Alpha particles from radium

The radioactive emission of alpha particles from radium, captured on photographic film. 

The neutron was discovered in 1932 by the English physicist James Chadwick (1891-1974). It had been observed in 1930 by two German investigators, Bothe and Becker, that a very penetrating radiation is produced when beryllium metal is bombarded with alpha particles from radium. Bothe and Becker considered the radiation to consist of y-rays. Frederic Joliot and his wife Irene Joliot-Curie then discovered that this radiation from beryllium, when passed through a block of paraffin or... 

Stable atoms can be converted into radioactive atoms by the collision of particles traveling at high speeds. In the early work the highspeed particles used were alpha particles from Bi (called radium C). The first nuclear reaction produced in the laboratory was that between alpha particles and nitrogen, carried out by Lord Rutherford and his collaborators in the Cavendish Laboratory at Cambridge in 1919. The nuclear reaction which occurs when nitrogen is bombarded vith alpha particles is the following ... 

Alpha emission (abbreviated a) emission of a tHe nucleus, or alpha particle, from an unstable nucleus. An example is the radioactive decay of radium-226. 

In this process, a radioactive mixture of radium and beryllium is lowered into a dry well along with radioactive detectors. Alpha particles from the radium interact ividi beryllium atoms to release neutrons. The gamma rays from the radium and the neutrons from the beryllium are reflected differently by the different strata underground. 

The experiment conducted by Rutherford and his co-workers involved bombarding gold foil with alpha particles, which are doubly charged helium atoms. The apparatus used in their experiment is shown in Figure 14-9. The alpha particles are produced by the radioactive decay of radium, and a narrow beam of these particles emerges from a deep hole in a block of lead. The beam of particles is directed at a thin metal foil, approximately 10,000 atoms thick. The alpha particles are delected by the light they produce when they collide with scintilltaion screens, which are zinc sulfide-covered plates much like the front of the picture tube in a television set. The screen... 

When thorium emits alpha particles, it disintegrates into other daughter radionuclides (radioactive materials), such as radium-226 and radon-222 (from thorium-230 in the uranium-238 decay series) or radium-228 and thoron (radon-220 from thorium-232 in the thorium decay series). It eventually decays to stable lead-208 or -206, which is not radioactive. More information about the decay of thorium can be found in Chapter 3. The toxicological characteristics of radon, radium, and lead are the subject of separate ATSDR Toxicological profiles. 

Gross alpha and gross beta activity can be determined by various radioactive counters, such as internal proportional, alpha scintillation, and Geiger counters. Radium in water can be measured by co-precipitating with barium sulfate followed by counting alpha particles. Radium-226 can be measured from alpha counting of radon-222. Various methods are well documented (APHA, AWWA, and WEF 1998. Standard Methods for the Examination of Water and Wastewater, 20 ed. Washington DC American Public Health Association). 

This was just the start. In 1919 Rutherford found that alpha particles emitted from radium could chip protons from the nuclei of nitrogen atoms. This was something new. Radioactive elements decayed spontaneously into other elements because they were fundamentally unstable. But there was nothing unstable about nitrogen. Yet Rutherford had nevertheless managed to transmute it artificially. The newspapers found a catchy phrase for this feat splitting the atom . 

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