Annual Report of the Radiation Center of Osaka Prefecture Vol. 1, 1961 Design of Irradiation Rooms Keisuke KAWABATA, Sin'ichi OKAMOTO, Tatsuo TABATA, Jun'ichiro FURUTA, Shigeru OKABE, Toshio AZUMA and Kiichi KIMURA (Received December 25, 7960) F,(*'JEo;q;+ /rl,#rBA, |)6/i,f-*, ,tt*jiJ<, frHf{ .Htj, ffi!,nlt, JEftlE, ,i,1'}11 . :t,t:jJ jlr) i1ffi&r'riErriif#Et]liic_*6'.si_6t.,l4.rPfx, r/J/, l-60'i,y i- J-)*s ILt).1 :7 y 7Lir4i?:,rDiitirlr EtO,?;J'*slL\tO;-l-Ht.rU.{i6-\6. :r/irrl-60'l-'y l-i-)lt10-tn,1.--r.J -, 5-}-=}r --\ *, 100,t=-, -oZjiii.fi!g{o:acl:D, )) =T.t,Wrl'i,J-, :a?..,1,-f -#lul4 2 -15 Mev, HirF]_iffi;iifil 900pA DE+ )) =7 ,y ) i.il i 6 L o (-B a. S 1. INTRODUCTION The irradiation facility of our Center was designed to satisfy many requirements in fields of physics, chemistry, botany, zoology and their applied flelds. The radiation sources are Cobalt 60 of multicuries and an electron linear accelerator. The construc- tion works were performed by HAZAMA GUMI, LTD., general constructors, and com- pleted at the end of October, 1960. In the present paper results of our calculation on the thickness of shielding walls of Cobait 60 hotcaves and the linac irradiation room are reported. $2. COBALT 60 ITOTCAVES Three sepatate caves were designed in order to store and to operate sources of 10 kilo-curies, 5 kilo-curies and 100 curies of Cobalt 60 independently. The shielding wall should be sufficiently thick enough to reduce the dose rate of the leakage iess than the permitted value, namely, 10 milli-rontgen per week. The roof and one side wall of each cave \,vere designed to be exposed outside. The effective thickness of a shielding wall may be caiculated from I-0.52 (C-Eid') -ts.exp (- px) to the first order approximation, provided the source is located at one point, where 1 is the intensity of gamma-rays outside of the shielding wall, d the distance from the souce in units of meter, C the source intensity in units of curie, ,E the energy of gamma-ray in units of the rest energy of an electron, .r the thickness of the shielding wall in cm, B the build up factor in units of cm '. Here B may be expressed as px, where p is the absorption coemcient of gamma-rays in units of cm '. Values used in our calculation are shown in Table 1. Heavy concrete of one meter thick was used for the front lvall of the cave for 10 kilo-curies, where manipulators and a shielding glass window were installed. Heavy concrete was made of cement, iron sand from Fukushima and ciashed pieces