Radioactive substances, helium from

Alpha particle Positively charged particle emitted at high speeds from certain radioactive substances (helium nuclei). 

The experiments consisted in bombarding a film of some substance (Rutherford used a piece of metal foil) with a stream of fast-moving alpha particles, and observing the direction in which the alpha particles rebound from the atoms. Alpha pakticles are particles sent out at high speeds by radium and other radioactive substances. It is now known that they themselves are the nuclei of helium atoms, but this was not learned until after Lord Rutherford had carried out his... 

At the beginning of the twentieth century, research turned to the newly discovered radioactive substances. Ramsay and Soddy (1903) showed that helium was derived by radioactive disintegration of radium, the ftrst demonstration that one element was derived from another. Once the decay constant of radium had been determined, the door was open for the ftrst application of the noble gases geochronology (Strutt, 1908), a methodology that has been pursued ever since. 

Positive electricity has only been found associated with masses of atomic magnitude. Positive rays have been produced and studied it will suffice to mention a-rays of radioactive substances, anode rays and canal rays. The determination of ejm from deviation experiments gave the mass of the a-particles to be that of the helium atom for the particles of the anode rays the mass is that of the atom of the anode material, while for the particles of the canal rays the mass is that of an atom of the gas in the tube. We must therefore assume that each atom consists of a positive particle, at which is concentrated most of its mass, and of a number of electrons. In the neutral atom the number of the elementary... 

Radioactivity is emitted from atomic nuclei that are unstable and spontaneously change their structure. In 1896, Henri Becquerel first discovered radioactivity when he placed a piece of zinc uranyl sulfate wrapped in paper on a photographic plate. Two years later, Marie and Pierre Curie discovered two highly radioactive elements, polonium and radium, in pitchblende. a particles, the nuclei of helium atoms, were among the radiations emitted by these substances which were spontaneously transmuting. Indeed, since the earth had billions of years ago lost its original complement of light, inert helium, all helium in our... 

Helium was identified by its characteristic emission spectrum as a component of the sun before it was found on earth. The major sources of helium on earth are natural gas deposits, where helium was formed from the a-particle decay of radioactive elements. The a particle is a helium nucleus that can easily pick up electrons from the environment to form a helium atom. Although helium forms no compounds, it is an important substance that is used as a coolant, as a pressurizing gas for rocket fuels, as a diluent in the gases used for deep-sea diving and spaceship atmospheres, and as the gas in lighter-than-air airships (blimps). 

Marie and Pierre Curie examined the radiation emitted by radium. They found that all substances near the radiation source became radioactive themselves. The activity even remained some time after the removal of the emitting radium. It was questioned whether there is some radioactive force that was transferred with the radiation and was induced in the receiving substance. In 1900 F. Dom in Halle, Germany, reported on a study of an isotope emanating from radium and, because of that, certainly incorrectly, was credited with the discovery of radon. In fact Ernest Rutherford (1871-1937) and Frederick Soddy (1877-1956) were the first to isolate radon and also the first to really understand the nature of radon. In the first decade of 1900 they worked at McGill University in Montreal, Canada, and carried out very comprehensive work on radioactivity [52.10]. They discovered that the emanation from radium was a gas of the same type as the noble gases. Ramsay at University College in London completed the spectral work. He showed that the spectrum of radon resembled that of xenon. He also showed that the formation of radon was accompanied by the simultaneous production of helium, as he also observed its spectrum. This observa-... 

Helium (He) is the only substance that remains liquid under its own pressure at the lowest temperature recorded. There are only about five parts per miUion of helium in the Earth s atmosphere, but it reaches substantially higher concentrations in natural gas, from which it is obtained. Helium is formed from the radioactive decay of heavy elements. For example, a kilogram of uranium gives 865 L of helium after complete decay. There s not much helium on Earth, but there is a lot in the universe. About 23% of the known mass of the universe is helium, mostly produced by thermonuclear fusion reactions between hydrogen nuclei in stars. So, an outside observer of our universe (whatever that means ) would probably conclude that helium is some of the most important stuff around. 

Apart from historical articles, Norwegian journals mainly addressed the periodic system in articles on radioactivity, and only some decades after the system had been published by Mendeleev and Meyer. The discovery of more than thirty new radioactive elements evidently became a puzzle to chemists before the concept of isotopy was introduced by Frederick Soddy (1877-1956) in 1913, chemists were worried about how to fit all the new elements into the periodic system. An instructor at the technical school in Christiania, Haavard Martinsen (1879-1967), conveyed this challenge in an article in Pharmacia, several years before many of the radioelements were recognized as isotopes of known chemical elements. Martinsen, who had spent the previous summer working in William Ramsay s laboratory in London, acknowledged the advantages of Mendeelev s periodic system. However, faced with the evidence that radioelements such as radium emit helium, chemists were, in Martinsen s opinion, left with two options Either to maintain the old established definition of the concept of element and according to this perceive radium and similar substances as common chemical compounds, or to throw the old definition overboard and admit the divisibility of the elements. ... 

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