Lovelace Res pir a t or y Res ea rch In stit u t e, Albu quer qu e, New Mexico, USA T h e au th ors h ave d eveloped a sim ple, accurat e m eth od to com bu st low-level, tritiu m -containin g tissu e sam ples by m odifyin g a tu be fu rn ace w ith tw o combu stion zon es. T he sam ple is pyrolyzed u pstream u n d er a slow stream of argon, after w h ich oxygen is add ed to th e gas stream , an d pyrolysis gases are com bu sted over a platin u m catalyst. T h e ch arred sam ple is com busted by ch an gin g th e gas from argon to pure oxygen. A sm all volu m e of steam is t hen passed th rough th e tu be fu rn ace to pu rge ad sorbed tritiated w ater from th e w alls of th e apparatu s. T h e origin al d esign w as ch an ged in tw o w ays. (1) Gas in lets w ere arran ged so th at baf¯es or porou s plu gs are n ot n eeded to m ain tain stable com bu stion . T h is ch an ge greatly redu ces the resid ual rad ioactivity carried over from on e sam ple t o th e n ext (typically(2) Com bu stion gases are com pletely cond en sed in a cold trap w ith liqu id n itrogen so th at 100% of th e tritiu m in th e sam ple is trapped. Th e colorless, trapped w ater is d irectly d issolved in scintillation¯u id , giving excellen t coun tin g ef® ciencies. R ecoveries of activity w ere 100% § pipett in g errors in blood spik ed w ith tritiat ed benzo[a]pyrene. Usin g th is m eth od , t issu e tritiu m levels » 50% above coun tin g back groun d w ere accurately qu an titated in 0.1± 2.0 g sam ples of blood, liver, fat, an d oth er tissues.Ke y w o rd s a n a lysis, biologica l m a t er ia l, 3 H , liqu id scin t illat ion coun t in g, sam ple pr epa ra t ion , t issues, t rit iu m A n u m ber of m et h ods, in clu din g a u t om a t ed syst em s, h a ve been r epor t ed for det er m in in g t r it iu m in biologica l sa m ples. Most m et h ods in volve sa m ple com bust ion followed by liqu id scin t illa t ion cou n t ing (LSC) [1]. Beca u se t r it ium is a wea k b -em it t er, LSC of t h is isot ope is ver y sen sit ive t o color qu ench in g of t h e sa m ple by in com p let e com bu st ion pr odu ct s. P r oblem s fr equ en t ly a r ise wit h t issu e sa m ples of low a ct ivit y con t a inin g Received 15 J u ly 1997; a ccep t ed 21 Novem ber 1997. Th is r es ea rch wa s spon sor ed by NIH Gr a n t RO1-5910 from NIE H S in fa cilit ies belonging t o t h e U.S. Depa rt m en t of E n er gy, Of® ce of H ea lt h a n d E n vir on m en t a l Res ea rch , u n der Cont r a ct DE -AC04-76E V01013.Addr es s cor responden ce t o Per Ger de, P h D, Lovela ce Resp ir a t ory Res ea r ch In st it u t e, P.O. Box 5890, Albuqu er qu e, NM 87185, USA. E -m a il: pger de@lr ri.org
This paper explains the analysis and elimination of BPO4 crystal formation in an Atmospheric Pressure Chemical Vapor Deposition BPSG film. Film deposition and furnace anneal/flow parameters were studied using full factorial techniques, with anneal/flow parameters having the most significant effect. It was learned that BPO4 crystals could be readily induced by performing the anneal/flow process in a POCl3/O2 ambient. Most testing was done in a POCl3/O2 ambient and inferences made concerning the standard anneal ambient.BPO4 formation is primarily dependent on thermal processing during anneal toprovide the activation energy necessary to initiate crystal growth. Other factors include 02:Hydride ratio during film deposition, phosphorous concentration in the deposited film, deposition temperature, and anneal/flow ambient. No tested level of these secondary factors completely eliminated crystal formation.The growth of BPO4 crystals can be eliminated by controlling the thermal environment ofthe anneal/flow step. The primary means employed was to increase the rate of heat dissipation by doubling the spacing between wafers. An alternative method involves utilization of reduced anneal/flow furnace temperatures.
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