Radiological P h y s i c s Section E n v i r o n m e n t a l and Radiological S c i e n c e s D e p a r t m e n t J u n e , 1966 PACIFIC NORTHWEST LABORATORY RICHLAND, WASHINGTON *Work p e r f o r m e d u n d e r t h e a u s p i c e s of t h e U. S. Atomic E n e r g y C o mm i s s i o n a t t h e Hanford L a b o r a t o r i e s , G e n e r a l E l e c t r i c Company and a t t h e Battelle Northwest L a b o r a t o r i e s in Richland, Washington. ? P r e s e n t a d d r e s s , Lockheed M i s

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... i l e s and Space Company f~a r t i c i~a t e d in t h i s w o r k a f t e ABSTRACT A reproducible version of the Hanson-McKibben long counter w a s built and a comprehensive experimental investigation of i t s c h a r a c t e r i s t i c s w a s made. T h e counter is m a d e carefully f r o m polyethylene and strengthened with aluminum instead of being paraffin strengthened with s t e e l . It is called a precision long counter ( P L C ) because m o d e l s built f r o m a standard s e t of drawings have closely reproducible p r o p e r t i e s . Data a r e given t o show how a P L C can be calibrated to within 1% f o r m e a s u r i n g neutron flux dens i t i e s f r o m radioactive s o u r c e s . T h i s calibration is obtained with a srnall calibrated PuBe neutron s o u r c e i n s e r t e d inside the P L C . T h e standard c o u n t e r , H-1 , is located at Battelle-Northwest in Richland, Washington and the standard s m a l l s o u r c e , M-1045, is located at Mound L a b o r a t o r y in Miamisburg, Ohio. One counter, H-3, w a s selected a s a "roving" counter, w a s calibrated against H-1, and w a s sent to the Mound L a b o r a t o r y and t o the Argonne National L a b o r a t o r y t o c a l i b r a t e the two c o u n t e r s , M L -1 and ANL-1. T h e problem of using a PLC with a c c e l e r a t o r neutrons is discussed and a solution offered.