ELSEVI ER A hi gh ener gy gamma camer a usi ng a mul t i pl e hol e col l i mat or and PSPMT Abst r act A hi gh ener gy gamma camer a usi ng a par al l el hol e t ungst en col l i mat or and a 7 . 62 cm squar e Posi t i on Sensi t i ve Phot omul t i pl i er Tube ( PSPMT) has been assembl ed and t est ed . The measur ed ener gy r esol ut i on is 12- 20% FWHMf or 137CS ( 662 keV) gamma r ays, and 17- 23%FWHMf or 57 Co ( 122 keV) . The measur ed spat i al r esol ut i on measur ed is 2 . 8- 3 .2 mm f or 122 keV and 3 . 4- 5 .3 mm f or 662 keV . The var i at i on in t he ener gy and spat i al r esol ut i on is due to t he cont i nuousl y var yi ng gai n acr oss t he PSPMT. Measur ed ener gy spect r a and i mages obt ai ned ar e pr esent ed. 1 . I nt r oduct i on Por t abl e gamma camer as capabl e of i magi ng hi gh en- er gy gamma r ays ( 1- 2 MeV) ar e of i nt er est in a var i et y of i ndust r i al set t i ngs . A second gener at i on gamma camer a desi gn whi ch i mproves upon t he ef f i ci ency of our si ngl e aper t ur e camer a [ 1] is pr esent ed her e . The camer a uses a3 in . squar e Posi t i on Sensi t i ve Phot omul t i pl i er Tube ( PSPMT) ( Hamamat s u, R- 2487- 05) [ 2] coupl ed to a Nal (TI ) sci nt i l l at or . The i ncom i ng gamma r ay di r ect i on is det er - m i ned by a segment ed col l i mat or [ 3] . The combi nat i on gi ves rise to a compact and yet ef f i ci ent gamma camer a capabl e of i magi ng hi gh ener gy gamma f i el ds . PSPMTs have r ecent l y been ext ensi vel y used f or i magi ng gamma r ays of subst ant i al l y l ower ener gi es [ 4- 9] . In an ef f or t to i mage hi gher ener gy gamma r ays, a pi nhol e col l i mat or with a segment ed sci nt i l l at or at t ached to t he PSPMT was pr esent ed in Ref . [ 10] . In t hi s wor k we expl or e usi ng PSPMTs to i mage hi gh ener gy gamma r ays usi ng a multi- pl e hol e col l i mat or . 2 . Camer a desi gn Nucl ear I nst rument s and Methods in Physi cs Resear ch A 353 ( 1994) 328- 333 S.V. Gur u *, Z . He, J .C. Fer r er i a, D .K. Wehe, G .F . Knol l Depar t ment of Nucl ear Engi neer i ng, The Unacer si t y of M i chi gan, Ann Ar bor , MI 48109- 2104, USA The assembl ed camer a (wi t hout shi el di ng) is shown in Fi g . 1 . The PSPMT, preampl i f i er ci r cui t , and sci nt i l l at or ar e mount ed wi t hi n a har dened al um i ni umbox. Thi s c om- Thi s wor k was suppor t ed under t he U .S. Depart ment of Ener gy, Robot i cs f or Advanced React or s, Gr ant No . DOE- FG02- 86NE37969 . * Cor r espondi ng aut hor . 0168- 9002/ 94/ $07 . 00 © 1994 El sevi er Sci ence B.V Al l r i ght s r eser ved SSDI 0168- 9002( 94) 00766- 7 pact uni t is connect ed to t he comput er t hr ough t he t r i gger and peak det ect i on ci r cui t r y boar d . 2 .1 . Col l i mat or 2 .2. Sci nt i l l at or NUCLEAR I NSTRUMENTS & METHODS IN PHYSI CS RESEARCH Sect i on A A segment ed col l i mat or with cyl i ndr i cal hol es with di ver gi ng axes is empl oyed to det er m i ne t he di r ect i onal i t y of t he sour ce di st r i but i ons . The pri mary i nt er est in devel - opi ng t hi s camer a is to i mage r adi oact i vi t y di st r i but i ons i nvol vi ng hi gh ener gy gamma r ays over l ar ge f i el ds of vi ew. W ith t hi s appl i cat i on in m i nd, a segment ed col l i ma- t or was desi gned with f i el ds of vi ew f r om adj acent hol es t hat over l ap onl y at i nf i ni t y ( negl ect i ng sept al penet r at i on) . In a r eal i st i c case, due to i ncr easi ng penet r at i on at hi gher ener gi es, t he di st ance at whi ch t he f i el ds of vi ews over l ap decr eases with i ncr easi ng ener gy of t he gamma r ays to be i maged . Thi s col l i mat or has t he di sadvant age of dead ar eas (i.e ., ar eas in t he sour ce pl ane whi ch will not be seen in t he i mage pl ane) when t he sour ce di st r i but i on is cl ose to t he col l i mat or f ace . However , t hi s dead ar ea r api dl y decr eases as t he sour ce- col l i mat or di st ance is i ncr eased [ 3] . The sci nt i l l at or chosen f or t hi s camer a was a 7 .5 cm X 7 .5 cm X 1 cm bl ock of Nal ( TI ) , housed in a machi ned al um i ni um can with a 0 . 2-mm t hi ck ent r ance wi ndow. Al l t he i nner f aces of t he sci nt i l l at or , except t he exi t wi ndow, ar e cover ed with a bl ack, l i ght absor bi ng coat i ng to pr e- vent l i ght spr eadi ng . The i nt er act i on ef f i ci ency wi t hi n t he sci nt i l l at or i ncr eases as t he det ect or t hi ckness is i ncr eased . However , t he l i ght spr ead, due to t he i sot r opi c em i ssi on of