Jukka Lehto

Person

Description of research and teaching

RESEARCH ACTIVITIES

  1.      ENVIRONMENTAL RADIOACTIVITY STUDIES

 At the end of 1990’s I started studying environmental radioactivity problems and from 2001, after retirement of our earlier professor Timo Jaakkola, these have been my major research field.

 1.1.Physicochemical forms of natural radionuclides in drilled well waters and their removal by ion exchange

 A large proportion of the Finnish population consumes drinking water from drilled wells that often contain unusually high concentrations of natural radionuclides. In the doctoral thesis of Kaisa Vaaramaa, which I supervised, we studied the presence of 210Po, 210Pb, 226Ra and uranium in particles of various sizes in waters taken from drilled wells. We found that most of the 210Po and 210Pb are bound in particles but that 226Ra and uranium are more or less soluble. We also tested a wide range of organic and inorganic ion exchange materials for the removal of these nuclides from waters. Since uranium is mainly present as an anionic carbonate complex UO2(CO3)34- in ground waters a strongly basic resin was the most effective ion exchanger for uranium. The strong cation exchange resin, zeolite  A and an aminophosphonate resin performed well with the removal of radium. However, polonium and lead could not be removed by ion exchange due to their particle-bound nature.

 1.2.Plutonium in the air in Kurchatov, Kazakhstan

 In 2000-2001 Laboratory of Radiochemistry was a partner in Finnish team testing  two air samplers in Kurchatov, Kazakhstan. Weekly air samples were taken over a one-year period in Kurchatov and another three month period in Astana, the capital of Kazakhstan. The purpose of this field trial was to test the samplers for the detection of undeclared nuclear activities. Kurchatov was chosen as a trial site since it is located at the edge of the Semipalatinsk nuclear test site which contains huge amounts of radioactivity in the ground. The role of the Laboratory of Radiochemistry in this study was to carry out the radiochemical separations of uranium and plutonium and to determine the plutonium isotopes. It was found that the plutonium concentrations in the air in Kurchatov were elevated and varied in a 100-fold range. The radiation doses to the local population caused by inhalation were, however, found to be rather low: 13 nSv/a.

 1.3.Radiological characterization of the Semipalatinsk nuclear test site in Kazakhstan

 In 2002-2006 I was a member in the International Atomic Energy Agency’s (IAEA) coordination group responsible for the comprehensive radiological characterization of the Semipalatinsk nuclear test site. The Semipalatinsk test site is a large area of almost 20,000 km2 and some parts of it are highly contaminated from the 460 nuclear weapons test carried out between 1949 and 1989. The purpose of the characterization programme was to provide the Kazakhstan government with recommendations as to which areas can be released for habitation and industrial use and which areas have to be decontaminated or sealed off.

 1.4.Long-term behaviour of radionuclides from nuclear weapons test fallout in the boreal forest environment in Finnish Lapland

 From the beginning of 1960’s the Laboratory of Radiochemistry has studied the behaviour of fallout radionuclides from atmospheric nuclear weapons tests in the environment and in food chains in Finnish Lapland. From 2001 onwards I have been in charge of these studies. The latest phase of these studies began in 1997 and ever since a large number of environmental samples have been collected from the Muddusjärvi area. These samples include sediment, water, fish, soil and vegetation from which 137Cs activity has been measured by gamma spectrometry, and from some soil and vegetation samples the 239,240Pu and 241Am activities have been determined as well. The purpose of the studies is to predict the long-term behaviour of these nuclides in northern boreal ecosystems.

 1.5.241Am fallout from Chernobyl accident in Finland

 Spatial distribution of 241Am in Finland was determined in 2003-2004 by measuring  241Am concentrations in peat samples from sixty peat bogs in Southern and Middle Finland collected immediately after the Chernobyl accident in May 1986. The 241Am fallout from the Chernobyl fallout was seen to be only 1.3% of the total 241Am inventory in Finland, the rest originating from nuclear weapons test fallout. The fallout pattern of americium fallout followed that of plutonium and the heaviest fallout was found in a sector from the south-western coast towards northeast.

 1.6.210Po and 210Pb in forest environment

 In 2005-2010 I was involved with Dr. Kaisa Vaaramaa’s postdoctoral research project in which 210Po and 210Pb in forest environment ere studied. Distribution of polonium and lead in various layers of podzolic soil and their transfer from soil into forest plants, mushrooms and wild berries, were explored.

 1.7.137Cs, 239,240Pu and 241Am in Lake Päijänne, Finland

 In 2007 sediment profiles and surface water samples were collected from the Asikkalanselkä, a southern basin of Lake Päijänne, where the drinking water is taken to the Helsinki metropolitan area. 137Cs activity in water was 19 Bq/m3 and in sediment 100 kBq/m2. Only 0.3% on the total cesium inventory was in the water phase. About 99% of the cesium activity originates from the Chernobyl accident. The situation in case of americium and plutonium was different: they originate by 98% from the nuclear weapons test fallout. Their activities in water were four to five thousand times lower than that of cesium: 4.9 mBq/m3 for plutonium and 4.1 mBq/m3 for americium. The deposition of plutonium and americium in the sediment were 20 Bq/m2 and 45 Bq/m2. The 241Am/239,240Pu ratio was higher in the water phase and in the upper sediment layers compared to the ratio in the deeper sediment layers indicating higher solubility on americium.

 1.8.Immobilization of radionuclides and heavy metals from mining mill tailings

 In 2010 I started supervising the doctoral thesis work of Hanna Tuovinen. The work will deal with the immobilization of radionuclides and heavy metals from mining mill tailings from Sokli phosphate ore (mine not in operation) in the Northern Finland and from Paukkajanvaara uranium mine (operated in 1958-19661) and possibly Talvivaara nickel mine. The four years’ project is financed by the Academy of Finland.

 1.9.Cleanup of large areas contaminated by nuclear accidents

 In 1990-1993 I worked as coordinator of the project in the Nordic Nuclear Safety Programme (NKS). The project dealt with the cleanup of large areas contaminated by nuclear accidents. In the project we studied various cleanup methods for urban, forest and agricultural environments, estimated the amounts of radioactive wastes obtained in the cleanup and planned options to dispose of these wastes.

2. STUDIES ON THE MIGRATION OF WASTE RADIONUCLIDES IN GEOSPHERE

 2.1. Sorption of trivalent actinides on clay mineral surfaces

 In 2007 I started supervision of Nina Huittinen’s doctoral work on the sorption of trivalent actinides on clay mineral surfaces. The objective of the study is to identify the actinide species taken by the various types of hydroxyl groups on clay surfaces. The clay minerals under study are gibbsite and kaolinite. In addition silica and γ-alumina have been studied. The actinide studied has been curium but also actinide analogues europium and gadolinium have been studied. Actinide/lanthanide speciation in solution and in the solid phase has been studied by Laser Induced Fluorescence, IR and NMR spectrometries. In addition batch sorption studies on lanthanides by the minerals have been carried out.

 2.2. Migration of long-lived radionuclides in soil

 From 2008 on I have been supervising two doctoral thesis work with Posiva Companys funding on the migration of long-lived radionuclides 135Cs, 129I, 99Tc, 94Nb, 93Mo and 79Se in soil of Olkiluoto where the final disposal repository will be constructed for the spent nuclear fuel from Finnish nuclear reactors. All these radionuclides, except 135Cs, may exist as anionic forms which make them very mobile in soil. Both sorption of radionuclides on various soil layers and sequential leaching of soils have been studied.

 3. ION EXCHANGE RESEARCH

3.1. Development of selective inorganic ion exchangers for the removal of radionuclides from nuclear waste effluents

I started my research career in 1980 by studying the ion exchange behaviour of sodium titanates for the selective removal of radionuclides from nuclear waste effluents. This was also the topic of my doctoral thesis in 1987. Since this was a novel topic in the Laboratory of Radiochemistry, University of Helsinki, I had to initiate and construct the research methodology. First by myself and later together with Dr. Risto Harjula  we have established a research group around this topic. In the last twenty-five years we have synthesised a wide range of inorganic ion exchangers, especially transition metal hexacyanoferrates, titanates and mixed metal oxides, such as titanium antimony oxides. The main purpose for the development of these radionuclide-selective ion exchangers has been to reduce nuclear waste volumes for final disposal and to reduce discharges to the environment from nuclear plants.

 A Finnish company, Fortum, is presently manufacturing three exchangers developed by the group:

  • CsTreat, a potassium cobalt hexacyanoferrate compound which is an extremely selective ion exchanger for the removal of radioactive cesium from nuclear waste solutions even in the presence of  very high concentrations of interfering cations, such as sodium and potassium
  • SrTreat, a sodium titanate compound which is highly selective for radioactive strontium from alkaline solutions
  • CoTreat, a titanate compound which is an effective ion exchanger for the removal of radioactive cobalt and other activation-corrosion products from power plant waste effluents

These unique exchangers have been utilised in industrial-scale separation processes in many countries (e.g. USA, UK, Japan, Finland, Hungary and Russia).

 Recently a new family of mixed oxides has been developed by our laboratory. These exchangers include pyroclore and rutile structured oxides of antimony, titanium and manganese. The primary aim of this development has been to obtain exchangers which are resistant to high concentrations of calcium in solution and which are suitable for use in acidic solutions.

 In the last few years I have focussed my main efforts into the field of environmental radioactivity and Dr. Harjula has taken over the leadership of the ion exchange research group.

3.2.  Characterization of inorganic ion exchange materials

 In addition to testing the inorganic ion exchangers with respect to their ability to remove radionuclides from nuclear waste effluents their physicochemical properties have been characterised in many ways:

  • structure determination by X-ray diffraction
  • radiation resistance
  • thermal decomposition
  • Their basic ion exchange parameters have been determined to predict the ion exchange equilibria and column performance

In the early 1980’s I also developed a solidification method for the final disposal of inorganic ion exchangers. In this method the ion exchangers were mixed with clay and ceramised into solid blocks by heating.

 3.3. Removal of heavy metals from metallurgical waste effluents

 In 1996-1999 I worked as a coordinator in the EU funded research project “Removal of heavy metals from metallurgical waste effluents by ion exchange”. In addition to Finland we had partners from UK and Germany. In the Laboratory of Radiochemistry we studied the use of chelating ion exchanger resins, activated carbons and inorganic ion exchangers for the removal Cd, Co, Ni, Cr, Zn and Cu from the waste effluents from metal plating plants. Based on this study the Finnair metal plating plant took into use an ion exchange facility to remove Cd and Ni as an end-polishing step following their existing waste treatment plant.

 3.4. Ion exchange properties of chelating ion exchange resins

 In the 1990’s I studied the basic ion exchange properties of chelating ion exchange resins, especially iminodiacetate and aminophosphonate resins. Special focus was paid to Zn and Ni ion exchange equilibria and to hydrolysis of the exchangers.

 4. OTHER STUDIES

 4.1. Study of cesium in blood plasma

 I have been a supervisor of the doctoral thesis of Matti Kaikkonen from the Faculty of Veterinary Sciences, University of Helsinki. This work deals with the determination of cesium (stable and radioactive) in blood plasma. We have developed a novel method to determine added stable cesium in plasma. The method is based on binding cesium in ammonium-iron(II)-hexacyanoferrate (AFCF) and precipitating AFCF with plasma proteins. The method can bE utilised, for example, in studying the plasma kinetics of cesium.

 4.2. Behaviour of heavy metals in lakes in the northwestern  Russia

 In 2005 water and sediment samples were taken from Lake Umbozero, the second largest lake in the Kola Peninsula. The purpose of the study was to see if the lake would have been affected by the atmospheric emissions from the metal smelters in the Kola region, especially by the Monchegorsk smelter 60 kilometres west of the lake. Clearly increasing trend of metals was seen in the sediment profiles but in general the lake was seen to be rather clean, especially compared to the Lake Imandra close to the Monchegorsk smelter.

 Similar study was done in 2007 in Kostamus region where there is a large iron mine and ore dressing mill only 30 kilometres east of the Finnish-Russian border. Water and sediment samples were taken from four lakes in a water stream leading from the waste pond of the plant to Lake Keskikuittijärvi 60 kilometres northeast of the plant. In this water system clearly increasing trend on most metals was seen to towards the plant. In another studied direction, 70 kilometres west of the plant, water and sediment samples were taken from two lakes in the Russian side and from another two lakes in the Finnish side. In this direction, where only atmospheric releases are possible, no effects of the plant were seen.

 

TEACHING

 Courses lectured

 Principles of radiochemistry I, years 2000-2002, 2008,  3 credit units

  • 14 hours lecturing and one week laboratory exercises

 Principles of radiochemistry II, 2000-2003, 3 credit units

  • 14 hours lecturing and one week laboratory exercises

 Chemistry and analysis of radionuclides, 2001-, 5 credit units

  • 26 hours lecturing and two weeks laboratory exercises

 Environmental radioactivity, 2001-, 3 credit units

  • 8 hours lecturing, after which each student gives a seminar presentation

 Radioactive tracer techniques, 1997-2000, 3 credit units

  • 10 hours lecturing and two weeks laboratory exercises

 Ion exchange and its use in the treatment of industrial waste effluents, together with Dr. Risto Harjula, 1999-2002, 2 credit units

  • 6 + 6 hours lecturing

 

Produced text books:

 J.Lehto and X.Hou, Chemistry and analysis of radionuclides, Wiley – VCH in 2010, 406 pages

Contents:  

1. Radioactivity, radionuclides, and radiation

2. Special characteristics of the chemistry and analysis of radionuclides

3. Need for radiochemical separations

4. Radiochemical separation methods

5. Yield determinations and source preparations in radiochemical analyses

6. Radiochemistry of alkali metals

7. Radiochemistry of alkaline earth metals

8. Radiochemistry of 3d transition metals

9. Radiochemistry 4d transition metals

10. Radiochemistry of lanthanides

11. Radiochemistry of halogens

12. Radiochemistry of noble gases

13. Radiochemistry of tritium and 14C

14. Radiochemistry of lead and polonium

15. Radiochemistry of actinides

16. Speciation – physical and chemical forms of radionuclides

17. Measurement of radionuclides with mass spectrometry

18. Sampling and pre-treatment of environmental samples

19. Chemical changes in the matter induced by the radioactive decay process

 

 J.Lehto, Principles of radiochemistry, 2000, 200 pages

Contents:

1.      What is radiochemistry

2.      What is radioactivity

3.      History of radiochemistry                                                                  

4.      Structure of atom and nucleus

5.      Nuclides, isotopes, isobars – nuclide chart

6.      Stability of nuclides

7.      Radionuclides

8.      Modes of radioactive decay

9.      Rate of radioactive decay – equilibria in successive decays processes

10.  Interaction of radiation with matter

11.  Detection and measurement of radiation

12.  Measurement of radiation with gas chambers

13.  Liquid scintillation counting

14.  Statistical treatment of results

15.  Nuclear reactions  

16.  Preparation of radionuclides 

17.  Isotope separations

18.  Radionuclide imaging

19.  Separation and speciation of radionuclides

 

Close

Curriculum Vitae

1.                   Full name: Jukka Kalevi Lehto

 2.                   Date and place of birth:  1st of October 1953, Nokia, Finland

 3.                   Current position:

  •  professor in radiochemistry, Laboratory of Radiochemistry, University of Helsinki 2005-
  • head of the Laboratory of Radiochemistry, University of Helsinki 2004-

 

 4.                  Education and training:

  •  M.Sc.                     1981              University of Helsinki
  • Lic.Phil.                  1985              University of Helsinki
  • Ph.D.                     1987              University of Helsinki

 

 5.                  Previous professional appointments:

  •  part-time junior counselling officer, 1978-1979 (18 months), University of Helsinki, Faculty of Science
  • researcher, 1980-1988, University of Helsinki, Department of Radiochemistry
  • visiting researcher, 1981 (9 months) Isotope Institute of the Hungarian Academy of Sciences, Budapest, Hungary
  • visiting researcher, 1985-1986 (12 months), Department of  Chemistry, Texas A&M University, College Station, USA
  • teaching assistant, 1988-1997, Department/Laboratory of Radiochemistry, University of Helsinki
  • senior scientist, 1995-2000, Academy of Finland
  • senior teaching assistant, 1998-2001, Laboratory of Radiochemistry, University of Helsinki
  • acting professor in radiochemistry, Laboratory of Radiochemistry, University of Helsinki, 2000-2002, 2004-2005
  • head of the Laboratory of Radiochemistry, University of Helsinki, 2000-2002
  • senior lecturer, (reader, dozent, associate professor) 2002-2004, Laboratory of Radiochemistry, University of Helsinki
  • docent in radiochemistry 1988-2004

 

 6.              Research awards, research honours and major stipendiary support for research

Research honours:

  • Professor Jorma K. Miettinen Award Medal  1993, Section of Radiochemists of the Finnish Union of Chemists

 Major research funding:

  •  Academy of Finland, 30,000 €, 1990
  • Finnish Technology Development Agency, 150,000 €,  1992
  • University of Helsinki Research Foundation, 130,000 €, 1994
  • EU Brite-EuramIII, 317,000 €, 1996
  • Academy of Finland, 33,000 €, 1996
  • Finnish Technology Development Agency, 530,000 €, 1998
  • Academy of Finland, 100,000 €, 1998
  • Academy of Finland, 13,000 €, 1999
  • Maj ja Tor Nesslingin Säätiö, 15,000 €, 2000
  • Maj ja Tor Nesslingin Säätiö, 6,500 €, 2001
  • Private foundations, approximately 50,000 €, 1980-1999
  • Ministry of Environment, Finland, 100,000 €, 2004
  • Nordic Nuclear Safety Programme (NKS), 6,000 DKK, 2004
  • Euregio, 25,000€, 2006
  • Nordic Nuclear Safety Programme (NKS), 50,000 DKK, 2006
  • Posiva, 400.000€, 2008-2009
  • Ministry of Employment and Economy, 140.000 €, 2008-2009
  • Academy of Finland, 400.000€, 2009
  • In total approximately 2,500,000 €

 7.                  Editorial board memberships

  • guest editor of Reactive&Functional Polymers 1994-1995

 8.                  Memberships in scientific societies

  • member of the Finnish Chemical Society

 9.                  Other academic and professional activities

  • Coordinator of the project ”Management and disposal of radioactive wastes generated in the cleanup of large areas contaminated in nuclear accidents” of the Nordic Nuclear Research Programme, 1990-1993.
  • Coordinator of the European Union BriteEuramIII Programme project ”Development of advanced ion exchange materials and methods for the removal of toxic metals from metallurgical waste effluents”, 1996-1999.
  • member in the International Atomic Energy Agency’s coordination group responsible for planning and commitment of the comprehensive radiological survey of the Semipalatinsk nuclear test site, 2002-

Further academic and professional activities:

  • Finnish Union of Chemists, Section of Radiochemists, chairman 1983-1985 and 1987-1988, deputy chairman 1985-1986 and 1988-1989
  • member of the organising committee of ION-EX 1995, ICIE’03, IEX 2004, Mendelev/Radiochemistry 2007 conferences
  • plenary lecturer in IOX-EX’93 and IEX’96 conferences (see publications 48 and 51)
  • referee in several international journals, such as Journal of Environmental Radioactivity, Langmuir, Applied Radiation and Isotopes, Separation Science and Technology, Reactive & Functional Polymers, Journal of Solid State Chemistry, Nukleonika, Separation and Purification Technology, Microchimica Acta, Adsorption, Journal of Alloys and Compounds, Journal of Nuclear and Radioanalytical Chemistry,  Journal of Chemical Technology and Biotechnology, 
  • deputy member of the steering group of the Department of Radiochemistry, University of Helsinki, 1992-1994

  10.                 Supervising and refereeing of graduate studies and docentships

Refereeing a docentship:

  • FT Jussi Paatero, docentship in radiochemistry, 2002
  • Ph.D. Daicing Cui, docentship if nuclear chemistry (KTH, Sweden), 2010

Supervising of doctor’s theses:

  • Risto Harjula (1993), Ion Exchange and Hydrolysis Reactions in Zeolites
  • Heikki Leinonen (1999), Removal of Harmful Metals from Metal Plating Waste Waters Using Selective Ion Exchangers
  • Kaisa Vaaramaa (2003), Physico-chemical Forms of Natural Radionuclides in Drilled Well Waters and their Removal by Ion Exchange
  • Risto Koivula (2003), Inorganic Ion Exchangers for Decontamination of Radioactive Wastes Generated by the Nuclear Power Plants
  • Pia Vesterbacka (2005), 238U-Series Radionuclides in Finnish Groundwater-Based Drinking Water and Effective Doses
  • Matti Kaikkonen (2006), A Novel Assay Method for Measuring Added Plasma Caesium and Its Application in the Measurement of Short-Term Kinetics
  • Jussi Jernström (2006), Development of Analytical Techniques in Studies on Dispersion of Actinides in the Environment and Characterization of Environmental Radioactive Particles

Supervising of licentiate thesis:

  • Airi Paajanen (2001), Koboltin erottaminen konsentroidusta matala-aktiivisesta jätevedestä

Acting as an opponent for doctor’s theses:

  • Jussi Paatero (2000), Deposition of Chernobyl-Derived Transuranium Nuclides and Short-Lived Radon-222 Progeny in Finland
  • Ole Christian Lind, Norwegian University of Life Sciences (2006), Characterisation of Radioactive Particles in the Environment Using Advanced Techniques

Refereeing doctor’s theses:

  • V.Narapareddy (1995), Studies on Some New Mixed Inorganic Exchangers for the Treatment of High Level Radioactive Liquid Wastes with Special Reference to Cs-137, Andhra University, India
  • Riitta Pilviö (1998), Methods for the determination of low-level actinide concentrations and their behaviour in the aquatic environment
  • Leena Pajo (2001), UO2 Fuel Pellet Impurities, Pellet Surface Roughness and n(18O)/n(16O) Ratios, Applied to Nuclear Forensic Science
  • Marja Siitari-Kauppi (2001), The Characterization of Low Porosity Media with the 14C-polymethylmethacrylate (14C-PMMA) Method – Application to Rocks in Geological Barriers of Nuclear Waste Storage
  • Teresia Möller (2002), Selective Crystalline Inorganic Materials as Ion Exchangers in the Treatment on Nuclear Waste Solutions
  • Pirkko Hölttä (2002), Radionuclide Migration in Crystalline Rock Fractures – Laboratory Study of Matrix Diffusion

Refereeing licentiate theses:

  • Sinikka Pinnioja (1988), Ydinjätenuklidien pidättyminen kallioperään tutkittuna autoradiografista menetelmää käyttäen
  • Jussi Paatero (1997), Plutonium, Americium ja Curium maaympäristössä Suomessa Tshernobylin ydinvoimalaitosonnettomuuden jälkeen
  • Airi Paajanen (2001), Koboltin erottaminen konsentroidusta matala-aktiivisesta jätevedestä

Latest publications

  1. Aerosol particle size distribution of atmospheric lead-210 in northern Finland

    Paatero, J., Ioannidou, A., Ikonen, J. & Lehto, J. Jun 2017 In : Journal of Environmental Radioactivity. 172, p. 10-14 5 p.

    Publication: Contribution to journalA1 Refereed journal article

  2. Efficient and Selective Recovery of Trace Scandium by Inorganic Titanium Phosphate Ion-Exchangers from Leachates of Waste Bauxite Residue

    Zhang, W., Koivula, R. T., Wiikinkoski, E. W., Xu, J., Hietala, S. H. O., Lehto, J. K. & Harjula, R. O. 20 Feb 2017 In : ACS Sustainable Chemistry & Engineering. 5, 4, p. 3103-3114 12 p.

    Publication: Contribution to journalA1 Refereed journal article

  3. Sorption and speciation of iodine in boreal forest soil

    Soderlund, M., Virkanen, J., Aromaa, H., Gracheva, N. & Lehto, J. Jan 2017 In : Journal of Radioanalytical and Nuclear Chemistry. 311, 1, p. 549-564 16 p.

    Publication: Contribution to journalA1 Refereed journal article

View all (228) »

Latest activities

  1. Assesment of a scientist promotion to assistant professor

    Lehto, J. (Participant)
    2017 → …

    Activity: OtherTypes for other activities - Other

  2. Assesment of a scientist promotion to full professor

    Lehto, J. (Participant)
    2017 → …

    Activity: OtherTypes for other activities - Other

  3. NRC9 Chairman

    Lehto, J. (Participant)
    2016

    Activity: OtherTypes for other activities - Other

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Latest projects

  1. Biosfääri ja mikrobitutkimus

    Lusa, M., Lehto, J., Knuutinen, J. & Kaipainen, M.

    01/01/201631/12/2016

    Project: Research project

  2. CINCH I: Cooperation in education In Nuclear CHemistry

    Koivula, T. & Lehto, J.

    01/02/201031/01/2013

    Project: Research projectEducation

  3. CINCH II: Cooperation in education and training in nuclear chemistry

    Koivula, T. & Lehto, J.

    01/06/2013 → …

    Project: Research projectEducation

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Education

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