Helium spots

Wakita, H., 1978. Helium spots caused by diapiric magma from the upper mantle. Science, 200 430-432. 

The 1996 Nobel Prize in physics went to three researchers who studied liquid helium at a temperature of 0.002 K, discovering superfluid helium. A superfluid behaves completely unlike conventional liquids. Liquids normally are viscous because their molecules interact with one another to reduce fluid motion. Superfluid helium has zero viscosity, because all of its atoms move together like a single superatom. This collective behavior also causes superfluid liquid helium to conduct heat perfectly, so heating a sample at one particular spot results in an immediate and equal increase in temperature throughout the entire volume. A superfluid also flows extremely easily, so it can form a fountain, shown in the photo, in apparent defiance of gravity. 

A light-ion microbeam system connected with the 3-MV single-ended accelerator was developed for high-resolution ion beam microanalysis [37]. The highest spatial resolution of 0.25 pm was achieved for 2-MeV proton and helium ions. The beam spot size was estimated from the intensity distribution of the secondary electrons emitted from a silicon relief pattern irradiated with the 2-MeV helium ion microbeam as shown in Fig. 10. 

Figure 10 Estimation of the spot size of the 2-MeV helium ion microbeam from the image of a silicon relief pattern obtained by detecting secondary electrons.

Fig. 3.4 (a) Simple metal field ion microscope which uses a Helium Displex Refrigerator for tip cooling. A tip is mounted on a 5 mil Pt wire heating loop with two 1 mil Pt potential leads spot welded onto it. An adatom deposition source, a coil supported by two degassable loops, is also shown. Vacuum is easier to achieve... 

Normally, if the assumed model for a crystal structure has an R value of 0.5 and resists attempts to refine to a lower residual, then the model structure is rejected as false, and a new model is tried until a fit between the observed and calculated structure factors yields an acceptable residual (R < 0.25). (Other models were tried for this complex, but they either gave Fourier maps which were uninterpretable or they converged to the present model). However, the normal crystal structure is solved with data obtained from crystals which have dimensions of the order of 0.1 mm. In the crystals available for this experiment, two of the dimensions were of the order of 0.01 mm. Thus, long exposures were required to give a small number of relatively weak diffraction spots. (Each Weissenberg photograph was exposed for five days with Cuka radiation 50 kv., 20 ma. loading, in a helium atmosphere). 

These measurements were made on an Auto EL-II Ellipsometer (Rudolph Research, Flanders, NJ). The laser source was a 1 mW continuous wave helium/ neon laser, with a wavelength of 6328 A. The angle of incidence was 70° and the spot size 2-3 mm. A refractive index of 1.5 was utilized for all the silane layers. The data were analysed on a Hewlett-Packard 85 computer using film 85 software package, version 30, program 13, and the film thickness was calculated using the McCrackin program. 

The strange carbon blast was produced by binary star 4U 1820-30, which consists of a dwarf star orbiting a neutron star. Gas from the dwarf flows in a spiral pattern around the neutron star. When some of the dwarf s gas collides with the neutron star s surface, a compressed slurry of hydrogen and helium is formed. Pressures and temperatures can get sufficiently high in the slurry layer that the elements flash-fuse in a thermonuclear explosion. Each blast leaves carbon, one of the byproducts of helium fusion. Gradually a layer of carbon several hundred meters thick reaches a critical temperature and ignites a carbon bomb that rages for hours. [For more information, see Robert Irion, Astronomers spot their first carbon bomb, Science 290(5495) 1279 (November 17, 2000).]... 

For example, say your setup takes one minute from the time you introduce helium to a leak until it is acknowledged by the helium leak detector. In addition, say your spray probe is being moved at four inches per minute (which is pretty slow if you think about it). You will therefore be four inches away from a leak when it is first identified. Generally, moving the spray probe at a rate of one foot per minute provides an adequate time response, which of course can be made faster or slower as conditions warrant. However, if you know the response time, you will know about how much to back up to retest the area in question to allow pinpointing the specific leak spot. 

In particular, the study of noble gas isotopes has provided a compelling case for mantle layering and the preservation of primitive mantle (see Chapter 2.06). For example, He/" He values for MORBs are nearly uniform, but large departures are seen for OIBs. Most oceanic hot spots have elevated He/" He values compared to MORBs. Helium-4 is generated by the decay of uranium... 

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