Fluke Biomedical 943-25 - Manual (Page 7)

Introduction
Functional Description
1
1-3
Beta particles that have enough energy to penetrate the end window and impinge upon the disc will
produce light pulses, proportional to the energy deposited in the disc. The disc is thin so that gamma rays
will not have a high incidence of interaction with the disc. This yields a high rejection of gamma rays while
still possessing good sensitivity to beta particles.
A photomultiplier tube, optically coupled to the scintillator disc, detects visible light emitted from the disc
and converts this light to pulses of electrical energy whose voltage is proportional to the energy deposited
by the beta particle. The electrical pulse is sent to a preamplifier in the detector housing.
The preamplifier circuit amplifies the pulses received from the photomultiplier tube/crystal assembly,
providing a fixed gain of six (6). The current drive output of the preamplifier circuit will drive a 50-ohm
transmission line up to 1500 feet without degradation of the signal.
Should a very high intensity beta source be detected, the photomultiplier tube may become saturated.
That is, visible light from successive photon collisions within the scintillation disc may occur so often that
they are essentially continuous. This would have the effect of holding the output voltage of the
preamplifier at a relatively constant output voltage. Since the readout is designed to count pulses that
represent individual beta particle collisions, a high intensity beta signal could be interpreted as a low or no
radiation condition. An anti-jam circuit must be provided in the ratemeter or scaler to which the detector is
connected to prevent misinterpretation of the existing radiation field.
1.5 Receiving Inspection
The single channel analyzer board can be supplied independently or as a component of a UDR. Once the
SCA board has been received, unpack it from the shipping carton and inspect for damage.
1.6 Storage
Storage of Victoreen instruments shall comply with level B storage requirements as outlined in ANSI
N45.2.2 (1972) Section 6.1.2(.2). The storage area shall comply with ANSI N45.2.2 (1972) Section 6.2
Storage Area, Paragraphs 6.2.1 through 6.2.5. Housekeeping shall conform to ANSI N45.2.3 (1972).
Level B components shall be stored within a fire resistant, tear resistant, weather tight, well-ventilated
building or equivalent enclosure.
Storage of Victoreen instruments must comply with the following considerations.
1.6.1 Control of Items in Storage
Inspection and examination of items in storage shall be in accordance with ANSI N45.2.2 (1972) Section
6.4.1. Requirements for proper storage shall be documented, and written procedures or instructions shall
be established.
1.6.2 In Case of Fire
Post-fire evaluation shall be in accordance with ANSI N45.2.2 (1972) Section 6.4.3.
1.6.3 Removal from Storage
Removal of items from storage shall be in accordance with ANSI N45.2.2 (1972) Sections 6.5 and 6.6.