Characteristics of the Neutron Irradiation Facilities of the PSI Calibration Laboratory

Hoedlmoser, H.; Schuler, Ch.; Butterweck, Gernot; Mayer, Sabine; Hamm, Marianne E.; Hamm, Robert W.

doi:10.1063/1.3665339

Cited by 10 publications

(13 citation statements)

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“…An example for the measured effect can be found in Figure 1. The effect has also been observed with a Thermo Wendi-2 (SN 18893) and a Berthold LB6419 (SNr 38), both instruments that use a similar 3 He proportional counter. For the investigated LB6411, the effect is not related to any warm up phase of the instrument, as the device is always operated for a minimum of 30 min before any irradiations or measurements take place.…”

Section: Measured Signal Driftmentioning

confidence: 80%

“…For practical purposes, it can be concluded that the LB6411 is best used in the conditioned state to ensure reproducible results, especially when used as a secondary or transfer standard. At the PSI Calibration Laboratory, all measurements to establish the reference models for the available 241 Am-Be and 252 Cf sources have been performed with a conditioned LB6411 (2,3) . When used routinely in the field, a conditioning may not be necessary, as the measurement uncertainties in an uncharacterised field can be expected to be much larger than the conditioning effect due to the energy response of the instrument.…”

Section: Discussionmentioning

confidence: 99%

“…A deviation in the reading produced by the test source needs to be taken into account by means of a correction factor c S for stability. In this work, the effect was investigated in several long-term measurements with varying dose rates and compared with the behaviour of a Berthold LB6419 (6) and a Thermo Wendi-2 (7) detector which both use similar 3 He proportional counters albeit with a different moderator design. All three instruments were found to reach a plateau after continued irradiation.…”

Section: Introductionmentioning

confidence: 99%

“…A known issue with LB6411 neutron probes is their signal drift during continuous irradiation. According to information from the manufacturer (5) , the instability of the LB6411 is attributed to a charge accumulation on insulating surfaces in the 3 He proportional counter of the device. The accumulated charge modifies the electrical field in the counter and lowers the effective discriminator level above which pulses are counted as neutrons, thus increasing the count rate.…”

Section: Introductionmentioning

confidence: 99%

“…This neutron detector is a 3 He proportional counter combined with an optimised spherical moderator (4) . The PSI instrument is calibrated at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig every 5 y.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the stability of commercial neutron probes

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At the Paul Scherrer Institute's Calibration Laboratory, neutron reference fields are provided for the calibration of ambient and personal dose equivalent (rate) metres and passive dosemeters. To ensure traceability to the standards of the Physikalisch-Technische Bundesanstalt (PTB) in Germany, the neutron fields are characterised by means of a PTB-calibrated Berthold LB6411 neutron probe which is used as a secondary standard. The LB6411 detector suffers from an unstable, increasing dose rate reading in the order of up to 15 % (according to the manufacturers, this is due to a charging effect in the 3 He proportional counter). In a calibration, this instability is usually corrected for based on the reading obtained with a test source. In this work, the instability was investigated by means of measurements under irradiation with ambient dose equivalent rates up to 24 mSv h -1 for up to 20 h and compared with the behaviour of an LB6419 and a Thermo Wendi-2 probe. The reading of the instruments was found to reach a plateau, e.g. it becomes stable after ∼90 min during irradiation with 10 mSv h -1 neutrons. The plateau is reached faster for higher dose rates. This supports the interpretation as a charging effect in the proportional counter. The effect could also be duplicated in an irradiation with photons from a 137 Cs source. The decay time of the accumulated charge was found to be very long, i.e. the instrument showed a stable reproducible reading for up to 6 h after the plateau was reached. From these observations, a conditioning procedure was derived which ensures a stable operation of the instrument after an irradiation of the instrument preceding its use in the reference measurements.

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Section: Measured Signal Driftmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 99%