Showing papers in "Journal De Physique Lettres in 1975"

Ferroelectric liquid crystals

Abstract: A general symmetry argument is presented, and experiments on newly synthesized p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate are described, demonstrating that chiral smectic C and H liquid crystals are ferroelectric. Some of the properties of this new class of ferro-electrics are discussed.

Collapse of a polymer chain in poor solvents

Abstract: The behavior of a single, flexible polymer chain near the Flory temperature Θ is analysed in analogy with a magnetic phase transition. The transition to a collapsed state is related to a tricritical point for the magnetic problem.

Local Frederiks transitions near a solid/nematic interface

Abstract: We consider a solid/nematic interface where long range van der Waals torques favor homeotropic alignment, while a direct steric effect tends to induce a planar alignment. Depending on the relative strength of the two contributions, one may find two transitions : planar ↔ conical and conical ↔ homeotropic. This is reminiscent of recent observations by Ryschenkow and Kleman on glass surfaces coated with carbon black. Similar local Frederiks transitions could occur by competition between two distinct planar arrangments.

Superconducting properties of aluminium thin films after ion implantation at liquid helium temperatures

Abstract: Using a recent modification of the Orsay ion implantor, Al, O, He, H and D were implanted into Al thin films at temperatures below 6 K. The critical temperature Tc of the implanted films depends on the implanted ion dose and range distribution as well as on radiation damage effects. The higher limit of Tc ranges from 2.7 K to 4.1 K for Al, O and He implantations. It reaches 6.75 K for H, at an average concentration near AlH2.

The electrical conductivity of TTF-TCNQ under pressure

Abstract: We report b-axis electrical conductivity data for TTF-TCNQ single crystals from 20-300 K under hydrostatic pressures of up to 6 kbar. There are two anomalies in the conductivity. Under pressure, the temperature of the well-known metal-insulator transition at 54 K increases slightly (in agreement with the earlier work of Chu et al.). We find that the temperature of the lower anomaly at 38 K decreases slowly with pressure. Since there is evidence that the conduction electron bandwidths increase substantially in the above pressure range it is not easy to interpret these results in terms of current theories of the Peierls transition.

Raman scattering : measurements of depolarization ratios and order parameters in an oriented nematic mesophase

Abstract: A recent Raman investigation technique [1,2] has been used to study the evolution, with respect to temperature, of two depolarization ratios and deduce the behaviour of the order parameters and in the nematic liquid crystal p-heptyl- p'-nitrile-biphenyl without recourse to a non-nematic probe. Results show that while values can be accounted for within the frame of existing mean-field theories, values are somewhat lower than what could be predicted by these theories.

Effects of phonon dynamics on electrons in one-dimensional conductors

Abstract: The exact conditions under which the critical behavior of the electron density of states involves the dynamical critical indices of the soft phonon, as well as the corresponding expressions for the electron density of states are derived for a model phonon structure factor. The application of these results to real materials is discussed. A good understanding of the anomalous conductivity behavior in the qua~i-one-dimensional systems requires a knowledge of simpler quantities, such as the density of states of the electron system. Beside this, the electron density of states is interesting in . itself, since it is directly related to the magnetic susceptibility and other derived quantities [1-4]. These data show that the phonon softening produces progressively a dip in the density of states at the Fermi level. This dip merges into the Peierls gap at the lattice instability temperature. An interesting problem which arises in this connection is the question of the phonon properties relevant to the electron density of states. Since the soft phonon modes become static at the transition temperature it is tempting to think [5-7] that only the static properties determine the forementioned dip in the density of states. While this is obviously true at the very transition temperature, we show that the behavior of the dip in the critical region can involve the dynamic phonon properties, i.e. the dynamical critical behavior. Among three limiting situations, which appear to be interesting in the model examined below, there is only one in which the static structure factor alone determines the electron spectrum. In this limit we recover the previously derived results [5-7]. At temperatures at which the thermal distribution of soft phonons becomes anomalous, the leading term in the first order (Migdal) approximation for electron self energy is Here g2 is the electron-phonon coupling constant, S(co~ is the phonon dynamic structure factor and G the (retarded) Green’s function of one-dimensional electrons. In references [6, 7] this latter was replaced by its value at w’ = 0. Then, after the use of KramersKronig relation, eq. (1) reduces to the starting point of reference [5], in which only the static phonon structure factor was involved from the outset. However this step is justified only if some general criteria on the functions S(c~) and G are satisfied [8]. In order to illustrate this point we choose here the simple form of the dynamic structure factor

Susceptibility of non-crystalline ferromagnetic FeF2

Abstract: 2014 In the temperature range 150 K > T > 25 K the magnetic susceptibility of noncrystalline FeF2 can be described by a Curie-Weiss law. A paramagnetic Curie temperature of 03B8 = (22 ± 1) K and an effective moment of peff = (5.2 ± 0.1) 03BCB are found. Temperature and field dependence of the magnetization between 15 K-20.5 K indicate superparamagnetic behaviour. At lower temperatures the magnetization shows hysteresis and a slightly time dependent remanence. The observation of moments which approach 4 03BCB/Fe2+ implies that the ordered state is ferromagnetic. Non-crystalline FeF2 can be prepared by condensation of a molecular beam of FeF2 on to a He-cooled substrate in a vacuum of 108 torr. We have shown previously by Mossbauer spectroscopy that noncrystalline FeF2 becomes magnetically ordered below N 21 K [1 ]. This is in contrast to the Neel temperature TN = 78 K found for crystalline antiferromagnetic FeF2 [2]. The non-crystalline samples of FeF2 are converted into the crystalline state only at temperatures above 800 K [3]. It is thus possible to warm such samples to 300 K, carefully brush the amorphous material from the substrate, and then transfer the powder under an inert atmosphere into a magnetometer (Foner type, vibrating sample method) without any structural changes taking place. The measured susceptibility in a field of H = 1 250 Oe and the temperature range 150 K > T > 25 K can be described by a Curie-Weiss law (Fig. 1). An extrapolated paramagnetic Curie temperature of 0 = (22 ± 1) K was found together with Peff = (5.2 :L 0.1) ,uB. The derived value g = 2.12 ± 0.05 of non-crystalline FeF2 is only slightly larger than g = 2.10 ± 0.05 for crystalline FeF2 [4]. The magnitude and temperature dependence of the quadrupole splitting and the magnitude of the magnetic hyperfine interaction as derived from the Mossbauer spectra indicate a less complete quenching of the orbital momentum in non-crystalline FeF2 compared to the crystalline phase [1, 3]. A simple (*) Work supported in part by Bundesministerium fur Forschung und Technologie. FIG. 1. Inverse susceptibility of non-crystalline FeF2 against temperature. perturbational treatment for the crystal electric field levels shows that an increase of the rhombic distortion at Fe2 + in the non-crystalline phase leading to a decrease of the splitting between the ground state and the first excited orbital state from 700 cm-’ 1 (crystalline phase [5]) to 500 cm-1 can explain the increase of orbital momentum. It would, however, only cause an increase of 0.03 in g-factor which agrees well with the data found. In figure 2 the magnetization curves between 1520.5 K are plotted as (M x Ms(T = 0))/M,(r) against H x Ms(T)/(T x Ms(T = 0)). The approximate ratios of the spontaneous magnetizations Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:01975003607-8019700

On the pressure dependence of superconductivity in transition metal dichalcogenide layer crystals

Abstract: 2014 Present evidence in this field suggests that high critical temperatures are due to large electronic densities at the Fermi level rather than to soft phonon modes. Recent measurements of the pressure dependence of superconductivity in transition metal dichalcogenide layer crystals have shown different behaviour in sulfur and selenium compounds [1]. In both 2H Nb S2 and 3R Nb S2, the critical temperature 7c and the critical field Hc2, show very little variation with pressure, at least up to 10 kbar (Fig.1 a, b). FIG. 1. Pressure dependence of the critical temperature 7. in transition metal dichalcogenide layer compounds (schematic) : a) 2H Nb S2 ; b) 3R Nb S2 ; c) 2H Nb Se2. In 2H Nb Se2, the critical temperature Tc increases rapidly with pressure up to 35 kbar, then shows little variation with pressure up to 140 kbar (Fig. tc). H~2 increases with pressure in the low pressure range (measured up to 13 kbar), when measured both parallel and perpendicular to the layers. The high value and pressure variation of Tc in the Se compound have been related to the fact that it exhibits a low temperature phase transformation which is clearly due to a Peierls instability, i.e. on cooling down, the electron-phonon couplings stabilizes a new phase which opens gaps at the Brillouin zone boundary near to the Fermi surface of the high temperature phase [2]. We want to suggest here that the superlattice phase disappears above 35 kbar, leaving the undistorted phase, as observed in the sulfur compound. This is strongly suggested by the constancy of Tc above 35 kbars. It would of course be of interest to check this directly or by a study of transport properties. If this suggestion is right, it should allow the contribution of soft phonon modes and a high electronic density at the Fermi level to the high T~s to be distinguished. 1) The existence of a large and pressure independent 7c ~ the Se compound over a very large range of pressures where the superlattice phase would be unstable would rule out the soft phonon modes associated with such a phase as responsible for high TJs. Indeed it is difficult to believe that any phonon mode could remain in the soft critical state over such a large range of pressures. It looks therefore extremely probable that the high Tc observed in the Se phase above 35 kbar is to be related to a large density of electronic states at the Fermi level N(Ep). Indeed one expects a narrower d band, thus a larger value of N(EF) in the Se compound than in the S ones, because the larger atomic radii of Se compared with S induce the Nb atoms to be further apart, both within metallic planes and between metallic planes. 2) The creation of the superlattice phase lowers Tc. This is difficult to understand on a soft phonon mode picture, where a minimum of Tc should be expected when the superlattice phase just disappears under pressure, thus tentatively at 35 kbars. It is again very Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:019750036011027900

Coexistence de forme dans le noyau 187Au

Abstract: 2014 In 187Au, studied by radioactivity and by the 175Lu(16O, 4 ny) 187Au reaction at 95 MeV, two decoupled bands are built on h9/2 and h11/2 intrinsic states, implying, as in 189Au, the coexistence of prolate and oblate deformations. The behavior of high spin states is analysed and compared to 186Pt. Recemment, des resultats sur les ors impairs obtenus par reaction (ions lourds, xn) ont permis d’attribuer (1) Reactions (ions lourds, xn). (2) Radioactivite (separateur ISOCELE). (*) Institute of Nuclear Study, Tokyo, Japon. (**) Universite Paris VII. .(***) Centre de Spectroscopie Nucleaire et de Spectrometrie de masse, 91406 Orsay. (****) Universite Paris VI. _ une deformation aplatie (oblate) aux ors les plus lourds (A = 195 a 191) [1] ; de plus, dans le noyau 189 Au [2, 3], la coexistence de deformations allongee (prolate) et aplatie a ete mise en evidence. En effet, pour les noyaux d’or, le niveau de Fermi en protons se trouve situe entre les couches h11/2 et h9/2. L’observation de bandes decouplees, par effet de Coriolis, pour une orbitale hi 1/2? indique [4, 5] une deformation aplatie ; pour le noyau 18 9Au, ou apparait en plus une bande decouplee sur 1’etat 9/2-, les deux formes FiG. 1. Schema partiel de la desintegration de 187Hg. Les transitions qui ont ete egalement observees dans la reaction 175Lu(160,4n)187Au ainsi que les niveaux qui en decoulent sont en traits epais. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:01975003609020500

On the temperature dependence of electrical resistivit in concentrated disordered transition binary alloys

Abstract: Using a two (s-d) band model and the CPA theory of conductivity, we calculate the effect of the phonon induced modification of the density of states on the T-dependence of the electrical resistivity in concentrated transition metal alloys. It is shown that this effect is not at all negligible and in some cases can yield a negative T-coefficient dρ/dT as observed in some of these alloys.

Quasi-fission reactions induced by 365 Mev 63Cu ions on a 197Au target

Abstract: 2014 Quasi-fission and complete fusion cross sections have been measured for the system 63Cu + 197 Au at a bombarding energy equal to 1.1 times the interaction barrier. Like the krypton case, very few complete fusion events are observed, and the quasi-fission cross section (250 ± 50 mb) is one half of the reaction cross section. A more precise determination of the mass of one of the products has been performed. The mass distribution of the quasi-fission products varies with the angle of detection. The light products (mass around that of copper) show a clear maximum at an angle slightly lower than the grazing angle. The results suggest that events found at the low angles correspond to projectiles with low l-values which have undergone a greater mass exchange than the high l-value projectiles. The total kinetic energy is constant as a function of the angle, or slightly increasing at forward angles. Since the reaction of quasi-fission has been observed [1] in bombardments of heavy nuclei with g4Kr ions, several features of this phenomena have been studied [2, 3] and our present experimental knowledge can be summarized as follows : two main fragments are produced, the mass of one fragment being close to the mass of the projectile and the mass of the other fragment close to that of the target nucleus. The fragment kinetic energies are close to (somewhat higher than) the values expected for fission of the compound nucleus [2] and at the energies where measurement have been made (from 1.1 to 1.3 times the interaction barrier) the cross section for quasifission accounts for more than one half of the total reaction cross section, while the fusion cross section is unexpectedly small. Perhaps the most puzzling feature, however, is that the angular distribution of the light quasi-fission products is strongly peaked at an angle slightly lower than the projectile grazing angle. Since the major fraction of the reaction cross section goes into a complete fusion process for projectiles up to 4°Ar, the question of the relative importance of complete fusion and of quasi-fission arose for reactions induced by projectiles between Ar and Kr. An answer to this question was provided by a preliminary result from an experiment done with the first 63Cu projectiles accelerated at the Orsay heavy ion accelerator ALICE. With 395 MeV 63CU ions incident on a 186W target, the main observed features were found to be similar to those of the Kr case : low fission cross section, high quasi-fission cross section and an angular distribution peaked near (but slightly lower than) the grazing angle [4]. It must be kept in mind that all the results of references [1-4] have been obtained by simply measuring the kinetic energies and angles of the two final products. More intense 63Cu beams allowed us to make a direct determination of the mass of one final product, by measuring its time-of-flight and energy. The choice of the 19’Au target and of the bombarding energy (365 MeV) are based on the following considerations : 1) The maximum angular momentum involved in the reaction is around 100 ~ and the compound Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:0197500360202300

d Surface states in transition metals

Abstract: The tight-binding model, including d band degeneracy, is used to calculate the local densities of states on low index surfaces of fcc Ni and bcc Fe. Charge transfer effects are investigated. The results show the existence of peaks of surface states inside the band on non dense planes of cleavage and a broadening of the band when the surface perturbing potential is strong enough. They are consistent with experimental data.

Cluster calculations of the electronic d-states in VO2

Abstract: An ab-initio cluster calculation of the electronic d-states in VO$sub 2$ has been made by using the self-consistent statistical exchange multiple scattering method. VO$sub 6$$sup 8-$ octaedron was used to represent the tetragonal phase, and a V$sub 2$O$sub 10$$sup 12-$ cluster with paired vanadium atoms was used for the monoclinic phase. Our results are in conflict with an explanation of the semiconducting gap in terms of simple distortion-induced band splitting. (FR)

Déplacement et élargissement de la transition à deux photons 3S-4D dans l'atome de sodium par collision contre des atomes de néon

Abstract: On etudie experimentalement l'elargissement et le deplacement de la transition a deux photons sans elargissement Doppler 3S-4D dans l'atome de sodium par collision contre des atomes de neon. On trouve pour l'elargissement α = 32 ± 5 MH z/torr et pour le deplacement β = - 7 ± 1 MHz/torr. Cette methode permet d'etudier l'effet des collisions dans des niveaux S et D avec de faibles pressions de gaz etrangers (environ 1 torr).

Hanle effect for monochromatic excitation. Non perturbative calculation for a J = 0 to J = 1 transition

Abstract: Exact theoretical expressions are derived for the fluorescent light observed in a level crossing experiment performed on a Jg = 0 to Je = 1 transition using monochromatic excitation. The effect of radiative broadening and Zeeman detuning is discussed.

Observation of the 6S1/2-7S1/2 single-photon transition of cesium induced by an external d. c. electric field

Abstract: We have observed the direct single-photon electric dipole excitation of the 7 2S1/2 state of cesium, by exciting the 6 2S1/2 ground state in an external d. c. electric field of 10 to 1 000 V/cm with a single-mode, c. w., tunable dye laser. The resonance was detected by monitoring the decay fluorescence from the excited state. We verified the selection rules obeyed by the hyperfine transitions which depend on the relative orientation of the linear polarization of the beam with respect to the field. When they are orthogonal, the line pattern reflects the existence of a spin-dependent part of the polarizability induced by spin-orbit effects, the size of which was measured with respect to that of the scalar part. Results in very weak fields show that the oscillator strength of the 6S-7S transition is smaller than 2 x 10-13.

Étude de la structure des chaines dans les différentes phases, solide, nématique, ou liquide, du méthoxy benzilidène butyl aniline (MBBA)

Abstract: Une analyse fine des spectres Raman du MBBA dans les phases solide, nematique et liquide est proposee : on montre que ce compose presente trois formes cristallines notees A, B et C et que les raies observees entre 1 100 et 650 cm-1 mettent essentiellement en jeu la chaine butyl. Les modifications importantes observees dans cette region lors des transitions de phases sont attribuees a des modifications structurales de cette chaine ; on montre en particulier que la fusion de la chaine n'est pas totale en phase nematique et on propose une methode de mesure directe de leur parametre d'ordre.

Shape change of the flexible polymer in solution with increasing concentration

Abstract: A few deuterated polystyrene chains are dispersed in a solution of protonated polystyrene and carbone disulfide. The neutron scattered intensity is measured at several concentrations of protonated chains. Already in the semidilute range, there is a striking contrast with the results obtained at equal concentrations in fully deuterated solutions. The dependence of the pair correlation function on concentration is discussed in terms of the excluded volume exponent.

Amplitudes of the logarithmic singularities for the four-dimensional critical behavior

Abstract: HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Amplitudes of the logarithmic singularities for the four-dimensional critical behavior E. Brézin

Temperature dependence of spin exchange frequency shifts in H-H collisions

Abstract: 2014 Experimental data on the spin exchange frequency shifts due to hydrogen-hydrogen spin exchange collisions are reported over the temperature range 77 K to 363 K. They are found to agree with the results of a theoretical calculation of the temperature dependence of the spin exchange frequency shift cross-section and with an experimental result obtained by a different technique near room temperature. Our experimental results confirm the prediction that the spin exchange frequency shift crosssection changes sign at low temperature. LE JOURNAL DE PHYSIQUE LETTRES TOME 36, DECEMBRE 1975,

Critical behaviour in a field for uniaxial ferroelectrics and ferromagnets with dipolar interaction

Abstract: 2014 The purpose of this paper is to obtain the logarithmic critical singularities for uniaxial dipolar systems (or for the four dimensional theory) in non zero external field. The result takes a simple form only for n = 1, n being the number of components of the order parameter. For example the inverse magnetic susceptibility behaves as ~-1 ~ ~-1m.f. | log ~-1m.f. |-1/3 in which m.f. refers to mean field value when H is non zero.

Ultrasonic investigation of rotational isomerism on mesomorphic compounds

Abstract: 2014 The attenuation coefficient of ultrasonic longitudinal waves in the nematic phase of the p methoxy p’ n butyl azoxybenzene (Licristal Merck IV) has been measured as a function of both frequency and temperature. For temperatures far below the nematic-isotropic transition, the frequency dependence of the attenuation can be accounted for by a single relaxational process. The temperature dependence of the relaxational frequency appears to support the assumption of rotational isomerism in the flexible ends of the molecules. The ultrasonic properties of liquid crystals have been examined by several investigators [1-11]. Most of the studies have been performed in the vicinity of the nematic-isotropic transition temperature 7~ where the sound wave propagation shows anomalous behaviour characterized by a sharp maximum of the low frequency attenuation and a sharp minimum of the velocity. In that temperature range the ultrasonic properties are characteristic of a multiply relaxing fluid. The averaged relaxation frequency diverges at Tc. Experiments performed on the p-methoxybenzylidene p-n butyl aniline (MBBA) have shown that, even at temperatures far below the transition temperature (T 7c 2013 200) a strong relaxational contribution to the attenuation still subsists, whose frequency dependence is satisfactorily described by a single relaxation [7, 12]. This relaxational process has been assigned to the perturbation by the sound wave of an intramolecular equilibrium [12, 13]. The MBBA, as well as all the (*) Work partially supported by D. R. M. E. Contract 71/034. mesomorphic compounds, consists of molecules having a rigid central part and two flexible end groups. Some of the possible conformations of these end groups differ in their free energy and then are acoustically effective. The internal relaxational process was first assigned to a cis-trans equilibrium of the methoxy group [12] (see Fig. 1) by analogy with esters or vinyl-ethers where relaxational processes have been observed in the range of 1-100 MHz [14]. In those compounds, the barrier for the rotation arises from the partial double bond Para Methoxy p’n butylazoxybenzene ( Licristal Merck ISZ ) FIG. 1. Molecules of MBBA and Licristal Merck IV. The arrows indicate the acoustically effective rotational isomerisms. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:0197500360101300

Rayleigh sound wave propagation on a gallium single crystal in a liquid He3 bath

Abstract: The observation of the Rayleigh sound wave propagation on a gallium single crystal at frequencies up to 120MHz and temperatures down to 0.4K is reported. The velocity and the attenuation are studied at different temperatures. The attenuation of Rayleigh waves by the He$sup 3$ bath is also studied at different temperatures and frequencies. (FR)

Étude de la configuration (d5/2)25+ dans 22Na et 24Na

Abstract: 2014 The 20,22Ne(03B1, d)22,24Na reactions have been studied at 21.5 MeV. Strongly excited levels are located at (1.529 ± 0.006) MeV in 22Na, and at (1.500 ± 0.008) MeV in 24Na, which we attribute to the principal configuration (d5/2)25+. DWBA adjustments have been performed ; both levels of interest are characterized by L = 4.

Determination of the hyperfine structure of the 2p levels of 21Ne using a cw tunable dye laser

Abstract: 2014 H.f.s. measurements on the 2p levels of 21Ne have been performed using the levelcrossing method. The investigated levels were optically pumped using a dye laser. Experimentally, the hyperfine structures of the excited levels of 21 Ne are rather poorly known. At the present time, there are available only a few spectroscopic determinations [1,2, 3] and (for the Is 5 level) one very accurate atomic beam determination by Grosof et al. [4]. From the available experimental values, Liberman [1] was able to determine the atomic parameters of several configurations and to predict their hyperfine structures. In this letter, hyperfine structure measurements on the 2p series (2ps 3p configuration) by the levelcrossing technique are reported. We have determined the position of the level-crossings between the hyperfine sublevels of the 2P2, 2p4, 2ps, 2p6, 2?~, 2p8 states and deduced their magnetic dipolar and electric quadrupolar hyperfine interaction constants a and b. The metastable (and excited) states were populated by a R.F. discharge (frequency 1 MHz), and alignment was induced with a linearly polarized CW dye laser tuned on one of the transitions between the Is states and the state under investigation. The transitions we used are given in Table I. Their wavelengths are all in the laser spectral range covered by Rhodamine 6G. The laser was a Coherent Radiation jet stream dye laser. The cavity length had been increased up to 1.5 m by moving the output mirror further off. Thus the number of modes in the Doppler profile was increased and the pumping signal was much less sensitive to intensity fluctuations between modes and to the frequency drift of these modes. The width of the emission spectrum of the dye laser, in which the wavelength selection is determined by the use of a Lyot filter, varied between 10 and 40 GHz, depending on the output power; thus the spectrum of the pumping light was several times broader than the hyperfine structure and Zeeman separations. FIG. 1. Sketch of the experimental set-up. A sketch of the experimental set-up is shown in figure 1. The cell containing neon, or a mixture of helium and neon, was illuminated by the laser beam

Resistivity annealing properties of aluminium thin films after ion implantation at liquid helium temperatures

Abstract: We present the first resistivity annealing curves of Al after implantation of Al-, H-, and O-ions at liquid helium temperatures. The Al-implantation produces a curve resembling that of neutron-irradiated Al ; low-dose H- implantation results in two strongly enhanced stage I recovery peaks, while high-dose H- implantation annealing results suggest that H-ordering or a phase transformation takes place.

Spin-dependent scattering lengths of slow neutrons with nuclei by pseudomagnetic measurements

Abstract: The spin-dependent scattering length of slow neutrons by the nuclei 23Na, 59Co, 63Cu, 65Cu, 195Pt, 197Au and 207Pb, as well as the mean value for the two isotopes of Tl and Ag in the natural element have been obtained by measuring the precession of the neutron spins as a function of nuclear polarization. A revised value for 91Zr is also given. The method has been extended for use with magnetic materials. Using f.c.c. and hexagonal cobalt, it is shown that these pseudomagnetic measurements may give precise information on the internal field seen by the nuclei.