Department of Applied Physics

Antimatter and Nuclear Engineering

The Antimatter and Nuclear Engineering group specializes in the development and applications of positron-based spectroscopic tools in condensed matter research. It also works on reactor and radiation physics research. The group has extensive facilities for positron annihilation spectroscopy and access to a wide range of experimental tools at the Department of Applied Physics.
Antimatter and nuclear engineering
Group leader professor Filip Tuomisto

Group leader

Filip Tuomisto

Research

Positron physics and defect spectroscopy

Positron annihilation spectroscopy enables the unambiguous identification and quantification of vacancy defects and their surrounding atoms in crystalline solids. For instance, in the case of semiconductor materials, this type of basic research aims at the understanding of e.g. mechanisms of electrical compensation, the origin of optical absorption and the nature of electronic transitions of photoluminescence. In the past, the group has contributed substantially to the understanding of defect and doping impurity structures both in silicon and compound semiconductors, as well as the physics of positrons in solids.

Our work in this field involves the study of defects in semiconductors, development of positron methods for the study of matter, and nuclear materials research. All the instrumentation has been designed and constructed in-house.

See review:  “Defect identification in semiconductors with positron annihilation: Experiment and theory”, Rev. Mod. Phys. 85, pp. 1583 – 1631 (2013).

Reactor and radiation physics

In reactor physics, the current research interests include Monte Carlo burnup calculation methodology, diffusion coefficient generation by the Monte Carlo method and uncertainty analysis in reactor physics. Essentially all research is computational using and/or developing codes such as SerpentMCNP and NJOY in close collaboration with VTT Technical Research Centre of Finland Ltd.

In radiation physics our interests are in the computational methods of gamma-ray spectrometry and identification. The group is the birthplace of SAMPO codes for spectrum analysis and the expert system SHAMAN for subsequent radionuclide identification and quantification. We also belong to the developers of LINSSI database for gamma-ray spectrometry and are active members of the LINSSI Users' Group.

We are active members of European Nuclear Education Network and Finnish Generation IV -project.

Facilities

We have two continuous variable-energy positron beams equipped with state-of-the-art detector systems and sample manipulation facilities and four measurement stations for fast positron spectroscopy, and a pulsed positron beam for positron lifetime measurements with low-energy positrons. All the instrumentation has been designed and constructed in-house.

Sample manipulation possibilities during positron experiments include:

  • Temperature control from 10 K up to 1000 K that allows for defect charge state determination in semiconductors, in-situ annealing experiments in semiconductors and metals, and, e.g., structural analysis of phase transitions in molecular matter.
  • Monochromatic sample illumination with light wavelength 400 – 2500 nm, allowing for studies of photoionization of defects in semiconductors and, e.g., structural photoresponse in polymers.
  • Sample biasing, allowing for studies of near-surface Fermi level modification effects in semiconductors and positron diffusion.

Courses

The Antimatter and Nuclear Engineering group promotes a few courses and offers positions and subjects for theses.

Courses on nuclear engineering

The courses related with nuclear engineering are lectured in Finnish. For an English alternative, please contact Professor Filip Tuomisto.

Introduction to nuclear energy technology

The course is intended for students minoring in energy sciences. It is lectured every spring. The course has three main parts: current, generation II and generation III nuclear reactors, future generation IV fission reactors and fusion reactors. The contents are basics of nuclear physics and technology, nuclear fuel cycle, nuclear waste management, safety and nuclear specific issues. Fusion reactor concepts, basics of fusion physics and material issues are also covered. The course is lectured in Finnish.

Introduction to reactor physics

The course is lectured every autumn. It gives an overall view of nuclear energy, reactors and power plants and an introduction to neutron physics, nuclear reactor theory, reactor kinetics, heat removal, thermal hydraulics, fuel cycles, nuclear waste management and safety viewpoints. The mathematics and physics courses of the first two years are adequate prerequisites. The course is lectured in Finnish.

Advanced course in nuclear engineering

The course is lectured every spring and concentrates on neutron physics. The course introduces a computational chain that can be used to model nuclear reactors. The course covers transport theory, Monte Carlo method, burnup calculation (Bateman equations) and diffusion theory as well as elementary heat transfer and thermal hydraulics. Applications of the computational chain are demonstrated.

Radiation physics and safety

The subject of the course is radiation, its interactions with matter and its health effects. The emphasis is on the ionizing radiation, its risks and their mitigation. The concept of risk is studied in connection with radiation and nuclear safety. The course includes laboratory exercises on sealed sources and X-ray equipment and gives a possibility to obtain a licence to use them in research and industry. For the licence adequate knowledge of the Finnish regulations on radiation and nuclear safety is required.

Solid-state and materials physics

Members of the group also contribute in teaching courses on solid-state and materials physics.

Laboratory courses

The group actively participates in organizing and developing the laboratory courses on Engineering Physics. These courses give hands-on experience of research work that is welcome among the theoretical physics courses.

Laboratory course on engineering physics

One of the exercises on this BSc-level course is titled "Positron measurements in semiconductors". The goal of this assignment is to familiarize oneself with the equipment used in a positron
lifetime measurement, studying vacancies with positrons and the physics of vacancy defects in GaN samples.

Advanced physics laboratory

One of the exercises on this MSc-level course is titled "Semiconductor studies with positrons". The goal of this assignment is to dig deeper into semiconductor characterization utilizing positron spectroscopy.

Theses

The Antimatter and Nuclear Engineering group offers a wide range of subjects for bachelor’s theses, special assignments and master’s theses. Many of our theses are written at the organizations in this field (VTT, Fortum, STUK, TVO) or instructed by their expert personnel.

For further information, please contact Professor Filip Tuomisto.

Latest publications

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se2 absorber materials

Andrew Ferguson, Rouin Farshchi, Pran K. Paul, Pat Dippo, Jeff Bailey, Dmitry Poplavskyy, Afrina Khanam, Filip Tuomisto, Aaron Arehart, Darius Kuciauskas 2020 Journal of Applied Physics

A demonstration of donor passivation through direct formation of V-As_i complexes in As-doped Ge_1−xSn_x

Afrina Khanam, Anurag Vohra, Jonatan Slotte, Ilja Makkonen, Roger Loo, Geoffrey Pourtois 2020 Journal of Applied Physics

Effect of interstitial carbon on the evolution of early-stage irradiation damage in equi-atomic FeMnNiCoCr high-entropy alloys

Eryang Lu, Ilja Makkonen, Kenichiro Mizohata, Zhiming Li, Jyrki Räisänen, Filip Tuomisto 2020 Journal of Applied Physics

Interfacial N Vacancies in GaN/(Al,Ga)N/GaN Heterostructures

Vera Prozheeva, Ilja Makkonen, Haoran Li, Stacia Keller, Umesh K. Mishra, Filip Tuomisto 2020 Physical Review Applied

Segregation of Ni at early stages of radiation damage in NiCoFeCr solid solution alloys

F. Tuomisto, I. Makkonen, J. Heikinheimo, F. Granberg, F. Djurabekova, K. Nordlund, G. Velisa, H. Bei, H. Xue, W. J. Weber, Y. Zhang 2020 Acta Materialia

Source/Drain Materials for Ge nMOS Devices

Anurag Vohra, Ilja Makkonen, Geoffrey Pourtois, Jonatan Slotte, Clement Porret, Erik Rosseel, Afrina Khanam, Matteo Tirrito, Bastien Douhard, Roger Loo, Wilfried Vandervorst 2020 ECS Journal of Solid State Science and Technology

Vacancy cluster growth and thermal recovery in hydrogen-irradiated tungsten

M. Zibrov, W. Egger, J. Heikinheimo, M. Mayer, F. Tuomisto 2020 Journal of Nuclear Materials

SYP2019 - Suomalaisen Ydintekniikan Päivät alkavat olla perinne

Jarmo Ala-Heikkilä, Tuomas Rantala 2019 ATS Ydintekniikka
More information on our research in the Research database.
Research database

Research group members

Jonatan Slotte

Vanhempi yliopistonlehtori
Department of Applied Physics
Jarmo Ala-Heikkilä

Jarmo Ala-Heikkilä

Asiantuntija
Department of Applied Physics
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