Harriet Brooks: Working with Radioactivity
Brooks began her relatively short career studying uranium, and soon expanded to other radioactive elements. She did this in part because Rutherford had discovered what he called the "emanations" given off by uranium. These emanations could be carried on air currents, and were eventually identified as additional radioactive substances.
Before Brooks' work, scientists assumed that elements in the periodic table were unchangeable, or immutable. But her discoveries in this area lead to the knowledge that these elements could change when their radioactivity was released. Brooks' study of the recoil of particles undergoing radioactive decay was an important step in the evolution of nuclear science.
Brooks' first real discovery came from working with radium, a radioactive element that had only been discovered a few years earlier, in 1898. After studying and observing the emanation from radium, Brooks decided that it had to be a gas. In an attempt to determine the atomic mass of the gas, she theorized that its atoms were also smaller than those of its radium parent, thus giving rise to the emanation's name, radon.
Brooks also studied the emanations of actinium B, a radioactive isotope of lead and the element thorium, each time trying to figure out what happened to the emanations and why it was happening. However, radium still intrigued her. She continued to watch the decay and noted that the process depended greatly on how long the element was exposed to the emanations. She also figured out the curve of decay for very short exposures.
From this, she also learned that radon, just like its parent, could change into other, still lighter, elements, and thus diffuse into air and other gases. Although Rutherford believed elements went through more than one change during radioactive decay, most scientists thought that decay was a one-time event. With Brooks' discovery however, it became apparent that it was a chain process.
To understand radioactive emissions, it's helpful to remember how atoms work. Each atom has a center, or nucleus. In the nucleus are protons, which are positively charged, and neutrons, which are negatively charged. Electrons circle around the center. Because there is an equal number of protons and electrons in the nucleus, the atom itself has a neutral charge.
Elements in the periodic table are made up of more than one atom, and all atoms of the same element contain the same number of protons. At the same time though, these atoms can have different numbers of neutrons. These are known as nuclides.
Some nuclides are unstable, and are called radionuclides. These radionuclides can then "decay" on their own and change into other nuclides. This decay is called radioactivity. This process of splitting apart is at the heart of understanding nuclear reactions that create massive energy, also known as fission.
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By Jennifer Hicks
Source: Harriet Brooks, 1/1/2006, p2, 1p