This paper reports on the development of a technology involving 100 Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed nextgeneration bolometric experiment to search for neutrinoless double-beta decay. Large mass (∼ 1 kg), high optical quality, radiopure 100 Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2-0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the doublebeta transition of 100 Mo (3034 keV) is 4-6 keV FWHM. The rejection of the α-induced dominant background above 2.6 MeV is better than 8σ . Less than 10 µBq/kg activity of 232 Th ( 228 Th) and 226 Ra in the crystals is ensured by boule recrystallization. The potential of 100 Mo-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only 10 kg×d exposure: the two neutrino double-beta decay half-life of 100 Mo has been measured with the up-to-date highest accuracy as T 1/2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] × 10 18 years. Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of 100 Mo.

The only naturally occurring isotope of bismuth, 209Bi, is commonly regarded as the heaviest stable isotope. But like most other heavy nuclei abundant in nature and characterized by an exceptionally long lifetime, it is metastable with respect to alpha-decay. However, the decay usually evades observation because the nuclear structure of 209Bi gives rise to an extremely low decay probability and, moreover, generates low-energy alpha-particles difficult to detect. Indeed, dedicated experiments attempting to record the alpha-decay of 209Bi in nuclear emulsions failed. However, scintillating bolometers operated at temperatures below 100 mK offer improved detection efficiency and sensitivity, whereas a broad palette of targets could be available. Here we report the successful use of this method for the unambiguous detection of 209Bi alpha-decay in bismuth germanate detectors cooled to 20 mK. We measure an energy release of 3,137 +/- 1 (statistical) +/- 2 (systematic) keV and a half-life of (1.9 +/- 0.2) x 10(19) yr, which are in agreement with expected values.

We describe a tunable electron paramagnetic resonance (EPR) spectrometer designed to operate at frequencies between 160 and 525 GHz and magnetic fields of up to 20 T. To operate in such a broad frequency range we use a very stable optically pumped far infrared laser. The performance of the spectrometer has been measured with solid and liquid samples. This allows us to outline the potential uses of the spectrometer.

The infrared instrument IKS flown on board the VEGA space probes was designed for the detection of emission bands of parent molecules, and for a measurement of the size and temperature of the thermal emitting nuclear region. The instrument had three channels with cooled detectors: an "imaging channel" designed to modulate the signal of the nucleus and two spectroscopic channels operating at 2.5-5 and 6-12 #m, respectively, equipped with circular variable filters of resolving power ~50. This paper presents and discusses the results from the spectral channels. On VEGA 1, usable spectra were obtained at distances D from the comet nucleus ranging from 250,000 to 40,000 km corresponding to fields of view 4000 and 700 km in diameter, respectively. The important internal background signal caused by the instrument itself, which could not be cooled, had to be eliminated. Since no sky chopping was performed, we obtain difference spectra between the current spectrum and a reference spectrum with little or no cometary signal taken at the beginning of the observing sequence (D ~ 200,000 km). Final discrimination between cometary signal and instrumental background is achieved using their different time evolution, since the instrumental background is proportional to the slow temperature drift of the instrument, and the cometary signal due to parent molecules or dust grains is expected to vary in first order as D -I.The 2.5-5 ~m IKS spectra definitely show strong narrow signals at 2.7 and 4.25 ~m, attributed to the ~; vibrational bands of H20 and CO2, respectively, and a broader signal in the region 3.2-3.5/tm, which may be attributed to CH-bearing molecules. All these signals present the expected D -1 intensity variation. Weaker emission features at 3.6 and 4.7 #m could correspond to the vl and l,s bands of H2CO and the (1 -0) band of CO, respectively. Molecular production rates are derived from the observed emissions, assuming that they are due to resonance fluorescence excited by the Sun's infrared radiation. For the strong bands of H20 and CO2, the rovibrational lines are optically thick, and radiative transfer is taken into account. We derive production rates, at the moment of the VEGA 1 flyby, of ~10 a° sec -1 for H20, ~2.7 x 1028 sec -1 for CO2, ~5 × 1028 sec -l for CO, and 4 xl02s sec -~ for H2CO, if attributions to CO and H2CO are correct. The production rate of carbon atoms in CH-bearing molecules is -9 x 10 29 sec -1 assuming fluorescence of molecules in the gas phase, but could be much less if the 3.2-3.5 pm emission is attributed to C-H stretch in polycyclic aromatic hydrocarbons or small organic grains. In addition, marginal features are present at 4.85 and 4.45 #m, tentatively attributed to OCS and molecules with the CN group, respectively. Broad absorption at 2.8-3.0 #m, as well as a narrow emission at 3.15/tm, which follow well the D -1 intensity variation, might be due to water ice. Emission at 2.8 /~m is also possibly present, and 404 0019-1035/88 $3.00 Copyright ,L~ 1988 by Academic Press, Inc. All rights o...

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Large lithium molybdate (Li 2 MoO 4 ) crystal boules were produced by using the low thermal gradient Czochralski growth technique from deeply purified molybdenum. A small sample from one of the boules was preliminary characterized in terms of Xray-induced and thermally-excited luminescence. A large cylindrical crystalline element (with a size of ⊘40 × 40 mm) was used to fabricate a scintillating bolometer, which was operated aboveground at ∼ 15 mK by using a pulse-tube cryostat housing a highpower dilution refrigerator. The excellent detector performance in terms of energy resolution and α background suppression along with preliminary positive indications on the radiopurity of this material show the potentiality of Li 2 MoO 4 scintillating bolometers for low-counting experiment to search for neutrinoless double beta decay of 100 Mo.

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The LUMINEU program aims at performing a pilot experiment on neutrinoless double beta decay of 100 Mo using radiopure ZnMoO 4 crystals operated as cryogenic scintillating bolometers. Growth of high quality radiopure crystals is a complex task, since there are no commercial molybdenum compounds available with the required level of purity and radioactive contamination. This paper discusses approaches to purify molybdenum and synthesize compounds for high quality radiopure ZnMoO 4 crystal growth. A combination of a double sublimation (with addition of zinc molybdate) with subsequent recrystallization in aqueous solutions (using zinc molybdate as a collector) was used. Zinc molybdate crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski technique; their optical, luminescent, diamagnetic, thermal and bolometric properties were tested.