Archived posting to the Leica Users Group, 2000/01/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]1.5 milliroentgen is nominally less than the MPD (maximum permissible dose for radiation workers) established by the US National Council on Radiation Protection and Measurements. The MPD was 0.2 roentgen in 1931 and has been lowered in three occasions. Now it is 0.02 roentgen per workday. I used the word "nominally" because the way cameras are used, some parts of the body will receive more radiation and I think the standard is for whole body exposure. I caution that trying to arrive at conclusions from a single number like 1.5 mR is even riskier than trying to assign a single numerical score to a lens. There are many factors at work here, i.e. the camera body itself will give a measure of protection, the lens cap may also help protect the photographer when the camera is not in use, different organs will have different sensitivities to radiation and many, many other things. So it's very hard to estimate the real absorbed dose. Dr. Amilcar de Oliveira Oral Radiology Rio de Janeiro MGMcGough@aol.com wrote: > The LHSA VF article by Bill Gordon was a follow up on the findings by Dr. > Cyril Blood of the British LHS. Gordons test of the half dozen Summicrons > with S/Ns under 1,000,000 showed that the average front element emitted > 1.5 miliroengtens and if laid front down on an unexposed piece of film, > would leave a dark circle after about one week. This is far less radio- > activity then the radium dial wrist-watches of the past. I dont mean the > calcium disulfide luminous type but the radium dial Omegas & Rolexs. > > For many years, the Leitz management denied using radioactive thorium > but when confronted with the actual findings, finally admitted to it, along > with many more lens manufacturers, but the Leica pre-1M are the most > famous and command a premium price today even though the yellowish > brown tint of the lenses will discolor chrome films. > > Frau Doktor Mary Grace McGough > > In a message dated 1/27/00 2:28:04 PM Pacific Time, zeissler@wt.infi.net > writes: > > > > According to my wife [who does radioactive particle analysis for a living], > > distance would play a crucial role in whether the film was exposed or not > by > > the Thorium elements. According to her, the alpha particles would not > > expose film outside of a fairly short distance [~2 inches or less, > depending > > on some variables], while gamma particles would travel several yards. > >