Os argumentos físicos fundamentais para a descrição da linha de ressonância resultante de transições de estados quânticos induzidos por radiações eletromagnéticas não são, muitas vezes, suficientemente bem compreendidos por estudantes iniciantes em ciências naturais ou não-especialistas em espectroscopia. Livros didáticos em geral tendem a tratar o problema com base em formalismos teóricos complexos, inacessíveis a todos aqueles que não estão suficientemente familiarizados com os argumentos físicos e matemáticos avançados da mecânica quântica. Neste artigo, são apresentados desenvolvimentos algébricos mais diretos e mais simples, com a intenção de oferecer uma alternativa didática e servir como fonte de referência a leitores com graus variáveis de domínio teórico em física avançada. O ponto central é mostrar que a largura da linha de ressonância da radiação gama é conceitualmente o dobro da largura de linha natural para a energia relacionada ao estado nuclear excitado da transição. Os argumentos algébricos são utilizados de modo a oferecer uma via direta e dedutiva, intencionalmente mais prontamente alcançáveis do que os ora encontrados na literatura científica. Este estudo de caso foi escolhido na perspectiva particular do princípio físico correspondente à espectroscopia nuclear Mössbauer.

The fundamental physical arguments for the description of a resonance line arising from quantum states transitions induced by electromagnetic radiations are often hardly understandable by beginning students in natural sciences or non-specialists in spectroscopy. Textbooks usually tend to treat the problem on the basis of deeper theoretical formalisms which are seldom accessible by all those who are not sufficiently familiar with the required advanced physical and mathematical backgrounds in quantum mechanics. More direct and simpler algebraic developments are presented in this article, intending to be a didactic alternative and to serve as a reference source for a broader range of readers, to some extent requiring less background in more advanced physics. The central point is to show that the resonance linewidth of a gamma-ray resonance is conceptually twice the natural linewidth for the related energy line of the nuclear excited state. The algebraic arguments are used to offer a direct deductive pathway, which is purposely more promptly achievable than those currently found in the scientific literature. This study of case was conceived taking into account the physical principles of nuclear Mössbauer spectroscopy.

Two selective chemieal treatments consisting of mixtures of (i) oxalic acid - ammonium oxalate at pH 3 (OX) and (ii) sodium citrate - ascorbic acid at pH 6 (CA) were used to selectively remove minerals from clay fractions of four volcanic soils: one from an Ultisol and three Andisols, of the southern Chile. Chemieal analysis shows that CA is more effective in removing iron from Ultisol, and OX extracts it more efficiently from Andisols. 6 K 57Fe-M6ssbauer data indícate that OX tends to remove all magnetically ordered species with low hyperfine fields; CA has no clear effect on the removal of those or the identified iron oxides in these volcanic soil materials

In the present work, clays pillared with aluminium and impregnated with transition metals (Fe, Co and Cr) were prepared, characterised and studied as catalysts in the oxidation of chlorobenzene. The pillared clay was synthesised using a natural montmorillonite from San Juan (Argentina) as the starting material and an aluminium polycation solution. The catalysts were prepared by impregnating the pillared clay and then calcinating at 500ºC. The catalysts were characterised by XRD, temperature-programmed reduction (TPR) and nitrogen adsorption isotherms. The samples were tested in the deep oxidation of chlorobenzene in some cases reaching more than 90% of total conversion.

O herbicida sistêmico imazapyr foi usado no controle da taboa (Typha subulata Crespo & Peres-Moreau f.) em drenos de irrigação, como alternativa ao controle mecânico. O resíduo do princípio ativo do herbicida na água foi analisado por cromatografia líquida de alta performance (HPLC). A curva de dissipação de imazapyr mostrou que o herbicida pode ser usado para o controle de taboa em drenos de irrigação, sem causar danos a culturas vizinhas, desde que a água seja usada, no mínimo, depois de 1,6 a 3,7 dias da aplicação das doses de 500 a 1500 g ha-1, respectivamente.

Imazapyr, a systemic herbicide, was used to control cattail (Typha subulata Crespo & Peres-Moreau f.) in irrigation project drains as an alternative for mechanical control. Residue of this herbicide was analysed in water by high performance liquid chromatography (HPLC). Imazapyr dissipation curve with applied doses ranging from 500 to 1500 g ha-1 showed that it could be used to control cattail without injuring neighbor crops, as long as water drain be used at least 1.6 to 3.7 days after application.