Neutron field measurements in a water filled head phantom

Iiro Auterinen, P. Ember, Karoliina Kaita, Tom Seren

Research output: Chapter in Book/Report/Conference proceedingConference abstract in proceedingsScientific


In Boron Neutron Capture Therapy (BNCT) the selective therapeutic dose is delivered by the neutron capture reaction 10B (n, alfa) 6Li reaction. The neutron capture crosssection of 10B is inversely proportional to the neutron velocity, thus thermal neutrons are most likely to cause the desired effect in the tissue. In epithermal beam irradiations the epithermal neutrons slow down in tissue through collisions, mainly with hydrogen, forming a thermal neutron field. The boron capture dose distribution can be calculated if both the boron and thermal neutron distributions are known. Experimental verification of treatment planning and beam characterisation requires that the thermal field intensity and distribution has to be measured in phantoms. Neutron activation dosimetry is the best method for accurate and quantitative determinations but it is not so practical for field mapping. Thermal neutron field mapping can be done using a continuously operated detector. Such a detector can be produced by using the reaction 6Li (n, alfa) 3H (Q=4,78MeV). The shape of the neutron capture cross-section of 6Li resembles that of 10B, so both the boron capture dose and the detector signal depend on the neutron spectrum the same way. The alfa and 3H particles can be detected with a silicon PN-diode. Such a detector was prepared using a PN junction diode with an aluminium layer on the P type surface in close contact with natural lithium (7,42% 6Li) containing epoxy. The measurements were done in a water filled cubic phantom with PMMA walls and a cylindrical extension, 20 cm in diameter and 20 cm long, simulating a human head. The detector was moved with a remote controlled 3D transport mechanism. The measured and calculated thermal flux distributions were in close agreement. Activation detectors i.e. foils of diluted 197Au were used to gain absolute quantitative information about the neutron flux in the phantom. Five detectors were placed into the phantom and the phantom was then exposed to irradiation. The activities induced by the 197Au (n, gamma) 198Au reaction were measured and the experimental reaction rates calculated from the activities and the irradiation history. The results were compared to the calculated reaction rates.
Original languageEnglish
Title of host publicationProceedings of the XXXI Annual Conference of the Finnish Physical Society
Subtitle of host publicationAbstracts
EditorsEero Rauhala, M.E. Sainio
Place of PublicationHelsinki
PublisherUniversity of Helsinki
ISBN (Print)951-45-7639-X
Publication statusPublished - 1997
MoE publication typeNot Eligible
EventXXXI Annual Conference of the Finnish Physical Society - Helsinki, Finland
Duration: 13 Mar 199715 Mar 1997

Publication series

SeriesUniversity of Helsinki: Department of Physics. Report Series in Physics


ConferenceXXXI Annual Conference of the Finnish Physical Society


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