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The production of “threshold” nuclear reactions in a graphite reactor
252
International Conference on Radioisotopes in &ientific Research
aerated with a n effort of 2'4 horsepower hr per kg of O 2 added. Lakes as e x p e r i m e n t a l models for oceanographic a n d isotope studies will be discussed.
189 T h e P r o d u c t i o n of " T h r e s h o l d " N u c l e a r R e a c t i o n s in a G r a p h i t e R e a c t o r . C. E. MELLISH, J . A. PAYNE, a n d A.E.R.E., Harwell, U.K.
R.
L. OTLET,
I n P a r t 1 of this work the reaction Ni5S(n,p)Co as has been used to m o n i t o r the flux of fast fission neutrons in the Harwell reactor B.E.P.O. in a series of different positions in the reactor, m a k i n g assumptions a b o u t the energy spectrum of the flux. T h e ratio of fast to slow flux is plotted t h r o u g h the reactor, a n d this gives the preferred positions for p r o d u c i n g threshold reactions, (n,p), (n,ct), etc., a n d the preferred positions for eliminating t h e m as far as possible. T h e importance of this elimination in some radioactivation analyses is pointed out. T h e occurrence of "exot h e r m i c " (n,p) reactions such as N14(n,p)C 1~ a n d Claa(n,p)S a5 is discussed. I n Part 2 cross-sections are presented for a n u m b e r of (n,p) reactions on elements r a n g i n g from t i t a n i u m to thallium in the Periodic Table, a n d for some (n,~) reactions on elements from t i t a n i u m to caesium. W h e r e the p r o d u c t isotope can also be formed by n e u t r o n capture in i m p u r i t y a m e t h o d is devised to correct for a n y i m p u r i t y present. T h e cross-sections m e a s u r e d are c o m p a r e d with those predicted by theory.
190 D e v e l o p m e n t of M e t h o d s for t h e P r o d u c t i o n of C e r t a i n S h o r t - l i v e d R a d i o i s o t o p e s . L. G . STANG, JR., W . D . TUCKER, R . F. DOERING, A. J . WEiss, M . W . GREENE a n d H . O . BANKS, JR., B r o o k h a v e n N a t i o n a l Laboratory, U.S.A. At the Brookhaven H o t L a b o r a t o r y methods are being developed for p r o d u c i n g radioisotopes which would be useful if they were available, or available in suitable form. Examples for which procedures have been completed include M g 2s, 1la2, 113'3 a n d F is. At B r o o k h a v e n these are reactor produced. This p a p e r will describe u n p u b l i s h e d recent results of this work. ~VIagnesium-28, 21-hour half-life, is a very i m p o r t a n t radioisotope for medical research a n d is the only isotope of m a g n e s i u m with a half-life long enough to be practical for use as a tracer. I t is produced in specific activities of a b o u t one millicurie per g r a m using a n e u t r o n flux of a b o u t 3 x l0 Is n sec -1 c m 2. T h e Brookhaven process involves irradiating 0-01 in. thick foils of a n alloy of natural M g with lithium which
has been enriched to 95 per cent Li 6. T h e nuclear reactions are Li~(n,t)He 4 a n d Mg26(t,p)Mg 2s. This p a p e r will describe theoretical considerations involved in a t t a i n i n g the present high specific activity a n d will present details of the present routine p r o d u c t i o n method. Iodine-132, 2-33-hour half-life, has been produced routinely at Brookhaven for the past four years. I t is supplied as fission p r o d u c t tellurium-132 c o n t a i n e d in a " g e n e r a t o r " from which the d a u g h t e r iodine can be " m i l k e d " conveniently, as desired. Recently a new m e t h o d of milking iodine from tellurium has been developed t h a t is simpler a n d faster, a n d which reduces the stable tellurium c o n t a m i n a t i o n to 0-1 m i c r o g r a m per millilitre of p r o d u c t solution. Radiotellurium c o n t a m i n a t i o n is less t h a n 5 × 10-3 per cent. Tellurium-132 is placed on a c h r o m a t o g r a p h i c a l m n i n a colunm a n d iodine-132 removed as desired by passing 0-01 .VI N H 3 t h r o u g h the column. Iodine132 yields are a r o u n d 65 per cent. Because of the high ratio of average beta-energy to avcrage g a m m a - e n e r g y of 21-hour iodine-133, its use in thyroid therapy is being explored by medical investigators. It is in routine use in conjunction with iodine-131 in double tagging experiments. A simple process has been developed which requires less t h a n one half-hour a n d by means of which the fission product iodines produced in irradiated UaO s are separated from u r a n i u m a n d the other fission products. Necessary conditions of irradiation time a n d cooling time to maximize the a m o u n t of iodine-133 over a practical period of use are discussed. T h e p r o d u c t contains a b o u t 85 per cent [la3 at time of use. T h e 112-minutefluorine-18 is the longest lived radioisotope of fluorine a n d is p r o d u c e d by the O TM(t,n)Fis reaction w h e n Li2CO 3 is irradiated in the nuclear reactor. A recently developed process for isolating the F 18 reduces p r o d u c t i o n time from two hours to one h o u r a n d increases the yield to two millicuries of F is per g r a m of L E C O 3 irradiated at a flux of 3 /. 1012 n sec 1 c m 2. T h e essential feature of the process, which results in very pure, high specific activity F TM, involves removal of radioactive c o n t a m i n a n t s by means of a cation exchange resin.
191--Withdrawn 192
Utilisation des verres comme dosimetres i n d u s t r i e l s . F. BALESTIO, M . BONNAUD, et P. LE CLERC, C o m m i s s a r i a t ~ l'Energie Atomique, France. O n utilise la propriete des verres de se colorer sous l'action des r a y o n n e m e n t s ionisants pour contr61er
International Conference on Radioisotopes in &ientific Research
aerated with a n effort of 2'4 horsepower hr per kg of O 2 added. Lakes as e x p e r i m e n t a l models for oceanographic a n d isotope studies will be discussed.
189 T h e P r o d u c t i o n of " T h r e s h o l d " N u c l e a r R e a c t i o n s in a G r a p h i t e R e a c t o r . C. E. MELLISH, J . A. PAYNE, a n d A.E.R.E., Harwell, U.K.
R.
L. OTLET,
I n P a r t 1 of this work the reaction Ni5S(n,p)Co as has been used to m o n i t o r the flux of fast fission neutrons in the Harwell reactor B.E.P.O. in a series of different positions in the reactor, m a k i n g assumptions a b o u t the energy spectrum of the flux. T h e ratio of fast to slow flux is plotted t h r o u g h the reactor, a n d this gives the preferred positions for p r o d u c i n g threshold reactions, (n,p), (n,ct), etc., a n d the preferred positions for eliminating t h e m as far as possible. T h e importance of this elimination in some radioactivation analyses is pointed out. T h e occurrence of "exot h e r m i c " (n,p) reactions such as N14(n,p)C 1~ a n d Claa(n,p)S a5 is discussed. I n Part 2 cross-sections are presented for a n u m b e r of (n,p) reactions on elements r a n g i n g from t i t a n i u m to thallium in the Periodic Table, a n d for some (n,~) reactions on elements from t i t a n i u m to caesium. W h e r e the p r o d u c t isotope can also be formed by n e u t r o n capture in i m p u r i t y a m e t h o d is devised to correct for a n y i m p u r i t y present. T h e cross-sections m e a s u r e d are c o m p a r e d with those predicted by theory.
190 D e v e l o p m e n t of M e t h o d s for t h e P r o d u c t i o n of C e r t a i n S h o r t - l i v e d R a d i o i s o t o p e s . L. G . STANG, JR., W . D . TUCKER, R . F. DOERING, A. J . WEiss, M . W . GREENE a n d H . O . BANKS, JR., B r o o k h a v e n N a t i o n a l Laboratory, U.S.A. At the Brookhaven H o t L a b o r a t o r y methods are being developed for p r o d u c i n g radioisotopes which would be useful if they were available, or available in suitable form. Examples for which procedures have been completed include M g 2s, 1la2, 113'3 a n d F is. At B r o o k h a v e n these are reactor produced. This p a p e r will describe u n p u b l i s h e d recent results of this work. ~VIagnesium-28, 21-hour half-life, is a very i m p o r t a n t radioisotope for medical research a n d is the only isotope of m a g n e s i u m with a half-life long enough to be practical for use as a tracer. I t is produced in specific activities of a b o u t one millicurie per g r a m using a n e u t r o n flux of a b o u t 3 x l0 Is n sec -1 c m 2. T h e Brookhaven process involves irradiating 0-01 in. thick foils of a n alloy of natural M g with lithium which
has been enriched to 95 per cent Li 6. T h e nuclear reactions are Li~(n,t)He 4 a n d Mg26(t,p)Mg 2s. This p a p e r will describe theoretical considerations involved in a t t a i n i n g the present high specific activity a n d will present details of the present routine p r o d u c t i o n method. Iodine-132, 2-33-hour half-life, has been produced routinely at Brookhaven for the past four years. I t is supplied as fission p r o d u c t tellurium-132 c o n t a i n e d in a " g e n e r a t o r " from which the d a u g h t e r iodine can be " m i l k e d " conveniently, as desired. Recently a new m e t h o d of milking iodine from tellurium has been developed t h a t is simpler a n d faster, a n d which reduces the stable tellurium c o n t a m i n a t i o n to 0-1 m i c r o g r a m per millilitre of p r o d u c t solution. Radiotellurium c o n t a m i n a t i o n is less t h a n 5 × 10-3 per cent. Tellurium-132 is placed on a c h r o m a t o g r a p h i c a l m n i n a colunm a n d iodine-132 removed as desired by passing 0-01 .VI N H 3 t h r o u g h the column. Iodine132 yields are a r o u n d 65 per cent. Because of the high ratio of average beta-energy to avcrage g a m m a - e n e r g y of 21-hour iodine-133, its use in thyroid therapy is being explored by medical investigators. It is in routine use in conjunction with iodine-131 in double tagging experiments. A simple process has been developed which requires less t h a n one half-hour a n d by means of which the fission product iodines produced in irradiated UaO s are separated from u r a n i u m a n d the other fission products. Necessary conditions of irradiation time a n d cooling time to maximize the a m o u n t of iodine-133 over a practical period of use are discussed. T h e p r o d u c t contains a b o u t 85 per cent [la3 at time of use. T h e 112-minutefluorine-18 is the longest lived radioisotope of fluorine a n d is p r o d u c e d by the O TM(t,n)Fis reaction w h e n Li2CO 3 is irradiated in the nuclear reactor. A recently developed process for isolating the F 18 reduces p r o d u c t i o n time from two hours to one h o u r a n d increases the yield to two millicuries of F is per g r a m of L E C O 3 irradiated at a flux of 3 /. 1012 n sec 1 c m 2. T h e essential feature of the process, which results in very pure, high specific activity F TM, involves removal of radioactive c o n t a m i n a n t s by means of a cation exchange resin.
191--Withdrawn 192
Utilisation des verres comme dosimetres i n d u s t r i e l s . F. BALESTIO, M . BONNAUD, et P. LE CLERC, C o m m i s s a r i a t ~ l'Energie Atomique, France. O n utilise la propriete des verres de se colorer sous l'action des r a y o n n e m e n t s ionisants pour contr61er