Decay, radioactive types

The beta-current neutron detector is a solid state ion chamber which is used in nuclear reactor technology. It consists of an emitter in which a nuclear reaction occurs, leading to the emission of primary /3 particles (e.g. through the reaction ( Rh(n,7) Rh(/8 , 4.2 s) Pd) or secondary electrons (e.g. through absorption of the prompt y s emitted in the neutron capture). These electrons represent a current and are collected by a collector. The radioactive decay type detectors have a response time depending on the product half-life, which the capture-y detectors lack. These detectors have a limited lifetime for the Co(n,y) Co it amounts to 0.1 % per month at 10 n cm s . The lifetime depends on... 

There are other less common types of radioactive decay. Positron emission results in a decrease by one unit in the atomic number K capture involves the incorporation of one of the extranuclear electrons into the nucleus, the atomic number is again decreased by one unit. 

Radon gas is formed in the process of radioactive decay of uranium. The distribution of naturally occurring radon follows the distribution of uranium in geological formations. Elevated levels have been observed in certain granite-type minerals. Residences built in these areas have the potential for elevated indoor concentrations of radon from radon gas entering through cracks and crevices and from outgassing from well water. 

State whether the following statements are true or false. If false, explain why. (a) The dose equivalent is lower than the actual dose of radiation because it takes into account the differential effects of different types of radiation, (b) Exposure to 1 X 1 ()x Bq of radiation would be much more hazardous than exposure to 10 Ci of radiation, (c) Spontaneous radioactive decay follows first-order kinetics, (d) Fissile nuclei can undergo fission when struck with slow neutrons, whereas fast neutrons are required to split fissionable nuclei. 

Three basic types of fundamental processes are recognized unimolecular, bimolecular and termolecular. Unimolecular processes are reactions involving only one reactant molecule. Radioactive decay is an example of a unimolecular process ... 

Radioactive decay provides splendid examples of first-order sequences of this type. The naturally occurring sequence beginning with and ending with ° Pb has 14 consecutive reactions that generate a or /I particles as by-products. The half-lives in Table 2.1—and the corresponding first-order rate constants, see Equation (1.27)—differ by 21 orders of magnitude. 

Analyses of this type are correct only if all of the product nuclide comes from radioactive decay. This is not known with certainty, but when age estimates using different pairs of nuclides give the same age and samples from different locations also agree, the age estimate is likely to be accurate. Note also that 3.8 X 10 years agrees with the qualitative limits derived from naturally occurring radioactive nuclides. 

The science of kinetics deals with the mathematical description of the rate of the appearance or disappearance of a substance. One of the most common types of rate processes observed in nature is the first-order process in which the rate is dependent upon the concentration or amount of only one component. An example of such a process is radioactive decay in which the rate of decay (i.e., the number of radioactive decompositions per minute) is directly proportional to the amount of undecayed substance remaining. This may be written mathematically as follows ... 

What is the difference between radioactive decay processes and other types of nuclear reactions ... 

Ans. Other types of reactions require a small particle to react with a nucleus to produce a nuclear reaction radioactive decay processes are spontaneous with only the one nucleus as reactant. 

The classic example of reactions of this type is a sequence of radioactive decay processes that result in nuclear transformations. The differential equations that govern kinetic systems of this type are most readily solved by working in terms of concentration derivatives. For the first reaction,... 

There are at present 116 known chemical elements. However, there are well over 2000 known nuclear species as a result of several isotopes being known for each element. About three-fourths of the nuclear species are unstable and undergo radioactive decay. Protons and neutrons are the particles which are found in the nucleus. For many purposes, it is desirable to describe the total number of nuclear particles without regard to whether they are protons or neutrons. The term nucleon is used to denote both of these types of nuclear particles. In general, the radii of nuclides increase as the mass number increases with the usual relationship being expressed as... 

Fig. 5.25. Nucleosynthetic outcome (after radioactive decay) of model W7 for Type la supernovae (Nomoto, Thielemann Yokoi 1984, and Thielemann, Nomoto Yokoi 1986), compared to Solar-System abundances. Dominant isotopes of multi-isotope elements are circled. Adapted from Tsujimoto (1993).

We can observe three common types of radioactive decay in nature. We can occasionally observe others. 

Gamma emission is the release of high-energy, short-wavelength photons, which are similar to x-rays. The representation of this radiation is y. Gamma emission commonly accompanies most other types of radioactive decay, but we normally do not show it in the balanced nuclear equation since it has neither appreciable mass nor charge. 

Three common types of radioactive decay are observed in nature, and two others are occasionally observed. 

Gamma emission, in which high-energy electromagnetic radiation is emitted from the nucleus. This commonly accompanies the other types of radioactive decay. It is due to the conversion of a small amount of matter into energy. 

So, now (1913) one has a set of rules which characterize the daughter atom in terms of a knowledge of the parent element and the type of radioactive decay. The rules work they give rise to the concept of isotopes elements which correspond to different atomic weights but which are chemically identical. However, the rules are purely empirical no explanation exists for the rules as the matter now stands. Something is still missing in this story. 

These two long rows of elements are traditionally moved to the base of the chart so the more important, lighter elements may be closer together for clarity. These two rows of metals each reflect the progressive addition of 14 electrons into an /-type subshell. The lanthanides occur in only trace amounts in nature and are often called rare earths. All of the actinides have large, unstable nuclei that undergo spontaneous radioactive decay. 

The mean reaction time during a reaction varies as the concentration varies if the reaction is not a first-order reaction. Expressions of mean reaction time of various types of reactions are listed in Table 1-2. In practice, half-lives are often used in treating radioactive decay reactions, and mean reaction times are often used in treating reversible chemical reactions. 

Radon (222Rn) is formed by the radioactive decay of uranium, BKU (Fig. 15.1a). As a result, the highest concentrations tend to be associated with soils derived from rocks with a high uranium content (Nazaroff and Nero, 1988 Boyle, 1988 Nero, 1989 Mose and Mushrush, 1997). Because radon is a gas that diffuses out of the soil, it can enter homes through cracks in the foundation, around loose-fitting pipes and wall joints, and through floor drains (e.g., Nero, 1989). The concentrations found in a home depend on the type of soil (including the moisture content) on which it sits and the extent of Rn penetration into the house. They also depend on the house ventilation rate and the particular location in the house in which the measurement is... 

Radioactive decay can take place in multiple ways. Chemists can use the type of decay to help determine the half-life of a radioactive isotope. 

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