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PubMed · 817123

Portable tissue equivalent calorimeter.

J C McDonald·J S Laughlin·R E Freeman
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Abstract

A portable tissue equivalent calorimeter has been constructed and employed to measure absorbed dose in a mixed fast-neutron and gamma-ray field. Design details and measurement techniques are described along with the limits of precision and absolute accuracy. Experiments have been carried out with a cyclotron produced neutron beam using the 9Be(d,n)10B reaction at dose rates ranging from 3 to 25 rad/min. A series of ten measurements at a dose rate of approximately 10 rad/min were performed with a precision of +/- 2% (standard deviation about the mean). The compact design of this calorimetric dosimeter system facilitates transport to other laboratories for the measurement of absorbed dose in several complex radiation fields.

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CalorimetryFast NeutronsGamma RaysRadiometryRadiotherapy DosageRadiotherapy, High-EnergyJournal ArticleResearch Support, U.S. Gov't, Non-P.H.S.Research Support, U.S. Gov't, P.H.S.

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J C McDonald, J S Laughlin, R E Freeman. Portable tissue equivalent calorimeter.. https://doi.org/10.1118/1.594273

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Conformations of dinucleoside phosphates in aqueous solution.

The conformations of dinucleoside phosphates have been reexamined by semiempirical potential energy calculations. Conformations I, II, and III, proposed by Lee & Tinoco [Lee, C. H., & Tinoco, I., Jr. (1977) Biochemistry 16, 5403], are possible species after refinement of their structures by potential energy minimization. These three conformers can represent three types of dinucleoside phosphate species in solution. Dhingra et al. [Dhingra, M. M., Sarma, R. H., Giessner-Prettre, C., & Pullman, B. (1978) Biochemistry 17, 5815] had concluded that conformations of type II and III were unlikely or impossible. They favored conformations g-g- (equivalent to I), g+g+,g+t, and tg+; the last three conformations have little stacking and are calculated to be energetically less favorable by more than 5 kcal/mol. Common structures of the types I, II, and III are found for dinucleoside phosphates with different purine-pyrimidine sequences. The sequence dependence of the potential energy of these three conformers has been calculated. The experimental nuclear magnetic resonance data of dinucleoside phosphates are consistent with these three conformations.

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