Sentec GmbH - Strahlenmesssysteme

                  Nukleare Messtechnik

Qualität und Erfahrung seit über 20 Jahren!


High Temperature Measuring Device

with NaI(Tl)-Detectors

Gamma-Energy range 0.1 - 7 MeV


- Qualified according to the German KTA3505 

- Separation of detector and preamplifier

- Logic signal & Analog signal

- Discriminator 

- Long term temperature range up to 75oC

- Short term temperature range up to 125oC

- Humidity up to 100% with dewing

- Vibration/Shock proofed

- Driver for signal transmission up to 400 meters

- Internal stabilisation against voltage drifts

- Warranty for operation in extreme conditions

by special selected components

- Direct connection to secondary electronics for pulse





"N-16"-measuring for leakage monitoring along the steam-

pipes of nuclear power plants for low to high energy gam-

mas (<2,5 MeV) from N-16.

Countrate measurements and spectroscopy at high temperatures e.g. in geological survey (drill hole measurements etc.).



The system NaI175A is typically used in regions with elevated temperatures. By spacial separation from detector head the preamplifier electronics is protected from damages caused by excessive temperature in the detection area.

Highly qualified components allow higher temperatures

compared to comparable instruments.

The compact design of the detector head and the transmission of the signals over distancess up to 400 m makes the system ideal for installations at inaccessible regions, at hot and contaminated areas.

The resulting signals are directly transmitted to succeeding

electronics (e.g. for shutdown at elevated radioactive levels), for countrate measurements or spectroscopy.


The system NaI175A consists of

detector DN175A,

preamplfier VN175A,

system cable SC175A.


Principle of Measurement:

The detector head consists of a ruggedized NaI(Tl)-scintillation crystal in combination with a extremely ruggedized photomultiplier tube and a voltage divider.

The preamplifier comprises the amplification and pulse shaping circuit, a discriminator stage an internal voltage supply and a driver stage.


By interaction of gamma rays with the thallium atoms of the crystal photons with wavelengths around 0.4 μm are emitted from the photomultiplier tube in a number proportional to the energy of the deposit gamma quant.

The photons are amplified by the dynode stage by a factor of 106 to 108 and transmitted accross the system cable to the preamplifier circuit for shaping..



Technical Data


Input high voltage/supply voltage

High voltage/maximum:              1400 V negative

High voltage/operating voltage:  factory set

Power consumption/maximum:  0.55 W at 1400 V

Power consumption/typical:        2*1.44 W

Preamplifier supply voltage:       typ. + 18 V/80 mA

Socket:                                       Fischer DBEE 105 A 096-11



Output/Logic signal

Amplitude:                     5.0 + 0.5 V in 75 Ohm 

Pulsewidth:                    500 + 200 ns (FWHM) 

Risetime:                       5-100 ns (10% - 90%) 

Pulseshape:                   rectangular 

Polarity:                         negative (opt. positive) 

Impedance:                   75 + 10 Ohm  

Socket:                          Fischer DBEE 105 A 005-11 



Output/Analog signal

Amplitude:                     0 - 5.0 V 

Pulsewidth:                    4 + 0.5 μs (FWHM) 

Risetime:                       100-700 ns (10% - 90%)

Pulseshape:                   Gaussian

Polarity:                         negative (opt. positive) 

Impedance:                   75 Ohm  

Socket:                          Fischer DBEE 103 A 002-11




Conversionfactor:          2.35 + 0.2 mV/keV

Lower Discriminator:     40 - 1000 mV negative

                                        factory set on request



Operation conditions

Long term temperature range                  10 - 75oC

Short term temperature range                75 - 125oC

Temperature gradient for detector           ≤ 4 degree/min.

Pressure resistance                                 0.7 - 1.3 * 105 Pa

Long term humidity                                  95% without dewing

Short term humidity                                 100% with dewing                       

Background countrate (at 0,1 μSv/h) < 50 cps



Frequency range 5 to 35 Hz:  6g, 1 oct/min.

35 to 100 Hz: 12g, 10 oct/min.




30g, 11ms for all components of the system



Magnetic Shielding

Influence of the earth magnetic field is negligible for all directions


Radioscreening                                     acc. VDE 0847


Electrical protection                              IP 65 acc. DIN 40050



Mechanical Assembly

(housing from stainless steel)


- Detectorhead DN175A with

NaI Crystal Bicron type 1F2-X special selected

Photomultiplier Hamamatsu type R1288-01 special selected

Length:                          276 mm

Maximum diameter:        49 mm

Weigth:                          about 1.4 kg


- System cable SC175A

(connection detector - preamplifier)

Length:                          4-8 m


- Preamplifier VN175A with


Pulse shaping electronics,

Internal generation of supply power,

Driver stage

Length:                          250 mm

Max. diameter:               94 mm

Weight:                          about 2.5 kg



Possible connections to secondary electronics

(not part of the system; test cables optional)


Signal cable

(Connection signal output - secondary electronics)

Cable:                            shielded coaxial cable

Mantle diameter:            9.1-10.5 mm

Max. length:                   400 m

Impedance:                    75 Ohm

Connector at preamplifier: Fischer SE 105 A 005-11


Supply cable

(Connection supply input - secondary electronics)

Cable:                            8 wire cable with 1 shielded coax and 7 trip lines

Mantle diameter:            9.1-10.5 mm

Max. length:                   400 m

Connector at preamplifier: Fischer SE 105 A 096-12



Test cable PK1

(Connection signal output - test devices)

Cable:                            BNC coaxial cable 75 Ohm

Mantle diameter:            9.1-10.5 mm

Max. length:                   10 m

Connector: Fischer SE 105 A 005-11 to BNC



Test cable PK2

(Connection Test output - MCA)

Cable:                            BNC-Coaxial cable 75 Ohm

Mantle diameter:            9.1-10.5 mm

Max. length:                   10 m

Connector: Fischer SE 103 A002-11 to BNC



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