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This paper presents off-line and on-line orientation results obtained with the new on line nuclear orientation device NICOLE in CERN. Magnetic moments of 187,185Pt g and 186Ir m, electric quadrupole moment ratios between Pt isotopes with mass number 185, 187 and 189, the spin of the 2 h isomer of 186Ir and a new decay scheme of 184Au involving a metastable state are established. The shape variation versus mass number of the Pt isotopes leads to sign change of the spectroscopic quadrupole moment between A=187 and 185. © 1990 J.C. Baltzer A.G., Scientific Publishing Company.

Nuclear orientation and nuclear magnetic resonance experiments were performed on185, 187, 189Pt isotopes oriented in Fe and single crystal Zn at temperatures down to about 6 mK. The hyperfine splitting frequencies of185Pt and187Pt in iron were determined to be 164.9(2) and 261.1(2) MHz, respectively. With the hyperfine field of -126.1(2.5) T, the g-factors are deduced to be |g(185Pt)|=0.172(3) and |g(187Pt)|=0.272(5). The spectroscopic quadrupole moment of187Pt was found to be negative with magnitude similar to that of189Pt, indicating a predominantly oblate ground state deformation for both isotopes. The spectroscopic quadrupole moment of185Pt was found to be positive, with the ratio Q(185Pt)/Q(189Pt)=-3.6(9), clearly indicating a change to prolate ground state deformation. © 1998 J.C. Baltzer A.G., Scientific Publishing Company.

Low-temperature nuclear orientation experiments on radioactive ${}^{56}\mathrm{Mn}$ ions implanted into insulating, antiferromagnetic crystals of ${\mathrm{MnCl}}_{2}\ensuremath{\cdot}4{\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{CoCl}}_{2}\ensuremath{\cdot}6{\mathrm{H}}_{2}\mathrm{O}$ are reported. In ${\mathrm{MnCl}}_{2}\ensuremath{\cdot}4{\mathrm{H}}_{2}\mathrm{O},$ comparison of the $\ensuremath{\gamma}$-ray anisotropy of the ${}^{56}\mathrm{Mn}$ nuclei with that of ${}^{54}\mathrm{Mn},$ doped into the sample during growth, showed that both the ${}^{56}\mathrm{Mn}$ and ${}^{54}\mathrm{Mn}$ spins felt a very similar hyperfine field. The site occupancy factor in a simple, two-site model was deduced to be ${0.96}_{\ensuremath{-}0.07}^{+0.04}.$ In ${\mathrm{CoCl}}_{2}\ensuremath{\cdot}6{\mathrm{H}}_{2}\mathrm{O},$ the average hyperfine field for the implanted ${}^{56}\mathrm{Mn}$ was significantly less than that for ${}^{54}\mathrm{Mn}$ and corresponded to $f=0.53\ifmmode\pm\else\textpm\fi{}0.10.$

Specific experiments, from solid state to elementary particle physics, require use of high-resolution particle detection in magnetic fields. When carefully designed, low-temperature microcalorimeters provide excellent energy resolution and low threshold. First results of Si-based microcalorimeters using state-of-the art implantation and bulk micromachining techniques are presented.

We have investigated the reorientation of the easy axis of magnetization in (0 0 1) Fe/Ag superlattices using vibrating sample magnetometry, Mossbauer spectroscopy and nuclear resonance scattering of synchrotron radiation. Clear evidence is found that the Fe-layer magnetization can be oriented considerably out of the plane of the sample at room temperature, even for Fe-layer thicker than 6 ML at which the spin-reorientation transition usually occurs in Fe/Ag. The spin canting is attributed to frustration and a strong contribution of a step-induced anisotropy.

Near perpendicular magnetic hyperfine fields in 110mAg have been observed in Fe/Ag multilayers. These fields are studied by low temperature nuclear orientation (LTNO) in multilayers [Ag(x ML)/Fe(y ML)]20, with (x,y) monolayer (ML) values of (2,10), (3,9), (5,10) and (3,18). The 110mAg γ-ray anisotropy was measured as a function of applied magnetic field parallel to the multilayer. The average induced hyperfine field of Ag is significantly influenced by the quality of the multilayer as measured by X-ray diffraction.

We report on the status of the measurements of the longitudinal polarization of positrons emitted by polarized 107In and 12N nuclei. Present results yield a lower limit of 306 GeV/c2 (90 % CL) for the mass of a possible W gauge boson with predominantly right-handed couplings, if interpreted in the framework of the manifest left-right symmetric model. In addition, the helicity structure of the weak interaction is discussed on the basis of experimental results at low and intermediate energies in the leptonic, semileptonic and hadronic sectors. Whereas in the minimal manifest left-right symmetric extension of the Standard Model the results from collider experiments are superior to results from other experiments, experiments in the three sectors of the weak interaction yield complementary information on the helicity structure of the interaction if interpreted in general left-right symmetric models.

The magnetic moment direction of Tb in an multilayer has been studied by the low-temperature nuclear orientation technique in external magnetic fields applied along and perpendicular to the sample plane. A perpendicular magnetic anisotropy of the Tb magnetic moments has been found at zero external magnetic field and the mean misalignment angle has been estimated to be about with respect to the sample plane normal. The external magnetic field applied along the sample plane turned the Tb magnetic moments to the plane, without reaching any saturation even at . A possible structure of misalignment within the Tb layer is discussed.

Low-temperature nuclear orientation has been used to study the magnetic behaviour of 54Mn and 57Co impurities in the AuFe alloy, below (14 at.% Fe-spin-glass state) and above (18 at.% Fe-re-entrant state) the percolation threshold. The anisotropy of the gamma -rays was monitored in the direction of the external magnetic field, as a function of the external magnetic field Bext up to 8.5 T and of the temperature in the range 4-40 mK. In Au86Fe14 we have found total misalignment of the Mn and Co spins when Bext to 0 and a rather easy alignment of Mn and Co with the application of Bext, which is typical for a spin-glass behaviour. On the other hand, both Mn and Co spins in Au82Fe18 show an alignment (mean value approximately 32 degrees ), even at Bext to 0, and are turned only slowly by Bext which corresponds to the re-entrant state. The difference in the Mn and Co results can be interpreted as an indication of the existence of local correlations between the Fe spins, supporting the necessity of using the finite-range model for the re-entrant state.

Results on the operation of a bolometer detector in high magnetic fields and at very low temperatures are presented. We tested a diamond absorber on a Ge thermistor in magnetic fields up to 8 Tesla and temperatures down to 10 mK using an55Fe X-ray and109Cd electron source. Heavily doped Ge shows a giant magnetoresistance effect. This was used to tune the thermistor impedance to an optimal value.

A new technique, based on relative measurements of the longitudinal polarization (P) of positrons emitted in two opoosite directions with respect to the nuclear polarization (R=${\mathit{P}}^{\mathrm{\ensuremath{-}}}$/${\mathit{P}}^{+}$), is used to provide constraints on extensions of the standard model (${\mathit{R}}_{0}$). The first result, i.e., R/${\mathit{R}}_{0}$=0.926\ifmmode\pm\else\textpm\fi{}0.041, was obtained with $^{107}\mathrm{In}$. Interpreted in the framework of left-right symmetric models and assuming no mixing, it provides a 90% C.L. lower limit of 225 GeV/${\mathit{c}}^{2}$ for the mass of a possible right-handed charged W gauge boson, reducing the mass range allowed by other semileptonic experiments.

The low-temperature nuclear orientation of54Mn in ferromagnetic Pt+5 at% Fe has been studied in the temperature range 4–50 mK andin the external magnetic field range 0.5–8.5 T. A considerable noncollinearity of Mn magnetic moments with respect to the bulk magnetization direction has been found in the wholeB ext range. A model based on the Heisenberg Hamiltonian in the first neighbour approximation is proposed, which fully describes our experimental data.

The first measurements of the longitudinal polarization of positrons emitted by polarized 107 In are reported. The positron polarization is deduced from the time-resolved decay spectrum of positronium hyperfine states. Our result is in agreement with the standard electro-weak model and provides a new lower limit for the mass of an eventual, predominantly right-handed charged W-gauge boson of 220 GeV/c 2 .

The low-temperature nuclear orientation of 54Mn in ferromagnetic Pt-10 at.% Fe has been studied in the temperature range 4-50 mK and in the external magnetic field range 0.5-8.5 T. Considerable noncollinearity of Mn magnetic moments with respect to the bulk magnetization direction has been found in the whole Bext range. A model based on the Heisenberg Hamiltonian in the first-neighbour approximation is proposed, which fully describes the experimental data. The authors found that the first-neighbor Mn-Fe exchange interaction is antiferromagnetic with the value JMn-Fe=-21(1) K, which lies in the range of the nearest-neighbor Mn-Mn or Fe-Fe exchange interaction parameters for Pt-based alloys.

A status report is given of the developments in Leuven concerning in-beam polarization of radioactive nuclei. Some properties of the setup are described and first test results are discussed.

On-line nuclear orientation was performed on70As. Anisotropy data have been obtained at 8.7mK for 29 gamma transitions. Multipole mixing ratios have been extracted for 17 transitions. Our results are in good agreement with existing data for the ten previously measured transitions. Our first time data for the 1496 keV, 2+→2+ γ-ray suggest the 2536 keV level is a good candidate for a mixed symmetry level.

A survey is given of particle emission from nuclei that have been spin oriented by cryogenical means. Experiments and recent developments with detectors in the low temperature environment and their on-line application are reviewed. The most recent results are mentioned. Some phenomena to be unraveled in future studies are pointed out.

Anisotropic α-emission from nuclei in the decay chain from223Ra to207Tl has been observed using low temperature nuclear orientation in combination with high resolution α-detection at 4.2 K. Information on partial wave amplitudes as well as hyperfine interactions has been extracted.

We report on the first measurements of the longitudinal polarization of positrons emitted by polarized nuclei, using cryogenically polarized107In. This so-called polarization-asymmetry correlation is very sensitive to the mass of a possible right-handed gauge boson, which is invoked by parity symmetric extensions of the standard V-A electroweak model to explain the experimentally observed strong violation of parity which, however, may not be complete. The positron polarization is deduced from the time-resolved decay spectrum of positronium hyperfine states. Our preliminary result points to a lower limit of about 210 GeV for the mass of an eventual right-handed charged W gauge boson. This result can still be improved.

The hyperfine field of NaFe has been measured using Low Temperature Nuclear Orientation of cold implanted24Na. The combination of both the γ-and β-anisotropies yields information on the implantation fraction of Na in Fe. Furthermore, an, upper limit for the relaxation time of Na in Fe could be deduced.

Dynamical nuclear polarization techniques are newly being applied at the Leuven Isotope Separator On-Line of the Cyclotron Research Center in Louvain-la-Neuve to polarize the intense radioactive ion beams which have become available. The experimental setup is described and first results are reported.

Recently semiconductor particle detectors, operational at low temperatures (4 K), have been incorporated in the low temperature nuclear orientation apparatus at ISOLDE-CERN. First test experiments with standard room temperature preamplifier components revealed a resolution of 4 keV at a 160 keV conversion electron line. This technical development makes it possible to study the anisotropic emission of α- and β-particles, conversion electrons and X-rays from oriented nuclei at the nuclear orientation facility at ISOLDE in addition to the standard γ-detection. Furthermore, we discovered that at 4 K the Si detectors are automatically fully depleted.

It is often impossible to determine the optimum detector geometry, thermistor doping and operating conditions prior to fabrication. We therefore suggest a software approach. A computer code, which allows to simulate the heat transport and electrical coupling, has been developed and is applied to actual calorimeters. The overall agreement between calculated detector features and corresponding experimental findings is found to be good.

The nuclear magnetic moments of the short-lived isotopes 199mPo, 201mPo, 201Po and 203Po, determined with on-line nuclear orientation, are reported for the first time. Together with other recently measured moments in this region, variations with Z and N can be derived which may offer a clue to an understanding of nuclear magnetism around 208Pb.

A system to polarize nuclear beams in-flight has been built at the central beam line of the Leuven Isotope Separator On Line (LISOL) at the Cyclotron Research Center in Louvain-la-Neuve. Surface collisions at grazing incidence as well as the tilted foil method are being applied as polarizing techniques. These methods are generally applicable and overcome the limitations imposed by the low temperature in situ nuclear orientation technique. First polarization tests have been carried out with a 50 keV N-14+ ion beam: (i) transmitted through a 2-mu-g/cm2 tilted C-foil and (ii) scattered at about 2.5-degrees from a flat Si(100) single crystal. The atomic polarization of the ions was detected by measuring the circular polarization of the 500 nm NII 2s(2)2p3p3D-2s(2)2p3d3F-degrees and the 567 nm NII 2s(2)2p3s3P-2s(2)2p3p3D optical transitions. Values for S/I of 10.2(1.9)% (500 nm) were deduced for the tilted foil and 7.7(1.1)% (500 nm) and 6.9(1.7)% (567 nm) for the scattering at the Si-surface.

Recently, a set-up to polarize nuclei 'in flight' has been developed at the LISOL isotope separator in Louvain-laNeuve. It is constructed in such a way that two complementary methods can be used: Tilted Foil (TF) and Ion Beam Surface Interaction at Grazing Incidence (IBSIGI). Both methods rely on an atomic polarization transfer to the nucleus, via hyperfine interaction. The atomic polarization is obstained by an anisotropic ion beam-surface interaction. This development completes the already existing Low Temperature Nuclear Orientation set-up and expands considerably the possibilities to polarize short lived nuclei. In a first run atomic polarizations of 50 keV N-14-beams were observed. Values up to 10% were obtained.

This paper reports on a low-temperature nuclear orientation (LTNO) study of Fe/Ag multilayers [Fe( x ML)/Ag( y ML)] 20 with ( x, y ) values of (9, 3), (18, 3) and (10, 5). The samples were prepared by molecular beam epitaxy (MBE) and the quality of the multilayers was checked by X-ray diffraction. The γ-ray anisotropy of the neutron activated 110 m Ag was measured as a function of the applied magnetic field. It was found that, in low external applied fields, the induced Ag hyperfine fields are directed out of the plane of the multilayer.

Since the first results continuous improvements and further developments of OLNO have been carried out; e.g. the sensitivity has been increased by the realization of particle detection. On—line nuclear orientation has evolved to a unique technique to study a broad range of physics topics from very fundamental interactions to applied material science. This has been proven by the results that already have been obtained. Apart from the well established low temperature NO technique, also the development of in—beam polarization methods is taking place. At NICOLE fine opportunities exist to work out specific and unique physics problems. Benefit can be taken of the high production rates at ISOLDE as compared to the other OLNO systems.

The low temperature nuclear orientation of54Mn in Pt99Fe1, Pt99,9Fe0.1 and Pt99,95Fe0.05 has been studied in the temperature range 5–60 mK and in the external magnetic field range 0–9 T. A considerable noncollinearity of Mn magnetic moments with respect to Bext has been found even at rather high Bext.

The hyperfine field of Fr in Fe and a highly substitutional occupancy in host Fe after cold implantation (T

The low temperature nuclear orientation of160Tb impurity in yttrium single crystal has been studied in the temperature range 5–60 mK and in the external magnetic field up to 9 T applied along a- or c-crystal axes. The experimental results are interpreted as a consequence of the interaction of Tb3+ ion with crystal field produced by the yttrium neighbours. A possible influence of technology used is also discussed.

The low temperature nuclear orientation of160Tb in gadolinium single crystal has been studied in the temperature range 5–60 mK and in the external magnetic field Bext ≤9 T, applied both in the a- and c-axis directions. The obtained results indicate the noncollinearity between the Tb magnetic moments and the magnetization of the gadolinium matrix.

We report on the first results obtained with a system designed to polarize on-line mass-separated radioactive ion beams by scattering the beams from very flat single crystal surfaces at grazing incidence angles. Polarizations of 1 to 2% were already observed for deuterium.

The direction of the magnetic moment of Tb in Fe(40 A)/Tb( x A) ( x = 10 and 20) multilayers has been studied using the low-temperature nuclear orientation technique in the temperature range 5–50 mK and in the external magnetic field range B ext = 0−8.5 T, with B ext applied along the sample plane. The anisotropy of the 299 keV 160 Tb γ-line was monitored in three directions with respect to B ext and the sample plane. The perpendicular magnetic anisotropy (PMA) of the Tb magnetic moments has been found at zero B ext for both systems. The PMA effect is increased when the Tb layers are thinner. An application of B ext turned the Tb magnetic moments towards the sample plane, without reaching a full alignment even at B ext = 8.5 T.

As a new nuclear physics application of low temperature detectors we propose the measurement of the beta asymmetry parameter for the allowed beta decay of 3H by means of low temperature nuclear orientation in high external fields. Since 3H is the lightest mirror nucleus these experiments are of particular interest in connection with the search for physics beyond the standard electroweak model. For an accurate measurement of the low energy beta particles, low thresholds and good energy resolution are equally important. Two types of detectors are discussed. The first type is based on the “standard” ionisation detectors and operates at 4.2 K. The low threshold is achieved by cooling the first stage of the preamplifier thereby reducing the electronic noise. More accurate results can be obtained with calorimetric detectors. We have shown that the use of bolometers in high magnetic fields is possible, with a very low threshold and a good energy resolution.

Behaviour of the Co magnetic moments in dilute PtFe alloys was studied in the temperature range of 5-50 mK and the external magnetic field range of 0-8.5 T using low-temperature nuclear orientation. Kondo behaviour of Co, known to exist in pure Pt, was found in the sample of lowest concentration only (Pt+0.22 at.% Fe). Large misalignment of the Co magnetic moments was seen, especially for alloys having Fe concentration slightly above the percolation limit 0.76 at.%. An anomaly in the hyperfine field value on the Co nucleus was also found in these alloys. >

A setup has been constructed which implements the techniques of grazing surface scattering and of the tilted foil method to produce nuclear polarized beams at the Leuven Isotope Separator On Line (LISOL), which is connected to the cyclotron Cyclone at Louvain‐la‐Neuve. This development makes it possible to use the intense radioactive ion beams (RIB), which will be available soon in the framework of the RIB−project at Louvain‐la‐Neuve, for polarization experiments. Especially solid state studies using polarized probe nuclei are envisaged in the beginning. First experiments to test the setup have been carried out and the results are very promising. The specific features of the setup are discussed together with the results of the test experiments.

We report on a new precision measurement of the longitudinal polarization of positrons emitted by polarized 107In nuclei. Preliminary results yield a lower limit of 303 GeV/c2 for the mass of a possible, predominantly right-handed, W gauge boson, if interpreted in the framework of the manifest, left-right symmetric model. In more general left-right symmetric models our result is complementary to those from muon decay experiments and to results from searches for a similar particle in collider experiments. Our data also provide new results on possible tensor contributions to the weak interaction.

We investigated the induced magnetic behaviour of the Ag of Fe/Ag multilayers with low temperature nuclear orientation. The experiments show induced magnetic moments in all samples. Furthermore, multilayers with 2ML and 4ML of Ag, these moments do not lie in the plane of the multilayer at low external magnetic fields.

We report on an extensive on-line nuclear orientation study of the angular distribution of $\ensuremath{\alpha}$ particles emitted in the favored decay of neutron deficient At and Rn nuclei near the $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}126$ shell closure. Surprisingly large anisotropies were observed, showing pronounced changes from one isotope to another. Comparing these data with several theoretical models shows that anisotropic $\ensuremath{\alpha}$ emission in favored decays from near-spherical nuclei can well be explained within the shell model, implying that it is mainly determined by the structure of the decaying nucleus.

The first measurement of the longitudinal positron polarization for polarized nucleus beta decay has been made for cryogenically polarized 107In. Time‐resolved decay of positronium hyperfine states was used to measure the positron polarization. Our preliminary result is in agreement with V‐A and sets a new semi‐leptonic limit on the mass of a possible right‐handed gauge boson.

The methods of time-resolved and time-integral on-line nuclear orientation have been applied to study short lived nuclei with the NICOLE facility (Nuclear Implantation into Cold On-Line Equipment) at ISOLDE-3 in CERN using beams of 182-186Hg. The half-lives in these decay chains are of the order of seconds and therefore comparable to the spin-lattice relaxation times of the nuclei in iron. As the relaxation rate depends strongly on the g-factor, g-factors of nuclei in the decay chains can be deduced from the observation of the time evolution of γ-ray anisotropy. Using this technique the existence of an isomer in 184Au has been found and the g-factors of 184Au, 184mAu and 182Au have been determined. Accurate half-lives have been extracted from the data. Time-integral nuclear orientation has been observed for short lived as well as longer lived isotopes of the Hg decay chains. From these measurements, after proper correction for incomplete relaxation, the magnetic moments of 183mPt, 183Ir and 182Ir have been derived. The applicability of the time-resolved nuclear orientation technique for nuclei far from stability and its possible limitations is discussed. © 1992 J.C. Baltzer A.G., Scientific Publishing Company.

Magnetic hyperfine fields in the Ag of Fe/Ag multilayers have been observed with low-temperature nuclear orientation for multilayers [Fe(xML)/Ag(yML)] with (x,y) values of (9,3), (18,3) and (10,5). The γ-ray anisotropy was measured as a function of the external applied magnetic field. The hyperfine fields from the measurements are then compared with those fields derived by the model developed by M.B. Stearns.

α-particle angular distribution data from an extensive on-line nuclear orientation study of the favoured decay of nearly spherical, neutron deficient At and Rn nuclei near N=126, as well as of deformed Fr and Pa isotopes are presented. From the comparison of these data with various theoretical models it is found that for nearly spherical nuclei, anisotropic α-emission in favoured decays can be well explained within the shell model but not by a tunnelling model. On the other hand, for the deformed nuclei studied here, a description on the basis of α-particle tunelling through the Coulomb barrier is quite appropriate.

Magnetic moment direction of Tb in [Fe(40 A)/Tb(x A)]30 multilayers (x=20 and 10) has been studied by the low-temperature nuclear orientation technique in the temperature range of 5–50 mK and in the external magnetic field (Bext) range of 0–1 T, applied along the sample plane. The γ-ray anisotropy of the 299 keV160Tb line was monitored. The perpendicular magnetic anisotropy (PMA) of the Tb magnetic moments has been found at zero Bext for both systems. The PMA effect increased when the Tb layer thickness decreased.

We present preliminary results concerning the non-linear conduction in the variable range hopping regime. The dependence of this non-linearity on the temperature and on the applied magnetic field is investigated.

Low-temperature nuclear orientation (NO) is presented as a useful tool to study the behaviour of rare earth (RE) ionic magnetic moments in magnetic multilayers. NO is shown to give rather direct information about the direction of RE ionic moments in such low-dimensional systems. In particular, the perpendicular magnetic anisotropy (PMA) can be directly monitored using RE atoms as probes. The potential of NO is demonstrated by our recent results, which concern the Fe/Tb multilayers. We have studied NO of 160Tb in Fe(40 Å)/Tb(x Å) (x = 5–30) and found that the Tb magnetic moments show PMA at low external magnetic fields (Bext). PMA of the Tb spins is found to be more pronounced when the Tb layer is thinner. It was found that Bext has a complicated influence on the Tb magnetic moment misalignment, which is connected with an interplay between PMA, the exchange interactions and the shape and magnetic crystalline anisotropy.