Fluke Biomedical 30-471 - Manual (Page 10)

Nuclear Associates 30-471
Operators Manual
2-2
2.2 Photon Detectors
These detectors are used in the measurement of radiation in the range of 1 MV to 25 MV. They are
available with a negative or positive output. They have been color coded for ease of identification.
Following is a list of the detectors, polarity, color codes, and range.
Model Number Range Polarity Color
30-471 1-4 MV Photon Positive Blue
30-471-8000 1-4 MV Photon Negative Blue
30-472 5-11 MV Photon Positive Yellow
30-472-8000 5-11 MV Photon Negative Yellow
30-473 12-17 MV Photon Positive Red
30-473-8000 12-17 MV Photon Negative Red
30-474 18-25 MV Photon Positive Green
30-474-8000 18-25 MV Photon Negative Green
30-475 5-25 MeV Electron Positive Gray
30-475-8000 5-25 MeV Electron Negative Gray
Build-up shields are utilized in their design to provide equilibrium and filtering of low energy radiation.
These build-up shields also increase the detector's stability along with increasing the sensitivity in their
respective ranges. The output of a typical detector is 1.2 nano coulombs/RAD (1.2 nC/cGy).
The semiconducting material in these diodes is planar and the diodes as a whole is hemispherical in
shape, thus they have a preferred direction. Following are typical angular dependence of these photon
detectors.
Angular Dependence
1-4 MV Diodes
The following figures show the results for incident angles rotation along the diode cable axis and along
the axis perpendicular to diode cable axis. For angle deflections less than 50 degrees from the diodes
preferred direction, 180 degrees, the diode output changed by less than 1%.
Gantry angle (degree with 180 being vertical)
Diode (type 471 [1–4 MV rated]) output vs. incident angle;
symmetric setup in 6 MV photons
Diode out
p
ut (n
ormalized
to
180°)