• Journal of Radiation Protection and Research
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• 제48권3호
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• pp.124-130
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• 2023

Background: When bipolar junction transistors (BJTs) are used as switches, their switching characteristics can be deteriorated because the recombination time of the minority carriers is long during turn-off transient. When BJTs operate as low frequency switches, the power dissipation in the on-state is large. However, when BJTs operate as high frequency switches, the power dissipation during switching transients increases rapidly. Materials and Methods: When silicon (Si) BJTs are irradiated by fast neutrons, defects occur in the Si bulk, shortening the lifetime of the minority carriers. Fast neutron irradiation mainly creates displacement damage in the Si bulk rather than a total ionization dose effect. Defects caused by fast neutron irradiation shorten the lifetime of minority carriers of BJTs. Furthermore, these defects change the switching characteristics of BJTs. Results and Discussion: In this study, experimental results on the switching characteristics of a pnp Si BJT before and after fast neutron irradiation are presented. The results show that the switching characteristics are improved by fast neutron irradiation, but power dissipation in the on-state is large when the fast neutrons are irradiated excessively. Conclusion: The switching characteristics of a pnp Si BJT were improved by fast neutron irradiation.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.501-506
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• 2022

Long turn-off time limits high frequency operation of Bipolar Junction Transistors (BJTs). Turn-off time decreases with increases in the recombination rate of minority carriers at switching transients. Fast neutron irradiation on a Si BJT incurs lattice damages owing to the displacement of silicon atoms. The lattice damages increase the recombination rate of injected holes with electrons, and decrease the hole lifetime in the base region of pnp Si BJT. Fast neutrons generated from a beryllium target with 30 MeV protons by an MC-50 cyclotron were irradiated onto pnp Si BJTs in experiment. The experimental results show that the turn-off time, including the storage time and fall time, decreases with increases in fast neutron fluence. Additionally, it is confirmed that the base current increases, and the collector current and base-to-collector current amplification ratio decrease due to fast neutron irradiation.

• 한국재료학회지
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• 제30권3호
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• pp.117-122
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• 2020

The effects of fast neutron irradiation on the electrical and optical properties of Li (3 at%) doped ZnSnO (ZTO) thin films fabricated using a sol-gel process are investigated. From the results of Li-ZTO TFT characteristics according to change of neutron irradiation time, the saturation mobility is found to increase and threshold voltage values shift to a negative direction from 1,000 s neutron irradiation time. X-ray photoelectron spectroscopy analysis of the O 1s core level shows that the relative area of oxygen vacancies is almost unchanged with different irradiation times. From the results of band alignment, it is confirmed that, due to the increase of electron carrier concentration, the Fermi level (E_F) of the sample irradiated for 1,000 s is located at the position closest to the conduction band minimum. The increase in electron concentration is considered by looking at the shallow band edge state under the conduction band edge formed by fast neutron irradiation of more than 1,000 s.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.209-215
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• 2017

Fast neutron irradiation was used to improve the switching speed of a 600-V nonpunch-through insulated gate bipolar transistor. Fast neutron irradiation was carried out at 30-MeV energy in doses of $1{\times}10^8n/cm^2$, $1{\times}10^9n/cm^2$, $1{\times}10^{10}n/cm^2$, and $1{\times}10^{11}n/cm^2$. Electrical characteristics such as current-voltage, forward on-state voltage drop, and switching speed of the device were analyzed and compared with those prior to irradiation. The on-state voltage drop of the initial devices prior to irradiation was 2.08 V, which increased to 2.10 V, 2.20 V, 2.3 V, and 2.4 V, respectively, depending on the irradiation dose. This effect arises because of the lattice defects generated by the fast neutrons. In particular, the turnoff delay time was reduced to 92 nanoseconds, 45% of that prior to irradiation, which means there is a substantial improvement in the switching speed of the device.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3334-3341
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• 2023

We studied the irradiation effects of fast neutron generated by a 30 MeV cyclotron on the electrical and switching characteristics of NPT-IGBT devices. Fast neutron fluence ranges from 2.7 × 10⁹ to 1.82 × 10¹³ n/cm². Electrical characteristics of the IGBT device such as I-V, forward voltage drop and additionally switching characteristics of turn-on and -off were measured. As the neutron fluence increased, the device's threshold voltage decreased, the forward voltage drop increased significantly, and the turn-on and turn-off time became faster. In particular, the delay time of turn-on switching was improved by about 35% to a maximum of about 39.68 ns, and that of turn-off switching was also reduced by about 40%-84.89 ns, showing a faster switching.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.201-208
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• 2023

The dependence of the electrical characteristics on the fast neutron fluence of an epitaxial 4H-SiC Schottky barrier diode (SBD) was investigated. The 30 MeV cyclotron was used for fast neutron irradiation. The neutron fluences evaluated through Monte Carlo simulation were in the 2.7 × 10¹¹ to 1.45 × 10¹³ neutrons/cm² range. Current-voltage and capacitance-voltage measurements were performed to characterize the samples by extracting the parameters of the irradiated SBDs. Neutron-induced defects in the epitaxial layer were identified and quantified using a deep-level transient spectroscopy measurement system developed at the Korea Atomic Energy Research Institute. As the neutron fluence increased from 2.7 × 10¹¹ to 1.45 × 10¹³ neutrons/cm², the concentration of the Z_1/2 defects increased by approximately 20 times. The maximum defect concentration was estimated as 1.5 × 10¹⁴ cm^-3 at a neutron fluence of 1.45 × 10¹³ neutrons/cm².

• 한국초전도ㆍ저온공학회논문지
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• 제16권1호
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• pp.9-13
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• 2014

Effects of neutron irradiation on the superconducting properties of the undoped $MgB_2$ and the carbon(C)-doped $MgB_2$ bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared $MgB_2$ samples were neutron-irradiated at the neutron fluence of $10^{16}-10^{18}n/cm^2$ in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature ($T_c$) and transition width were estimated from the M-T curves and critical current density ($J_c$) was estimated from the M-H curves using a Bean's critical model. The $T_cs$ of the undoped $MgB_2$ and C-doped $MgB_2$ before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The $T_cs$ decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of $7.16{\times}10^{17}n/cm^2$, and decreased to 22.6 K and 24.0 K, respectively, at $3.13{\times}10^{18}n/cm^2$. The $J_c$ cross-over was observed at the high magnetic field of 5.2 T for the undoped $MgB_2$ irradiated at $7.16{\times}10^{17}n/cm^2$. The $T_c$ and $J_c$ variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1472-1482
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• 2017

Zirconium alloy cladding tube specimens were irradiated at $380^{\circ}C$ up to a fast neutron fluence of $7.5{\times}10^{24}n/m^2$ in a research reactor to investigate the effect of neutron irradiation on hydride reorientation and mechanical property degradation. Cool-down tests from $400^{\circ}C$ to $200^{\circ}C$ under 150 MPa tensile hoop stress were performed. These tests indicate that the irradiated specimens generated a smaller radial hydride fraction than did the unirradiated specimens and that higher hydrogen content generated a smaller radial hydride fraction. The irradiated specimens of 500 ppm-H showed smaller ultimate tensile strength and plastic strain than those characteristics of the 250 ppm-H specimens. This mechanical property degradation caused by neutron irradiation can be explained by tensile hoop stress-induced microcrack formation on the hydrides in the irradiation-damaged matrix and subsequent microcrack propagation along the hydrides and/or through the matrix.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2419-2431
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• 2023

Experiments related to Boron Neutron Capture Therapy (BNCT) accomplished at the Institute of Nuclear Techniques (INT), Budapest University of Technology and Economics (TUB) are presented. Relevant investigations are required before designing BNCT for vivo applications. Samples of relevant boron compounds (H₃BO₃, BDTPA) usually employed in BNCT were investigated with neutron beam. Channel #5 in the research reactor (100 kW) of INT-TUB provides the neutron beam. Boron samples are mounted on a carrier for neutron irradiation. The particle attenuation of several carrier materials was investigated, and the one with the lowest attenuation was selected. The effects of boron compound type, mass, and compound phase state were also investigated. To detect the emitted charged particles, a traditional ZnS(Ag) detector was employed. The neutron beam's interaction with the detector-detecting layer is investigated. Graphite (as a moderator) was employed to change the neutron beam's characteristics. The fast neutron beam was also thermalized by placing a portable fast neutron source in a paraffin container and irradiating the H₃BO₃. The obtained results suggest that the direct measurement approach appears to be insufficiently sensitive for determining the radiation dose committed by the Alpha particles from the ¹⁰B (n,α) reaction. As a result, a new approach must be used.

• Radiation Oncology Journal
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• 제17권1호
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• pp.65-69
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• 1999

목적 : 온열치료는 엑스선 또는 감마선 등 LET 가 낮은 방사선에 대한 세포 및 조직에서의 반응을 증강시킬 수 있음이 이미 잘 알려져 있다. 그러나 다른 종류의 방사선과 온열치료의 상호작용에 대해서는 연구가 미미한 실정이다. 따라서 저자들은 속중성자와 온열치료의 순서 및 시간간격에 따른 병용효과를 파악하고자 이 연구를 시행하였다. 재료 및 방법 : 사람 위암세포주인 MKN-45 세포에서 1.5Gy 의 중성자조사 전후 각 6, 4, 2, 0(5분) 시간 간격으로 41$^{\circ}C$ 또는 43$^{\circ}C$ 에서 30분간의 온열치료 시행하여 세포생존율을 측정하였다. 결과 : MKN-45 의 D$_{0}$ 와 n 은 각각 0.8Gy 와 2.5 이었고, 1.5Gy 에서의 생존분획은 0.36($\pm0.34$) 이었다. 시간 간격에 따른 상호작용력은 대부분 1 과 2 사이였으나, 41$^{\circ}C$ 의 온열치료후 4 또는 6시간에 시행한 중성자조사에서는 상호작용력이 각각 3.0 과 2.7 이었다. 결론 : 속중성자와 온열치료의 병용효과는 주로 상가적(additive) 이나, 약온열치료(41$^{\circ}C$, 30분) 가 4 또는 6시간 전에 시행된 경우 후속 중성자조사에 대한 내성이 유발될 수있다.