Fluke 943-35 User Manual

Victoreen®

943-35, 943-36

943-36H, 943-37

March 2005
Manual No. 943-35-1 Rev. 2
©2004, 2005 Fluke Corporation, All rights reserved. Printed in U.S.A.
All product names are trademarks of their respective companies

943-237A

Gamma Scintillation Detector

Operators Manual

Fluke Biomedical

Radiation Management Services

6045 Cochran Road
Cleveland, Ohio 44139

440.498.2564

www.flukebiomedical.com/rms

Table of Contents

Section 1: Introduction................................................................................................ 1-1

1.1 General Description ..................................................................................... 1-1

1.2 Application ................................................................................................... 1-1

1.3 Detector Variations ...................................................................................... 1-1

1.4 Specifications............................................................................................... 1-2

1.5 Functional Description ................................................................................. 1-4

1.6 Receiving Inspection.................................................................................... 1-5

1.7 Storage ........................................................................................................ 1-5

1.8 Procedures, Warnings, and Cautions .......................................................... 1-5

Section 2: Operation.................................................................................................... 2-1

2.1 Installation.................................................................................................... 2-1

Section 3: Theory of Operation................................................................................... 3-1

3.1 Introduction .................................................................................................. 3-1

Section 4: Maintenance, Calibrations, and Troubleshooting................................... 4-1

4.1 Maintenance ................................................................................................ 4-1

4.2 Calibration.................................................................................................... 4-3

4.3 Troubleshooting ........................................................................................... 4-4

Appendix A: Applicable Drawings and Bill of Materials ............................................... A-1

A.1 Applicable Drawings ....................................................................................A-1

A.2 Applicable Bill of Materials ........................................................................... A-1

i

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Introduction

General Description

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

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.

Scintillation Detector Consists of an integral 1.5 inch diameter by 1.0 inch thick

1-1

Victoreen 942-35,943-36,943-36H, 943-37,943-237A

Operators Manual

Model 943-36

The 943-36 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 aluminum crystal housing protrudes through the process end of the detector for maximum
efficiency. The detector is normally used for monitoring of radioactive iodine, or in liquid process monitors,
where the detector is protected from the process by a stainless steel well that is part of the detector shield
assembly. The well is provided separately.

Model 943-36H

The 943-36H is similar in construction to the 943-36, and is modified to operate at process temperatures
of up to 160°F with less than a 10% decrease in output at low photon energies (below 662 keV), and less
than a 5% decrease in output at high energies (662 keV and above). This detector is recommended for
use in applications where the process temperature is above 120°F.

Model 943-37

The 943-37 Gamma Scintillation Detector consists of an integral 2.0 inch diameter by 2.0 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 2 inch crystal provides more sensitivity to both ambient and process
radiation than the 943-35 or 943-36 detectors, and is used in applications where low ambient background
radiation is anticipated.

Model 943-237

The 943-237A Americium Detector contains a small capsule of Americium 241, which is inserted in the
sodium iodine (Nal) crystal. The function of the Americium is to provide a high-energy pulse output for
regulation of the high voltage power supply under conditions where fluctuations in the process
temperature are expected, or where pulse height spectrometry is desired. The americium-doped
detectors are designed to be used in conjunction with the 960AM series Americium Regulator Module or
the 942-200-90 SCA/Americium Regulator board for dynamic regulation of the detector high voltage.

Americium 241 is selected as the source of calibrating energy for the regulated detector, because the
equivalent energy level of the pulse (approximately 5.4 MeV) is relatively distant from that of the isotopes
normally being monitored.

1.4 Specifications

The 943 series Gamma Scintillation Detectors have been assembled with parts selected for the high
reliability required in nuclear applications. Unauthorized repairs made to the detector will void the
warranty and may affect the nuclear qualification. The detectors should be returned to Fluke Biomedical
for authorized, qualified (ANSI 45.2.6, Skill Level II) service or repair.

The following detector models are no longer
manufactured, and may be replaced as shown
below.

Obsolete Model Description Replacement

943-38 2 x 2 in crystal, carbon steel housing 943-37

943-238A 2 x 2 in crystal, carbon steel housing, with Americium 943-237A

NOTE

1-2

Detector

Dimensions 943-35: 9.5 x 2.5 in (24.1 x 6.4 cm)
943-36, 943-36H: 9.5 x 2.5 in (24.1 x 6.4 cm)
943-37, 943-237A: 10.5 x 2.5 in (26.7 x 6.4 cm)

Weight Approximately 3 lbs (1.4 kg)

Housing Material Stainless Steel

End Window Material 943-36, 943-36H: Aluminum

943-35,943-37, 943-237A: Stainless Steel

Photomultiplier Tube 2 inch photocathode, 10-stage, integral crystal

Crystal Size 943-35, 36, 36H: 1.5 in diameter x 1 in thick

943-37,943-237A: 2 in diameter x 2 in thick

Crystal Material 943-3X: Sodium Iodine (Nal)
943-23X: Sodium Iodine (Nal) with Americium

Power Requirement +1000 VDC @ 500, +15 VDC @ 15 mA,

-15 VDC @ 50 mA

Introduction

Specifications

1

Connector MS3106E 2427B (supplied with detector)

Detector Cable Length 8 feet (2.4 meters) (supplied with detector)

Cable Type 50-111: (two 50 ohm coax and two #18 AWG)

Interconnecting Cable 50-100: (one 50 ohm coax, one 75 ohm coax, two #18 AWG, four #18

AWG twisted pairs)

Operating Temperature 32° to 122°F (0° to 50°C), (160°F for 943-36H)

Storage Temperature 32° to 122°F (0° to 50°C), (160°F for 943-36H)

Relative Humidity 0 to 95% non-condensing

Maximum Pressure 15 psig (without well)

Preamplifier

Rise Time < 250 ns

Input Impedance > 50 kilo ohms

Output Coupling AC

Voltage Gain 6.1 V/V

Configuration Voltage Sensitive

Current Polarity Negative

Output Impedance 50 Ohms

Maximum Cable Length 1500 Feet

Max. Pulse Amplitude @ -6 VDC
Max. Cable Length

1-3