= 3.5, y 0 = 2.5, and rc^SxlO 12 cm" 3 (i.e., al.3-MeV, 150-kA beam of 1.4 cm radius) and a hydrogen plasma of density n p~1 0 14 cm" 3 so that n B /n p x0.05.The final temperature is (T e +T { ) f «30 keV by Eq. (7) with/«y 0 /i/. The time required to achieve this temperature falls in the range 30 nsec<^ 0.5 K) demonstrates that some 3 He is adsorbed on the surface of the liquid. In Andreev's model the adsorbed 3 He is assumed to be in a set of independent quasiparticle states with energy spectrum 2 * = ~ € 0 +p 2 /2M.(1)The surface tension of the solution, a, is then the surface tension of liquid 4 He, a 4 , reduced by the two-dimensional "pressure" of the 3 He quasiparticle gas on the surface. From measurements of Aa=a 4~ a at T>0,5K and assuming that the sur-port No. . 7 Only a small drift of the ions t^{ m e /m i )vv p in the beam direction results from momentum conservation. 8 The factor d in Eq. (7) depends on the geometry and is given by d-\ +21n(b/a), where b is an outer radius where the field energy integral is cut off. 9 H. (to be published).face quasiparticle gas could be treated by Boltzmann statistics, Zinov'eva and Boldarev 3 determined approximate values for the surface binding energy e 0 and the effective mass M.There is considerable interest in studying the many-body properties of adsorbed helium particularly in this case since the substrate (liquid helium) is uniquely perfect and homogeneous. We therefore have made further measurements of a down to low temperatures (0.04 K) and over a wide range of X, the concentration in the bulk phase (30 ppm to saturation). Under these conditions the adsorbed 3 He can be changed from a fraction of an atomic layer, when it behaves like Some properties of 3 He adsorbed on the surface of liquid helium are determined from measurements of the surface and interfacial tension of 3 He-4 He mixtures. As a mixture approaches phase separation, the 3 He adsorbed on the surface grows continuously into the upper, 3 He-rich phase. At all temperatures the limit of low surface density is well described by the Andreev model, although there is some evidence for a weak, attractive quasiparticl...
We have developed a scanning magnetic microscope (SMM) with 25 µm resolution in spatial position for the magnetic features of room temperature objects. The microscope consists of a high-temperature superconductor (HTS) dc SQUID sensor, suspended in vacuum with a self-adjusting standoff, close spaced liquid nitrogen Dewar, X -Y scanning stage and a computer control system. The HTS SQUIDs were optimized for better spatial and field resolutions for operation at liquid nitrogen temperature. Measured inside a magnetic shield, the 10 pT Hz −1/2 typical noise of the SQUIDs is white down to frequencies of about 10 Hz, increasing up to about 20 pT Hz −1/2 at 1 Hz. The microscope is mounted on actively damped platforms, which negate vibrations from the environment as well as damping internal stepper motor noises. A high-resolution video telescope and a 1 µm precision z-axis positioning system allow a close positioning of the sample under the sensor. The ability of the sensors to operate in unshielded environmental conditions with magnetic fields up to about 15 G allowed us to perform 2D mapping of the local ac and dc susceptibility of the objects.
The solubility curve has been measured at the saturated vapor pressure down to 0.025°K, and the limiting solubility at absolute zero has been determined to be (6.37 ± 0.05)% He 3 . Measurements of the density show that at 0°K and small concentration the volume occupied by a He 3 atom in solution is 1.284± 0.005 times the volume occupied by He 4 .
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