7 To further observe the rays he positioned a screen in front of the tube.He began placing various objectsbetween the screen and the tube thatwas emitting the X-rays.
8 He discovered that the rays or “invisible light” passed right through pieces ofblack paper and thin sheets ofaluminum and copper but that the lightdid not pass through blocks of lead andhis bones, and instead these objectscasted shadows on the screen.
9 Roentgen’s Wife’s Hand X-ray of a colleagues hand after presenting the“new ray” to the Physics – Medical Association1st X-ray?Roentgen’s Wife’s Hand
10 X-Ray-Tube The main parts of the x-ray tube are Cathode/filament Typical electron current is A for short exposures (< 100 ms)Anode/targetGlass/metal envelopeAccelerating voltageTypical voltage is kVp
16 Bremsstrahlung x-rays produce a continuous spectrum of radiation, up to a maximum energy determined by the maximum kinetic energy of the incident electron.The closer the electron passes to the nucleus, the greater the interaction of the incident electron with the nucleus, and the higher the energy of the resulting x-ray.
17 The energy of the x-rays varies from zero to the maximum kinetic energy ofthe electron (x-ray tube kVp).The probability of bremsstrahlung goesas Z2, hence high Z targets are moreeffective than low Z
18 Maximum photon energies correspond to minimum x-ray wavelengths. -The majority of x-rays produced in x-ray tubes are via the bremsstrahlung process.-Bremsstrahlung x-ray production increases with the accelerating voltage (kV) and the atomic number (Z) of the anode.
20 Characteristic radiation Characteristic radiation is the result of ionization and is produced when inner-shell electrons of the anode target are ejected by the incident electrons.-To eject a bound atomic electron, the incident electron must have energy greater than the binding energy.
24 Characteristic x-rays occur only at discrete energy levels, unlike the continuous energy spectrum of bremsstrahlung.-Each anode material emits characteristic x-rays of a given energy, as listed in Table 2.1.
26 K-shell characteristic x-ray energies are always slightly lower than the K-shell binding energy. (Table 1.4 lists K-shell binding energies).-K-shell electrons are ejected only if incident electrons have energies greater than the K-shell binding energy.-For tungsten, K-shell characteristic x-rays are only produced when the applied voltage exceeds 69.5 kV (K-shell binding energy is 69.5 keV).
28 For molybdenum, K-shell characteristic x-rays are only produced when the applied voltage exceeds 20 kV.-L-shell radiation also accompanies K-shell radiation, but because L-shell characteristic x-rays have very low energies, they are absorbed by the glass of the x-ray tube.-Only K-shell characteristic x-rays are important in diagnostic radiology.