Biomedical Engineering Reference
In-Depth Information
Fig. 13.4
Direct and indirect action of
radiation. Double-helical array of dots
represents positions of bases and sugars on a
200-Å straight segment of double-stranded
DNA. The other dots show the positions of
reactants formed in neighboring water from
10
-11
sto3
×
10
-8
s after passage of a 5-keV
electron perpendicular to the page in a straight
line 50 Å from the center of the helix. In
addition to any direct action (i.e., quantum
transitions) produced in the DNA by passage
of the electron, indirect action also occurs later
when the reactants diffuse to the DNA and
react with it. Reactants can also disappear by
scavenging in this example, crudely simulating
a cellular environment. See text. (Courtesy
H. A. Wright and R. N. Hamm, Oak Ridge
National Laboratory, operated by Martin
Marietta Energy Systems, Inc., for the
Department of Energy.)
in a cellular environment. Thus, reactants disappear at a much faster rate here than
in the previous examples for pure water.
Depending on the dose, kind of radiation, and observed endpoint, the biologi-
cal effects of radiation can differ widely. Some occur relatively rapidly while others
may take years to become evident. Table 13.1 includes a summary of the time scale
for some important biological effects caused by ionizing radiation. Probably by
