[en] This paper presents results from the performed combined mechanical and thermal stress analysis of the reactor pressure vessel of the HPLWR with its feedwater and steam flanges and of the steam plenum above the core. Due to different coolant temperatures and thus material temperatures, these components experience the largest thermal deformations. In 2006, a pressure vessel design for a single pass core has been presented, which has been optimized now to reduce thermal loads. As a consequence of the three pass core design, the diameter of the core and therefore the diameter of the reactor pressure vessel were increased. To minimize the wall thickness, a preliminary mechanical analysis is performed in accordance with the safety standards. The optimized design is then verified with a finite element analysis which includes mechanical and thermal loads. The steam plenum also experiences high temperature differences causing thermal deformations and stresses which need to be checked carefully. Deformations at all sealing need to be minimized to exclude leakage, and thermal stresses may not exceed the fatigue limit. The performed finite element analysis confirms that deformations and stresses are acceptable. (authors)

[en] The ROSEBUD collaboration measured the differential flux of fast neutrons inside a shielding of lead irradiated with a source of ²⁵²Cf using two scintillating bolometers of LiF and Al₂O₃ at 20 mK. We compare an unfolding method using a three parameter model for the fast component of the neutron flux with a multigroup method in which the energy interval of interest is divided into groups. Some issues regarding the neutron monitoring with LiF or Al₂O₃ in a cryogenic experiment searching for dark matter WIMPs are discussed.

[en] Scintillating bolometers of LiF and Al₂O₃ can monitor the fast neutrons flux in WIMPs searches. With both materials we merge the traditional fast neutron detection methods of induced reactions and scattering. The ROSEBUD collaboration devoted an underground run in the old Canfranc laboratory to study the response of LiF and Al₂O₃ to fast neutrons from ²⁵²Cf. Both bolometers were used simultaneously in a common experimental set-up resembling those of current WIMPs searches, which could give valuable insights into future WIMPs searches with cryogenic detectors as EURECA.

[en] The ROSEBUD Collaboration has dedicated several underground runs to study different types of bolometers, mainly for the search of dark matter. Some of these runs, profiting from the good energy resolution of one bolometer of BGO and the ultra-low background of the underground laboratory of Canfranc (LSC), allowed the measurement of the L/K electron capture ratio of the ²⁰⁷Bi decay to the 1633 keV level of ²⁰⁷Pb. This paper constitutes the first published measurement of this magnitude. (orig.)

[en] In the frame of the ROSEBUD (Rare Objects SEarch with Bolometers UndergrounD) collaboration, we have tested at surface level (Orsay) and underground (Canfranc) properties at low temperature of a BGO scintillating bolometer developed as a prototype for dark matter searches. The response of the detector to different particles, both in heat and light, using internal and external radioactive sources is reported. We have focused on its sensitivity as dark matter target and as γ-ray spectrometer to monitor external background. An algorithm implemented to analyze high energy events, which produce saturated pulses in low energy experiments (like dark matter searches), is also discussed.

[en] The LUMTNEU program aims at performing a pilot experiment on 0ν2β decay of "1"0"0Mo using radiopure ZnMoO_4 crystals enriched in "1"0"0Mo operated as cryogenic scintillating bolometers. Large volume ZnMoO_4 crystal scintillators (∼ 0.3 kg) were developed and tested showing high performance in terms of radiopurity, energy resolution and α/β particle discrimination capability. Zinc molybdate crystal scintillators enriched in "1"0"0Mo were grown for the first time by the low-thermal-gradient Czochralski technique with a high crystal yield and an acceptable level of enriched molybdenum irrecoverable losses. A background level of ∼ 0.5 counts/(yr keV ton) in the region of interest can be reached in a large detector array thanks to the excellent detectors radiopurity and particle discrimination capability, suppression of randomly coinciding events by pulse-shape analysis, and anticoincidence cut. These results pave the way to future sensitive searches based on the LUMTNEU technology, capable of approachingand exploring the inverted hierarchy region of the neutrino mass pattern

[en] Scintillating bolometers are very suitable detectors for dark matter searches. They offer a wide absorber choice allowing to tune up different masses and couplings of WIMPs, background rejection capability and high efficiency in the conversion into heat of nuclear recoil energy releases. In a previous work we have shown that undoped sapphire can be an excellent dark matter detector since, due to its high light yield at very low temperature, very low particle discrimination energy thresholds are achievable. In this Letter, we report the results of an experiment devoted to the estimate of its thermal relative efficiency factor (REF) for nuclear recoil versus gamma events which is a relevant parameter in WIMP search experiments. Taking advantage of the discrimination capability of scintillating bolometers, we have registered the energy spectrum of ²⁰⁶Pb recoiling nuclei from a ²¹⁰Po alpha-source. Ensuing from the analysis we obtain an REF=1.044±0.008_{stat-0.008syst}^+0.056 close to but slightly greater than unity

[en] Neutrons are a relevant background in rare events physics. Detectors based on fast neutron-induced nuclear reactions are commonly used for fast neutron spectroscopy. In this subject, scintillating bolometers provide an excellent energy resolution and particle discrimination by the simultaneous measurement of the heat and emitted light. Our group has constructed several ⁶Li and ¹⁰B based massive scintillating bolometers (LiF, Li₆Eu(BO₃)₃, Li₆Gd(BO₃)₃), with energy resolutions ranging from 16 to 200 keV. First results of a 32 gr ⁶LiF scintillating bolometer enriched at 95% in ⁶Li operated at 20 mK are presented. The use of this material in a multi-target cryogenic dark matter experiment, like EURECA, would allow monitoring the incident neutron flux in the detector during the data-taking.

[en] Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of ${}^{100}$Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li${}_2$MoO${}_4$ crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov-Trofimov-Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li${}_2$MoO${}_4$ scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index ∼10${}^{-<!--\; ???\; -->4}$ counts/keV/kg/year with 280 g Li${}_2$MoO${}_4$ (${}^{100}$Mo enriched) bolometers at 3034 keV, the Q${}_{\mathrm{\beta <!--\; ??\; -->}\mathrm{\beta <!--\; ??\; -->}}$ of the double-beta decay, and target the goal of a next generation experiment like CUPID.

[en] The scintillation properties of undoped sapphire at very low temperature have been studied in the framework of the ROSEBUD (Rare Objects SEarch with Bolometers UnDerground) Collaboration devoted to dark matter searches. We present an estimation of its light yield under gamma, alpha and neutron excitation