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Dose and Dose Rate Monitoring

LB 123 N Neutron Dose Rate Meter

Connected to the neutron probe LB 6411 the LB 123 UMo becomes a very sensitive neutron dose rate monitor for the measurement of the ambient dose equivalent for neutrons. The high response sensitivity of the LB 6411 of about 3 counts per nSv allows a measuring range from 30 nSv/h to 100 mSv/h. For the first time in a commercial neutron monitor, the energy dependence was adapted to the new conversion factors stipulated by ICRP 60. 

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

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.

Features of the Neutron Dose Rate Meter

The neutron dose rate monitor LB 123 N 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