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Re: Lead aprons in nuclear medicine

Karin Gordon wrote:

> Murphy et al concluded that the photon-attenuating properties were quite adequate
> (attenuation  >88%) for x-rays up to about 120 kVp.  However, for the 140 keV gamma rays
> from Tc-99m, the attenuation of the 0.5 mm "lead-equivalent" aprons is in the range of
> 35 - 40 %, compared to 70 - 78% for the conventional 0.5 mm lead apron.  A 140 keV gamma
> ray is ROUGHLY equivalent to a 280 kVp  x-ray, much higher than the diagnostic x-ray
> range for which the lead composite "lite" aprons are designed. 

If a "standard" lead apron is 96%* efficient for x-rays, then a "lite"
apron allows twice the amount of radiation through, i.e., the dose to
the individual wearing a lite apron doubles.  One should look at
transmission because comparisons of attenuation can be deceiving -- lite
apron salespersons say that there is only 6% (or 4% or 2%) difference
between those old fashion, heavy, uncomfortable standard lead aprons and
their new, improved, lightweight aprons, when the transmission is 200%
of the conventional lead.

Note that transmission nominally doubles for the 140 keV gamma between
lightweight and conventional lead aprons.

*I don't know this attenuation to be true (it's probably pretty close
for scatter, but low for primary radiation), but I use it only to
illustrate the point.

Kent N. Lambert, CHP