Tri-X anomaly during 1950s photography

[Peter Kuran]

Tri-X anomaly in photographing nukes in the 1950's

I have been working on a project for a few years now in researching atomic testing photography from the 1950s and 1960s. There is a certain type of photography done on a camera called the Rapatronic which was developed by EG&G (Doc Edgerton's company). The Rapatronic took single shots. Two type of rapatronic cameras were developed. The original camera which has a basic exposure of 4µsec photographs the image onto a 3x4 glass plate. The newer Rapatronic (developed in 1956-1957) had a basic exposure of 5µsec and was imaged on 3x4 sheet film.

On all of the sheet film negatives, there are additional images of what looks like what is called a "corona discharge" or similar to krilian photography around the blast. I believe this is in the UV range and if photographed in color, would be bluish purple. However, this additional imagery shows up only on the sheet film at 5µsec exposure whereas the same image, shot with the same focal length lens, same film type (Tri-X) on glass and NO FILTRATION on either, does not show this anomaly at all. Not even a hint of it.

Is it possible that the Tri-X sheet film and Tri-X glass plate react to images and spectrum differently, especially in the UV range that would explain why anomaly shows up on one but not the other. Is the difference between a 4µsec and 5µsec exposure that great? Maybe 1/3 of a stop difference? Any thoughts?