Journal of Nuclear and Radiochemical Sciences, Vol. 4, No. 1, pp. 1-3, 2003

ArticlesSequential Separation of 61Cu, 62,63Zn, 66,67,68Ga, 71,72As, and 73Se Produced
by Heavy Ion Activation on Cobalt Target
Dalia Nayak and Susanta Lahiri*
Chemical Sciences Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700 064, INDIA
Received: March 3, 2003; In Final Form: April 30, 2003
A thick cobalt foil has been irradiated consecutively with 16O, 7Li, and 12C beams to produce the ‘tracer packet’
containing carrier free radiotracers of Cu, Zn, Ga, Ge, As, and Se. The present work describes sequential separation of these product radionuclides by liquid-liquid extraction method.

1. Introduction
Recently, we have introduced the concept of “tracer packet”
and developed radiochemical heavy ion activation method forthe production of “tracer packet of micronutrient elements”,
e.g. Cu, Zn, Ga, Ge, As, and Se altogether by consecutive irradiation of a thick cobalt target with medium-energy 16O, 7Li,and 12C projectiles followed by chemical separation of bulk
cobalt from the carrier free products.1, 2 The importance of theproduction of tracer packet lies in the fact that the behaviour of
all the micronutrient elements can be studied simultaneously insome definite physical, chemical or biological systems.
However the use of multiple beam consecutively on a single
target has another aspect, i.e., number of carrier free radionuclides are produced in a single target which reduces or minimizes the following: i) radiation hazard, ii) time required forhandling of multiple targets, iii) chemical work up, etc.
All the essential elements discussed above have their own
importance in biological systems and environment individually. For example, zinc plays an important role in many
processes of metabolisms of living beings. 65Zn has been usedin food for the zinc bioaccumulation study.3 The contamination of arsenic, even in a minute scale in water or soil cancause serious impact on human health via the food chain. It isthus necessary to study the migration of arsenic either fromground water or from soil to the living systems. Radiotracer ofarsenic would be more effective in studying the migration orpresence of other elements in different media. Liquid waste
arising from the processing of 131I contains significant quantities of 75Se (T1/2 = 119.7 d) along with other radionuclides.
The presence of this radionuclide necessitates the long-term
storage of liquid waste prior to its disposal for the decay of75
Se. To minimize the storage time and to avoid consequences
arising from prolong storage, a simple method for selective
separation of selenium radionuclide is necessary. Moreover,selenium is also another important trace element in plant or
animal metabolism. 75Se has been used to analyse the foodquality in the Mediterranean crab Pachygrapsus marmolatus.4
Therefore, in the present work we have aimed to develop theradiochemical method for separation of individual elements
contained in the tracer packet solution by liquid-liquid extraction (LLX).
2. Experimental
2.1. Irradiation. Cobalt foil of thickness 17 mg/cm2 was*Corresponding author. E-mail: slahiri@hp1.saha.ernet.in. FAX:
0091-33-2337-4637.

subjected to irradiation with a collimated beam of 96 MeV
16 7+
O at BARC-TIFR Pelletron, Mumbai, India, with an average beam current of 300 nA for five hours. The total dose was4700 µC. Immediately after the irradiation with 16O, the projectile was switched to 48 MeV 7Li3+ of 100 nA beam current
and the same target was irradiated for ten hours with a total
dose 8000 µC. The time required to change the beam andbeam tuning was less than 30 min. The same target was again
irradiated (without removing the target from the irradiationchamber) with 84 MeV 12C6+ of 250 nA average beam current
for two hours with a total dose 1500 µC. The beam current
was measured by a Faraday cup situated at the end of the target
in conjunction with a current integrator. An electron suppresser was used to suppress the electrons at the Faraday cup.
The thick target was used with the idea that the incident
beam will traverse through the target, losing its energy gradually, and at different degraded energy different nuclear reactions will be favored, resulting isotopes of different elementsin the cobalt matrix. However, the thickness of the target waslower than that would be required for beam dumping, which
was checked by the software TRIM5 for all the projectiles.
Terminal voltage (12 MV) of the Pelletron was the deciding
factor for choosing the projectile energy. The basis of choicein the beam sequence was that the longer half-life radionuclides should be produced first. For example, the products ofCo( 16 O, xn) reaction have longer half-lives than those ofCo(7Li, xn) or Co(12C, xn) reaction. Similarly the products ofCo( 7 Li, xn) reaction have longer half-lives than those ofCo(12C, xn) reaction. After the third irradiation, cobalt target
was removed from the irradiation chamber cooled for fourhours and series of non-destructive gamma spectra were taken
in regular interval. The corresponding photopeaks as well as
decay profiles identified the product radionuclides.
An HPGe detector of 2.13 keV resolution at 1.33 MeV in
conjunction with a PC based MCA, PCA2 (OXFORD), wasused for γ spectrometric studies.
2.2. Chemical Procedure. The liquid cation exchanger, di(2-ethylhexyl) phosphoric acid (HDEHP), the liquid anion
exchanger, trioctylamine (TOA), and the neutral co-reagent,tributylphosphate (TBP), were procured from Merck. The
extractant solution of desired concentrations was prepared byadding calculated amount of HDEHP, TBP or TOA to cyclohexane. After taking non-destructive spectra, the cobalt foil
was dissolved in dilute HNO3. In order to study the behaviorof bulk cobalt radiometrically in the LLX system, 60Co wasspiked at the time of dissolution. After dissolution of thecobalt foil the solution was evaporated to dryness and taken in
0.1 M HNO3 medium.
In each step of the separation procedure, a few drops of the© 2003 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 05/29/2003

2J. Nucl. Radiochem. Sci., Vol. 4, No. 1, 2003

Nayak

active stock solution were vigorously shaken with equalvolume of the aqueous and organic solutions. The resulting
solution was then allowed to settle and after the disengagement
the separated phases were subjected to γ spectrometric studies.
3. Results and Discussion
Nondestructive spectrum of 16 O, 7 Li, and 12 C activatedcobalt target and analysis of decay pattern confirms the presence of 61Cu, 62,63Zn, 66,67,68Ga, 71,72As, and 73Se in the matrix.
To remove bulk cobalt from the solution, extractions werecarried out with varying concentrations of HDEHP and 25%
NH3 solution. It was found that at 1% HDEHP concentration,
the bulk cobalt was transferred into the organic phase quantitatively with some amount of carrier free 61Cu and 62,63Zn. The
extraction of cobalt from the aqueous phase may be due to theformation of the cationic ammine complex, which wasextracted by the cationic exchanger HDEHP. To prevent
copper and zinc extraction TBP was mixed with HDEHP.
Extractions with 1% HDEHP and 10% TBP mixture (v/v =3:7) removed 92% bulk cobalt from the aqueous phase in asingle run (Figure 1). Cu (20%) and Zn (13%) were also partly
extracted with bulk cobalt in this condition. Extractions forthree times in this condition removed almost all the bulk cobalt
into the organic phase leaving the carrier free product radionuclides in the aqueous phase.
The ammoniacal solution containing 6 1 , 6 2 Cu, 6 2 , 6 3 Zn,
66,67,68
Ga, 71,72As, and 73Se was shaked with 5% HDEHP. In thiscondition, 61,62Cu and 62,63Zn were extracted into the organic
phase leaving 66,67,68Ga, 71,72As, and 73Se in the aqueous phase.
This is due to the fact that copper and zinc form [Cu(NH3)4]2+and [Zn(NH3)4]2+, respectively, which in turn were extracted by
the organic reagent HDEHP. Cu and Zn were back-extractedusing 1 M HCl as an aqueous solution. Then Zn was extracted
by 0.1 M TOA keeping Cu in 1 M HCl solution. Extraction ofZn by TOA from HCl medium is attributed to the fact that inHCl medium zinc forms strong anionic complexes of the type[ZnCl 4 ] 2− which were taken up completely by the anionicexchanger (Separation factor, SZn/Cu = 1370). Zinc was backextracted using 0.1 M diethylenetriaminepentaacetic acid(DTPA) in 1 M NaOH.
The ammoniacal solution containing Ga, As, and Se was
evaporated to dryness to remove ammonia and then brought
into HCl medium. Gallium was extracted in the organic phaseat 6 M HCl and 10−3 M TOA concentration. 66,67,68Ga radionuclides were transferred into the organic phase leaving As andSe completely in the aqueous phase (SGa/Se = 13000, SGa/As =648000). The high extractability of carrier free gallium
radionuclides in a HCl medium might be explained by theformation of [GaCl4 ] − , which in turn was extracted by the100Extraction / %8060CoGaZnSeCuAs

40
2000246810Vol. of TBP in 10 mL
TBP + HDEHP mixture / mL
Figure 1. Extraction profile of tracer packet and bulk cobalt with
25% NH3 and varying proportion of 1% HDEHP and 10% TBP (v/v).

6anionic extractant TOA. Extracted Ga was back extracted
into the aqueous phase by using 0.1 M DTPA in 1 M NaOH.
Separation of As from Se was achieved when extracted with
10−2 M TOA and 8 M HCl. In this optimal condition, 60% ofselenium was extracted in the organic phase keeping arsenic in
the aqueous medium (SSe/As = 600). The reason might be due tothe fact that at a particular HCl concentration Se preferably
forms anionic complex [SeCl 6 ] 2 − and is extracted by theanionic extractant TOA.7 Distribution ratios at all optimal
conditions have been tabulated in Table 1.
Schematically Figure 2 describes the sequential separation
method of all these radionuclides.

Irradiated cobalt foil dissolved in dil HNO3 ,spiked with 60Co tracer

Evaporated to dryness andtaken in 0.1 M HNO3Extraction 25% N H 3 +Three times 1% HDEHP +10% TBP (3:7)

Aqueous Phase
Cu, Zn, Ga, As, Se
Extraction

25% N H 3 +5% HDEHP

Aqueous Phase
Ga, As, Se

Organic Phase
Cu, ZnBack
Extraction

Evaporated to dryness,taken in dil HCl medium
Extraction

Aqueous Phase
As, Se6 M HCl
10-3M TOA

1 M HCl

OrganicPhase
discard

AqueousPhase
Cu, Z n1 M HCl
10-1 M TOA

Extraction

Organic Phase
GaExtraction 8 M HCl
Back-extracted
Three times 10-2M TOA in 0.1 M DTPAin 1 M NaOH
AqueousPhase
AsOrganic Phase
CoOrganicPhase
Zn

AqueousPhase
Cu

Back-extracted
in 0.1 M DTPAin 1 M NaOH

OrganicPhase
SeFigure 2. Schematic diagram for the sequential separation of tracer
packet of essential nutrient elements.

Table 1: Distribution Ratios (D) of Co, Cu, Zn, Ga, As, andSe at Optimal Conditions
ExperimentalCondition

DCoDCu

DZn

DGa

DAs

DSe

25% NH3+
1% HDEHP+
10% TBP100.24

0.14

25% NH3+
5% HDEHP-132.360

2 × 10−4

6 M HCl
10−3 M TOA---

386

6 × 10−48 M HCl
10−2 M TOA----

1.3 × 10−3 0.81

1 M HCl
10−1 M TOA

-

0.07

100-

1.4 × 10−4 0.008 4.1 × 10−4

0.08 5.7 × 10−5-

0.03

-

Sequential Separation of 61Cu, 62,63Zn, 66,67,68Ga, 71,72As, and 73Se

Acknowledgements. The authors gratefully acknowledge
Pelletron operation staff of BARC-TIFR Pelletron, Mumbai
for their help and co-operation during this work. The authors
sincerely thank to Mr. Ajoy Das, Chemical Sciences Division,
Saha Institute of Nuclear Physics, Kolkata, for his help intarget preparation.
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