Single radioactive atoms

Problems associated with the disintegration of a single radioactive atom will not be developed here However, an understanding of the decay appears rather important in one-atom-at-a-time chemistry [2,10],... 

Moreover, the half-life of a single radioactive atom cannot be measured, and even if the half-life is knwon, the instant at which the atom will undergo disintegration cannot be predicted. Radioactive decay, chemical kinetics and chemical equilibria are governed by the laws of probability and many measurements with single atoms are necessai7 to establish the statistics and to obtain relevant results. With regard to chemical properties, it is important that all the atoms are present in the same chemical form (same species). 

The low detection limits of radioactive substances are very attractive for use in analytical chemistry. In principle, a single radioactive atom can be detected provided that it is measured at the moment of its decay. In practice, however, a greater number of radioactive atoms is necessary to measure their radioactivity with a sufficiently low statistical error. The mass m of a radionuclide and its activity A are correlated by the half-life ti/2-... 

Consider a single radioactive atom of some kind. Let p denote the probability that it will disintegrate within a certain observation period A t. Suppose that the atom is ageless in the sense that p is independent of how long it had existed before its observation was started. It stands to reason that the chance of decay increases with the length of the observation period. Moreover, it also seems reasonable to assume that for short enough At there is a proportionality... 

Radioactivity is equal to the rate of decay of a given radioisotope. This quantity is proportional to the number of radioactive atoms present, so that for a single isotope,... 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

The beta particle is an ordinary electron or positron ejected from the nucleus of a beta-unstable radioactive atom. The beta has a single negative or positive electrical charge and a very small mass. 

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... 

The detection of individual species is possible with certain methods. One can, with radioactive isotopes, measure a single atom. This, however, does not imply that methods using radioisotopes are better than those using stable isotopes. This paradox is explained by considering that in order to measure a radioactive atom, it is necessary that it decomposes during the time of the measurement. Thus if a radio-element has a long lifetime, the chance of observing this decomposition will be small. 

While at Manchester. Rutherford produced the first human nuclear reaction with the disintegration of a non-radioactive atom, dislodging a single particle. He became famous as the man who split the atom. In 1919, Rutherford succeeded J.J. Thomson as Cavendish Professor of Physics at Cambridge. He was a leader of a research team encouraging others in the investigation of the nucleus. 

This is an estimate that assumes emission of a single gamma ray of 1 MeV by each radioactive atom and that detector and sample both are points. 

That is the advantage of fission. Its drawback is the deadly radioactivity it generates, particles whose mass, from one type of reactor, is almost equal to the mass of the fuel consumed. Waste from a fission reactor typically requires thousands of years before it breaks down into biologically safe levels. Fission reactors are also relatively inefficient. They can use but a single isotope (atoms of an element that have the same number of protons but a different number of neutrons) of uranium, U-235, which makes up less than 1 percent of natural uranium ore. (More than 99 percent of natural uranium is nonfissionable U-238.) So-called fast breeder reactors might overcome the supply limitation by breeding fissionable fuel from U-238. But the fuel it produces from the uranium is plutonium, the same stuff that was inside the Nagasaki bomb—not an ideal by-product in a politically unstable world. 

Let us briefly discuss again the limitations of radioactive decay measurement. The observation of the radioactive decay of a single atom is possible, consequently, with efficient apparatus for the detection of the decay particles and a radioactive species with a half-life of seconds and minutes, it is possible to detect all or nearly all of a small number of radioactive atoms in the presence of a large number of nonradioactive atoms with radiation detection techniques. However, as the half-life increases, the time taken to carry out an experiment with a small number of radioactive atoms naturally increase, for half-lives, of say, 10 years efficient detection of the radioactive decay products becomes impossible unless the measurement can be continued for 10 years. Therefore, studies of long-lived radioactive isotopes invariably use very large numbers of atoms and the apparatus detects the decay of only a small fraction of the total during the experiment. In this situation the mass spectrometric detection sensitivity surpasses by far the sensitivity of radioactive counting methods. 

The K(3 IKOi x-ray intensity ratio is an easily measurable quantity with relatively high precision and has been studied extensively for /f-x-ray emission by radioactive decay, photoionization, and charged-particle bombardment (1-3). Except for the case of heavy-ion impact where multiple ionization processes are dominant, it is generally accepted that this ratio is a characteristic quantity for each element. The experimental results are usually compared with the theoretical values for a single isolated atom and good agreement is obtained with the relativistic self-consistent-field calculations by Scofield (4). 

In addition to the standard type of unusual compoimds mentioned above, any radioactively labeled products that are formed in nuclear recoil systems and that cannot be prepared by conventional means may also be regarded as imusual. However, the species thus formed are always singly labeled. The chance of double labeling is negligible because in a typical recoil system only about 10 radioactive atoms are formed in an environment consisting of about 10 reactant molecules. 

Repetition Since the moment in time at which a single transactinide atom is synthesized can currently not be determined and chemical procedures often work discontinuously, the chemical separation has to be repeated with a high repetition rate. Thus, thousands of experiments have to be performed. This inevitably led to the construction of highly automated chemistry set-ups. Due to the fact, that the studied transactinide elements as well as the interfering contaminants are radioactive and decay with a certain half-life, also continuously operating chromatography systems were developed. 

An important property of the MOT is the ability to catch atoms whose optical frequencies are shifted from the laser frequency by only a few natural linewidths. This property has been applied for ultrasensitive isotope trace analysis. Chen et al. (1999) developed the technique in order to detect a counted number of atoms of the radioactive isotopes Kr and Kr, with abundances 10 and 10 relative to the stable isotope Kr. The technique was called atom trap trace analysis (ATTA). At present, only the technique of accelerator mass spectrometry (AMS) has a detection sensitivity comparable to that of ATTA. Unlike the AMS technique based on a high-power cyclotron, the ATTA technique is much simpler and does not require a special operational environment. In the experiments by Chen et al. (1999), krypton gas was injected into a DC discharge volume, where the atoms were excited to a metastable level. 2D transverse laser cooling was used to collimate the atomic beam, and the Zee-man slowing technique was used to load the atoms into the MOT. With the specific laser frequency chosen for trapping the Kr or Kr isotope, only the chosen isotope could be trapped by the MOT. The experiment was able to detect a single trapped atom of an isotope, which remained in the MOT for about a second. 

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

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