We present simple analytic solutions for the ionization rate \zeta _ { SLR } arising from the decay of short-lived radionuclides ( SLRs ) within protoplanetary disks . We solve the radiative transfer problem for the decay products within the disk , and thereby allow for the loss of radiation at low disk surface densities ; energy loss becomes important outside R \gtrsim 30 AU for typical disk masses M _ { g } = 0.04 M _ { \odot } . Previous studies of chemistry/physics in these disks have neglected the impact of ionization by SLRs , and often consider only cosmic rays ( CRs ) , because of the high CR-rate present in the ISM . However , recent work suggests that the flux of CRs present in the circumstellar environment could be substantially reduced by relatively modest stellar winds , resulting in severely modulated CR ionization rates , \zeta _ { CR } , equal to or substantially below that of SLRs ( \zeta _ { SLR } \lesssim 10 ^ { -18 } s ^ { -1 } ) . We compute the net ionizing particle fluxes and corresponding ionization rates as a function of position within the disk for a variety of disk models . The resulting expressions are especially simple for the case of vertically gaussian disks ( frequently assumed in the literature ) . Finally , we provide a power-law fit to the ionization rate in the midplane as a function of gas disk surface density and time . Depending on location in the disk , the ionization rates by SLRs are typically in the range \zeta _ { SLR } \sim ( 1 - 10 ) \times 10 ^ { -19 } s ^ { -1 } .