Alpha decay recoil

Such alpha-recoil plays a fundamental role in fractionating the nuclides from one another in the low-temperature environment. During igneous processes, on the other hand, alpha recoil is probably not important in the generation of disequilibria ( °Th, Ra, and Pa). Beattie (1993) pointed out that the time scale of annealing of alpha decay damage at high temperatures was much shorter than the time scale of decay of these nuclides. 

While it is expected that the source rocks for the radionuclides of interest in many environments were deposited more than a million years ago and that the isotopes of uranium would be in a state of radioactive equilibrium, physical fractionation of " U from U during water-rock interaction results in disequilibrium conditions in the fluid phase. This is a result of (1) preferential leaching of " U from damaged sites of the crystal lattice upon alpha decay of U, (2) oxidation of insoluble tetravalent " U to soluble hexavalent " U during alpha decay, and (3) alpha recoil of " Th (and its daughter " U) into the solute phase. If initial ( " U/ U).4 in the waters can be reasonably estimated a priori, the following relationship can be used to establish the time T since deposition,... 

The recoil factors r define the probability of whether an attached radioactive atom desorbs from the particle surface in consequence of an alpha decay or not. Mercer and Strowe (1971) found a recoil factor = 0.81 in their chamber studies in contradiction to the value of ri 0.4 measured by Kolerski et al. (1973). No other results about the recoil factor are available in the literature. 

Although alpha decay carries away positive charge, electrons are stripped from the parent atom by its recoil, and decay products are formed as positive ions. Before discussing their properties, it is convenient to summarise briefly the formation, neutralisation and attachment to condensation nuclei of ordinary small ions in air, as described for example by Chalmers (1967). 

Alpha decay is characterized by the emission of an alpha particle from the parent nucleus. In this process, energy is released in the form of kinetic energy of the escaping alpha particle and the recoiling daughter nucleus. For example ... 

Alpha decay leads to a decrease of the atomic number by two units, Z — Z — 2, and causes an expansion of the electron shell, as illustrated in Fig. 9.5 for the a decay of radioisotopes of Bi. EHffercnccs in the binding energies arc marked for electrons in the inner shells. Furthermore, there arc two surplus electrons after a decay. However, in the case of a decay the excitation effects due to the change of the atomic number are relatively small compared with the recoil effects that have been discussed in the previous section, with the result that the recoil effects dominate. 

Fig. 22 Schematic illustration of the RDT technique. Prompt gamma rays are observed at the target position. The nucleus then recoils out of the target and flies through the separator where it is implanted in a Si detector. After a while the nucleus decays by a characteristic alpha decay in the same position, identifying the earlier implant. In the bottom panel a calcnimetric electron signal additionally indicates the decay of an isomeric state...

Fig. 23 Illustration of the RDT technique. The top panel shows all gamma rays emitted in the reaction of Ar on Sm. The middle panel shows all gamma rays associated with recoiling nuclei reaching the focal plane of the separator. The main reaction channel leading to Pt is pulled out of the background. In the bottom panel only those gamma rays associated with implanted nuclei followed by the characteristic alpha decay of Hg are shown [64]. Note the different scales on the axis. This technique is able to identify gamma rays belonging to a particular reaction channel on an event-by-event basis, which makes it so powerful...

Fig. 24 Gamma ray spectra showing the ground state rotational band of The top spectrum shows all gammas associated with recoils at the focal plane of RITU while the bottom spectrum shows only those gammas where the associated implanted nucleus was followed by a characteristic alpha decay of All peaks in the top spectrum apart from the X-rays of Pb at...

The as-received specimens were polished with diamond suspensions down to 1 pm. They were subsequently irradiated with heavy ions. This kind of irradiation aims to simulate the interactions present in reactors (impacts of fission products, recoil atoms of alpha-decays, and neutrons) without... 

The identification of element 102 by a double-recoil technique following alpha decay is well known. Much of the American evidence for the existence and isolation of element 104 hinges on the identification of the element 102 daughter particle which could be separated from the element 104 parent by a recoil method (see for example ref. 26). The recoil technique has been further exploited in the separation of fission fragments. The measurement of short half-lives (ca. 300 radioactive series is facilitated by recoil separation techniques. Recoils have been used to enrich Ca and Cs as well as to produce Xe compounds. ... 

Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either lOB or IIB. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6 MeV alpha particle with a half-life of 8 s. 

The study of the chemical behavior of concentrated preparations of short-Hved isotopes is compHcated by the rapid production of hydrogen peroxide ia aqueous solutions and the destmction of crystal lattices ia soHd compounds. These effects are brought about by heavy recoils of high energy alpha particles released ia the decay process. 

There are two main sources of Rn to the ocean (1) the decay of sediment-bound "Ra and (2) decay of dissolved "Ra in a water column. Radon can enter the sediment porewater through alpha recoil during decay events. Since radon is chemically inert, it readily diffuses from bottom sediments into overlying waters. The diffusion of radon from sediments to the water column gives rise to the disequilibrium (excess Rn) observed in near-bottom waters. Radon is also continuously being produced in the water column through the decay of dissolved or particulate "Ra. 

When Rn-222 decays with the emission of a 5.49 Mev alpha particle the recoiling energy of the newly formed Po-218 atom is 0.10 Mev which is sufficient for a range of about 50 micrometers in air. However, the velocity of the recoiling Po-218 atom is still small compared with that of the orbital electrons. 

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

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