Design of an $X$-band electron linear accelerator dedicated to decentralized ${}^{99}\mathrm{Mo}/{}^{99m}\mathrm{Tc}$ supply: From beam energy selection to yield estimation

The most frequently used radionuclide in diagnostic nuclear medicine, ${}^{99m}\mathrm{Tc}$, is generally obtained by the decay of its parent radionuclide, ${}^{99}\mathrm{Mo}$. Recently, concerns have been raised over shortages of ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$, owing to aging of the research reactors which have been supplying practically all of the global demand for ${}^{99}\mathrm{Mo}$ in a centralized fashion. In an effort to prevent such ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$ supply disruption and, furthermore, to ameliorate the underlying instability of the centralized ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$ supply chain, we designed an $X$-band electron linear accelerator which can be distributed over multiple regions, whereby ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$ can be supplied with improved accessibility. The electron beam energy was designed to be 35 MeV, at which an average beam power of 9.1 kW was calculated by the following beam dynamics analysis. Subsequent radioactivity modeling suggests that 11 of the designed electron linear accelerators can realize self-sufficiency of ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$ in Japan.

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Figure 1

Operation periods and global ${}^{99}\mathrm{Mo}$ production capacities of large-scale research reactors.

Figure 2

Schematic representation of the $X$-band electron linear accelerator. The abbreviations are explained in Table 1.

Figure 3

Solid line, associated with the left $y\text{-axis}$: microscopic cross section of ${}^{100}\mathrm{Mo}(\gamma ,n){}^{99}\mathrm{Mo}$. Lines with points, associated with the right $y\text{-axis}$: bremsstrahlung fluences simulated at different electron ($e$) beam energies.

Figure 4

${}^{99}\mathrm{Mo}$ activity calculated from Eq. (5) at different irradiation times, varying with electron beam energy.

Figure 5

(a) ${}^{99}\mathrm{Mo}$ activity calculated from Eq. (5), varying with electron beam energy and ${}^{\text{enr}}\mathrm{Mo}$ target irradiation time; and (b) its two-dimensional projection. The contour lines begin at $0.25\mathrm{GBq}{\mu \mathrm{A}}^{-1}$ from the bottom and are spaced by $0.25\mathrm{GBq}{\mu \mathrm{A}}^{-1}$.

Figure 6

superfish-calculated effective shunt impedance per unit length as a function of accelerating cavity gap length.

Figure 7

Accelerating cavity of the SCS. ${\beta }_b=1$ is the beam velocity normalized to the speed of light $c$; other parameters are given in Table 5.

Figure 8

rf-to-beam power efficiency as a function of accelerator structure length.

Figure 9

Accelerating voltage and beam current in the SCSs given by Eq. (6).

Figure 10

Beam energy and current at the beam exit $z=5\mathrm{m}$ obtained from gpt; $i_b$, beam intensity per keV; $E_{e,\text{min}}$ and $E_{e,\text{max}}$, the lowest and highest beam energies, respectively; $E_{e,\text{peak}}$, the beam energy at which $i_b$ is the largest.

Figure 11

Beam size in (upper) $xz$- and (lower) $yz$-planes.

Figure 12

(a) Modeled activities of photonuclear-produced ${}^{99}\mathrm{Mo}$ and (b) its ${}^{99m}\mathrm{Tc}$ eluates.

Figure 13

Comprehensive view of the modeled activities of photonuclear-produced ${}^{99}\mathrm{Mo}{/}^{99m}\mathrm{Tc}$.