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NASA plans astrometric mission

Like ESA’s recent Hipparcos mission, FAME will use the parallax method to determine the stars’ positions: as the telescope and the Earth orbit the sun, the position of the stars will change slightly. The smaller the change, the further the star is from the Earth. FAME will also look in two directions at once to achieve its high accuracy.

“Astrometric observations are the foundation of almost all of astrophysics,” says Sean Urban of the US Naval Observatory and a member of the FAME team. Over the 2.5-year mission, each of the stars selected by the telescope will be scanned 950 times. The solar sail will be used to move the craft smoothly, thus avoiding frequent thruster burns and disruption to the spacecraft’s observations.

Unlike Hipparcos, FAME will be able to detect the “wobbling” of stars due to objects such as other stars, brown dwarfs, and planets twice the mass of Jupiter. The FAME team also hopes to use the telescope to look for dark matter in the Milky Way.

Could carbon-60 molecules be used in particle physics?

As the highly energetic particles pass through conventional carbon-rich rocks, they would form carbon-60 molecules in their wake. The fact that these geological detectors have been “collecting data” for millions of years, combined with the stability of carbon-60 molecules, could give this geological approach to particle physics a “winning edge” according to Collar. Another bonus is that natural radioactive processes in rocks are not energetic enough to form carbon-60 molecules.

Physicists discovered only recently that carbon-60 molecules could form under heavy Ion irradiation. Collar and Zioutas are now trying to irradiate geological samples at CERN to “calibrate” the response of these detectors. “The nice thing is that the technique can be put into practice immediately using available fullerene detection methods,” says Collar. “Its sensitivity to some exotic particles should immediately exceed existing limits – which is a hard thing to do.”

Magnetic resonance sees the heart beat

Ultrasound is commonly used to look at the heart, but it is unsuitable for the 10-20% of the population that have breathing difficulties (emphysema) or who are medically obese. In both techniques, patients are given drugs to speed up their hearts and promote vigorous pumping. In a healthy heart both sides of the heart contract with equal force. If some of the blood vessels are blocked, however, one side of the heart wall will not contract normally.

Magnetic resonance imaging also allows the patient to be checked for symptoms of other medical conditions. “MRI allows us not only to locate a blockage, but to determine whether it limits blood flow enough to warrant treatment,” says Hundley. “A lot of new doors have been opened with this technology.”

Climate modelling for the masses

US rejects nuclear test ban treaty

The treaty will only come into effect if the 44 countries that have the capability to develop nuclear weapons ratify it. Although 26 countries, including France and the UK, have ratified the treaty, Russia, China and the US have not. “This decision is a serious blow to the entire system of agreements in the field of nuclear disarmament and non-proliferation,” said Vladimir Rakhmanin of the Russian foreign ministry. The Senate is concerned that that it would be too difficult to verify whether nations are keeping to the treaty.

Despite the Senate’s decision, President Clinton has said the US would retain its moratorium against nuclear tests and abide by the terms of the test ban treaty. Joseph Rotblat, the nuclear and medical physicist who shared the 1995 Nobel Peace Prize, called the Senate’s decision “perverse”. Rotblat added that “once the treaty has come into force you have access to a world-wide network of seismic stations that can look for nuclear tests.”

Wave-particle duality seen in carbon-60 molecules

The Vienna team sent a collimated beam of carbon-60 molecules through a slit made of silicon nitride and detected the interference pattern by ionizing the molecules with a laser and then counting the ions. The slits in the diffraction grating were 50 nanometres wide and the grating had a period of 100 nanometres. The team detected the central maximum and the two first-order diffraction peaks in the interference pattern. The molecules had a most probable velocity of 220 metres per second, which corresponds to a de Broglie wavelength of 2.5 picometres (2.5×10^-12 metres) – some 400 times smaller than the diameter of the molecules. They also observed wave-particle duality in carbon-60 molecules that contained one or two atoms of ¹³C, the heavy isotope of carbon.

One of the deepest mysteries of quantum mechanics is that an interference pattern is formed even if there is only one particle in the experimental set-up at any given time. The Vienna team write that “all these observations support the view that each carbon-60 molecule interferes with itself only.” They also confirmed that the interactions of the molecules with their environment – such as the spontaneous emission of photons by the thermally excited molecules – could not reveal which slit they had passed through. Even the mere possibility of being able to know which slit the particle passes through would be enough to wipe out the interference pattern.

Another mystery in physics is the length scale at which quantum behaviour breaks down. The carbon-60 molecules in the Vienna experiment are the largest objects ever to have shown quantum behaviour, but they are still 15 orders of magnitude smaller than true macroscopic objects. In the quest to establish when and how quantum mechanics breaks down and classical physics takes over, Arndt and co-workers plan to repeat their experiments with larger macromolecules and possibly even viruses.

Chemical physicist wins Nobel chemistry prize

Prior to Zewail’s work chemists had thought that chemical reactions occurred on the same time scale as molecular vibrations — that is, on the femtosecond scale. In the late 1980s, Zewail developed a technique that could follow the motion of atoms and molecules on these time scales. A strong laser pulse was used to start a chemical reaction, and a second, weaker, laser was used to probe the reaction. By varying the time interval between the two laser pulses it was possible to monitor different stages of the reaction. This technique is now widely used throughout chemistry.

Ahmed Zewail was born in Egypt and received his first degree from the University of Alexandria. He received his PhD from the University of Pennsylvania in 1974, and has been at Caltech since 1976. Zewail, who currently holds the Linus Pauling Chair of Chemical Physics, won the Wolf Prize for chemistry in 1993.

Nobel prize goes to ‘t Hooft and Veltman

‘t Hooft and Veltman were both born in the Netherlands. In 1966 Veltman was appointed as professor of physics at the University of Utrecht, and ‘t Hooft became his PhD student in 1969. By 1971 ‘t Hooft had made several important breakthroughs in the theoretical effort to renormalize the electroweak interaction. Then using a computer program developed by Veltman, the pair verified ‘t Hooft’s partial theory and showed how to perform precise calculations with it.

Salam and Weinberg’s theory had predicted the existence of the W and Z bosons, which carry the electroweak force, but their theory had to be renormalized before it could predict the physical properties of these particles, such as their masses. These predictions were confirmed when the W and Z particles were detected for the first time in 1984.

‘t Hooft is now professor of physics at Utrecht. He received the Wolf Prize in 1982 and the High-Energy Physics Prize of the European Physical Society (EPS) earlier this year. Veltman moved from Utrecht to the University of Michigan in the US in 1981, and won the EPS High Energy Physics Prize in 1993. He retired recently and now lives in the Netherlands.

Good news for the planet

Global warming – sometimes called the greenhouse effect – is caused by gases in the atmosphere that absorb and then re-emit infrared radiation, thereby ‘trapping’ the heat on the Earth instead of allowing it to escape into space. The three most common greenhouse gases are carbon dioxide, water vapour, and ozone. However, some greenhouse gases have larger impacts than others: methane, for example, is 21 times more damaging than carbon dioxide over a 100-year period. Other greenhouse gases include the sulphur hexafluoride used in semiconductor manufacturing, and the methane produced by landfill sites and livestock. Carbon dioxide emissions can be countered by ‘carbon sinks’, such as trees, but it is difficult to model this process and therefore to predict how successful such measures will be.

Reilly and colleagues analysed the climate, financial and environmental effects of three possible emissions policies until 2100: controls on fossil fuel emissions; a multi-gas target with controls only on carbon dioxide emissions; and controls and targets on multi-gas emissions. They found that there were no significant differences in the impact on the climate and ecosystem of the second and third approaches. Moreover, the multi-gas strategy was cheaper over this time scale and, if new stricter emission targets are set, may also be the only way to meet these targets.

Organic magnets

The material – 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) – is non-magnetic at very low temperatures. The paramagnetic effect is strong at room temperature, but as the compound is cooled, it becomes diamagnetic below 230 K. However, it is heated again, it does not become paramagnetic until the temperature reaches is 305K. This is an unusually wide hysteresis loop for a magnetic material.

Fujita and Awaga suggest that the reason for this unusual behaviour is a change in the crystalline structure of the compound. As the structure changes, so do the molecular orbits of unpaired electrons in the crystal. This change increases the electrostatic repulsion pressure on other unpaired electrons in the compound, leading to paramagnetism.

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