[en] A new versatile detector for ultracold neutrons (UCN) has been built and operated which combines multi-pixel photon counters and GS10 lithium-doped scintillators. Such detectors can be very small and can be used to monitor UCN inside storage vessels or guides with negligible influence (of order 10^-6) on the UCN intensity itself. We have shown that such detectors can be used in a very harsh radiation environment of up to 200Gy/h via the addition of a 4m long quartz light guide in order to place the radiation-sensitive photon counters outside the hot zone. Additionally we have measured the UCN storage times in situ in this harsh environment. (orig.)

[en] High precision mapping of weak magnetic fields is of interest for several branches of pure and applied research. This paper presents a resume of the progress made at Fribourg in adapting laboratory style laser-pumped optical Cs magnetometers to multisensor field mapping problems. Progress has been made in sensor head design and manufacture, laser beam splitting and control, and signal treatment electronics. A summary of the technology and its applications are presented.

[en] In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n^', could potentially mix and undergo nn^' oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n^' amplitude in the n wave function and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time τ_nn^'>103 s (95% C.L.) is derived

[en] We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w, obtained by fitting the micro-roughness model to the data are in the range 1≤b≤3 nm and 10≤w≤120 nm, in qualitative agreement with independent measurements using atomic force microscopy. (orig.)

[en] We performed ultracold neutron storage measurements to search for additional losses due to neutron (n) to mirror-neutron (n^') oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B^', ultracold neutron losses would be maximal for B≅B^'. We did not observe any indication for nn^' oscillations and placed a lower limit on the oscillation time of τ_nn^'>12.0 s at 95% C.L. for any B^' between 0 and 12.5 μT.

[en] A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and ¹⁹⁹Hg atoms, is reported. No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field b_{perpendicular}<2x10^-20 eV (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron |g_n|<0.3 eV/c² m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit |g_n|<3x10^-4 eV/c² m.

[en] We report the design and test of a compact, large-diameter spinflipper for ultracold neutrons based on the principle of adiabatic spinflip. A solenoid rf coil with a high diameter-to-length ratio (d/l∼1.7) is surrounded by up to three short magnet coils (d/l∼0.4...1.7) to provide the static gradient field. The device is optimized for low power consumption and operation in high vacuum. The magnetic field conditions necessary for full spinflipper efficiency over the full diameter were evaluated with ultracold neutrons. The measured spinflipper efficiency vs. adiabaticity correlation is in good agreement with a calculation based on an ideally linear gradient.

[en] The hard X-ray polarimeter POLAR aims to measure the linear polarization of the 50-500 keV photons arriving from the prompt emission of γ-ray bursts (GRBs). The position in the sky of the detected GRBs is needed to determine their level of polarization. We present here a method by which, despite of the polarimeter incapability of taking images, GRBs can be roughly localized using POLAR alone. For this purpose scalers are attached to the output of the 25 multi-anode photomultipliers (MAPMs) that collect the light from the POLAR scintillator target. Each scaler measures how many GRB photons produce at least one energy deposition above 50 keV in the corresponding MAPM. Simulations show that the relative outputs of the 25 scalers depend on the GRB position. A database of very strong GRBs simulated at 10 201 positions has been produced. When a GRB is detected, its location is calculated searching the minimum of the χ² obtained in the comparison between the measured scaler pattern and the database. This GRB localization technique brings enough accuracy so that the error transmitted to the 100% modulation factor is kept below 10% for GRBs with fluence F_tot≥10^-5ergcm^-2. The POLAR localization capability will be useful for those cases where no other instruments are simultaneously observing the same field of view.

[en] This paper summarizes the results from measurements aiming to characterize ultracold neutron detection with "6Li-doped glass scintillators. Single GS10 or GS20 scintillators, with a thickness of 100-200μm, fulfill the ultracold neutron detection requirements with an acceptable neutron-gamma discrimination. This discrimination is clearly improved with a stack of two scintillators: a "6Li-depleted glass bonded to a "6Li-enriched glass. The technique of optical contact bonding is used between the two glasses in order to eliminate the need for optical glue or grease between them. Relative to a "3He Strelkov gas detector, the scintillator's detection efficiency is lower for UCN energies close to the scintillator's Fermi potential (85-100 neV), but becomes larger at higher UCN energies. Coupled to a digital data acquisition system, counting rates up to a few 10"5 counts/s can be handled. A detector based on such a scintillator stack arrangement was built and has been used in the neutron electric dipole moment experiment at the Paul Scherrer Institute since 2010. Its response for routine runs of the neutron electric dipole moment experiment is presented. (orig.)

[en] We report on the design and first tests of a device allowing for measurement of ultracold neutrons polarisation by means of the simultaneous analysis of the two spin components. The device was developed in the framework of the neutron electric dipole moment experiment at the Paul Scherrer Institute. Individual parts and the entire newly built system have been characterised with ultracold neutrons. The gain in statistical sensitivity obtained with the simultaneous spin analyser is (18.2 ± 6.1) % relative to the former sequential analyser under nominal running conditions. (orig.)