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The laboratory experimental setup for development of pyroelectric neutron generator for calibration of neutrino and dark matter detectors for direct search of Weakly Interacting Massive Particles (WIMP) has been developed. The setup allows providing and controlling the neutrons generation process realized during d-d nuclear fusion. It is shown that the neutrons with energy 2.45 MeV can be generated starting from a level of electric potential generated by pyroelectric crystal about 30 kV, in contrast to the typical neutron tubes which need the applied outer high voltage level about 100 kV. 1. Operational principals Energy calibrations of dark matter and neutrino detectors are required for a correct interpretation of the collected data. Also neutron calibrations are necessary because an elastic scattering of neutrons by nuclei of detector’s target leads to nuclei recoil which perfectly simulate the signal from WIMP or a coherently scattered neutrino. Several variants of the neutron calibration systems for low-background detectors are proposed [1,2] including use of the system, based on pyroelectric neutron source [2,3]. The few cm gap between the charged surface of pyroelectric crystal and deuterated target is enough to accelerate D-ions to initiate D-D reaction and produce fast neutrons with energy 2.45 MeV. Neutrons generation in D-D reaction with tantalate lithium (LiTaO3) pyroelectric crystal was confirmed experimentally [3–5]. The neutrons generation requires forevacuum conditions with a residual gas about 1 mTorr of deuterium, in order the molecules could be ionized in the strong electric field. The field with magnitude about of 10 kV/cm appears close to the crystal surface during the crystal temperature changing. The tungsten tip with pin’s diameter of several hundred nanometers is mounted on the pyroelectric crystal surface to generate such high electric potential. The principle of the pyroelectric neutron sources operation is shown schematically in figure 1. 1 International Conference on Particle Physics and Astrophysics IOP Publishing IOP Conf. Series: Journal of Physics: Conf. Series 798 (2017) 012119 doi:10.1088/1742-6596/798/1/012119 International Conference on Recent Trends in Physics 2016 (ICRTP2016) IOP Publishing Journal of Physics: Conference Series 755 (2016) 011001 doi:10.1088/1742-6596/755/1/011001 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd Figure 1. Operating principle of pyroelectric neutron source. When pyroelectric crystal generates negative high electric potential (left), electrons are accelerated away from the crystal and produce Xrays from the target. Positive D-ions are attracted to the crystal surface. When pyroelectric crystal generates positive high electric potential (right), electrons are attracted to the crystal surface and produce X-rays from the crystal. Positive D-ions are accelerated away from the crystal to the target and initiate D-D reaction with fast neutrons output. Pyroelectric mono-energy (2.45 MeV) neutron source is considered as a useful tool for the neutron calibrations. Such sources have to be of several tens of cubic centimeters size and should have as low as possible consumption power. It is important that it could be constructed without any radioactive materials and do not require an external high voltage power supply. By the way, some of the features of the pyroelectric neutron source should be taken into consideration for application in lowbackground experiments. There is a significant X-ray background with the energy up to 100 keV and an intense heat exchange with the surrounding environment. The optimal way to minimize their contribution is a reduction of temperature range variation applied to the pyroelectric crystal but, as a result, a reduction of electric potential obtained by the pyroelectric crystal will happen. 2. The experimental setup The experimental setup for a pyroelectric source development was assembled as shown in figure 2. Figure 2. The scheme of the experimental setup. The pyroelectric high potential source contains cylindrical pyroelectric crystal LiTaO3 with 20 mm diameter and 10 mm height, Peltier element, duralumin thermal conductor with the cooler fan at the end in the air. All elements of the assembly are glued by vacuum epoxy. The stainless steel disk with a tungsten tip is mounted on the crystal surface. The tip has 8 mm length and 400 nm diameter. 2 International Conference on Particle Physics and Astrophysics IOP Publishing IOP Conf. Series: Journal of Physics: Conf. Series 798 (2017) 012119 doi:10.1088/1742-6596/798/1/012119

Development of pyroelectric neutron source for calibration of neutrino and dark matter detectors