A solid scintillator in an embodiment includes a polycrystal body of an oxide having a garnet structure. In the solid scintillator, a linear transmittance at a wavelength of 680 nm is 10% or more. The oxide constituting the solid scintillator has a composition represented by, for Example, General formula: (Gd 1-±-²-³ Tb ± Lu ² Ce ³ ) 3 (Al 1-x Ga x ) a O b , wherein 0 <; ± ‰¤ 0.55, 0 <; ² ‰¤ 0.55, 0.0001 ‰¤ ³ ‰¤ 0.1, ± + ² + ³ <; 1,0 <; x <; 1,4.8 ‰¤ a ‰¤ 5.2, 11.6 ‰¤ b ‰¤ 12.4.