Source Fails to Return on the Second Exposure

First, the physics, because it drives everything else. 2 R/h at 10 ft is what a fully exposed 40 Ci Ir-192 source produces (0.48 × 40 / 3.05² ≈ 2.1 R/h). So the working assumption is that the source is out of the shield and in the guide tube or on the ground.

Boundary: d = 10 ft × √(2000/2) = 10 × 31.6 ≈ 316 ft, so post at about 320 ft (roughly 100 m) for a 2 mR/h line. That is most of the station yard, so plan on using the station fence and the road as the physical limit and control the gate.

Actions, in order:

1. Stop. Do not crank further, do not touch the guide tube, do not try to reseat the connector by hand.
2. Move the assistant, the radiographer, and the welder's helper away, upwind if there is any possibility of airborne contamination, to beyond the boundary.
3. Post the boundary, control the gate, and keep someone at the control point so no one wanders in.
4. Call the RSO and licensee management immediately, and have the assistant's direct-reading dosimeter read and recorded before it is reset.
5. Keep the survey meter running at the control point; log readings and times.
6. Do not attempt recovery with the crew's own resources unless the RSO directs it and the equipment for it (shielded container, long-handled tools, additional shielding, functioning meters with correct alarm set points) is on site.

Dose estimate. At 5 ft the dose rate is 2000 mR/h × (10/5)² = 8,000 mR/h. For 45 seconds: 8,000 × (45/3,600) = 100 mrem - 0.1 rem, or about 1 mSv. Confirm against her direct-reading dosimeter and her TLD, and note that whole-body badge results lag by weeks, so the pocket dosimeter reading is the number you act on tonight.

Reporting. 0.1 rem is well below the thresholds that trigger immediate or 24-hour notification (the 25 rem and 5 rem criteria), so this is not an NRC or Agreement State event report on dose grounds. It is also not an overexposure against any limit. What it must be is:

• Recorded on her exposure record and in the event file, with the basis of the estimate.
• Reviewed as part of the event investigation, because the dose came from a procedural failure, not from the radiation.

Investigate specifically:

• Why the assistant's first instinct was to walk up to an exposure device whose crank had just gone slack. That is the training failure, and it is more important than the mechanical failure.
• Whether the guide tube connector was fully seated and whether the guide tube was bent tighter than the manufacturer's minimum bend radius, which is a common cause of a source hanging up or a connector popping.
• Whether the crank was forced at any point, which can push a disconnected source out of the guide tube entirely.

Also confirm nobody else received dose - the welder's helper at 25 ft was in a much lower field, but calculate it rather than assume, and check whether they were wearing a dosimeter at all.

Approach:

1. Characterize before touching. Survey the trench bottom, the guide tube run, and the ground around the camera with a long probe and the meter on its most sensitive range, working from outside in. Locate the source before anyone goes near it.
2. Assume time, distance, and shielding, in that order. Rotate personnel so no one accumulates meaningful dose, use the longest tools available, and place temporary shielding between the source and the workers where the geometry allows.
3. Bring the shield to the source, not the source to the shield. Lower the shielded container over the source if it is on the ground, rather than picking it up and carrying it.
4. Two-person rule with real alarm set points. Working alarm dosimeters set well below the administrative dose limit, plus a second meter watching the first operator.
5. Re-survey continuously. Every move gets a reading before and after, and the readings go in the log with distances and instrument identification.
6. Containment check. Once the source is back in a shield, wipe test the tools, the area, and the container before anyone leaves; a source that has been out of its shield and has been dropped, dragged, or driven over may no longer be leak-tight.

Stop and escalate if:

• The source cannot be located or is buried/under equipment where no safe geometry exists.
• The source capsule appears damaged, or wipe tests show removable contamination that you cannot control.
• Recovery would require an individual to take a dose you cannot justify against the administrative limits.
• The equipment on site is not adequate to keep the container over the source.

In any of those cases, keep the boundary and surveillance in place, notify the licensee and the regulatory agency, and bring in the manufacturer or a qualified recovery contractor. A stuck source that is contained and guarded is a bad night; an improvised recovery by a tired crew at 03:00 is how a bad night becomes an accident. The written follow-up should record the crank failure, the boundary, all survey readings, all doses, and the root cause.