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Published: 1952

Total Pages: 80

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The measurement reported here were made in the BNL water tank shielding facility. Measurements were made with: (1) a brass-walled GM counter, 1 inch in diameter by 4 inches in length, shielded on all sides by 2.5 inches of lead; and, (2) a graphite-walled ion chamber, 1 inch in diameter by 4 inches in length. The GM counter has the advantage of high sensitivity permitting measurements of high precision for the determination of the detailed shape of flux patterns. It has the disadvantage of an energy response which is enhanced in the high energy region of the spectrum, due to the heavy lead shield which is used to reduce the flux to a measurable value. The ion chamber has an approximately tissue-equivalent response to gamma ray flux but has too low a sensitivity to permit measurements with small voids. The experimental arrangement is indicated, which shows the GM counter in position to measure the leakage through a spherical void. The tank is filled with water to a depth of 143.25 inches. An outlet is provided at the top of the tank, so that the water level remains constant when a void is placed in the tank. The counter or ion chamber is mounted with its axis of symmetry vertical and with a clearance of 1 inch between the bottom of the detector and the water surface. Flux measurements are then made at various points in the horizontal plane.