Search

The project in producing the hyperpolarized 3He and 19F are addressed in pursuit of radiation free medical diagnosis. The program for production of the hyperpolarized 3He by the brute force method with the Pomeranchuk cooling and the rapid melting of the solid 3He started a few years ago, and is still on the way, while a new program for production of the hyperpolarized 19F by means of the PHIP (ParaHydrogen Induced Polarization) has just got started. Particular attention is placed upon a new idea of the hyperpolarization catalyst to be used for 19F.

The CUORE Crystal Validation Runs (CCVRs) have been carried out since the end of 2008 at the Gran Sasso National Laboratories, in order to test the performances and the radiopurity of the TeO$_2$ crystals produced at SICCAS (Shanghai Institute of Ceramics, Chinese Academy of Sciences) for the CUORE experiment. In this work the results of the first 5 validation runs are presented. Results have been obtained for bulk contaminations and surface contaminations from several nuclides. An extrapolation to the CUORE background has been performed., 11 pages, 8 figures

We optimized the design and operation of a low-Tc direct current superconducting quantum interference device (dc SQUID) with an integrated coupling coil of 1.5 muH inductance taking into account typical effects observed for similar devices. Numerical simulations were performed on a model including the capacitance of the Josephson junctions, thermal noise of the integrated shunt- and damping- resistors as well as a complex frequency dependent impedance of the SQUID loop originating from the integrated coils. The experimentally and numerically determined characteristics and sensitivity are in good agreement. A minimum additional coupled energy resolution of 700 (h/2p) and 250 (h/2p) was measured at a temperature of 4.2 K and 1.5 K, respectively.

The Mario Schenberg gravitational wave detector has been constructed at its site in the Physics Institute of the University of Sao Paulo as programmed by the Brazilian Graviton Project, under the full support of FAPESP (the Sao Paulo State Foundation for Research Support). We are preparing it for a first commissioning run of the spherical antenna at 4.2 K with three parametric transducers and an initial target sensitivity of h ~ 2 × 10−21 Hz−1/2 in a 60 Hz bandwidth around 3.2 kHz. Here we present the status of this project.

For future configurations, we study the relation between the abatement of the noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our aim is not the proposition of a new design, but an indication of where in the bandwidth or for which noise source, a noise reduction would be most efficient. We take VIRGO as the reference for our considerations, solely applicable to the inspiralling phase of a coalescing binary. Thus, only neutron stars and small black holes of few solar masses are encompassed by our analysis. The contributions to the SNR given by final merge and quasi-normal ringing are neglected. It is identified that i) the reduction in the mirror thermal noise band provides the highest gain for the SNR, when the VIRGO bandwidth is divided according to the dominant noises; ii) it exists a specific frequency at which lies the potential largest increment in the SNR, and that the enlargement of the bandwidth, where the noise is reduced, produces a shift of such optimal frequency to higher values; iii) the abatement of the pendulum thermal noise provides the largest, but modest, gain, when noise sources are considered separately. Our recent astrophysical analysis on event rates for neutron stars leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO, respectively, while a recently proposed and improved, but still conservative, VIRGO configuration would provide an increase to 1.5 events per year. Instead, a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such gain could be achieved.

The Schenberg gravitational wave detector is almost completed for operation at its site in the Physics Institute of the University of Sao Paulo, under the full support of FAPESP (the Sao Paulo State Foundation for Research Support). We have been working on the development of a transducer system, which will be installed after the arrival of all the microwave components and the completion of the transducer mechanical parts. The initial plan is to operate a CuAl6% two-mode parametric transducer in a first operational run at 4.2 K with nine transducers and an initial target sensitivity of h ~ 2 × 10−21 Hz−1/2 in a 50 Hz bandwidth around 3.2 kHz. Here we present details of this plan and some recent results of the development of this project.

The CUORICINO ββ-decay detector is an array of 62 TeO2 bolometers; 44 are 5×5×5-cm crystals made with natural tellurium (33.8% 130Te). There are 18, 3×3×6-cm crystals, 14 of which are made of natural tellurium, 2 are isotopically enriched to 75% in 130Te, and 2 are enriched to 82.3% in 128Te. The total mass of 130Te is ∼ 11 kg. The background rate is 0.23 ± 0.04 counts/keV/kg/yr in the energy interval 2480 to 2600 keV. During the cooling process, some of the wires became disconnected and only 32 of the large and 16 of the smaller crystals could be read out. The data presented here come from 29 of the 5×5×5-cm crystals containing 6.2 kg of 130Te. The new limit on the half-life is \(T_{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}}^{0\nu } \geqslant 5 \times 10^{23} yr\), corresponding to an effective Majorana mass of the electron neutrino 〈mν〉 between 0.42 and 2.05 eV, depending on the nuclear model used to analyze the data.

The first results are reported on the limit for neutrinoless double decay of 130Te obtained with the new bolometric experiment CUORICINO. The set-up consists of 44 cubic crystals of natural TeO2, 5 cm on the side and 18 crystals of 3×3×6 cm3. Four of these latter crystals are made with isotopically enriched materials: two in 128Te and two others in 130Te. With a sensitive mass of ∼40 kg, our array is by far the most massive running cryogenic detector to search for rare events. The array is operated at a temperature of ∼10 mK in a dilution refrigerator under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. The counting rate in the region of neutrinoless double beta decay is ∼0.2 counts keV−1kg−1y−1, among the lowest in this type of experiment. No evidence for neutrinoless double beta decay is found with the present statistics obtained in about three months with a live time of 72%. The corresponding lower limit for the lifetime of this process is of 5.5×1023 years at 90% C.L. The corresponding limit for the effective neutrino mass ranges between 0.37 to 1.9 eV depending on the theoretically calculated nuclear matrix elements used. This constraint is the most restrictive one except those obtained with Ge diodes, and is comparable to them.

In order to investigate the anomalous response at ultra-low temperatures of the resonant-mass gravitational wave detector NAUTILUS, the RAP experiment has been planned to measure the vibrations in a small cylindrical aluminium bar when hit by 10 5 510 MeV electrons from the DANE beam test facility, corresponding to the energies released by typical extensive air showers. The results of the measurement at low temperature and in the superconducting regime are crucial to understand the interaction of ionizing particles with bulk superconductors and to confirm the results on the thermoacoustic model of the past experiments. The first run of RAP experiment is scheduled for the end of June. The scheme of operation and the preliminary results at room temperature will be presented.

We are building the Schenberg gravitational wave detector at the Physics Institute of the University of Sao Paulo as programmed by the Brazilian Graviton Project. The antenna and its vibration isolation system are already built, and we have made a first cryogenic run for an overall test, in which we measured the antenna mechanical Q (figure of merit). We also have built a 10.21 GHz oscillator with phase noise performance better than -120 dBc at 3.2 kHz to pump an initial CuA16% two-mode transducer. We plan to prepare this spherical antenna for a first operational run at 4.2 K with a single transducer and an initial target sensitivity of h ∼ 2 x 10 -21 Hz -1/2 in a 50 Hz bandwidth around 3.2 kHz soon. Here we present details of this plan and some recent results of the development of this project.

We are developing nearly quantum limited two-stage SQUID systems for the readout of the MiniGRAIL, the first spherical gravitational wave detector with a diameter of 65 cm and a mass of 1150 kg. The two-stage SQUID systems are based on a conventional dc SQUID as the sensor and a double relaxation oscillation SQUID (DROS) as the second stage. The SQUID systems will be coupled to the detector via a multi-mode inductive transducer. The large flux-to-voltage transfer of the two-stage SQUID system allows a direct voltage readout scheme, i.e. without (ac flux) modulation. At T = 4.2 K, the energy resolution in flux-locked loop was measured to be e = 27 h, and at a temperature around 20 mK, the energy resolution is expected to reach the quantum limit.

The CUORE experiment projects to construct and operate an array of 1000 cryogenic thermal detectors of TeO2, of a mass of 760 g each, to investigate rare events physics, in particular, double beta decay and non baryonic particle dark matter. A first step towards CUORE is CUORICINO, an array of 62 bolometers, currently being installed in the Gran Sasso Laboratory. In this paper we report the physics potential of both stages of the experiment regarding neutrinoless double beta decay of 130Te, WIMP searches and solar axions., Comment: 36 pages, 5 figures. Submitted to Astrop. Phys

Neutrino physics represents today a hot topic in elementary particle physics, due to the observations of flavour oscillations both in the atmospheric and in the solar sector. This proves the existence of finite neutrino masses. In order to fix their absolute values, sensitive experiments on Neutrinoless Double Beta Decay (a rare nuclear process) must be carried on. The experiment here described, named Cryogenics Underground Observatory for Rare Events (CUORE), can extend the neutrino mass sensitivity down to 30 meV . CUORE will consist of a large, closely packed, high-granularity array of 1000 tellurite (TeO2) low-temperature calorimeters, operated at 10 mK and with a total mass of 800 kg . The final structure of the detector and the preliminary tests are presented and discussed.

It is shown experimentally that the exciton luminescence λ=172 nm) quantum yield excited by excess electrons drifting through solid xenon at 77 K in fields of 10 kV/cm amounts to 20±5 per electron and that luminescence takes place during the entire drift process. A CW bulky discharge through solid xenon (with a current up to 20 A/cm2) is realized, and intense visible luminescence due to excitation of impurities by electron impacts is observed. The prospects for using solid rare gases as matrices for studying processes in low-temperature plasmas and for creating effective electric energy converters in the vacuum ultraviolet range are discussed.

An overview is given on the possibilities of building low cost omni-directional gravitational wave detectors using resonant spheres. Sensitivity curves of arrays and xylophones of spheres fabricated from different materials show that spherical detectors can be competitive with the large interferometers at frequencies above 1 kHz, with the additional advantage of being omni-directional and being able to determine the direction and polarization of the gravitational wave. MiniGRAIL is the first spherical resonant detector, being built at the Kamerlingh Onnes Laboratory of Leiden University in the Netherlands. The detector is planned to operate at a temperature of about 20 mK and will have a quantum limited strain sensitivity for a burst signal of the order of 4 × 10−21. We present the progress concerning cryogenics and transducer development.

We have developed a new technique to imbed impurities in solid 4He. It consists in injecting helium gas mixed with the impurity on the top surface of Helium liquid-solid interface, with the solid continuously moving downwards by pumping at the bottom of the cell. Due to the large temperature gradient, sedimentation occurs through the thin (1–2 mm) upper layer of liquid helium. We achieved a guest-particle density of 3 ⋅ 1019 per cm3 and a doped crystal growth rate of 0.05 mm/s. The possibilities of this novel method for matrix isolation spectroscopy as well as for quantum crystal studies are discussed.

The first phase of the Brazilian Graviton Project is the construction and operation of the gravitational wave detector Mario Schenberg at the Physics Institute of the University of S?o Paulo. This gravitational wave spherical antenna is planned to feature a sensitivity better than h = 10?21 Hz?1/2 at the 3.0?3.4 kHz bandwidth, and to work not only as a detector, but also as a testbed for the development of new technologies. Here we present the status of this detector.

We are developing a two-mode inductive resonant transducer for MiniGrail. We report several quality factor measurements, down to 4.2 K, performed on a scaled size resonator in different conditions: when suspended from a wire and when clamped, by thermal contraction techniques, into a hole of a sphere of 150 mm diameter and 14 kg mass. Q-factor measurements of a first resonator prototype at 4.2 K for MiniGrail are also presented. Finally, a fabrication process for a Nb film pick-up coil is described.

The results of the first cooldown of MiniGRAIL are presented. MiniGRAIL is a 65 cm diameter spherical gravitational wave detector made of CuAl6%, having a mass of 1150 kg. The sphere is suspended from a seven-stage vibration isolation system with a total weight of about 950 kg. The sphere should be cooled to below 20 mK. During the first run the sphere was cooled down to 1.8 K. A forced helium flow was used to cool the sphere down to 4 K, which took only two days. Further cooling to 1.8 K was done using a 1 K pot. We measured the temperature dependence of the mechanical quality factor and made an evaluation of the heat leaks (for more details see www.minigrail.nl).

Thermal detectors are introduced and their possible impact on neutrinoless double-beta-decay (2β0ν) search is discussed. The thermal experiment MIBETA is described, reporting the up-to-date limits on 130Te and 128Te. A new generation experiment, consisting in a large expansion of MIBETA and known as CUORE, is presented and discussed.

We have introduced guest particles into superfluid helium using a directed helium jet containing traces of species under study. The distinguishing peculiarity of the method consists in that the whole system is sealed from the cryostat main helium bath. This allows: (i) on the account of the absence of evaporating helium upflow to realize a complete capture of the impurities from the jet into liquid helium; (ii) to eliminate the dependence of the process conditions on liquid He level position in the main bath as well as on the amount of liquid He condensed inside a cell; and (iii) this method can be used to introduce impurities into liquid 3He. Two modifications of the technique have been designed—one for an optical cryostat and another for a cryostat with narrow 1” tail typical for use in a very high magnetic field. Optical and X-ray diffraction studies have confirmed the possibility of embedding in superfluid helium samples consisting of submicron D2 particles with a rate of 10mmoles per hour. Such samples are necessary for the achievement of strong D2 nuclear spin polarization by the brute force method.

We report on our analysis of the melting process of highly magnetized solid 3 He. Akimoto et al. found that the solid-liquid interface becomes unstable during melting in a magnetic field of 9 T. The liquid then penetrates into the solid in the form of cellular dendrites. The instability, which was predicted by Puech et al., was attributed to a Mullins-Sekerka type of instability due to the magnetization gradient on the solid side. The measurements on which we base our analysis clearly show gradients on both sides of the interface. We present an extension of the linear stability analysis for this situation, as well as a numerical calculation of the dispersion relation of interface deformations. Our results are in good agreement with the experiment and explain the initial suppression of the instability, caused by the magnetization gradient in the liquid.

We developed a cryostat for optical observations at ultralow temperatures and in strong magnetic fields. The optical system consisted of a LED, a light transmission path and a CCD chip, with all components installed inside the inner vacuum can of the cryostat. We have been able to cool a 3He sample to a temperature of 0.6 mK in zero magnetic field and to 2 mK in 9 Tesla, while looking at the crystallization and melting of the solid 3He. The CCD chip gives a heat leak of only 200 pW to the 3He in our Pomeranchuk cell. The performance of the nuclear demagnetization cryostat as well as the optical system are described.

We elucidate the melting process of highly magnetized solid 3He by observing the magnetization profile and the liquid-solid interface simultaneously. Clear enhancements of magnetization and magnetization gradients at the interface of both the solid and the liquid were observed during melting. These measurements provide a mesoscopic confirmation of the melting scenario of Castaing and Nozieres, and explain the long delay before the instability sets in: The magnetization gradient in the liquid leads to an initial suppression of the melting instability, in accordance with our extension of the stability analysis of Puech et al. This resolves the discrepancy between theory and experiment.

A melting instability has been observed during rapid melting of highly magnetized solid ${}^{3}\mathrm{He}$. The instability occurred only if the solid is grown at low initial temperature and in high magnetic field, i.e., with high magnetization, and if the solid is melted sufficiently rapidly. After the instability of the interface occurred, the solid formed many cellular dendrites, directed parallel to the magnetic field. This is the first observation where a clear influence is seen of the magnetic field and the magnetization on a growth and melting process. The instability is attributed to a Mullins-Sekerka\char21{}type instability due to the magnetization gradient at the interface in the solid.

We present preliminary results of growth and melting at the interface between spin ordered solid 3 He and superfluid liquid 3 He both in a low magnetic field of 0.2 T and in a high magnetic field of 8.9 T. Measurements of the growth and melting velocity were performed by simultaneously observing the crystal using optical techniques with a low-temperature CCD camera and by using precise pressure measurements. Our results in low magnetic field agree qualitatively with those of Nomura et al. (J. Low Temp. Phys. 95 (1994) 715).

We investigated the temperature dependence of the dielectric susceptibility of amorphous silica below 300 mK. The influence of glass matrix and hydroxyl concentration ( ) was studied to investigate the suitability for thermometry. We obtained Suprasil samples with between 200 and 1000 ppm by annealing in vacuum. We also measured commercial Homosil glass. The sensitivity is proportional to , but saturation of the dielectric susceptibility occurs at the same temperature for all samples.

We present new results on the magnetic field dependence of the superfluid transition temperatures of the A1and A2phases of3He. The \(T_c^{A_1 } \) transition temperature has been measured up to 15 T, the \(T_c^{A_2 } \) up to 12 T, at the melting pressure. The temperature was measured by an in situ field independent glass thermometer. The results are in agreement with extrapolations from earlier experiments, and with calculations of the splitting \(T_c^{A_1 } - T_c^{A_2 } \) versus magnetic field. We were also able to obtain an estimate of the quadratic terms of the splitting, and of each of the transition temperatures. The measured quadratic terms are smaller than calculated, the negative coefficient for the \(T_c^{A_2 } \) quadratic term being quite unexpected.

The recent discovery that inhaling polarized3He or129Xe allows high resolution MRI images of the lungs to be made is having a large impact among the medical and physics communities. In fact, this technique could become the first high resolution, harmless diagnostic tool for several lung diseases. Neutron–lean nuclear fusion would also benefit from the use of polarized fuel (D,3He) through an enhanced fusion cross–section. At present, laser techniques are being used for polarizing3He and129Xe, but the yield is still quite low, at most a few tens of liters per day. Cryogenic techniques combining high magnetic fields and low temperatures could be used to produce much larger quantities of highly polarized3He through adiabatic compression. In a reasonable field of 15 T and 5 mK the polarization of the resulting solid is larger than 95%. Once polarized the solid is melted. The magnetization remains in the liquid for several minutes and the cell could be moved to a region at 6–7 K where the liquid would evaporate. The resulting gas could be removed and kept in a convenient vessel. Extraction could in principle be done in a time much shorter than the relaxation time T1of the liquid, which has a minimum around 300 s at 1 bar pressure. This process could produce large quantities of gas in the range of 100 to 1000 l/day. We have also demonstrated that by condensing molecular deuterium (catalized to mostly J= 0) inside the3He cell it was possible to polarize the D2molecules to 13%. Production of finely divided D2should lead to quite larger polarizations. Using this technique one might consider the polarization of129Xe.

Cryogenic techniques combining high magnetic fields and low temperatures could be used to produce larger quantities of highly polarized 3 He through adiabatic compression. This process could produce large quantities of gas in the range 100–1000 l/day. By condensing molecular deuterium (catalyzed to mostly J = 0) inside a 3 He cell it was possible to polarize the molecules to P = 0.13 limited by the relatively large size of the “snow” grains. Production of finely divided D 2 should lead to a quite higher polarization. Using these techniques, one might consider the polarization of 129 Xe, which has found important applications in MRI of humans, just as 3 He.

This paper focuses on the hydrodynamics of third sound on a superfluid 3 He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.

We present the first measurements of the viscosity of superfluid {sup 3}He in magnetic fields up to 15 T , at temperatures down to 2 mK along the melting curve, using an assumption for the temperature dependence of the normal density. At fields higher than 4 T , the viscosity shows a minimum in the A{sub 1} phase, and reaches a local maximum at the A{sub 2} transition which becomes global at 14.6 T . The sharp decrease just below the A{sub 1} transition can be understood within the Ginzburg-Landau framework and is consistent with both theory and experiments in lower fields. At temperatures below the minimum, the viscosity in the A{sub 1} phase is dominated by a term with T{sup {minus}2} dependence. Additionally, we have calculated the temperature dependence of the viscosity tensor in the low temperature limit using the method of temperature asymptotes. {copyright} {ital 1997} {ital The American Physical Society}

HiSPARC (High-School Project on Astrophysics Research with cosmics) is a project that envisages the use of a large array of cosmic ray detectors placed at high-schools and scientific institutions in the Netherlands in order to measure high-energy cosmic ray showers. Besides contributing to the HiSPARC project, Leiden University also uses the cosmic ray detectors as veto for the resonant gravitational wave antenna MiniGRAIL.

At the end of 2001 the Milano Double Beta Decay (MI-DBD) experiment on double beta decay of 130Te has been completed. The project Cryogenic Underground Observatory for Rare Events (CUORE), proposed as a natural extension of MI-DBD, will be a tightly packed array of 1000 TeO2 bolometers, each being a cube 5 cm on a side with a mass of 790 g. The array will consists of 25 vertical towers, arranged in a square of 5 towers by 5 towers, each containing 10 layers of 4 crystals. A single CUORE tower has been constructed as a smaller scale experiment called CUORICINO. The technical feasibility of CUORE is now being tested in CUORICINO, running since few weeks. The CUORICINO experiment consists of 44 TeO2 detectors 5×5×5 cm3 and 18 TeO2 detectors 3×3×6 cm3 for a total mass of approximately 41 kg. An analysis of the detector performances is presented together with the new limit obtained on neutrinoless double beta decay of 130Te.

RAP is an experiment aimed to measure the effects caused by high-energy electrons impinging on bulk superconductors. The motivation is the anomalous high-energy cosmic ray rate detected by the gravitational wave antenna NAUTILUS when operated in superconducting regime.

Massive metallic spheres cooled to millikelvin temperatures could reach quantum-limited sensitivities high enough to detect gravitational waves from supernovae explosions up to 100–200 Mpc which would include millions of galaxies. They could provide sensitivity (in the frequency range above 700 Hz) and directionality, superior to the large interferometer arrays presently under construction, which will be better at lower frequencies and can have a larger bandwidth. World wide gravitational wave observatories will probably use both types of detectors. In this paper we give a brief overview of the problems involved in making a resonant spherical gravitational wave detector of very large mass working in the low millikelvin range.

A CCD camera operating at T = 65 K was mounted in the vacuum space of our nuclear demagnetization cryostat. This has allowed us to make observations of3He crystals at temperatures below the superfluid phase transitions, in contrast to direct optical observations, which have so far been limited to T ≥ 20 mK.1 The good thermal equilibrium provided by the superfluid allows us to nucleate single crystals of3He in the region of the cell visible to the optical system. This occurs either spontaneously (due either to gravitational pressure gradients or local surface defects) or as a result of a small applied heat pulse.

We investigate the possibility of a large enhancement of the T = 0 finite solubility of3He in4He due to spin-polarization. The size of the effect depends on the fraction of3He atoms in the system. We present two different approaches for the limits of a small and a large number of3He atoms compared to the number of4He atoms. Since the possible3He superfluid phase transition depends on3He density, we calculate the consequences of this change in the solubility for its superfluid transition temperature. It is shown that for small fractions of3He, the transition temperature is enhanced mostly due to the enlargement of the up-spin Fermi sphere. In the opposite limit the transition temperature is enhanced as a result of the increased3He solubility.

A new design for conventional,3He re-circulating, dilution refrigerators has been developed and tested. The units are made out of plastic and can be designed to have very small diameters (

We report on our observations that the solid–liquid interface of highly magnetized solid 3 He becomes instable during melting. The liquid penetrates in the solid in the form of cellular dendrites. One-dimensional magnetic resonance imaging of the magnetization profile shows clearly the magnetization gradients in the solid and the liquid during melting, as well as enhanced magnetization at the interface. This enhanced magnetization disappears when the instability is complete. We discuss the results with the melting scenario of Castaing and Nozieres (J. de Physique 40 (1979) 257), and determine the spin diffusion coefficient of solid 3 He .

Microwave experiments in dilution refrigerators are a central tool in the field of superconducting quantum circuits and other research areas. This type of experiments relied so far on attaching a device to the mixing chamber of a dilution refrigerator. The minimum turnaround time in this case is a few days as required by cooling down and warming up the entire refrigerator. We developed a new approach, in which a suitable sample holder is attached to a cold-insertable probe and brought in contact with transmission lines permanently mounted inside the cryostat. The total turnaround time is 8 hours if the target temperature is 80 mK. The lowest attainable temperature is 30 mK. Our system can accommodate up to six transmission lines, with a measurement bandwidth tested between DC and 12 GHz. This bandwidth is limited by low pass components in the setup; we expect the intrinsic bandwidth to be at least 18 GHz. We present our setup, discuss the experimental procedure, and give examples of experiments enabled by this system. This new measurement method will have a major impact on systematic ultra-low temperature studies using microwave signals, including those requiring quantum coherence., 18 pages, 6 figures, accepted in Review of Scientific Instruments

We describe a new setup for optical observations (particularly of helium crystals) at ultralow temperatures. It is conceptually different from the usual optical setups, which require the use of optical windows in the cryostat. Our optical system, including the light source and camera, is placed inside the vacuum can of a dilution refrigerator cryostat. We have succeeded in filming the growth of3He crystals in contact with the superfluid B phase, down to 1 mK. The optical system can easily be combined with a nuclear demagnetization stage, and a simple extension of the image transport system will allow us to study3He crystals in high magnetic fields. The entire setup is described, and some typical images are shown.

We have polarized the J=0, I=2 spins in solid D 2 in 14.5T to 13%. We condensed D 2 in the form of small particles in a Pomeranchuk cell attached to a large dilution refrigerator. In this way we could cool the spins to 35 mK. The polarization was measured with cw NMR and a relaxation time at 35 mK of 360 sec was measured with a hole burning experiment.

Large metallic cylinders of several tons of mass have been cooled to liquid heliumtemperatures and recently have been cooled to T ∼ 100 mK leading to the most sensitive gravitational wave detector (NAUTILUS). The sensitivity is still not enough to detect waves from distances so large that the number of events would be several per year. Cooling spherical detectors of mass around 100 ton to temperatures around 10 mK could achieve this goal giving rise to a new astronomy.

International audience; We report on experimental work on a small prototype of a hollow sphere, aiming at assessing the feasibility of such a resonator as a third generation g.w. resonant detector. We measured the resonant frequencies and quality factors of the spheroidal quadrupolar modes of a welded hollow sphere. The eigenfrequencies are found where predicted by the theory, and the quality factors were degraded from a minimum of 20 % to a maximum of 60 % with respect to the bulk sphere.

Bergman`s general treatment of third sound waves has been extended to a (restricted) parallel plate geometry. In a parallel plate geometry two independent third sound modes can propagate: a symmetric and an antisymmetric one. Calculations show that at temperatures below 1 K the antisymmetric mode carries the most important part of the temperature amplitude. Because of the relatively strong substrate influence the temperature amplitude of the symmetric mode is suppressed. The {Delta}T/{Delta}h versus T measurements by Laheurte et al. and of the {Delta}T/{Delta}h versus {omega} measurements by Ellis et al. are explained. 7 refs., 2 figs.

Strongly polarized liquid mixtures of3He in4He of high concentration have been obtained for the first time, using quick melting of polarized3He solid in a 9 T field, inside a solid4He matrix (a variation of the Castaing-Nozieres effect). We measured relaxation times which were as long as 4000 s for a 5.5% mixture at T=350 mK with a polarization enhancement Δ/Δ0≅15 where Δ0 is the equilibrium polarization in an external field of 9.3 T. We discuss an improved cell which will be used for similar experiments in a 15 T field.

The attenuation of ultrasonic waves at moderately high frequencies has been measured in Stycast 1266 in the temperature range from 0.1 to 4.2 K to verify the very low attenuation expected from similar data observed in another epoxy resin. Below about 0.5 K the attenuation data are compatible with a T3 dependence and a frequency independent behavior reminiscent of the standard result predicted by the Two Level System (TLS) theory and observed in amorphous materials. The observed low attenuation in Stycast 1266 confirmed our earlier expectation that this is a good material to use for acoustic microscopy purpose at very low temperatures.

There are at present three methods for cooling samples to temperatures below 300 mK: dilution, Pomeranchuk, and nuclear refrigeration. We give the basic principles of these methods with more details concerning dilutions refrigerators. This should allow the construction of a simple all plastic refrigerator for temperatures lower than 15 mK, or an even simpler Pomeranchuk cell. The source of heat leaks and other important points for reaching temperatures in the microkelvin range with nuclear refrigerators are given in the lecture by F. Pobell