2 an ee A a aml the incident gamna rate, whils the lead-covered one detected 1/100 of this rate, and also received only 1/100 of the total exposure. To calibrate the station with the normal head, the first method was used as described in Soction 2.2.1. This required tha placemnt of a ' density-four neutral filter between the crystal and tha photonultiplier tuba of tha normal station to increase tha range %9 10° r/hr. The leadcovered head required only a dsnsity-two noutral rilter, inasmuch ag the lead covering s:rved to attonuate the Incident gamua radiation by a face . tor of 100 (equivalent to a donsity-two filter). If tha two delector heads track, tha crystals are not being differ= entially effected by gamma ratos ond cumulative exposures. If tho deteco tors do not track, it is an indication that there is a rate or cumulative exposure doperndance of tho .system or a significant changes in the spectral quality of incident radiation. In the evant thet scintillation crystals are shown to ba nsither rate nor docega dependent, the assuzption may ba mad? that a naarly linear extrapolation of low-intensity calibration can be porformed. 2.2 CALIBRATION 2.2.1 Hivh-Intensity Calibration. Calibration for high rates was based on the assutption that tha light output.of the scintillation crys~ te is a linear function of the incident rediation at least up to 10! r/nre Two techniques ware used to calibrate the high~level instruzents. l. the first method, tha dotector head was calibrated from 0.2 r/ir to 104 r/tr, using en 28-eurla Cosources. To extend thea ranva of the ine . struvent to 10% r/hr, a density-four nautral filter was placed bot-xen the crystal end the photomiltiplier tubs. Uffectively tha systen would then seasure rediation from about 0.2 x 10° x/nr to 10 r/ar st It was nocassary to put jvitelding eround the photo:attiplier tube, sinca it was sensitive to radiation. Tho purpose of the sideiding was a sttonpt to attenuata tho incident guia ceiletion on tho ph: hotonal “Inlles by tha sum order of te gnituds as the noutral de asity ftiter attrnuatas the light from tha erystel. (This was not possitle in tha field, as the éaount of seatter radiation striking the photo ultiplier through tha light pire pmeludad an ottenuation factor greater than 16}) In the cocond highwinteneity calibration mthod, tho detestor tead was first calibrated from 0.2 r/hr to 10! t/bz using on Etseurts com source. The crystal was thon replsced by a lichb couceca of the sar spectral quality as the stilbana erystel outwit, Tha ovtput of tiie light sourea could ba voriad dn inova inerevontae A shot v3 nado of this output versus tho rolativa ineteont luntnous flux. The esl loretion curve thus obtainsd was then rocuelized to the curva obbained vith rodias tion and was found to tresk very cloroly up to ths nextmun of 164 r/hr (Figure 2.2). Eacaurs of the esroement botwen tha Lichb end the rediac tion calibrations at tha lew levils, the light calibration was tired ag a basis for extranolating the rrdiatioan enlibration curyos up to 1c? r/ne. ' . 16 SECRET meen ae ena eS tn ne pe ne ne eTSE a ieeeehe Iranetehcnen detoaeeateeetennt ad iene neem lien nee ne ¢