Tae-Ik Ro

EFFECTIVE DOSE MEASUREMENT FOR CONE BEAM COMPUTED TOMOGRAPHY USING GLASS DOSIMETER

During image-guided radiation therapy, the patient is exposed to unwanted radiation from imaging devices built into the medical LINAC. In the present study, the effective dose delivered to a patient from a cone beam computed tomography (CBCT) machine was measured. Absorbed doses in specific organs listed in ICRP Publication 103 were measured with glass dosimeters calibrated with kilovolt (kV) X-rays using a whole body physical phantom for typical radiotherapy sites, including the head and neck, chest, and pelvis. The effective dose per scan for the head and neck, chest, and pelvis were 3.37±0.29, 7.36±0.33, and 4.09±0.29 mSv, respectively. The results highlight the importance of the compensation of treatment dose by managing imaging dose.

Measurement of neutron capture cross-section of indium in the energy region from 0.003 eV to 30 keV

Abstract The neutron capture cross-section of indium (In) has been measured in the energy region from 0.003 eV to 30 keV by the neutron time-of-flight (TOF) method with a 46-MeV electron linear accelerator (linac) of the Research Reactor Institute, Kyoto University. An assembly of Bi 4 Ge 3 O 12 (BGO) scintillators, which was composed of 12 pieces of BGO and placed at a distance of 12.7±0.02 m from the neutron source, was employed as a total energy absorption detector for the prompt capture γ-ray measurement from the sample. In order to determine the neutron flux impinging on the capture sample, a plug of 10 B powder sample and the 10 B(n,α) standard cross-section were used. The data measured by Haddad et al. (Haddad, E., Friesenhahn, S., Lopez, W.M., 1963. Report of Gulf Energy and Environmental Systems, p. 3874) seem to be in good agreement with the present measurement. Popov et al. obtained the poor energy resolution data in the resonance region with a lead slowing-down spectrometer and the consistent data with the present above about 300 eV. The experimental data measured by Kononov et al. (Kononov, U.N., Jurlov, B.D., Poletaev, E.D., Timokhov, V.M., Manturov, G.N., 1977. Report of Obninsk, pp. 22–29) and Gibbons et al. (Gibbons, J.H., Macklin, R.L., Miller, P.D., Neiler, J.H., 1961. Phys. Rev. 122, 182) showed good agreement with the present values in the higher energy region. However, the data measured by Block et al. (Block R.C., Kaushal, N.N., Hockenbury, R.W., 1972. Conference on New Developments in Reactor Physics and Shielding at Kiamesha Lake, Vol. 2, p. 1107) seem to be a little higher than the present measurement above 800 eV. The evaluated data in ENDF/B-VI, JENDL-3.2, and JEF-2.2 have been in general agreement with the present result in the relevant energy region, although the JENDL-3.2 are higher than the measurement, the ENDF/B-VI and the JEF-2.2 from 2 to about 10 keV. Most of the previous experimental and the evaluated thermal neutron cross-sections are generally close to the present value of 199.6±5.6 b at 0.0253 eV.

Neutron Capture Measurements and Resonance Parameters of Gadolinium

Abstract Neutron capture measurements were performed with the time-of-flight method at the Gaerttner LINAC Center at Rensselaer Polytechnic Institute (RPI) using isotopically enriched gadolinium (Gd) samples (155Gd, 156Gd, 157Gd, 158Gd, and 160Gd). The neutron capture measurements were made at the 25-m flight station with a 16-segment sodium iodide multiplicity detector. After the data were collected and reduced to capture yields, resonance parameters were obtained by a combined fitting of the neutron capture data for five enriched Gd isotopes and one natural Gd sample using the multilevel R-matrix Bayesian code SAMMY. A table of resonance parameters and their uncertainties is presented. We observed 2, 169, 96, and 1 new resonances in 154Gd, 155Gd, 157Gd, and 158Gd isotopes, respectively. Resonances in the ENDF/B-VII.0 evaluation that were not observed in the current experiment and could not be traced to a literature reference were removed. This includes 11 resonances from the 156Gd isotope, 1 resonance from 157Gd, 1 resonance from 158Gd, and 6 resonances from the 160Gd isotope. The resulting resonance parameters were used to calculate the capture resonance integrals in the energy region from 0.5 eV to 20 MeV and were compared to calculations obtained when using the resonance parameters from ENDF/B-VII.0 and previous RPI results. The present parameters gave a resonance integral value of 395 ± 2 b, which is ∼0.8% higher and ∼1.7% lower than that obtained with the ENDF/B-VII.0 parameters and with the previous RPI parameters, respectively.

Capture Cross Section Measurements of 161Dy and 162Dy in the Energy Region Between 10 keV and 90 keV

The neutron capture cross sections of 161Dy and 162Dy have been measured in the neutron energy region from 10 to 90 keV using the 3-MV Pelletron accelerator of the Research Laboratory for Nuclear Reactors at the Tokyo Institute of Technology. Pulsed keV neutrons were produced from the 7Li(p, n)7Be reaction by bombarding the lithium target with the 1.5-ns bunched proton beam from the Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a TOF method with a 6Li-glass detector. Capture γ-rays were detected with a large anti-Compton Nal(Tl) spectrometer, employing a TOF method. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained by using the standard capture cross sections of 197Au. The present results were compared with the previous measurements and the evaluated values of ENDF/B-VI.

A Study on Efficiency Error in Distance Inverse Square Law using Cylinder NaI(Tl) Scintillation Detector

Abstract Generally, its known fact that intensity of radioactivity satisfies inverse-square law. However, the law was dissatisfied with practical experiment because of limited shape of scintillation detector. Especially, in the case of near distance between the surface of detector and the radioactive source, the difference grows larger. In the present study, reason of this difference was confirmed by experiment with 2˝×2˝o NaI(Tl) scintillation detector and 60 Co(1.174 MeV, 1.333 MeV)and 137 Cs(0.662 MeV) gamma ray sources. From the experiment, the correction coefficient was obtained with ga mma ray detection efficiency and geometrical volume. In the result of the present study, the eff iciency difference of the detector was corrected with the coefficient. In the present result, we obtai ned that the inverse-square law experiment have to consider the efficiency and geometrical value of the de tector. Key words: scintillation detector, inverse-square law, gamma ray source 요 약 일반적으로 방사선 선원의 강도는 거리의 역자승 법칙을 따른다. 그러나 방사선 선원과 검출기와의 거리가 가까울수록 거리의 역자승 법칙 실험은 이론과 실험의 일치하지 못하는 오류를 가져오게 된다. 본 연구에서는 방사선 선원과 검출기와의 거리에 따른 거리의 역자승 법칙이 실제 실험에서는 정확하게 성립하지 않는 이유를 실험적으로 확인하였다. 그리고 이 문제를 해결하기 위하여 측정된 방사능을 보정하기 위하여 보정계수를 실험적으로 얻었다. 측정에 사용한 검출기는 2˝×2˝o NaI(Tl) 신틸레이션 검출기를 사용하였고, 방사선에너지의 변화에 따른 효과를 확인하기 위하여 감마선 선원

Measurements of keV-Neutron Capture Cross-Sections and Capture γ-rays of 105Pd

The neutron capture cross-sections and capture γ-rays of 105Pd were measured for keV-neutron using the 3-MV Pelletron accelerator of the Research Laboratory for Nuclear Reactors at the Tokyo Institute of Technology. Pulsed neutrons were produced from the 7Li(p,n)7Be reaction, and the incident neutron spectrum on a capture sample was measured by neutron time-of-flight method with a 6Li-glass detector. The capture γ-rays were detected with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to measure the capture γ-ray pulse-height spectra to derive capture yields. The capture cross-sections were obtained by using the standard capture cross-section of 197Au. And we obtained the γ-ray energy spectrum of capture γ-ray by the pulse-height unfolding method. The present results were compared with the previous measurements and the evaluated data of ENDF/B-VII, JEFF-3.1, and JENDL-3.3.

Measurements of Neutron Capture Cross Sections for Gd Isotopes in the Energy Region from 10 keV to 90 keV

The neutron capture cross sections of Gd isotopes (155Gd, 156Gd, 157Gd, and 158Gd) have been measured in the neutron energy range from 10 to 90 keV using the 3‐MV Pelletron accelerator of the Research Laboratory for Nuclear Reactors at the Tokyo Institute of Technology. Pulsed keV neutrons were produced from the 7Li(p,n)7Be reaction by bombarding the lithium target with the 1.5‐ns bunched proton beam from the Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a TOF method with a 6Li‐glass detector. Capture γ‐rays were detected with a large anti‐Compton NaI(Tl) spectrometer, employing a TOF method. A pulse‐height weighting technique was applied to observed capture γ‐ray pulse‐height spectra to derive capture yields. The capture cross sections were obtained by using the standard capture cross sections of 197Au. The present results were compared with the previous measurements and the evaluated values of ENDF/B‐VI.

Measurement of Total Cross Sections at Pohang Neutron Facility

The Pohang Neutron Facility, which consists of an electron linear accelerator, a water‐cooled Ta target with a water moderator, and a time‐of‐flight path with an 11 m length has been operated since 2000. We report the status activities on the neutron total cross‐section measurements in the neutron energy region from 0.01 eV to 100 eV by the neutron time‐of‐flight method at Pohang Neutron Facility. A 6Li‐ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.5 cm has been used as a neutron detector. The background level has been determined by using notch‐filters of Co, In, and Cd sheets. In order to reduce the gamma rays from Bremsstrahlung and that from neutron capture, we have employed a neutron‐gamma separation system based on their different pulse shape. The present measurements for Ag, Hf, and Ta samples are compared with the previous ones and the evaluated data in ENDF/B‐VI. The resonance parameters for Ag and Hf samples have been extracted from the transmission data by using the SAMMY ...