Field trials were conducted to determine the effectiveness of shields in reducing off-target droplet drift from ground-rig sprayers. Sprayer booms ranging in width from l0 to 13.5 m and equipped with com--e.ciully avaltitti shields *ere operated along a 150-m swath in a field of approximately 2O-cm-tall spring wheat in wind speeds ranging from lb to 35 km h-r. Airborne drift was measured using aipiriteO air samplers. ihe ure of an 80" flat fan tip (8001) at a pressure of 275 kPa and a ground speed of 8 km h -I resulted in 7 .5% of the 50 L ha -r spray solution drifting off the target area. The ule of protective cones with 8fi)1 tips without lowering the boom reduced airborne drift by 337o at_ a 20 krir h-r wind speed, while a Si-gSn drift reduction was accomplished with the combination of solid or perforated s-hielding and lowering the sprayer boom. Increasing the application rate to 100 L ha -r by using 8002 tips reduced drift of the unshielded sprayer by 65% . Decreasing application rate to 15 i ha-riy using tOOOtZ tips increased drift by 29% despite the use of a shield. Off-target drift increased withincreaiing wind speeds for all sprayers, but the increase was less for shielded sprayers and coarser sprays. The decreased droplet size of spray from 1 10" tips increased drift when the boom height was the same as for 80o tips. High wind speeds, lower carrier volumes and finer sprays, 110" tipJ, and solid shields tended to dicrease on-swath deposit uniformity, whereas a perforated shield or cones did not affect deposit uniformity.
Half-value thicknesses of a wall of ordinary concrete bricks were determined for fast neutrons emitted from a variety of cyclotron beam-target combinations.The neutrons used in the study were produced at the Oak Ridge Isochronous Cyclotron by bombarding thick targets of carbon/ aluminum, copper and tantalum with beams of protons, deuterons, alpha particles and carbon ions. Attenuated and unattenuat. d dose rate measurements of these neutrons were made at a 80 cm thick concrete block wall which served as one side of the target room where the irradiations occurred. The ratios provided by these shielded and unshielded dose rate measurements were translated into half-value thicknesses.
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