7.1 TYPES OF SEALED SOURCES
A sealed radioactive source is a radioisotope that is fully encapsulated in metal or other container such that there is no contact between the radioactive material and the equipment. Sources commonly used in teaching and research are of the following types:
- Low activity beta or gamma sources, usually of activity in the range 1-10 KBq (0.03 - 0.03Ci), free-standing (i.e. not permanently installed in a specific equipment). Examples are I-129, Cl-36 and C-14.
- Low activity beta or gamma sources, permanently installed in an instrument such as a gas chromatograph or a liquid scintillation counter. Examples are Ra-226 and Cs-137 of activity 0.1 - 1 TBq (3-30 Ci) for liquid scintillation counters and Ni-63 of activity 100-500 MBq (3-15 mCi) for gas chromatographs.
- High activity gamma sources, usually Cs-137 or Co-60, permanently housed in an irradiator. The source activity in this case is usually at least 10 TBq (0.3 kCi) and may be considerably higher.
- Neutron sources such as Cf-252 or Pu-238/Be, which may be either free-standing or housed in equipment (eg. neutron activation equipment). Typical source activity is 0.3 - 1 TBq (10-30 Ci).
Every Permit Holder must establish and maintain an inventory of sealed sources in their possession. The inventory must include the following information (see Appendix J-2):
- Nature of each source, i.e. radionuclide, chemical form, physical form (e.g. tube, plaque, wire, with type of encapsulating material and approximate external dimensions), activity on a specified date.
- Whether the source is "free-standing" or permanently housed in an instrument or equipment. In the latter case: nature, manufacturer, model and serial number of the equipment.
- Location of each source, i.e. the number of the room in which a free-standing source is (a) stored and (b) normally used, if different from (a), and/or the normal location of any equipment housing a sealed source.
- Details, including date of the disposal or transfer of any source.
Permit Holders must ensure that all sealed sources in their possession are:
- protected at all times from loss or physical damage;
- in the case of "free-standing" sources, kept in a safe storage area when not in use. The storage area should be shielded so as to provide protection of the standard specified in Section 6.7. Low activity sources permanently installed in equipment such as liquid scintillation counters are normally provided with adequate shielding by the manufacturer;
- subject to yearly leak tests where the source activity in use is equal or greater than 50 MBq (1.35 mCi) or every two years for the radionuclide in storage or every six months for the free standing sealed source. This may be accomplished by means of a "wipe test" (see Sections 5.4 and 5.7) on the surface of the source and on the exposed surfaces of the equipment in the vicinity of the source. These leak tests should be performed as directed by the manufacturer. In the absence of this information, procedures must be written and approved by the CNSC prior to execution. The Permit Holder must maintain records of all leak tests carried out by Environmental Health & Safety.
Free-standing radioactive sources of any type or activity should be handled with care, using forceps and/or laboratory gloves rather than bare fingers. Where the activity of the source(s) and the nature and duration of the procedure warrant it, protection should be provided for the user.
Sources of high activity, permanently housed in apparatus intended for irradiating animals or cells or other materials, require special precautions, as follows:
- Irradiators must be fitted with a shutter or other mechanism which effectively shields the sources, when in the "off" position, so that any accessible area in the vicinity of the irradiator is protected to the standard set out in Section 6.7. Where this is not possible, an appropriate area surrounding the irradiator must be rendered inaccessible to non-authorized persons.
- When the sources are in the "duty" position, the "useful beam" of radiation must be either:
(a) completely inaccessible, i.e. the irradiator is fully enclosed and self-protected when in use; or
(b) inaccessible, such that the irradiator is housed in a shielded room, the floor of which is interlocked with the on/off mechanism. In the latter case, no irradiation may take place when any person is inside the room. The shielding of the room should be sufficient to comply with the requirements of Section6.7, taking into account the maximum "on duty" time per week of the irradiator; and the nature of the occupancy of the adjacent areas.
- Not withstanding any shielding or interlocks provided in the irradiator and/or the room in which it is located, users must take care at all times to avoid exposure of any part of their bodies to the direct radiation of sources in the "on" position.
- Leak tests on surfaces of the equipment in the vicinity of the source(s) must be carried out annually by Environmental Health & Safety and the results documented (see Sections 5.4 and 5.7 for further details).
- The dose-rate (Gray/minute) at a suitable and readily reproducible reference point in the irradiator should be measured annually, with the source(s) in the "on" position. When allowance is made for radioactive decay, such measurements provide an index of the continued integrity of the source(s) and of the on/off mechanism.