radiation and photographic film
Home page

If you have not yet read the radiation primer, you are invited to do so.

David Groves, PhD, has shown that the x-ray environment of space would quickly render any photographs unusable. [Bennett and Percy, Dark Moon, p. 540]

Dr. Groves' study contains a number of serious errors.

Although Dr. Groves gives figures for the x-ray dosage to which he submitted his test films, he does not in any way show that this is the expected amount of x-ray energy that exists anywhere in cislunar space or on the lunar surface. This key omission makes Dr. Groves' study of questionable applicability.

Dr. Groves used a Bronica ETRSi 120 roll film camera in his tests. He does not explain why he did not use a Hasselblad EL/500 or EL/700 camera, the type of camera supplied to NASA for use in the Apollo missions. It is still manufactured by Hasselblad and suitable period examples of which can be obtained easily from second-hand dealers. Use of a dissimilar camera limits the extent to which Dr. Groves' results can be applied to Apollo photographs.

Further, Hasselblad claims they added additional protection to the film magazines. Dr. Groves does not document any similar changes he may have made to the film magazine of his test camera. Nor does he comment upon the possible effect of any of those modifications. Dr. Groves' inattention to the specifics of the Apollo camera design questions his ability to accurately simulate the effects of x-rays on Apollo film.

Dr. Groves first took pictures of a standard color chart, then bombarded that film with x-rays. Then he used standard procedures to develop the film and observe the results. He found that the images were significantly fogged in some cases, and completely obliterated in more extreme cases.

He provided absolutely no shielding around the film during its exposure to the x-rays. It is unclear whether he left the film inside its magazine as the Apollo astronauts would have done. Since the Hasselblad magazines were modified to provide thicker material for the casing, and the film was kept in the magazines during the entire mission, it is not clear whether Dr. Groves' procedure constitutes an adequate comparison.

What is clear, however, is that Dr. Groves exposed the film to x-rays thousands of times more intense than what occurs in space. He used a linear accelerator to bombard the film with an 8 MeV (million electron-volts) beam of x-rays. X-ray astronomers say the x-rays from celestial sources radiate at energy levels of less than 5 keV (thousand electron-volts). The measurement of x-ray energy is similar to the rating of light bulbs by wattage. The difference between five thousand electron volts -- ambient x-rays in space -- and eight million electron-volts -- Dr. Groves' experiment -- is obviously very large. This factor alone invalidates Dr. Groves' study as an accurate depiction of the ambient x-ray conditions in space.

Dr. Groves exposed his film to x-rays more than a thousand times more energetic than occur in space.
Energy level is quite important. Not only do more energetic x-rays fog film to a greater extent, they also penetrate various substances to a greater extent. This makes the question of shielding very acute. 3 keV x-rays, for example, will not even penetrate air for more than a dozen centimeters.

The experiment subjected the film to three levels of exposure, all at the absurdly intense 8 MeV energy level. The levels are given in the study as "25 rem", "50 rem" and "100 rem". Those who have read the primer and studied the nomenclature of radiation will immediately realize that this is the wrong unit. "Rem" applies only to absorbed radiation in human tissue. It is completely inapplicable to radiation absorbed by photographic film. The appropriate unit of measure for this study would be either "rads" or "Grays". It so happens that for x-rays 1 rad is equivalent to 1 rem, but Dr. Groves' apparent misunderstanding of the concepts of absorbed dose is very much out of place in a study purporting to give an expert opinion on radiation exposure.

If we graciously correct Dr. Groves' error of nomenclature and assume he means exposures in rads, we are still faced with two further questions. First, how was absorbed dose computed? It is notoriously difficult to measure the amount of radiation actually absorbed by any given substance.

Second, the 25-100 rads to which Dr. Groves exposed the films is quite excessive. It would take nearly six years in a spacecraft in cislunar space -- barring any serious solar events -- to absorb 25 rads of dosage from all sources combined, not just from x-rays.

Dr. Groves' study contains far too many egregious errors to be considered predictive in any way of the behavior of Ektachrome film under the conditions experienced during Apollo space flights. He has employed levels of radiation far in excess of what can be defensibly claimed for ambient x-ray radiation in cislunar space.

Prev Next