The ionization produced when Pu239 -particles were completely absorbed in binary gas mixtures having acetylene as one of the components was measured. The W value (electron volts per ion pair) was computed from the known energy and the indirectly measured ionization for various percentages of the two gases in the mixture. The W values for varying proportions of a binary gaseous mixture were then compared to Wm as determined by the equation 1/Wm = (1/Wil/Wi)Z + /W, where Z = /( + aP2) and Wm is the W value for a mixture of two gases having partial pressures Pi and P2 and W values W¡ and Wi, respectively. Good agreement was found when the following values were used for the empirical constant "a":

As used in the above, " person acting on behalf of the Commission" includes any em ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, dissem inates, or provides a ccess to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. P r in te d in th e U n ite d S ta t e s o f A m e r ic a A v a ila b le fr o m C le a r in g h o u s e fo r F e d e r a l S c ie n t if ic and T e c h n ic a lIn fo r m a tio n N a tio n a l B u r ea u of S ta n d a r d s , U . S. D e p a r tm e n t o f C o m m e r c e S p r in g fie ld , V ir g in ia 22151 P r ic e : P r in te d C op y $3.00; M ic r o fic h e $0.65

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R e c a l c u l a t i o n of S h i e l d i n g for t h e A d d i t i o n of a PAR . 0 I n t r o d u c t i o nThe s h i e l d i n g estimates f o r t h e E l e c t r o n and P o s i t r o n Linacs and t h e Booster Synchrotron, c o n t a i n e d i n t h e 1987 Conceptual Design Report (CDR) of t h e APS (ANL-87-15), have been reviewed and r e c a l c u l a t e d , along w i t h newly i n i t i a t e d c a l c u l a t i o n s of t h e r e q u i r e d s h i e l d i n g f o r t h e a d d i t i o n of a P o s i t r o n Accumulator Ring (PAR).S e v e r a l new assumptions with respect t o beam i n t e n s i t y , p r o j e c t e d l o s s e s i n t h e system, and assumed o p e r a t i o n a l t i m e have been i n c o r p o r a t e d i n t o t h e c a l c u l a t i o n s . Details of t h e p r e v i o u s c a l c u l a t i o n s , which d e s c r i b e t h e methodology used, may be found i n APS LightSource Note LS-90. 2iO S h i e l d i n g Design O b j e c t i v eThe Department of Energy's (DOE) guidance (DOE 81), concerning t h e ALARA d e s i g n g o a l for new f a c i l i t i e s , s t a t e s t h a t t h e d e s i g n o b j e c t i v e i s t o l i m i t exposures t o one-f i f t h of t h e 5-rem-per-year l i m i t given i n t h e same document.T h i s i m p l i e s a n average dose rate l i m i t of 0.5 mrem/h, based on a 40-h work week. S u f f i c i e n t c o n c r e t e as a bulk s h i e l d is used t o a c h i e v e r e a s o n a b l e g l o b a l s h i e l d i n g of a c c e l e r a t o r components f o r d i s t r i b u t e d l o s s e s i n t h e system. Localized s h i e l d i n g , which may c o n s i s t of i r o n , l e a d and/or dense polyethylene, i s used a t h i g h l o s s p o i n t s t o supplement t h e g l o b a l s h i e l d . I nsome cases, e x c l u s i o n zones may be r e q u i r e d d u r i n g t h e o p e r a t i o n a l t i m e of t h e p a r t i c u l a r component i n o r d e r t o m e e t t h e g u i d e l i n e . An a d d i t i o n a l c o n s i d e r a t i o n used i n t h e s h i e l d i n g e s t i m a t e s w a s t o l i m i tt h e dose r e c e i v e d by any i n d i v i d u a l , due t o any s i n g l e beam dump loss, t o less t h a n 100 mrem. . 0 Types Of R a d i a t i o n ConsideredDepending upon t h e energy of t h e a c c e l e r a t e d p a r t i c l e s , one o r more of t h r e e r a d i a t i o n components, each with d i f f e r i n g a t t e n u a t i o n l e n g t h s i n a g i v e n A

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