Variation of the magnetic susceptibility of artificial graphite with exposure in the materials testing reactor

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Hie iBagsetic su see pti bill tj of artificial grapMte has been deur. itRed as a &sctioi} of exposure i a the ^Wa ""line spsciaens ^ e r e studied x*:«J!i iiposares ranging from *>0? t o 82 s Iv ait where the iwt refers to rieiit«*fiPs Bith. ea0r ^ i a excess of 1 Mevo These saiaples were sullied by 1, Fa-^sl of the IfB fac il it j © Tns fliases were determined b j aieaas of X-raj •ii, clt-*'err}i:i5aig these fluzes bas beea described by Fast ( l ) . The method i s sx~i}DT lo fchat esployed "by bliis laboratozy i n eTalmating tlie damage eaii-l-valcnce between the Haaford cooled t e s t bole aad the Brookhavea pileC2)o The messwremsiits tiere mads Bsiag the Faraday apparatus described by er i l "sr i o03 x 10"^ cgs units depending upoa wbieli i s larger© Tbe saapled shj'^-'-d l-lie oc'ieuiation typical of an extruded tjpe graphiteo The iraliie f o r ilif I'lr^iii sample ifas 20oS^ x 10° lAich is slightly less ttian the cmstoaary of 2 aF»% so"i' excessive for artificial graphitco Bie results of the iaeaB«re<=» wiCT'b'j are slioifn ill Table Ie fhs f i r s t coltmn sbons tbe flmx as detenaiiied by raa&e Tlie second colaiia gi¥Gs the tot ^ siisceptibilityo The third coluaa 5*1 %eo die Tstio of tlie sus sep ii bil it yat eacb exposwe with tfee unirradiated irc!.TiK3o I t should be» noted that tMs ratio is not the so called Pie irl s ratio© Ift orla-v to determine tlie true Pie irl s ratio it would be aeeessaiy to subtract f. im liie lot «1 susceptibility both a diaiiagaStie core term and a paraaagnetic spin tern (h)o For the purpose of this report at trill be sufficient t o use

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only •'-PC inixiGVTectQd ratio of the two s usc ep tibi li ties s It has been SIMWH •GIT-.S "tu cJiperclence of tliis r e t i o on ©sposttre i s iaiepeadeat of grapMte type alt'icpp-h tiie im.t:,ai values raay change as aacb as 2 per cent (5) C6}o Tile dat'i i s presested graphically i a Figwe lo The ratio of tMe s r - c jo tiM li ties lias been plotted as a faactioB of the square root of erp on roe Tae square root is iised pi'Saarily tecaise i t contracts the scale so tfiat largfj e2iposiires can be easily plottedo ioweirerj i a acMitioa one would esf-ec'b 'che degensracy energy t o be dependent oa the exposnre t o tlie half powero ffee, festiires of the curwe are 3iKi.lar t o those whieli imwe been obtaiaed for Ha:x?cird exposures» I t ia interesting to note that either a flattening or a peaic occurs i n the early dajaage rsEge; ioe» beloK .O?^ A similar peak has been observed in graph it is at ioa studies C?) in brom-grapMte studies (8} and in ajiiieaiing data (9)a Tlie ci3r¥ss obtained as a fmietion of Hanford e35)ostire are shova i a t e cJctermSlie tlie equivaleace befeiees MTE flmx and Hanford i'WD/CTs The ticrisoatal lines IE Figure I I indicate the MTE data© The results are shoi-ia i a Figurs i l l where the corresponding MMD/GT i s shown f a ' each .-ITE flux iraliiSc. Tr.e results give astra i gl it liu e whose s l ^ e wliea sipa « d gi¥es the eqtri-vale:.^ce fectoro ^PMis pro-tes to be 2 Y. 10 a t t for each »iD/CTc Itis possible t o detersiiie tte equivalence factor for the Haaford cooled test hole© Froi the Haafore Speeial Irradiation Maanalj the to'fcal tfcsrf.isl neiatroii flux a t any point iii the reactor is gi¥en as rjfierr; J*'! Pis 6. viae factor -Mhieh foi' the cooled test hole i s IsSeCU)© ience fhs i-atio of the flmt &^&T 1 Me%- to the t h e r a a l flax i s 0«22 as shosn tj the atjrirss tovnd on page 56 lM-SS<=.2iil (12}© Ience the to tel integrated neatroa

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fJxjj for nsiitroas with eiierwicr; i a ev.essF. of 1 Jfet i s ?o2 x 10 a¥t/MH3/Af« I t iiQuld tbas appear OE the basis ol these sieasareinents that toe ap xsj-fjat fast flirc a t M'ffl, i s almost fi¥e tisos more flsFiagiiig than corresponding be a-t,G!iipt8d a t the present tiiBe© I t is hoped that future correspondeace ifith tin t'.io sites will shed some light on the qxestloUa