176 research outputs found
Adaptive tree multigrids and simplified spherical harmonics approximation in deterministic neutral and charged particle transport
A new deterministic three-dimensional neutral and charged particle transport code, MultiTrans, has been developed. In the novel approach, the adaptive tree multigrid technique is used in conjunction with simplified spherical harmonics approximation of the Boltzmann transport equation.
The development of the new radiation transport code started in the framework of the Finnish boron neutron capture therapy (BNCT) project. Since the application of the MultiTrans code to BNCT dose planning problems, the testing and development of the MultiTrans code has continued in conventional radiotherapy and reactor physics applications.
In this thesis, an overview of different numerical radiation transport methods is first given. Special features of the simplified spherical harmonics method and the adaptive tree multigrid technique are then reviewed. The usefulness of the new MultiTrans code has been indicated by verifying and validating the code performance for different types of neutral and charged particle transport problems, reported in separate publications.VÀitöstutkimuksen tuloksena on kehitetty uusi tietokoneohjelma varauksettomien ja varauksellisten hiukkasten kuten neutronien, fotonien ja elektronien etenemisen mallinnukseen. MultiTrans-ohjelma mahdollistaa sÀteilyn etenemisen mallinnuksen mielivaltaisessa 3D-geometriassa. Laskentageometria generoidaan suoraan CAD-mallista, jolloin voidaan kÀyttÀÀ moderneja suunnittelutyökaluja. Laskentaverkko on puumaisesti itsetarkentuva materiaalien rajapinnoilla, joissa hila muodostuu automaattisesti hienojakoisimmaksi. NÀin monimutkainenkin geometria voidaan kuvata yksityiskohtaisesti merkittÀvÀsti pienemmÀllÀ hilapisteiden mÀÀrÀllÀ verrattuna tasajakoiseen hilaan. Laskentaverkon puumaisuudesta seuraa ettÀ ongelmalle löytyy aina myös karkeammat hilaesitykset. TÀllöin kuljetusyhtÀlön iteratiivisessa ratkaisussa voidaan kÀyttÀÀ ns. moniverkkotekniikkaa jossa ongelma ratkaistaan ensin hyvin karkeassa esityksessÀ ja tÀtÀ ratkaisua kÀytetÀÀn alkuarvauksena yhÀ hienojakoisemmissa hiloissa. NÀin nopeutetaan iteratiivisen ratkaisun löytymistÀ huomattavasti. Myös laskentaverkon puumaisuus ja sen myötÀ hilapisteiden vÀhÀisempi mÀÀrÀ nopeuttaa iteratiivista ratkaisua. KyseessÀ on tiettÀvÀstÀ ensimmÀinen puumoniverkkotekniikan sovellutus sÀteilyn etenemisen mallinnukseen.
MultiTransia on testattu erilaisten sÀdehoitojen (esimerkiksi VTT:n Otaniemen ydintutkimusreaktorilla annettavan boorineutronikaappaushoidon) sekÀ reaktorifysiikan laskentaongelmiin. Ongelmaksi on jossain mÀÀrin osoittautunut sÀteilyn kulkeutumisyhtÀlölle kÀytetty yksinkertaistettu palloharmoninen kehitelmÀ, jonka tarkkuus ei kaikissa tapauksissa vastaa asetettuja vaatimuksia
MAGIC polymer gel for dosimetric verification in boron neutron capture therapy
"Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry.""Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry.""Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry."Peer reviewe
Neutron transport code development for P(N) theory in co-operation with the Finnish BNCT project
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