Fluke Biomedical 943-35 - Manual (Page 5)

Introduction
General Description
1
1-1
Section 1
Introduction
1.1 General Description
The 943 series Gamma Scintillation Detectors consist of an integral gamma sensitive Nal crystal, a photo
multiplier tube, a preamplifier assembly, and various interconnecting cables for connecting the detector,
readout, and power supply. Refer to Figure 1-1 for a general view or to Appendix A for each specific
detector. All are functionally identical. The size of the crystal employed, the housing material, and whether
or not an Americium source is included in the assembly are the only differences. All photomultiplier
tube/crystal assemblies are an integral line construction.
The 943 series Gamma Scintillation Detectors are designed to be sensitive to gamma radiation. The
Gamma Scintillation material photomultiplier tube and preamplifier are contained within a cylindrical
housing. This assembly provides protection from the environment, and provides a mechanism for
installation without damaging the detector assembly.
When gamma or x-rays enter the scintillation crystal, pulses of light are emitted. The light pulses striking
the photocathode of the photomultiplier tube excites the electrons in the cathode to a high-energy state
causing them to escape from the surface of the cathode. The freed electrons are attracted by a voltage
potential to the first dynode of the photomultiplier tube. This starts a cascading effect where a charge is
passed from dynode to dynode increasing in size at each stage until a shower of electrons is passed on
to the preamplifier.
The preamplifier provides pulse conditioning and cable driving capabilities to match the input
characteristics of the Victoreen Universal Digital Ratemeter or the 960 Digital Radiation Monitoring
System (DRMS), used to monitor the detector output. The detector is supplied with an 8-foot coaxial cable
that normally terminates in a junction box supplied as a part of a complete monitoring channel.
1.2 Applications
The 943 series Gamma Scintillation Detectors may be used with Victoreen digital ratemeters or with the
960 Digital Radiation Monitoring System (DRMS). Ratemeters are used in systems where individual
control room readouts are employed, while the 960 DRMS is used when a complete digital system is
supplied.
1.3 Detector Variations
Model 943-35
The 943-35 Gamma Scintillation Detector Consists of an integral 1.5 inch diameter by 1.0 inch thick
sodium iodine (Nal) crystal/photomultiplier tube assembly and preamplifier, enclosed in a stainless steel
housing. The stainless steel housing completely encloses the scintillator and is used where direct contact
with the process is required. The response of the detector is slightly less than the 943-36 detector, due to
the 0.045 inch thick housing.