Appendia
THEORY OF INSTRUMENT OPERATION
Pulfilinent of tha objectives of this project required an instrument of known operatiocal chare
acteristics {nm varythigh radiation fields, and with en extremely large dynanie range. The former
yeyulrumat Icilcated that a sclovillation datector would te tush suited; the latter lod to the
ehoice of a fasd~back circuit that kept the photomiltipliar-tubes anods current substantially
constant and thus prevented fatigue cf the photocathode under high flux.
The protoaltipliar dynoda voltaga Js davelsred esroas thy cathoda resistor of a cathode followr, whoes tupat eignal is dorived from the photozultiplisr e.oda curm.t (Aigure A.l). fo
inereace in the incidant Juss flux on the plotocathids tenda to incrwssa the photosultiplier=
Figura Awl
Sehotatic die ran of a typlool cotactor system.
Highwtnteaelty mecun ania wera roto vith a le2l photomultiplier tute whoireas falloud roasuminnts wom mde with
a 58lo-type tube.
tuba acede curmate Tecresstd ancda current posante e@ ocesilve atonel to the contol tub, diac
cote ing Gta fopedanew of that tubs ard Joweriry ths soltes anemng the py’ atoviltipl ioretute
dyes
Frew tra acclitsation of tha ct ste:
tha vwoltace,
ths
Coote volte y will onura a
rina es dittea is
Garideces th udynoda
piv igo lot ibitopel
tube ond C21 4 am
Ting voltastorte
Tis ter ca of ane fecteurrant variation ema be calculated for 3 gavaa control tube and feod-
back resistor.
If tho control tuts bas a grid bea of 5 volta (shat fa, the tobe cuts off at
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