Nature of radioactivity

The atomic nucleus is made up of protons and neutrons. The number of protons determines the atomic number and hence the identity of an element and is equal to the number of orbital electrons, a feature necessary to ensure the electrical neutrality of the atom. The atomic mass of the nucleus is made up by the additional neutrons that are present. Hence  

This information is normally shown as a superscript (atomic mass) and a subscript (atomic number) to the symbol for the element. Hence 1%C represents the isotope of carbon (atomic number 6) with the atomic mass of 14. In practice the subscript is often omitted because the atomic number is unique to the element that is represented by the appropriate letter (e.g. C for carbon). For simplicity in the spoken form and often in the written form, isotopes are often referred to as carbon-14, phosphorus-32, etc. 

The stability of the atomic nucleus depends upon a critical balance between the repulsive and attractive forces involving the protons and neutrons. For the lighter elements, a neutron to proton ratio (N P) of about 1 1 is required for the nucleus to be stable but with increasing atomic mass, the N P ratio for a stable nucleus rises to a value of approximately 1.5 1. A nucleus whose N P ratio differs significantly from these values will undergo a nuclear reaction in order to restore the ratio and the element is said to be radioactive. There is, however, a maximum size above which any nucleus is unstable and most elements with atomic numbers greater than 82 are radioactive. 

If a nucleus is too heavy and its atomic number exceeds 82, it may revert to a more stable arrangement by releasing both neutrons and protons. This is effected by the emission of an alpha particle, which contains two protons and two neutrons and is a helium nucleus, 2He2+. 

Alpha particles are relatively large particles and are emitted with a limited number of energy levels. They carry a double positive charge and as a result attract electrons from the atoms of the material through which they pass, causing ionization effects. They have an extremely short range, even in air, and as a result present very little hazard as an external source of radiation but their effects within living cells or tissues can be serious. 

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Rutherford E (1904) The succession of changes in radioactive bodies. Philos Trans R Soc 204 169-219 Rutherford E, Soddy F (1902) The cause and nature of radioactivity Part 1. Philos Mag 4 370-396 Soddy F (1910) Radioactivity. In Annual Reports on the Progress of Chemistry, Vol. 7. The Chemical Society, London, p 257-286... 

Russell AD, Emerson S, Mix AC, Peterson LC (1996) The use of foraminiferal U/Ca as an indicator of changes in seawater uranium content. Paleoceanography 11 649-663 Rutherford E, Soddy F (1902) The cause and nature of radioactivity Part 11. Phil Mag Ser 6 4 569-585 Sacked WM (1960) Protactnium-231 content of ocean water and sediments. Science 132 1761-1762 Sacked WM (1958) Ionium-uranium ratios in marine deposited calcium carbonates and related materials. 

Rutherford, E. and Soddy, F. (1902). The cause and nature of radioactivity. Philosophical Magazine Series 6 4 370-396. 

Since elimination of these apolar cyclodienes does take place in fish, we examined the nature of radioactivity in both fish and water. 

D. Holme and H. Peck, Analytical Biochemistry, 3rd ed. (1998), Addison Wesley Longman (Essex, UK), pp. 196-209. Nature of radioactivity and use of isotopes. 

These techniques helped to sort out elements and, as it turned out, also isotopes. The nature of radioactive dements was not initially clear. Did they all correspond to distinct chemical elements To researchers in radioactivity, the word element long denoted a radioactive species, be it a proper chemical element or an isotope. Thus Lise Meitner described protactinium not just as a long-lived radioactive element, but also as chemical one . The title of one of Otto Hahn s papers on the same element is also telling Das Protactinium als radioaktives und als chemisches... 

Ernest Rutherford a, (3, and -y emissions gold-foil experiment nuclear model of the atom Determined the nature of radioactive particles. His gold-foil experiment established the presence of a positively charged nucleus and that the atom is mostly empty space. 

The discovery of isotopes was made by Frederick Soddy in 1910. Earlier, Soddy had worked with Ernest Rutherford at McGill University, where they laid out the basis for understanding radioactivity in their paper The Cause and Nature of Radioactivity. From Montreal, Soddy went first to London for one... 

The nature of radioactive disintegration within each of the four series—the emission of yS-particles, with mass nearly zero, or of a-parti-cles, with mass 4—is such that all the members of a series have mass numbers differing by a multiple of 4. The four series can hence be classified as follows n being integral) ... 

Discovery and Nature of Radioactivity—Radioactive Constants—The Uranium Series—The Disintegration Products of Uranium and their Separation— Uranium I—Uranium Xj—Uranium Xj—Uranium Z—Uranium II— Ionium—Uranium Y—Protoaetinium. 

A summary of the nature of radioactive contamination would be incomplete without some mention of the human health effects related to radioactivity and radioactive materials. Several excellent reviews at a variety of levels of detail have been written and should be consulted by the reader (ATSDR, 1990a,b,c, 1999, 2001 Harley, 2001 Cember, 1996 BEIR V, 1988). The subject is extremely complex, with a number of important controversies that are beyond the scope of this chapter. Some general principles, however, are summarized below. 

A comprehensive description of the nature of radioactivity and its interaction with matter is beyond the scope of this chapter, and such information can easily be found elsewhere (Shleien et al., 1998 CPEP, 2003 Tykva, 2004). Here we give only a brief sketch of the basic principles. Radioactivity is a natural phenomenon, discovered in 1896 by Henri Becquerel. The nuclei of some atoms are unstable and decay spontaneously, emitting ionizing radiation to attain a more energetically favorable state. Radioisotopes are characterized by the nature of the... 

In Figure 4.8 the ratio of the number of nuclei at any time t to the original number at time / = 0 (i.e. N/Nq) has been plotted on both a linear (left) and logarithmic (right) scale as a function of t. The linearity of the decay curve in the semi-logarithmic graph illustrates the exponential nature of radioactive decay. Since A oc N, the equation can be rewritten as... 

Even if the experimental design and execution are perfect so that the determinant error is eliminated in experiments involving radioactivity there is always a random error due to the statistical nature of radioactive decay. Each radioactive atom has a certain probability of decay within any one time interval. Consequently, since this probability allows unlikely processes to occur occasionally and likely processes not to occur in any particular time interval, the number of decays may be more or less than the number in another similar... 

The statistical nature of radioactive decay also leads to an uneven distribution of decays in time which is important when handling dead-time corrections and discussing required system time resolution. Let us first assume that a decay has occurred at time t = 0. What is then the differential probability that the next decay will take place within a short time interval, dr, after a time interval t has passed Two independ t processes must then occur in series. No decay may take place within the time interval from 0 to r, probability P 0),... 

Experiments were under way to understand how electricity and matter interact when the discoveries of x-rays and radioactivity were announced. Scientists trying to understand this new phenomena radioactivity experimented day and night. Ernest Rutherford was one of the many. He tried to understand the nature of radioactivity and classified it into three basic types. While trying to find out more about radioactivity, he conducted his gold foil experiment that ultimately provided greater insight into the subatomic nature of the atom by discovering the nucleus. He also identified the proton present in the nucleus. 

On account of the statistical nature of radioactive decay it is advisable to perform each measurement three times. 

As a measure for the mixture homogeneity the relative standard deviation of the measured count rates can be used. It is important to subtract the variations due to the statistical nature of radioactive decay, which would otherwise contribute to the measured variance. It has to be noted that the determination of homogeneity is not unambiguous. The variations in tracer concentration of samples depend on the sample size and on the microstructure of the material. 

Finally, the last member of the noble gases, radon, was discovered by the German chemist Frederick Dom in 1900. A radioactive element and the heaviest elemental gas known, radon s discovery not only completed the Group 8A elements, but also advanced our understanding about the nature of radioactive decay and transmutation of elements. 

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