Atomic decay

Because of the way in which rate of decay is measured (Figure 19.3), it is often described by the activity (A) of the sample, which expresses the number of atoms decaying in unit time. The first equation above can be written... 

Activity can be expressed in terms of the number of atoms decaying per second, or bec-querels (Bq). 

Activity, nuclear Rate of radioactive decay number of atoms decaying per unit time, 518... 

The radiation from exposure to americium is the primary cause of adverse health effects from absorbed americium. Upon entering the body by any route of exposure, americium moves relatively rapidly through the body and is concentrated in bones where it remains for a long time. While in the bone, americium atoms decay, releasing alpha particles and gamma-rays. Alpha... 

Radioactive decay is a stochastic process that occurs at random in a large number of atoms of an isotope (see Textbox 13). The exact time when any particular atom decayed or will decay can be neither established nor predicted. The average rate of decay of any radioactive isotope is, however, constant and predictable. It is usually expressed in terms of a half-life, the amount of time it takes for half of the atoms in a sample of a radioactive isotope to decay to a stable form. 

During the transport in the chamber, radon atoms decay to form RaA atoms. The RaA atoms except those diffused to the wall of the chamber are collected on the exit filter. The sample collected on the exit filter is removed and counted. The present method is able to simultaneously measure radon and thoron concentrations by alpha spectroscopic technique (Ikebe et al., 1979). 

Therefore, N0 = number of 238U atoms remaining + number of 238U atoms decayed = number of 238U atoms remaining + number of 206Pb atoms produced... 

The rate at which radioactive atoms decay is unaffected by the chemical or physical form of the nucleide and depends only on the number N of atoms present and the decay constant Vs-1 for that particular nuclide. In a single... 

Because of its importance in natural phenomena, e.g., radioactive decay and population dynamics, let us introduce the exponential distribution through an illustration, n atoms are assumed to decay over the time interval [0 — 0], each atom having the same probability of decaying at any time in this interval. In other words, the time at which an atom decays is uniformly distributed over [0 — 0]. Let us call N(t) the number of decay events between 0 and t. The probability that a single atom has not decayed at time t, is 1—f/0 (Figure 4.3). The probability that none of the n atoms has decayed at time t is... 

Team led by physicist Peter Armbruster Presumably solid white or gray metal produced by bombarding lead with accelerated nickel atoms decays after 0.0005 second. 

Physically, ds, measures the distance over which the probability of finding a diffusing atom decays as one moves away from the step edge. In the small q limit, the eigenvalues of M are given by,... 

Despite their instability, some unstable atoms may last a long time the half-life of uranium 238, for example, is about 4.5 billion years. Other unstable atoms decay in a few seconds. Radioactive decay is one of the topics of nuclear chemistry, and it involves nuclear forces, as governed by advanced concepts in chemistry and physics, such as quantum mechanics. Researchers do not fully understand why some atoms are stable and others are not, but most radioactive nuclei have an unusually large (or small) number of neutrons, which makes the nucleus unstable. And all heavy nuclei found so far are radioactive—nuclides with an atomic number of 83 or greater decay. 

Number of atoms of radioactive 87Rb and daughter 87Sr as a function of time in units of half-life. For each half-life the number of radioactive 87Rb atoms drops by a factor of two as the 87Rb atoms decay to 87Sr. After 10 half-lives, the parent isotope is effectively gone. 

Figure VIII-2 shows the principle of isotope enrichment by two-photon ioni/.ation of 233U atoms. The excitation wavelength is 4266.275 0.02 A. A band width of 0.1 cm 1 is much narrower than an isotope shift of 0.32cm 1. Since the preferentially excited 235U atoms decay in 10-7sec the second laser source to ionize the excited atoms must be pulsed within 10 - 7 sec. The wavelength of the second laser must be shorter than 3777 A, as the combined photon energy must exceed the ionization potential, 6.187 eV, of U atoms. If the first laser is set at 4266.325 A in coincidence with an absorption line of 238U atoms, an isotopic yield ratio of 3000 1 for 238U/23,U is obtained in comparison with 140 1 for the same ratio in the starting material.

In fact, the ratio of carbon-12 atoms to carbon-14 atoms in all living things is basically constant. Even though the carbon-14 atoms decay, these atoms are... 

The age of an art object can provide a valuable clue to whether it is real or a forgery. Because the half-life for a specific isotope is constant, half-life can be used to find the age of an object. The isotope put to use for radioactive dating is carbon-14. The half-life of carbon-14 is 5,730 years. The amount of carbon-14 in our atmosphere remains fairly constant. When an object such as a plant is alive, it absorbs C02. The carbon atoms in the C02 are made of a specific ratio of carbon-14 atoms to carbon-12 atoms. The carbon-14 atoms decay by emission of beta particles ... 

S. B. Sinclair, J. J. Thomson and the chemical atom from ether vortex to atomic decay , Ambix, 1987, 34, 89-116. 

Core - excitations are created, usually by 1 to 10-keV incident electrons Auger electrons of characteristic energies are emitted through a two - electron process as excited atoms decay to their ground state. AES gives information on the near - surface chemical composition. 

Uranium in nature may be measured either radiometrically or chemically because the main isotope - 238U - has a very long half life (i.e., relatively few of its radioactive atoms decay in a year). Its isotopes in water and urine samples usually are at low concentrations, for which popular analytical methods are (1) radiochemical purification plus alpha-particle spectral analysis, (2) neutron activation analysis, (3) fluorimetry, and (4) mass spectrometry. The radiochemical analysis method is similar in principle to that of the measurement of plutonium isotopes in water samples (Experiments 15 and 16). Mass spectrometric measurement involves ionization of the individual atoms of the uranium analyte, separation of the ions by isotopic mass, and measurement of the number of separated isotopic ions (see Chapter 17 of Radioanalytical Chemistry text). 

In contrast to the use of large Sf ratios, where attention is focussed on the wall of the tube, Wood and Wise [62, 63] have used short tubes to determine j for the material simulating the end plate. They investigated the recombination efficiency of several metals for H atoms. In the later study [63], their terminal probe was in the form of a heated spiral filament of the metal under investigation. The decrease in energy necessary to maintain the filament at constant temperature was measured and assumed to be proportional to the atom concentration at the cross-section occupied by the filament. The method is preferable to the use of thermocouple probes, whose change in temperature might affect the atom decay profiles. Wood and Wise attribute differences in their results obtained... 

The 7 energy is much greater than the positronium mass, and the branching ratio for the atomic decay... 

The trap is loaded in a time of a few seconds, and after a preselected delay its contents are dumped into the resonator region by lowering the field of one of the pinch solenoids. The signal from the hyperfine resonance detector provides a measure of the total number of atoms N in the trap. The stored atoms decay by dipole relaxation (described below) with a rate that is proportional to the density n. From values of N and n one can find the effective volume of the trap. The effective volume depends on the field geometry and the temperature. This roundabout route is... 

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