A Reference number ISO 1 1 537 1 998(E) INTERNATIONAL STANDARD ISO 1 1 537 First edition 1 998 07 1 5 Non destructive testing — Thermal neutron radiographic testing — General principles and basic rule[.]
I N TE RN ATI ON AL STAN D ARD I SO 1 537 Fi rst ed i ti on 998-07-1 N on -d estru cti ve testi n g — Th erm al n eu tron rad i og raph i c testi n g — G en eral pri n ci pl es an d basi c ru l es Essai s n on d estru cti fs — Essai d e n eu tron og raph i e th erm i q u e — Pri n ci pes g én érau x et règ l es d e base A Referen ce n u m ber I SO 1 537: 998(E ) I SO 1 537: 998(E) Contents Pag e Scope Backg rou n d m ateri al N eu tron rad i og raph y m eth od Faci l i ti es N eu tron sou rces N eu tron col l i m ators I m ag i n g m eth od s an d versi on screen s Fi l m Cassettes 10 Appl i cati on s for th erm al n eu tron rad i og raph y 11 I m proved trast 12 I m ag e q u al i ty i n d i cators 13 N eu tron acti vati on An n exes A (i n form ati ve) G l ossary of terms rel ated to n eu tron rad i og raph y B (i n form ati ve) u si n g Th erm al averag e n eu tron scatteri n g l i near an d attenu ati on th erm al 10 coeffi ci en ts absorpti on cross secti on s for th e n atu ral l y occu rri n g el em en ts 12 C (i n form ati ve) Bi bl i og raph y 15 © I SO 998 Al l ri g h ts reserved U n l ess oth erwi se speci fi ed , n o part of th i s pu bl i cati on m ay be reprodu ced or u ti l i zed i n an y form or by an y m ean s, el ectron i c or m ech an i cal , i n cl u d i n g ph otocopyi n g an d m i crofi l m , wi th ou t perm i ssi on i n wri ti n g from th e pu bl i sh er I n tern ati on al Org an i zati on for Stan d ard i zati on Case postal e 56 I n tern et • Pri n ted i n Swi tzerl an d ii CH -1 21 G en ève 20 i so@ i so ch ã Swi tzerl an d â ISO I SO 1 537: 998(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work of preparing International Standards is normally carried out through ISO Technical Committees Each member body interested in a subject for which a Technical Committee has been established has the right to be reprensented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization Draft International Standards adopted by the Technical Committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote International Standard ISO 1 537 was prepared by Technical Committee ISO/TC 35, Non-destructive testing , Subcommittee SC 5, Radiation methods Annexes A, B and C of this International Standard are for information only iii I SO 1 537: 998(E) © I SO Introducti on Th i s I n tern ati on al co n si sten t q u al i ty Stan d ard is i n ten d ed ch aracteri sti cs, an d as to an provi d e d to g u i d el i n es th e u ser in for th e prod u cti on d eterm i n i n g th e of n eu tron su i tabi l i ty of rad i og raph s th erm al n eu tron i n specti o n for a parti cu l ar appl i cati on Recom m en d ed practi ces are stated wi th ou t d etai l ed d i scu ssi on of th e tech n i cal backg rou n d for th e preferen ce iv th at possess rad i og raph i c I NTERN ATI ON AL STANDARD © I SO 1 537: 998(E) I SO Non-d estru cti ve testi ng — Th ermal neu tron radi og raph i c testi ng — G eneral pri nci pl es and basi c ru l es Radi ati on protecti on - Heal th warni ng Exposure of any part of the human body to neutrons, X- or gamma rays can be injurious to health It is therefore essential that whenever neutron radiographic equipment or radioactive sources are used, adequate precautions should be taken to protect the radiographer and any other person in the vicinity Limits for the safe levels of neutron, X- or gamma radiation as well as the recommended practice for radiation protection are those valid in different countries If there are no official regulations or recommendations in a country, the latest recommendations of the International Commission on Radiological Protection should be applied Scope Th i s I n tern ati on al Stan d ard speci fi es th e basi c practi ces an d d i ti on s th at rad i o g raph y of m ateri al s an d com pon en ts for fl aw d etecti on record i n g i t recog n i zes th at al tern ati ve m eth od s of i m ag i n g scope m ed i u m i n cl u d es H owever, n eu tron pro d u cti on an d co l l i m ati on I t i s cern ed m eth od s, wi th co n verter rad i o g raph i c i n specti on tech n i q u es an d th e type of m ateri al to be i n spected are to be tech n i q u es observed u si n g for th erm al ph otosen si ti ve m ay be u sed m ore wi d el y i n screen sel ecti o n , n eu tron fi l m th e fu tu re rad i og raph i c fi l m , as a Th e n eu tron Th i s practi ce i s g en eral l y appl i cabl e to speci fi c m ateri al com bi n ati on s, processes an d tech n i q u es Background materi al A g l ossary of term s rel ati n g to n eu tron rad i og raph y i s presen ted i n an n ex A Atten u ati on of n eu tron s i n m atter i s presen ted i n an n ex B Neu tron radi ograph y meth od N eu tron rad i og raph y an d X-rad i og raph y sh are som e si m i l ari ti es bu t prod u ce d i fferen t resu l ts wh en appl i ed to obj ect N eu tron s repl ace X-rays as th e pen etrati n g beam of rad i ati on wh ose i n ten si ty i s m od u l ated by an obj ect, a fi l m i m ag e of th e featu res of th e obj ect d i fferen t, th e two tech n i q u es presen ted i n fi g u re g en eral l y th e sam e resu l ti n g i n Si n ce th e absorpti on ch aracteri sti cs of m ateri al s for X-rays an d n eu tron s are very ten d to com pl em en t on e an oth er N eu tron an d X-ray atten u ati on coeffi ci en ts, as a fu n cti on of atom i c n u m ber, are a m easu re of th i s d i fferen ce I SO 1 537: 998(E) Fi g u re — A com pari son of m ass atten u ati on coeffi ci en ts for th erm al n eu tron s an d X-rays © I SO © I SO 1 537: 998(E) I SO Faci l i ti es A neu tron radi ograph y faci l i ty typi cal l y i ncl u des a sou rce of th erm al n eu trons, a neu tron beam col l i m ator, a conversi on screen, fi l m and an exposu re cassette A sch em ati c di agram of a representati ve n eu tron radi ograph y faci l i ty i s sh own i n fi gu re Key Sh i el d i n g Di verg en t n eu tron beam N eu tron sou rce Obj ect M od erator Fi l m G am m a fi l ter 10 Em u l si on Apertu re - d i am eter ( D ) 11 Con versi on screen Col l i m ator 12 Len g th ( L ) Figure — Typical neutron radiography facility with divergent collimator Neu tron sou rces N eu tron sou rces su i tabl e for th erm al neu tron radiograph y can be cl assi fi ed i nto th ree general categori es: — radi oacti ve i sotopes; — seal ed tu bes and accel erators of parti cl es; and — nu clear reactors Each of th ese sou rces produ ces h igh -energy neu trons th at requ i re m oderati on (slowi ng down) to th erm al energies Th is can be accom pl i sh ed by su rrou ndi ng th e neu tron sou rce wi th beryl l i u m , graph i te, water, oi l , pl asti c or som e oth er m oderator m ateri al I SO 1 537: 998(E) 5.1 © I SO Isotopic sources I sotopi c sou rces h ave th e advantage of bei ng sm al l and portabl e bu t becau se of th ei r rel ati vely l ow neu tron yi el d requ ire l ong exposu re ti mes to ach i eve a given radiograph i c qu al i ty M any i sotopic sou rces h ave been u sed for neu tron radi ograph y and th e m ost com m on of th ese are sh own in tabl e Cal i forniu m ( 252 Cf) is one of th e m ost popu l ar i sotopi c sou rces u sed for th erm al neu tron radiograph y becau se of its l ow neu tron energy and sm all ph ysi cal si ze wh i ch perm i t effi ci ent moderati on and h i gh total neutron yi el d Tabl e — Rad i oacti ve sou rces for n eu tron rad i og raph y Radiation source 241 241 21 24 Reaction Half-life Remarks ( α, n) 63 days h i gh neu tron yi eld bu t sh ort h al f-l i fe Am -Be ( α, n) 458 years gam m a easil y sh i elded, very l ong h alf-l i fe Po-Be ( α, n) 38 days l ow gam ma backgrou nd, sh ort h al f-l ife Sb-Be ( , n) Am - 242 Cm -Be g 60 days h i gh gam m a backgrou nd, sh ort h alf-l i fe, hi gh neu tron yi el d, easi ly m oderated 252 Cf spontaneou s fi ssi on 2, 65 years sm all si ze, h i gh neu tron yi el d, l ong h al f-li fe, and easy moderation of neu tron energi es m ake th i s an attracti ve portabl e sou rce 5.2 Accelerator sources Seal ed tu bes and l ow-vol tage accel erators u ti l i zi n g th e H (d, n) H e reacti on, h i gh -energy X-ray m ach i nes u ti l i zi ng th e (x, n) reacti on, and Van de Graaff accel erators and cycl otrons u si ng ch arged-parti cl e neu tron reacti ons h ave been u sed as neu tron sou rces for th erm al neutron radi ograph y Th e targets of th ese accel erators are su rrounded by m ateri al s th at wi l l m oderate th e neu trons to th erm al energi es Th e th erm al neu tron fl u ence rate of accel erator sou rces before col l i m ati on can -2 -1 sec be as h i gh as neu trons cm 5.3 Nuclear reactors N u cl ear reactors are a preferred neu tron sou rce for th erm al neu tron radi ograph y becau se of thei r h igh neutron yi eld Th e h i gh neu tron i ntensi ty m akes i t possi bl e to provi de a ti gh tl y col l i m ated beam an d h i gh -resol u ti on radi og raph s can be produ ced wi th a relati vel y short exposu re ti m e Som e of th e di sadvantages of u si ng nu cl ear reactors for neu tron radi ography are th e h i g h cost of i nstal l ati on and operati on, l ack of portabi l i ty, and vu l nerabi l i ty to stri ct and compl ex regu l ati on Neu tron col l i mators N eu trons are em i tted i n all di recti ons from a sou rce and are fu rth er scattered random l y by th e moderator A m eans of col l i m ati n g th erm al neu trons i nto a beam i s provi ded to produ ce a h i gh qu al i ty neu tron radi ograph A wel l col l i m ated th erm al neu tron beam cou pl ed wi th th e abi l i ty to pl ace th e object bei ng i nspected cl ose to th e i m agi ng system wi l l provi de th e best radi ograph i c resol u ti on 6.1 General collimator desig n considerations N eu tron col l i m ators u ti l i ze m ateri al s h avi ng a h i g h cross secti on for th e absorpti on of th erm al neu trons su ch as boron or cadm i u m Th ese m ateri al s sh ou l d be appl i ed to m axi m i ze th e n u m ber of neu trons reach i ng th e i m agi ng system di rectl y form th e source and m i ni mi ze th e nu m ber of neu trons scattered back i nto th e beam Often, a com binati on of m aterial s i s u sed to ach i eve th e best n eu tron col l i m ati on and to m ask ou t u nwanted secondary radi ati on from th e beam I t i s som eti m es necessary to u se m ateri al s, su ch as l i th i u m carbonate, th at produ ce neu tron captu re decay produ cts th at wi l l n ot resu l t i n fog gi ng of th e i m ag i ng fi l m M ateri al s th at h ave a h i gh neu tron scatteri ng cross secti on, su ch as h ydrogeneou s m ateri al s, or m ateri al s th at em i t radi ati on du ri ng n eu tron captu re th at m ay fog th e im agi ng fi l m sh ou l d not be u sed i ndiscri m i natel y near © I SO 1 537: 998(E) I SO th e i m agi n g system Exam pl es of th i s l atter cl ass of m ateri al s i ncl u de i n di u m , dysprosi u m and cadm i u m Fi l m foggi n g m ay al so resu l t from th e 470 keV gam ma ray produ ced by neu tron captu re i n boron Th e spati al resol u ti on of a neu tron radi og raph y system i s i nfl u enced by th e l en gth ( L) of th e col l i m ator, th e di am eter, or l ongest dim ensi on of th e i nlet apertu re ( D ) and aperture sh ape Th e rati o of L /D i s u sed general l y to descri be th e effecti ve col l i m ati on of th e system For exam pl e, i f th e L /D rati o of a system i s several h u ndred, one can expect th e system to be capabl e of produ ci ng radi og raph s of h i gh er resol uti on th an a system h avi ng an L /D of Alth ou gh L /D i s an im portant m easu re of system capabi l i ty, oth er factors, su ch as object si ze and scatteri n g ch aracteri sti cs, obvi ou sl y affect th e u l ti m ate radi ograph ic qual i ty th at can be ach i eved I n addi tion to th e L /D val u e, th e L val u e i tself i s i m portant Becau se th e L val u e i s fi ni te, a separati on, l, between th e object and i m agi ng devi ce resu l ts i n an u nsh arpness i n th e i mage descri bed by m agn i fi cati on factor L /( L- l ) 6.2 Collimator types Al th ou gh th ere h ave been m any di fferent col l i m ator desi g ns th at h ave been u sed experi m ental l y, few of th ese h ave su rvi ved for u se in com m erci al neu tron radi ograph faci l i ti es Th e need to radi ograph y rel ati vel y l arge objects h as l ed to th e wi despread u se of th e di vergent col l i m ator desi gn sh own i n fi gu re Th e di vergent col l i m ator consi sts of a tapered ch annel m ade of neu tron-absorbi ng m aterial and ori gi nating at i ts sm al l end (i nl et apertu re) at th e sou rce of h i gh est neu tron fl u x i n th e m oderator Anoth er col l i m ator type worth y of note i s th e pin h ol e col l i m ator sh own i n fi gu re H i gh resol u ti on neu tron radi ograph y can be produ ced wi th system s u ti l i zi ng pi nh ol e col l i m ators Th e pi n h ol e i s fabri cated from m ateri al su ch as cadm i u m , gadol i n i u m or boron wh i ch h ave a very h igh attenu ati on for th erm al neu trons Key Sh i el d i n g Obj ect N eu tron sou rce Fi l m M od erator E m u l si on G am m a fi l ter 10 Con versi on screen Pi n h ol e apertu re d i am eter ( D ) 11 Len g th ( L ) D i verg i n g n eu tron beam Figure — Typical neutron radiography facility with pinhole collimator I SO 1 537: 998(E) 6.3 © I SO Beam filters I t i s often desi rabl e to m i ni m i ze th e g am m a radi ati on th at contam i nates th e neu tron beam Th i s gam m a radi ati on comes from th e neu tron sou rce and can cau se fi l m foggi ng and reduced i m age contrast Fil ters made of l ead or bi sm u th m ay be instal l ed near th e col l i mator i nl et to redu ce th i s u nwanted g am m a radi ati on i n th e beam Wh en u si ng a bi sm u th fi l ter i t i s advi sabl e to encase th e fi lter i n a seal ed al u mi ni u m can to prevent th e spread of al ph a contam i nati on du e to th e neu tron captu re reacti on i n 6.4 209 21 Po produ cted by th e Bi Neutron scattering Back-scattered radi ati on from th e wal l s or equ i pment can be redu ced by maski ng th e neu tron beam to th e sm al l est practi cal exposu re area and by th e carefu l u se of neu tron absorber and gamm a sh i eldi ng m ateri al s Back-scattered radi ati on can be detected by pl aci ng a m arker m ade of neu tron absorbing m aterial su ch as gadol i niu m and a marker m ade of gamm a sh i el ding m aterial su ch as l ead, on th e back of th e fi l m cassette du ri ng neu tron exposu re I f back-scattered radi ati on i s a probl em, one or both of th e m arkers wi l l appear on th e fi l m I f backscatteri ng i s present, one sh ou l d m in i m i ze materi al s th at scatter or em it radi ati on i n th e exposu re area (see ) Gadol ini u m or som e oth er su i tabl e neu tron absorber can be pl aced beh i nd th e detector to effecti vel y m i ni m ize th e infl u ence of back-scattered neu trons on th e im age Imagi ng methods and conversi on screens N eu trons, as th ei r nam e i m pl ies, carry no el ectri cal ch arge and are th erefore non-i oni zi ng and produ ce l i ttl e effect on radi ograph i c fi l m To produ ce a neu tron radi ograph i c i m age on fi l m i t i s necessary to em pl oy a conversi on screen th at, u pon neu tron captu re, wi l l em i t i on i zi ng radi ati on or l i gh t th at can expose th e fi l m as sh own i n fi gu re I t i s i m portan t th at th e conversi on screen be i n i nti mate contact with th e fi l m i n order to produce th e best qu ali ty radi ograph Si nce conversi on screens are expensive and represent a si zeable i nvestment, care sh ou l d be taken to store th em i n an envi ronment th at wi l l protect th em from ph ysi cal dam age and corrosi on Stori n g dysprosi u m screen s i n a vacu u m wh en not i n u se wi l l m i n i m i ze atm osph eri c corrosi on and su bstanti al l y l en gth en th ei r u sefu l l i fe 7.1 Direct exposure method I n th e di rect exposu re m eth od, th e fi l m and th e conversi on screen are placed i n a l igh t-ti ght cassette and exposed to the neu tron beam Gadoli ni u m Th e fi lm screens are i s exposed preferred by th e em issi on for m ost of el ectrons from appl i cati ons and are th e conversi on avai l abl e ei th er as screen upon a standi ng free neu tron foi l captu re or as a sapph i re-coated, vapou r-deposi ted gadol i ni u m coati ng on an al u m i ni u m su bstrate Gadol i ni u m em i ts a 70 keV el ectron as th e resu l t of neu tron i nteracti on A second type of versi on screen i s th e l i gh t-em i tti n g fl u orescen t screen su ch as g adol i ni u m oxysu l fi de (Gd 2O 2S:Gd 6) or l i th i u m fl u ori de/zi nc su l fi de ( Li F/ZnS) I t i s recom ended th at th e spectral response of th e screen emi ssi on and fi l m be match ed for opti m um resu lts Th e di rect fi l m m eth od u si ng gadol i ni u m m etal screens provi des h i gh resol u ti on and excel l ent trast and h as becom e th e reference agai nst wh i ch oth er neu tron radiograph y tech ni qu es are com pared Th i s meth od cannot be u sed i f th e neu tron beam contai ns su bstanti al gamm a radi ati on or i f th e object i s h i gh l y radi oacti ve Oth er direct exposu re m eth ods are u sed bu t are beyond th e scope of th i s I nternati onal Standard 7.2 Indirect exposure method Th e i ndi rect exposu re m eth od i s u sed al m ost excl u si vel y for th e radi ograph i c i n specti on of radi oacti ve objects Th i s m eth od i s i nsensi ti ve to gam m a radi ati on and u ti l i zes conversi on screen s, wi th ou t fi l m , th at becom e tem porari l y radi oacti ve wh en exposed to th e neu tron beam Th e fi l m i m age i s m ade by pl aci n g th e acti vated foi l i n a cassette or oth er l i g h t-ti gh t devi ce togeth er with fi l m after th e neu tron exposu re i s term i nated Beta particl es emi tted by th e decay process of th e acti vated foi l s sensi ti ze th e fi l m wh i ch can th en be processed Dysprosi u m , i ndi u m , rh odi u m and gol d are al l candi dates for i n di rect conversi on screens Dysprosi u m and indi u m are th e best ch oi ce for m ost appl i cati ons wi th dysprosi u m havi ng th e greater speed Som e materi al s su ch as gol d are l ess desi rabl e for produ cti on neu tron radi ograph y becau se of thei r rel ati vel y l ong h al f-l i fe (2, days) wh i ch resu l ts i n u n acceptabi l i ty l ong exposu re an d decay ti m es © I SO 1 537: 998(E) I SO I ndi rect conversi on screens sh ou l d be exposed for a peri od of ti m e not to exceed th ree h al f-l i ves of th e m aterial bei ng u sed Fu rth er i rradi ati on provi des no benefi t si nce th e acti vati on rate and decay rate are nearl y th e sam e at th at poi nt Th ree or fou r h al f-l i ves i s al so su ffici ent ti m e to transfer th e i m ag e from th e acti vated foi l to th e fi l m al th ou gh th ey are som etim es l eft in contact overni gh t as a m atter of conveni ence X-ray im age i ntensifi cati on screens may be used to i ncrease th e speed of the transfer process i f desi red Th e indi rect conversi on screens can safel y be reu sed wi th ou t fear of dou ble exposu re after decayi ng for fou r h al f-li ves 7.3 Oth er imaging methods Oth er i m agi ng system s cou l d be u sefu l for som e appl i cati on s H owever th ese are n ot addressed i n detai l i n th i s I nternati onal Standard wh i ch is concerned wi th fi l m radi ograph y Tabl e — Som e Represen tati ve Th erm al N eu tron Detector Materi al s Element Nuclear reaction Product half-life Cross-section Boron Dysprosi u m Gadol i ni u m 10 64 55 57 I ndi u m Li th i u m Rh odi u m γ Dy(n, ) γ Gd(n, γ) Gd(n, ) 97 Gol d α) Li B(n, γ Au (n, ) 115 γ I n(n, ) 03 Li (n, 65 56 58 98 2) 837 di rect Dy 39 m i n 000 i ndi rect Gd prompt 61 000 di rect Gd prompt 254 000 di rect Au 2, d 99 i ndi rect 54 m i n 65 i ndi rect prom pt 940 di rect 42 s 39 i ndi rect 1 6m In 04 Method of prom pt α) H Rh (n) 1) radiography barns Rh 2) ) Cross-secti ons are for th e reacti on and i sotope sh own for th ermal neu trons (sou rce BN L-325, 3rd edi ti on, vol u me I , 973) 2) Th ese detectors are often u sed for track-etch n eu tron radi og raph y Fi l m N early any ph oto-sensi tive fi l m m ay be used for neu tron radi ography bu t i t i s recomm ended th at i ndu stri al radi ographi c fi l m be u sed for m ost appl i cations, ei th er di rect or i ndi rect, for best resu l ts Si ngl e-si ded fil m s produ ce th e best resol u tion I n appl i cati ons requ i ri ng th e addi ti on al speed of a fi l m h avi ng em u l si on on both si des som e resol u ti on m ay be sacri fi ced Th e recom mendati ons and practi ces th at appl y to th e m anu al or au tom ati c processi ng of radiograph i c fil m s can al so be appl ied generall y to th e processi ng of radi ograph ic fi l ms u sed for neu tron radi ograph y 9 Cassettes G en eral Cassettes are requ i red for exposu re of th e fi l m and conversi on screens i n th e di rect m eth od, for exposu re of th e conversi on screens i n th e i ndi rect m eth od, and for th e decay transfer process in th e i ndirect m eth od Vacu um cassettes are h i gh l y recom m ended for al l appl i cati ons i nvol vi ng fi l m , as th ese ensu re th at th e fi l m and conversi on screens are i n i nti m ate contact and th u s prevent fi l m flaws du e to poor contact 9.2 M aterial of constru ction M aterial s used i n th e fabri cati on of cassettes to be u sed in th e neu tron beam sh ou l d be sel ected wi th care to avoi d i m age degradati on cau sed by neu tron scatteri ng or secondary radi ation from th e cassette Th e cassettes shou l d be fabri cated from I SO 1 537: 998(E) © I SO al u m ini u m or m agnesi u m , both of whi ch are rel ati vel y transparent to neu trons I f com merci all y avai labl e cassettes are to be u sed, th ey sh ou ld be free from pl asti c m ateri al s and th e face-pl ate sh ou l d be m ade of th i n al um i ni u m (Al 99, Cu (1 00) reactor grade or Al M g Si Cu -TF (6061 T6) al u m ini u m are recom mended) Cassettes h avi ng o-ri ngs or oth er hydrogeneou s gasket m ateri al s sh ou l d be avoi ded enti rel y or at l east consi dered carefu l l y For th e i ndirect screen-to-fi l m exposu re, th e cassette materi al is not a cri tical consi derati on becau se th e cassette i s never exposed to th e neu tron beam , th erefore th ere are no neu trons to be scattered and no secondary radi ati on to consider I nexpensi ve com m erci al l y-avai l abl e fl exi bl e vacu u m cassettes can even be u sed for th i s pu rpose 10 Appl i cati ons for thermal neutron radi og raph y Al th ou gh th ere are m any si m il ari ties between X- and neu tron radiograph y, th e di ssi m il ari ties between th e two tech ni qu es m ake th em each val u abl e i n th ei r own respecti ve dom n N eu tron radi ograph y is parti cu l arl y u sefu l i n som e speci fi c appl i cati ons as sh own i n th e fol l owi ng For addi ti onal i nform ati on see annex C 0.1 Detection of low-density materials surrounded by high-density materials Th ermal neu tron radi ograph y i s u sefu l for th e detecti on and i nspecti on of l i gh ter el em ents encased in a m ore dense m ateri al su ch as m etal A cl assi c dem onstrati on i s th e neu tron radi ograph y of a wax-coated stri ng em bedded i n several inch es of l ead Al th ou g h l ead i s very di ffi cu l t to penetrate wi th X-rays, i t i s easi l y pen etrated by a neu tron beam Exam pl es of th i s type of appl i cati on i ncl u de th e i nspecti on of ordnan ce and oth er expl osi ve devi ces, l ocati on and m easu rem ent of h ydrogen i n m etal s, detecti on of m oi stu re or l i qu i ds i n metal contai ners, i nspecti on of adh esi ve bondi ng of h oneycom b stru ctu res, veri ficati on of th e l ocati on of o-rings and gaskets wi thi n an assem bl y, detecti on of corrosi on i n rcraft stru ctu res, stu dies of fl u i d fl ow i n system s, and th e detecti on of fi ssi on produ cts i n n u cl ear fu el el em ents 0.2 Detection of materials having similar densities Th erm al neu tron radi ograph y can be u sed effecti vel y wh en objects consi st of si m i l ar densi ty m ateri al s th at wou l d be di ffi cu l t to i m age with X-rays Wh ereas X-rays i nteract wi th elem ents of increasi ng densi ty i n a fai rl y l i near fash ion, neu trons i nteract m ore ran dom l y as sh own i n fi gu re Becau se of th i s ph enom enon, som e m ateri al s h avi ng very si m i l ar den si ti es h ave total l y di fferent responses to neu trons and can be di fferenti ated on a neu tron radi ograph Exampl es of th ese appl i cations i ncl u de neu tron radi ograph i c eval u ati on of cadm i u m and si l ver brazi ng m ateri al s, m i g rati on of m ateri al s i n sol i d-state el ectroni c com ponents, electrol yte m i grati on i n batteri es, di ffu si on between l i gh t and h eavy water, and absorpti on of m oi stu re by concrete For exam pl e, contrast agents su ch as gadol ini u m m ay be u sed to pre-im pregnate th e core m aterial of investm ent casti ngs and th u s enabl e resi du e parti cl es wi th i n core gall eri es to be detected u si ng neu tron radi ograph y Th i s tech niqu e i s u sed routi nel y to d i n th e i nspecti on of gas-cool ed tu rbi ne bl ades 0.3 Differentiation between isotopes of the same element N eu tron attenu ati on i s governed by the nu cl ear cross secti on of th e m aterial , wh i ch m ay vary even between i sotopes of a gi ven el em ent, rath er than density or any oth er ph ysi cal or ch em ical property of th e m ateri al For exam ple, because of th e strong di fference i n neu tron absorpti on between fi ssi onabl e 235 235 U and 238 U , fu el pell ets h avi ng different concentrati ons (enri ch ment) of th e U i sotope can easi l y be i denti fi ed i n a neu tron radi ograph Anoth er exam pl e i s 113 Cd wh i ch i s th e onl y i sotope of cadm iu m wi th a h igh th erm al neu tron attenu ati on Al so, one can di fferenti ate between i sotopes su ch as h ydrogen and deu teri u m 0.4 Inspection of highly radioactive materials I ndi rect neutron radi ograph y is i nsensi ti ve to gam m a radi ation ei th er form th e neu tron beam or from a radi oacti ve object Th erefore th i s tech ni qu e i s extrem el y u sefu l i n th e nu cl ear i ndu stry for in-servi ce i nspecti on © I SO 1 537: 998(E) I SO 11 Improved contrast C e rtai n m ate ri al s h avi n g n e u tro n rad i o g raph s cal e m ake to it An highly high n e u tro n e xam pl e vi s i bl e in is a atte n u ati o n th e u se th e rm al of can be u s e fu l fo r g ad o l i n i u m - o xi d e n e u tro n rad i o g raph tag g i n g wh i ch Oth e r is a o th e r m ate ri al s po wd e r co n tras t th at ag e n ts to can i n cl u d e i n cre as e be wi pe d cad m i u m , th ei r on to co n tras t a bo ro n or in a m ach i n i s t' s e ve n wate r or oi l 12 Imag e qu al i ty i ndi cators Fu tu re I SO n e u tro n s tan d ard s rad i o g raph y cri te ri a be twee n 13 d e s cri be Th e a ve n d o r an d d e vi ce s m e th o d s an d te ch n i q u e s d e s cri be d th e re i n u sed can to be ch aracte ri z e u sed as a th e bas i s to tal fo r s ys te m e s tabl i s h i n g re s po n s e fo r re pe atabi l i ty a th e rm al an d q u al i ty cu s to m e r Neu tron acti vati on Som e m ate ri al s captu re cro s s Al th o u g h th i s an d of l oss n e u tro n beco m e s e cti o n s e co n d ary co n tras t, of th e th e o bj e ct h an d l i n g C as s e tte s can can in re s u l t cas s e tte s C o n ve rs i o n high e s pe ci al l y sh i el d i n g s cre e n s an d afte r m aj o r s h al l be wh en th i s can e xpo s ed m ay re s u l t h ave a co n s i d e rati o n m ate ri al s u sed pe rfo rm e d acti vate d in in to th e to th e n eu tro n rad i ati o n d e tri m e n tal is th at e ffe ct pre ve n t n e u tro n be am m ay on th e faci l i ty e xpo s u re d u ri n g pe rs i s t pe rs o n n e l rad i o g raph y fo l l o wi n g s u ch as cau s e fi l m fo r u sed expo s u re an d th e U si n g rad i o g raph y h o u rs a fo r or n e u tro n Som e o bj e cts s h o rt D e pen d i n g d ays fo l l o wi n g rad i o g raph y, co n s i d e rati o n be i n g d e cay on be is al l th at is n e u tro n e xpo s u re cau s i n g s h al l rad i o g raph e d ti m e th e i r n eu tro n fo g g i n g g i ve n Al s o , to th e rad i ati o n re q u i red be fo re n e u tro n if u sed s ch e m e th at re pe ate d l y wi l l d u ri n g m i n i m i ze a s h o rt e xpo s u re i n te rval to of ti m e pe rs o n n e l It M o n i to ri n g of rad i ati o n i m po rtan t to ke e p is l e ve l s acti vate d fi l m g ad o l i n i u m , pro bl e m s capabi l i ti e s e xpo s u re o u t m o s t o f th e e s pe ci al l y m an ag e m e n t u n e xpo s e d sel d om acti vati o n rad i ati o n of cas s e tte fo rm h al f- l i fe , re s u m e be co m e a away pro pe rti e s can rad i o acti ve an d ch aracte ri s ti cs s u rve ys n o rm al th e i r wi l l faci l i ty rad i ati o n Th e s e an d fro m bo ro n or C o n ve rs i o n s cre e n s u n ti l th e th e s e l i th i u m u sed s cre e n s be co m e s cre e n s are fo r u sed d i re ct n e u tro n fo r i n d i re ct rad i o acti ve l o ad e d i n to d u ri n g th e rad i o g raph y n e u tro n fi l m u s u al l y rad i o g raph y e xpo s u re cas s e tte an d Th e are s h al l h ave ch o s e n be cas s e tte l ow h an d l e d is acti vati o n s pe ci fi cal l y u s u al l y wi th fo r care , e ffe cti ve in s cre e n s I SO 1 537: 998(E) © I SO Annex A (i n form ati ve) Gl ossary of terms rel ated to neu tron radi og raph y activation: Process of cau si ng a su bstance to becom e artifi ci all y radi oacti ve by su bjecti ng i t to bom bardm ent by neu trons or oth er parti cl es attenuation coefficient: Term rel ated to th e rate of ch ange in th e i ntensi ty of a beam of radi ati on as it passes th rou gh m atter (see li near and m ass absorpti on coeffi ci ent) attenuation cross section: Probabi li ty, expressed i n barns, th at a neu tron wi l l be total l y absorbed by th e atom i c nu cl eu s barn: U ni t of area expressi ng nucl ear cross secti ons (1 barn = -24 cm ) cadmium ratio: Rati o of th e response of two i denti cal neu tron detectors, u su al l y acti vati on types su ch as i ndi u m or gol d, one exposed bare to th e beam and th e oth er cadm iu m covered (th e cadm i u m covered detector records prim ari ly neu trons h avi ng an energy above 0, eV and th e rati o i s a m easu re of th erm al i zati on i n th e neu tron spectru m) cassette: Li gh t-ti gh t devi ce for h ol ding fi l m or conversi on screens and fi l m in cl ose contact du ri ng exposure contrast agent: M ateri al added to a com ponent to enh ance detai l s by sel ecti ve absorpti on of th e i nci dent radi ati on conversion screen: Devi ce th at converts th e i m aged neu tron beam to radi ation or l igh t th at exposes th e radi ograph i c fil m cross section: Apparent cross-secti onal area of th e n u cl eu s as cal cu l ated on th e basi s of th e probabi l i ty of occu rrence of a reacti on by col l i si on wi th a parti cl e I t does not necessari l y coi n ci de wi th th e geom etri cal cross-secti onal area πr I t i s g i ven i n u ni ts of area direct exposure imaging: In th e di rect exposu re i m aging m eth od, the conversi on screen and i mage recorder are si mu l taneou sly exposed to th e neutron beam electron volt: Ki neti c energy gai ned by an el ectron after passi ng th rou gh a potential di fference of V gamma ray: El ectrom agneti c radi ati on h avi ng i ts ori gi n i n an atom i c n u cl eu s half-life: Ti m e requ i red for one h al f of a gi ven nu mber of radi oactive atom s to u ndergo decay half-value layer: Th i ckness of an absorbi ng m ateri al requ i red to redu ce th e intensi ty of a beam of i nci dent radi ati on to one-h al f of i ts ori gi nal i n tensi ty indirect exposure: M eth od i n wh i ch onl y a g am m a-i nsensi ti ve conversi on screen i s exposed to th e neu tron beam After exposu re, th e conversi on screen is pl aced in contact wi th the i m age recorder isotope: One of a grou p of nu cl i des of th e sam e el em ent h avi ng th e sam e nu m ber of protons ( Z) i n th e nu cleu s, bu t di fferi ng i n th e nu m ber of neu trons, resu l ti ng i n di ffering val u es of atom ic wei gh t ( A) L/D ratio: Ratio of th e di stance from th e entrance apertu re to th e i m age pl ane ( L) to the di ameter of th e entrance apertu re ( D ) I t i s one m easu re of resol u ti on capabi l i ty of a neu tron-radi ograph i c system linear attenuation coefficient: M easu re of th e fracti onal decrease i n radiati on beam i ntensi ty per u ni t of distance travell ed i n th e m aterial (cm -1 ) mass attenuation coefficient: M easu re of th e fracti onal decrease in radiati on beam i ntensi ty per u ni t of surface densi ty (cm g -1 ) moderator: M ateri al u sed to sl ow fast neu trons N eu trons are sl owed down wh en th ey col l i de wi th atom s of l i gh t el em ents su ch as hydrogen , deu teri u m , beryl l i u m and carbon 10 © I SO 1 537: 998(E) I SO neutron: N eu tral el em en tary parti cl e h avi n g a m ass cl ose to In th e free state ou tsi d e of th e n u cl eu s, th e n eu tron is u n stabl e h avi n g a h al f-l i fe of approxi m atel y m i n neutron radiography: P rocess of m aki n g a d u rabl e i m ag e of th e i n tern al d etai l s of an obj ect by th e sel ecti ve atten u ati on of a n eu tron beam by th e obj ect thermal neutron: N eu tron s of th ese en erg i es are prod u ced by sl owi n g d own of fast n eu tron s u n ti l th ey are in th erm al eq u i l i bri u m wi th th ei r en vi ron m en t total cross section: vacuum cassette: Su m of th e absorpti on an d scatteri n g cross secti on s Li g h t-ti g h t d evi ce h avi n g a fl exi bl e en tran ce wi n d ow wh i ch , wh en operated u n d er a vacu u m , h ol d s th e fi l m an d versi on screen i n i n ti m ate tact d u ri n g exposu re 11 I SO 1 537: 998(E) © Annex B (i nform ati ve) Th erm al n eu tron l i n ear atten u ati on coeffi ci en ts u si n g averag e scatteri n g an d th erm al absorpti on cross secti on s for th e n atu ral l y occu rri n g el em en ts Cross-secti on El em en t barn s 12 Scatteri n g 1) Li n ear atten u ati on 2) coeffi ci en t Sym bol H He 0, 76 Li 0, 95 Be 6, 5 B 4, 27 C 4, 74 N 0, 03 ,9 g as O 3, 761 0, 001 g as F 3, 64 0, 096 g as 10 Ne 2, 41 0, 039 g as 11 Na 3, 025 0, 53 0, 09 12 Mg 3, 41 0, 063 0, 50 13 Al , 41 0, 231 0, 14 Si 2, 043 0, 71 0, 1 15 P 3, 34 0, 72 0, 0, 53 0, 06 20, 49 0, 978 Absorpti on 0, 333 0, 007 70, 0, 007 767 0, 003 cm -1 Atom i c N o g as g as 3, 31 0, 76 01 , 79 0, 55 16 S 17 Cl 18 A 0, 647 0, 675 19 K 2, 04 2, 0, 05 20 Ca 2, 93 0, 43 0, 08 21 Sc 22 Ti 4, 09 6, 09 0, 58 23 V 4, 5, 08 0, 71 24 Cr 3, 38 3, 07 0, 54 25 Mn 2, 26 Fe 1 , 35 27 Co 28 Ni 7, 29 Cu 5, 22, 33, 27, 3, g as g as , 99 , 24 2, 56 ,1 37, 3, 93 4, 49 2, 04 7, 78 3, 78 0, 98 30 Zn 4, 08 ,1 0, 34 31 Ga 6, 2, 0, 48 32 Ge 8, 37 2, 0, 47 33 As 5, 43 4, 0, 46 34 Se 8, 56 1 ,7 35 Br 6, 6, 0, 74 0, 31 I SO © I SO 1 537: 998(E) I SO Cross-secti on El em en t barn s Scatteri n g Li n ear atten u ati on 2) coeffi ci en t Sym bol 36 Kr 7, 37 Rb 6, 38 Sr , 28 0, 20 39 Y 7, 67 , 28 0, 27 40 Zr 6, 0, 85 0, 28 41 Nb 6, 37 ,1 0, 42 42 Mo 5, 59 2, 55 0, 53 43 Tc – 44 Ru 6, 45 Rh 5, 46 Pd 4, Absorpti on 25 0, 38 20 2, 56 45 6, g as 0, 07 , 43 0, 67 0, 89 0, 75 47 Ag 5, 08 48 Cd 5, 49 In 50 Sn 4, 909 0, 626 0, 51 Sb 4, 5, 0, 31 52 Te 3, 74 4, 0, 25 53 I 3, 54 6, 0, 23 54 Xe 23, g as 55 Cs 56 Ba 3, 42 57 La 0, 58 Ce 59 Pr 2, 54 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 2, 45 4, 20 63, cm -1 Atom i c N o 520 93, 29, – 38 – 72 65 Tb 66 Dy 6, 92 67 Ho 8, 65 68 Er 69 05, 4, 01 1 7, 7, 52 0, 42 ,2 0, 07 8, 97 0, 51 0, 63 0, 28 1 ,5 0, 41 50, , 89 400 251 , 79 670 71 , 76 565 94, 82 48 890 483, 88 23, 940 0, 95 33, 64, 2, 35 259, 5, 49 Tm 6, 05 3, 70 70 Yb 23, 35, , 43 71 Lu 6, 76, 2, 82 72 Hf 0, 73 Ta 6, 4, 77 04, 20, 5, , 47 74 W 8, , 46 75 Re 1 ,3 89, 6, 86 76 Os 15 2, 21 77 Ir 4, 425, 30, 86 13 I SO 1 537: 998(E) © Cross-secti on El em en t barn s Li n ear atten u ati on 2) coeffi ci en t Sym bol 78 Pt 79 Au 80 Hg 81 Tl 0, 01 3, 43 0, 47 82 Pb 1 , 26 0, 71 0, 38 83 Bi 9, 0, 033 0, 26 84 Po – – — 85 At – – — 86 Rn – – g as 87 Fr – – — 88 Ra – 2, 0, 89 Ac – 90 Th 91 Pa 92 U 238 U Absorpti on 2, 7, 84 26, – 4, 0, ,5 98, 65 6, 372, 890 2, 97 7, 37 21 680, – – 94 Pu – 0, 62 8, 41 2, 68 Np 6, 21 23, 77 9, 38 93 cm -1 Atom i c N o 235 Scatteri n g I SO 756 33, 75 0, 58 d en si ty u n kn own 85, 96 (absorpti on + fi ssi on ) ) U pd ated wi th d ata pri m ari l y from N eu tron Cross Secti on s: N eu tron Reson an ce Param eters an d Th erm al Cross Secti on S F M u g h abg h ad , Acad em i c Press, I n c , San Di eg o, 981 2) Al l cross secti on val u es are th e m ost probabl e val u es 14 © I SO 1 537: 998(E) I SO Annex C (i nform ati ve) Bi bl i ography [1 ] B ARTON , J P , Contrast Sensi ti vity i n N eu tron Radi ography , Appl i ed M ateri al s Research , Vol u m e 4, N o 2, 965, pp 90-96 [2] B ARTON , J P , Radi ographi c Exam inati on Throu gh Steel U si ng Cold N eu trons , Bri ti sh J ou rnal of Appl i ed Ph ysi cs Vol u m e 6, 965, pp 833-1 840 [3] B ARTON , J P , Radi oi sotope Sou rces and N eu tron Radiography , Ch em i cal Engi neeri ng Process , Sym posi u m Series Vol u me 66, N o 06, 970, pp 91 -1 06 [4] B ARTON , J P and H ARDT, P , Eds, Proceedi ngs of th e Fi rst Worl d Conference on N eu tron Radi ography, VON DER D Rei del Pu bl i sh i ng Co , Dordrecht, H ol l an d, 981 [5] B ERGER , H , Characteri sti cs of a Therm al N eu tron Televi si on I m aging System , M ateri al s Eval u ati on Vol u m e 24, N o 9, 966, pp 475-481 [6] B ERGER , H , N eu tron Radi ography El sevi er Pu bli sh i ng Co , Arnsterdam , 965 [7] B ERGER , H., Radi ography With Track — Etch Detectors , Proceedi ngs of th e Seventh Conference on N on-destru cti ve Testi ng, Warsaw, B, 973 [8] [9] Cali forniu m -252, Process Report N o 7, U SAFC, Aiken, SC, 974, pp 40-41 D ANCE , W E , C LUZEAU , S and M AST, H U , I ntegrati on of an advanced sealed neu tron tube generator i nto a m obi le neu tron radi ology system and resu lting perform ance N u cl ear I nstru m ents and M eth ods in Ph ysi cs Research B - N I M B 56/57 (1 991 ) 907-91 [1 0] H ARMS , A A and WYMAN , D R , M athem ati cs and Physi cs of N eu tron Radi ography D Rei del Pu bl i sh i ng Co , Dordrech t, H oll and, 986 [1 ] H AWKESWORTH , M R , Film s for N eu tron Radi ography: an I ri vesti gati on of Fi lm — I ntensi fyi ng Screen I m age Recorders , J ou rnal of Ph ysi cs E (London) , Vol u me 2, 969, pp 235-242 [1 2] H AWKESWORTH , M R , N eu tron Radi ography: Equ i pment and Methods , Atom i c Energy Revi ew, Vol u m e 5, N o 2, 977, pp 69-220 [1 3] H OLLAND , L and H AWKESWORTH , M R , Low Voltage Parti cle Accelerators for N eu tron Generation , N on-destru cti ve Testi ng, Vol u m e 4, N o 971 , pp 330-337 [1 4] M ATFI ELD , R S , N eu tron Radi ography, Atom (London) , Vol u m e 74, 971 , pp 84-99 [1 5] N eu tron Radiograph y N ewsl etter, Am eri can Soci ety for N on-destru cti ve Testi ng, Col u m bus, OH , 964 to Present [1 6] P ERSON , J L and R OTTGER, H , Eds, Proceedi ngs of th e Second Worl d Conference on N eu tron Radi ograph y, D Rei del Pu bl i sh i ng Co , Dordrech t, H ol l and, 987 [1 7] P ETER , O Z , N atu rforsch u ng, Vol u m e , 946, p 557 [1 8] Practi cal Appl i cati ons of N eu tron Radi og raph y and Gagi ng, ASTM STP 586, Am eri can Soci ety for Testi ng and M ateri al s, 976 [1 9] Radi ograph y Wi th N eu trons, Bri ti sh N u cl ear Energy Soci ety, London, 975 15 I SO 1 537: 998(E) [20] S PORTWART, A R , U se of a 01 © I SO N /S N eu tron Generator for N eu tron Radi ography, N u cl ear I nstru m ents and M eth ods Vol u m e 92, 971 , pp 61 3-61 [21 ] S TADE , J , N eu tron Radi ography Wi th an Electron Linear Accelerator , M ateri al prufu ng, Vol u me 9, N o 0, 977, pp 436-439 [22] VON DER H ARDT, P and R OTTGER, H , Eds, N eu tron Radi ograph y H andbook D Rei del Pu bl i sh i ng Co , Dordrech t, H ol l an d, 981 [23] WHI TTEMORE , W L , LARSON , J E and S HOPTAUGH , J R , A Fl exi ble N eu tron Radi og raphy Faci li ty U si ng a TRI GA Reactor Sourcell , M ateri al s Eval u ati on Vol u m e 3, 971 , pp 93-98 [24] WI LSON , L E , H I LDRETH , G A and F USSA, A D , I ndu stri al Developm ent an d Appli cati on of the Van de Graaff Accelerator for N eu tron Radi ography, M ateri al s Eval u ati on, Vol u m e 29, N o 4, 971 , pp 69-74 [25] [26] H ARMS , A A , M athemati cs and Physi cs of N eu tron Radi ography D Rei del Pu bl i sh i ng Co , H ol land, 986 D OMANUS , J C , Colli m ators for Therm al N eu tron Radi ography An overvi ew compi l i ed by J C Dom anu s, Ed by J F W M arkgraf D Rei del Pu bl i sh ing Co , H ol l and, 987 [27] B ERGER , H , Early Development of N eu tron Radi ography in the U SA , M ateri al s Eval u ati on, Vol u m e 49, N o 9, September 991 , pp 202-1 21 [28] ASTM E 545-91 , Standard Method for Determ i ni ng the I mage Qu ali ty i n Direct Thermal N eu tron Radi ographi c Exam i nati on [29] KOBAYASHI , H , Evalu ati on of three dim ensi onal u nsharpness on N R i m ages , N ondestru cti ve Testi ng Evalu ati on 1 (1 994) 7-85 [30] KOBAYASHI , H and KI GANAGE , Y , Basi c concept and characteri sti cs of beam qu ali ty i ndi cator for continu u m neu tron spectru m Topi cal m eeti ng on N eu tron Radi ograph y; System Desi gn and Ch aracteri zati on: Sh onam Vi l l age Center, Tokyo U ni versi ty, J apan, 2-1 N ovem ber 995 16