Probably the most important single event in 1996 concerns the experimental facilities at the X-ray laboratory. Based on the Faculty of Science supported materials science research program the Seifert diffractometer was supplemented with high and low temperature sample environment units. These new facilities will be in potential use next year providing excellent possibilities in the studies of the properties of condensed matter.
The use of the synchrotron sources has been continued effectively. The two-year projects "Properties of high temperature superconductors" together with Warwick University (U.K.) and Cavendish Laboratory and "Magnetic scattering at high X-ray energies" together with Warwick University were completed successfully at the European Synchrotron Radiation Facility (ESRF, Grenoble). The latter experiment where extremely high X-ray photon energies of up to 1 MeV were used, was selected to be one of the "ESRF Highlights" in 1996. High resolution inelastic scattering experiments were performed both at ESRF and the National Synchrotron Light Source (NSLS, USA) to study especially Fermi surface and electron-electron correlation effects. A theory project to support these experiments has been started with the Helsinki University of Technology.
The beam time of the four-circle diffractometer has been fully booked. There have been several visits by Russian and Czech scientists related to the high temperature supeconductor and nonlinear optical material projects.
Fruitful co-operation with Helsinki University of Technology has produced interesting results in tailored polymer systems. Versatile techniques including small- and wide angle scattering experiments at the X-ray laboratory combined with time-resolved studies at synchrotron sites have given new information about the order-disorder transition in polymer-surfactant systems. Several joint projects in materials science with the Department of Chemistry have also continued.
The role of external funding has been increasing. This funding was used to employ both M.Sc. and postgraduate students, for traveling expenses and updating scientific instruments.
Aerosol and Environmental Physics Laboratory
The research activity has focused on basic and applied aerosol science and cloud microphysics during 1996. Studies on heat and mass transfer, nucleation, condensation, aerosol dynamics, aerosol measurement technique, atmospheric aerosols, deposition of atmospheric gases, and formation and growth of cloud droplets were performed. The main aim of the studies is to develop practical applications, based on mastering fundamental physical and chemical phenomena, to solve different aerosol and environment-related problems. The effect of condensable trace gases on cloud droplet formation was studied using computer models developed in the laboratory. Other topics of theoretical and numerical investigations were heat and mass transfer, formation and growth of aerosol particles, and nucleation processes.
Continuous measurement activity at the field station SMEAR II (in Hyytiälä), constructed during 1995, started in 1996. The main output so far was numerous observations of atmospheric nucleation bursts. The field measurements were also performed during different field campaigns. The preparations for ACE-2, (the North Atlantic Regional Aerosol Characterization Experiments) have been one of the main activities. The laboratory has also participated in the ARCTIC OCEAN-96 expedition.
The main output of our experimental laboratory work has been the development of tools for investigating nucleation phenomena and cloud condensation nucleus activation. We have also carried out measurements of aerosol particle size distributions in a variety of laboratory systems as well as in atmospheric conditions. Our special interest has been targeted on the nanometer size range using recent aerosol instrumentation such as electrical mobility spectrometry and diffusion battery technique, whereas for micron-sized particles optical counting of particles is typically used.
International co-operation has had a significant role in both theoretical and experimental activities of the group. During 1996 various projects (including three EU projects) continued in co-operation with research groups from ten countries. On the national level we have had close collaboration especially with the department of Forest Ecology in the University of Helsinki, and with the Air Quality Department of the Finnish Meteorological Institute.
The international postgraduate training program for aerosol and environmental physics (started in the beginning of the fall semester 1994) was continued during1996.
Electronics and Industrial Physics Research Laboratory
We have continued the work in developing new instruments using electronics, optics and ultrasonics. In 1996 a record number of four Ph.D.Õs graduated.
The so-called ultrasonic ice detector has a rather bright outlook as will be described later. A new interesting application seems to open up in the monitoring of ice formation in deep-freezers. We are also able to detect bacterial contamination of milk and sauce packages using ultrasound without opening the package. This may be regarded as remarkable since no other method has yet been developed.
In general, examination of food products with physics-based test methods is rather much in infancy and the present method is one of the first ones. It seems that the reasonable succes is leading to increased interest from the foods industry.
We have co-operated with several industrial enterprises in applying our knowledge of electronics, optics and ultrasonics. For example, we are setting up a demonstrator project to develop a universal, low-cost air flow sensor for building ventilation. We also are doing initial preparations for a mould sensor in buildings or like. Mould is regarded as a serious health-hazard.
Laboratory of Medical Physics
The research interests have been focused on four main areas: boron neutron capture therapy (BNCT), patient dosimetry in diagnostics and treatments, medical imaging applications, and modelling of physiological and biological systems for clinical studies. Research has been done in co-operation with the Helsinki University Central Hospital (HUCH), the Technical Research Center of Finland (VTT) and Finnish Centre for Radiation and Nuclear Safety (STUK).
BNCT is one of the most complex cancer therapeutic modalities, and its ultimate success is dependent on how adequate concentrations of boron and neutrons can be delivered to the tumour. In September 1996 a conical beam collimator was installed at the reactor operated by the Technical Research Center of Finland (VTT). This collimator enables the use of an epithermal field for animal and human experiments.
In radioimmunotherapy the knowledge of patient dosimetry is essential when planning the treatments. A method for measuring absorbed doses at the patient skin in order to approximate doses of the critical organs has been studied in collaboration with HUCH and STUK. New calculation methods have also been developed to obtain more accurate dose distributions in the patient. Both experimental and computational methods have been used to investigate the patient doses in X-ray diagnostics.
The calculation methods used in radioimmunotherapy have been further developed to be applied with abdominal fusion images for more precise results. New MRI techniques (magnetization transfer and spin lock) for increasing the tissue contrast and characterization have been studied. The study was performed in vitro and in vivo in normal and in brain tumour patients.
Work has been done in the field of modelling platelet kinetics. The main interest has been focused on BPA and bleomycine kinetics. The models are to be used in BNCT-research.
Theoretical Nuclear Physics
Dan Olof Riska
The research in theoretical nuclear and hadron physics concerned the application of the chiral quark model to the structure of the baryons - the spectra of the light flavor baryons as well as the heavy hyperons. The exchange current contributions consistent with a complete dynamical version of the quark model, which can predict the spectra of the light flavor baryons and the strange hyperons satisfactorily, were derived.
Another line of research concerned the development of a consistent method of quantizing Skyrme's topological soliton models for the baryons. The topological soliton model was also employed to investigate the contribution of the vibrational breathing mode N(1440) on the spin-orbit component of the nucleon-nucleon interaction.
Finally a solution based on short range exchange mechanisms to the puzzle of the near complete cancellation to near threshold cross section for p0 production in pp collisions that is implied by chiral perturbations theory was proposed.
Experimental Nuclear Physics
Collaboration with the Accelerator Laboratory of the University of Jyväskylä has been continued. The research effort has concentrated on studies of nuclides not far from lead. Two specific cases are the discoveries of two new alpha emitting nuclides: the mercury isotope 174Hg and the actinium isotope 206Ac. A tentative identification of an oblate 0+ state in 188Pb, showing up its existence through a weak alpha fine-structure line in the decay of 192Po, was possible through an ingenuous use of an array of silicon detectors. The use of rotating target wheels was introduced in our studies of neutron-deficient U and Pu isotopes.
High spin spectroscopy studies were carried out in co-operation with groups at the Physics Department at the Royal Institute of Technology and the Svedberg Laboratory in Sweden, and at the University of Jyväskylä. Level properties of nuclei in the lead region and in the mass 120 region were studied.
The LEP/DELPHI Experiment
Heimo Saarikko *
The year 1996 was the first year of data taking at LEP200. In October 1996 an operational e+e collision energy of 172 GeV was achieved. This means that the collision energy is well above the W-pair production threshold, for the first time in accelerator produced e+e collisions. In the coming years, with increasing LEP energy, accurate W-boson mass measurements are foreseen at LEP200. The LEP Upgrade phase will continue until about the year 2000 so that a possibly existing light Higgs with mass below 100 GeV would be discovered.
Being the traditional responsibility of the Finnish DELPHI group the Hadron Calorimeter detector activity has included the maintenance of the calorimeter as well as tuning, testing and repairs during the shutdowns of the experiment. As a part of the LEP200 Upgrade, the final version of the anode read-out electronics, anode trigger card, event timer card, control card and anode trigger system have been developed.
A method to identify KL0 with the aid of the Hadron Calorimeter cathode read-out has been developed. The cluster reconstruction and pattern recognition program for the Vertex Detector barrel part of 1996 Delphi Silicon Tracker was also developed.
The group has also participated in doing the centrally manned shifts for Slow Control and Data Quality checking as well as expert shifts of the Hadron Calorimeter and Vertex Detector.
The data set of about 3.5 million Zo Æ hadrons achieved in 1989-1996 is being analyzed, the Finnish group concentrating in fields closely related to the use of the detectors to which the group is presently contributing. Preparation for the LEP200 physics program has been initiated, the main area of interest being the search for the Higgs bosons in specific final state decay modes.
* The Research Institute for High Energy Physics (SEFT) was the official Finnish collaboration institute with CERN. Doc. Heimo Saarikko from the Department of Physics has been nominated the chief coordinator of the Finnish participation in the DELPHI project.
The group has continued its "Project of Perceptional Approach", i.e. search of constructive principles of teaching based on the conceptual and processual structure of physics and on development of different kinds of applications for all levels of physics instruction. This includes a.o. planning of didactically relevant courses for both primary and secondary school teacher education, development of the "teachers' laboratory of perceptional experimentality", development or adaption of demonstrations, writing of two text-book series with extensive Teachers' guides for secondary school physics, and participation in the Idea-Bridge (Ideasilta) project on science for talented basic-school pupils.
The great event of the year was the start of the DFCL project, an extensive complementary-education programme in Didactical Physics for teachers (see Adult Education). This project is planned and realized as a part of the research in didactical physics.
The task in itself and, morever, the surprisingly favourable response by the physics teachers shown by over 200 applications in such a short notice is a remarkable recognition of the work of the group. The experiences from the project will yield valuable information for further development of complementary education.
The work of the group is closely connected with the Graduate School for Mathematics, Physics and Chemistry Education with prof. K. Kurki-Suonio as the president. In its first full year of existence two more university departments joined the school having now 21 member institutes from 7 universities and more than 100 graduate students.
The activity during 1996 has been focused strongly on materials research and it has enforced its significance in the laboratoryÕs research profile. The central research themes cover a wide range of topics. Physical processes taking place in semiconductors and metals during and after implantation or irradiation with energetic ions have been studied and modeled. Ion beam techniques have been used to investigate doping, diffusion, and surface and interface structures in elemental and compound semiconductors. Diamond films and their composites, nanocrystalline coatings and multilayers of new metal-ceramic materials have been studied and developed. Also the research in nuclear and applied physics has been continued successfully. Several extensive domestic and international co-operation projects have been progressing during the year under the above mentioned topics.
Also some equipment renovations and developments have taken place. The Accelerator Mass Spectrometry (AMS) project is being started by modifying the EGP-10-II accelerator to a certain extent. Also the upgrading of the laboratory isotope separator has engaged significant financial and man-power efforts. In addition to the laboratory's own investment outside funding from various sources has helped us to realise the modernization of the electrical power supplies and the improvement of the apparatus's vacuum systems.
The research associated with laser physics has continued according to the pattern of the previous year. Visible diode laser systems have been developed to be used both for nonlinear spectroscopy and optical metrology. The equipment has been utilized extensively during a laser physics course and for educational demonstrations.
The activity in molecular physics has historically evolved around the Raman spectrometer. Several collaborative projects with research groups both in Finland and abroad are going on in the fields of liquid spectroscopy, intermolecular forces, molecular modeling, optics and digital spectrum analysis.
A noteworthy factor which has had a significant impact on the Accelerator Laboratory activity this year has been the rather good level of outside funding. This has enabled us to support postgraduate students, as well as expand and strengthen our activity in traditional fields of our expertise. Several new students have joined the research groups during this year, aiming at M.Sc. and Ph.D. degrees.
HIGH ENERGY PHYSICS DIVISION
Theoretical High Energy Physics
The research activity covers several topics of current interest in theoretical physics and in the theory of elementary particle physics. These topics include Anyons and Fractional Statistics, Cosmology, Quantum Field Theory, Quantum Chromodynamics, Quantum Groups, Meson Spectroscopy, Supersymmetry and Weak Interactions, Ultra-Relativistic Heavy Ion Collisions and Quark-Gluon Plasma. The group maintains close research and scientific contacts with several theoretical high energy groups in Europe and in other Nordic countries, as well as with several research centres in USA, Japan and with CERN.
Experimental High Energy Physics
The research is based on experiments done with the big particle accelerators at CERN, the European Laboratory for Particle Physics. In 1996 the experimental program consisted of the NA52 experiment at the CERN SPS accelerator and on the design and simulation of the CMS experiment for the future Large Hadron Collider at CERN.
The NA52 experiment is a collaborative effort with the University of Bern and the Research Institutes of Annecy and Strasbourg. The High Energy Physics Laboratory is mainly responsible for the development of the on-line and off-line software for the analysis of the experiment.
The NA52 experiment searches for a new form of strange matter, the strangelet particles. This form of matter could have been formed in the early universe and in neutron stars and it is a possible candidate for dark matter in the universe. It could also be produced in collisions of heavy ions of high enough energy. In NA52 a fully ionized lead ion beam at the CERN SPS accelerator is shot at different lead targets. The energy density and strangeness concentration in these collisions is such that strangelets could be formed, if they exist.
The second topic of the NA52 experiment is the study of antinuclei production. Also here the experiment has unique capabilities in the world. In the lead ion collisions a large number of particles are produced. Their properties give information on the complex collision process. Antinuclei production is particularly interesting from this point of view.
Until now some 1012 lead ions with an energy of 158 GeV / nucleon have been shot on targets to produce new particles. The momentum, energy and time of flight of these particles were recorded to determine their mass. The analysis of these data was continued in 1996. No clear candidates for strangelets have yet been found, which in the mass range of 5-50 GeV/c2 sets an upper limit of 10-7-10-9 (model dependent) for their production probability. Results on the production of antiprotons, antideuterons and anti 3He-nuclei have been published.
Simulation and design of the Compact Muon Solenoid detector (CMS) was continued in 1996. The High Energy Physics Laboratory has contributed to the simulation and assessment of the physics discovery potential of the CMS design, particularly in the search for the Higgs bosons and supersymmetric scalar top quarks.
THEORETICAL PHYSICS DIVISION
The research activity comprises of a number of fields. The main thrust is in Particle Cosmology, Phenomenological Particle Physics, Physics of Hadrons and in Atomic, Molecular and Optical Physics. There is also research in Biophysics, Mathematical Physics, Astrophysics and Many Body Physics.
In particle cosmology, which is the principal research activity of the Division, the main research topics have been the dynamics of the electroweak phase transition and the physics related to the primordial magnetic fields. A central issue has been the question of the possible creation of baryon asymmetry of the Universe during the electroweak phase transition.
Research in phenomenological particle physics has been concentrated on the study of the beyond-the-Standard-Model physics in high energy phenomena. The Division has been represented in the DESY (Deutsches Elektronen-Synchrotron, Hamburg) working group for a conceptual design of a TeV-scale linear collider.
The research in particle cosmology and in phenomenological particle physics are intimately connected. They both aim at a better understanding of the fundamental laws of the basic matter constituents and their interactions.
The Theoretical Physics Division has considerable interaction with the Helsinki Institute of Physics (HIP), and close contacts are maintained with the Department of Geophysics of the Finnish Meteorological Institute, as well as with theoretical physics groups at CERN, NORDITA and several other institutions and universities in Finland and abroad.