Nucleus disintegration

EXAMPLE 22.7. When a 2 1 gamma particles accompanies practically every disintegration and since gamma particles do not change the atomic number or mass number of an isotope, they are not listed.) Show that each isotope produced has a mass number that differs from 238 by some multiple of 4. 

The rate at which an unstable nucleus disintegrates varies from isotope to isotope. Some isotopes can decay over a number of years others may completely disintegrate in just a couple of seconds. Chemists often look at the half-life of an isotope to determine how long a sample of the particular isotope will remain unchanged over a certain period of time. The half-life of an isotope is the amount of time it takes for half of a radioactive substance to decay. Each nuclide has its own half-life that does not change. 

Maintaining a deep anterior chamber can be considered the conditio sine qua non for successful anterior segment intraocular surgery. There are diverse pre- and intraoperative precautionary measures available to achieve this oculopression, addition of adrenalin and hyaluronidase to retrobulbar anesthesia, hyperventilation and blood pressure reduction during anesthesia, closed system operation as made possible by phacoemulsification (lens nucleus disintegration via ultrasound), or by intravenous infusion of hyperosmolar substances (Voros-marthy, 1967 Kelman, 1967). 

Consider first the question of the energy released when a nucleus disintegrates. As an example, let us take the case of the neutron-induced fission of the nucleus which results in the formation of two fragments and of masses M and Mj, respectively. On the basis of the compound-nucleus concept, this reaction may be written... 

Atoms consist of comparatively large particles (protons and neutrons) that are concentrated in a central nucleus and smaller particles (electrons) that are relatively distant from the nucleus. If the number of protons in the nucleus equals the number of electrons in orbit, the atom is electrically neutral. If not, it is electrically charged and is known as an ion. Radioactivity is the result of the nucleus being unstable. An excess of neutrons results in the nucleus disintegrating by emitting electrons, also known as beta particles, in a process called beta decay. If the nucleus has an excess of protons, the nucleus can capture an electron, emit a positive electron (positron), or both. Another type of radioactivity, alpha decay, occurs in heavy elements when the nucleus emits a helium nucleus — two neutrons and two protons bound together. 

As chemists write chemical equations to describe chemical changes, they write nuclear equations to describe nuclear changes. A nuclear equation shows the reactant nuclides or particles on the left and the product nuclides or particles on the right. The first step in the natural radioactive series observed by Becquerel is an alpha decay reaction. In it, a nucleus disintegrates, or decays, into a He nucleus (alpha particle) and a nucleus. The nuclear equation is... 

In reaction (25.9), instead of a nucleus disintegrating spontaneously, it must be struck by another small particle to induce a nuclear reaction. gO is a naturally occurring nonradioactive isotope of oxygen (0.037% natural abundance). The situation with fgP, which can also be produced by a nuclear reaction, is somewhat different. 

Decay The spontaneous disintegration of an unstable atomic nucleus to form another more stable element or isotope of a lower atomic mass. 

Kem-umwandlung, /. nuclear transformation, transmutation, -verknlipfung,/. linkage to a nucleus, -verschmelzimg, /. nuclear fusion, -weehselwirkung, /. nuclear interaction, -werkstoff, m. core material. -woUe,/. prime wool, -zahl, /. number of nuclei, -zelle, /. nuclear cell, -zerfall, m. nuclear disintegration. -zerplatzen, n. nuclear explosion or disintegration. 

We can use Fig. 17.13 to predict the type of disintegration that a radioactive nuclide is likely to undergo. Nuclei that lie above the band of stability are neutron rich they have a high proportion of neutrons. These nuclei tend to decay in such a way that the final n/p ratio is closer to that found in the band of stability. For example, a l4C nucleus can reach a more stable state by ejecting a (3 particle, which reduces the n/p ratio as a result of the conversion of a neutron into a proton (Fig. 17.15) ... 

Spontaneous nuclear fission takes place when the natural oscillations of a heavy nucleus cause it to break into two nuclei of similar mass (Fig. 17.21). We can think of the nucleus as distorting into a dumbbell shape and then breaking into two smaller nuclei. An example is the spontaneous disintegration of americium-244 into iodine and molybdenum ... 

When Z gets big enough, no number of neutrons is enough to stabilize the nucleus. Notice in Figure 2-20 that there are no stable nuclei above bismuth, Z — 83. Some elements with higher Z are found on Earth, notably radium (Z = 88), thorium (Z = 90), and uranium (Z = 92), but all such elements are unstable and eventually disintegrate into nuclei with Z < 83. Consequently, the set of stable nuclei, those that make up the world of normal chemistry and provide the material for all terrestrial chemical reactions, is a small subset of all possible nuclei. 

Decay, Radioactive—Transformation of the nucleus of an unstable nuclide by spontaneous emission of charged particles and/or photons (see Disintegration). 

Disintegration, Nuclear—A spontaneous nuclear transformation (radioactivity) characterized by the emission of energy and/or mass from the nucleus. When large numbers of nuclei are involved, the process is characterized by a definite half-life (see Transformation, Nuclear). 

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