Production of 57Co, 109Cd, 111In and 117mSn using CV-28 cyclotron at IPEN-CNEN/SP

Abstract

Several radioisotopes produced in Cyclotrons have physical properties of decay suitable to be used as: radiopharmaceuticals, for in vivo Diagnosis images (with the techniques of SPET and PET, Single Photon Emission Tomography and Positron Emission Tomography, respectively) and for Therapy, in Nuclear Medicine; calibration sources of several instruments applied in the nuclear area and in Metrology; and as radioactive tracers of elements investigated in many fields, such as Chemistry, Physics and Biology. This work describes the production of four of these radioisotopes that are very important in these areas: 57Co, 109Cd, 111ln and 117mSn. They can be obtained using the CV-28 Cyclotron at IPEN, because it can accelerate proton beams with energies up to 24MeV and currents up to 20μA (external). 57Co (t1/2=271.3 d) decays by electron capture to 57Fe with the emission of γ-rays and one characteristic X-ray. It is widely used as calibration source of detectors such as: Ge(Li), Ge(HP), Nal(TI) and dose calibrators (well type detectors). Besides these applications, 57Co Flood Sources are used to test the response uniformity of gamma cameras, in Nuclear Medicine. 109Cd has a half-life of 462.6 d and decays by electron capture to 109Ag with the emission of one γ-ray and one characteristic X-ray. This radioisotope can be employed as calibration source of X-ray and γ-rays detectors; as a radioactive tracer of Cd, an environment pollutant and used in the EDXRF (Energy Dispersion X-Ray Fluorescence) technique. 57Co was produced through the irradiation of natNi. Thick target yields for 55Co, 56Co, 57Co, 58CO, 56Ni and 57Ni were measured and the mean values were 346.69kBq/μA.h (9.37μCi/μA.h), for the direct production of 57Co and 150.59kBq/μA.h (4.07μCi/μA.h), through the decay of 57Ni (11.31 days after EOB - End of Bombardment). A solution of 57CoCl2 was prepared, to fill a flood source for calibration of gamma camera, with activity of 222MBq (6mCi) of 57Co and impurity levels of 1.13 and 1.29% for 56Co and 58Co, respectively, at delivery time. In order to achieve these results, a chemical separation method was developed with a separation yield of 93% for 5'7Co and a negligible loss of Ni. A composite target of Ni and Ag was prepared and a chemical separation method proposed to allow the separation between the targets and the products of interest, 57Co and 109Cd. The yields obtained in the irradiation of the composite target were: 947.94kBq/μA.h (25.62μCi/μA.h) of 57Co - direct reaction, 259-00kBq/μA.h (7μCi/μA.h) of 57Co - indirect reaction (11.31 days after EOB) and 71.41kBq/μA.h (1.93μCi/μA.h) of 109Cd, which showed the efficiency of its use, as well as the chemical separation, with a yield of 80% for 57Co and 109Cd. 111ln (t1/2=67.5 h) has appropriate characteristics for Diagnosis in Nuclear Medicine due to its decay mode (100% by electron capture) and its adequate half-life to slow biological studies, that makes it one of radioisotopes of interest of Brazilian Physicians. It can also be used in angular correlation studies in Nuclear Physics. 111In was produced by the 112Cd(p,2n)111ln reaction, that has the highest yield. The Cd targets were prepared by electroplating of CdSO4 solution in copper and copper/nickel backings. After being irradiated, a chemical separation was performed by an acetic acid extraction method, with an overall recovery yield for 111ln higher than 95%. The level of the chemical impurities of Cd, Ni and Cu were bellow than the permissible values. 117mSn (t1/2=14 d) has suitable characteristics of decay to be used as a tracer of SnCl2 in the labeling of organic molecules with 99mTc and also in radiotherapeutical applications. It was prepared by the irradiation of natural tin through the nuclear reactions natSn(p,xn)117Sb→117mSn. The production thick target yield of 117mSnnn was 784.4kBq/μA.h (21.20μCi/μA.h) and with the proper decay time of its precursor, 117Sb, no radionuclidic impurities appeared in the final product. A chemical separation method was developed to separate first 117Sb from the irradiated Tin and then 117mSn from Sb with a good chemical yield. The quality control procedures showed the good quality of the final product, 117mSn.