ABSTRACT
This article examines crop varietal standardization in the United States. Numerous committees formed in the early twentieth century to address the problem of nomenclatural rules in the horticultural and agricultural industries. Making shared reference to a varietal name proved a difficult proposition for seed-borne crops because plant conformity tended to change in the hands of different breeders. Moreover, scientific and commercial opinions diverged on the value of deviations within crop varieties. I review the function of descriptive difference in the seed trade and in the framework of evolutionary theory before examining the institutional history of varietal standardization. Pimento peppers are used to represent how vegetables were treated differently than cereals. Lack of stability within a popular pimento variety caused problems for food packers in middle Georgia, which public breeders addressed by releasing new peppers. To conclude, the article questions the role of taxonomy in intellectual property, as breeding history and yield became defining attributes for making varietal distinctions.
Subject(s)
Agriculture , Crops, Agricultural , United StatesABSTRACT
PURPOSE: This study performed a dosimetry intercomparison for synchrotron-produced monochromatic x-ray beams. Ion chamber depth-dose measurements in a polymethylmethacrylate (PMMA) phantom were compared with the product of MCNP5 Monte Carlo calculations of dose per fluence and measured incident fluence at 25 and 35 keV. The ion chamber measurements are being used to calibrate dose output for cell irradiations designed to investigate photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. METHODS: Monochromatic beams of 25 and 35 keV were generated on the tomography beamline at CAMD. A cylindrical, air-equivalent ion chamber was used to measure the ionization created in a 10×10×10-cm3 PMMA phantom at depths of 0.6 - 7.7 cm. AAPM TG-61 protocol was applied to convert measured ionization into dose. MCNP5 simulations of the irradiation geometry were performed to determine the dose deposition per photon fluence in the phantom. Photon fluence was determined using a NaI detector to make scattering measurements of the beam from a polyethylene target at angles 15 - 60 degrees. Differential Compton and Rayleigh scattering cross sections were used to derive the incident fluence. RESULTS: At 35 keV dose measurements for equal exposures determined using the MCNP5-fluence results underestimated those of the ion chamber by 1.8 - 4.8% for PMMA depths from 0.6 - 7.7 cm, respectively. At 25 keV there was an overestimate of 6.6 - 1.9%. CONCLUSIONS: These results show that TG-61 ion chamber dosimetry, used to calibrate the dose output for the cell irradiations, is accurate within approximately 7% for beam energies 25-35 keV. This research was supported by contract W81XWH-10-1-0005 awarded by The U.S. Army Research Acquisition Activity, 820 Chandler Street, Fort Detrick, MD 21702-5014. This report does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.
ABSTRACT
PURPOSE: This work investigates the dose-response curves of Gafchromic EBT2 and EBT3 radiochromic films using synchrotron-produced monochromatic x-ray beams. These dosimeters are being utilized for dose verification in photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. METHODS: Monochromatic beams of 25, 30 and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth-dose measurements were used to calculate the dose delivered to films irradiated simultaneously at depths from 0.7 - 8.5 cm in a 10×10×10-cms polymethylmethacrylate phantom. AAPM TG-61 protocol was applied to convert measured ionization into dose. Calibrations of films at 4 MV were obtained for comparison using a Clinac 21 EX radiotherapy accelerator at Mary Bird Perkins Cancer Center. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the optical density (OD) derived from the red channel. RESULTS: For EBT2 film the average sensitivity (OD/dose) at 50, 100, and 200 cGy relative to that for 4-MV x- rays was 1.07, 1.20, and 1.23 for 25, 30, and 35 keV, respectively. For EBT3 film the average sensitivity was within 3 % of unity for all three monochromatic beams. CONCLUSIONS: EBT2 film sensitivity shows strong energy dependence over an energy range of 25 keV - 4 MV. EBT3 film shows weak energy dependence, indicating that it would be the better dosimeter for Auger electron therapy. This research was supported by contract W81XWH-10-1-0005 awarded by The U.S. Army Research Acquisition Activity, 820 Chandler Street, Fort Detrick, MD 21702-5014. This report does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.
