Positron chemistry

Positron chemistry is a specific field which aims at determining which solutes react with e+ to form a bound-state, comparing the related constants and studying the effects of temperature [3, 5, 6, 13, 18, 25, 46-48]. The results are scarce, because the bound-states can only be characterized through AC or DB experiments, which are less used than PALS as it seems, the lifetimes of all e+ bound-states known are very close to those of the free positrons, so that PALS cannot sufficiently distinguish these two states and is therefore unable to provide useful information. 

At present, essentially the halide, pseudo-halide and sulfide anions have been shown to react with e+, either directly [3, 6, 25,46,48] or after previous e capture by hologenated compounds (see Figs. 4.4 and 4.6) [19, 20]. However, it is not excluded that most anions are able to react with the positron. 

As expressed by reaction (VIII), all positron scavengers characterized in polar solvents lead to partial inhibition and therefore are supposed to react specifically with the localized particles. The reasons for this are not well established but, in the same way as for those Solutes that are very poor quasi-ffee electron scavengers although reacting effectively with the solvated electron (e.g., H+), the explanation may lie on thermodynamics. Too much energy may be released upon reaction with the quasi-free particles, either e or e+, so that the bound-state is unstable localization or solvation would reduce the energetics of the process, allowing the reaction to occur. Note that most of the partial inhibitors, whether electron (e.g. H+, Tl+) or positron (Cf, 

S=) scavengers, are monatomic species for which the release of extra energy is difficult because of the lack of vibrational modes. 

Nevertheless, some contribution to the increase in I4 with solute concentration due to e+aq capture (i.e., capture of solvated positrons that would not have formed Ps) cannot be discarded [5], 

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Mogensen, O.E. (1979). Solvated positron chemistry. II. The reaction of hydrated positrons with Cl, Br and I- ions. Chem. Phys. 37 139-158. 

The areas of inorganic and organic positron chemistry deal mainly with material characterization and industrial applications using PAS. Both chemical and electronic industries have found PAS to be a powerful method. In addition to the traditional solution chemistry of the positron and Ps [11], PAS has been developed to determine the free volume Bom-Oppenheimer approximation, such as molecular solids [14] and polymers [15]. The unique localization property of Ps in free volumes and holes has opened new hope in polymer scientific research that determination of atomic-level free volumes at the nanosecond scale of motion is possible. During the last ten years, most positron annihilation research has involved a certain amount of polymer chemistry, polymers and coatings, which will be discussed in Chapters 12 and 13. For inorganic systems, oxides are mostly studied using the positron and Ps. Silicon oxides and zeolites are the most important systems in positron and Ps chemistry. The developments in this area have on the cavity structure and chemical states of inner surfaces. Chapters 8 and 14 will discuss this subject. 

In polymer systems, positron chemistry can occur if the e+ is able to attach itself to a particular atom or group. Halogenated polymers, radicals and certain electron rich unsaturated structures have the capability of forming stable species of the form (e+,R ), with free positrons. These processes can lead to quenching and inhibition of Ps formation. 

In 1921, Irene Curie (1897-1956) began research at the Radium Institute. Five years later she married Frederic Joliot (1900-1958). a brilliant young physicist who was also an assistant at the Institute. In 1931, they began a research program in nuclear chemistry that led to several important discoveries and at least one near miss. The Joliot-Curies were the first to demonstrate induced radioactivity. They also discovered the positron, a particle that scientists had been seeking for many years. They narrowly missed finding another, more fundamental particle, the neutron. That honor went to James Chadwick in England. In 1935,... 

O.E. Mogensen, Positron Annihilation in Chemistry, Springer, Berlin, Heidelberg, 1995. 

Schrader, D. M. Jean, Y. C. 1988. Positron and Positronium Chemistry. Elsevier, Amsterdam, The Netherlands. 

Eowler JS (1993) The synthesis and application of F-18 compounds in positron emission tomography. In Filler R (eds) Organofluorine compounds in medicinal chemistry and biomedical applications. Elsevier Science Publishers BV, Amsterdam, p 309... 

Ding Y-S, Eowler JS (1996) 18F-Labeled tracers for positron emission tomography studies in the neurosciences. In Ojima 1, McCarthy J, Welch JT (eds) Biomedical frontiers of fluorine chemistry. ACS Symp Series 639. The American Chemical Society, Washington DC, chap 23, p 328... 

The next two chapters are dedicated to radiopharmaceutical contrast agents starting with a detailed description of the chemistry of p -emitting compounds based on fluorine-18. Particular emphasis is laid on the different radiolabeled precursors and their suitability for the rapid synthesis of compounds useful for positron emission tomography. 

Fluorine-18 Chemistry for Molecular Imaging with Positron Emission Tomography... 

P.H. Elsinga, Radiopharmaceutical chemistry for positron emission tomography. Methods 27 (2002) 208-217. 

JOLIOT-CURIE. IRENE 11897-195ft. A French nuclear scientist who won the Nohel prize for chemistry with her husband Frederick Joliet-Curie. Their joint work involved production of artiliciul radioactive elements by using t/-rays to bombard boron. They discovered that hydrogen-containing material when exposed to what they considered p rays would emit protons. Tliev were involved in many firsts they gave Ihe first chemical proof of aitillcial transmutation and of capture of alpha particles, and were the firsi to prepare positron emitter. Her career started with a Sc.D. at the Univ ersity of Paris, and included scores of honors and awards. 

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