Diploma work in the Nuclear Physics group at Frescati.

Medical Imaging techniques

1. The TOF- PET equipment of KTH is operational since1999. It is a unique piece of detector system with state of the art time resolution. The detector array consists of 48 BaF₂ scintillation crystals and a dedicated decoding electronics to register photons from positron annihilation. Hardware has to be added and software remains to be written to fully exploit its capabilities, i.e. the slow control system for manipulating the movement of the object table and the detector wheel.
2. Gamma Camera, installation and improvement/modification. We will in the near future obtain a Gamma Camera. The work contains the installation of the system and improvement by using more modern detection technique.

Single Event Effects

1. When ionizing radiation penetrates working electronic circuits the charges created by the absorbed energy might alter the content of digital circuits like memories. This type of error is temporary "soft" and disappears when the memory content is rewritten. The effect is called Single Event Setup and is one of the major problems for electronics in satellites. The effect can be measured in the laboratory using radioactive spontaneous fission sources emitting heavy ions. We would like to build a device so that the SEU capability of different ions can be determined.
2. SEUs are obseved also for circuits subject to neutron radiation. As an example SEUs have been observed in air borne electronics (in aeroplanes). The neutrons at high altitudes are secondary particles created by proton bombardment of the atmosphere. The neutron induced SEUs in electronic circuits are due to nuclear reactions. We are studying these phenomena at the TSL cyclotron at Uppsala. Next experiment will take place week 25 (19-21 June). The diploma work is to prepare and participate in this experiment, and take care of the analysis of data.
3. The Nuclear physics group of KTH is responsible for radiation hardness tests of some of the components of the European research satellite SMART-1. This satellite has a new type of engine using an electric propulsion technique. The drawback, and challenge, of this technique is the long time of passage through the Van Allen Belt, the radiation belt around the Earth. The components of the satellite have to withstand the radiation during the 90 days passage of the Belt, compared to 3 days for normal satellites. The work consists of participation in these tests at different laboratories, i.e. for proton tests at the The Svedberg Laboratory in Uppsala. (MUNIN?)

Monitoring of radioactivity in the environment

1. The new Physics Center, the common place of education and research for the University of Stockholm and KTH will accommodate a laboratory for monitoring of radioactivity in the air. It will be located in the Observatory Tower of the building and with access to a balcony on the top of the building. We want to build a filter collector station, similar to the one used at FOI in Ursvik to collect samples. The samples will be measured in the Low Radiation Level Laboratory of the Physics Center, in the basement of the building. The diploma work include to build up the gamma monitoring station for collecting and analyzing data recorded with Germanium detectors.
2. Similar to the above, but the collected air samples are measured for detecting alpha activities, mostly from radon decay.
3. The annual death-rate in Sweden due to diseases caused by radon radiation is exceeding the number of mortal car accidents. To reduce the number of houses with high radon content in the air is a truly multidisciplinary task. By the authorities accepted level of indoor radioactivity in existing buildings is 400 Bq/m³. The upper limit for new constructions is 200 Bq/m³. To illustrate the problem we plan to build a "doll-house" made of bricks containing natural uranium (blåbetong). The test setup will contain equipment for monitoring the radon content and will provide a test facility for different methods for reducing the radiation such as controlled ventilation, mechanical filtering and electrostatic collection of radioactivity.

Work at the CRYRING accelerator of the Manne Siegbahn Laboratory

1. In the present diploma work the aim is to improve the sensitivity of YAP and/or BaF₂ scintillator detector systems for singly charged ions of fairly low energy. Ions that get neutralized or change their charge state by collision with rest gas molecules leave the beam orbit. Neutralized ions can be detected after a bending magnet (there are 12 dipole magnets in CRYRING, see figure). We have one scintillator placed outside the beam i.e. at a position where the circulating beam is not affected. We have a number of ideas of how to improve the detection efficiency for low energy ions. These ideas concern both improved electronics and improved light collection efficiency and comparison of different detector materials at low and medium ion energies.
2. A channel electron multipliers (channeltron) or multi channel plates (MCP) could also be used both as detector for low energy ions as well as for ions of very high energy. A very special detector made up of a thin gold foil and a channel plate should be constructed for studies of a so called "crystal beam". CRYRING has a device called "Electron Cooler". This device "cools" the stored ions i.e. improves the velocity distribution so that the energy spread of the ions becomes » 10^-5. CRYRING has the best electron cooler in the world. It was recently discovered that the energy resolution suddenly improves further (10^-7 10^-8) when the number of ions stored in CRYRING becomes below » 5000. A few questions have appeared after the recent experiments: What happens when the beam "switches" to very low energy spread? Does the ions order in some particular way? We have started experiments to study this new phenomenon. The challenge is to detect 5000 ions within a few microseconds. We have made a first experiment. Data from that experiment are available for analysis immediately. However the main task of this diploma work is to build a new detector, based on micro channel plates, that are fast. Fast means that it should be able to resolve different ions with a time resolution of about 200 ps.

Other detectors.

1. Neutron monitor for use at SEU experiments at TSL, Uppsala.
2. Small scintillators for high intensity gamma radiation. Operating with mirrors or light guides that brings the light out from the hot region to a less "hot" region where sensitive parts of the detector system can be placed.

Testing facilities

1. The V d G can deliver beams of p, ³He and a particles in the energy range 400 keV - 2.5 MeV. With the help of the nuclear reaction ²H(³He,p)⁴He the energy range of protons can be extended to about 13 MeV. The ¹⁹F(p, a )¹⁶O nuclear reaction yields about 8 MeV a particles emitted at about 90^o and about 2 MeV ¹⁶O ejected in the same direction (other ion energies in other directions). However radioactive sources can also be used and give a particles in the range of 5 - 7 MeV.
2. A small 40 keV mass separator is also available. It can deliver ions of the same kind as MINIS, the main ion source at CRYRING for singly charged ions.
3. We can also make detector studies at the Uppsala Tandem Accelerator Facility. Presently a new Tandem van de Graaff is being installed. It will be available for experiments during the second half of 2001.
4. Gamma irradiations can be done at Karolinska Institutet in Stockholm, and at ATOMKI at Debrecen in Hungary.

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