Radionuclide Generators - American Chemical Society

8 Large-Scale Isolation of Sr-82 for Generator Production Κ. E .

THOMAS

and J. W.

BARNES

Downloaded by UNIV OF LIVERPOOL on November 24, 2016 | http://pubs.acs.org Publication Date: January 30, 1984 | doi: 10.1021/bk-1984-0241.ch008

G r o u p I N C - 3 , L o s A l a m o s N a t i o n a l Laboratory, L o s A l a m o s , NM 87545

A new chemical separation process has been developed at Los Alamos f o r the i s o l a t i o n of Sr-82 from irra diated molybdenum t a r g e t s . Large (up to 500 gram) molybdenum metal t a r g e t s are i r r a d i a t e d f o r approx imately one month at the Los Alamos Meson Physics Facility (LAMPF). Following i r r a d i a t i o n , a no -carrier-added r a d i o c h e m i c a l l y pure strontium f r a c t i o n is obtained from a chemical s e p a r a t i o n process i n v o l v i n g one or two i o n exchange columns. The new process i s simpler to perform and r e s u l t s in a purer product than the process used i n the past. T h i s new procedure has been used i n the production of up to 28 Curies of Sr-82 at end-of-bombardment. The product will be made a v a i l a b l e f o r commercial pro duction of the Sr-82/Rb-82 generator system f o r medical use.

The Medical Radioisotope Research Group (INC-3) at Los Alamos N a t i o n a l Laboratory has produced Sr-82 f o r use i n c o l l a b o r a t i v e experiments f o r s e v e r a l years. This has g e n e r a l l y been from small (IO

01 M |HCl

Hi ζ

UJ 3

8

AQUEOUS

Sr Rb, OTHERS

HCl "

t

ORGANIC^ Y.Zr.Nb

Figure 1.

Flow scheme f o r the e a r l i e r strontium

Rb

process.

Knapp and Butler; Radionuclide Generators ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Sr


8.

THOMAS A N DBARNES

Large-Scale

Isolation

of

Sr-82

125

the number of manipulations and the time i n v o l v e d becomes cumbersome. T y p i c a l l y , r a d i o a c t i v e contaminants would i n c l u d e Mn-52, Mn-54, and Y-88, at higher than d e s i r e d l e v e l s . This procedure was not designed f o r removal of manganese s i n c e t h i s was never considered to be a problem; however, the e x t r a c t i o n step was included to remove Y-88. The Y-88 problem was probably a r e s u l t of entrainment and cross-contamination of phases i n the e x t r a c t i o n . Réévaluation of the process brought to mind a l t e r n a t i v e p u r i f i c a t i o n methods that should not only y i e l d a c l e a n product, but also be simpler to run. The new chemistry i s based on a Sr-90/Y-90 s e p a r a t i o n using α-hydroxyisobutyric a c i d (a-HIB) and c a t i o n exchange chromatog raphy ( 5 ) . Once the a c t i v i t i e s are loaded onto the column, the steps to prepare the column f o r the a-HIB e l u t i o n remove s e v e r a l of the p o s s i b i l e contaminants i n c l u d i n g rubidium and c o b a l t . F i n a l l y , the a-HIB e l u t i o n a l s o removes a wide range of other elements as w e l l , l e a v i n g strontium on the i o n exchange column (6). Experimental Targets. The t a r g e t c o n s i s t s of stacks of 0.25-0.50 mm t h i c k molybdenum metal d i s k s . One of s e v e r a l c o n f i g u r a t i o n s i s used de pending on the q u a n t i t y of Sr-82 d e s i r e d . Various combinations of up to three stacks 2.5-cm and 1.9-cm i n diameter with a thickness of 1.25 cm may be used to give t a r g e t masses of 60 to 170 grams. Larger mass t a r g e t s termed " b i g molys," may be prepared using 6.4-cm diameter stacks with thicknes ses of 1.25 cm to 1.9 cm. Targets as great as 460 grams have been prepared i n t h i s manner. Target packaging i s i l l u s t r a t e d i n Figure 2, which shows two 1.9-cm and one 2.5-cm diameter stacks, 1.25-cm t h i c k , held t o gether with copper r i n g s . The stacks are enclosed i n a screwedshut can to p r o t e c t the t a r g e t from the c o o l i n g water. The can i s then contained i n s i d e the t a r g e t c a r r i e r . T h i s e n t i r e package i s attached to the end of a s t r i n g e r f o r i r r a d i a t i o n . I r r a d i a t i o n s . The i r r a d i a t i o n s are performed at the Isotope Production F a c i l i t y (IPF) at the Los Alamos Meson Physics F a c i l i t y (LAMPF). Target handling has been described elsewhere (7-9). I r r a d i a t i o n lengths vary from 2 to 29 days at a nominal beam i n t e n s i t y of 500 μ-amps (at the IPF). G e n e r a l l y , the t a r g e t s are located i n i r r a d i a t i o n p o s i t i o n s ( s t r i n g e r s ) 2 or 3. Chemistry. Figure 3.

A flow chart of the new

strontium process i s shown i n

The d i s s o l u t i o n procedures

f o r the Br-77 process (10).

are the same as described

The ΗΝΟ,^-Η,^ΡΟ^ d i s s o l u t i o n i s per

formed i f Br-77 i s to be recovered; otherwise, H2O2 i s used f o r the d i s s o l u t i o n .

The HN0~-HJP0, d i s s o l v i n g s o l u t i o n i s composed


RADIONUCLIDE

GENERATORS


126

Figure 2. Target arrangement and packaging f o r ;· threestack molybdenum metal t a r g e t .


8.

THOMAS AND BARNES

Large-Scale

Isolation

127

of Sr-82

Mo TARGET


DISSOLVE TARGET HNO3/H3PO4

OR H Q 2

Γ CATION EXCHANGE COLUMN ADSORB Sr AND OTHER CATIONS

Ϊ N H 4 C I WASH OF COLUMN REMOVE Rbi CONVERT TO HH% FORM 1 α - H I B WASH OF COLUMN REMOVE Y, Z r . Z n . M n ,Co

~

0.5M HCl WASH OF COLUMN REMOVE Mn CONVERT TO H+ FORM ;

i 6 M HCl WASH OF COLUMN REMOVE Sr

τ

EVAPORATE 6M HCl TO SMALL VOLUME Sr PRODUCT Figure 3 . Flow scheme f o r the new strontium process. If H2O2 was used to d i s s o l v e the t a r g e t , an anion exchange column i n 12 M HCl i s r e q u i r e d to remove zirconium strontium product.

from the


128

of

RADIONUCLIDE GENERATORS

550 ml cone. HN0

3>

250 ml cone. H P 0 , and 200 ml Ry). 3

4

One

l i t e r of t h i s s o l u t i o n has been used to d i s s o l v e as much as 170 grams of molybdenum metal. This s o l u t i o n i s d i l u t e d with an equal volume of dioxane p r i o r to the s e p a r a t i o n procedure. A second procedure uses 30% H^O^ as a d i s s o l v i n g s o l u t i o n ; f i v e l i t e r s of


H2O2 have been used to d i s s o l v e about 300 g of the metal. Once a l l the metal has been d i s s o l v e d , the s o l u t i o n i s passed through a c a t i o n exchange column (AG 50W-X8, 100-200 mesh; BioRad L a b o r a t o r i e s ) . A bed volume of as l i t t l e as 40 ml has been used s u c c e s s f u l l y i n t h i s work. The r e s i n removes the c a t i o n s present from the l a r g e q u a n t i t y of molybdate and any other anions that might be present. The column i s now converted to the ammonium form by passing 0.5 M NH^Cl through the column u n t i l the pH of the e f f l u e n t i s the same as the feed s o l u t i o n (^pH 4.5). Next, ap proximately f i v e column volumes of 0.5 Μ α-ΗΙΒ (pH 4.5-5.0) are passed through the column. The a-HIB i s now removed from the column v i a an ^ 0 wash. To convert the column back to the hydro gen form, about f i v e column volumes of 0.5 M HCl are used. F i n a l l y , strontium i s removed from the column with 6 M HCl. If HNO^-H^PO^ was used i n the d i s s o l u t i o n , the strontium product i s r a d i o c h e m i c a l l y pure and i s evaporated to dryness, d i s s o l v e d i n Η\>0, and then strontium a c t i v i t y i s determined f o r eventual s h i p p i n g .

I f #2®2 was

used, the product contains some

zirconium and i s taken to dryness, d i s s o l v e d i n concentrated HCl, and loaded onto an anion exchange column (AG 1X8, 100-200 mesh; BioRad L a b o r a t o r i e s ) . T h i s i o n exchange step must be performed very soon a f t e r the f i r s t column due to growth of Y-88 from the zirconium contamination. Strontium passes through the anion column; t h i s s o l u t i o n i s evaporated to dryness, d i s s o l v e d i n ^ 0 and prepared f o r shipment. Data A n a l y s i s . A l l samples are analyzed f o r r a d i o a c t i v e n u c l i d e s by a G e ( L i ) - p u l s e height analyzer system c a l i b r a t e d f o r counting 5-ml s o l u t i o n samples. In a l l cases, appropriate d i l u t i o n s are made to reduce the a c t i v i t y l e v e l of the counting sample so that counting system dead-time i s l e s s than 15%. Gamma peak i n t e n s i t i e s are determined using a modified v e r s i o n of the peak f i t t i n g program GAMANAL (11). I n d i v i d u a l n u c l i d e s are determined by i d e n t i f i c a t i o n of t h e i r a s s o c i a t e d gamma r a d i a t i o n s . No h a l f - l i f e measurements are made as part of the i d e n t i f i c a t i o n process. Results L i s t e d i n Table I are the r e s u l t s of nine production runs f o r strontium. Targets ranging i n mass from 64 to 457 grams have been i r r a d i a t e d with production as h i g h as 28 C i at end-of-bombardment



8.

THOMAS A N D BARNES

Large-Scale

Isolation

of

Sr-82

129

(EOB). Run number 30-1-2 was processed s e v e r a l months a f t e r EOB; t h i s allowed observation of Sr-82 i n the d i s s o l v e d t a r g e t s o l u t i o n . Normally t h i s i s not p o s s i b l e due to the l a r g e number of other n u c l i d e s present s h o r t l y a f t e r i r r a d i a t i o n , s e v e r a l of which have the same gamma ray energy as Sr-82. Measurement of Sr-82 i n the t a r g e t s o l u t i o n of run 30-1-2 allowed an e s t i m a t i o n of the strontium o v e r a l l chemical y i e l d . This was determined to be _>90%. The o v e r a l l y i e l d on some of the l a t e r runs was roughly estimated to be 50-75%. In these s t u d i e s some strontium y i e l d was s a c r i f i c e d to i n s u r e a pure f i n a l product and to shorten the time i n v o l v e d i n preparing the sample f o r s h i p p i n g . The r a t i o ôf Sr-82 to Sr-85 at EOB i s a l s o shown i n Table I. The Sr-83 to Sr-82 r a t i o has been determined f o r the l a s t three runs. This r a t i o was determined to be 7.2, 6.5, and 3.0 f o r runs 33-1-14, -18, and -21, r e s p e c t i v e l y . The times required f o r the various procedure steps are given i n Table I I . The d i s s o l u t i o n takes as long as three hours no matter which technique i s used. S o l u t i o n and column p r e p a r a t i o n time i s roughly three hours and clean-up and waste d i s p o s a l take about four hours.

Table I.

Run

No.

30-1-2 33-1-1 33-1-3 33-1-4 33-1-9 33-1-13 33-1-14 33-1-18 33-1-21

Hours i n Beam

uA-hr 2.27 1.92 2.24 1.16 3.16 1.60 5.18 4.92 4.08

Production of Sr-82

χ 10^ χ 10^ χ 10^ χ 10^ χ 10^ χ 10^ χ 10 χ 10 χ 10 4

4

5

654 47 569 ^350 677 403 142 125 695

Target Mass 457 166 334 166 64 450 64 167 289

Total Ci Sr-82 at EOB

Ratio at EOB 82/85

24.0 1.1 28.0 9.6 ^12.0

* 1.7 5.1 20.0

1.16 1.28 λ,Ι.ΟΟ

1.12 1.13 1.06 1.38 1.43 1.05

*Not a l l of t a r g e t d i s s o l v e d . Discussion The 0.5 M NH^Cl wash of the i o n exchange column i s a good decon tamination step f o r rubidium r a d i o i s o t o p e s and a l s o removes some cobalt and vanadium. Often, the ammonium c h l o r i d e and the a-HIB s o l u t i o n s appear blue-green which probably r e s u l t s from massive amounts of copper from the t a r g e t packaging. Both of these column


130

RADIONUCLIDE GENERATORS

Table II·

Time Requirements f o r the New

Step

Time Required

Dissolution Cation Column Evaporation Anion Column Evaporation Downloaded by UNIV OF LIVERPOOL on November 24, 2016 | http://pubs.acs.org Publication Date: January 30, 1984 | doi: 10.1021/bk-1984-0241.ch008

Strontium

Process

(hours)

^3 50 mCi/ml D i l u t e HCl

Radionuclidic Purity*: Sr-85 Sr-83 Rb-83 A l l Other

15 mCi/mCi Sr-82

Radionuclide Generators - American Chemical Society

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