This paper provides information on the effects of distance and attenuation in lead sheet and gypsum board of the 0.511 MeV photon produced by positron annihilation. Exposure rates are projected external to an adult injected with 185 MBq (5 mCi) of 18F in a fluorodeoxyglucose solution and for the same activity in a small unshielded container. These data have been applied to estimate the shielding requirements for the Positron Emission Tomography (PET) suite operated by the Nuclear Medicine Department of Our Lady of the Lake Regional Medical Center. To assure that exposures are as low as reasonably achievable, lead was added to the walls of the room where the 18F is stored, handled, and injected into the patients. The PET scanner is installed in a room that formerly contained a Computerized Axial Tomography scanner; the existing 1.6 mm of lead sheet was left in place even though it is not required for personnel protection. During the initial phase of operation, a shield test program was conducted to estimate annual exposures to personnel inside and outside the suite. Projection of measured rates over a year of operation demonstrate that whole body doses are well below regulatory limits.
An in vivo dosimetry system that uses p‐type semiconductor diodes with buildup caps was characterized for clinical use on accelerators ranging in energy from 4 to 18 MV. The dose per pulse dependence was investigated. This was done by altering the source‐surface distance, field size, and wedge for photons. The off‐axis correction and effect of changing repetition rate were also investigated. A model was developed to fit the measured two‐dimensional diode correction factors.PACS number(s): 87.66.–a, 87.52.–g
Summary A formula has been derived which as a first approximation, predicts the quantum yields for the inactivation of enzymes. The enzymes can be divided into a group containing cystine and the subtilisins which do not. The formula applied to subtilisin gives good agreement. For some of the enzymes, only cystine needs to be considered in the calculation; for others good agreement is found if contributions from aromatic groups are included. On this basis a quantum yield for tobacco mosaic virus protein is computed as 0.0047 at 2537 Å.
The origin of chemically modified histidine in photochemically inactivated lysozyme has yet to be explained.
Abstract— Initially photoreactivation of irradiated (2537 Å) nucleic acid on pinto bean increases linearly with time of illumination with white light of 250 ft‐c. Maximum amounts of photo‐reactivation depend on the quality of light used. The action spectrum shows a peak in the ‘black light’ region, where the greater amount of photoreactivation is found, and a shoulder in the blue light region. Maximum repair is obtained with ‘black light.’ Photoreactivation does not occur at wavelengths above 550 nm. Photoprotection by illumination of leaves prior to inoculation by irradiated RNA was not found. The action spectrum for photoreactivation does not resemble the action spectrum for photosynthesis.
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