Fluke Biomedical TNT 12000 - Manual (Page 96)

TNT 12000
Users Manual
A-2
Window Density .................................................... 91 mg/ cm
2
Active Window Area ............................................. 100 cm
2
, centered within the chamber body
Connector .............................................................. Side-mounted triaxial two-lug BNC connector
Collector Plate....................................................... Centrally mounted collector is a 0.8 mm thick graphite-coated acrylic
plate, 10.80 cm in diameter. Thirty-five, 6.4 mm diameter holes are
drilled through the plate. A 2.16 x 2.85 cm guard region is electrically
isolated from the collector area.
Foam Supports...................................................... Two, 1.30 x 1.30 x 0.94 cm pieces of Styrofoam DB are used to
support the collector plate and provide mechanical stability.
Electrical Specifications
Sheet Resistivity ................................................... All areas sprayed with graphite conductive coating measure less than
6 k/square but greater than 3 k_/square.
Leakage Current.................................................... With 300 volt bias in effect and 0.1 volt potential imposed between the
guard and collector, at 20 ° C and 50 % relative humidity, the leakage
current is < 10 fA within 60 seconds of applying the voltage. The
leakage under the above bias conditions is < 100 fA within 60 seconds
of applying the voltage over both the full operating temperature range
of 8 – 38
° C and for 20 – 80 % relative humidity, but only for conditions
in which the absolute humidity is _ 20 g/m
3
(the equivalent R.H. is
75 % at 25 ° C, 60 % at 30 ° C, and 50 % at 35 ° C).
Radiological Specifications
Energy Range........................................................ 30 to 150 kVp
Nominal Sensitivity............................................... H60:
2.08 x 10 7 R/C ( 1.82 x 10 5 Gy/C ) at 22 ° C and 1013 hPa
DV70: 2.12 x 10 7 R/C ( 1.86 x 10 5 Gy/C ) at 20 ° C and 1013 hPa
DH70: 2.07 x 10 7 R/C ( 1.81 x 10 5 Gy/C ) at 20 ° C and 1013 hPa
Multiply values by 0.00876 to convert from R to Gy.
Sensitivity Range .................................................. Sensitivity range is ± 5 % of nominal
Reference Point..................................................... The reference point of measurement for the chamber is 1.05 cm
directly below the center of the top of the entrance window. This
corresponds to the center of the active region.
Incident Beam Direction....................................... A small sticker with the word "FOCUS" is secured to the top, entrance
window of the chamber. The reference direction of incident radiation is
perpendicular to this surface.
Angular Dependence ............................................ The ion chamber response to radiation incidence variations up to ± 5 °
of normal is within ± 1 % of the response to incident radiation striking
perpendicular to the entrance window surface.
Ion Transit Time .................................................... Maximum of 1.0 ms in the center of the chamber at STP with a bias
voltage of 300 volts.
Collection Efficiency............................................. The collection efficiency for both continuous intensity and 120 Hz half
wave rectified intensity is theoretically calculated using Boag's
equations. An ionization potential of 300 V is used in both cases. An
effective plate separation distance of 0.8 cm was determined
experimentally and used to generate the curves in Figure A-2.