- radiation reaction
- radiation resistance
- radiation scattering
- radiation shielding
- radiation thermocouple
- radiation treatment
- radiation zone
- radiation-resistant
- radiationless
- radiationless transition
- radiative absorption
- radiative excitation
- radiative reaction
- radiative recombination
- radiator
- radiator grouping
- radiator hose
- radio attenuation
- radio communication
- radio control
- radio isotope
- radio luminescence
- radio mirage
- radio navigation
- radio paging
- radio scattering
- radio sextant
- radio star
- radio transformer
- radio wave
- radioactive aerosol
- radioactive ash
- radioactive effluent
- radioactive radiation
- radioactive tracer
- radioactivity
- radioactivity detection
- radioactivity prospecting
- radioastronomy
- radiobeacon
- radiobeam
- radiobiology
- radiobroadcasting
- radiocarbon
- radiocarbon age
- radiochemical
- radioecho
- radiogalaxy
- radiogenic
- radiogram
- radiography
- radiolocation
- radiolocator
- radiolysis
- radiometric
- radiometric pressure
- radiometric prospecting
- radiometry
- radioopacity
- radiopaque
- radiophysics
- radioresistance
- radioscopy
- radiotelegram
- radiotelegraphy
- railcar refrigeration
- radiophone
- radiotherapeutics
- radiothorium
- radiotube
- radius-vector
- radix
- radome
- rain gauge
- ram air
- ramp
- range delay
- range finding
- range probe
- rapidity
- rate
- rate receiver
- rated value
- ratio controller
- ratio resistor
- rational
- ray acoustics
- raying
- rayleigh balance
- rayleigh loop
- rayleigh scattering
- react
- reaction
- reactivation cycle
- reactive component
- reactive load
- reactive power
- reading
- reading instrument
- ram effect