Studies of dose distribution to Lung and Stomach and Estimation of Second Cancer Risk due to Outfield Dose in Radiotherapy with 60Co Teletherapy Beam

A critical component of the radiation regimen for treating cancer patients is the precise dose delivery to the treatment organ while minimizing the dose to the healthy tissue. This study aims to evaluate in-field organ dose and dose distribution outside the target organs to estimate the excess lifetime risk of second cancer. The study was carried out with a male Alderson Rando Phantom. 20 sets of thermoluminescence dosimeters (MTS-100) were used in this study. The in-field organs absorbed dose was measured by inserting TLDs at different geometrical depths of the left lung, right lung, and stomach, and for peripheral organs skin dose TLDs were placed at the surface of the corresponding organs. Target organs were irradiated at 100 cGy and 200 cGy by a 60Co teletherapy unit, and irradiated TLDs were read out by a RE-2000 TLD reader. For precise dose delivery to the cancerous organs by 60Co teletherapy, the depth dose correction factor for lung cancer treatment is 0.8667 ± 0.01, and for the stomach is 0.7856 ± 0.017. In the case of the treatment for the lung and stomach, the closest organs received significant doses compared to the other distant organs. Thus, the risk of second cancer due to the peripheral dose is obtained. The stomach is at the highest risk when the lung is the target and the liver is at the highest risk when the stomach is the targeted organ

Experimental neutron capture data of 58Ni from the CERN n_TOF facility

The neutron capture cross section of 58Ni was measured at the neutron time of flight facility n_TOF at CERN, from 27 meV to 400 keV neutron energy. Special care has been taken to identify all the possible sources of background, with the so-called neutron background obtained for the first time using high-precision GEANT4 simulations. The energy range up to 122 keV was treated as the resolved resonance region, where 51 resonances were identified and analyzed by a multilevel R-matrix code SAMMY. Above 122 keV the code SESH was used in analyzing the unresolved resonance region of the capture yield. Maxwellian averaged cross sections were calculated in the temperature range of kT = 5 – 100 keV, and their astrophysical implications were investigated

GEANT4 simulation of the neutron background of the C6D6 set-up for capture studies at n_TOF

The neutron sensitivity of the C6D6 detector setup used at n_TOF facility for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a natC sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured natC yield has been discovered, which prevents the use of natC data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross-section measurements

Fission fragment angular distribution measurements of 235U and 238U at CERN n_TOF facility

Neutron-induced fission cross sections of 238U and 235U are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection effciency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new 235U(n,f) and 238U(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data

High accuracy 234U(n,f) cross section in the resonance energy region

New results are presented of the 234U neutron-induced fission cross section, obtained with high accuracy in the resonance region by means of two methods using the 235U(n,f) as reference. The recent evaluation of the 235U(n,f) obtained with SAMMY by L. C. Leal et al. (these Proceedings), based on previous n_TOF data [1], has been used to calculate the 234U(n,f) cross section through the 234U/235U ratio, being here compared with the results obtained by using the n_TOF neutron flux