Kerma (physics)

Kerma is a physical quantity in radiation physics . The term is an abbreviation for the words Kinetic Energy released per unit mass or Kinetic Energy released in matter . The Kerma is based on secondary particles transferred to the first generation of kinetic energy E _kin divided by the irradiated mass m :

${\displaystyle K={\frac {\mathrm {d} E_{\mathrm {kin} }}{\mathrm {d} m}}={\frac {1}{\rho }}\ {\frac {\mathrm {d} E_{\mathrm {kin} }}{\mathrm {d} V}}}$

The kerma always depends on the irradiated medium. It is only calculated or measured for indirect ionizing radiation (neutrons, photons) and describes how much energy is transferred to matter in a mass element. Secondary particles in photon interaction are secondary electrons. In the secondary electron equilibrium, the absolute value is the same as that of the absorbed dose , since as much energy is introduced as is removed. In the case of low-energy radiation, as can be found in radiological diagnostics, the absorbed dose therefore corresponds approximately to the kerma.

In the case of higher-energy radiation, such as that used in radiation therapy, the kerma is considerably higher than the absorbed dose, since high-energy electrons and bremsstrahlung can leave the volume element without interacting. This part of the radiation that leaves the volume is added to the kerma, but not to the absorbed dose.

unit

The SI unit of the kerma is the gray (Gy), in other words joule / kilogram .

Kerma performance

The Kerma performance is the differential quotient of the Kerma over time.

${\displaystyle {\dot {K}}\ =\ {\frac {\mathrm {d} K}{\mathrm {d} t}}\ }$

The SI unit is gray / second or watt / kilogram .

See also

• Radiation dose

swell

• H. Warrior. Radiation Physics, Dosimetry and Radiation Protection, Volume 2 3rd, revised edition, Stuttgart, Leipzig, Wiesbaden 2001, ISBN 3-519-23078-X
• W. Schlegel, J. Bille (Eds.). Medical Physics 2 - Medical Radiation Physics Berlin, Heidelberg, New York 2002, ISBN 3-540-65254-X
• DIN 6814-8 Terms in radiological technology - Part 8: Radiation therapy , December 2000

Individual evidence

1. ↑ Stefan Scheidegger: Fundamentals of radiation physics and dosimetry . Ed .: Stefan Scheidegger. 1st edition. Stefan Scheidegger, Paul Scherrer Institute, Villigen 2002, p. 24-25 .