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GSI-Nachrichten 01-1998
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Therapy Project enters Medical Phase - First Patients Treated
In December 1997, for the first time in Europe,
tumour patients were treated with a beam of high-energy carbon ions at the heavy-ion
accelerator of GSI. Two technical novelties, the raster scan method for a precise
application of the beam dose, and the control of the beam position by positron emission
tomography (PET) were used.
More...
For the treatment the patient's head is fixed with
millimeter accuracy by means of a mask. Above and below the patient the PET cameras
are mounted. The beam leaves the accelerator vacuum through the quadratic exit window
of the beam control system visible behind the patient.
Dielectric Recombination - Spectroscopy of Doubly Excited Atomic States at ESR
According to our current understanding of the
synthesis of the chemical elements, all elements heavier than iron are created during
supernova explosions. Such explosions are characterised by extreme temperatures and,
consequently, the newly created atoms are almost completely ionised. But how do these
highly charged ions capture the electrons they need to transform themselves into neutral
atoms? And which elementary processes play a significant role in these transformations?
Such questions can be answered with the help of the experimental storage ring ESR and
its electron cooler.
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While passing the electron cooler lithium-like gold ions stored
in the ESR can capture an electron into a bound state with principal quantum number n.
If one plots the rate coefficent, which is obtained by folding the capture cross
section with the relative velocity, versus the kinetic energy of the electrons, a
series of pronounced resonances is observed that can be explained by dielectronic
recombination.
Writing with Single Ions - A New Way of Producing Microstructures
In microsystems technology, particle beams and
chemistry are increasingly replacing the traditional tools for milling and drilling.
With the growing demand for faster and cheaper production of ever-smaller structures,
testing the possibilities offered by utilizing heavy ion-beams in new microtechnology
applications is certainly justified.
More...
Picture of Hermann von Helmholtz written with single ions to
a polycarbonate foil (nickel, 3.6 AMeV). After irradiation with the microprobe for about
half a minute, the tracks were made visible by etching.
Strange Particles Probe Compressed Nuclear Matter
How does nuclear matter respond when it is compressed
and heated? What role do strange particles play in hot, dense nuclear matter? Do the
properties of the particles change under such extreme conditions? The answers to these
questions are of fundamental significance for our understanding of the strong interaction.
They also have great relevance for topics in astrophysics, where they can help answer
questions such as: Under what conditions will the explosion of a supernova result in a
neutron star and when will it produce a black hole? Two particles, the kaon K+ and its
antiparticle K-, are highly relevant to the answer. Using the synchrotron at GSI in
Darmstadt, it is possible to study heavy-ion collisions in which kaons are created.
With a magnetic spectrometer the number, energy, and emission angle of the kaons produced
can be determined. Thereby, we not only acquire information about the state and properties
of nuclear matter under extreme conditions, but also obtain first indications that the
nuclear environment itself affects the kaon properties. The fact that substantially more
antikaons than expected are produced in hot dense nuclear matter - at first, a surprising
result- opens up several interesting possibilities.
More...
The kaon spectrometer is capable of determining the momentum and
charge of the particles, their emission angle, the centrality of the reaction including the
total number of participating nucleons, and the orientation of the reaction plane. The
momentum is measured via the deflection angle of the particle in the magnetic field and
its recorded hit position in the focal plane. The velocity is deduced by reconstructing
the flight path and measuring the time of flight. With these quantities known, the rest
mass and thus the particle species can be unambiguously determined.
Fission Studies with Secondary Beams
Nuclear fission is a particularly dramatic example
of the collective motion of cold nuclear matter. As the form of the nucleus fundamentally
changes, the individual nucleons in their quantum mechanical states must adapt to this
movement. Even after nearly 60 years of intensive research, the complex interaction
between this collective motion influenced by repulsive electrical forces and the motions
of the individual nucleons is not completely understood. One reason for this is the
limited experimental information available on the nuclear fission process. So far only
about 15 percent of fissile nuclei have been accessible for fission experiments, because
only spontaneously fissioning and long lived nuclei could be investigated. At the GSI
fragment separator, through the use of secondary beams, the investigation of the fission
characteristics of short-lived nuclei is now possible for the first time.
More...
Overview of mass and element distributions for low energy
fission. Blue circles represent nuclei whose mass distributions were previously measured
at excitation energies less than 10 MeV above the fission barrier. Exemplary mass
distributions are given for several nuclei. Green crosses mark nuclei investigated in
recent fission studies with the help of secondary beams from the GSI fragment separator.
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