Gamma induced reactions

High energy radiation exists under many forms, but the most important types for the potential applications they have in polymer science and technology are X-rays and gamma rays on the one hand, and accelerated electrons on the other. The recent development of swift ion beam accelerators that induce reactions exhibiting some common features with widespread radiation treatments cited at first will be also accounted for. 

Shenton JM, Popovic M, Chen J, Masson MJ, Uetrecht JP (2005) Evidence of an immune-mediated mechanism for an idiosyncratic nevirapine-induced reaction in the female Brown Norway rat. Chem Res Toxicol 18(12) 1799-1813 Steiniger B, Van der Meide PH, Falk P, Klempnauer J (1988) Induction of class IIMHC antigen expression in rat organs after systemic application of recombinant gamma interfiaoiL Adv Exp Med Biol 237 795-799... 

Charged particle-induced reactions, such as (p,n) and (p,a) reactions, yield radionuclides that are too rich in protons and consequently decay by positron (yS" ") emission or electron capture (EC), mostly followed by gamma (y) emission. Positrons are emitted with... 

While neutrons, charged particles, and gamma photons can be equally used for irradiation, the most frequent choice is the irradiation by neutrons. Since the neutron lacks an electric charge, it is more penetrating and makes the analysis of bulk samples possible. Additionally, the high cross-sections of neutron-induced reactions offer extremely high analytical sensitivities for many elements. 

Because of its high penetrating power, gamma radiation induced reactions can be carried out in opaque vessels and metal autoclaves. Consequently, the temperature range within which a chain reaction can be studied in a given solution, extends from its freezing point to its critical temperature. Thermally induced reactions can also be studied in autoclaves. However, the tempe-... 

This can be put in another way. It is to be expected that exposure to light will use up the postulated precursors. Since both light-induced and gamma-ray induced reactions involve the same carriers they should produce the same effects. Consequently after exposure to gamma rays crystals might... 

Neutron Activation Analysis Few samples of interest are naturally radioactive. For many elements, however, radioactivity may be induced by irradiating the sample with neutrons in a process called neutron activation analysis (NAA). The radioactive element formed by neutron activation decays to a stable isotope by emitting gamma rays and, if necessary, other nuclear particles. The rate of gamma-ray emission is proportional to the analyte s initial concentration in the sample. For example, when a sample containing nonradioactive 13AI is placed in a nuclear reactor and irradiated with neutrons, the following nuclear reaction results. 

In terms of atomic spectrometry, NAA is a method combining excitation by nuclear reaction with delayed de-excitation of the radioactive atoms produced by emission of ionising radiation (fi, y, X-ray). Measurement of delayed particles or radiations from the decay of a radioactive product of a neutron-induced nuclear reaction is known as simple or delayed-gamma NAA, and may be purely instrumental (INAA). The y-ray energies are characteristic of specific indicator radionuclides, and their intensities are proportional to the amounts of the various target nuclides in the sample. NAA can thus... 

NRA is a powerful method of obtaining concentration versus depth profiles of labelled polymer chains in films up to several microns thick with a spatial resolution of down to a few nanometres. This involves the detection of gamma rays produced by irradiation by energetic ions to induce a resonant nuclear reaction at various depths in the sample. In order to avoid permanent radioactivity in the specimen, the energy of the projectile is maintained at a relatively low value. Due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass < 30). 

Nuclear science in particular obtains from laser-driven electron sources a brand new input to perform interesting measurements in the context of many laboratories equipped with ultrashort powerful lasers. The ultrashort duration of these particle bunches represent a further attractive feature for these kinds of studies. In the following, we will focus on nuclear reaction induced by gamma radiation produced by bremsstrahlung of laser-produced electrons in suitable radiator targets. This way is usually mentioned as photo-activation and is particularly efficient for photons of energy close to the Giant Dipole Resonance of many nuclei. 

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