PRODUCTION AND APPLICATION - POSTERS P5-6 AN ALTERNATIVE METHOD FOR THE PRODUCTION OF THALLIUM RADIONUCLIDES
S. Lahiri1, D. Nayak1, A. Ramaswami2, and S. B. Manohar2 1Chemical Sciences Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700 064, India 2Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
Over the past 15 years numerous studies have established the use of 199,201Tl in the field of nuclear medicine. Thallium-201 is used for myocardial perfusion imaging and evaluation of coronary artery disease, while occasionally also 199Tl is used. Till date various methods have been proposed for the production of 201Tl/199Tl. It was first reported by Lebowitz et al.  through the reaction 203Tl(p, 3n)201Pb(EC)201Tl and worked out in detail by Lagunas-Solar et al. and Qaim et al [2,3]. Other routes of the production of thallium radionuclides are: 197Au(α, 2n)199Tl, 200Hg(p, n)200Tl, 200Hg(p, 2n) 199Tl, 200Hg(p, 3n)198Tl. The emission characteristics of 199Tl for imaging are not worse than those of 201Tl, but the associated equivalent dose is 10 times less per unit of activity in comparison with that of 201Tl. The purpose of this study is the evaluation of an alternative production route for 199Tl by heavy ion irradiation. In view of this a gold foil was irradiated with 7Li3+ beam at BARC-TIFR Pelletron, Mumbai, India. Thallium radionuclides were produced through the reaction 197Au(7Li, xn)199-201Pb(EC)199-201Tl(EC)199mHg ;(x = 3-5). To remove the impurity radionuclides 200,201Tl it is necessary to choose the optimal projectile energy. Gold foils were irradiated in stack foil technique to determine the optimal projectile energy in order to get the maximum 199Tl activity. It was found that at 49 MeV 7Li beam energy 199Pb has the highest production cross-section, while 200,201Pb have the lowest cross section. An attempt has been made for the separation of carrier-free 199Tl from bulk tantalum target using trioctylamine (TOA) as an extractant. The irradiated gold foil was dissolved in minimum quantity of aqua regia and was taken in 1M nitric acid medium. The gold fraction was separated from the carrier free products by extracting with 0.1 M TOA. It was found that at this condition, gold was quantitatively extracted by the liquid anion exchanger from the aqueous acid medium. Then the aqueous phase containing Pb, Tl and Hg radionuclides , was evaporated to dryness and taken in 3 M HCl medium. During evaporation Hg volatilises, leaving Pb and Tl in the aqueous phase. Thallium was extracted in the organic phase quantitatively by 10-3 M TOA and was re-extracted by 0.1 M EDTA at pH= 8.5.
References: 1. Lebowitz et al., J. Nucl. Med., 16, 151, (1975). 2. Lagunas-Solar et al., Int. J. Appl Radiat Isot., 29, 159, (1978). 3. Qaim et al., Int. J. Appl Radiat Isot., 30, 85, (1979).