Nuclear charge radioactivity

In the second of their 1915 papers (Harkins and Wilson 1915b), Harkins and Wilson note from their study of the light elements (up to atomic number 27) that the main isotopic species had atomic masses which are integral multiples of 4. They concluded from this that, for those light nuclei, an important constituent must be the alpha particle just as it must be in the heavier radioactive nuclei which undergo alpha decay. In order to rationalize all the nuclei, including their nuclear charges, they... 

The efficient screening approximation means essentially that the final state of the core, containing a hole, is a completely relaxed state relative to its immediate surround-ing In the neighbourhood of the photoemission site, the conduction electron density of charge redistributes in such a way to suit the introduction of a core in which (differently from the normal ion cores of the metal) there is one hole in a deep bound state, and one valence electron more. The effect of a deep core hole (relative to the outer electrons), may be easily described as the addition of a positive nuclear charge (as, e.g. in P-radioactive decay). Therefore, the excited core can be described as an impurity in the metal. If the normal ion core has Z nuclear charges (Z atomic number) and v outer electrons (v metallic valence) the excited core is similar to an impurity having atomic number (Z + 1) and metalhc valence (v + 1) (e.g., for La ion core in lanthanum metal, the excited core is similar to a Ce impurity). 

Note how the nuclear equation for the radioactive decay of uranium-238 is written. The equation is not balanced in the usual chemical sense because the kinds of nuclei are not the same on both sides of the arrow. Instead, a nuclear equation is balanced when the sums of the nucleons are the same on both sides of the equation and when the sums of the charges on the nuclei and any elementary particles (protons, neutrons, and electrons) are the same on both sides. In the decay of 2 U to give He and 2 oTh, for example, there are 238 nucleons and 92 nuclear charges on both sides of the nuclear equation. 

In the first place, as described in the earlier Section, the j3-decay changes the atomic number, and therefore the valency and all the chemical properties of the radioactive atom. This change alone is often sufficient to cause disruption of the molecule, particularly in those cases where the product of the radioactive decay is a noble gas atom. In the second place, an initially neutral molecule will become positively charged, as a result of the increased nuclear charge, and all the sources of electronic excitation discussed for the decay of isolated atoms will of course affect the molecule as well. 

When the nuclear charge changes due to radioactive decay and/or an inner-shell vacancy is produced, the bound electrons in the same atom or molecule experience the sudden change in the central potential and have a small but finite probability to be excited to an unoccupied bound state (shakeup) or ejected to the continuum (shakeoff). We calculated the shakeup-plu.s-shakeoff probabilities accompanying PI and EC using the method of Carlson and Nestor [45]. 

The Uranium Series o Radioactive Disintegrations. When an alpha particle (He++) is emitted by an atomic nucleus the nuclear charge decreases by two units the element hence is transmuted into the element two columns to the left in the periodic table. Its mass number (atomic weight) decreases by 4, the mass of the alpha particle. 

In 1918 Aston discovered isotopes in a number of non-radioactive elements that led to a strengthening of Paneth s case. Paneth pointed out that elements in Fajans s sense of the word seemed to be multiplying each day and were thus endangering the chemists picture of the world. It would have been far-fetched for chemists to restructure the foundations of their science on the grounds that "elements" had turned out to be composite structures. At about this time Paneth stated clearly what had previously remained as an implicit definition of a chemical element "A chemical element is a substance of which all atoms have the same nuclear charge" (Paneth, 1925 p. 842). 

While the early optical measurements suffered from limited resolution, the development of atomic beam methods provided a useful tool in the study of atomic and nuclear magnetic moments [ 12,13] (for a review see [ 14]) and it became possible to measure the nuclear magnetic moments (and nuclear spins) in a direct way for both stable and radioactive isotopes, by using a variety of methods ] 15]. The study of optical IS was, however, limited to Doppler-limited optical spectroscopy until the invention of the laser and the development of suitable high-resolution optical methods (a review can be found in [16]). It is also possible to obtain information on the nuclear charge distribution by electron scattering experiments and from muonic X-ray transitions and electron K X-ray IS [17], perhaps even with a higher accuracy than with optical spectroscopy. 

With the development of nuclear reactors and charged particle accelerators (commonly referred to as atom smashers ) over the second half of the twentieth century, the transmutation of one element into another has become commonplace. In fact some two dozen synthetic elements with atomic numbers higher than naturally occurring uranium have been produced by nuclear transmutation reactions. Thus, in principle, it is possible to achieve the alchemist s dream of transmuting lead into gold, but the cost of production via nuclear transmutation reactions would far exceed the value of the gold. SEE ALSO Alchemy Nuclear Chemistry Nuclear Fission Radioactivity Transactinides. 

We use X to indicate any element defined by its nuclear charge, Z and Z-2 in this equation. Examples are given in Ch. 1, and can be found e.g. in the natural radioactive decay series, see next chapter. 

Bohr learned about radiochemistry from de Hevesy. He began to see connections with his electron-theory work. His sudden burst of intuitions then was spectacular. He realized in the space of a few weeks that radioactive properties originated in the atomic nucleus but chemical properties depended primarily on the number and distribution of electrons. He realized—the idea was wild but happened to be true—that since the electrons determined the chemistry and the total positive charge of the nucleus determined the number of electrons, an element s position on the periodic table of the elements was exactly the nuclear charge (or atomic number ) hydrogen first with a nuclear charge of 1, then helium with a nuclear charge of 2 and so on up to uranium at 92. 

In this chapter we learn how to describe nuclear reactions by equations analogous to chemical equations, in which the nuclear charges and masses of reactants and products are in balance. Radioactive nuclei most commonly decay by emission of alpha, beta, or gamma radiation. 

R. Sanchez et al., The nuclear charge radii of the radioactive lithium isotopes. GSI report,... 

At the time, of course, no atomic numbers existed as yet, they were introduced by Van den Broek in 1912, assuming that the nuclear charge of the individual elements and hence the number of electrons revolving around it is identical with the ordinal number occupied by the given element in the Mendeleev table (Van den Broek 1913). At the time, shortly after the discovery of radioactivity, atomic structure investigations were still at their very beginnings, statements now already based on experimental facts that the atoms are not indivisible, but consist - as so many earlier nature philosophic concepts maintained - of common components. It was thus... 

The displacement law provided for harmonious relationship between radioactive families and the periodic system of elements. After several successive alpha and beta decays the originators of the families converted into stable lead giving rise in the process to the natural radioactive elements found between uranium and bismuth in the periodic table. But then each box in the system had to accommodate several radioelements. They had identical nuclear charges but different masses, that is, they looked as varieties of a given element with identical chemical properties but different masses and radioactive characteristics. In December 1913 Soddy suggested the name isotopes for such varieties of elements (from the Greek for the common place ) because they occupy the same box in the periodic system. 

When the majority of stable chemical elements were found to have isotopes—up to ten isotopes per element—the scientists started to study the laws of isotopism. The German theoretical physicist J. Mattauch formulated one of such laws at the beginning of the thirties (the basic premise of this law was noted back in 1924 by the Soviet chemist S. Shchukarev). The law states that if the difference between the nuclear charges of two isobars is unity one of them must be radioactive. For instance, in the K- Ar isobar pair the first is naturally weakly radioactive and transforms into the second owing to the so-called process of K-capture. 

There are about 300 stable isotopes and over 1,000 unstable (radioactive) isotopes which have been characterized. Nuclei with the same mass number A but having different nuclear charges Z are... 

Methods for influencing the radioactive decay rate have been sought from early years of Nuclear physics. Nuclear transmutation (i.e. change in the nuclear charge) induced by nuclear reactions are often accompanied by a redistribution of the electrons, muons (mesons in the hadronic atoms) around the final transmuted nucleus. Muonic atoms have always been useful tools for nuclear spectroscopy employing atomic-physics techniques. Muonic atoms also play an important role... 

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