Gamma Prompt Nitrogen

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Journal of Radioa nalytical and Nuclear Chemistry, Articles, V ol. 169, No. 2 (1993) 333 -33 8

D E T E R M I N A T I O N O F N I T R O G E N I N P O R K M E A T U S I N G I N - V IV OP R O M P T G A M M A - R A Y A C T IV A T IO N T E C H N I Q U E

C H I E N C H U N G , Y A - Y U C H E NInstitute of Nuclear Science, National Tsing Hu a University,

Hsb~chu 300 (Taiwan, R.O.C.)(Rece iv ed N o v em b er 1 6 , 19 9 2)

T h e c o n c e n t r a t i o n o f n i t ro g e n i n p o r k m e a t i s d e te r m i n e d b y i n - v i v o p r o m p t g a m m a - r a y a c t i v a ti o na n a l y s i s u s i n g t h e r ea c t o r n e u t r o n b e a m a n d a h i g h p u ri ty g e r m a n i u m g a m m a - r a y s p e c t ro m e t e r . T h ep h o to p e ak a r ea o f t h e 1 0 8 2 7 k e V h ig h en erg y p ro m p t g am ma - ray , o r i g in a t ed f ro m l* N(n , "r r eac t i o n o nth e p o rk med iu m, i s an a ly zed t o d e t e rmin e t h e co n cen t r a t i o n o f n i t ro g en . Urea so lu t i o n s wi th v a r i o u sc o n c e n t r a t i o n o f n i t r o g e n a r e u s e d t o c a l i br a te t h e a b s o l u te e f f ic i e n c y o f t h e g a m m a - r a y s p e c t r o m e t e r .In 9 0 0 0 s i r r ad i a t i o n an d co u n t i n g p e r i o d, t h e m in im u m d e t ec tab l e co n cen t r a t i o n i s 1 .7 g o f N /1 0 0 g o fmea t u s in g t h e i n -v iv o t ech n iq u e . Th e r esu l t i s a l so co mp ared t o d a t a o b t a in ed b y an o th er an a ly t i ca lme th o d . Th i s n o n d es t ru c t i v e , i n -v iv o tech n iq u e , w i th n o min a l r ad ia t i o n d o se , is a r e l iab l e an d p ro m is in gme th o d t o d e t e rm in e t h e n i t ro g en co n cen t r a t i o n i n li v in g b o d y .

Introduction

A t o t a l b o d y m e a s u r e m e n t o f n i t r o g e n a n d p r o t e i n p r o v i d e s aq u a n t i t a t i v e e s t i m a t e o f t h e n u t r i t i o n a l s t a t u s o f a l i v i n g b o d y .R e c e n t d e v e l o p m e n t s u s i n g i n - v i v o p r o m p t g a m m a - r a y a c t i v a t i o na n a ly s i s( I VP C 4 K~ ) t o s c a n b o d y n i t r o g e n i s o f c o n s i d e r a b l e v a l u e f o rm e d i c a l d i a g n o s i s ; h i g h e n e r g y, h i g h i n t e n s i t y p r o m p t g a m m a - r a y se m i t t e d f r o m t h e 1 4 N( n , 7 ) r e a c t i o n b y i r r a d i a t i n g a l i v i n g b o d yw i t h a n e u t r o n b e a m c a n b e d e t e c t e d q u a n t i t a t i v e l y u s i n g a s c i n t i l -l a t i o n c o u n t e r * I a s w e l l a s a h i g h r e s o l u t i o n s e m i c o n d u c t i n gd e t e c t o r . * 3

I n o u r l a b o r a t o r y , a n I V P G A A s y s t e m u s i n g a t h e r m a l n e u t r o nb e a m f r o m t h e l o w f l u x T s i n g H u a M o b i l e E d u c a t i o n a l R e a c t o r ( T H M E R ) ,h a s b e e n d e v e l o p e d . , 4- , 9 T h e e f f e c t i v e d o s e e q u i v a l e n t f o r e a c hI V P G A A s c a n h a s b e e n m e a s u r e d a n d a s s e s s e d u s i n g a h u m a n p h a n t o m ; " ~l i v i n g r a t s h a v e b e e n d i a g n o s e d i n - v i v o t o d e t e r m i n e t h e c a d m i u mu p t a k e a n d r e l a t i o n s t o i n - v i t r o b i o c h e m i c a l t e s t s , z ,- z I n t h i sw o r k, t h e c o n c e n t r a t i o n o f n i t r o g e n i n p o r k m e a t is m e a s u r e d i n - v i v ou s i n g a c o m p l e t e l y s h i e l d e d h i g h p u r i t y g e r m a n i u m ( H P G e ) d e t e c t i n gs y s t e m . F e a t u r e s o f e a c h i n - v i v o d e t e r m i n a t i o n a r e c o m p a r e d t oa n o t h e r a n a l y t i c a l m e t h o d a n d i t s c h a r a c t e r i s t i c s a r e d i s c u s s e d f o rp o s s i b l e c l i n i c a l a p p l i c a t i o n o n h u m a n b e in g s .

Elsevier Sequoia S. A., LausanneAkad~miai Kiadr, Budapest


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CHIEN CHUNG, YA-YU CHEN: DETERMINATION OF NITROGEN

M a t e r i a l a n d m e t h o d

T h e i r r a d i a t i o n f a c i l i t y a n d c o u n t i n g e q u i p m e n t u s e d in thiswork are identical to those reported elsewhere I and therefore onlydescribed briefly here. About 3.6 kg of pork medium, acquired froma local market in frozen condition, was placed on top of the externalthermal beam port of the modified THMER facility. A portable HPGedetector with 10% relative efficiency was positioned immediatelynext to the meat, while t he attached 7 L liquid nitrogen(LNz) dewarwas surrounded by layers of GLi~COa neutron shield and lead gammashield. The 10827 key prompt gamma-ray photopeak with associate descape peaks, emitted fro m the '4N(n, 7 ) reaction, were an alyzedin the high-resolut ion spectrum collected in a period of 9000 s.

The absolute concent ration of nitrogen in the pork medium wasconverted from the prompt photopeak count rate using a nitrogen-containin g phantom, similar to our previous work. z3 A solution ofknown nitrogen concentration, such as LN, or urea, was used to fillup the phantom and the count rate of the nitrogen photopeak wasrecorded during irradiation.

The nitrogen concentratio n in pork was also analyzed using theKjeldhal method. About 1 g of perk was digested in boiling HzSO~,followed by the NaOH treatment to distill the NH3 gas, collectedin HCI solution and finally titrated quantitatively. In order toensure the homogeneity, four meat samples taken from differentportions of pork were digested and each of them was analyzed inde-pendently. The average result was compared to that determined bythe non-de structive IVPGAA technique.

R e s u l t s

High-resolu tion prompt gamma-ray spectra using IVPGAA techniquewere taken in the CANBERRA 10-plus portable multichannel analyzer(MCA)system. A typical prompt gamma-ray spectrum of LN z in the phantomis shown in Fig. l(a). The prompt gamma-ray peaks of nitrogen,together with those from shielding materials of the THMER facility(Pb and H), are clearly observed. The high-energy portion of theprompt spect rum of urea solution in the phantom, with a nitrogenconcentration of 40 g of N/100 g, is illustrated in Fig. l(b). Thephotopeak(10827 keV), together with its single escape peak(10316keV) and double escape peak(9805 keV), can be quanti tativelyidentified.

334


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CHIEN CHUNG, YA-YU CHEN: DETERMINAqqON OF NITROGEN

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P r o m p t g a m m a - r a y e n e r g yP r o m p t g a m m a - r a y s p e c t r a f o r s a m p l e s o f ( a) l i q u i d n i t r o g e nand (b) urea solu tion in a phantom as well as (c) in porkm e d i u m ; e a c h s a m p l e i s i r r a d i a t e d b y a n e x t e r n a l t h e r m a ln e u t r o n b e a m f r o m t h e T H M E R f a c i l i t y a n d m e a s u r e d b y ap o r t a b l e H P G e / M C A - 1 0 d e t e c t i n g s y s t e m f o r 9 0 0 0 s .

T h e p h a n t o m c a l i b r a t i o n u s i n g k n o w n c o n c e n t r a t i o n s o f n i t r o g e nw a s c o n d u c t e d i n t h e I V P G A A ex p e r i m e n t . T h e c o u n t r a t e o f p r o m p tp h o t o p e a k s , a s t h o s e s h o w n i n F i g. l ( b) , w a s e v a l u a t e d u s i n g ab u i l t - i n c o m p u t e r c o d e i n M C A, a n d i t s c o r r e l a t i o n t o n i t r o g e n c o n -c e n t r a t i o n i s p l o t t e d i n F i g. 2 . T h e n e t c o u n t r a t e o f t h e 1 0 8 2 7k e V a n d i t s a s s o c i a t e d e s c a p e p e a k s i s c o r r e l a t e d t o t h e n i t r o g e nc o n c e n t r a t io n i n t h e p h a n t o m w i t h in t h e r a n ge o f 2 ~ i 0 0 g o f N / 1 0 0 g.T h e b a c k g r o u n d c o u n t r a t e o f t h e p h o t o p e a k a r e a o f i n t e r e s t w a sarou nd 0.15 cpm.

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CHIEN CHUNG, YA-YU CHEN: DETERMINATION OF NITROGEN

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P o r k S a m p l e~- . . . . . B l a n k P h a n t o m

1 5 10 50 100Nitrogen Concentrat ion, g of N /10 0 g

T h e c o r r e l a t i o n o f n i t r o g e n p r o m p t p h o t o p e a k n e t c o u n t r a t et o t h e n i t r o g e n c o n c e n t r a t i o n i n a p h a n t o m f o r t h e a b s o l u t ec a l i b r a t i o n o f I V P G A A e x p e ri m e n t .

T h e h i g h - e n e r g y p o r t i o n o f t h e p r o m p t s p e c t r u m f o r p o r k m e d i u mi r r a d i a t e d f o r 9 0 0 0 s w i t h t h e r m a l n e u t r o n s i s i l l u s t r a t e d i nF i g. l ( c) . T h e i n t e g r a t i o n o f t h e 1 0 8 27 k e y p h o t o p e a k a n d i t sa s s o c i a t e d e s c a p e p e a k a r e a s a r e e n h a n c e d . T h r e e I V P G A A s c a ns i nd i f f e r e n t p o r t i o n s o f t h e p o r k m e d i u m a r e c o n d u c t e d a n d t h e i r n e tc o u n t r a t e s o f * d N( n , 7 ) p r o m p t p h o t o p e a k s a r e r e g i s t e r e d i n F i g. 2 .T h e w e i g h t e d a v e r a g e c o n c e n t r a t i o n o f n i t r o g e n, c o n v e r t e d f r o m t h ec a l i b r a t i o n l i n e i l l u s t r a t e d i n F ig . 2 , i s e v a l u a t e d a s 1 . 9 + 0 . 3 go f N / 1 0 0 g .

T h e n i t r o g e n c o n c e n t r a t i o n a n a l y z e d b y t h e c o n v e n t i o n a l K j e l d h a lm e t h o d i s m e a s u r e d a s 2 . 7 + 0. 3 g o f N / 1 0 0 g , 4 0 % h i g h e r t h a n t h a tu s i n g t h e I V P G A A t ec h n i q u e . H o w e v e r , t h e w e i g h t e d a v e r a g e o f n i t r o g e nc o n c e n t r a t i o n i n p o r k m e di u m , i n v e s t i g a t e d b y t h e T a i w a n e s e C o u n c i lof Agricult ure, is 2.3 + 0.I g of N/100 g. Z4 Cons ider ing theu n c e r t a i n t y a s s o c i a t e d w i t h o u r m e a s u r e m e n ts , r e s u l t s o f n i t r o g e nc o n c e n t r a t i o n d e t e r m i n e d b y e a c h m e t h o d a r e s t i l l o u t s i d e t h eu n c e r t a i n t y o f a d o p t e d v a l ue .

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CHIEN CHUNG, YA -YU CHEN: DETERMINATION OF NITROGEN

Di scu s s i on

The nitrogen c oncentratio n in pork samples, deter mined by IVPCq%Atechnique, is less than the result analyzed by the conventiona lchemical method, and about 17% lower than the weighted average valueadopted by local authority. The underestim ate is due primarily to thedifferent attenuati on and subsequent absorption ability of the thermalneutron beam in the phantom and in pork meat. In our previous waterphantom study, the thermal neutron flux at a depth of 6 cm drops to75% of its maximum value at the skin sur face and drops further to50% at i0 cm depth. * As pork samples contain elements other thanhydrogen and oxygen, the slowing down power and moderating ratio forneutrons are less than that of water phantom; the phantom calibr ationunderestimates the nitrogen concentration by around 25% on the average.

The background count rate of the photopeak area of interest(Rb) is due partly to the interacti on of penetrating neutrons wi ththe shielded LNz in the HPGe detecting system. The minimum detec-table concentration(MDC) of nitrogen in pork samples, est imated fromMDC = 3.29(Rb/ te)*/'/S with S the sensitivity of nitrogen countingrate in cpm/g, '3 is 1.7 g of N/100 g for at e = 9000 s scan with aneffective dos e equivalent of 0.34 mSv. ,0 The MDC is still below thenitrogen concentra tion of 2.59 g of N/100 g in the Referenc e Man. '6Thus, in a 2.5-ho ur IVPGAA scan, the MDC of nitrogen in a patientcan be measu red as low as 65% of its normal content.

In conclusion, the feasibility of I V PC ~ measurea~.=nt of n itroge nc o n c e n t r a t i o n h a s b e e n d e m o n s t r a t e d b y p a r t i a l b o d y s c a n o n p o r ksamples. The quantitative determination of nitrogen has been cali-brated by means of a phantom and the results are compared to thosemeasured by the conven tional method as well as to an adopted value.The non-destructive, rapid, in-vivo technique, with nominal radiationdose, is a reliable and proraising method to determine the nitr ogenconcent ration in living body. Future application on human beingsmay use a modified epithermal neutro n beam and a detecting systemof higher efficiency.

%

This work was spo nsored by the Atomic Energy Council of t heRepublic of china under contract number AEC79-025-K2. The authorswish to thank the oper ating crew of THMER facility who support thiswork without reservation. The authors also wish to express theirgratitude to Prof. W. K. Chen of Chung-Shan Medical and Denta lCollege, Taichung, for his valuable discussion an d comment on IVPGAA.

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C H I E N C H U N G , Y A - Y U C H E N : D E T E R M I N A T I O N O F N I T R O G E N

Re f e r e n c e s

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2 . J. M. M ER NA GH , J . E . HA RRIS ON , K. G, McN EILL, P hys . Med . B io l. , 22 (1977) 831 .3 . K . J . ELLIS , D. VAR TS K Y, S . H . CO HN , P roc . on Nuc lea r Ac t iva t ion Techn iques in the L i fe S c ience , IAE A

S M -227 , Vienn a , 1979 , p . 733 .4 . D . VA RT S K Y, K. J . ELLIS , S . H . COH N, J . Nuc l. M ed . , 20 (1979) 11 .5 . D . V A R T S K Y , W . V . P R E S T W I C K , B . J . T H O M A S , J . T . D A B E K , D . R . C H E ' I T L E , J . H . F R E M L I N ,

K. S TA M M ER S , J . Rad ioana l. Chem . , 48 (1979) 243 .6 . J . S . C O H N , A . N . V A S W A N I , D . V A R T S K Y , S . Y A S U M U R A , A . S A W 1 T SK Y , W . G A R T E N H A U S ,

K. J . EL LIS , Am . J . Clin. Nutr . , 35 (1982) 1186.7 . S . H . C O H N , B . L . B R E N N A N , S . Y A S U M U R A , D . V A R T S K Y , A . V . V A S S W A N I , K . J . E L L I S , A m . J .

Clin. Nutr . , 38 (1983) 52.8 . A . H. BE DD OE , H. Z UID ME ER, G. L . HILL , P hys . Med . B io l. , 29 (1984) 371 .9 . B . J . A L L E N , N . B L A G O J E V I E , K . G A S K I N , V . S o u T r E R , R . H O W M A N - G I L E S , Pr o e . C o n f . o n C a p t ur eP rom pt Gam m a-ray S pec t ro scopy and Re la ted Topics , AIP 125 , NY, 1984, p . 820 .1 0. L . L A R S S O N , M . A L P S T E N , S . M A T r S S O N , P r o c . 7 th I n te rn . C o n f . M T A A R N L , R o s k i ld e , 1 9 86 ,

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S ym pos iu m S er ie s 445 , W ash ing ton D. C . , 1990 , p . 215 .23 . L . A . C UR RIE , X -Ray F luorescence Ana lys i s o f Envi ronm enta l S an ' p ie s , Chap te r 15 , T . G . DZU BA Y (Ed . ) ,

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Gamma Prompt Nitrogen

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