Our group at the Laboratorio do Acelerador Linear (IFUSP- USP) is currently developing several studies related to the interaction of different kinds of radiation with DNA. Initially, our plan is to study the interactions proton-DNA, gamma-DNA and neutron-DNA. In this work we describe the most important features of the neutron-DNA study, which we plan to perform by selecting thermal, epithermal and fast neutrons. To improve the information about radiation-DNA interaction is important in order to achieve more secure and efficient cancer treatments by using radiation therapy. Nowadays, one important technique is the boron neutrons capture therapy, where neutrons are used to initiate a nuclear reaction at the tumor site. The effects of the neutrons on the health tissue, however, must be better understood. The study of neutron-DNA interaction, in this scenario, is of great importance. The research facility for Boron Neutron Capture Therapy (BNCT) in the IEA-R1 Reactor of the IPEN-CNEN/SP[1] will be used for studying the neutron-induced DNA damage. At present, we are evaluating the characteristics of the neutron flux at the biological sample, and we are carrying out simulations of the experimental procedure through Monte Carlos N Particle transport code system version 4C (MCNP-4C)[2] to find the experimental conditions necessary to minimize such contamination, and also verify the effects of those gamma's on the DNA molecule. The first step is the selection of filters configurations, which will allow us to irradiate the DNA sample with thermal, epithermal and fast neutrons. We present the results of our simulations, and describe the experimental setup show the best sets of materials necessary to obtain neutron spectra for different neutrons energies.

Neste trabalho são relatados os resultados de produção e vigor das plantas em um experimento de competição de seis clones de limoeiro-taiti (Citrus latifolia Tanaka) enxertados no porta-enxerto limoeiro-cravo (Citrus limonia Osbeck). Os resultados de seis anos consecutivos mostraram que o clone IAC 5 foi o mais produtivo superando, em média, todos os outros nas colheitas de janeiro, julho e outubro. Em segundo lugar colocou-se o IAC 2, cuja produção máxima se localizou, porém, no mês de abril, quando os preços do mercado são os mais baixos. O IAC 6 foi inferior a todos. Os clones IAC 1, IAC 3 e IAC 4, comportaram-se de maneira intermediária e a distribuição da produção do IAC 1 foi a mais favorável. O clone IAC 5 foi também o mais vigoroso e não apresentou fissuras na casca do tronco e dos ramos. IAC 2 foi o clone de menor vigor e juntamente com IAC 1 e IAC 6, o mais suscetível à incidência de fissuras.

Six selected clones of Tahiti lime (Citrus latifolia Tanaka) were evaluated in a field trial at the Estação Experimental de Limeira for fruit production and plant vigor, during six consecutive years. All six clones had the Rangpur lime (Citrus limonia Osbeck) as rootstock. The relationship between monthly fruit price and seasonal yield data was also investigated. The clone IAC 5 showed the highest yield in January, July, and October when Tahiti lime price is maximum. This selection had the most vigorous plants with absence of cracks in the bark of the trunk and branches. The least vigorous material was the IAC 2 selection with a top yield in April, when fruit price is minimum. The clones IAC 1, IAC 3, and IAC 4 showed intermediate production while IAC 6 revealed the lowest yield.