X-TRONIX SciTech Blog

LHC at a glance

Xavier — Wed, 02 Jun 2010 08:08:00 GMT

Get to know the inner works of the LHC collider at CERN, Geneva

On March 30, 2010 two beams tavelling in opposite direction were ramped up to reach 3.5 TeV colliding at a combined energy level of 7 TeV at exactly 13:00. Click this link for the streaming video of that historic moment!

Click 'more' below for 2 additional highly interesting videos on the LHC.

'Perfect' Liquid Hot Enough to be Quark Soup

Xavier — Tue, 16 Feb 2010 00:44:00 GMT

Protons, neutrons melt to produce ‘quark-gluon plasma’ at RHIC

Recent analyses from the Relativistic Heavy Ion Collider (RHIC), a 2.4-mile-circumference “atom smasher” at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, establish that collisions of gold ions traveling at nearly the speed of light have created matter at a temperature of about 4 trillion degrees Celsius — the hottest temperature ever reached in a laboratory, about 250,000* times hotter than the center of the Sun. This temperature, based upon measurements by the PHENIX collaboration at RHIC, is higher than the temperature needed to melt protons and neutrons into a plasma of quarks and gluons. Details of the findings will be published in Physical Review Letters.

These new temperature measurements, combined with other observations analyzed over nine years of operations by RHIC’s four experimental collaborations — BRAHMS, PHENIX, PHOBOS, and STAR — indicate that RHIC’s gold-gold collisions produce a freely flowing liquid composed of quarks and gluons. Such a substance, often referred to as quark-gluon plasma, or QGP, filled the universe a few microseconds after it came into existence 13.7 billion years ago. At RHIC, this liquid appears, and the quoted temperature is reached, in less time than it takes light to travel across a single proton.

The Kelvin Probe Principles

Xavier — Thu, 07 Jan 2010 12:02:00 GMT

When two conducting materials with different work functions are brought together, for example via an external wire contact, electrons in the material with the lower work function flow to the one with the higher work function. If these materials are made into a parallel plate capacitor, equal and opposite surface charges form. Measuring the contact potential is then exquisitely simple: an external potential is applied to the capacitor until the surface charges disappear, and at this point the external potential equals the contact potential. Kelvin realized this experimentally measured using two large flat polished disc's of Zinc and Copper and a gold-leaf electroscope to measure the charge transfer upon electrical contact.

In 1932 William Zisman of Harvard University introduced a new method to measure the contact potential. He mounted a vibrating reference surface, or tip, just above a sample electrode. The output voltage varies periodically as the tip vibrates, and the peak-to-peak voltage depends upon the difference between the contact potential and the external voltage. Changes in contact potential can then be detected by determining the external potential that yields a minimum or "null" output voltage. This technique lead to development of systems that automatically track shifts in the contact potential due to changes in the work function of the sample.

A major improvement of this new method is that the surfaces do not need to touch each other. It only requires very weak electric fields, which are not likely to influence the electrical or chemical structure of the material. Biasing of the sample rather than the tip will reduce noise, and the use of a low impedance current sensitive amplifier rather than a high impedance voltage sensitive amplifier minimizes the interference from parasitic capacities. However this isn't the whole story: real-world commercial systems inherently produce talkover from the driver (the device used to vibrate the tip).

This can substantially influence work function measurements and consequently an "off-null" technique has been developed by Baikie, (see for instance, Baikie et al, 'Noise and the Kelvin Method, Review of Scientific Instruments, Vol. 62, page 1326, 1991). This system has the added advantage of allowing accurate measurements of mean capacity which can be used to perform scanning measurements at a constant height allowing the user to automatically perform measurements under identical experimental parameters. Without this feature the apparent work function difference will be different each time the user starts an experiment.

It is important to recognize that the Kelvin Probe is a relative technique capable of approximately 1 mV relative resolution. The work function of the tip must therefore be known in order to obtain the absolute work function of the sample. This problem has been addressed by illuminating a low work function reference sample with monochromatic ultraviolet light, and then measuring the energy at which current starts to flow. This technique can detect changes in absolute work function of 30-50 meV, (see Baikie et al, 'Work Function study of rhenium oxidation using an ultra-high vacuum scanning Kelvin probe, Journal of Applied Physics, Vol. 88, page 4371, 2000.)

Now that you're exposed to the "principles", discover the "theory" behind the Kelvin Probe!

In situ work function study of oxidation and thin film growth on clean surfaces

Xavier — Tue, 05 Jan 2010 23:14:00 GMT

Authors: I.D. Baikie, U. Petermann, B. Lägel

Abstract: Using a novel ultra high vacuum compatible Kelvin probe a study is made of the work function (f) changes on semiconductors and metals occurring during basic surface processing, for example, surface cleaning, sputtering, oxidation and thin film growth. It shows that damage of the 7×7 reconstruction due to Ar ion bombardment has a profound influence on the work function changes (Δf) during oxidation on the Si(111) surface, tending to decrease or even reverse the surface dipole. Also following the variable temperature oxidation kinetics of Si(111) in the range of 100–600 K and show that magnitude of the Δfpeak during the initial adsorption curve decreases in a linear fashion with increasing substrate temperature. This is interpreted as being due to the rapid onset of oxygen permeation through the surface layer at higher temperatures producing a reverse or zero net dipole. Combining work function data with a localized technique such as scanning tunneling microscopy permits monitoring of surface processes at both microscopic and macroscopic levels. In conjunction with Professor Behm’s group at Ulm University, Germany, this study monitored work function changes during evaporation of Al on Ru(0001) and show correlation between changes in f with topographic features such as island growth mechanism, monolayer formation, etc.

Read the full application note

Helium atoms get the ride of their life

Xavier — Fri, 30 Oct 2009 08:44:00 GMT

Author : James Dacey, www.physicsworld.com

To the adrenaline junkie mid-way through a bungee jump, gravity must feel like it can accelerate matter at a spectacular rate. At the atomic scale, however, when it comes to shifting around neutral particles, gravity is incredibly ineffective compared with other fundamental interactions such as the strong and weak nuclear forces.

Now, however, a team of physicists in Germany has shown that a little-known interaction caused by electric fields known as the "ponderomotive" force can accelerate neutral particles at up to 1014 times the Earth's gravitational acceleration. As well as being of interest to fundamental physics, this ability to transfer large amounts of momentum to neutral particles could lead to a host of novel applications in surface science, say the researchers.

.....read the full article

About Static and Dynamic SIMS

Xavier — Fri, 02 Oct 2009 20:10:00 GMT

In static SIMS, dedicated to the analysis of the top monolayer, the primary ion dose is kept below 112 ions/cm2 and the mass spectrum reveals MOLECULAR information. In dynamic SIMS mode, the primary ion dose is not limited and exceeds 112 ions/cm2. In this mode, ELEMENTAL and ISOTOPIC information can be obtained from the mass spectrum. It allows surface, "bulk" and 2D/3D analysis.

The ionization yield of most elements varies by decades, depending on the chemical environment. This property is used in SIMS instruments to increase the sensitivity of the technique: a dynamic SIMS instrument must be equipped with Oxygen and Cesium primary ion beams in order to enhance, respectively, positive and negative secondary ion intensity by 2 to 3 orders of magnitude compared to the use of noble gas ions. Oxygen gas can also be flooded onto the surface to oxidize it and increase positive ion emission.

When sending keV ions onto a solid surface, three important phenomena occur simultaneously:

the sputtering of mainly the top monolayer atoms, induced by the collision cascade,
the ionization of a small fraction of the secondary particles,
the primary ion implantation in the solid (and associated change of composition, surface work function, etc...).

Starting from the surface (or going through an interface), the concentration of the implanted primary species (oxygen or cesium) will vary, and then reach an equilibrium (after a few nm, depending on the conditions). As soon as this is achieved, reliable quantification is possible with reference standard samples, using Relative Sensitivity Factors.

One of the main applications of dynamic SIMS is the analysis of trace element depth distribution (for example, dopant in semiconductors). Impact ion energy is adjusted depending on the applications. Low energy (down to 200-300 eV) is used to reduce atomic mixing due to the collision cascade and improve depth resolution to the nanometer level. High energy (up to 20-30 keV) is chosen to go deeper (10-20 microns), faster (µm per min), and improve detection limits and image resolution.

The Cameca IMS 7f magnetic sector SIMS can cater to Depth Profiling with high sensitivity - down to parts per billion atomic concentration - and 2D or 3D imaging of trace elements. It is widely used for dopant implant dose matching, junction depth measurement, process development (characterization of implant, deposition, annealing,...), failure and light element analysis.

The Cameca IMS 1280 is based on a double focusing mass spectrometer with a large radius magnetic sector (585 mm). It is particularly suited for minerals studied in geology where complex materials contain many different species at trace levels. This results in a large number of mass interference that makes trace element analysis impossible without High Mass Resolution capability. Moreover, the need for in-situ analyses at continuously decreasing scales - which are not achievable with conventional technique (TIMS or ICP-MS) - has led to the development of a new generation of SIMS instruments providing High Sensitivity at High Mass Resolution.

Another important feature of the IMS 1280 is the multi-collector system equipped with 5 moveable detectors (Electron Multiplier or Faraday Cup) to perform high accuracy isotope ratio analyses from lithium to lead in multi-collection mode. It also increases the throughput of the instrument by reducing the total acquisition time.

The NanoSIMS 50 & 50L multi-detector instruments but also more oriented for ultra fine feature analysis in Materials, Geology, Planetary and Life sciences. This instrument would be ideal also for cosmic dust analysis. Among the unique new features offered by the NanoSIMS 50 are:

the ability to extend the SIMS analysis to extremely small areas or volumes (50 nm size in cesium, 150 nm in oxygen) while maintaining extremely high sensitivity at High Mass Resolution. This derives from the revolutionary coaxial optical design of the ion gun and secondary ion extraction, and from a new design of the magnetic sector mass analyzer.
the capability to measure up to 5 (NS50) or 7 (NS50L) masses (ions) in parallel, ensuring perfect isotopic ratio from the same small volume, or perfect image superimposition

In the area of quadrupole SIMS, the SIMS 4550 is the benchmark instrument with top performances in depth profiling.
Some of the key points ensuring its success are:

Reference performances in high depth resolution analysis. This derives mainly from:
- Oxygen and cesium Floating Low energy Ion Gun technology (FLIG), exceeding by far the performance of conventional or extraction floating ion columns used in other conventional SIMS. The performance in cesium beam has been impressively improved with the adaptation of the CAMECA Microbeam high brightness ion source, now common on all our SIMS range.
- A total flexibility concerning the primary ion angle of incidence, even in unattended chained analysis.
- A low field of extraction of the quadrupole analyzer facilitating the use of low energy primary ions.
Reference performances in automation and reproducibility for metrology, deriving mainly from:
- a superior redesign of the quadrupole analyzer optics (extraction, transfer, gating, post-acceleration),
- a user-friendly chain analysis software and a renowned ease of use of the instrument, reducing the need for highly-trained operators,
- ultra stable ion sources and electronics for unattended overnight measurements.
Easy insulator analysis thanks to:
- the low extraction field of the quadrupole,
- a low energy electron flood gun for charge compensation,
- unique OCE (Optical Conductivity Enhancement) for SiGe analysis.

Finally, the unique Checkerboard capability allows the operator to check the validity of the results, remove artifacts from sample inhomogeneity or dusts, without having to re-run the analysis. This adds greatly to the throughput of the instrument, reproducibility and reliability of the results.

- We refer you also to the ‘Applications’ area at our main web www.xtronix.ch
- Ref. www.cameca.fr

Is dark matter mostly 'dark atoms'?

Xavier — Thu, 24 Sep 2009 13:32:00 GMT

By: Edwin Cartlidge is a science journalist based in Rome
Sep 21, 2009 - www.PhysicsWorld.com

Physicists currently believe that most of the dark matter in the universe is made up of individual particles, and the challenge is to work out what kind of particles these are. New research, however, overturns this assumption and says that observational and experimental data are better explained if dark matter exists as composite particles – atoms of dark protons and dark electrons that are acted on by the dark-matter equivalent of the electromagnetic force.

Dark matter is thought to make up more than 80% of the matter in the universe. As its name suggests, dark matter does not reveal itself by emitting light because it does not interact via electromagnetism. Its existence is instead inferred through its gravitational effects on normal matter.

>>> click for full article

Space Simulation Vacuum / Simulation Vide Spatial

Xavier — Tue, 08 Sep 2009 12:03:00 GMT

The Extent Of Our Universe In Time & Space

Xavier — Mon, 10 Aug 2009 20:37:00 GMT

Here is the real story of how we know the extent of our universe in time and space.
(Music: Wagner's Lohengrin Prelude)

Part 1

Part 2

Inhomogeneity of a highly efficient InGaN based blue LED studied by 3D atom probe tomography

Xavier — Tue, 28 Apr 2009 09:46:00 GMT

The InGaN based multiple quantum well (MQW) structure in a commercially available white light emitting diode (LED) was studied by transmission electron microscopy (TEM) and three-dimensional atom probe tomography (APT). The average In mole fraction by three-dimensional (3D) APT was found to be about 18% in the InGaN well which is consistent with the secondary ion mass spectrometry (SIMS) analysis.

The In distribution in the InGaN well layer was analyzed by the iso curve mapping of 3D APT and found to be nonuniform in the InGaN active layer. In clustering or In rich regions in the range of 2–3 nm size were found, in contrast to recent reports. Our results thus indicate that In clustering is essential for high-brightness InGaN based LEDs. We have also observed a discontinuity in the range of 50–100.

Group III-nitride semiconductors have been recognized as very important materials for opto-electronic devices such as light emitting diodes (LEDs) and laser diodes (LDs) for applications in the visible and ultra-violet (UV) regions. To produce highly efficient light emission in LEDs, it is important to realize pure and almost perfect semiconductor materials in epitaxial growth. In most LED materials, it is desirable to have dislocation densities.....

Link to the full article: Phys. Status Solidi RRL 3, No. 4, 100– 102 (2009) / DOI 10.1002/pssr.200903007
Link to the Instrumentation: 3D APT

DNA sequencing using STM

Xavier — Fri, 27 Mar 2009 08:50:00 GMT

Stuart Lindsay and his collaborators use genetic material to bridge the gap between a scanning tunneling microscope and a sample of interest.

As the tip scans along the surface, the genetic material either bonds or ignores the underlying genetic material - leading to a varying tunneling current. The resulting image reveals the identity of the DNA sample under inspection.

Quantum physics could come to the aid of medical science as a new technique for identifying DNA utilizes the quantum effect of tunneling. The method, developed by physicists in the US, will enable users to read genetic codes directly by studying DNA with a scanning tunneling microscope (STM). This new approach could be developed into a low cost commercial technique for sequencing DNA, say the researchers.

An electric bond: biology and quantum physics

Unlocking the secret of the human genome in 2003 involved more than a decade’s hard graft at a cost of more than $1 bn. The technology that made it possible is known informally as the “shotgun approach” because it involves replicating a strand of DNA millions of times before blasting the replicates into tiny fragments

<< full article, from Physics World >>

© Institute of Physics (the “Institute”) and IOP Publishing.

Tips & Tricks - Vacuum Viewports

Xavier — Tue, 13 Jan 2009 14:54:00 GMT

This had already been posted back in September 2007 and as it did attract tremendous interest I'm happy to give it a makeover with more detail !

For those who do not often change things on a UHV vacuum system, here's some tips if you need to mount a viewport. First, never use a viewport that appears to be, or is known to be damaged. A replacement viewport costs far less than repairing a system that has been subject of an implosion caused by a faulty viewport.

SAFETY
Pressure differentials: Kodial VPZ viewports are designed to withstand 1 Bar differential pressure. Other standard viewports are designed to withstand 2 Bar differential pressure. The pressure on the ‘vacuum side’ of the viewport must not exceed a positive pressure differential of 1 bar. The viewports are designed for vacuum applications.

WARNING: Pressures in excess of this or high reverse pressures may cause catastrophic failure and result in serious injury.

Mounting

Viewport bolt-up procedure: Always use annealed copper gaskets and a washer with each bolt. Tighten opposing mounting bolts equally over several passes. Use a torque wrench to ensure equal sealing torque. Do not over tighten. Failure to follow this procedure will invalidate any warranty.

Handling

WARNING: The optic surface is very delicate and will scratch easily. Always wear lint-free or surgical rubber gloves when handling. Never touch the optic surface.
Storage: It is recommended best practice that all viewports are covered when not in use.
Use: If the viewport is to be used in a vacuum system where materials are deposited or plasma cleaned, an internal viewport shutter should be fitted.
Humidity: Anti-reflective coatings are durable and resistant to atmospheric moisture and other common contaminants

Cleaning

WARNING: All viewports are supplied UHV clean and ready for use. Optical coatings are typically 10-300nm thick and as such are extremely delicate. Any materials deposited or removed from the coating will affect optical performance. Cleaning should only be attempted when absolutely essential.
Dust: Dust should be removed using a particulate and water-free low pressure air-gun, aerosol or puffer.
Light smudges (e.g. finger prints): Smudges should be removed by wiping very gently using a lint free optical quality wipe moistened with isopropanol (IPA). Do not use tissue paper.
Other marks: Products with more serious marks and contamination should be returned to the supplier for cleaning and/or recoating.

Temperature Specs.
Baking: When baking, ensure the viewports are shielded from direct heat and strong temperature gradients, by, for example covering them with aluminium foil.

Heating/ Cooling rates: Heating and cooling rates must be kept below 3 °C/min.
Max Temperatures: Exceeding the temperatures bellow can invalidate warranty:

Viewport Type | Max Temp °C

Brazed Sapphire        | 450

Standard VPZ Kodial | 350

Brazed Fused Silica    | 200

Brazed Quartz     | 200

Bonded | 120

Mechanically sealed    | 130

Thunderbolts Of The Gods

Xavier — Mon, 25 Feb 2008 09:52:00 GMT

"The cosmic theatre has outgrown the Newtonian stage, and we need a larger setting to understand the broader cosmic drama. Instead of a vision of isolated bodies turning gear-like in a vacuum, we need a vision of electrical circuits embedded in a conducting medium whose components drive each other and may be in resonance. We have left the familiar world of solids, liquids and gases. We have entered a world of plasma, where the rules are different and more complex. We now live in an Electric Universe."

You've understood it, this is controversial material - so intrinsically stimulative to our intellect!

According to the promoters, David Talbott and Wallace Thornhill, "the Thunderbolts Project calls into question not only countless modern scientific assumptions, but also the billions of dollars of big-science government and corporate funding that continues to preserve and entrench questionable theories - elevating them to the status of doctrine - while systematically excluding legitimate alternatives that threaten the status-quo. Alternatives that may represent the future of science".

On this posting you can watch the 4 minutes video introduction to the subject. Yet if interest goes beyond this short clip, and regardless on which side of the scientific fence one sits, readers may wish to explore the full 64-minute long video playing at this link.

The Thunderbolts Project www.thunderboltsdvd.com, according to the promoters, "offers remarkably simple explanations for 'black holes', 'dark matter', the electric sun, comets that are NOT made of ice, planetary scarring and many other 'mysterious' phenomena".

It proposes that "much of the currently observable phenomena of deep space can be intelligently explained by already known principles of electricity".

Editor's note: This posting is purely informative and for intellectual reflection; no attempt is made to take sides.

Life on Earth

Xavier — Mon, 18 Feb 2008 09:41:00 GMT

Science informs us that microbes were the first inhabitants of Earth. These are single-celled organisms which we commonly call bacteria, fungi and protozoa. Microbes are still found everywhere today, in boiling hot thermal springs, as well as deep below the surface of the Antarctic, and even high in the atmosphere.

Microbes decompose the waste products of other living things, creating nutrients. They are also used to make beer, bread, and yogurt. Did I hear you say...yak!?

Earth formed about 4.5 billion years ago. No one knows for a fact when or how life began. The final, most important events leading to the beginning of life are possibly the least understood chapters of the story.

Yet some things are pretty well agreed upon. Early Earth was dominated by volcanoes, a gray, lifeless ocean and a turbulent atmosphere. Intense chemical activity occurred in heavy clouds; these were fed by volcanoes and penetrated both by lightning discharges and also solar radiation.

The oceans received organic matter from land and atmosphere, as well as from the falling in of meteorites and comets. Substances as H2O, CO2, methane and hydrogen cyanide formed key molecules as sugars, amino acids and nucleotides. Such molecules are the building blocks of proteins and nucleic acids, compounds ubiquitous to all living organisms.

An early triumph was the development of critical RNA and DNA molecules, which directed biological processes and preserved life's 'operating instructions' for future generations down the ladder of time. Yet the origin of life was triggered not only by special molecules as RNA or DNA, but also by the chemical and physical properties of Earth's then very primitive environments.

Most of life's history involved the biochemical evolution of single-celled micro-organisms. We find individual fossilized microbes in rocks dating to over 3 billion years.

A decade ago, in an interesting finding - cover story of the Nov. 7, 1998 issue of the journal Nature - scientists reported that life on Earth began at least 3.85 billion years ago. The international team was composed of scientists from UC San Diego's Scripps Institution of Oceanography, UCLA's Department of Earth and Space Sciences, the Australian National University and England's Oxford Brookes University. They present evidence that pushes back the emergence of life on Earth by some 400 million years.

The evidence comes from a rock formation discovered on Akilia Island in southern West Greenland that is at least 3.85 billion years old. The research -- funded primarily by the National Science Foundation and NASA -- has provocative implications.

"Our evidence establishes beyond reasonable doubt that life emerged on Earth at least 3.85 billion years ago, and this is not the end of the story," said Stephen J. Mojzsis, a graduate student in geochemistry at Scripps and the lead author of the article. "We may well find that life existed even earlier".

"We look in rocks like this for chemical suggestions and isotopic evidence, and we found both," said T. Mark Harrison, professor of geochemistry at UCLA and director of UCLA's W. M. Keck Foundation Center for Isotope Geochemistry. "It would be wonderful to see a head and toes, and while we don't have those, we have found very strong isotopic evidence for ancient life".

"But in the cases of Earth's most ancient rocks and minerals, we are actually better off relying on this type of isotopic evidence -- chemo fossils -- rather than on the shape of life-like objects with which nature has often been deceiving the unwary," said Gustaf Arrhenius, professor of oceanography at UC San Diego and principal investigator for the research project.

The carbon inclusions in the rock were analyzed with UCLA's high-resolution CAMECA IMS 1270 ion microprobe -- an instrument that enables scientists to learn the exact composition of samples - which Mojzsis described as the "world's best instrument" for this research; (meanwhile a newer version, the IMS 1280, has been released to the markets). The microprobe shoots a beam of ions -- charged atoms -- at a sample, releasing from the sample its own ions that are analyzed in a mass spectrometer. Scientists can aim the beam of ions at specific microscopic areas of a sample and analyze them.

- www.cameca.fr -

The team of scientists, Mojzsis; Arrhenius, who is his research adviser; Harrison; Kevin McKeegan, a researcher in UCLA's Department of Earth and Space Sciences; Allen Nutman, a research fellow at the Australian National University; and Clark Friend, a geologist at Oxford Brookes University, presents the following evidence for the ancient life:

Most importantly, a high ratio of one form -- an isotope -- of carbon to another, which provides a "signature of life", Mojzsis said. The carbon aggregates in the rock have a ratio of about 100 to one of 12C (the most common isotope form of carbon, containing six protons and six neutrons) to 13C (a rarer isotopic form of carbon, containing six protons and seven neutrons). "The light carbon, 12C, is more than three percent more abundant than scientists would expect to find if life were not present, and three percent is, in this case, a very large amount," Arrhenius said.

The inclusion of the carbon in a phosphate mineral called apatite, which is also the material of which bones and teeth are made. Apatite is often formed by microorganics, but it can also be formed inorganically. The association of the carbon with the apatite is "suggestive, and not surprising, but does not in itself establish life," Arrhenius said.

The form of life discovered was probably a simple micro-organism, although its actual shape or nature cannot be ascertained, Mojzsis said, because heat and pressure over time have destroyed any original physical structure of the organisms.

Harrison, who directs UCLA's ion microprobe, said of the research, "This was a scientific problem that was waiting for a new generation microprobe of this resolution. The individual samples are very small, and no other instrument would have been sensitive enough to reveal precisely the isotopic composition and location of the carbon inclusions in the rock".

It is unknown when life first appeared on Earth, which is approximately 4.5 billion years old. The previous earliest evidence for life was presented by UCLA paleobiologist J. William Schopf, who showed that on the basis of bacteria-like fossils, primitive life, much like modern "pond scum," existed on Earth 3.46 billion years ago. "The evolution of lifeless matter into primitive life forms, and their organization into the complex structure of cells like those found by Schopf, represent an enormous development in the earliest history before the deposition of the Akilia sediments," Arrhenius said.

The residues of ancient life that the scientists have discovered existed prior to the end of the "late heavy bombardment" of the Moon by large objects, which ended approximately 3.8 billion years ago, Harrison said. The implication, he added, is that the often assumed simultaneous bombardment of Earth did not lead to the extinction of life.

This research shows that life on Earth began during the first approximately 700 million years after the formation of the planet, placing an upper limit on the time needed for the creation of life on Earth, or on the time period available for it to arrive here from elsewhere, the scientists said.

"Life is tenacious, and it completely permeates the surface layer of the planet," Mojzsis said. "We find life beneath the deepest ocean, on the highest mountain, in the driest desert and the coldest glacier, and deep down in the crustal rocks and sediments. Not knowing what conditions are needed for the emergence of life, it is only possible to speculate about its existence elsewhere in the universe. An important contribution to the solution of this problem could come from exploration of the surface of Mars for traces thereof extinct life".

An equally interesting question, the scientists agreed, that is currently studied in laboratories on Earth is how life originally could have arisen from lifeless molecules, and evolved into the already sophisticated isotope fractioning life forms recorded in the Akilia rocks.

Sources: www.nature.com, www.space.com, www.xtronix.ch

Neutrinos could probe Earth’s structure

Xavier — Fri, 07 Dec 2007 08:41:00 GMT

In the absence of a 6,000 km-deep hole to conduct observations, scientists hoping to learn about the internal structure of the Earth presently have few options but to monitor seismic waves. However, this technique, which relies on models of how waves are affected by rock properties, is indirect and so potentially unreliable. A truly direct method, suggest researchers from Spain, Japan and the US, might be to monitor the proportion of atmospheric neutrinos that are absorbed while passing through the Earth.

This isn’t the first time that atmospheric neutrinos, which are produced when cosmic rays collide with atomic nuclei in the upper atmosphere, have been proposed to probe the Earth’s structure. Although these chargeless, almost massless particles pass straight through the Earth unimpeded when they have a low energy, at energies above 10 TeV (10¹³ eV) they are very occasionally absorbed.

Since this absorption depends on the density of the neutrino’s travelling medium, a neutrino travelling through a slice of the Earth close to the surface, for example, would be less likely to be absorbed than a neutrino travelling straight through the dense core. So by counting how many neutrinos come through different slices, it should be possible to see where the transition between the core and the inner mantle occurs, or between other structural layers.

Read more @ physicsworld.com

Understand Relativity......at last

Xavier — Thu, 06 Dec 2007 09:09:00 GMT

Einstein's theory of special relativity includes electricity and magnetism in a simple, logical extension of the relativity of Galileo and Newton. Its conclusions, including time dilation, length contraction, and E=mc²have changed profoundly our ideas of time and space, matter and energy.

These multimedia modules (click here for the PDF) developed by the University of New South Wales, one of Australia's leading research and teaching universities, give a brief overview of relativity - they present the main ideas. Inevitably, you will have questions. So related links give more complete explanations.

Related Links for each module:

GALILEO - Mechanics and Galilean relativity
MAXWELL - Electricity, magnetism and relativity
EINSTEIN - The principle of Special Relativity
TIME DILATION - How relativity implies time dilation and length contraction
E = mc² - How relativistic mechanics leads to E = mc²
BEYOND RELATIVITY

Animations from Einstein Light require the Flash Plugin. The multimedia modules have animations and film clips and are typically 2Mb. The much smaller HTML versions have only text and images.

Comparative study between Bellows and Diaphragm Gas Valves

Xavier — Tue, 06 Nov 2007 08:55:00 GMT

Contributed by Alain Dahmani – Flowlink, France

The seal of a diaphragm valve is made through the controlled deformation in a Hastelloy® diaphragm across a Kel-F® seat. The stroke, or deformation travel, of the diaphragm between open and closed positions is in the order of 0.2mm - 0.3mm.

The seal of a formed bellows valve is made by the displacement across the axis of the bellows via the expansion of the undulations. One such undulation is equivalent to about two diaphrams.

Example:

	Number of undulations	Total stroke at opening	Stroke for 1/2 undulation
Diaphragm	1/2 (1x 1/2 undulation)	0.3mm	0.3mm
Bellows	20 (10x 2x 1/2 undulation)	1.2mm	1.2mm / 20 = 0.06mm

So, for an opening 4x greater (1.2mm vs 0.3mm) of the bellows valve, the unit stoke is 5x smaller (0.06mm vs 0.3mm).

As a consequence, for equivalent dimension valves, the bellows valve will have a better Cv and a longer life expectancy over a diaphragm valve. Therefore, in a highly automated process where the gas valves are cycled continuously, it would stand to logic to give preference to a bellows valve.

The corrosion-resistant Hastelloy® alloys have become widely used by the chemical processing industries. The need for reliable performance has also lead to their acceptance and growth in the areas of energy, health and environmental, oil and gas, pharmaceutical and flue gas desulfurization industries. The attributes of these alloys include high resistance to uniform attack, outstanding localized corrosion resistance, excellent stress corrosion cracking resistance, and ease of welding and fabrication.
Kel-F® homopolymer of chlorotrifluoroethylene has the lowest vapor transmission rate of any plastic. It is specified in many aerospace valve, seal and gasket applications. It also has excellent thermal characteristics and maintains an operating temperature range of 33°Kelvin to 204°Celsius. It can be machined to precise dimensions. Compression, impact and tensile strength are high over a wide temperature range. Non-wetting and zero-moisture absorption are inherent in Kel-F®.
Both materials find wide use in high quality precision gas valves.

Toys & Consumer Goods Screening with Handheld XRF

Xavier — Fri, 26 Oct 2007 07:47:00 GMT

You surely heard of the Mattel Chinese-made toy recalls, and later the CEO’s televised apology about the incidents and the effects on the Chinese supply chain. One Chinese factory executive even took his life as a result.

Errors happen, often with no intension of wrongdoing. That’s maybe why in scientific research, peer review and revalidation is so important and so ingrained in the way this community functions.

You might have asked yourself how do they test that stuff anyway. Any chemist reading this blog would have no trouble figuring out more than one method to run such tests. There are enough varieties of instruments on the market to reveal to us the surface as well as inner most secrets of just about everything and anything!

We recently delivered a custom-designed vacuum exhaust system to evacuate and gas backfill a component for instruments that often end up in production analysis areas. As we later discovered, those instruments from ThermoFischer Scientific also have smaller field versions, such as this hand-held gun that is typically used to check toxic element content in very diverse objects.

Toys recalled from store shelves for lead in paint. The Sierra Club threatens lawsuits against importers and distributors of Chinese products with potentially high lead levels. Each week seems to bring a new report of more problems with toys and costume jewelry. Ultimately, contract manufacturers, importers, distributors, retailers and brand owners all face potential liability when they fail to comply with laws which restrict lead in their products.

Hand-held x-ray fluorescence (XRF) analyzers provide quick and easy screening of toys and other consumer goods for lead, cadmium, mercury and other toxic metals. Importers, brand owners and retailers can implement a standardized inspection protocol for incoming shipments to verify compliance, while simultaneously requiring supply chain documentation based on empirical testing. Due diligence with XRF analyzers has already become the norm in the metal alloy and electronics markets. These proven and accepted tools are now increasingly being used with consumer goods, throughout the supply chain.

Hand-held energy-dispersive x-ray fluorescence (EDXRF) analyzers, commonly known as XRF analyzers, are able to quickly and nondestructively determine the elemental composition of:

● Metal and precious metal samples
● Rocks and soil
● Slurries and liquid samples
● Painted surfaces, including wood, concrete, plaster, drywall and other building materials
● Dust collected on wipe samples
● Airborne heavy elements collected on filters

Up to 30 or more elements may be quantified simultaneously by measuring the characteristic fluorescence x-rays emitted by a sample. XRF analyzers can quantify elements ranging from magnesium (element 12 in the periodic table) through plutonium (element 94), measuring fluorescent x-ray energies from twelve hundred fifty electron volts (1.25 keV) up to 100 keV. XRF analyzers also measure the elastic (Raleigh) and inelastic (Compton) scatter x-rays emitted by the sample during each measurement to determine, among other things, the approximate density and percentage of the light elements in the sample.

XRF Excitation Model

So how does EDXRF work? Each of the atomic elements present in a sample produces a unique set of characteristic x-rays that is a fingerprint for that specific element. EDXRF analyzers determine the chemistry of a sample by measuring the spectrum of the characteristic x-rays emitted by the different elements in the sample when it is illuminated by high energy photons (x-rays or gamma rays). These photons are emitted either from a miniaturized x-ray tube, or from a small, sealed capsule of radioactive material.

A fluorescent x-ray is created when a photon of sufficient energy strikes an atom in the sample, dislodging an electron from one of the atom's inner orbital shells (the lower quantum energy states). The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom's higher quantum energy orbital shells. The electron drops to the lower energy state by releasing a fluorescent x-ray, and the energy of this fluorescent x-ray - typically measured in electron volts, equal to the specific difference in energy between two quantum states of the dropping electron.

Because the quantum states of each electron orbital shell in each different type of atom (each of the atomic elements) is different, the energies of the fluorescent x-rays produced by different elements are also different: When a sample is measured via XRF, each element present in the sample emits its own unique fluorescent x-ray energy spectrum. By inducing and measuring a wide spectrum of the range of different characteristic fluorescent x-rays emitted by the different elements in the sample, hand-held XRF analyzers rapidly determine the elements present in the sample and their relative concentrations- in other words, the elemental chemistry of the sample. For samples with known ranges of chemical composition, such as common grades of metal alloys, an XRF analyzer also identifies most sample types by name, typically in seconds.

Batch Production Vacuum Exhaust System

Xavier — Fri, 19 Oct 2007 20:53:00 GMT

The VES-210 was recently delivered to ThermoFisher Scientific, a world-class scientific & industrial analytical instrumentation company. It will be used for production in their state-of-the-art X-ray collection techniques facility. Thermo Fisher Scientific X-ray Fluorescence and X-ray Diffraction products provide elemental composition and structural information from a variety of materials. Such systems are typically used in cement and metallurgy industries, among others.

The VES-210 consists of 2x 10 vacuum evacuation and gas backfill ports; 10 in each heated zone. The ports can be batch pumped - so either 10 or 20 ports can be pumped simultaneously - yet can be isolated individually by toggle valves. High vacuum is achieved by a turbo-molecular pump; slightly over-sized to allow for possible future modifications to the system. The vacuum cycle is fully automated via a miniature Siemens PLC controller. High vacuum and gas hardware is of stainless steel throughout. Except for the seals of two high vacuum valves and two high precision micrometer gas valves, all high vacuum gaskets are of oxygen-free high-conductivity copper. The system was fully engineered and built locally to CE norms.

To compensate for barometric pressure variances we used one of the world’s most precise absolute pressure sensors. The sensors for rough and high vacuum are an X-TRONIX broad-range Bayard-Alpert with thoria-coated iridium filament and two thermocouple heads. Rough and high vacuum hardware are mostly right out of our 90-page vacuum components catalog, with some minor custom modifications to T-pieces. The turbo is from Oerlikon (Leybold), the mechanical pump from Adixen (Alcatel) and the high vacuum pneumatic valves from VAT.

CERN / ALICE ToF Detector

Xavier — Fri, 14 Sep 2007 12:01:00 GMT

The Alice Collaboration is building a dedicated heavy-ion detector to exploit the unique physics potential of nucleus-nucleus interactions at LHC energies. The collaboration's aim is to study the physics of strongly interacting matter at extreme energy densities, where the formation of a new phase of matter, the quark-gluon plasma, is expected.

The existence of such a phase and its properties are key issues in QCD for the understanding of confinement and of chiral-symmetry restoration. For this purpose, the collaboration intends to carry out a comprehensive study of the hadrons, electrons, muons and photons produced in the collision of heavy nuclei. Alice will also study proton-proton collisions both as a comparison with lead-lead collisions in physics areas where Alice is competitive with other LHC experiments

CAEN will supply the Alice experiment at CERN / Geneva with 710 TDC boards, to be known as “TRM”: TDC Read-out Module and their 77 special crates with VME64X bus and power supply.

The whole system will be used in the Time-of-Flight detector and is to work under huge magnetic field and moderate radiation.

The TRM is a custom-board developed by CAEN and to be known as VX1390 - derived from the standard V1290A - with 240 TDC channels with 25 ps resolution. Each board hosts 30 TDC chips developed by CERN's ECP-MIC Division (HPTDC).

Because of the radioactive environment, an accurate choice of components is required and the TRMs implement protections from Single Event Latch-up and from Single Event Upset.

The boards will be inserted in a special crate developed by CAEN and to be known as SY2390 - 'Alice-ToF-box'. The same crate hosts the power supply modules for both the TRMs and the TOF detector front-end modules. CAEN is also in charge for the design and implementation of the water-cooling system of the crate. The whole power supply system to guarantee smooth operation in a magnetic field up to 5 thousand gauss.

Schematic of ALICE
The detector is 25 m wide, has a diameter of 15 m and weighs 10'000 tons

Viewport Type	\|	Max Temp °C
Brazed Sapphire	\|	450
Standard VPZ Kodial	\|	350
Brazed Fused Silica	\|	200
Brazed Quartz	\|	200
Bonded	\|	120
Mechanically sealed	\|	130