The recoil angular distribution of __Sc nuclei
Dougherty, Robert Worden, Jr
Class, C. M.
Master of Arts
The recoil of radioactive 41Sc nuclei, produced by the 40Ca(d,n)41Sc reaction, has been investigated in preparation for a measurement of the magnetic moment of the ground state of the 41Sc nucleus [Emax(?) = 5.5 MeV, T1/2 = 0.6 sec.]. The measurement will employ nuclear magnetic resonance in a method that utilizes the anisotropy in the decay of 41Sc nuclei, polarized in the (d,n) stripping-reaction process and emplanted in a suitable material by recoil. The present experimental work includes a study of the production and recoil of 41Sc with the purpose of determining the optimum condition, with respect to beam energy and laboratory angle, under which the recoil yield is a maximum. The total cross section for the production of 41Sc by the 40Ca + d reaction was measured from threshold (1.2 MeV) to 4.0 MeV bombarding energy, and was found to vary from 2 millibarns at 2 MeV to 18 millibarns at 4 MeV. In an analysis of the composite decay-curve of the total target radiation, it was determined that the positron from the decay of 41Sc comprised about 60 to 70 % of the total yield, with the positron decay of 38K made by the competing (d,cc) reaction the principle interference. The effects of multiple scattering on the recoil angular distribution of 41Sc ions were studied using the 40 Ca (?)41Sc reaction at 4.0 MeV. Results indicated that for fresh targets ? 10 vg/cm2 in thickness, the recoil distribution was only moderately altered from that determined by the kinematics of the reaction. However, scattering produced by thicker targets, or those substantially oxidized or otherwise contaminated, was found to be excessive. The angular distribution of 41Sc recoils produced by the 40Ca(d,n)41Sc reaction was measured at 4.0 MeV over an angular range from 0 to 45 degrees, using a thin target 6 pg/cm2 thick and 50 % oxidized. The recoil differential cross section was found to vary between 5 and 12 millibarns per steradian, and to extend past the origional kinematic limit of 36 degrees to about 60 degrees. The shape of this distribution was found to agree quantitatively with a predicted distribution calculated by application of multiple-scattering theory to previously measured cross sections of the neutrons produced in conjunction with the 41Sc recoils in the (d,n) reaction.