Rutherford and

Gr. helios, the sun). Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Frankland suggested the name helium for the new element. In 1895 Ramsay discovered helium in the uranium mineral clevite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907 demonstrated that alpha particles are helium nuclei. 

In 1903, Rutherford and associates were finally able to deflect the a-rays by electric and magnetic fields, showing that these are positively charged. Measurement of the charge-to-mass ratio indicated that a-rays were of atomic dimensions. In 1908 definitive experiments showed a-rays to be doubly chaiged helium atoms, ie, helium nuclei. 

Element 86, the final member of the group, is a short-lived, radioactive element, formerly known as radium-emanation or niton or, depending on which radioactive series it originates in (i.e. which isotope) as radon, thoron, or actinon. It was first isolated and studied in 1902 by E. Rutherford and F. Soddy and is now universally known as radon (from radium and the termination-on adopted for the noble gases Latin radius, ray). 

The development of particle accelerators grew out of the discovery of radioactivity in uranium by Henri Becquerel in Paris in 1896. Some years later, due to the work of Ernest Rutherford and others, it was found that the radioactivity discovered by Becquerel was the emission o particles with kinetic energies o several MeV from uranium nuclei. Research using the emitted particles began shortly thereafter. It was soon realized that if scientists were to learn more about the properties of subatomic particles, they had to be accelerated to energies greater than those attained in natural radioactivity. 

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... 

The next thing, of course, is to see whether things work out as they should. Do radioactive counts in fact distribute themselves according to the unique Gaussian defined by N and < = VN As Figure 10-3 shows, Rutherford and Geiger6 proved in 1910 that they do. 

Fig. 10-3. Experimental proof that x-ray emission speetrography and radioactivity both conform to the unique Gaussian fluctuation curve based on N alone. Crosses = data of Rutherford and Geiger circles = x-ray emission data solid line = theoretical Gaussian curve. (Liebhafsky, Pfeiffer, and Zemany, Anal. Chem., 27, 1257.)...

These data are plotted in Figure 10-3 about the Gaussian curve for which the standard deviation is the square root of the mean. The data of Rutherford and Geiger, which were obtained by counting alpha-particles, are plotted about the same curve. In the figure, both sets of data fit the Gaussian about equally.well. 

Gaussian distribution, discussion and equation, 61,269-274 of Rutherford and Geiger radioactivity data, 274, 275... 

These salts can be made easily since tetrafluoroboric acid (HBF4) and hexa-fluorophosphoric acid (HPF6) are commercially available. However, the main advantage of the diazonium salts with the anions of these acids is their stability, which is significantly higher than that of probably all other diazonium salts. 4-Nitrobenzenediazonium tetrafluoroborate is nowadays even a commercial product. Preparative diazotization methods with these two acids can be found in Organic Syntheses (tetrafluoroborate Starkey, 1943 hexafluorophosphate Rutherford and Redmont, 1973). 

Schiemann and Winkelmuller (1943 a, 1943 b), Flood (1943), and Rutherford and Redmont (1973) provided specific examples of Balz-Schiemann reactions for Organic Syntheses. 

The discoveries of Becquerel, Curie, and Rutherford and Rutherford s later development of the nuclear model of the atom (Section B) showed that radioactivity is produced by nuclear decay, the partial breakup of a nucleus. The change in the composition of a nucleus is called a nuclear reaction. Recall from Section B that nuclei are composed of protons and neutrons that are collectively called nucleons a specific nucleus with a given atomic number and mass number is called a nuclide. Thus, H, 2H, and lhO are three different nuclides the first two being isotopes of the same element. Nuclei that change their structure spontaneously and emit radiation are called radioactive. Often the result is a different nuclide. 

Over the next several years, Rutherford and other researchers bombarded assorted nuclei with alphas. Boron, sodium, and other elements all produced the same results a hydrogen nucleus. This strongly suggested that the hydrogen nuclei were... 

As early as 1902, Rutherford and his colleague, the chemist Frederick Soddy, realized that emissions of alpha and beta rays changed the nature of the emitting substance. One example of such a change is the spontaneous radioactive decay of the uranium-238 isotope, which emits an alpha particle and produces thorium ... 

Decay of the nuclide itself. The conceptually simplest approach is to take a known quantity of the nuclide of interest, P, and repeatedly measure it over a sufficiently long period. The observed decrease in activity with time provides the half-life to an acceptable precision and it was this technique that was originally used to establish the concept of half-lives (Rutherford 1900). Most early attempts to assess half lives, such as that for " Th depicted on the front cover of this volume, followed this method (Rutherford and Soddy 1903). This approach may use measurement of either the activity of P, or the number of atoms of P, although the former is more commonly used. Care must be taken that the nuclide is sufficiently pure so that, for instance, no parent of P is admixed allowing continued production of P during the experiment. The technique is obviously limited to those nuclides with sufficiently short half-lives that decay can readily be measured in a realistic timeframe. In practice, the longest-lived isotopes which can be assessed in this way have half-lives of a few decades (e.g., °Pb Merritt et al. 1957). 

The normal or constant radioactivity possessed by thorium is an equilibrium value, where the rate of increase of radioactivity due to the production offresh active material is balanced by the rate of decay of radioactivity of that already formed (Rutherford and Soddy 1902). 

In the same paper, Rutherford and Soddy also suggested that elements were undergoing spontaneous transformation. The use of the word transformation smacked of alchemy and Rutherford was loath to use it, but by then it seemed clear that elements were really changing and that radioactivity may therefore be considered as a manifestation of subatomic change (Rutherford and Soddy 1902). 

Fig. 5.9. A possible structure of the Mn/Ca site for the synthesis of oxygen from water. Other structures have been proposed. The site is not very stable and the whole protein holding the metal ions must be replaced frequently. There is a chloride ion nearby (see Rutherford and Boussac and Biesiaka et al., in Further Reading).

But until the discovery of radioactive transmutation by Rutherford and Soddy, many outside of occult circles were content to view alchemy as simply... 

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