Question

1. Describe LET and RBE. What is the relationship between them? (2 points)
2. If the exposure rate to an individual standing 4.0m from a source of radiation is 30Sv/min, what will be the dose received after 2 minutes at a distance of 5m from the source? (1 point)

Answer 1

(A) LTE: linear energy transfer is the amount of energy that an ionizing particle transfers to the material traversed per unit distance. It is the energy transferred per unit length of a track (keV/um).

RBE: It can vary with cell line studied. Different cell types can vary in their ability to repair damage from X-rays which will affect RBE. The effect for densely ionizing radiation is less variable.

LET and RBE increase slowly at first then rapidly between 10 & 100 keV/um. 100 keV/um is maximum then RBE begins to fall.

(B)Use inverse-square law of radiation

30/x = 25/16;

x = 19.2 Sv/min

Thus, x = 19.2 Sv in one minute, therefore, 34.8 Sv in 2 minutes.