Half-life radioactive decay

The nature of the radioactive decay is characteristic of the element it can be used to fingerprint die substance. Decay continues until bodi die original element and its daughter isotopes are non-radioactive. The half-life, i.e. die time taken for half of an element s atoms to become non-radioactive, varies from millions of years for some elements to fractions of a second for odiers. 

Radioactivity serves as a useful clock only for times that are the same order of magnitude as the decay half-life. At times much longer than t j2, the amount of radioactive nuclide is too small to measure accurately. At times much... 

Isotope (Curie Symbol) Mode of Decay Half-life Major Radioactive Emissions Energies (MeV)... 

The conceptual problems start when considering materials such as plutonium, which is a by-product of the nuclear electricity industry. Plutonium is one of the most chemically toxic materials known to humanity, and it is also radioactive. The half-life of 238Pu is so long at 4.5 x 108 years (see Table 8.2) that we say with some certainty that effectively none of it will disappear from the environment by radioactive decay and if none of it decays, then it cannot have emitted ionizing a and f) particles, etc. and, therefore, cannot really be said to be a radioactive hazard. Unfortunately, the long half-life also means that the 238Pu remains more-or-less for ever to pollute the environment with its lethal chemistry. 

The radioactive decay of a nucleus is a random process, but the decay of a particular element is characterized by a number known as the half-life (7 1/2), which is the time taken for half of the original material to change into another element by radioactive decay. Half-lives vary from fractions of a second to many billions of years, depending on the isotope. The half-life is only meaningful when considered in terms of the behavior of an assemblage of atoms of the radioactive element for any particular atom, the probability that it will undergo radioactive decay in any particular time period is essentially unpredictable it may happen in the next second, or it may not happen for millennia. It is possible that the atom we have selected to watch... 

A radioactive /3-emitting (0.156 MeV) carbon nuclide. The decay half-life is 5715 years. 

The half-life of a radioactive decay is the period of time required for half of the initial amount of the substance to disintegrate. The shorter the half-life of a radioactive decay, the higher the rate of radioactive decay and the more radioactivity. The half-life is the characteristic property of each element. 

Habitat The place where a population (e.g., human, animal, plant, microorganism) lives and its surroundings, both living and nonliving Half-life The term that denotes the time required for the elimination of one half of the total dose of a chemical from the body. For instance, the biochemical half-life of DDT in the enviromnent is 15 years. Similarly, the time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years)... 

Why is radon, a noble gas, a pollutant Although Rn is a member of the noble gas family, 222 Rn is a radioactive gas (half-life = 3.8 days) that decays first into 218Po (half-life = 3 min), ending in 210Pb (half-life = 22.3 years). Radon enters a building from the subjacent ground, either carried by a convective flow of soil gas or dissolved in the ground-water. 

The half-life is the time it takes for half of a given amount of a radioactive isotope to undergo decay. Half-life, which is symbolized ti/2, is easy to measure and has been determined for many different radioisotopes, some of which have important uses. Some half-lives are only fractions of a second, whereas others are billions of years. Half-lives for some of the most commonly used radioisotopes are listed in Table 21.1. The concept of half-life is illustrated in the graph in Figure 21.7. 

The source of 7 rays needed for the teehnique is typically an excited-state nucleus, which is itself formed by a nuclear decay process from another nueleus. The most widely used Fe (where denotes excited state) is formed in an electron-capture proeess from radioactive 27C0 (half-life 270 days). This in turn is readily obtained by cyclotron irradiation of iron. f Co decays to Fe with nuclear spin quantum number 7 = 5/2, for which two relaxation processes exist, one with a 15% probability that leads directly to the Fe ground state (by emission of a 7 photon of 136.32 keV), and another with an 85% probability that leads to a different excited-state nucleus with 7 = 3/2. This is what is actually used for the Mossbauer experiment. It has a transition to the ground state (7 = 1/2) with emission of a 7 photon of 14.41 keV (Figure 6.1). 

Radioactive rays radiopharmaceuticals that have short decay half-life time, are entered into the body by injection or through the digestive system. The temporal distribution of the radiopharmaceuticals in body is a main structure factor. It s measured from the intensity of gamma rays that are released from the body. Also the gamma absorption rate of tissues in volume is defined too. 

The C exchanges with C in living organisms, but exchange ceases on death. The radioactive content decays with a half-life of 5730 years. Hence the age of a once living material may be established by determining the amount of C. 

Since the half-life is independent of the number of radioactive atoms, it remains constant throughout the decay process. Thus, 50% of the radioactive atoms disintegrate in one half-life, 75% in two half-lives, and 87.5% in three half-lives. 

Radon-222 [14859-67-7] Rn, is a naturally occuriing, iaert, radioactive gas formed from the decay of radium-226 [13982-63-3] Ra. Because Ra is a ubiquitous, water-soluble component of the earth s cmst, its daughter product, Rn, is found everywhere. A major health concern is radon s radioactive decay products. Radon has a half-life of 4 days, decayiag to polonium-218 [15422-74-9] Po, with the emission of an a particle. It is Po, an a-emitter having a half-life of 3 min, and polonium-214 [15735-67-8] Po, an a-emitter having a half-life of 1.6 x lO " s, that are of most concern. Polonium-218 decays to lead-214 [15067-28A] a p-emitter haviag = 27 min, which decays to bismuth-214 [14733-03-0], a p-emitter haviag... 

Radiocarbon dating (43) has probably gained the widest general recognition (see Radioisotopes). Developed in the late 1940s, it depends on the formation of the radioactive isotope and its decay, with a half-life of 5730 yr. After forms in the upper stratosphere through nuclear reactions of... 

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