Wednesday, May 27, 2009
It seems that what was used in the aircraft dials was a radioluminescent paint, i.e. one that contains a radioactive isotope combined with a radioluminescent substance. It appears that the radioactive isotope used was radium-226, although is undermined by a parallel claim (in Wikipedia) that the preferred emissions were beta particles because they do not penetrate an enclosure (e.g. the glass cover of the dial). Unfortunately, radium-226 is an emitter of alpha particles, which certainly cannot penetrate glass. However it takes 6 mm of aluminium to stop beta particles. So my guess is that it was radium-226 that was the radionuclide.
According to Wikipedia, the dangers in using Ra-226 were recognized in the 1920s and 30s and were replaced by safer alternatives (‘progressively’) in the ‘second half of the 20th century’ (i.e. after the war). So when were these luminous dials made? Rob Edwards’s 1997 article (New Scientist) claims that radium-226 was used before 1960 in paints to make aircraft dials glow in the dark.
Ra-226 decays into radon (Rd) 222 by alpha particle emission and Rd-222 is also an alpha particle emitter.
Ra-226 also results from the decay of U-238 (U-238>Th-234>Pa-234>U-234>Th-230>Ra-226). Ra-226 decays to stable lead via its ‘daughters’ (Ra-226>Rn-222>Po-218>Pb-214>Pb-210>Bi-210>Po-210>Pb-216).
Instruments are available that will record various alpha, beta and gamma emissions, but they will not identify the radionuclide responsible. There are hand-held instruments available for radionuclide identification but they are all gamma-sensing instruments (gamma spectrometers) that identify respective radionuclides by the energies of the gamma rays emitted and detected. It seems that all radioactive decay is accompanies by some gamma radiation. Consequently, a gamma spectrometer could be used to identify radionuclides. However, this process could not tell how the radionuclide arose. I do not see how anyone could determine that a particular emission came from a natural radionuclide rather than an artificial one. Of course ‘artificial’ here merely means that the radionuclide was used in some product; it must have a natural origin ultimately.
Radium-226 has a half-life of about 1600 years.
Rd-222 has a half-life of only 3.8 days.
Ra-226 is one of the decay product of uranium or thorium
A layer of soil 30 cm deep and 1.6 km square would contain on average 1 g of radium (depends on locality, moisture content and the presence of buildings and roads. It would also contain ~3 tonnes of uranium and 6 tonnes of thorium. The Ra concentration is about one part in a trillion.
The radiation dose from typical ground is on average ~350 μSv per year.
[Neil - highlights are mine; since the "daughter" element of radium is radon (Rn) which is one the Noble gasses it could not be found mixed with radium & SEPA's claim is ridiculous; if they can't identify separate nuclides then they simply cannot say it isn't natural; 1,6km square is 1 mile square)]
Steuart Campbell is a science writer. He was in the LibDems indeed he was the other speaker in the Conference debate on nuclear I spoke at & found his membership untenable as they got less liberal & more Luddite. He is a regular contributor to the letter columns of the Scotsman in the pro-nuclear cause & a fellow member of SONE. He also rang in & spoke on the Radio Scotland programme where SEPA's lies started this investigation & I would like to thank him for the scientific facts which have so thoroughly proven SEPA's dishonesty.