Detector Laboratory

Staff of the detector laboratory within EM-AMCT support instrument responsibles and users ensuring smooth operation of neutron detectors and associated equipment during their experiments and measurements at the BER II neutron source. The ambition is to guarantee technically faultless operation to allow for an efficient use of the valuable beam time. Our expertise includes primary detectors (monitors, delay line detectors, and counter tube arrays), amplifier- and discriminator electronics, as well as data acquisition interfaces. Finally, support for the software packages DeLiDAQ and qmesydaq is provided.

Helium-3 Crisis and Projects of ICND

In the years after 2009 there has been a dramatic global shortage of the widely used neutron converter gas helium-3. This has increased pressure to develop new detector technologies. To facilitate this, the International Collaboration for the Development of Neutron Detectors (ICND) was formed [1] by the leading neutron laboratories, including FRM-II, FZJ, ILL, ISIS, SNS, JPARC and HZB. The detector group of the Working Group EM-AMCT took a very active role in this effort, coordinating the development of detectors using boron-trifluoride (BF3) gas. Two other alternatives which the collaboration is investigating are: (i) scintillation detectors (coordinated by ISIS), and (ii) detectors with multi-layers boron-10 detectors (coordinated by ILL). The urgency of finding an alternative to helium-3 is underlined by the development of large area detector arrays covering dozens of square meters and requiring the replacement of several thousand liters of helium-3, i.e. time-of-flight spectrometers. The project, no longer pursued today, had been taken to a stage where promising approaches for a safe operation of BF3-filled position-sensitive multi-tube detectors for the detection of cold neutrons in time-of-flight spectrometers had been developed [2]. 

Another focus of the activities of the detector lab was the development of a micro-strip gas chamber (MSGC) with gadolinium-157 as a neutron converter. This detector is characterized by a very high count rate capability (~1E7 n/s) and a very good 2-dimensional position resolution (<0.5 mm). In test measurements, a position resolution of ~100 µm could be extracted and a count rate capability of ~10 MHz could be extrapolated [3].

Detectors for Instruments at BER II

The expertise in neutron detector systems is also provided to the instrument responsibles for the choice of detectors suitable for the conceptual design of new instruments. Detailed simulations guarantee in advance that the suggested detector concept meets the scientific demands. As a matter of course, the mechanical construction is accompanied as equally as production of the detector assembly. The detector system is then setup and tested in the lab. Finally, after the detector system has been assembled and commissioned, it is handed over to the instrument responsible. Examples of developments are four detector panels each equipped with 48 linear position-sensitive detectors (LPDs) for the EXED instrument and the new SANS and VSANS instrument with 112 LPDs each.

Recently, the large detector laboratory was used to build-up four large-area detector panels for the HFM-EXED project. These panels created in the so-called multi-tube design were build in close co-operation with the detector group of ILL. Ready-to-use mechanical concepts, perfectly suited production and test facilities as well as Helium-3, which was procured before 2009, could be used in this project. Two of the detector panels consist of 31 tubes with a diameter of ¾” and a length of 238 cm while the other 2 panels have only 23 tubes with the same diameter, but a length of 200 cm. A major challenge in this project was to ensure the long-term helium-tightness of the large-area end flanges of the detector panels with an internal pressure of 10 bar. This was finally achieved by means of Helicoflex seals and special, high-strength screws. The detectors were certified according to the new directive 2014/68 / EU for pressure vessel equipment. Today the detectors are in routine use at the instrument EXED enabling neutron scattering experiments with the highest magnetic fields.

Detector Test Stand V17

For test measurements and characterization of detectors, the detector laboratory operates the test stand V17 in the neutron guide hall 1 of HZB. Here, neutrons with a wavelength of 0.335 nm and an intensity of up to 3*105 neutrons/cm² are available for measurements. To determine the position resolution of detectors, the neutron beam can be precisely collimated by means of two X-Y diaphragms made of borated aluminum. Detectors with a weight of up to 80 kg can be positioned by 1100 mm in the vertical direction and about 800 mm in the horizontal direction in front of the stationary neutron beam. Various electronic modules and a data acquisition system are available in the detector laboratory, which allow to readout and characterize a wide variety of detectors types.

References

[1] www.icnd.org
[2] Th. Wilpert, Boron trifluoride detectors, Neutron News 23/4 (2012) 14-19.
[3] B. Mindur, S. Alimov, T. Fiutowski, C. Schulz, T. Wilpert, Performance of a Micro-Strip Gas Chamber for event wise, high rate thermal neutron detection with accurate position determination, J. Instrum. 9 (2014) P12004.