Sun in a Bottle - Charles Seife [20]
Not surprisingly, researchers were so excited about finding new kinds of radiation that some of their discoveries were entirely fictional. In 1903, the French physicist René Blondlot thought he had discovered a new type, which he dubbed the “N-ray.” But Blondlot had deceived himself; his desire to believe in N-rays made him ignore the evidence against them. When a skeptical researcher removed a crucial component of the experimental apparatus and the unsuspecting Blondlot continued to observe the N-rays, N-rays were exposed as a fiction. Blondlot was made a laughingstock.
There was one type of radiation, though, that did not fit neatly into the pattern scientists had been seeing. High-energy light, such as x-rays or gamma rays, penetrates matter easily; its beams are hard to block. Fragments of atoms—charged particles like protons and electrons and alpha particles—tend not to penetrate matter much at all. Because of their charge, they get tangled in the electrons and protons in a given hunk of matter and quickly slow to a halt. But a new type of radiation, discovered in the 1930s, seemed like a weird cross between light and atom fragment. Scientists generated this bizarre radiation by shining a beam of alpha particles upon certain kinds of atoms (such as beryllium atoms). This new kind of radiation did not have an electric charge: it was unaffected by electric or magnetic fields. It penetrated matter as readily as gamma rays did, but it did not behave as a light beam should. It behaved like a heavy particle: it would hit a block of paraffin and knock protons out; mere light couldn’t do that so easily. In 1932, the British physicist James Chadwick concluded, correctly, that this new type of radiation consisted of particles almost identical to protons but for one major difference: they had no electric charge. Chadwick won the Nobel Prize for his discovery: the neutron.
The neutron is just a tiny fraction of a percent heavier than a proton, so it has quite a bit of oomph. But because it is electrically neutral, it doesn’t “feel” the electrical charges of the electrons and protons in a material. It is only affected by an atom when it slams directly into the nucleus. However, since atoms are mostly empty space and atomic nuclei are very small, a neutron can zoom straight through a chunk of matter without ever encountering something that deflects it. Neutrons penetrate matter extremely well, going through lead bricks almost as if they didn’t exist. But when a neutron does, by chance, hit an atomic nucleus, it packs a punch. A light atom (such as hydrogen) might be kicked out of the substance altogether. A heavy atom (such as uranium) might shiver and break apart when struck with the right amount of force. (As described in chapter 1, neutrons doing just this is what causes the chain reaction at the heart of the atom bomb.)
The discovery of the neutron also solved a puzzle that was beginning to vex physicists. When chemists and physicists used their newfound knowledge of protons and electrons to understand the nature of the elements, they were surprised by a strange inconsistency. They discovered that an atom of a given element did not have a fixed weight. For example, in 1932 scientists found that hydrogen came in several flavors. There was ordinary hydrogen—which was thought to be made up of one proton (and one very light electron, whose weight is negligible). Then there was a heavier form of hydrogen that weighed twice as much. They called it deuterium. Soon, they