Definitions
Sealed Source:
Radioactive material sealed in a capsule that is strong enough to prevent dispersion of the radioactive material under the conditions of use for which it was designed. Also an assemblage of sealed sources in array utilized in an irradiator. (IAEA Safety Series No. 107, 1992)
Activity:
Activity of sources is expressed as “equivalent activity” defined as the activity equal to the activity of a point source of the same radionuclide which gives the same exposure rate at the same distance from the centre of source.
Activity tolerance: ± 10%.
Source Working Life:
The “recommended working life” (RWL) is our recommendation of the period within which the source should be replaced.
This information is given in the Test Report. The period has been assessed on the basis of such factors as, toxicity of nuclide, total initial activity, source construction (capsule design, source insert type, etc.) half-life of nuclide, typical application environments, operational experience, test performance data.
The relationship between equivalent activity and exposure rate is different for each radionuclide, depending on the type and quantity of radiation emitted in each nuclear transformation.
The equivalence between the old and the new units
| Nuclide | Equivalent Activity | Exposure Rate at 1 Meter | Absorbed Dose-rate in Air at 1 Meter (approx.) |
| Cobalt-60 | 1 Ci | 1.30 R/h | 11 mGy/h |
| Iridium-192 | 1 Ci | 0.48 R//h | 4.2 mGy/h |
ICRU have approved the following SI units for radioactivity and absorbed dose
| Physical Quantity | SI Unit | Traditional Unit | Relationship |
| Radioactivity | Becquerel (Bq) | Curie (Ci) | 1 Ci = 3.7×1010 Bq 1 Bq = 2.70×10-11 Ci |
| Absorbed Dose | Gray (Gy) | Rad | 1rad = 0.01 Gy 1 Gy = 100 rad |
Sealed Source Performance Requirement for Typical Use
| SEALED SOURCE USE | SEALED SOURCE TEST AND CLASS | ||||
Temperature |
Pressure |
Impact |
Vibration |
Puncture |
|
| Radiography-Industrial | |||||
| 1. Unprotected Source | 4 | 3 | 5 | 1 | |
| 2. Source in Device | 4 | 3 | 3 | 1 | 3 |
| Medical | |||||
| 1. Radiography | 3 | 2 | 3 | 1 | 2 |
| 2. Teletherapy | 5 | 3 | 5 | 2 | 4 |
| 3. Needles / Implants | 5 | 3 | 2 | 1 | 1 |
| 4. Surface Applicators | 4 | 3 | 3 | 1 | 5 |
| Medium and High Frequency γ -Gauges | |||||
| 1. Unprotected Source | 4 | 3 | 3 | 3 | 3 |
| 2. Source in Device | 4 | 3 | 2 | 3 | 2 |
| Low-energy ß, γ or Fluorescence Analysis X-ray-source Instruments (Excluding Gaseous Sources) | 3 | 3 | 2 | 2 | 2 |
| Radioactive Carottage | 5 | 6 | 5 | 2 | 2 |
| Portable Moisture Density Gauges (Incl. Hand-held and Dolly Transported) | 4 | 3 | 3 | 3 | 3 |
| General Neutron Source Application (Excluding Reactor Start-up) | 4 | 3 | 3 | 2 | 3 |
| (MSZ 14339/2.) | |||||
Classification of Sealed Sources
| Test | Temperature | External Pressure | Impact from 1 m | Vibration | Puncture from 1 m |
| 1. | No test | No test | No test | No test | No test |
| 2. | -40°C (20 min) +80°C (1 h) | 0.025 MPa to atmospheric pressure | 50 g | 3 x (10 min) 25 Hz to 500 Hz at 49.05 m/s2 (5g) peak acceleration amplitude | 0.001 kg |
| 3. | -40°C (20 min) +180°C (1 h) | 0.025 MPa to 2.0 MPa | 200 g | 3 x (10 min) 25 Hz to 50 Hz at 49.05 m/s2 (5g) peak amplitude and 50 Hz to 90 Hz at 0.635 mm amplitude peak to peak and 90 Hz to 500 Hz at 98.1 m/s2 (10g) peak acceleration amplitude | 0.01 kg |
| 4. | -40°C (20 min) +400°C (1 h) and thermal shock 400°C to 20°C | 0.025 MPa to 7.0 MPa | 2.0 kg | 3 x (10 min) 25 Hz to 80 Hz 1.5 mm amplitude peak to peak and 80 Hz to 2000 Hz at 196.2 m/s2 (20g) peak acceleration amplitude | 0.05 kg |
| 5. | -40°C (20 min) +600°C (1 h) and thermal shock 600°C to 20°C | 0.025 MPa to 70 MPa | 5.0 kg | 0.3 kg | |
| 6. | -40°C (20 min) +800°C (1 h) and thermal shock 800°C to 20°C | 0.025 MPa to 170 MPa | 20.0 kg | 1.0 kg |
Controls
Testing for Leakage Contamination
The standard methods used routinely for each source are as follows
Wipe Test “A”
The source is wiped with a swab moistened with distilled water. The activity removed must not exceed: 185 Bq (0.005 ľCi).
Ultrasonic Test
The source is placed in a reservoir of an ultrasonic equipment for 1 hour. The equipment must guarantee at least 40 watts as output. The activity of the handling solution measured after the testing procedure must not exceed 185 Bq (0.005 ľCi). Sources found to be free of contamination and leak are held for seven days and retested.
Ultrasonic Test “A”
The handling solution in the reservoir is 1.5 mol/l HNO3
Vacuum Bubble Test
Using analytical reagent grade ethylene glycol, water, or oil as the leak-test fluid in a suitable vacuum chamber, lower the air pressure to atmospheric and submerge the sealed source to depth of at least 5 cm below the fluid level. Reduce the absolute pressure in the chamber to 15-25 kPa. Observe for bubbles emanating from the sealed source over a period of not less than 1 min. If none are observed, the sealed source is considered to have a leak-rate less than 1.33×10-6 Pa m3/s and is considered to be leak-free.
Prototype Test
Besides the individual tests each type of the source capsules is tested by the prescription of the Hungarian standard MSZ 14339/2, which is based on ISO 2919 (Sealed radioactive sources Classification) and fully corresponds to ST CMEA 3839-82.