Electron-Target interaction steps

1. mA controls amount of electrical current to filament on cathode

2. Prep button spins a rotor and sends electricity to filament.

3. As long as prep button is held down, anode will spin.

4. Friction/resistance causes filament to heat up.

5. Electrons are subsequently boiled off of the filament at 2000*C (Thermionic Emission.)

6. “Space Charge Effect” tends to limit the amount of electrons escaping filament.

7. Both the filament and the anode are made of Tungsten.

8. Exposure switch is pressed, while still holding prep button.

9. KvP is applied across the cathode/anode

• 90 KvP = 90,000 voltage.
• Cathode becomes negative 90,000 volts and anode is pos. 90k.
• Cathode pushes electrons away, anode attracts them.
• ½ to ¾ inch space between anode and cathode.

10. 1 ampere = 1 coulomb = 6.3 x 10(18) electrons/sec

11. Only about 1% of the electrons reach the xray stage, other 99% dispersed as heat.

- Focal spot controls the clarity of an xray image

- Outer shell electrons of the anode are temporarily excited.

- As shells fall back into their orbit they produce infrared radiation (heat)

- Heat is directly related to both mA and KvP.

- Heat units are calculated as mAs x KvP.

Category: Radiology Notes