Isotopic production of ⁹⁹Tc via proton- and deuteron-induced reactions and new analytical model for its longitudinal momentum distribution

The disposal of spent fuels from nuclear power plants is a worldwide problem. The high-level radioactive wastes are the residual of spent fuels, which contain minor actinides and fission products. To evaluate the reaction cross sections of the long-lived fission products, we have systematically measured the p- and d-induced cross sections for ⁹⁰Sr, ¹³⁷Cs [1], ⁹³Zr [2], ¹⁰⁷Pd [3], etc. As a next step, we started a study on ⁹⁹Tc (T_1/2 = 2.1×10⁵ y). Tc is the element with atomic number 43 and has no stable isotopes.

The experiment was performed at the RIBF. A secondary beam including ⁹⁹Tc was produced by the in-flight fission of ²³⁸U at 345 MeV/nucleon on a 3-mm-thick ⁹Be target, selected and identified event-by-event using the TOF-Bρ-∆E method. It also included ^99mTc (T_1/2 = 6 h), which is indistinguishable by the method. Cocktail beams of ⁹⁹Tc and ^99mTc at 114 MeV/nucleon were bombarded on CH₂, CD₂, and C reaction targets. Backgrounds of carbon from CH₂ and CD₂ targets and beam-line materials were subtracted by using the C and empty target runs.

For estimating the yield of residual nuclei, a new analytical model was developed to fully reproduce the longitudinal momentum distribution. The asymmetry of the distribution was evaluated quantitatively. In this talk, we will show the model and report the obtained isotopic production cross sections.

[1] H. Wang et al., Phys. Lett. B 754, 104 (2016).

[2] S. Kawase et al., Prog. Theor. Exp. Phys. 2017, 093D03 (2017).

[3] H. Wang et al., Prog. Theor. Exp. Phys. 2017, 021D01 (2017).