perform
a pre-operational check. The pre-operational check consists
of:
- a battery check
- a background check (background for a G-M meter should be
25-75 cpm; background for a scintillation meter should be
200-300 cpm)
- verifying that the meter has been calibrated within the
last 12 months
- a performance check using the check source attached to the
side of the meter. The expected check source reading
is posted on the calibration label on the side of the meter.
If the meter does not read within +20% of the expected
check source reading, do not use the meter. Contact
EHS to arrange for repairs.
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Cloud Chamber Sources
Radioactive sources used in cloud chamber experiments typically are
rods or needles plated with very small amounts of Sr-90 (for beta activity)
or Po-210 or Pb-210 (for alpha activity). The activity of these sources
is low enough that shielding is not necessary, but it is important to
handle the source by holding the cork, rather than by touching the needle
part of the source on which the radioactivity is plated.
Specific Requirements for Category B & C Sources (top)
Category B & C source users must comply with additional requirements per the University's Contained Source Use Policy. The requirements have been instituted to prevent excessive radiation exposures due to loss of radioactive material and potential contamination of laboratory facilities and personnel. The following requirements apply only to Category B & C sources; Category D sources are so rigorously tested that damage is extremely unlikely.
- An inspection of the source must be conducted to identify damage to the potentially fragile active surface of the source.
- In order to verify the physical integrity of a source, each contained source user must conduct a visual inspection of the source prior to each usage where such an inspection is practicable.
- Visual inspection is considered to be practicable, for instance, where the source is readily accessible or where such an inspection would not require unauthorized dismantling of the source or its holder.
- Particular attention should be paid to any fragile surfaces (e.g., foil, surface emission material).
- Mirrors may be used to avoid looking directly into a source.
- If there is any doubt about the integrity of the source, the user must immediately cease handling/use of the source and must immediately contact EHS.
- Disposable Gloves must be worn whenever directly handling category B & C radioactive sources and/or source assemblies.
- A handheld survey meter must be available in the research area capable of detecting the radiation associated with the source in use (for other than alpha-emitters). The user must perform a post-use contamination survey following each instance of direct handling of the source or source assembly.
DON'T FORGET - YOU MUST DOCUMENT YOUR SURVEYS (Radiation Survey Form)
Anyone seeking an exception to these requirements must apply to the Radiation Safety Committee (Contact the RSO for an application).
Source Modification is Strictly Prohibited (top)
Contained sources must be used as designed by the manufacturer and are not permitted to be dismantled, opened or otherwise modified unless application has been made to the RSO, and written approval has been granted.
Applications for modified use of contained sources must be submitted to the Radiation Safety Officer (RSO) for review. Applications will be reviewed, at a minimum, by the RSO and may require approval by the Radiation Safety Committee prior to approval.
Security (top)
Contained sources are typically small in size and may be readily portable.
It is important to pay extra attention to ensuring that contained sources are secured.
Princeton University policy for securing radioactive materials requires
that:
- Contained sources must be locked in a secured container or
secured storage area when not in use.
- Any room in which an contained source is being used must be
locked when unattended.
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Leak Testing and Source Recertification (top)
Under the terms of the University's NJ
Department of Environmental Protection (NJDEP) license, EHS must
perform leak tests of Category C and D contained sources to ensure that the
integrity of the source encapsulation is intact. Such leak tests are
required at three- or six-month intervals depending on the nature of
the source. Leak testing is not required for some low-activity sources,
for example, if they contain 100 microcuries or less of a beta/gamma-emitter
or 10 microcuries or less of an alpha-emitter.
5-Year Source Use Review
EHS will conduct an assessment of the condition of Category B, C and D sources every five years. For each source, this assessment will include an interview with the researchers to determine the frequency and method of use of the source, verification that the source is being used as authorized, and must include a visual inspection of the source where practicable and where such inspection does not result in significant radiation exposure.
The interview portion of the assessment will also be conducted when authorizations are transferred to new Authorized Users or when there is a change of faculty responsible for instructional labs.
10-Year Source Recertification
EHS will recertify Category C and D sources every ten years. The recertification program shall consist of a leak test, a visual inspection of the source where practicable and where such inspection does not result in significant radiation exposure, and a review of the source’s use to determine the frequency and method of use. If the RSO determines that the source can continue to be safely used and that a need for the source can be reasonably anticipated before the next recertification date, the RSO will issue a Source Recertification Form which will be maintained in the source file.
If you suspect that a contained source has been damaged, notify
EHS and do not use the source until EHS has leak tested the source.
Radiation Incidents (top)
Missing source
If you
discover that a contained source is missing, notify EHS
promptly at 8-5294. Once you suspect that a source is missing,
it may be reasonable to take a short time to attempt to find it, but
do not take more than a few hours to notify EHS. Under some circumstances,
the University must notify the NJDEP when a radioactive
source
cannot be located. EHS will make the determination whether notification
is necessary and will assist in efforts to locate the source.
Overexposure to a Source
If you suspect that you have been received a significant exposure to
a radioactive source, contact EHS immediately at 8-5294.
Emergency Response Guidelines
For assistance in dealing with a radiological or chemical incident
or any other incident, consult the Emergency Response Guidelines for
Laboratory Personnel, which are posted in each lab.
Contacting EHS Outside of Normal Business Hours
Call Public Safety at 8-1000. Public Safety will contact EHS personnel
though home or cellular phones.
This is the end of the Working Safely with Contained Sources
Module, which is the seventh of the eight Contained Source Radiation Basics
modules. If you work with the americium-beryllium source, go to the next module. If you do not work with the americium-beryllium source, you may now go to the test or you may go to any of the previous modules::
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