A new fission product: 74Ga

J. Inorg. Nucl. Chem., 1960, Vol. 12, pp. 223 to 227. Pergamon Press Ltd. Printed in Northern Ireland

A N E W FISSION PRODUCT:

74Ga

J. A. MARINSKY* a n d E. EICHLER Oak Ridge National Laboratory,~" Oak Ridge, Tennessee (Received 30 April 1959)

Abstract--The 8 min 74Ga has been separated from the fission products of 2ssU. This is believed to be the first observation of mass 74 in the fission process. The gallium activity was characterized as 74Ga by comparison of its ~-ray spectrum with that obtained from (n,p)-produced 74Ga. Chemical separation of the 74Ga was effected by a combination of extraction, volatilization, ionexchange, and precipitation steps. Its fission yield has been determined to be about 3.4 × 10-* per cent, in good agreement with the yield expected for mass 74 from interpolation of the smooth massfission yield curve for ~35U.

AN 8 rain activity observed by bombarding natural germanium with fast neutrons was tentatively assigned to 74Ga b y MORINAGA. tl) This assignment was c o n f i r m e d b y EICHLER et aL ~2~ t h r o u g h i r r a d i a t i o n o f enriched 74Ge with 14 M e V n e u t r o n s a n d t h r o u g h subsequent chemical separation. I n addition, the yield o f the 8 n'fin activity was d e m o n s t r a t e d to be p r o p o r t i o n a l to the isotopic e n r i c h m e n t o f 74Ge. T h e v - r a y s p e c t r u m o f 74Ga is d o m i n a t e d b y intense p e a k s at 0-60 a n d 2.3 M e V ; w e a k e r transitions with energies o f 0.86, 1-1, 1.5 a n d 1.9 M e V are also observed. Since m a s s 74 h a d n o t y e t been r e p o r t e d in fission, it was o f interest in the present study to d e m o n s t r a t e the occurrence o f the 8 rain 7iGa activity in the fission process a n d to c o m p a r e its yield with t h a t p r e d i c t e d b y the s m o o t h mass-fission yield curve ta) f o r ~~U. Sufficient k n o w l e d g e o f its half-life a n d v - r a y s p e c t r u m was available to aid in the identification. I n a d d i t i o n , the availability o f a m u l t i - c h a n n e l analyser p r o v i d e d r a p i d m e a s u r e m e n t capability. EXPERIMENTAL Separation

The separation procedure that was used in this study was a composite of standard techniques.C4,5.6.7~ Each separate operation, however, was performed as rapidly as possible to minimize loss by decay of the 8 min gallium activity. As a result, optimum decontamination was sacrificed in some instances. For example, the ion exchange and precipitation steps would undoubtedly have provided more * Permanent address: University of Buffalo, Buffalo, New York; Oak Ridge Institute of Nuclear Studies Research Participant, June-September 1958. "~Operated by Union Carbide Corporation for the U.S. Atomic Energy Commission. tl) H. MORINAGA,Phys. Rev. 103, 504 (1956). ~ E. EICHLER,N. R. JOHNSONand G. D. O'KELLEY,Abstract of a paper submitted at the New York meeting of the American Physical Society, January 29 to February 1 (1958); E. ElCnLER,J. MAmNSgY, N. R. JOHNSONand G. D. O'KELLE','. TO be published. ~a~S. KATCOFE,Nucleonics 16, 78-85 (1958). t4~ L. E. GLEND~NIN,Radiochemical Studies: The Fission Products, (Edited by C. D. CORYELLand N. SUGARMAN)NNES, Plutonium Project Record, Div. IV, Vol. 9, Book llI, pp. 1657-1661. McGrawHill, New York (1951). 15~j. M. SIEGBLand L. E. GLENDENIN, Radiochemical Studies: The Fission Products, (Edited by C. D. CORYELLand N. StrGARMAN)NNES Plutonium Project Record, Div. IV, Vol. 9, Book III, pp. 1436-1439. McGraw-Hill, New York (1951). csJ G. E. LUNt)ELLand J. I. HOFFMAN,Outlines of Methods of Chemical Analysis. John Wiley, New York (1938). t¢~ K. KRAUSand F. NELSON, Metal Separations by Anion Exchange. A.S.T.M. Symposium on Ion-Exchange and Chromatography in Analytical Chemistry, Atlantic City, New Jersey, June 18 (1956). 223

224

J . A . MARINSKYand E. EICHLER

complete separation from the other fission products than was obtained if slower flow rates and longer digestion periods had been employed. A 2 ml sample of uranyl nitrate solution (--,850 mg U/ml) contained in a pneumatic transfer tube "rabbit" was irradiated for 2 min in the OKNL Graphite Reactor in a typical experiment. The micarta "rabbit" that was used is similar to that described by O'KELLEYet aL (8) except that it contained a stainless steel liner to hold the liquid sample. The "rabbit" was ejected from the reactor and dropped

t0" I

I

1

._

I

I

I

I

I

I

-

0"60

103

-

o o

Ji

"

•

i0 z

i

0'86

tlo

l

'

I

2.35

1

-

! o

to

I, 0

20

40

1

[

60

80

I

I

I

100 120 140 CHANNEL NUMBER

I

I,,

1

160

t80

zoo

220

Fso. la.--The 7-ray spectrum produced by fission product gallium. into a shielded holder for 2 min at the end of an irradiation to permit decay of the very short-lived nuclides. The liquid sample was then transferred pneumatically to a separatory funnel containing 2 ml of gallium carrier (,~10 mg of Ga]ml), 2 ml of barium carrier (,-40 nag of Ba/ml) and 6 rnl of 12 M hydrochloric acid. The solution was then contacted with 12 ml of diisopropyl ether for 15 to 30 sec. The 12.8 day l~0Ba was separated from aliquot samples of the aqueous phase to provide a fission-yield standard. The separation procedure of GLENOENIN,(~) which is based on the simple precipitation of BaCI2.2H20, was used. The gallium was back extracted into 10 ml of water after washing the ether layer with three 5 ml portions of 6 M hydrochloric acid. This solution was made about 1 M in hydrofluoric acid and then was passed rapidly with compressed air through a Dowex-1 resin column to adsorb the molybdenum. The effluent was collected in 5 ml of concentrated hydrobromic acid. The hydrobromic, hydrofluoric acid mixture was evaporated over an open flame. Excessive loss of.gallium due to volatilization was avoided by evaporating the sample just to dryness. The residue (s) G. D. O'KELLEY,N. H. LAZARand E. EICHLER,Phyx. Rev. 102, 223 (1956).

A new fission product: ?4Ga

225

was immediately dissolved in 10 ml of chilled 6 M hydrochloric acid and the gallium was extracted with 10 ml of cold diisopropyl ether. After washing the ether extract twice with 5 ml portions of 6 M hydrochloric acid, the gallium was back extracted once more into 10 ml of water. This aqueous sample was then made 0-3 M in hydrochloric acid after adding bismuth (-~10 mg) and molybdenum (,~3 mg) scavengers. After their precipitation with hydrogen sulphide and removal of the precipitate, additional molybdenum (3 mg) was precipitated with ct-benzoinoxime. The filtrate to 5

t - 0.606

J

I

]

t

I

I

i

104

~-o.88 1'2t A ~,~3i - -

2.3~

_

0 U

g 10 3

L: 1oz I

I

I

I

I

I

I

/

]

I

I

0

20

40

60

eo

100

120

t40

160

180

200

220

C H A N N E L NUMBER

FIG. lb.--The ))-ray spectrum produced by 74Ga from T4Ge(n,p). from the oxime precipitate was then made slightly basic with 6 M ammonium hydroxide and precipitated with 8-hydroxyquinoline reagent. The gallium 8-hydroxyquinolate precipitate was filtered on a weighed filter-paper disk and mounted for activity measurement. Nuclear measurement

y-ray spectra were measured with a 3 in. × 3 in. cylindrical sodium iodide crystal. Normally a 1 "3 g/era ~ polystyrene disk was placed between source and crystal to absorb E-radiation. Two types of spectral runs were performed: (1) complete spectra were observed for comparison with the spectral shape obtained from (n,p)produced 74Ga; (2) the decay of the intense 0"60 MeV },-ray was observed by measuring the low-energy portion of the spectra as a function of time. The E-decay of 7~Ga samples was followed with an end-window gas-flow proportional counter. For fission yield determinations, both the 74Ga and the l~°Ba disintegration rates were obtained from y-ray spectra. The 14°Ba spectra were taken soon after separation to minimize l~°La growth.

226

J . A . MARINSKY and E. EICHLER

t000 0 0

"o

500

o

~.°o

:k-%.~-',,~ 200 X ~ ° ° = ~:

100

0~ __

o

%

5O

o

20

.-.--~f~l=zt3~ 3 10 5

\ 20

0

40

60 80 TIME(rain)

t00

120

t40

FI~. 2.--The fl-decay of a fission product gallium sample.

1000 500 ~ e

>

200

c~,

o

t00

~fl/i=

50

~ 1

8"3+0"4

~5 "6

t0

5 0

20

40

60 80 TIME (rain}

t00

120

t40

FIG. 3.--The decay of the 0.60 MeV 7-ray from a fission product gallium sample. The long-lived component was determined by an additional point at 270 rain.

A new fissionproduct: 7aGa

227

RESULTS

Isotope identification The ),-ray spectrum produced by the gallium sample after separation from fission products is shown in Fig. la, while that produced by a sample of 74Ga resulting from ~4Ge(n,p) is given in Fig. lb. The spectrum in Fig. la is a composite of two spectra: the portion below ,--,0.80 MeV from a very pure but weak source, the portion above ,~,0.80 MeV from a source with more activity but somewhat contaminated with ~°~Tc which has essentially no high energy ),-rays. It is seen that the fission product gallium produces a spectrum in good agreement with that from r4Ga. TABLE 1.--RESULTS OF DETERMINATION OF FISSION YIELD OF 74GA

Bombardment Experiment time (min)

[

L40Ba

,4Ga

1

Time before counting Chemical I Corrected yield peak area (min) [

Absolute ;,-ray intensity (%)

Fission yield (%)

21.5c9~

6.3213~

75~,

3.42 × 10-4 3.35 × 10-~

i

i

2

I

2.0 2.3

2I

l

2.0 2.3

I_

1670 4550 31"2 33"5

0"360 1"67 × 1071 0.704 11'88 × 107I 0'395 0'475

3.16 × 103t 3.48 × 103J

tgl W. S. LYON. Private C o m m u n i c a t i o n (August, 1958).

A fl-decay study of the fission-produced 74Ga is shown in Fig. 2. The indicated half-life of 7.7 4- 0.4 min is in good agreement with the value of 7"8 ± 0.2 min previously assigned to this nuclide, t2~ The extrapolated activity of the longest-lived component relative to that of 8 min 74Ga is of the magnitude to be expected from 5 hr r~Ga, produced in the fission process, t3~ and the ~-,13 min component probably is l°lMo-Te. The decay of the 0.6 MeV y-ray is shown in Fig. 3. An 8"3 4- 0.4 min half-life is resolved from this independent study.

Fission yield The area under the 0-60 MeV )'-ray peak of 7aGa and the 0"54 MeV y-ray peak of 14°Ba were corrected for decay, for degree of saturation during irradiation, forchemical yield, and for intrinsic peak efficiency. The fission yield of 74Ga was then calculated relative to the absolute fission yield ofl4°Ba using the respective absolute y-ray intensities (the number of y-rays per disintegration). Table 1 lists the data for two separate determinations. Averaging the two results gives a yield of 3.4 × 10-~ per cent with an expected error of 10-20 per cent; this is in good agreement with the value obtained by interpolation of the ~ U mass-yield data. ~3~

Acknowledgements--Wewould like to thank Drs. G. D. O'KELLEY, N. R. JOHNSONand G. E. BOYD for their assistance and encouragement.