015

Musée Curie, Paris, France

48° 50′ 36″ N, 2° 20′ 39″ E

Radium

Visitors to the Musée Curie at the Institut Curie, where Marie Curie worked with radioactive materials with absolutely no safety equipment, will be happy to know that the building was decontaminated in the 1980s, making it safe to visit. The Curies were so unaware of the danger of radioactivity that Pierre Curie carried a sample of radium around in his pocket to show people, and Marie Curie had a glowing jar of radium salt as a night light.

The museum covers the life and work of two couples: Pierre and Marie Curie, and their daughter and her husband, Irène and Frédéric Joliot-Curie.

Pierre and Marie Curie discovered the radioactive elements polonium (named after Marie Curie’s home country, Poland) and radium; they were also the first to use the word radioactive. The Joliot-Curies discovered “artificial radioactivity”—they were able to take a non-radioactive element like aluminum and make it radioactive by bombarding it with alpha particles emitted by polonium. All four of the scientists won Nobel Prizes.

The main part of this small museum consists of Marie Curie’s office and her chemistry laboratory. Both have been restored to the state they were in at the time of her research. There’s a good collection of the Curies’ notes and equipment, including the apparatus used to detect radiation.

An amusing (and somewhat frightening) part of the museum details the craze of the 1920s and 1930s for using radioactivity in a variety of products. The museum has a “radium shop,” which has a reproduction of a fountain producing radioactive water to drink, advertisements for radioactive wool (which was apparently especially good for babies), and a beauty powder containing radium and thorium.

The museum also details the rapid discovery that radioactivity could be used to treat cancerous tumors. This led to the creation of the Radium Institute, where Curie worked on radiation and other scientists worked on the medical use of radioactivity. The Radium Institute became the Institut Curie in 1978.

Pierre Curie didn’t die of radiation-induced sickness (he was hit by a carriage while crossing the street), but Marie Curie almost certainly did: she died of leukemia in 1934. Marie Curie is the only woman honored by a place in the Pantheon in Paris (see Chapter 13), where she is buried alongside her husband.

Practical Information

The museum is part of the Institut Curie, a French cancer research organization. Details are available (in English) from the institute’s website at http://www.curie.fr/. The museum organizes tours in English once per week; the tours are free, and no reservation is needed.

Ionizing Radiation and Smoke Detectors

The Curies were able to detect radiation (and determine which elements were radioactive) by exploiting a technique developed by Marie Curie’s doctoral supervisor Henri Becquerel. The radiation emitted by the uranium Becquerel was working with, and by Curie’s radium, is ionizing—that is, the radiation has enough energy that it is capable of removing an electron from an atom. Removing an electron causes the atom to become charged, and the charge can be detected.

A radioactive source can ionize air, and a simple detector is a pair of metal plates connected to a DC source. One plate is negatively charged, and the other is positively charged. When radiation ionizes the air between the plates, the positively charged ionized atoms are attracted to the negatively charged plate, the free electrons knocked off by the radiation are attracted to the positively charged plate, and a measurable current flows through the plates.

The Curies’ equipment had three parts (see Figure 15-1): piezoelectric quartz, Q; a quadrant electrometer, E; and an ionization chamber (the gap between plates A and B). The sample to be examined was placed on a plate of the ionization chamber, and that plate was connected to a battery. The other plate was connected to the electrometer, which was then connected to the piezoelectric quartz.

Figure 15-1. Piezoelectric quartz electrometer with ionizing chamber

The Curies would add weight to the quartz, changing the charge it created using the piezoelectric effect: certain materials, mostly crystals, will create an electric charge when stressed. By adding the right amount of weight, they were able to balance out the charge from the battery and ionized air. The electrometer served to indicate when the charges were balanced.

From the weight applied to the quartz, the charge could be calculated; from that, the strength of the radiation from the sample could be calculated in turn.

Most modern homes contain a small radioactive source and an ionization chamber—inside the household smoke detector. A smoke detector typically has a tiny piece of radioactive Americium 241 emitting alpha particles into an ionization chamber. The plates of the ionization chamber are charged by the smoke detector’s battery.

When there’s no fire, the ionized air creates a small current across the plates. But when smoke enters the chamber, it attaches to the ions and removes their charge. When this occurs, the current across the plates drops and the alarm will sound.