Biomedical Engineering Reference
In-Depth Information
Fig. 10.22
Silicon diode electronic dosimeter. See text for
description. (Courtesy MGP Instruments, Inc.)
The sensitive lung counter in Fig. 10.26 employs three coaxial HPGe crystal
detectors. It is specially designed to measure the relatively low-energy (15 keV-
400 keV) gamma and X rays emitted by uranium and other actinides in the lung
(e.g.,
241
Am,
239
Pu,
238
Pu,
237
Np). If there is insoluable material in the organ, it is
not amenable to bioassay monitoring. External measurements to identify the weak
photons in the presence of background entail considerable technical challenges.
The counter is calibrated with torso phantoms, employing a series of chest-wall
plates, like the one shown in the figure. Calibration phantoms, having differing
thicknesses of overlay and fat-to-muscle ratios are used to better represent a wide
