Thermo Scientific SAM12, Руководство пользователя

Страница: 29 / 176

Issue: 1.0 Specification
Thermo Fisher Scientific SAM12 User Manual 3-3
the SAM12 detects a stable background (see Changes to the
Normal Background Monitoring (page 5-49) ).
When the mandatory 100 second background count has been
accumulated, the monitoring time required to achieve the
specified alarm level is calculated. Providing the monitoring
time calculated falls within the maximum and minimum limits
(see
Params 2 (page 5-10) ), the instrument will be ready for
monitoring. If, however, the monitoring time calculated is
greater than the maximum allowed, a “high background”
condition exists and monitoring will be inhibited.
A high background condition indicates that the alarm level set
and statistical certainties required are not achievable, under the
current background conditions. This may be overcome when
either the background falls or more suitable operational
parameters are entered by the Health Physicist. It is advisable
to check for residual contamination if this occurs unexpectedly
or persists.
The lower the background field the more sensitive, stable and
accurate the measurements will be.
Detectors
Type: 5569A
Construction:
Large area scintillation counter using a plastic
phosphor type BC408 wrapped in foil, plastic and a
aluminium jacket.
Thickness: 2.25" (57 mm)
Area: 15" (381 mm) x 15" (381 mm) = 225"sq (145,161
mm
2
)
Photomultiplier: 1" (25 mm) extended cathode
Shielding:
1" (25 mm) or 2" (50" mm) of aged lead on all
external faces
Energy
Response 20 keV upwards (minimum detectable depends on
liner material)
Operating voltages should normally be set up using the NBR
method, although they may also be set up using the Figure of
merit (S
2
/B shown in figure 9.1) to yield the operating
Photomultiplier voltages. These settings are determined and set
using the HV Scan feature (Calibration|HV Scan (see
HV Scan
(page 5-25) ). The recommended values, based on the NBR
optimization method, can be found in the Calibration certificate
for each individual instrument.
This can have all thresholds adjustable under software control:-
Programmable Threshold 1 0 - 4095mV in 1 mV steps
Programmable Threshold 2 0 - 4095mV in 1 mV steps
Four or Six Detectors
Detector HV settings
Energy Window