Elementary analysis of fluorine by neutron activation

International Journal of Applied Radiation and Isotopes, 1963, Vol. 14, pp. 105-111. Pergamon Press Ltd. Printed in Northern Ireland

Elementary Analysis of Fluorine by Neutron Activation B. V A N Z A N T E N * , D. DECAT and G. LELIAERT~" S t u d i e c e n t r u m voor Kernenergie, Mol, Belgium

(Received 6 June 1962) Activation analysis provides a h a n d y tool for elementary fluorine d e t e r m i n a t i o n , with a relative error of 1-2 p e r cent. As fluorine standards, a m m o n i u m fluoride a n d p°fluorobenzoic acid can be used. T h e values o b t a i n e d for the fluorine contents show a good reproducibility w i t h p l a t i n u m as flux monitor. As a result of the analysing t e c h n i q u e used, most interferences are negligible or can be eliminated a n d the r a d i a t i o n d a m a g e can be restricted to a m i n i m u m so t h a t in most cases the c o m p o u n d is not lost for f u r t h e r use. T h e m e t h o d is applied to determine the changes in fluorine content of teflon by pile irradiation. L'ANALYSE ELEMENTAIRE DU FLUOR AU MOYEN DE L'ACTIVATION AUX NEUTRONS L'analyse p a r activation est une m~thode assez simple p o u r l'analyse 616mentaire d u fluor. L ' e r r e u r r61ative est de 1 ~ 2 p o u r cent. C o m m e ~talon de fluor on peut utiliser le fluorure d ' a m m o n i u m et l'acidep-fluorbenzoique. Les rfisultats, obtenus avec le platine c o m m e contr61e des variations d u flux, d o n n e n t des valeurs en pour cent de fluor bien r6productibles. C o m m e r~sultat de la technique utilisfie presque toutes les interf6rences sont nfigligeables ou peuvent fitre ~limin~es et la d6composition p a r radiation-7 est minime. Ainsi dans la majorit~ des cas le compos~ dos~ n'est pas p e r d u p o u r u n e rfit~tilisation 6ventuelle. L a m~thode est employ6e p o u r une d~termination d u c h a n g e m e n t des teneurs en fluor d u teflon apr~s irradiation a u r6acteur. D J I E M E H T A P H B I f l A H A J I H 3 (I)TOPA H Y T E M H E I ~ T P O H H O ~ AHTI4BAIII/IH Ana~rl3 nyT~M a H T ~ n a t I ~ yxOfiHb1~l ~ ~JieMetITapHoro onpe~eJIeHrI~ ~Topa n p n OTHOCI4TeJIBHOI~ omn6ge 1 - 2 % . B g a q e c T n e C V a H ~ a p T o n npnMeHfltOTCH ~TOpMCTBI~ aHHOHM~I H n-~TOpO~eH3Oi~lHaH RMC:IOTa.

Be:IHqt~nbI, no~yqenHbie ~ co~ephgaHrIA dpTopa, xopomo BOCnpOrmBO~r~M~I npx~ na~Inqnn H~aTI4H~ B ~aqecTBe n:mBHn. 1-[pr~ T e x H ~ e aHa~tfsa, np~MenneMoll 3~ecb, nHTepdpepeH~n~ n 60JIBIIII4HCTBe c ~ y q a e B He3HaqPlTeJIbHa, ItJII4 MO~eT 6BITB y c T p a H e H a . Pa~na~nonHb~f yIuep6 MOh~eT ~BITB o r p a H n q e H H b I i i KO MgHMMyM T a ~ , qTO B e ~ e c T B O He IIoTepflHO ~5I}:I ~aYIbHeitmero

HO2IB3OBaHtIfl.

MeTO~I npI4MeHfleTC~I ~JI}:I o n p e ~ e ~ e a r ~

rISMeHeHI41~

co~eph~aH~

dpTopa n vedp~oHe Bc~e~ICTB~e I~8~yqeH~g pea~Topa. ELEMENTANALYSE

VON FLUOR MITTELS AKTIVIERUNG DURCH NEUTRONEN Die Aktivierungsanalyse ist ein einfaches Werkzeug zur A u s f i i h r u n g einer Elementanalyse des Fluors, wobei d e r relative Fchler I b i s 2 Prozent bctr/igt. Als F l u o r s t a n d a r d k a n n A m m o n i u m fluorid u n d ~-Fluorobcnzocs~iurc beniitzt werden. Die Resultate, e r h a l t e n mit Platin als Fluxmonitor, zeigen eine gute R e p r o d u z i c r b a r k e i t . Als Folge d e r b e n u t z t e n Analysentcchnik sind die meisten Interferenzen zu vemachl/issigen oder zu eliminieren u n d die Strahlungssch~idigung k a n n a u f ein M i n i m u m beschr~inkt werden, sodass in d e n meisten F/illen das Pr~iparat n i c h t verloren ist fiir weitere Zwecke. Die M e t h o d e w u r d e v c r w e n d e t zur Bestimm u n g von .~hnderungen des Fluorgehaltes yon Teflon bei Bestrahlung i m Reaktor. * O n leave from the Vrije Universiteit, A m s t e r d a m , Netherlands. T h e untimely d e a t h of Mr. Leliaert occurred d u r i n g the course of this study. 105

106

B. Van Zanten, D. Decat and G. Leliaert

INTRODUCTION ALTHOUGH several c h e m i c a l m e t h o d s o f fluorine d e t e r m i n a t i o n in o r g a n i c c o m p o u n d s a r e described in .literature, the analysis is n o t yet very simple as c a n be illustrated b y the g r e a t n u m b e r o f publications in this field. (1-51 I n almost all o f these p r o c e d u r e s destruction o f the c o m p o u n d is necessary, b u t it is sometimes very difficult, e.g. in the case of the f l u o r o c a r b o n polymers.(6, 7) M o r e o v e r , the k n o w n m e t h o d s are time cons u m i n g a n d use u p a r a t h e r g r e a t q u a n t i t y of material.

reaction F19(n,7)F 2°, w h i c h gives results with a relative error of 1-2 per cent.

ACTIVATION

AND

MEASUREMENT

Calculation shows that the reaction F19(n,7)F 2° yields a b o u t 1.4 × l0 s d.p.s. i m m e d i a t e l y after a n i r r a d i a t i o n for 10 sec of 1 m g o f fluorine in a slow n e u t r o n flux of l012 n.cm-~.sec -1. T h e n u c l i d e F 2° decays w i t h a half-life of 10.7 sec, giving a 7 - r a y o f 1.63 M e V (n). T h e i r r a d i a t i o n s are c a r r i e d o u t in the BR-1 reactor at Mol, b y means o f a fast

TABLE 1. Radioactivation methods used for the determination of fluorine Reaction F19(n,7)F2° (10-7 sec) F 19(n,y) F 2° (10.7 see) Fla(n,~) N xa (7.4 sec)

Irradiation ~p = n.cm-2.sec -1 Pile ~o = 3.1011 Accelerator ¢p = ca. 109 Accelerator q~ = not given

I n view of these facts, it is interesting to d e t e r m i n e the fluorine content b y means o f n e u t r o n a c t i v a t i o n analysis, a v o i d i n g s a m p l e destruction a n d c h e m i c a l separation. T y p i c a l n e u t r o n - i n d u c e d reactions used a r e s u m m a r i z e d in T a b l e 1. I n all cases a fast c o n v e y o r system has been used. I n the experiments o f LEVEQUE (s), large statistical errors w e r e i n t r o d u c e d because counting was started only 30 sec after the i r r a d i a t i o n a n d as most of the m e a s u r e m e n t s were d o n e with a G . M . c o u n t e r w i t h a n a b s o r b e r o f 1 0 0 0 m g . c m -2. M o r e o v e r , s t a n d a r d a n d s a m p l e were c o u n t e d simultaneously b y two different counting units. T h e l o w - n e u t r o n flux in the experiments o f ATCHISON a n d BEAMER(9) was the reason for their i n a c c u r a t e results. ANDERS(1°) h a d even to use m u l t i a c t i v a t i o n a n d c u m u l a t i v e counting in o r d e r to get r e a s o n a b l e c o u n t i n g statistics. I n n o n e o f these p r o c e d u r e s a r e s t a n d a r d a n d s a m p l e i r r a d i a t e d t o g e t h e r a n d m e a s u r e d alternatively b y the same c o u n t i n g system. T h i s m e a n s t h a t possible flux a n d detection variations d u r i n g the experiments could n o t be corrected for. W e have established a m e t h o d based on the

Detector G.M., NaI

Fluorine standard

Author

NH4F

LEVE•UE (s)

G.M.

KF

ATCmSONc9)

NaI

LiF

ANDERS (10)

p n c u m a t i c a l conveyor system designed b y CAMPBELL a n d FETTWEIS (12). T h e sample, p a c k e d in a nylon container, is shot in a n d out of the core o f the r e a c t o r u n d e r c a r b o n dioxide pressure. A b o u t 0-1 sec after the e n d of the i r r a d i a t i o n the s a m p l e is p l a c e d a u t o m a t i c a l l y before the d e t e c t o r a n d at the same m o m e n t counting is started. T h e d e c a y is followed b y c o u n t i n g on ten s e a l e r s - connected in c a s c a d e - - f o r a 10-see p e r i o d on each of them. C o u n t i n g is p e r f o r m e d w i t h a fiat 2 × 2 in. N a I ( T l ) scintillator, c o n n e c t e d to a linear amplifier with a pulse h e i g h t selector biased at a b o u t 1.4 M e V . After the d e c a y of F 2°, the b a c k g r o u n d can be m e a s u r e d w i t h the s a m p l e still in the same position before the detector. All t i m i n g d a t a like i r r a d i a t i o n time, counting time, etc. a r e d e r i v e d from a t e m p e r a t u r e controlled q u a r t z oscillator a n d are r e p r o d u c i b l e w i t h i n 1 msec. Since in all the experiments the half-life was found to be 10.8 ± 0.2 sec, c o r r e s p o n d i n g to t h a t of F 2°, the y - a c t i v i t y m e a s u r e d d u r i n g the first 40 or 50 sec after the end of the i r r a d i a t i o n was t a k e n as a r e p r e s e n t a t i v e value for the fluorine content.

Elementary analysis offluorine by neutron activation INTERFERENCES Elements, which on irradiation give nuclides with half-lives in the order of 1-200 see and emit ~,-rays of energies greater than 1.4 MeV, can interfere. Calculation of the yield of the reactions 01S(n,y)O lg, N15(n,y)N 1~ and O16(n,p)N 16, shows that no interference is to be expected under the irradiation conditions mentioned above. I f however, the irradiations are performed in an environment with fast neutrons (energy about 14 MeV), the reactions S~(n,p)P ~ and PSl(n,~)AlZS can interfere, but experiments with sulphur and a m m o n i u m biphosphate indicated that the influence on the fluorine determination is quite negligible in the case of irradiation in the BR-1. Sodium can interfere in the reaction Na~Z(n,a)F~0 and chlorine in ClZ~(n,~)P~ and ClS7(n,T)CI 3s, but the influence of the (n,~) reaction on chlorine is negligible and the ClSS-activity can be eliminated by a graphical analysis of the mixed decay curve o f F 2° and CI3s (tl/2 : 37"3 min) Is). From these considerations it follows that by short irradiations of samples containing only the elements C, H, O, N, S, P, C1 and F, no long-living activities are induced, so that if radiation damage can be avoided, the samples are not lost by the analysis.

EXPERIMENTAL (i) Variations in the detection during the experiments Counting rate measurements are very sensitive to changes in geometry. Since in the present case the sample is shot before the detector under gas pressure without visual control of the place of the sample after the return from the reactor core, the reproducibility of the place was checked in the following way. In a nylon container of the type used, 0.5 ml of a carrier-free solution of Fe59(t1/2 = 45 days, activity about 0.5/tc) was evaporated to dryness. This sample was irradiated several times during 1 sec and, after each irradiation, shot before the detector. T h e activity was counted in cascade for 10 × 300see and corrected for background. No decay could be found and in all experiments the counting error was within the statistical error (0-5 per

107

cent). It appeared necessary to maintain an identical geometric form of the samples in the containers. Experiments with teflon of different shape (slices, rings and powder), but of identical weight and origin, showed differences of 15 per cent in the specific fluorine activity. Therefore, powdered material was used in the experiments and if necessary, the containers were filled up with powdered cane sugar in order to get the same geometric conditions. In preliminary experiments no interference of cane sugar could be detected on the measurements. (ii) Variations in the flux during the experiments As sample and standard could not be Irradiated together, a method for monitoring the integrated flux had to be found. First of all vanadium was tried as a flux monitor. Vanadium activates fail ly well and the isotope formed has a half-life of 3.7 rain m). After irradiation, a mixed decay curve can be measured without changing the bias setting of the pulseheight selector. This is possible as the ~-ray energies of V 52 and F 2° are 1.44 and 1.63 MeV, respectively. T h e extrapolated value of the VS'-activity can serve as the monitor activity. Because F 2° and V ~2 are measured together, one should be able to correct for possible detection variations during the counting period. However, the experiments showed that by introducing V~Z-activities the statistical errors on the FZ°-measurements increase from 3 to 6 per cent. Only using a flux of about 10x4 n.cm -2. see -~ (BR-2 reactor), is expected to give more accurate results. Gold proved to be very unsatisfactory as monitor. Self shadowing effects were found in gold platelets of a total weight even as low as 6-8 mg. Platinum wire, on the contrary, serves very well. After a short irradiation.time (10see) practically only Pt 199 is formed. This nuclide decays rapidly (ill 2 30 min) to Au agg (tl/~ = 3-15 days), so that about 24 hr after the irradiation only Au 1~9 is measured. The monitor activities are registered on a separate counting unit, the detector being a 1.5 × 1.5 in. NaI(T1) well-type scintillator. During the F2°-measurements, no interference of the monitor activities can be detected because =

108

B. Van Zanten, D. Decat and G. Leliaert TABLE 2. Fluorine determination with p-fluorobenzoic acid as a standard Compound O~o F (calc.) % F (found) Number of expt. Deviation of the mean (°o) Deviation from calc. value (%)

NH4F*

BaFzt

PbF2:~

KHF2**

51-29 51.16 6 1.1

21.67 21.09 5 0.6

15.50 15.64 5 2.4

48-65 47-81 3 1.0

-0.2

-2.7

+0-9

-1.8

* Merck, pro analysi. I" Hopkins & Williams, technical grade. :~ Prepared from UCB chemicals, pro analys~. ** UCB, technical grade. TABLE 3. Composition of organic compounds used for fluorine determinations C (%)

H (%)

N (%)

V

(%)

Compound 821 822 823

Calc.

Found

Calc.

Found

Calc.

Found

Calc.

56.26 61.92 63-54

56.61 61-94 63-96

3.15 5.63 5-75

3.16 5.63 6.06

-3.01 2.85

-3.14 2.90

35.60 12.25 11.60

the pulse-height selector is biased on 1.4 M e V a n d n e i t h e r Pt 197, Pt 199 n o r A u 199 have )~energies g r e a t e r t h a n 1 M e V Ill). E x p e r i m e n t s in w h i c h the i n t e g r a t e d flux v a r i e d by a factor o f 5 showed t h a t for the specific activity of F 2° an a c c u r a c y can b e r e a c h e d of a b o u t 1 p e r cent. I n the s u b s e q u e n t experiments the statistical e r r o r on the measurem e n t s Was always better t h a n I p e r cent.

D E T E R M I N A T I O N OF T H E FLUORINE CONTENT OF SOME INORGANIC COMPOUNDS Samples of 2 0 - 1 0 0 r a g o f carefully d r i e d m a t e r i a l were taken a n d 15-20 m g o f p l a t i n u m wire was a d d e d as flux monitor. T h e y were i r r a d i a t e d for l0 s e e - - s a t u r a t i o n is 0"5 for F 2°-at a slow n e u t r o n flux o f a b o u t 10 TM n.cm-2.sec -1. E a c h o f the ten sealers was used for counting d u r i n g a preset time of 10 sec. Para-fluorobenzoic acid ( H o p k i n s & Williams, M A S 4299.2) was chosen as s t a n d a r d , its fluorine content being certified to be 13.56 p e r cent. T h e flux correction i n t r o d u c e d b y the p l a t i n u m m o n i t o r was o f the o r d e r of 5 - 6 per cent in some determinations. F r o m T a b l e 2 we can see t h a t there is a good

r e p r o d u c i b i l i t y (0-6-2"4 per cent) a n d t h a t in the case ofthepro analysi c o m p o u n d s an excellent a g r e e m e n t exists b e t w e e n t he theoretical a n d the observed value.

D E T E R M I N A T I O N OF T H E FLUORINE CONTENT OF SOME ORGANIC COMPOUNDS A m o n g others, three p.a. organic fluorine c o m p o u n d s * were examined, b u t because ot their p o t e n t i a l industrial usefulness they are symbcCAzed by code n u m b e r s in T a b l e s 3 a n d 4. T h e other e x a m i n e d c o m p o u n d s were: ofluorobenzoic acid I" (824), t r i m e t h y l t i n trifluoroacetate++ (825), triethyltin trifluoroacetate+* (826). Measurements, i r r a d i a t i o n conditions a n d fluorine s t a n d a r d were the same as in the foregoing experiment. * Kindly provided by N. V. Koninklijke Pharmaceutische Fabrieken v/h Brocades & Stheeman, Amsterdam, Netherlands. I" Chem. Fabr. Buchs S.G., purity stated as "purum". ++Kindly provided by TNO, Organic Chemistry Department, Utrecht, Netherlands. Purity is not given.

Elementary analysis of fluorine by neutron activation

109

TABLE 4. Fluorine determination with p-fluorobenzoic acid as a standard Compound

821

822

823

824

825

826

c}~ F (calc.) o~ F (found) Number of expt. Deviation of the mean (%) Deviation from the calc. value (%)

35.60 34-84 1

12.25 12.12 2

11.60 11.30 2

13-56 11.74 2

20.59 21.42 2

17.87 17.52 2

--

0.6

0.5

0.3

1.5

2.1

-- 1.0

-2.6

+4.0

-2.0

--2.1

- 13.4

TABLE 5. Fluorine determination with ammonium fluoride as a standard 824

825

826

827

828

Teflon (CaF2n)

13.56 11.88 2

20.59 21.78 2

17.87 17.61 2

24.66 23.57 2

9.49 9-22 2

75.98 71.49 2

2-4

1.9

2.2

0.9

1.9

0.7

--12.4

+5.8

--1.4

--4-4

--2-8

--5.9

Compound % F (calc.) o/,,o F (found) Number of expt. Deviation of the mean (%) Deviation from the O/ calc. value (/o)

As the a g r e e m e n t between calculated a n d observed fluorine c o n t e n t for a m m o n i u m fluoride p.a. was excellent (Table 2), the analysis was repeated with a m m o n i u m f l ~ , ~ d e p.a. as s t a n d a r d on some of the above e x a m i n e d c o m p o u n d s (824, 825 a n d 826) as well as on fluoroacetamide* (827), 0-fluorobenzophenon* (828), a n d teflon.~" F r o m Tables 4 a n d 5, it m a y be concluded that p-fluorobenzoic acid as s t a n d a r d can easily be replaced by the more readily available a n d cheaper a m m o n i u m fluoride p.a. Moreover, it is proved that determinations carried out in twofold give good reproducible results. T h e m e a n values, o b t a i n e d from two experiments for each standard, for the compounds 824, 825 a n d 826 are given in T a b l e 6.

VALUE

OF T H E

METHOD

T h e e l e m e n t a r y analysis of fluorine by n e u t r o n activation proves to be very valuable. For the different c o m p o u n d s stated to be "pro analysi"--NH4F , PbF2, 821, 822 a n d 8 2 3 - - t h e deviation of the observed fluorine content from the calculated one does not exceed 2.6 per cent. T h e same deviation for products given as " p u r u m " or " t e c h n i c a l " can a m o u n t to

TABLE 6. Comparison of fluorine determinations with two different standards Compound

824

825

826

% F (found), 1 % F (found), 2

11.74 11.88

21.42 21.78

17.52 17.61

13"4 per cent in the case of 0-fluorobenzoic acid, b u t this p r o d u c t is only g u a r a n t e e d by the m a n u f a c t u r e r to be more t h a n 90 per cent pure. T h e error on the determination, expressed as the deviation of the m e a n , is 1.3 per cent on a n average. This means that the accuracy of the m e t h o d is good ( T a b l e 6) in comparison with a n y other m e t h o d of fluorine analysis. For instance, the accuracy reached with a titration of the F - ion with t h o r i u m nitrate a n d with alizarin-S as indicator 19~ is a b o u t 3-4 per cent if the q u a n t i t y of fluorine present is not too small. I f the analysis is carried out with a n organic fluorine c o m p o u n d a supplem e n t a r y error can be i n t r o d u c e d by the destruction of the p r o d u c t a n d the distillation ot the fluosilicic acid. * Aldrich Chem. Co., technical grade. t E. I. Du Pont de Nemours & Co., teflon No. 1.

110

B. Van Zanten, D. Decat and G. Leliaert

F u r t h e r m o r e , the m e t h o d described in this article is fast a n d cheap. I t is possible now to analyse a b o u t t w e n t y samples in 2 days including preparation, irradiation and measurem e n t o f the samples a n d calculation o f t h e results, a n d in most cases the c o m p o u n d s a r e n o t lost b y the analysis. APPLICATION As a n a p p l i c a t i o n of the foregoing m e t h o d , the c h a n g e in fluorine c o n t e n t o f teflon on pile i r r a d i a t i o n was d e t e r m i n e d . F r o m the l i t e r a t u r e it is k n o w n t h a t t h e d e g r a d a t i o n

n a t u r a l u r a n i u m r e a c t o r w i t h air cooling, t h e slow a n d fast n e u t r o n fluxes a r e b o t h a b o u t 1011-1019 n . c m - 2 . s e c -1. T h e y - r a y intensity is o f the o r d e r o f 10nr/hr. T h e i r r a d i a t i o n times v a r i e d from 1 h r to 11 days. T h e integ r a t e d t h e r m a l flux was d e t e r m i n e d b y m e a n s o f a c o b a l t m o n i t o r (a 2 p e r cent Co-A1 alloy). After 4 d a y s ' cooling the samples were w e i g h e d a g a i n a n d the fluorine c o n t e n t was d e t e r m i n e d by the p r o c e d u r e given b e l o w ( T a b l e 7). T h e fluorine content is c a l c u l a t e d in respect to the weight o f the samples before i r r a d i a t i o n . T h e teflon used in this series o f e x p e r i m e n t s

TABLE 7

Irradiation time (days) 0.04 1.00 5.00 11.00

Weight before irradiation (mg) 137.62 137.02 131.67 131.39 132-93 132-66 135.14 132.89

Loss in weight on irradiation (rag)

Integrated thermal flux (n.cm -~)

Received y-dose (r)

o/ /o F *

%F

found

calc.

<0-05

2.9 × 1015

2.0 × 105

71.4 + 0.7

71.5

<0.05

2.8 × 10le

4.8 × 10 7

71-0 ± 0.7

71.5

.0-40 4- 0.15

1.4 × 1017

2,4 × l0 s

70.9 ± 1.1

71-3

1.55 4- 0.10

1.2 x l0 is

5.3 × l0 s

69.1 4- 0.2

71.1

* Results are the mean values and deviations of four determinations. o f teflon starts at a y-dose o f a b o u t 10 e r ~13,14) a n d t h a t fluorine, a n d fluorine c o m p o u n d s escape. ~15-2°~ RYAN t2°~ has given a n e m p i r i c a l f o r m u l a for the relation b e t w e e n r a d i a t i o n dose a n d the q u a n t i t y o f fluorine e s c a p i n g : X = 3-78 X 10 -7 . y1.151 in w h i c h X ---- p g o f fluorine escaping p e r g r a m o f teflon, a n d Y = r a d i a t i o n dose in roentgen. As all l i t e r a t u r e d a t a are b a s e d on the determ i n a t i o n o f the q u a n t i t y o f fluorine lost, it was interesting to d e t e r m i n e the fluorine c o n t e n t o f i r r a d i a t e d teflon itself. EXPERIMENTAL RESULTS Disks o f teflon, h a v i n g a d i a m e t e r o f 9 rnm a n d a thickness o f 1 ram, were i r r a d i a t e d in the BR-1 reactor. I n this g r a p h i t e - m o d e r a t e d

c o n t a i n e d 71.5 p e r cent o f f l u o r i n e - ( T a b l e 5). T h e percentages o f fluorine m e n t i o n e d in the last c o l u m n o f T a b l e 7 a r e c a l c u l a t e d w i t h h e l p o f the relationship o f RYAN a n d a r e b a s e d on the a s s u m p t i o n t h a t t h e samples received 2 × l0 s r / h r d u r i n g the pile irradiations. F r o m these results can b e c o n c l u d e d t h a t only after a n i r r a d i a t i o n time o f I1 days a significant decrease in fluorine c o n t e n t can be found. REFERENCES 1. ROBINSON J . W. and WEST P. W. A Survey of Literature on the Detection of Fluoride Ion and Possible Research Lines. Report AD-75098 (1955). 2. OSHESKY G. D. Comparative Methods of Fluorine Analysis. Report WADC-TR-55-421 (1956). 3. M A T . S. Analyt. Chem. 30, 1557 (1958). 4. KLEINBERG J. and COWAN G. A. The Radiochemistry of Fluorine, Chlorine, Bromine and Iodine. Report NAS-NS-3005 (1960).

Elementary analysis offluorine by neutron activation

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5. MEINKE W. W. Indirect Neutron Absorbtiometry. 13. MOKUL'SKIIM. A., LAZUmaN Yu. S., FivmsxaI Report TID-6325 (1957). M. B. and KozIN V. I. Dokl. Akad. Nauk. SSSR 6. HASLAMJ. and WHzrax~t S. M. A. J. appl. Chem. 125, 1007 0959). 14. McCARTHY P. B. Flexure Tests on Irradiated 2, 339 (1952). 7. KOJIMAR. and UENO H. Kdgyo Ragaku Zasshi 61, Teflon Bellows. Report HW-35284 (1955). 270 (1958). 15. CHARLESBY A. The Decomposition of Polytara8. LEvEQtm P. and GOENVEC H. Bull soc. chim. fluorethylene by Pile Irradiation. Report AEREFr. 1213 (1955); Proceedings of the First InterM/R-978 (1952). national Conference on the Peaceful Uses of Atomic 16. RYANJ. W. and BAm.D S. L., JR. The DecompoEnergy, Geneva, P/342, Vol. 15. United Nations, sition of Teflon in High-Level Gamma Irradiation. New York (1956). Report AECD-3741 (1952). 9. ATCHISON Cr. J. and BEAMER W. H. Analyt. 17. HOI~NBECK R. Radiation Chemistry of Teflon. Chem. 28, 237 (1956). Report ER-10317 (1958). 10. ANDEaSO. U. Analyt. Chem. 32, 1368 (1960). 18. GOLDENJ. H. J. Polym. Sci. 45, 534 (1960). 11. STROMINOERD., HOLLANDERJ.M. and S~.ABORG 19. FLANAO~ T. B. d. Electron. Contr. 6, 337 (1959). G. T. Rev. rood. Phys. 30~ 2, II (1958). 20. RYAN S. W. Industr. plastiques mod. 6, (6) 40 12. CAMPBELL E. C. and FETTWEIS P. F. Nucl. (1954). Instrum. Meth. In press).