Radioisotopes, unstable

Radioisotope Unstable isotope of an element that decays generating alpha particles, electrons, positrons, or gamma rays. 

Unstable niobium isotopes that are produced in nuclear reactors or similar fission reactions have typical radiation hazards (see Radioisotopes). The metastable Nb, = 14 yr, decays by 0.03 MeV gamma emission to stable Nb Nb, = 35 d, a fission product of decays to stable Mo by... 

Radioisotope—An unstable or radioactive isotope of an element that decays or disintegrates spontaneously, emitting radiation. Approximately 5,000 natural and artificial radioisotopes have been identified. 

The structure of some isotopes, generally referred to as stable isotopes, is immutable (see Textbox 13). Others, known as radioactive isotopes or radioisotopes, are unstable in time they undergo what is known as... 

FIGURE 10 The half-life. It is impossible to predict when a radioisotope or an unstable substance (molecule) will decay or be decomposed. On an average, however, only half of any type of radioisotope or unstable substance (molecule) remains after one half-life (A/2) one-quarter will remain after two half-lives (A/A), one-eighth after three half-lives (A/8), and so on. The half-life is characteristic of every radioisotope and unstable molecule that of radioisotopes is not affected in any way by the physical or chemical conditions to which the radioisotope may be subjected. Not so the half-life of chemically unstable molecules, which is altered by changes in temperature and by other physical and chemical conditions. 

The half-life (t1 ) of a radioisotope is the amount of time it takes for that isotope to undergo radioactive decay and be converted into another. It is also a measure of the stability of the isotope the shorter its half-life, the less stable the isotope. The half-life of radioisotopes ranges from fractions of a second for the most unstable to billions of years for isotopes that are only weakly radioactive. In the case of radiocarbon (carbon-14), for example, the half-life is 5730 years (see Fig. 61). 

Table 4.4 The four unstable radioisotopes and their decomposition products...

Radioisotopes are unstable and decay by particle emission, electron capture, or y-ray emission. The decay is a random process, i.e., one cannot predict which atom from a group of atoms will decay at a specific time. The decay of radioisotopes, therefore, is described in terms of the average number of radioisotopes disintegrating during a period of time. The disintegration rate (or the number of disintegrations per unit time), -dN/dt, of a radioisotope at any time is proportional to the total number of undecomposed radioisotopes present at that time. This may be expressed as follows ... 

ISOTOPES There are no stable isotopes of francium found on Earth. All of its 33 isotopes (ranging from Fr-201 to Fr-232) are radioactive therefore, the one with the longest half-life of about 20 minutes (Fr-223) is the one used to determine its atomic weight. Fr-223 is the only radioisotope of francium that is found naturally as a decay product from other unstable elements. 

The radioisotopes of einsteinium are highly unstable and radioactive. The small amount of the element and its compounds produced are not likely to be available in most laboratories. Thus, they do not pose any general hazard except in the case of scientists working with nuclear materials who must take precautions in handling exotic elements. 

J Ju elements in the periodic table exist in unstable versions called radioisotopes (see Chapter 3 for details). These radioisotopes decay into other (usually more stable) elements in a process called radioactive decay. Because the stability of these radioisotopes depends on the composition of their nuclei, radioactivity is considered a form of nuclear chemistry. Unsurprisingly, nuclear chemistry deals with nuclei and nuclear processes. Nuclear fusion, which fuels the sun, and nuclear fission, which fuels a nuclear bomb, are examples of nuclear chemistry because they deal with the joining or splitting of atomic nuclei. In this chapter, you find out about nuclear decay, rates of decay called half-lives, and the processes of fusion and fission. 

The stability of a nucleus depends on the ratio of neutrons to protons. Some nuclei are unstable and undergo spontaneous nuclear disintegration accompanied by emission of particles. Unstable isotopes of this type are called radioisotopes. Three main types of radiation are emitted during nuclear decay a particles, j8 particles, and y rays. The a particle, a helium nucleus, is emitted only by elements of mass number greater than 140. These elements are seldom used in biochemical research. 

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

There are two types of isotopes those which are stable and those which are unstable. The isotopes which are unstable, as a result of the extra neutrons in their nuclei, are radioactive and are called radioisotopes. For example, uranium-235, which is used as a source of power in nuclear reactors (p. 93), and cobalt-60, which is used in radiotherapy treatment (Figure 3.5), are both radioisotopes. 

Some nuclei are unstable and emit particles and electromagnetic radiation. These emissions from the nucleus are known as radioactivity the unstable isotopes are known as radioisotopes and the nuclear reactions that spontaneously alter them are known as radioactive decay. Particles commonly involved in nuclear reactions are listed in the following table ... 

The selection of proper elements and compounds needs to take into account the very complex situation. The chemical state of the radioisotopes in the reactive carrier gas and the standard sublimation enthalpy of this chemical state must be known. In principle all compounds, which are unstable under the selected conditions, have been rejected as well as compounds, which undergo diffusion processes or irreversible reactions with the stationary phase. The following correlations (Method 8) were obtained experimentally for elements and selected compound classes, see also Figure 8 A-C ... 

Radioisotopes decay because their nuclei are unstable. The time it takes for nuclei to decay varies greatly. For example, it takes billions of years for only half of the nucleus of naturally occurring uranium-238 to decay. The nuclei of other radioisotopes — mainly those that scientists have synthesized — decay much more rapidly. The nuclei of some isotopes, such as sodium-22, take about 20 years to decay. 

All uranium isotopes, for example, have unstable nuclei. They are called radioactive isotopes, or radioisotopes for short. Many isotopes are not radioisotopes. Oxygen s three naturally occurring isotopes, for example, are stable. In contrast, chemists have successfully synthesized ten other isotopes of oxygen, all of which are unstable radioisotopes. (What products result when radioisotopes decay You will find out in Chapter 4.)... 

The nuclei of some isotopes of some elements are unstable and give off radiation - they are said to be radioactive . Isotopes that are radioactive are called radioisotopes. 

A radioactive isotope (radioisotope) is an unstable isotope of an element that decays into a more stable isotope of the same element. They are of great use in medicine as tracers (to help monitor particular atoms in chemical and biological reactions) for the purpose of diagnosis (such as imaging) and treatment. Iodine (-131 and -123) and Technetium-99 are used for their short half-lives. 

H, C, P, and l. The word isotope comes from Greek, meaning at the same place , a useful way to remember that all isotopes of an element are in the same place in the Periodic Table of elements. While not quite correct, often the words isotope and nuclide are used interchangeably. Thus, radioisotopes may be termed radionuclides. The later refers to an atom with an unstable nucleus that undergoes radioactive decay, and these may be naturally occurring or artificially produced. 

The stable isotopes have nuclei that do not decay to other isotopes on geologic timescales, but may themselves be produced by the decay of radioactive isotopes. Radioactive (unstable) isotopes have nuclei that spontaneously decay over time to form other isotopes. For example, C, a radioisotope of carbon, is produced in the atmosphere by the interaction of cosmic-ray neutrons with stable... 

On this view, it would seem that in general Szilard-Chalmers experimentation has been directed at the theoretieally less interesting feature of the annealing curve, namely the rapidly rising part whereas solid-state research has dealt with the kinetics of what the chemists have considered as the plateaus of their curves. It is unfortunately not always easy to obtain reliable data for long-term annealing in Szilard-Chalmers systems. The half-life of the radioisotope employed is frequently too short, and in addition the crystalline compound investigated may be thermally unstable. As mentioned above, potassium chromate is a particularly favorable case in that neither of these difiSculties interfere. 

As you may recall, isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called radioisotopes. These unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay. During radioactive decay, unstable atoms lose energy by emitting one of several types of radiation. The three most common types of radiation are alpha (a), beta ((3), and gamma (7). Table 25-2 summarizes some of their important properties. Later in this chapter you ll learn about other types of radiation that may be emitted in a nuclear reaction. 

Beta decay A radioisotope that lies above the band of stability is unstable because it has too many neutrons relative to its number of protons. For example, unstable C has a neutron-to-proton ratio of 1.33 1, whereas stable elements of similar mass, such as and have neutron-to-proton ratios of approximately 1 1. It is not surprising then that undergoes beta decay, as this type of decay decreases the number of neutrons in the nucleus. 

Radioisotopes, isotopes of atoms with unstable nuclei, emit radiation to attain more stable atomic configurations. 

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