Applications of positron annihilation spectroscopy in nuclear materials research

Janne Heikinheimo

Positroniannihilaatiospektroskopian sovelluksia ydinmateriaalitutkimuksessa

Janne Heikinheimo

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Tässä työssä positroniannihilaatiospektroskopiaa käytettiin periodisten rakenteiden pistevirheiden tutkimiseen merkittävissä ydinteknillisissä materiaaleissa. Tämän lisäksi ilmaisinten vaikutusta tuloksiin tutkittiin sekä elinaika- että Doppler-levenemäspektroskopiassa. Ilmaisimilla on merkittävä vaikutus elinaika- ja Doppler-levenemäspektroskopioiden suorituskykyyn ja saatavien tulosten laatuun. Elinaikaspektroskopia on hyvin herkkä mitattavien näytteiden ylimääräiselle säteilylle, mikä rajoittaa sen käyttöä ydinteknillisten materiaalien tutkimuksessa. Ainoa tapa lisätä mittauslaitteiston säteilytoleranssia on ottaa käyttöön kolmas koinsidenssi-ilmaisin. Doppler-levenemälaitteistossa säteilyilmaisimen energiaresoluutio vaikuttaa suoraan mittaustuloksiin. Kahden ilmaisimen elinaikaspektroskopian herkkyyttä väärille koinsidenssitapahtumille tutkittiin lisäämällä koboltti-60 -lähde tutkittavien piinäytteiden viereen. Säteilytoleranssin kasvua kolmen ilmaisimen elinaikaspektroskopiassa arvioitiin yksinkertaisilla teoreettisilla malleilla. Doppler-levenemäspektroskopiassa tutkittiin energiaresoluutiota liittämällä natrium-22 -positroni-lähde suoraan tutkittaviin näytteisiin, jolloin pystyttiin samanaikaisesti mittaamaan sekä Doppler-levenämäspektriä että yksienergistä fotoabsorptiospektriä. Tässä työssä tutkittiin lähde-ilmaisingeometrian vaikutuksia tuloksiin ja keskustellaan muuttuvien tulosten syistä perustuen systemaattisiin kokeisiin ja Monte Carlo -simulaatioihin. Mikroskooppisilla virheillä on merkittävä vaikutus ydinmateriaalien ominaisuuksiin, kuten korroosioon ja säteilykestävyyteen. Zircaloy-4 on yksi eniten käytetyistä polttoaineen suojakuoriseoksista ydinvoimalaitoksissa, mutta sen hapettuminen reaktoriolosuhteissa on monimutkainen prosessi, johon kuuluu hapettumisnopeuden periodisuus. Fuusiovoimalaitoksissa plasmaa lähellä olevat materiaalit joutuvat äärimmäisen ankariin olosuhteisiin, joissa korostuvat korkea lämpötila ja suuret hiukkassäteilyannokset. Volframia pidetään lupaavana materiaalikandidaattina tähän tarkoitukseen. Zirkoniumoksidin perustavanlaatuisia ominaisuuksia tarkasteltiin perustuen mikroskooppisten hilavirheiden muuttumiseen tutkittavissa Zircaloy-4 -näytteissä, joita oli hapetettu painevesireaktoria vastaavissa olosuhteissa. Doppler-levenemäspektroskopiaa ja teoreettista mallinnusta sovellettiin hapettumiskerrosten hilavirheiden tutkimiseen. Positronien elinaikaspektrokopiaa käytettiin toivutettujen ja protonisäteilytykselle altistettujen volframinäytteiden monovakanssien tutkimiseen. Välisija-atomien ja monovakanssien migraatioenergiarajat pystyttiin havaitsemaan suoraan elinaikaspektrometrilla, joka oli yhdistetty kylmäsäteilytyslaitteistoon.

Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Tuomisto, Filip, Valvoja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7721-5
Sähköinen ISBN	978-952-60-7722-2
Tila	Julkaistu - 2017
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

positroniannihilaatiospektroskopia
germaniumilmaisin
volframi

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-7722-2Lisenssi: Määrittelemätön

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Siteeraa tätä

Heikinheimo, J. (2017). Applications of positron annihilation spectroscopy in nuclear materials research. Aalto University.

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title = "Applications of positron annihilation spectroscopy in nuclear materials research",

abstract = "In this work, positron annihilation spectroscopy was used in studying lattice point defects in some of the technologically relevant nuclear materials. In addition, the behaviour of the detectors were studied to deepen understanding of their influential properties in lifetime and Doppler broadening spectroscopy. Detectors play a significant role in the performance of a measurement setup and in the quality of the obtained results, both in lifetime and Doppler broadening spectroscopy. Lifetime spectroscopy is very sensitive to the excess activity of studied samples, which limits its use in the study of nuclear materials. The only way of improving the tolerance of lifetime spectrometry is to add an extra coincidence detector to the setup. In Doppler broadening spectroscopy a detector energy resolution function directly affects the obtained results. The sensitivity of two-detector lifetime spectroscopy to false coincidence events was studied by adding a cobalt-60 source next to the studied Si reference samples. The improvement of the radiation tolerance in a three-detector setup was estimated based on simple theoretical models. To study energy resolution function in Doppler broadening spectroscopy, a sodium-22 positron source was directly attached to the studied samples enabling simultaneous recordings of Doppler broadening and discrete photoabsorption spectrum. The impact of the source-detector geometry on the obtained results was studied and the reason behind the changing results is discussed based on systematic experiments supported by Monte Carlo simulations. Microstructural defects play an important role in the properties of nuclear materials, such as corrosion and irradiation resistivity. Zircaloy-4 is currently the most used cladding alloy in nuclear power plants, but its oxidation in reactor conditions is a complex process including cyclic oxidation rates. In fusion power plants, materials close to the plasma are exposed to a very hostile environment including high temperatures and high particle irradiation fluxes. Tungsten is considered a promising candidate material for this purpose. The fundamental oxidation properties of zirconium are discussed based on microstructural defect evolution in the studied Zircaloy-4 samples that were oxidized in pressurized water reactor -type conditions. Doppler broadening spectroscopy supported by theoretical modelling was harnessed to characterize lattice point defect behaviour in the sample oxide layers. Positron lifetime spectroscopy was applied in the study of mono-vacancies in pre-annealed proton-irradiated tungsten samples. Migration barriers for interstitial atoms and mono-vacancies were directly detected with a positron lifetime spectrometer connected to the cold temperature irradiation facility.",

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N2 - In this work, positron annihilation spectroscopy was used in studying lattice point defects in some of the technologically relevant nuclear materials. In addition, the behaviour of the detectors were studied to deepen understanding of their influential properties in lifetime and Doppler broadening spectroscopy. Detectors play a significant role in the performance of a measurement setup and in the quality of the obtained results, both in lifetime and Doppler broadening spectroscopy. Lifetime spectroscopy is very sensitive to the excess activity of studied samples, which limits its use in the study of nuclear materials. The only way of improving the tolerance of lifetime spectrometry is to add an extra coincidence detector to the setup. In Doppler broadening spectroscopy a detector energy resolution function directly affects the obtained results. The sensitivity of two-detector lifetime spectroscopy to false coincidence events was studied by adding a cobalt-60 source next to the studied Si reference samples. The improvement of the radiation tolerance in a three-detector setup was estimated based on simple theoretical models. To study energy resolution function in Doppler broadening spectroscopy, a sodium-22 positron source was directly attached to the studied samples enabling simultaneous recordings of Doppler broadening and discrete photoabsorption spectrum. The impact of the source-detector geometry on the obtained results was studied and the reason behind the changing results is discussed based on systematic experiments supported by Monte Carlo simulations. Microstructural defects play an important role in the properties of nuclear materials, such as corrosion and irradiation resistivity. Zircaloy-4 is currently the most used cladding alloy in nuclear power plants, but its oxidation in reactor conditions is a complex process including cyclic oxidation rates. In fusion power plants, materials close to the plasma are exposed to a very hostile environment including high temperatures and high particle irradiation fluxes. Tungsten is considered a promising candidate material for this purpose. The fundamental oxidation properties of zirconium are discussed based on microstructural defect evolution in the studied Zircaloy-4 samples that were oxidized in pressurized water reactor -type conditions. Doppler broadening spectroscopy supported by theoretical modelling was harnessed to characterize lattice point defect behaviour in the sample oxide layers. Positron lifetime spectroscopy was applied in the study of mono-vacancies in pre-annealed proton-irradiated tungsten samples. Migration barriers for interstitial atoms and mono-vacancies were directly detected with a positron lifetime spectrometer connected to the cold temperature irradiation facility.

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