[en] The aim of this study was to create a model for the kinetics of ¹⁰B in glioma patients after p-boronophenylalanine fructose complex (BPA-F) infusion in order to predict the ¹⁰B concentration in blood during the neutron irradiations in BNCT. The more specific aim was to create a flexible model that would work with variable infusion duration and variable amounts of infused BRA, by forehand carrying out only 1 to 2 kinetic studies per different trials. Previously used bi-exponential fitting and open compartmental model are capable, but, however, heavy kinetic studies are needed before they are reliable enough. A model probe with a memory effect based on phenomenological findings was created. The model development was based on the data from 10 glioblastoma multiforme patients from the Brookhaven National Laboratory BNCT trials. These patients received i.v. 290 mg BPA/kg body weight as a fructose complex during two hours. Blood samples were collected during and after the infusion. The accuracy of the model was verified with distinctive fitting of 10 new glioma patient data from the Finnish BNCT-trials. The ¹⁰B- concentration in whole blood samples was determined by ICP-AES method. In the study it is concluded that the constructed non-linear model is flexible and capable in describing the kinetics of ¹⁰B concentration in blood after a single infusion of BPA-F. (author)

[en] Standard dosimetric phantoms are used in radiotherapy to compare irradiations under standard conditions. They provide volumes of tissue substitute for the measurement of absorbed dose and are large enough to ensure that full contribution to the absorbed dose from scattered radiation is received at the point of measurement. Aim of this study was to find out a recommendation for the boundary values of size of a reference phantom. These reference conditions for the reference measurement methods are created for 'A code of practise for dosimetry, of BNCT in Europe' project. The major objective of the project is to prepare detailed guidelines for the dosimetry of epithermal neutron beams to be used for treatment of cancer patients by Boron Neutron Capture Therapy (BNCT) at European research reactors and accelerators. For this objective Monte Carlo simulations have been carried out with MCNP 4B code in three different cubic phantoms for studying effect of different phantom sizes in important radiation components. These three phantoms are the proposed reference (measurement) phantom (20*20*20 cm), a phantom that was assumed to model an infinite phantom, and a smaller (15*15*15 cm) cubic phantom which exists in Petten BNCT facility in Netherlands. Function of the smallest phantom was to study acceptable lower limit to the phantom size to still reach the reference conditions. All the simulated phantoms were cubic water phantoms with one 0.5 cm thick (beam side) wall and three 1 cm thick walls of PMMA (polymethyl-methacrylate). The comparisons were done with calculations of the thermal, epithermal and fast neutron fluence rates in analogous points. The source specification of the MCNP runs were accordance of 250 kW FiR 1 research reactor neutron beam with 14 cm beam aperture. In order to minimise the statistical error of the Monte Carlo calculations, over 60*106 source particles were simulated for infinite and reference phantom cases. Calculation results were in good agreement with each other. According to these results, the proposed reference phantom can be considered as a good model of an infinite phantom, and all the larger phantoms with same wall thickness and materials are usable as standard dosimetric phantom for BNCT dosimetry. The lower limit for the standard dosimetric phantom size will be presented in addition, when the simulation results are acquired for the indicated smaller phantom (author)

[en] The new neutron deficient nuclide ¹⁹⁵Rn and the nuclide ¹⁹⁶Rn have been produced in fusion evaporation reactions using ⁵⁶Fe ions on ¹⁴²Nd targets. The gas-filled recoil separator RITU was used to separate the fusion products from the scattered beam. The activities were implanted in a position sensitive silicon detector. The isotopes were identified using spatial and time correlations between implants and decays. Two α decaying isomeric states, with E_α = 7536(11) keV (T_1/2 = 6⁺³_-2 ms) for the ground state and Eα = 7555(11) keV (T₁₇₂ = 5⁺³_-2 ms) for an isomeric state were identified in ¹⁹⁵Rn. In addition, the half-life and α-decay energy of ¹⁹⁶Rn were measured with improved precision. The reduced widths deduced for the neutron deficient even-mass Rn isotopes suggest an onset of substantial deformation at N=110. Results from this study will be presented and discussed (author)

[en] The 35th Physics Days of the Finnish Physical Society will have the traditional structure with plenary lectures, short contributions of young researchers, poster sessions, and social events. The number of members of the society has exceeded 1000 and nearly half of them, more than 400, are expected to participate the Physics Days. The Finnish physicists and the Society can be proud of keeping up this tradition. The annual meeting of the Finnish Physical Society will take place during the Physics Days. I wish all the members of the Finnish Physical Society to attend the meeting and continue the discussions more informally at the conference dinner following the annual meeting. The fifth Magnus Ehrnrooth Price for Physics will be given during the opening ceremony of the Physics Days. Also the winners of the SOLIS competition for high school students will be announced. Traditionally, the Days will end by giving prices for the best poster and the best talk. The 35th Physics Days are held in the new congress center Jyvaeskylae Paviljonki and arranged by the University of Jyvaeskylae. The proceedings includes all the abstracts of the presentations given during the 35th Physics Days

[en] The phenomenon of shape coexistence is experimentally well established in even-even light Pb, Hg and Pt nuclei. The light Po isotopes are predicted to exhibit similar features. Due to the experimental difficulties when approaching the proton drip-line, the lightest Po isotope for which in-beam γ-ray data exists prior this work has been ¹⁹²Po. Since shape coexistence should be most pronounced at the neutron mid-shell (N=104), information about the excited states in lighter Po isotopes would be valuable in verifying the existence and possibly understanding the origin of the phenomenon in these nuclei. In the present work the recoil decay tagging method has been used to study excited states in the neutron deficient isotopes ^190,191Po. Prompt γ-rays were detected with the Jurosphere Ge detector array coupled to the gas- filled separator RITU. The ¹⁹¹Po nuclei were produced in the ¹⁴²Nd(⁵²Cr,3n)¹⁹¹Po reaction at a bombarding energy of 240MeV. The observed prompt γ-rays correlated with the α-decay of the ^191mPo 13/2⁺ state were placed in two cascades. Similar sequences have been observed in ^193,195Po and presumably correspond to favoured and unfavoured states in the vi₁₃ band. The unfavoured states are lowered below the favoured ones, resulting in a strongly coupled scheme which suggests oblate deformation. In a separate experiment the ¹⁴²Nd(⁵²Cr,4n)¹⁹⁰Po reaction was used at higher beam energy. The production cross-section was approximately 200nb. Four prompt α-transitions correlated with the ¹⁹⁰Po α-decay were observed and intepreted to form a cascade of E2 transitions up to spin 8⁺. In comparison to the heavier even Po isotopes, a drop in 6⁺ and 8⁺ energies is observed. This suggest an onset of prolate deformation in light Po isotopes as predicted by Oros et al. The results will be discussed in the framework of intruder states (author)

[en] The Centre for Underground Physics in Pyhaesalmi (CUPP) project is aiming to establish an underground laboratory in the Pyhaesalmi zinc mine, offering a potential location for small-to-medium-scale scientific experiments, which require, e.g., a low level of background radiation. The pilot experiment of CUPP is Muons UnderGround (MUG), consisting of muon detectors placed at different depths. The MUG experiment extends the field of cosmic-ray and heliospheric research of the University of Oulu to underground studies in addition to the long-term neutron monitor observations of cosmic rays on ground level in Oulu. As the first active experiment of the CUPP project, the MUG experiment is also used to evaluate and prove the suitability of the facilities of the Pyhaesalmi mine for underground scientific work. The Pyhaesalmi mine is located 156 m above the sea level, and its geographical coordinates are 63 deg C 39.6' N. 26 deg C 2.5' E. The mine is dry, the surrounding bedrock is stable, and the background radiation level is low. There are several possible experimental sites at different depths down to 1050 m, accessible with small trucks. The locations are, or can easily be equipped with electricity as well as with telephone and data lines. The mining activity is going on below the 1050-m level down to 1400 m, ensuring the maintenance of the mine until at least 2010. The MUG experiment includes five detector units consisting of three pairs of vertically overlapping plastic scintillators, each equipped with standard NIM electronics and a personal computer for data storage. A data acquisition unit designed and manufactured by Detection Technology Inc is used for data recording and pulse height AD- conversion. A substantial part of the equipment is borrowed from the Space Research Laboratory of the University of Turku. One of the MUG units is on the ground level, two units have already been installed in a cavern 210 m underground, and two units will be installed in a container 90 m underground (author)

[en] Ion Bernstein waves (IBWs) may offer a viable method for heating ions and driving plasma rotation in fusion plasmas. Within present experiments at the FTU tokamak, the IBW at 433 MHz is first launched from waveguides at the plasma edge as a slow wave. In a region of lower hybrid resonance, the slow wave is mode transformed into an ion Bernstein wave by finite Larmor radius effects. In the IBW coupling problem, nonlinear and kinetic effects are important. The particle-in-cell (PIC) method takes them into account, because the electric fields and the particle motion are solved self- consistently. Using the particle-in-cell technique, IBW excitation has so far been studied only for parameters significantly different from those in real experiments. Specifically, only small ion to electron mass ratios and excitation frequencies in the range between the first and the second harmonic frequencies have been used in the simulations. The reason for this is that simulations with real parameters are computationally very heavy, which can easily be understood: Firstly, in order to obtain accurate results, the grid spacing has to be of the order of the Debye length, which decreases with increasing density. Secondly, the time step also has to be decreased with increasing density. Artificially reducing the ion mass and decreasing the excitation frequency leads to lower densities in the simulation region and thus to more manageable simulations. In this work, IBW excitation is for the first time simulated with realistic parameters resembling those of the FTU tokamak. The electrostatic PIC code XPDP2 is used. The electrostatic approximation is justified, because the ion Bernstein wave is essentially an electrostatic wave. A wave launcher model has been added to the 2d3v PIC code. A new energy flux diagnostics based on first principles is presented. The total energy flux launched by the radio frequency (RF) grill is the best indicator of any successful excitation of waves. The necessary resolution and time step for the results to be accurate are determined. Then, edge absorption and coupling are systematically studied as a function of RF power. The temperature effect on the excitation is also investigated. Finally, the results are compared to those obtained in experiments at FTU (author)

[en] The Phase I clinical trials for boron neutron capture therapy (BNCT) started in May 1999 in Otaniemi, Espoo. For BNCT no uniform international guidance for the quality assurance of dosimetry exists, so far. Because of the complex dose distribution with several different dose components, the international recommendations on conventional radiotherapy dosimetry are not applicable in every part. Therefore, special guidance specifically for BNCT is needed. To obtain such guidelines a European collaboration project has been defined. The aim of the project is a generally accepted Code of Practice for use by all European BNCT centres. This code will introduce the traceability of the dosimetric methods to the international measurement system. It will also ensure the comparability of the results in various BNCT beams and form the basis for the comparison of the treatment results with the conventional radiotherapy or other treatment modalities. The quality assurance of the dosimetry in BNCT in Finland covers each step of the BNCT treatment, which include dose planning imaging, dose planning, boron infusion, boron kinetics, patient positioning, monitoring of the treatment beam, characterising the radiation spectrum, calibration of the beam model and the dosimetric measurements both in patients (in viva measurements) and in various phantoms. The dose planning images are obtained using a MR scanner with MRI sensitive markers and the dose distribution is computed with a dose planning software BNCT_Rtpe. The program and the treatment beam (DORT) model used have been verified with measurements and validated with MCNP calculations in phantom. Dosimetric intercomparison has been done with the Brookhaven BNCT beam (BMRR). Before every patient irradiation the relationship between the beam monitor pulse rate and neutron fluence rate in the beam is checked by activation measurements. Kinetic models used to estimate the time-behavior of the blood boron concentration have been verified using independent patient sample data. For the measurement of the absorbed doses in patients and phantoms, TL dosimeters and activation foils are used. At the moment the quality assurance of dosimetry in BNCT in Finland is according to the EU rules and planned recommendations and thus sufficient. Nevertheless microdosimetric measurement methods and gel dosimeters are planned to bring to use in addition to the dosimetric methods already utilised in order to strengthen the quality assurance (author)

[en] The existence of an instability of convective motion in a two- dimensional ideal fluid which transforms convection into sheared flow is now a well established fact, and provides a model, e.g., for Venus superrotation. Also, turbulence shear suppression by E x B zonal flows (plasma flows induced by an electric field perpendicular to the magnetic field line), and related bifurcations of the rotations speed, are the most likely mechanism responsible for the transition to various forms of enhanced confinement regimes observed in magnetically confined plasmas. By use of low-noise numerical algorithms and massively parallel computers, key features of generation of such shear flows can presently be investigated. A multi-dimensional Monte Carlo particle simulation method for advancing rotating plasmas is presented. Including the ion polarisation current and exploiting the current balance condition for quasineutrality, gives the time rate of change of the electric field E and related evolution of the rotation velocity components. Here, q and M are the ion charge and mass, respectively, and Ω = qB/M is the cyclotron frequency, n is the plasma density. For not too low density, i.e., ω²_p >> 1, where ω_p is the ion plasma frequency, this method provides an enhancement of computing speed by a factor of ω²_p/Ω² over a standard method of solving the Maxwell equations. A special orbit initialisation for a quiscent start as well as an efficient radial flux solving algorithm with reduced numerical noise are developed. Numerical stability of the method with respect to the strength of the gyroviscosity and Mach number of the rotation is investigated. This new approach enables one to separate the nonambipolar transport characteristics from the ambipolar ones. Because nonambipolar transport can support sheared flows, this model provides an efficient tool for the analysis of the latter. Results are presented for generation of poloidal rotation in plasma tori, and related tearing of turbulent convective cells. Gyrokinetic extension of the method for the self- consistent simulation of turbulence and zonal flows is presented. Both space and fusion plasma applications of the method are discussed, including ionospheric ambipolar diffusion and electric field generation, rotation in planetary atmospheres, and high confinement transitions in tokamaks (author)

[en] The goal of the ion trap project in Jyvaeskylae is to improve the quality of radioactive beams at IGISOL (Ion Guide Isotope Separator On-Line), in terms of transverse emittance, energy spread and purity. This improvement is achieved with an aid of an RFQ cooler/buncher and a mass-selective cylindrical Penning trap (mass resolving power up to 10⁵). Their final purpose is to produce cooled isobarically pure beams of exotic radioactivities mainly of exotic neutron-rich isotopes from fission (including refractory elements). In the Penning trap ions are confined in three dimensions in a superposition of static quadrupole electric and homogeneous magnetic fields. The magnetic field confines the ions in two dimensions in a plane perpendicular to the field direction. A confinement in the third, magnetic field direction (parallel to the trap axis) is done by a quadrupole electric field. The Penning trap system in Jyvaeskylae (JYFLTRAP) will contain two cylindrical Penning traps placed inside the same superconducting magnet (B=7 T). The first, purification trap, will accept cooled (continuous or bunched) beams from the RFQ cooler/buncher and perform the isobaric purification. The latter is - done using a combination of a buffer gas cooling and an azimuthal quadrupole RF-field providing mass- dependent centering of ions. This, in turn, allows mass-selective ejection of ions in short pulses. Clean monoisotopic bunched beams will be delivered for the nuclear spectroscopy studies, collinear laser spectroscopy experiments and precise nuclear mass measurements (10^-7 precision). The latter will be performed in the second, precision Penning trap (author)