Radiation-induced synthesis of ZrO2 nanoparticles by thermal decomposition of zirconium acetylacetonate

ZrO₂ nanoparticles were obtained by the thermal decomposition of un-irradiated and γ-irradiated zirconium acetylacetonate (ZrAcAc) precursors. Several influencing factors, including absorbed dose, calcination times, calcination temperatures and addition of surfactants, were thoroughly investigated. The results showed that the best conditions for the preparation of ZrO₂ nanoparticles were achieved by calcinations of ZrAcAc for 5 h at 600°C in the presence of 1 mL of benzyl alcohol as the surfactant. Different phases, morphologies and sizes for the as-prepared ZrO₂ nanoparticles were obtained by varying the dose of γ-ray absorbed. ZrO₂ nanoparticles obtained by thermal decomposition of un-irradiated ZrAcAc have mixture of monoclinic and tetragonal crystal systems, the particles are monodispersed with an irregular shape. In the case of γ-irradiated ZrAcAc with 10, 10² and 10³ KGy, ZrO₂ nanoparticles have only a tetragonal system with different morphologies depending on the γ-ray dose absorbed. Thermal stability of ZrO₂ nanoparticles was studied using thermogravimetric/differential thermal analyzer techniques. Thermodynamic and kinetic parameters were evaluated and discussed.     

In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co⁶⁰ gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co⁶⁰ neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy^?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.     

Microdosimetry for the characterization of the THOR epithermal neutron beam

The epithermal neutron beam of the Tsing Hua Open-pool Reactor (THOR) was constructed for the study of boron neutron capture therapy (BNCT). The THOR epithermal neutron beam was mainly composed of thermal neutrons, fast neutrons, and photons. For fast neutrons and photons, the absorbed dose and the relative biological effectiveness (RBE) were used to characterize radiation dose and radiation quality. The short-ranged alpha particles and lithium ions produced from ¹⁰B(n,α)⁷Li reactions in the BNCT required cellular- and micro-dosimetry characterizations. Due to the non-uniform microdistribution of boron in cells, these characterizations should depend on the source–target geometry. In this case, the geometry-dependent specific cellular dose and lineal energy could be used to describe radiation dose and radiation quality. In the present work, cellular- and micro-dosimetry were studied for the THOR epithermal neutron beam. The specific cellular dose and lineal energy were calculated for thermal neutron-induced α-particles and ⁷Li-ions with different source–target geometry and various cell sizes. Applying the linear energy dependent-biological weighting function, the geometry-dependent RBE of thermal neutron-induced heavy particles was determined. Finally, the effective RBE of the THOR epithermal neutron beam was estimated for tumors and normal tissues of specified ¹⁰B concentrations. This effective RBE should be multiplied by the total absorbed dose to determine the corresponding biological dose required in the treatment planning.     

A capture-gated fast neutron detection method

To address the problem of the shortage of neutron detectors used in radiation portal monitors(RPMs),caused by the ~3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture γ-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register γ-rays. This design removes the volume competing relationship in traditional ~3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ± 1.22% has been achieved with a 40.4 cm × 40.4cm × 20 cm overall detector volume. This detector can measure both neutrons and γ-rays simultaneously. A small detector(20.2 cm × 20.2 cm × 20 cm) demonstrated a 3.3 % false alarm rate for a ~(252)Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low(0.06%) false alarm rate for a 3.21 × 10~5 Bq ~(137)Cs source. This detector offers a potential single-detector replacement for both neutron and the γ-ray detectors in RPM systems.     

Assessment of fast and thermal neutron ambient dose equivalents around the KFUPM neutron source storage area using nuclear track detectors

A set of five ²⁴¹Am–Be neutron sources are utilized in research and teaching at King Fahd University of Petroleum and Minerals (KFUPM). Three of these sources have an activity of 16 Ci each and the other two are of 5 Ci each. A well-shielded storage area was designed for these sources. The aim of the study is to check the effectiveness of shielding of the KFUPM neutron source storage area. Poly allyl diglycol carbonate (PADC) Nuclear track detectors (NTDs) based fast and thermal neutron area passive dosimeters have been utilized side by side for 33 days to assess accumulated low ambient dose equivalents of fast and thermal neutrons at 30 different locations around the source storage area and adjacent rooms. Fast neutron measurements have been carried out using bare NTDs, which register fast neutrons through recoils of protons, in the detector material. NTDs were mounted with lithium tetra borate (Li₂B₄O₇) converters on their surfaces for thermal neutron detection via and nuclear reactions. The calibration factors of NTD both for fast and thermal neutron area passive dosimeters were determined using thermoluminescent dosimeters (TLD) with and without a polyethylene moderator. The calibration factors for fast and thermal neutron area passive dosimeters were found to be 1.33 proton tracks and 31.5 alpha tracks , respectively. The results show variations of accumulated dose with the locations around the storage area. The fast neutron dose equivalents rates varied from as low as up to whereas those for thermal neutron ranged from as low as up to . The study indicates that the area passive neutron dosimeter was able to detect dose rates as low as 7 and from accumulated dose for thermal and fast neutrons, respectively, which were not possible to detect with the available active neutron dosimeters.     

Anomalies of neutron and γ-ray emission in light charged particle accompanied fission of 252Cf

Correlations between the neutron and γ-ray emission and the kinetic energy of light charged particles (LCPs), such as protons, deuterons, tritons and alphas, from the fission of ²⁵²Cf were studied in a four parameter experiment. A ⊘ 16 cm × 5 cm liquid scintillator with n-γ discrimination and a ⊘ 10 cm × 10 cm NaI(Tl) crystal were employed to detect the neutrons and the γ rays, respectively, while a thin CsI(Tl) crystal, which had the ability to separate the LCPs, was used to determine the LCP energy. The experimental results show that for the α particle accompanied fission, the average total number of neutrons emitted per fission increases in the case of varying the alpha particle energy E_α from 7 to 11 MeV and then falls off linearly in a first approximation with increasing E_α, and the average total energy and the average total number of γ-rays per fission as well as the average γ-ray energy as functions of E_α show similar correlation features. For the hydrogen-ion accompanied fission, the correlations of the neutron and γ-ray emission with hydrogen ion (t, d and p) energy are very similar to those for the alpha-particle accompanied fission. The correlations of the neutron and γ-ray emission in the low LCP energy region, in contrast to that observed in the high LCP energy range, are called anomalies. On the basis of the results obtained by the three-point charge model and the liquid drop model calculation with shell and pairing correction, the anomalous behavior of the neutron and γ-ray emission is explained tentatively.     

Characterisation of 32P beta source for external radiation protection

Custom-made design of ³²P patch sources are used in brachytherapy applications. Use of this source requires external radiation protection. This implies measurement of absorbed dose rate to tissue at a depth of 0.07 mm. Towards this goal, 2.75 mCi ³²P patch source was locally developed. Characterization of this source has been carried out by measuring source parameters such as uniformity in the activity distribution and beam uniformity. The characterization also includes output measurements in terms of absorbed dose rate to air using an extrapolation chamber at 11, 20 and 30 cm from the source. Various correction factors which are dependent on the cavity length as well as independent of the cavity length were also determined in this study. The backscatter correction and Bragg–Grapy stopping power ratio were calculated using the Monte Carlo techniques. Using these correction factors and the measured absorbed dose rate to air, absorbed dose rate to tissue at a depth of 0.07 mm was determined. The study also includes measurements of H_p(0.07) and H_p(10) at different source-to-detector distances using an electronic pocket dosimeter.     

Kinetics of isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate

In this study, isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate Zr(acac)₄ using 10³ kGy absorbed γ-ray dose was carried out in static air. The isothermal operating temperatures were selected to be 150, 170, 190 and 210°C. The kinetics of the decomposition were followed using both model-fitting and model-free approaches. The results of the model-fitting approach with regard to the investigated data showed that the decomposition behaviour was best described by a first-order (F1) reaction model. The analysis of the data using the model-free approach signified the dependency of activation energy E _a on the extent of conversion (α). Pre-γ-irradiation of zirconium acetylacetonate Zr(acac)₄ with 10³ kGy absorbed γ-ray dose had no significant effect on the thermal decomposition behaviour of Zr(acac)₄. The thermodynamic and kinetic parameters of the decomposition process were calculated and evaluated.     

The 51V(n, γ)52V reaction studied with polarized neutrons and polarized vanadium nuclei

Circular polarization of γ- radiation following capture of polarized thermal neutrons by unoriented nuclei and the angular distribution of such radiation, using polarized neutrons and polarized nuclei, made it possible to assign spins to 13 levels of ⁵²V. In addition the admixtures of spin-3 and spin-4 reaction channels could be derived for 20 primary γ-ray transitions. With this information interference phenomena in the ⁵¹V(n, γ) reaction were studied. The low-lying levels of ⁵²V are compared with shell-model calculations. The capture mechanism is discussed in terms of a doorway-state model.     

Radiation-induced synthesis of RuO2 nanoparticles by thermal decomposition of Ru-tris-acetylacetonate

Pure-phase RuO₂ nanoparticles were obtained by thermal decomposition of unirradiated and γ-irradiated Ru-tris-acetylacetonate precursors. Several influencing factors including absorbed dose, calcination times and temperatures and addition of surfactants were thoroughly investigated. The newly synthesized RuO₂ nanoparticles were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results showed that the best conditions for the preparation of mono-dispersed RuO₂ nanoparticles were achieved by calcinations of unirradiated Ru-tris-acetylacetonate for 6 h at 600°C. For γ-irradiated Ru-tris-acetylacetonate with 10² Gy total γ-ray doses, the optimal conditions for RuO₂ preparation were calcination for 2 h at 200°C. Thermal stability of RuO₂ nanoparticles was studied using thermogravimetric (TG) and differential thermal analysis (DTA) techniques, and the results were evaluated and discussed.     

Simulation of energy and fluence dependence of heavy ion induced displacement damage factor in bipolar junction transistor

This article presents the theoretical calculation of the variation of displacement damage factors as a function of energy and rad equivalent fluence in bipolar junction transistor for various particulate radiation viz., He, Si, Cl, Ti, Ni, Br, Ag, I, and Au. The calculation is based on the experimental data on γ-ray induced gain degradation in a commercial space borne BJT (2N3019). The method involves the calculation of γ-ray dose (rad(Si)) equivalent of effective particle fluence. The linear energy transfer (LET) in silicon for different particle radiation obtained from TRIM calculation has been used for the conversion of γ-dose into fluence of various particles. The estimation predicts a smooth increase in the displacement damage factor as the mass of the ion increases. Further, the displacement damage factor reaches a maximum at the same value of energy, which corresponds to maximum LET for all heavy ions. The maximum value of damage factor marginally decreases with increasing ion fluence for an ion of given energy. The results are compared with the data available in the literature for proton, deuteron, and helium induced displacement damage.     

On amplifications of photonuclear neutron flux in thunderstorm atmosphere and possibility of detecting them

The reliability of communications reporting observations of neutron flux enhancements in thunderstorm atmosphere is analyzed. The analysis is motivated by the fact that the employed gas-discharge counters on the basis of reactions ³He(n, p)³H and ¹⁰B(n; ⁴He, γ)⁷Li detect not only neutrons but any penetrating radiations. Photonuclear reactions are capable of accounting for the possible amplifications of neutron flux in thunder-storm atmosphere since in correlation with thunderstorms γ-ray flashes were repeatedly observed with spectra extending high above the threshold of photonuclear reactions in air. By numerical simulations, it was demonstrated that γ-ray pulses detected in thunderstorm atmosphere are capable of generating photonuclear neutrons in numbers sufficient to be detected even at sea level.     

Effect of γ-irradiation on structural,morphological and luminescence properties of cerium-doped Y3Al5O12 nano-material

ABSTRACT

Cerium-doped yttrium aluminum garnet (YAG: Ce³⁺) nanopowder phosphors have been elaborated by sol–gel process and annealed at 900°C for 2?h. The prepared phosphors were exposed to gamma radiation, using ⁶⁰Co source, at different doses ranging from 5 to 100?kGy. The influence of γ-irradiation on the structural, morphological and luminescence properties of YAG: Ce³⁺ phosphors were investigated in detail by X-ray diffraction, ?eld emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence measurements. The XRD analysis confirmed the presence of single cubic phase for all samples of YAG: Ce³⁺ nanophosphors independent of γ-rays dose. FESEM micrograph results revealed that the particles present flate-like shapes and high density of dislocation for sample irradiated at 100?kGy of γ-ray. The YAG: Ce³⁺ nanophosphors showed broad green–yellow emission band in the range of 450–700?nm with maximum intensity at 538?nm assigned to the 5d → 4f transitions of Ce³⁺ ion. The emission intensity of YAG: Ce³⁺ phosphors vary with the γ-ray irradiation and reach the maximum for sample irradiated to a dose of 25?kGy. The variation of luminescence intensity is related to the crystallite size and Ce⁴⁺ ions content in YAG host nanomaterial.     

BL Lac天体的γ射线和射电辐射的统计特性

给出了一个带有射电5.0GHz,8.4GHz 和γ射线辐射流量密度的22个γ噪BL Lac天体的样本,研究了它们在1GeV处的γ射线辐射流量密度最大值、平均值及最小值与射电5.0GHz,8.4GHz辐射流量之间的可能关系.结果表明：1）射电5.0GHz,8.4GHz辐射与γ射线辐射在低态时没有相关,但在高态和平均态时都存在较强的相关,最大相关系数r=0.85,置信度均好于10^-4;2）γ射线谱指数和射电谱指数之间也有一个弱相关关系存在.因此,认为γ射线的辐射主要是同步自康普顿辐射. 关键词： BL Lac天体 γ射线 射电辐射 谱指数     

The influence of field size and off-axis distance on photoneutron spectra of the 18 MV Siemens Oncor linear accelerator beam

At present, high energy electron linear accelerators (LINACs) producing photons with energies higher than 10 MeV have a wide use in radiotherapy (RT). However, in these beams fast neutrons could be generated, which results in undesired contamination of the therapeutic beams. These neutrons affect the shielding requirements in RT rooms and also increase the out-of-field radiation dose to patients. The neutron flux becomes even more important when high numbers of monitor units are used, as in the intensity modulated radiotherapy. Herein, to evaluate the exposure of patients and medical personnel, it is important to determine the full radiation field correctly. A model of the dual photon beam medical LINAC, Siemens ONCOR, used at the University Hospital Centre of Osijek was built using the MCNP611 code. We tuned the model according to measured photon percentage depth dose curves and profiles. Only 18 MV photon beams were modeled. The dependence of neutron dose equivalent and energy spectrum on field size and off-axis distance in the patient plane was analyzed. The neutron source strength (Q) defined as a number of neutrons coming from the head of the treatment unit per x-ray dose (Gy) delivered at the isocenter was calculated and found to be 1.12 × 10¹² neutrons per photon Gy at isocenter. The simulation showed that the neutron flux increases with increasing field size but field size has almost no effect on the shape of neutron dose profiles. The calculated neutron dose equivalent of different field sizes was between 1 and 3 mSv per photon Gy at isocenter. The mean energy changed from 0.21 MeV to 0.63 MeV with collimator opening from 0 × 0 cm² to 40 × 40 cm². At the 50 cm off-axis the change was less pronounced. According to the results, it is reasonable to conclude that the neutron dose equivalent to the patient is proportional to the photon beam-on time as suggested before. Since the beam-on time is much higher when advanced radiotherapy techniques are used to fulfill high conformity demands, this makes the neutron flux determination even more important. We also showed that the neutron energy in the patient plane significantly changes with field size. This can introduce significant uncertainty in dosimetry of neutrons due to strong dependence of the neutron detector response on the neutron energy in the interval 0.1–5 MeV.     

锆英石的抗γ射线辐照能力和Rietveld结构精修

为研究放射性核素固化介质备选矿物锆英石的抗γ射线辐照结构稳定性,以澳大利亚锆英石为研究对象,通过⁶⁰Co源γ射线辐照装置对样品施以1728 kGy的γ射线辐照.利用X射线荧光光谱仪、扫描电子显微镜和X射线衍射仪对样品的元素含量、γ射线辐照前后的微观形貌及物相变化进行表征,同时利用Rietveld方法对γ射线辐照前后的样品进行了结构精修.结果表明:澳大利亚锆英石经1728 kGy剂量的γ射线辐照后未发生物相变化,射线辐照前后样品的晶胞参数仅发生了10^-4 量级的变 关键词： 锆英石 γ射线 辐照 Rietveld结构精修     

重离子加速器示范装置被动式束流配送系统次级中子特征的蒙特卡罗研究

在碳离子放射治疗中,碳离子束在剂量配送过程中会与束流输运线相互作用,形成以中子辐射为主的外辐射场.由于中子是高LET射线,具有较高的相对生物学效应,减少碳离子放疗中产生的次级中子有助于降低放疗后正常组织并发症几率及二次肿瘤风险.利用蒙特卡罗方法对保守情况(能量为400 MeV/u,多叶光栅完全闭合)下碳离子治疗被动式束...     

The reaction 35Cl(n,γ)36Cl studied with non-polarized and polarized thermal neutrons

The γ-radiation following capture of non-polarized and polarized thermal neutrons in ³⁵Cl has been investigated. Of the 420 γ-rays ascribed to the ³⁵Cl(n,γ)³⁶Cl reaction, 236 have been placed in a ³⁶Cl decay scheme. The branching ratios and the excitation energies (with 0.04–0.9 keV errors) of 72 bound states have been determined. Unambiguous spin assignments are given for 11 levels. The multipole mixing ratios for some primary γ-ray transitions have been determined. There exists a significant correlation between (d, p) stripping strengths and (n, γ) reduced primary transition probabilities for transitions to l_n(d, p) = 0 levels.     

Transitions in41K studied with the (n,n′γ) reaction

Singles gamma ray spectra of the⁴¹K(n, n′γ)⁴¹K reaction have been measured with fast reactor neutrons. The populated states and γ-ray intensities are compared with those of the⁴⁰K(n, γ)⁴¹K reaction. About 91% of the observed gamma ray intensity was assigned to the decay of 35 states in⁴¹K. The energy and spin dependence of the gamma ray fluxes in both reactions are discussed.     

PGAI瞬发伽玛射线活化成像技术理想化模型的模拟

为了讨论PGAI技术分析的准确性,并验证冷中子和热中子应用于PGAI技术的可行性,通过蒙特卡罗模拟计算软件对PGAI技术理想化模型进行了研究,采用高准直的冷中子及热中子束和高纯锗探测器,对一块5 cm× 5 cm×1 cm均匀铁单质样品进行了模拟计算及图像重建,选取的等效体积大小为1 cm×1 cm×1 cm。结果显示:两种能量中子可以用于PGAI技术实现元素分布测量,但无论使用何种能量中子,由于物料体效应带来的中子自屏效应、中子散射效应以及伽马射线自吸收作用,即便在对均匀单质样品进行测量时,图像重建结果也无法保证各位置元素响应的一致性。因此,在后续工作中,需理清PGAI物理机制,建立相应的修正模型。