Speaker
Description
Technetium-99 is a long-lived fission product (LLFP) which undergoes $\gamma$-decay with a half-life of 211,100 years. This long-lived nature and relative abundance of production (approximately 6% of fission events produce $^{99}$Tc) and environmental mobility makes long term waste storage challeng-ing. As such it is a possible candidate for being reduced via nuclear transmutation. The $^{99}$Tc(n, γ)$^{100}$Tc produces $^{100}$Tc which undergoes $\gamma$-decay to the stable $^{100}$Ru with a half-life of 15.46 min. To design systems that could drive these reactions, more accurate neutron capture cross-section data is required. There are large differences between experimental data of the neutron capture cross-sections, especially in the keV neutron energy range [1][2][3][4]. This motivated the present measurement of the neutron capture cross-sections of $^{99}$Tc.
The experiment was conducted at the Accurate Neutron-Nucleus Reaction measurement In-strument (ANNRI) beamline at the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC). Capture $\gamma$-rays from neutron capture events were measured using a NaI(Tl) detector placed at a 90 degree angle to the neutron beam axis. The total mass of the 99Tc sample was 78 mg with a diameter of 6.3 mm and an activity of 1.4 mCi at time of preparation and was contained in an aluminum sample case. The sample was placed at a neutron flight distance of 27.9 m and capture $\gamma$-rays were measured from thermal to the keV energy range. The time-of-flight (TOF) method was employed to determine the incident neutron energy. The incident neutron spectrum was determined by placing a sample of boron enriched with 10B at the sample position and detecting 478-keV γ-rays from the $^{10}$B(n,γ)$^{7}$Li reaction. A blank run, a dummy case and a carbon sam-ple were also measured for the purposes of background subtraction. From this raw TOF spectrum the neutron capture yield was calculated using the pulse height weighting technique. Self-shielding and multiple scattering were accounted for using PHITS simulation code. The neutron capture-cross section of $^{99}$Tc from the thermal to keV energy region were derived. This presentation will compare present results with past data and provide a discussion.
References:
[1] G. Noguere et al. Phys. Rev. C, 102, 015807 (2020).
[2] N. Iwamoto Journal of Nuc. Sci. and Tech., Vol. 49, No. 2 (2012).
[3] D. Rochman et al. Nuc. Sci. and Eng., 158, 68-77 (2008).
[4] N. Iwamoto et al. EPJ Web of Conferences, 146, 02049 (2017).
