The C38 Mysteron detector is a portable Roentgen radiation ("x-ray") camera used to detect Mysteron likenesses.
How the detector's base principle was discoveredEdit
The principle behind the Mysteron detector was discovered accidentally, when the Mysterons's likeness of Dr. Theodore Magnus attempted to assassinate General J. F. Tiempo in "Operation Time." The original Theodore Magnus, a neurosurgeon, was one of the few physicians who still relied on x-rays in the 2060s.
(The Mysterons's intended weapon against Tiempo was a cerebral pulsator of the original Dr. Magnus's own design, which apparently worked by generating microwaves with two electrodes that were attached to the patient's scalp. These would then bombard the brain tissue at which the electrodes were aimed, burning and thereby necrotising it out of the brain. If the microwave intensity was adjusted too high, however, as the Magnus likeness did, they would instead turn the entire brain into what amounted to cooked meat.)
The Magnus likeness brought his hand in front of the x-ray camera when shooting the last picture of Tiempo. After the x-ray film was developed, the image of the Magnus likeness's hand and forearm gradually became visible in monochrome, clearly blocking the area that was being x-rayed. One of the assistants of the original Magnus noted this at first with annoyance, then with growing horror. For it indicated that a Mysteron likeness would be impervious to Roentgen radiation.
How the detector worksEdit
The detector works by projecting Roentgen radiation at a suspected Mysteron likeness whilst its user shoots a photograph of the same. After not longer than five seconds, the image has developed and is printed. If the subject is a normal Earthman, the printed image will show a skeletal view; if a Mysteron likeness, it will show a photographic view in monochrome. Since Captain Scarlet was once under Mysteron control, his body has become impervious to Roentgen radiation, and hence use of the detector on him will produce a positive result, making him an ideal "control" subject for its use. Indeed, this has enabled fan-fiction writers to speculate that Mysteron detectors are calibrated by using them on him whilst he is standing side by side with another Spectrum senior officer.
Owing to the Law of Inverse Squares, the maximum practical range of the detector is approximately fifty yards, or roughly fifty metres. The Mysteron rifle has a similar such effective range.