[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
radiation is radiation
Well Norm, here's how it works when radiation is radiation. What we are
saying is that there is more than one way to get from point a to point
b. Say that the distance is 100 miles. You can either drive 25 miles
an hour and get there in 4 hours, 50 mph and get there in 2 hours, or
100 mph and get there in 1 hour. In each case you travel 100 miles.
Now think of each mph as a different type of radiation. Think of the
time as a quality of radiation or in radiobiological terms, RBE or
relative biological effectiveness. Another term for RBE is quality
factor. It tells you how much more effective a particular type of
radiation is in producing a specific effect compared to a standard type
of radiation. In order to determine 1 rem you multiply the number of
rads, here the mph, by the quality factor, the time in the above
example. Now it the number of rems is 100 in the above example, there
are several ways to get there. The QF or RBE is related to the amount
of energy deposited per path length.
Now as for the differences between Sr-90 and I-131. Yes they are
deposited in different parts of the body. But as radiation biologists
have determined from animal experiments, irradiation to small local
parts of the body do not due as much damage as whole body irradiation at
the same dose. That is why cancer treatment can give high doses of say
Co-60 gamma irradiation to a tumor. If the same dose were given to the
whole body the person would die. This is the whole basis for radiation
therapy.
The "laws" governing radiation sensitivity were first stated by two
French scientists in, I believe it was, 1916. Radiobiologists have
refined these laws since then but they stand basically the same. So if
different radionuclides (by the way, not radionucleotides, nucleotides
are a whole different ball game) wind up in different parts of the body
we account for that by assigning different parts of the body different
weighting factors (WF) based on that part's probable susceptibility to
cancer, where, again the WF is based on a long history of
radiobiological evidence.
Kjell Johansen
Milwaukee, WI
kajohans@powercom.net
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html