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Tuesday, July 22, 2014

Radium Girls

Radium is a naturally-occurring element with the atomic number 88 (has 88 protons and electrons).  All known isotopes of Radium are radioactive, and so eventually all Radium will decay into something that is stable, such as Barium or Lead. 

Radium is a metallic element in the decay chain of naturally occurring Uranium and Thorium, a transient state as these elements eventually decay into stable elements.  For this reason, there is no primordial Radium. 

Minute quantities of Radium are found in Uranium ore, and that Radium is transient, being radioactive.  There are four naturally-occurring isotopes of Radium, of which Ra-226 is the most abundant, due to its long-ish half-life of 1600 years.  That is, in 1600 years, half of the original Radium-226 will remain.  The other half of the original Radium-226 will have decayed in a series of radioactive decays into Lead-206, which is stable.

Below is a description of the decay chain of Radium-226: 
Radium-226 decays to Radon-222 after emitting an alpha particle (helium nucleus) and a gamma ray.  Radon-222 is also radioactive, and will decay to Polonium 218 by another alpha/gamma decay.  This in turn alpha/gamma decays to Lead-214, with a half life of 23 minutes, which beta/gamma decays to Bismuth-214.  This is also radioactive, (19m half life)  and beta/gamma decays to Polonium-214.  Polonium 214 has a VERY short half life (164 microseconds) and alpha/gamma decays to Lead-210, which is STILL radioactive.  The Lead-210 has a half life of 22 years and beta/gamma decays to Bismuth-210.  Bismuth-210 has a half-life of 5.5 days and beta/gamma decays to Polonium-210.  Polonium-210 has a half-life of 138 days, and alpha decays into Lead-206, which is non-radioactive.

The reason I went to the trouble of looking up and describing the Radium decay chain is to explain why this stuff is so nasty.  If you are exposed to a single Radium-226 atom, you could conceivably get 5 alpha particle events, 3 beta particle events, and and 8 gamma rays.  That's a lot of biological damage for a single radioactive atom.  Because of the decay chains embedded in Radium-226, it has a very high specific activity  (disintegrations per second).  In fact, the original measure of radioactivity, the Curie, is 3.7 x 10^10 disintegrations per second, was based on the activity of Radium (mostly Radium-226).  That is 37 Billion radioactive decays in a single second!!!

This gives Radium some really cool, if dangerous, properties.  For one thing, it glows faintly blue, due to ionization of the surrounding air by all those nuclear decays.  When mixed with a chemical compound that emits light when struck by radiation, Radium-226 can make awesome glow-in-the dark paint, that will glow brightly, for as long as anyone is alive.  Tritium, a far safer nuclide, is used in modern watches, but its half-life is only 12.3 years, so the brightness will noticeably fade in less than a decade.

Below is an image of a Radium painted watch dial.  I really would love to have one of these!!!

Radium, because of its high activity, and tendency to emit several alpha particles in part of a decay chain, is dangerous to be around, unsheilded.  Recall minimizing the biological damage of each type of radiation is mainly a matter of shielding and distance.  You have neither of these if you ingest radioactive substances.  Which brings us (finally) to the topic at hand, the Radium Girls.

The story of the Radium Girls is slowly passing into the mists of history, which is quite a shame.  These were young women hired by the U.S. Radium Corporation to paint watch and clock dials with a glow-in-the-dark paint.  This paint was made from Radium and Zinc Sulfide, and which went by the trade name "UnDark".

From the website "Damn Interesting", by Alan Bellows:
In 1922, a bank teller named Grace Fryer became concerned when her teeth began to loosen and fall out for no discernible reason. Her troubles were compounded when her jaw became swollen and inflamed, so she sought the assistance of a doctor in diagnosing the inexplicable symptoms. Using a primitive X-ray machine, the physician discovered serious bone decay, the likes of which he had never seen. Her jawbone was honeycombed with small holes, in a random pattern reminiscent of moth-eaten fabric.

As a series of doctors attempted to solve Grace's mysterious ailment, similar cases began to appear throughout her hometown of New Jersey. One dentist in particular took notice of the unusually high number of deteriorated jawbones among local women, and it took very little investigation to discover a common thread; all of the women had been employed by the same watch-painting factory at one time or another.
From here I will turn things over to Wiki:
Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. A typical self-luminous watch that uses radium paint contains around 1 microgram of radium. In the mid-1920s, a lawsuit was filed against the United States Radium Corporation by five dying "Radium Girl" dial painters who had painted radium-based luminous paint on the dials of watches and clocks.

The dial painters routinely licked their brushes to give them a fine point, thereby ingesting radium. Their exposure to radium caused serious health effects which included sores, anemia, and bone cancer. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow and can mutate bone cells.

During the litigation, it was determined that the company's scientists and management had taken considerable precautions to protect themselves from the effects of radiation, yet had not seen fit to protect their employees. Worse, for several years the companies had attempted to cover up the effects and avoid liability by insisting that the Radium Girls were instead suffering from syphilis. This complete disregard for employee welfare had a significant impact on the formulation of occupational disease labor law.

As a result of the lawsuit, the adverse effects of radioactivity became widely known, and radium-dial painters were instructed in proper safety precautions and provided with protective gear. In particular, dial painters no longer licked paint brushes to shape them (which caused some ingestion of radium salts). Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This highlighted that the harm to the Radium Girls could easily have been avoided
Doesn't look like "syphilis" to me.  Looks more like "Radium Jaw"...  Very sad images indeed.

Sunday, July 13, 2014

CANDU reactors

I had intended to write up a post about NMRI, or Nuclear Magnetic Resonance Imaging.  I may or may not get to that post.  To be frank, I don't find flipping atoms back and forth in a big magnet quite as interesting as discovering X-rays or splitting atoms.

So instead of a post on NMRI, I am going to write a post about splitting atoms :)