Ludlum Measurements 43-5, Manual

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Model 43-5 Alpha Scintillator
February 2021
page 1
1. GENERAL
The Model 43-5 Alpha Scintillator is a detector
(probe) designed for alpha radiation survey
when used with general purpose survey meters,
ratemeters, and scaler instruments. It utilizes a
zinc sulfide scintillation crystal doped with
silver [ZnS(Ag)] and a 3.8 cm (1.5 in.)
diameter magnetically shielded photomultiplier
tube (PMT).
The welded detector body is fabricated from
16-gauge (1/16 inch) aluminum alloy and
painted with a beige powder-coat finish. The
window protective screen is made of 0.13 cm
(0.05 in.) thick unpainted aluminum alloy, and
the window is aluminized metallized polyester,
typically 0.8 mg/cm
2
thick. When intended for
outdoor use, an extra layer of metallized
polyester is recommended (total of 1.2 mg/cm
2
thickness).
A plastic protective cover is provided for
protection of the detector face against puncture
of the metallized polyester when the detector is
not in use. Pinholes in the window will cause
light leaks and malfunction of the detector.
2. SPECIFICATIONS
WINDOW: typically 0.8 mg/cm
2
aluminized
metallized polyester (1.2 mg/cm
2
for outdoor
use)
WINDOW AREA: 52 cm
2
(8.1 in
2
) open, 79
cm
2
(12.2 in
2
) active
EFFICIENCY:
13% of 4

emission with
239
Pu source in contact with probe protective
screen
BACKGROUND: 3 cpm or less
SCINTILLATOR:
ZnS (Ag)
TUBE: 3.8 cm (1.5 in.) diameter
DYNODE STRING RESISTANCE: 100
megohm
OPERATING VOLTAGE: 500-1200
volts
CONNECTOR: Series “C” (others
available)
SIZE:
7.6 x 6.4 x 34.3 cm (3 x 2.5 x 13.5
in.) (H x W x L)
WEIGHT: 0.9 kg (2 lb)
3. MAINTENANCE
Normally, causes of malfunction of the Model
43-5 are due to either light holes in the thin
metallized polyester or a defective multiplier
tube. The malfunction caused by light holes
gives an increase in background noise up to
complete saturation where the instrument may
indicate zero count. If the instrument indicates
zero count, reduce the high voltage and cover
probe face with an opaque material. By
movement of the opaque material, a light leak
should be discernible.
3.1 Repair of Probe Face
To repair the face of the probe, perform the
following steps: (Refer to Drawing 77 x 23 for
assembly view.)