delayed-neutron activation determination of uranium in twelve rock reference standards

3
153 Ddaycd - Neutron Activation Determination Of Uranium in Tw~lv~ Rock Reference Standards E.B. LEDGER*, T.T. TIEH* AND M.W. ROWEO Departments of GeologyX and Chemistry9 Texas A&M University, College Station, TX 77843, USA The uranium content of twelve rock refe- rence samples, five from the Canada Centre for Mineral and Energy Technology, four from the Czechoslovakian Institute of Mineral Raw Mate- rials and three from the United States Geologi- cal Survey was determined by neutron activa- tion followed by delayed-neutron counting. Uranium contents measured ranged from 0.20 to 560 ppm. Three of the Canadian samples have relatively well established uranium contents. Of these we agree well with two of them; our value on the third is - 13% lower than the recommen- ded value. Comparison of our data on the other samples with other researchers is not yet possible because (il no determinations are yet reported on several of these samples and (iil even when several reported values are availa- ble, the wide disparity of those values does not allow meaningful comparison. W e have reported earlier our measurements of the uranium contents of rock reference samples from the Geological Survey of Japan (11, the South African National Institute for Metallurgy (2), the United States Geological Survey (2) and the Centre de Recherches PBtrographiques et GBochimiques of France (3). W e have argued in these reports that the overall uncertainty in our analysis at the ppm uranium level is N 5%. Now we report our measurements on five reference samples from the Canada Centre for Minerals and Energy Technology (CANMET) , four from the Czechoslovakian Institute of Mineral Raw Materials (UNS), and three from the United States Geological Survey (USGS). Unfortunately, two of the three USGS reference samples (BIR-1 and DNC-1) contain uranium in amounts below our limit of detection (- 0.1 ppm). The knowledge of the uranium content of these samples varies widely ranging from CANMET'S BL-1 which is certified to contain 0.022% uranium with 95% confidence between 0.021 t o 0.023%. t o CANMET'q MRG-1 with reported values ranging from 0.19 to 150 ppm, to others which have t o our knowledge no published uranium data. ANALYTICAL TECHNIQUE In our earlier report to this Journal (3) we described our method and the analytical technique in sufficient detail that it need not be repeated here. W e have now added more primary standards prepared from U30,; otherwise the technique has remained essentially the same. The CANMET samples BL-1, SY-2, SY-3 and MRG-1 were prepared and run as follows: from a single bottle of each of these standards two samples of -1 gram each were weighed into a 2/5 dram [1.73 CC] polyethylene vial. These were then run four times. Since no discernible difference could be seen, the uranium listed for this work simply represents the average of all eight measurements. The CANMET sample DL-2, presently undergoing certification was handled slightly differently. In that case, we were sent two different bottles (Nos. 292 and 700). T w ~ samples were prepared from each of the bottles and were each analyzed four times. Again there was no discernable difference between the uranium contents of any of the four samples and our preferred value is just the average of all determinations. For the UNS determinations, we prepared three samples from each of the four standard rock samples supplied to us. KK, Kaolin, from Karlovy Vary, was then run once each, SS, SklMski Pisek, Str616c, glass sand was run in duplicate and the M and F, magnesite and fluorite samples, respec- tively, were run in triplicate. The average values are shown in each case. With regard to the USGS samples, W-2 was handled exactly like CANMET DL-2. BIR-1 and DNC-1, which were both below our limit of detection for uranium, were prepared in tripli- cate samples from single bottles and analysed three times. RESULTS Our measurements of the uranium contents i n the twelve rock standards are shown in Table 1. -tuldnds Newsktter, Vol. 4, No 2, Octobre 1980, p. 153 B 155

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Page 1: Delayed-Neutron Activation Determination Of Uranium in Twelve Rock Reference Standards

153

Ddaycd - Neutron Activation Determination Of Uranium in T w ~ l v ~ Rock Reference Standards

E.B . LEDGER*, T.T. T I E H * AND M.W. ROWEO

Departments of GeologyX and Chemistry9 Texas A&M Univers i ty , Col lege S t a t i o n , TX 77843, USA

The uranium content of twelve rock refe- rence samples, f i v e from the Canada Centre for Mineral and Energy Technology, four from the Czechoslovakian Institute of Mineral Raw Mate- r ials and three from the United States Geologi- cal Survey was determined b y neutron activa- tion followed b y delayed-neutron counting. Uranium contents measured ranged from 0.20 to 560 ppm. Three of the Canadian samples have relat ively well established uranium contents. Of these we agree well with two of them; our value on the third i s - 13% lower than the recommen- ded value. Comparison o f our data on the other samples with other researchers i s not ye t possible because ( i l no determinations are ye t reported on several of these samples and (i i l even when several reported values are avai la- ble, the wide dispari ty of those values does not allow meaningful comparison.

We have r e p o r t e d ear l ier our measurements of t h e uranium c o n t e n t s of rock r e f e r e n c e samples from t h e Geological Survey o f Japan ( 1 1 , t h e South Afr ican Nat ional I n s t i t u t e f o r Metal lurgy (2), t h e United S t a t e s Geological Survey (2) and t h e Centre de Recherches PBtrographiques e t GBochimiques of France ( 3 ) . We have argued i n t h e s e r e p o r t s t h a t t h e o v e r a l l u n c e r t a i n t y i n o u r a n a l y s i s a t t h e ppm uranium l e v e l is N 5%. Now we r e p o r t our measurements on f i v e r e f e r e n c e samples from t h e Canada Cent re f o r Minerals and Energy Technology (CANMET) , four from t h e Czechoslovakian I n s t i t u t e o f Mineral Raw Materials (UNS), and t h r e e from t h e United S t a t e s Geological Survey (USGS). Unfor tuna te ly , two of t h e t h r e e USGS r e f e r e n c e samples (BIR-1 and DNC-1) conta in uranium i n amounts below our l i m i t o f d e t e c t i o n (- 0.1 ppm).

The knowledge of t h e uranium c o n t e n t of t h e s e samples v a r i e s widely ranging from CANMET'S BL-1 which is c e r t i f i e d t o c o n t a i n 0.022% uranium with 95% confidence between 0.021 t o 0.023%. t o CANMET'q MRG-1 wi th r e p o r t e d v a l u e s ranging from 0.19 t o 150 ppm, t o o t h e r s which have t o our knowledge no publ ished uranium data.

ANALYTICAL TECHNIQUE

I n our earlier r e p o r t t o t h i s J o u r n a l (3) we descr ibed o u r method and t h e a n a l y t i c a l technique i n s u f f i c i e n t d e t a i l that it need n o t be r e p e a t e d here . We have now added more pr imary s tandards prepared from U30,; otherwise t h e technique has remained e s s e n t i a l l y t h e same.

The CANMET samples BL-1, SY-2, SY-3 and MRG-1 were prepared and run as fo l lows: from a s i n g l e b o t t l e o f each of t h e s e s tandards two samples of -1 gram each were weighed i n t o a 2/5 dram [1.73 CC] po lye thylene v i a l . These were then run f o u r times. S ince no d i s c e r n i b l e d i f f e r e n c e could be seen , t h e uranium l i s t e d for t h i s work simply r e p r e s e n t s t h e average of a l l e i g h t measurements. The CANMET sample DL-2, p r e s e n t l y undergoing c e r t i f i c a t i o n was handled s l i g h t l y d i f f e r e n t l y . I n t h a t case, we were s e n t two d i f f e r e n t b o t t l e s (Nos. 292 and 7 0 0 ) . T w ~ samples were prepared from each o f t h e b o t t l e s and were each analyzed f o u r times. Again t h e r e was no d i s c e r n a b l e d i f f e r e n c e between t h e uranium c o n t e n t s of any of t h e f o u r samples and our p r e f e r r e d va lue is j u s t t h e average o f a l l de te rmina t ions .

For t h e UNS de termina t ions , w e prepared three samples from each of t h e f o u r s tandard rock samples suppl ied t o us . KK, Kaol in , from Karlovy Vary, was then r u n once each, SS, S k l M s k i P isek , S t r616c , glass sand was r u n i n d u p l i c a t e and t h e M and F , magnesi te and f l u o r i t e samples , respec- t i v e l y , were run i n t r i p l i c a t e . The average va lues are shown i n each case.

With regard t o t h e USGS samples , W-2 w a s handled e x a c t l y l i k e CANMET DL-2. BIR-1 and DNC-1, which were both below our l i m i t o f d e t e c t i o n f o r uranium, were prepared i n t r i p l i - cate samples from s i n g l e b o t t l e s and analysed t h r e e t imes.

RESULTS

Our measurements of t h e uranium c o n t e n t s i n t h e twelve rock s t a n d a r d s are shown i n Table 1.

-tuldnds Newsktter, Vol. 4 , N o 2 , Octobre 1980, p . 153 B 155

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Table 1. Uranium contents of some standard rock samples and c e r t i f i e d reference materials from Canada, Czeckoslovakia and the United States

NO. OT SAEPLE SOURCE* Measurements U ppn ( t h i s work) U ppn

8L-1 DL-2 sv-2 sv-3 M(G 1

55 KK

I4 F

w-2 BIR-1 DNC-1

CANMET 8

16 8

8 a

UNS 6 3 9

9

USGS 17 9 9

22123 220t 10( 4 )

115t1 116 ? 3 (8)

55723 640 ( 5 ) 0.20+0.02 0.4 (5)

0.46t0.04 5.80k0.05 0.54t0.04 3.3h0.08

278t3 280 ( 5 )

0.4ZtO. 02 0.1

* 0.1

WANMET, Dr. Henry P. Stsgcr, Canada Centre for Mineral and Knncrgy Technology; URS, Dr. Vaclav Zyka, Ustav Neroatnych Surivin ( I n s t i t u t e of Raw Materials, Czeckoslovakia); USGS, Dr. F.H. Flanwan, United States Geological Srirvey.

O f these , two were below our l i m i t of de tec t ion which we estimate t o be 5 0.1 ppm uranium. The unce r t a in t i e s shown on our analyses represent a ca l cu la t ion of t he standard e r r o r , i . e . , t h e standard deviation /a, where N is the number of measurements. The standard devia t ion w a s estimated by

Our previous experience leads us t o expect t h a t our a c t u a l uncer ta in ty may be -f 5% a t the 1 ppm uranium l eve l , a value which includes a l l random e r r o r s a r i s i n g i n our analyses.

Table 1 includes a comparison of our analyses with previous "recommended" values. For HRG-1, t h e value suggested ( 5 ) with ' 7 ' is 0.4? ppm uranium which represents a compilation of only two research l abora to r i e s ( 5 , 6 ) . These two values are 1 ppm and 0.24 ppm (an average of four determinations). Our value of 0.20 f 0.02 ppm is i n good agreement with t h e value of 0.24 f. 0.03 pprn of Korkisch and Hiibner ( 6 ) .

The agreement i n our value for CANMET's c e r t i f i e d standard BL-1 is good. For t h e CANMET samples SY-2 and SY-3, Abbey (5) lists those 'recommended' values as category B , i n which 'I

' A ' i s reserved f o r those cons t i t uen t s f o r which a t least 20 r e s u l t s were repor ted , where there is no evidence of b i a s i n t h e histogram and where the re is c lose agreement between mode, median, mean, ad jus ted mean and select mean. The ' ? I

category includes the values mentioned above, and a l s o o the r s where e r r a t i c d i s t r i b u t i o n or o the r

f a c t o r s cast doubt on the derived value. The I B '

is intended f o r values intermediate between t&e. o t h e r two". With t h a t designation, we are in agreement with the uranium contents 'recommended' f o r SY-2 and SY-3, s ince w e are v i r t u a l l y i d e n t i c a l with t h e 'recommended' value for SY-2 and only 13% less t h a t t he 'recommended' value for SY-3. Thus w e a r e confident t h a t we are accura te within our s t a t e d estimated uncer ta in ty of - * 5% f o r uranium determinations.

In a r ecen t i s sue of t h i s journa l w e reported our measurements of t h e uranium concen- t r a t i o n s i n t h i r t e e n French rock reference samples -(3). O f t h e t h i r t e e n , only f i v e have uranium values reported previously. However, i n t he same i s sue of t h e Geostandards Newsletter, Govindaraju (7) reported the latest r e s u l t s on three more of those re ference rocks, r e s u l t s which included uranium determinations f r o m nume- rous l abora to r i e s . I n p a r t i c u l a r , Govindaraju a r r ived a t a recommended value for t h e uranium content of t h e g r a n i t e MA-N of 12 ppm, a value ind is t inguishable from our value of 11.7 f 0.6 ppm. For t h e b a s a l t BE-N,*an adopted value of 2.4 ppm of uranium was es tab l i shed , i n e s s e n t i a l agreement with our value of 2.27 f. 0.09 ppm. F ina l ly , fo r t h e anor thos i t e , AN-G, which w e repor ted t o be below our l i m i t of de t ec t ion (I 0.2 ppm), no acceptable recommended value could be a r r ived a t . Values were repor ted i n t h e range 0.18 t o 2.24 ppm uranium. O u r l i m i t is toward the lower end of t h a t scale, so t h a t w e con t r ad ic t any values greater than - 0 . 2 ppm uranium. Once again these comparisons demonstrate t h a t our accuracy is wi th in f 5% as w e estimated e a r l i e r .

ACKNOWLEDGEMENTS

We are g r a t e f u l t o the staff a t the Nuclear Science Center of Texas A&M Univereity, e spec ia l ly M r . K. Walker, for t h e i r cooperation i n providing t h e necessary i r r a d i a t i o n s and for t h e i r a s s i s t ance i n maintaining the counting equipment. We acknowledge support from t h e Office o f Universisty Research and the Center f o r Energy and Mineral Resources, both of Texas AM Univer- s i t y .

RESUME

Douze k h a n t i l l o n s ghchimiques de reference dont cinq provenant du "Centre f o r Mineral and Energy Technology", quatre du "Czechoslovakian I n s t i t u t e of Mineral Raw Materials' e t t r o i s du "United States Geology Survey" ont @t@ analyses pour l eur teneur en uranium par act ivat ion nucle- a i r e avec des neutrons retard&. La game deter- minge var ie de 0.20 a 560 p p . Parmi l e s t r o i s k h a n t i l l o n s Canadiens, pour deux d 'ent re eux nos resul ta ts sont concordants tandis que p u r l e troisieme nos resul ta ts sont fa ib les de 13%. Une discussion p l u s poussee sur nos resul ta ts devient d i f f i c i l e s o i t par l a dispersion analytique ou par l e manque de donnees publiees.

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REFERENCES

(1) W . W . Rowe a r d J . K . Herndpn (1975; Uranium i n rock s t a n d a r d s J G - 1 and J B - 1 , Geochemical J o u r n a l , 1 0 : 163-164.

(21 M . W . Rowe and J . M . Herndon (1976) Uranium i n NIMROC s t a n d a r d igneous rock samples , Geoche- mical J o u r n a l , 1 0 : 219-221.

(3) E . B . Ledger , T . T . T i eh and M.W. Rowe (1980) Delayed-neutron a c t i v a t i o n d e t e r m l n a t l o n of uranium i n t h i r t e e n French r o c k r e f e r e n c e samples , Geos tanda rds N e w s l e t t e r , 4 : 5-8.

( 4 ) J . C . I n g l e s , R . S u t a r n o , W.S. Bowman and G . H . Faye (1977) R a d i o a c t i v e O r e s DH-1, DL-1, BL-1, BL-2, BL-3 and RL-4 c e r t i f i e d r e f e r e n c e m a t e r i a l s , CANMET Repor t : 77-64.

( 5 ) S. Abbey, A . H . G i l l i e s o n and G . P e r r a u l t (1975) SY-2, SY-3 and MRG-1 a r e p o r t on t h e c o l l a b o r a t i v e a n a l y s i s of t h r e e Canadian r o c k samples f o r use as c e r t i f i e d r e f e r e n c e m a t e r i a l s , CANMET Repor t MRF'/MSL: 75-132 ( T R ) . and

S . Abbey (197b) SY-2, SY-3 and MRG-1 r e p o r t on t h e c o l l a b o r a t i v e anaiy:;:. o f t h r e e Canadian r o c k samples f o r u s e a c e r t i f i c r%fe rence materials, Supplement 1 , CANMET R e p o r t : 76-36.

( 6 ) J . Kork i sch and H . Hubner (1976) De te rmina t ion of uranium i n m i n e r a l s and r o c k s , T a l a n t a 23: 283-zea.

( 7 ) K . Gov inda ra ju (1980) Repor t (1980) on t h r e e GIT-IWG rock r e f e r e n c e samples : A n o r t h o s i t e from Green land , AN-G; B a s a l t e d 'Essey-la-CBte, RE-N; G r a n i t e de Beauvo i r , MA-N, Geos t anda rds N e w s l e t t e r , 4 : 49-138.

( 8 ) Note added i n p r e 5 s : A f t e r o u r submiss ion of t h i s r e p o r t t o Geos tanda rds N e w s l e t t e r , w e r e c e i v e d a p e r s o n a l communi- c a t i o n from Dr. kienry F. S t e g e r s t a t i n g t h e recommended v a l u e and 95 % conf idence l i m i t s f o r DL-2 as 0.0116 i 0.0003 % uranium, i n e x c e l l e n t agreement w i t h our va lue of 0.0115 + 0.0001 % uranium.