@misc{oai:repo.qst.go.jp:00070991,
 author = {Hirano, Yoshiyuki and et.al and 平野 祥之},
 month = {Nov},
 note = {The OpenPET geometry enables to visualize a physically opened space between two detector rings. One of the targets is in-beam positron emission tomography (PET). In particle therapy, secondary particles created by primary beam potentially influence not only a patient dose but also a PET scan. In this work, we investigated effects of secondary particles on the small OpenPET which is prototype detector of OpenPET by use of Monte Carlo code, Geant4. We reproduced a small OpenPET experiment in which a PMMA cylindrical phantom was irradiated by 11C beam. Energy spectra of frequent entering particles were calculated. Many singles irrelative to PET scans were observed, however, almost of these signals would be discriminated by energy selection. Gamma-ray, proton and neutron were main particles entered into the scintillator.  We also calculated activation in scintillators, and 1.3 kBq was expected 1 hour later of 10 min irradiation. The activity however reduced to 70 Bq at 1 day later. Finally, we estimated background which is indistinctive by the energy selection and coincidence triggering. The ratios of background to total coincidence were evaluated during and after irradiation. 96 % and 2 % of the total coincidence were background for during and after irradiation, respectively., 2012IEEE NSS&MIC},
 title = {Monte Carlo estimation of background true coincidence events in the OpenPET detector},
 year = {2012}
}