[en] In the first part of this thesis, properties of the UCN-converter material solid deuterium (sD₂) are studied. A series of investigations of various sD₂ crystals by means of optical spectroscopy and neutron scattering resulted in: (i) a freezing technique suitable for UCN sources (ii) an efficient method to achieve a high ortho concentration, (iii) a direct way to calculate the UCN production cross-section from the dynamic structure factor S(q, ω), (iv) the identification of six excitations responsible for UCN production (v) the interpretation of one excitation at E=12 meV as a multi-phonon process (vi) the discovery of an additional spin-dependent UCN loss mechanism at q=2.1A^-1 and E=1.8 meV. A complementary series of experiments was performed at the FRMII, testing the production of UCN with the studied sample preparation after different the characterization mentioned above. Besides establishing a technique for annealing sD₂ crystals to improve the UCN production rate, an additional loss cross section (σ_x=8 barn at 4.5 K indirect proportional to the ortho concentration) was found. Based on these findings, a new conceptual layout of the miniD₂ source was developed. In the second part, the diffuse scattering probability f and the loss probability per wall collision μ were measured for differently prepared UCN guides using the storageand the so called two-hole method. Electropolished, rough stainless steel and Al tubes with different coatings at temperature variation and surface conditions were measured. The third part deals with the development of a proton detector for the neutron lifetime experiment PENeLOPE, which is based on gravitational and magnetic UCN storage and counting of the protons from the decay. A concept for a large-area proton detector based on thin scintillation counters operating in cryogenic environment was developed based on simulations and experimental studies. In addition to the characterization of CsI(Tl) and CsI scintillators, a small scale detector with a 1.5μm thick CsI layer was built. The detector was irradiated with 40 keV protons and 18 keV electrons. The light detection was done using large area photo diodes (LAAPD) at 50 K. The two LAAPD types (high voltage and low voltage ones) used for these tests were characterized down to 20 K. It was found that the noise is highly reduced by cooling down to 200 K or below. For both types cooling increased the usable amplification which reached a plateau at 60 K. In the context of these tests the tunable proton accelerator paff was built, which provides us with tunable proton intensities in the range of 10 s^-1 to 10¹² s^-1 and energies of 1-45 keV. (orig.)