The Dial Painter Dose Rates Revisited

Corrected bad radium half-life, 2024-06-01.

Figure 1. Dial Painter Time to Diagnosis, Ref. \cite{rowland-1996}}

This piece is a follow on to The Radium Dial Painters and SNT. It assumes familiarity with both the SNT radiation harm model, and the radium dial painter experience. It borders on technical trivia. It indicates that SNT is not quite as conservative as I had claimed earlier, but still quite conservative.

Figure 1 may be the most interesting of all the radium dial painter graphs. It shows the time to diagnosis of all the bone cancers as a function of cumulative dose. Focus on the circled, upper left hand square. This lady was diagnosed with bone cancer 63 years after receiving a dose of 13 Gy (~208,000 mSv). Her average dose rate for that period was just over 9 mSv/day. All the other cancer victims had average dose rates that were at least four times higher.

SNT and any reasonable radiation harm model needs to know the dose rate profile. Unfortunately, the dose rate profile is almost never recorded, only as in this case the cumulative dose, an almost meaningless number. However, we can made a very rough guess at her profile.

The ladies licked their brushes between about 1915 and about 1925, after which the practice was strongly discouraged. The dial painter study ended in the 1980's; and this woman had been studied for at least 63 years. Let's assume she built up her radium evenly for ten years, and then the build up stopped. Ra-226 has a decay half-life of 1620 years. It's a non-factor. However, the biological half-life in bone is about 40 years. So the radium was leaving her body at that rate. If in addition we assume an uptake rate, we have concocted a dose rate profile for this lady.

Figure 2. Possible dose rate profiles for subject lady.

Figure 2 shows four such profiles. If the uptake rate is 0.0043 mSv/d (the green curve), the cumulative dose is about 208,000 mSv which matches the Argonne number. Under these assumptions, this woman experienced a dose rate of over 10 mSv/d for about 25 years. This is the lowest dose rate that clearly resulted in radiation induced cancer that I have found in the literature.

According to SNT, this dose rate profile has a probability of cancer incidence of just under 50%. In fact, this woman was the only lady out of over one hundred who suffered cancer at this dose rate. Based on this analysis, SNT is highly conservative, but not outrageously so.

This analysis also supports the ICRP/NCRP pre-1950 tolerance dose of 2 mSv/d. Lauriston Taylor's 1980 statement that

No one has been identifiably injured by radiation while working within the first numerical standards first set by the NCRP and then the ICRP in 1934. [2 mSv/day]

is intact.