In case of electromagnetic radiation, constant parameter is:

Ans: d (Velocity) Ref:Resnick and Halliday Fundamentals of General physicsElectromagnetic radiation is the spectrum of waves propagated through space or matter by the oscillation of electric field and a magnetic field at right angle to one another.Waves travel perpendicular to both electric and magnetic field.They have a constant velocity of 3 x 10s m/s in vacuum.Remember the formula E= me2 where c is the constant velocity.Electromagnetic waves include radio waves, heat waves, light waves, UV waves, X-rays, gamma raysNote:X rays are produced from orbital electrons where as gamma rays are produced from the nucleus of an atomSource of radiation that cause heat cataract -infra red radiationPrinciple used in radiotherapy -ionization of moleculeFunctional basis of ionizing radiation -excitation of electrons from orbitIn therapeutic x rays - Compton effectIn diagnostic x-rays - photoelectric effectIn accidental x-ray work * pair productionDevices used in radiotherapyLinear accelerator- used to accelerate electrons and produce x-ray beamCyclotron- produces neutrons and photonsMicrotron- an electron accelerator, combines principles of linear accelerator and cyclotronBetatron- device for accelerating electrons used for production of electron beam for RT and an x-ray beamTypes of therapy:Superficial therapy - treated with x-rays produced at a energy ranging from 50- 150 kvOrthovoltage or deep therapy - treated with x-rays ranging from 150- 500 kvSuper voltage therapy - x-ray therapy in the range of 500 - 1000 kvOxygen enhancement ratio is maximum with neutrons