Thick target yield

The relevant nuclear reaction for tellurium is primarily Sb-121(p,4n)Te-118 with some contribution from the (p,6n) reaction on Sb-123 (42.7% abundance). The nuclear excitation functions for these reactions have not been measured. A series of stacked foil irradiations is planned to determine thin target cross sections. This will allow selection of optimal bombardment parameters for thick target irradiation at the BLIP. A calculated excitation function for the (p,4n) reaction is shown in Figure 8. This calculation is based on the interpolation method of Munzel et al. (11) and should allow prediction of thick target yields to within a factor of 2 or 3. 

Nuclear reaction Optimal energy range (MeV) Thick target yields at EOB (MBq/pAh) Major impurities at EOB %)... 

An alternative method of studying [py) resonance curves, which is sometimes useful, is based on observation of positron activity of the residual nucleus, e.g. in the reactions [py) and Mg [py) Absolute thick target yields may be more easily obtained by this method, and it is also useful for weak resonances since the efficiency of positron detection is high. 

The thick target yield over the optimum energy range for the production of each radionuclide was calculated using the known excitation function. In the case of and... 

Suitable energy range Thick target yield of Impurity [%J ... 

Among the four main production routes listed in O Table 42.2, the 0(p,n) F nuclear process on highly enriched H2 0 is the most effective. This process and the alternative route via 0( He,n) F leads to F-fluoride ([ F]Faq ) suitable for nucleophilic substitutions in high specific activities. To recycle and thus to minimize the quantities of enriched H2 0 to be used and to eliminate cationic impurities from the target material, [ F]Faq is trapped after irradiation on suitable anion exchange resins (Schlyer et al. 1990 Jewett 1991 Hamacher et al. 1990) and subsequently eluted. [ F]p2, the corresponding primary species for electrophilic fluorination, can only be obtained in lower specific activities and lower thick target yields. For a detailed discussion about the production of F see Chap. 39 of this Volume. 

Perhaps the most useful cyclotron produced lead Isotope for tracer use In terms of half-life and decay characteristics Is 52 hour, lead-203. This Isotope has been prepared by deuteron Irradiation of thalllumToxide powder by Garrison and Hamilton (06) who report the thick target yield of 1.5 mlcrocurles per microampere hour of Irradiation (for short, 10 hour or less. Irradiations) when 19 Mev deuterons are used. The Isotopic ratio of lead-203 to other lead Isotopes produced Is 3. sl. Stable lead-204, produced by a (d,n) reaction is the principle other contaminant. 

I. J. Gruvermann and P. Kruger, "Cyclotron-Produced Carrier-Free Radioisotopes. Thick Target Yield Data and Carrier-Free Separation Procedures", Intern. J. Appl. Rad. and Isotopes 5, 21 (1959). 

Curves that give the thick target yield, i.e. the activity produced by a given nuclear reaction in a given thick target, as a function of the energy are sometimes also useful. When it is difficult to obtain thin targets of the elements of interest, these curves are more easily determined experimentally than the excitation functions. 

Fig. 11-26 Normalized thick target yield as a function of beam energy (51)...

Fig. 11-27 Thick target yield for various reactions with 1 min irradiations with 2-3.5 MeV tritons. The curve corresponding to oxygen is for AI2O2. those for gallium and arsenic are for GaAs (51)...

Fig. 11-28 Errors on E and x as a function of the particle energy (A,B) calculated for an estimated error of 0.5 jjm in the mechanical system (C,D) calculated for a total error of 5 % on the thick target yield for the matrix activation method (51)...

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