V O L U M E 23, NO. 9, S E P T E M B E R 1 9 5 1 Preamplifier. The unc~-tubepreaniplifier, or cathode follo\vei' derriihed by Jordan and Bell 15)was found satisfactory, although frequvnt replacement of electron tuhe 6.1Ii5 seemed necess -4C ' e n t ralab ceramic. c o i i i i c ~ i i w\rith a rXOO-volt rating \vas for tltwupling. Amplifier. Thr .ltoinic Inqtrunient ('o.'s .\lode1 201.l iq corisitlriwl excellent i n this application. From the various output. it was posible, simi~ltanc~ously, to count pulscs, to vie>\\theln o i i an oscjllogrdph, aiid to nionitor them with a counting rate inester. A discriminator, wliich is e.ssentia1in nrutron munting, i. a part of this a er. It was used to determiiicl the, optimum gain or pul-r niinatioii lc~velfor obtnining r~c~pr~oducilJl(, rewlts. Scaler. A convt:nti~iiral kfigiritwthaiii waler \vas usid, with 11 scnlt~of 64 or 512 ac*iwtliiig to thc counting rate. A r)u\lont Type 248A oscillograph nith triggcwtl sweep of various duratioii, u'aq e~xcedinglyhelpful t hivughoul t lie u-ork, T i 1 oi,tler to set u p a lalxxator>- for ilrterrnining beryllium by tlii. ~)hc)todieintegratioiinit,thod, several instruments arc>needed.
In addition, one must hiivc. H high-intrnsity gamma source and nimiis lor handling anti nioiiitoring it. The source ran he had froin the Atomic Energy Coniniission (as ratlioantinion!~) at a nomirial cost, as 1 month's irradiation of ti thimble filled ivith antimony producw an activity in excess oi 1 curie. Thc :tut1ioi.s' n-ork started with 2 ruriew and continued for ci nionths (tlirtvs hrtlf-lives), aftclr \vlii(*h thc3 0.25 cwie remaining continued to lx uvful. Except over v w y long periods, radioantimony is far l e n r expensive than radium, but it appears to have ariot1ic.r outstailding advantage. Ordinary radium sources emit sonic. neuti~i~ns as a result nf u,n reactions with light metal inipuritic+ contained in them. The neutron background from the I-grain ~ authors was found to reduce thr racliuni so>.ircestried L J the sensitivit,?;of the method 1 1 ) ~ :til order of magnitude. Should on(% havr :t Van de Graafl or other type of high-voltage x-ray generator available, even hetter results would be ohtained, for the beam could t)ta directed at, the sample and riot at t,he detectors. The.
1265 effrct of i r d i a t i o i i on the tulicts 1ra.4 to cause sonit: reduction i l l pular sins, a diminution in length of the voltage plateau, and ail
incroast. i i i t)ackground "noisr." all of which are hindranws t o stable opcaration. I n spite of the experimental difficulties, the authors believe this nichthod has many attractive possibilities. It may, for inatanw, be adapted to automatic- assaying by means siniilar to the automatic sample changers ( 7 ) used in routine beta counting. As ail entirc'ly instrumental nicthotl &in, almost, to the measuremelit o f y H . i t may be applicahlr to plant voiitrol. kCKNOU LE:DG\IEN'I'
Thc. authors are most appreciative of the intcwst and advice of Clark Goodman and Matthew Simds, Mmsacliusetts Institute of Technology, and of R. TV.T>odsoiiand I!. IV. I k v e n s , Jr., Cohinibia University. L I l E H . \ ' L ' l ~ K ECITEL) 1) ('holak. .J., a i d Huhhard. D. lf., I s . 4 ~ CHWM., . 20, 7 3 (194Si. (2) I h i d . , p. 9 i O . ( 3 ) (iaudin, .I.51..Dasher, .J.. Pmnell, ,J. H.. and Freyberger, \T', L., AvMining Eng., 187, 4 9 5 4 (1950). :1) Guth. E.. and IIullin, C . .J.. P h y s . Rtu., 74, 833 (1948). (*5j .Tordaii, W. H.. and Hell. P. R . , Atomir Energy Conirnissi~~ii, MonP-323. ( 6 ) Kei~n.13. D.. Zaffarano. I). .J.. :itid lIitchell, ..I.C . G , , P i i ~ s KIJO., . 73, 1142 (1948). ( 7 ) P e ~ ~ lW, i ,C ' , , r t d Good, \ V , AI., Rw. Sc.1'. I / i s t ~ t r ~ e17, ~ ~255 t~, I
i1946 1. 'X)
Saildell. 14:. I
