1965, l' 01. X I' !II
J"I'HN \L 01'
TlI~
SOI'TII
\1
RI<'~"
Oll-.MICA!.
IN"TITl'T~
THE PREPARATION OF POTASSIUM HEXACYANOCOBALTATE(I1I)
LABELLED WITH COBALT-58 AND -60 FOR
HYDROLOGICAL STUDIES
by
M. PEISACIP
(ll'SO:\BIL\( ;
Kobalt-SS, in 'n n'aktor \{'f\",ar(\!g d"IH (he k('Tnr,'ak~i" ";";I(n,p)· "Co, en kobalt-60 deur
6 9Co(n,y) 60CO, wonl g,.j'T1l1k om "1''''' rd l'T"l']' 'SSIIl;(, van K,Co(('~). te berei vir hidralagiese
ondrrsoek... Knbalt-5S \\ (lrd ;(l',k"l met ~):--. 1[('1 "I' '11 allloall-uilruilhars en gedut'l'r met N He].
Kabalt-60 "oru regstre,·],.s \L'rkr) ,kur llell(n'nlH'~tr,dlllg ,an kl>iJalh:hlorit'd. Tot 300 mC 60Ca
word op een 51ag lH'w,·rk.
Sl':\['\r\ln"
Reactor-produced cobalt-58, by th,' Tca('tirm • ":><i(n,p)' 'Cn and cohalt·60, by 5 9Cu(n,y) 6 DCa
were used to prepare tracer "nlutinn~ of K,.c"W"I. for bydrological ~tud;es. Cobalt-58 was separated by an;on-l'xchange r{'~m \~itlt ~I" liel and ..I lit. oJ "Ith ~ lIn. ('obalt-6U was obtained by
direct neutron irra(liatlon of cobalt chloT1<te. Batchl'~ containing up to 301) me ··Co were handled.
I:\TIWDu(:no:,\
Aqueous lll'xacyanocobaltatl' (III) has bl'cn dcmun;.trated to be superior to
other cobalt complt'xcs for hydrological tl'~ts in 1iml'stone 1 and for use in measuring
the period of retention in percolating filtl·rs. 2, 3 ~rat''fial labelled with cobalt-60 was
used for hydrological tracing. but lwcaus(' its long half-life made subsequf'nt tests on
the same site open to doubt. the shortL'f lived 71-day cobaH-5!:l may sometimes be
preferred. This paper Lle~cribt:s tht: rrcparati(Jn of the traccr material labelled either
with cobalt-58 or with cubalt-fiO.
\Vhen used for hydrological studies, tIll' lll'xacyanocobaltate tracer solutions are
mixed with relatively large amounts (1f carrier, lkcau;,l' problems from too Iowa
specific activity are unlikely to ari~e. cobalt-60 could be prepared by the reaction
6 9Co(n,y} 6 0(0 by the (lirect irnvliatiun u [ a suitabll' cohal t salt in a reactor. Cobalt-58,
as prepared by thc reactiun oSNi(n,p) iiHCO, howcver, yields a high specific activity
(carrier-free) product. Tim!>, in this prucedure it was necessary to dllute the cobalt-58
with stable cobalt to obtain the required specific activity.
EXPEHL\IE:\T.\J.
Preparation ({lid irradiation oj Ilickel.-Nickd carbonate, low in iron and cobalt,
as supplied by The British Drug Housl's, LtLl" was u~ed to 1m'pare the target material.
The common impurities were iron (...H) p.p.m.), cobalt (<:20 p.p.m,) and zinc
«25 p.p.m.). Of these, the ml)~t ;,l'Tious was cobalt, which, on activation would produce cobalt-60 contaminatiun, and which th('rdore had to be removed before irradiatiun. Cobalt-60 tracer was usnl tu check the efficiency of this proce;,s.
>I<
Present address: Southern L'niversities Kudear Institute, Faure, South Africa.
2
JOERNAAL VAN DIE SUID-AFRIKAANSE CI-IEMIESE INSTrrUUT
1965, Deel XVIII
The nickel carbonate was dissolved in hydrochloric acid and the acid concentration adjusted to 9N. A small amount of cobalt-GO solution was added as tracer and the
solution passed through a column of Amberlite Il{A-400, 30 cm in length and 2'S cm
in diameter, when all the cobalt activity was retained in the top centimeter. 4. 5 Nickel.
free from cobalt, was precipitated from the eluate with cobalt-free sodium carbonate.
Weighed amounts of the washed and dried precipitate were sealed in quarlz vials for
irradiation in aluminium cans placed in a dummy fuel element of the reactor core
of IRR-l.
The separation of cobalt-S8.-The nickel carbonate was irradiated, and left for
about a week to allow short-lived products, such as 2'5-hour 65Ni and IS-hour HNa
produced in the aluminium can by the reaction 2 7Al(n,a) 2 4Na, to decay. The ampoule
was then smashed, and the powder dissolved in hydrochloric acid to give a solution 9N
with respect to acid.
Radiocobalt was separated from the irradiated nickel in two stages. In this way
the volumes eluted could be kept manageably small. Firstly. the solution was passed
through the same column as used for purification, where most of the nickel was
recovered. Secondly, the radiocobalt, with some Ilickel eluted from the first column.
was passed through a smaller column of Amberlite 1RA-400, 10 em in length and
1 crn in diameter, to remove all remaining nickel salts. A typical elution curve for
the first stage is shown in Fig. 1 where the 3G-hour 57Ni, produced by the reaction
5SNi(n,2n) 57Ni, served as a tracer for nickel.
I
I
I
Co"
200000
100000 I-
50 000 l-
~
Nr
1
20 DaO
c!
E
~ 10000 t:::-
r-
~
,::
5000
t-
2000
1000
500
::-
-
t-I
100
9N Hel
200
300
--NHCL
~o
a
FIG. 1-Typical elution curve for the prelimmary separation of cobalt-58 from nickel.
1965, Vol.XVIII
3
JOURNAL OF TI-lE SOUTH AFRICAN CI-lEMICAL INSTI'rUTE
The cobalt-58 eluate was concentrated, its activity measured and cobalt chloride
added to obtain the required specific activity. The solution was then evaporated just
to dryness to remove the excess acid and the residue taken up in water slightly acidified with hydrochloric acid for conversion to potassium hexacyanocobaltate(III).
The yield of cobalt-58 obtained at IRR-l corresponded to a saturation activity
of 103 mC per g nickel at a fiux of 10 13 neutrons/cm 2 sec. This is compared with
corresponding irradiations elsewhere in Table 1.
TARLE I
YIeld uf cubalt-58 normalised to saturation activity for 1 g nickel
irradiated at a flHX of 10 13 I1wtwns/CIn ~sec
____~_I
Reference
Mellish and Payne·
Yjeld~
[mC~
Remarks
.~~-----------------~
89.8
85.2
82.6
85'0
Levin and Bochkarev'
37'5
Shikata, Shikata and Shibata 8
44'3
73'3
Harwe 11 Hollow uranium bar
Thermal flux 1·4 x ] () 1 'n/em ~sec
1·2xl0 12
]·0 x 10 12
JRR-I Hole 2
JRR-I Hole 1
This work
103
IRR-I Position 46
Calculated
197'3
206'7
cr = 105 mb· (fission
0"=111 mb lG
~pcctrum
neutrons)
Preparation and irradiation of cobalt.--Cobalt metal was not convenient as a
target material because it required relatively harsh conditions for its dissolution.
Similarly, cobalt oxide would have to be dissolved in acid, excess of which was
detrimental at later stages of processing. Cobalt chloride, being readily soluble in
water, is suitable as a target, but its water of crystallisation has to be removed to
prevent pressure building up from radiolysis.
Cobalt chloride, containing small amounts of impurities such as iron «30 p.p.m.),
nickel «12 p.p.m.) and zinc «50 p.p.m.), was dried, weighed and sealed in quartz
vials for irradiation. The vial was kept for the short-lived radionuclides, notably
3 BCI and 2 'Na, to decay and then smashed, the cobalt chloride dissolved in water
and the solution, acidified with a few drops of hydrochloric acid, was used for conversion to potassium hE'xacyanocobaltate(III).
Self-absorption in cobalt chloride.-Because both cobalt and chlorine have
relatively high thermal neutron capture cross sections, It was expected that the
activity obtained from irradiated cobalt chloride would be lower than calculated
because of neutron self-absorption within the sample. Fig. 2 shows the activity of a
10 g sample contained in a cylindrical vial of diameter d plotted as a function of d and
calculated relative to the hypothetical case where no self-absorption exists.
4
]OERNAAL VAN DIE SlJlD-AFRIKAANSE CHEMIV:SI;. INsTlTlJl'T
1965, J)"l XI'III
-l
JOo'/,
90'/,
.!.
A,
eo'/,
70'1.
10
15
20
25
30
35
~o
45
~t
5;;
Dtameter of cyll ....der (mm.)
FIG. 2-Self-ahsorption in cobalt chlonde. The df'pl'llrknce of the rclath'e activity produced in
a lO-g sample contaIn{'d ]il a cylllldncal vial, on the dlamct~r of tht' viaL
At the reactor core position where the samples ,wrE' irradiated there was an
appreciable variation of flux with height, so that it was undesirable to irradiat(' a long
sample. Rather than to minimise self-absorptiun, the self-abs(Jrption of tht> "ampl!' wa,;
calculated 11 and the irradiation duration increaseu accurdingly.
Preparation of potassium hexacyanocobaltate(III). ·The solution of radiocubalt,
as 58CO or 60eo, was treatcu with a slight {'xc('~s of pota:osium cyanide solution and
the resulting buff precipitate of cubaltuus eyanidt', which grauual1Y darkened to
yeI1o\\'-brown, filtered off and thoroughly wa~hl'd ,\ ith \yater. It was then stirred with
a 10% excess of 37% w/v aqueous potassium cyanid(', A greenish precipitate, probably
K2COLCO(C~)6~' formed but it ,vas readily cOTIVt'rted to a deep yellOW solution of
Ka~eo(CN)6J by the addition of hydrogen peroxiut' at H)(,m temperature in neutral
solution, or without the hydrogen peroxide by llfating to abuut 7OCC.
Gamma ray meaSl,rements showed that the cobaltcfjS contained !Pss than 0'1 %
of cohalt-60, whilst no impurity could be dct('cted in the cobalt-oO. Thf' ;J('tivities of
the preparations wpre calibrated by cumparison with standards and by ionisation
chamber measurements. ~onnally, batches containing- about 100 mC cobalt-60 were
processed, but when 300 mC Were n'cluircu, samph s were irrJ.(liateti to a somewhat
higher specific activity and di[utpd with non-radioactiw ht'xucyanocobaltate as
required.
Two tests were carried out to dctermim' cationie cobalt. In the ol1l', cobalt was
precipitated with carrier cobalt as sulphide and tht' activity ITlC'asured; in the ;,('ctln<l,
the solution was pass{'d through a cation-PAcharlgf' column ;l1ul the activily ri'tailll'd
on the column measnred, ,\11 ~amplc>s wen' a~say('cl to be lwtt!'f than 99%.
DISn'S~r():\"
The yield of cobalt-58. ·Although the r<'actiun 5~Xi(n,p) ~8(O is !'x()I'T~ic
(Q:...;; +0'39MeY), the high coulomb barrier rais('s the effecti\'(' thrC'slI()]ll nE'utron
1965. Vo/.XVIII
JOURNAL OF THE SOUTH AFRICA;';: CHEMICAL I:-<STlTUTE
5
enprgy to about 1·5 Me\'. The yield calculated from the effective cross section fur
fission spectrum nC'utrons, 9, 1 () (Table 1) is very much higher than that obtained,
showing that the energy distribution in the irradiation neutron flux differed apprecia bly from that in fission. Tlw extt'nt of modl'ration of the neutron flux can be seen
by comparing the mt'ast1l"l,d and calculated yidds, but the result is qualitative rather
than quantitati \"(' without COrTf'sponding mea"uremen ts with threshold detectors at
higlwf neutnHl cTll'rgies. The relatiwly high yield obtained at IRR-l (<;ee Table 1)
showed that the l'xtt'nt uf moderation was 11'5;-' than dsewherf' and confirmed that tIll'
irradiation !>ik was "uitl'd for radioisotope produetion with fast neutrons.
R(ldinrhrmical purity of the products. -In the case of cobalt-60, the nuclear
reactions ~9(o(n,p) 59Fe and 59(0(n,2n) 58(0 will lead to contamination by iron-59
and cobalt-58. Using the accepted value for the reaction cross sections for fission
spectrum neutrons 9 and allowing for the contribution of thennal neutrons, the iron-59
was calculated to contribute 1·7 X 10- 2 % of the activity of the samples. Because the
threshold for the formation of cobalt-58 is so high, about 10·2 MeV, the probable
contribution of cobalt-58 was calculated to be less than 4 X 10- 4 %. Radioactivation
of Impurities wuuld contribute less than 10- I ~~ of the activity. Such low levels of
impurity would be difficult to detect and the level would fall still fUrther during the
course of the investigation, because their half-lives are less than that of cobalt-60.
Accordingly, the cobalt-60 was accepted as radioC'hemically pure.
In the case of cobalt-58, the more important impurities were removed during
pUrification and could not lead to radioactive contaminants. The main nuclear reaction
leadillg to radiocontarnill<Llioll is 6 (}Ni(n,p) 60CO which would produce cobalt-oO
activity of about 2·8 X 10- 2 ~ ~ and this impurity would not be chemically separable.
Moreover, because of its longer life, the relative contribution of cobalt-60 would
increase with the age of the preparation and the duration of the experiment. Accordingly, this limits the purity of cobalt-58. Other nuclear reactions such as 5 BNi(n,a) 55Fe
and £ 2~i(n,a) 59Fe produce radio-iron which would not follow cobalt through the
chemical processing.
Israel Atomic Energy Commission,
P.O. Yavne, Israel.
Received July 14th, 1964.
]{EFERENCES
1
E. \. Hal,...·\", \. NiT, Y. Harpa7. and S. Mandel, Proc. L'S. Inti'Yn. Cunf. Peaceful Uses At.
JiNL'iI?Y, 2;jd Gen,','u, 1!-158 1'11613.
E. Edl'll and!\: V. !\Il'lb()urtll', in/all ). Appl. Radwlwn Isotopes, l!-lGll, 8,172.
a E. Halevyantl A. ;"lr. J (;c"phys Nt's., l!-l62. 67, 2403.
~ :.i". \'. Slugwick, Th,. Ch">lIeul t-IClJl, fit' and Th"17 C'lfnpouHds, VoL 11, Clar('nuon Press,
•
(~
Oxford, 1950 .
E. -l\loOtl' ~m,1 K. _\. Kraus, /_ .~iIl. Chou. Soc, 1952,74,843.
E. ~It'llish an,l J .\. rayne, ,Vatw·c. 1\'l58, 178, 275.
I. Ll'vin ann V. V. Hochkart'v, C.A , HI62, 56, 11145 .
Sbikata, E. Shlkata and N. Shibata,) .. ~I. Hncrgy Soc japaH. Hl62, 4,105.
• J. C. Roy and J. J. Ha"ton .. ~I . .Enev::;v Can Ld., 1960, AECL-1181.
10 J. F. Barry, Reactor SClewe a11d Technology, J. Nucl. cneYfiV
PI A <Old B, 1962. 16.467.
11 J. {~11at and Y. Gnrfinkl'l, .\'WiC<>H/CS, 1963, 21, 1'\0. R, 143.
• (~.
• C.
7 V
• C.