Excitation function measurements and integral yields estimation for natZn(p,x) reactions at low energies
Introduction
Recently, the status of nuclear data for medical radioisotopes produced by accelerators has been reviewed by Gandarias-Cruz and Okamoto (1988), Qaim (2001), Qaim et al. (2002) and Takács et al. (2005). This summarizes available data on experimental measurements of cross-sections and thick target yields for medical radioisotopes of current interest besides the presentation of exhaustive reference material. The statues also shows that although many reactions were frequently studied in the past, especially in the above-mentioned energy range, results of new precise cross-sections certainly could be useful for some data bases even for the most commonly used radioisotopes including 67Ga, 111In, 123I and 201Tl.
The three radioisotopes 66Ga, 67Ga and 68Ga are well known and widely used in the field of nuclear medicine. 67Ga has become one of the most frequently employed cyclotron produced radioisotope over the last two decades (Ruth et al., 1989; Taylor and McCready, 1986) and is a widely used single photon marker for detecting the presence of malignancy and for diagnosis of inflammatory diseases (Hoffer, 1980; Noujaim et al., 1981). The positron emitter 68Ga, usually obtained through a 68Ge (t1/2=288 d)→68Ga generator, is employed at PET centers for blood–brain barrier investigations, in diagnostics of some tumor diseases of liver and other organs (Qaim, 1987) and for transmission measurements for encoding calibration and normalization of detector efficiencies of PET scanners. Recently, 66Ga was proposed for studying some slow dynamic processes by PET (Goethals et al., 1988). It is noticed that the use of natural zinc for practical purposes is very limited because of the lower yield and/or high contaminations.
This article reports on the cross-sections and production yields of 66Ga, 67Ga, 68Ga, 62Zn and 65Zn, which have been measured in our laboratory for the compilation of the existing data base. The cross-sections and the production yields are plotted in the energy range from 3.7 to 27.5 MeV to give the excitation functions and thick target yield functions for 66Ga, 67Ga, 68Ga, 62Zn and 65Zn in natural zinc. The results and the relevant errors are compared with the data published in the literature.
Section snippets
Experimental technique
The excitation functions of the natZn(p,x) reactions were measured by the well known stacked foil irradiation technique (Gul et al., 2001; IAEA TECDOC-1211). Targets were prepared via electrolytic deposition of natural zinc on commercially high purity natural Ni foils (99.9%) from Goodfellow Metals Ltd., UK. The stacks of thickness (12.6 μm) were used as targets (circular foils of 10 mm diameter). Natural Cu and Al foils of varying thickness were sometimes inserted into the stacks as energy
Results and discussions
The decay characteristics and half-live of the resulting isotopes are summarized in Table 1 with Q-values and threshold energies of the contributing reactions (Chu et al., 1999). The resulting reaction cross-sections with the corresponding proton energies are presented in Table 2.
Integral yields
The integral yields for the reactions leading to 67Ga, 66Ga, 68Ga, 62Zn and 65Zn were calculated during this work using the present measured excitation functions. The results are shown in Fig. 6. Although the production of 67Ga for medical uses is practically impossible from natural zinc target, the following remarks could be considered from the figure. The ratio of the produced 62Zn and 65Zn impurities with the required 67Ga isotope is small and they could be chemically separated. The isotopic
Conclusions
New cross-section data have been measured in the energy range from 3.7 to 27.5 MeV for five reaction products from the natZn(p,x) reactions. The selected cross-section data sets show very good agreement with most of the previous studies over the specified energy region, while some other data set could not be confirmed. 67Ga should be produced with high integral yield in the energy range between 15.0 and 27.5 MeV. The estimated integral yield according to the specified energy region was about (49
Acknowledgments
The authors would like to thank Dr. Al-Sudairy Sultan (Chairman of the KFSH Research Center) for providing us the opportunity to use the cyclotron facility for target irradiation. Also, thanks to the cyclotron staff, Eng. Miliebari Salman (Section Head) Eng. Rahma Salama and Eng. Al-Ghaith Ahmed, for their great help during the irradiation.
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