LB 6411 Neutron Probe

Since the International Commission on Radiological Protection (ICRP) has issued in Publication 60 new recommendations on radiation protection quantities, there is increasing interest in commercially available instruments optimized and calibrated for the measurement of neutron ambient dose equivalent H*(10) (Conversion factors as published in ICRP74).

Therefore the neutron doserate meter LB 6411 was designed in a joint cooperation between BERTHOLD and the Research Center Karlsruhe. The detector system with integrated electronics has a patented He-3 proportional counter tube centered in a moderator sphere with diameter 250 mm. The geometrical arrangement was optimized with the help of extensive MCNP Monte-Carlo calculations and is patented too.

Tabs

Features

The instrument has an extremely high sensitivity of approximately 3 counts per nSv and can be used both as portable instrument or as a stationary monitor. Fluence responses have been measured in monoenergetic neutron beams at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany.

  • Calibrated to neutron ambient dose equivalent H*(10)
  • Neutron detection from thermal energies up to 20 MeV
  • Energy dependency ± 30% between 50 keV and 10 MeV
  • Extremely high sensitivity and therefore low measuring times in weak neutron fields
Details

The neutron doserate probe LB 6411 was designed in a joint cooperation between BERTHOLD and the Research Center Karlsruhe GmbH.

The LB 6411 probe consists of a polyethylene (PE) moderator sphere (diameter 250 mm) with a composite 3He recoil proton counter tube, the LB 6410, at its center. The probe also includes a high voltage supply and a preamplifier.

The geometrical arrangement of the detector, the moderator and the internal absorbers provides high sensitivity of approximately 3 counts per nSv together with an excellent energy dependent response of ±30% between 50 keV and 10 MeV which is more than 5 times better than obtainable from detectors of conventional design. The respective design was patented in 1997.

The response for gamma radiation is approx. 10-3 counts per nSv. This means a discrimination factor of 3 x 103.

The instrument is calibrated to bare 252Cf. For this spectrum it shows a fluence response of 1.09 cm² and a calibration factor of 1.27 μSv/h per cps. The response function over the whole energy range from thermal energies up to 20 MeV was carefully calculated with MCNP Monte-Carlo calculations. For several energies these results were cross-checked with monoenergetic neutron measurements performed at the PTB in Braunschweig.

The neutron dose rate probe LB 6411 can be used as a portable monitor LB 123 N, for direct connection to the LB 123 UMo, and as a stationary measuring instrument for connection to the dataloggers LB 112 or LB 111 Micro-Gamma.

Specifications

 

Neutron Monitoring Specifications
Measured quantity:Ambient dose equivalent H*(10) rate for neutrons in Sv/h according to ICRP60
Measuring range:30 nSv/h to 100 mSv/h
Neutron energy range:Thermal to 20 MeV
Calibration:bare Cf-252 spectrum
Fluence Response:1.09 cm²
Ambient dose equivalent H*(10) response:

2.83 counts per nSv or 0.79 cps per µSv/h

Calibration Factor:1.27 µSv/h per cps
Energy dependency:± 30 % between 50 keV and 10 MeV
γ-sensitivity:< 40 µSv/h in 10 mSv/h, Cs-137 gamma-field
Temperatur range:-10° C to 50° C

 

Moderator
External diameter:250 mm
Material:Low pressure polyethylene with 2 % carbon additive
Density:0.95 g/cm3
Weight:9.2 kg

 

Counter Tube LB 6410
External dimensions:Ø 40 mm x 100 mm
Material counter tube housing:Stainless steel 1 mm
Active length:~ 40 mm
Active volume:~ 45 cm³
Counting gas:He-3/Methane
Filling volume:He-3 60 µg (not subject to any export or import restrictions)
Operating voltage:2700 Volt
Detection efficiency for thermal neutrons:approx. 90 %
Background:< 0.02 cps
Dead-time:several µs

 

LB 6411-Pb for High Energies
For high energy applications at several hundred MeV or even higher there is a special verson with an external layer of 10 mm lead available. The response to high energy neutrons is enhanced by utilizing spallation neutrons, which are generated in the lead.

 

References and Patents

The neutron fluence and H*(10) response of the new LB 6411 remcounter
B. Burgkhardt, F. Fieg, A. Klett, A. Plewnia and B.R.L. Siebert
Radiation Protection Dosimetry, Vol. 70, Nos. 1-4, pp. 361-364, 1997

The new remcounter LB 6411: Measurement of neutron ambient dose equivalent H*(10) according to ICRP60 with high sensitivity
A. Klett and B. Burgkhardt,
IEEE Transactions on Nuclear Science, Vol. 44, No. 3, June 1997

German Patent 19627264 granted Oct 23, 1997

German Patent 4344955 granted Feb 16, 1995

 

Applications

The neutron dose rate probe LB 6411 can be used as a portable monitor LB 123 N, for direct connection to the LB 123 UMo, and as a stationary measuring instrument for connection to the dataloggers LB 112 or LB 111 Micro-Gamma.

Major areas of applications are reactors and the nuclear fuel cycle in the nuclear-technical field, accellerators in research, and the use of neutron sources in the industrial field.

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