A new pixelated prompt gamma imaging detector (PPGID) was developed for prompt gamma spectrum and gamma source position measurement. The PPGID prototype is composed of 30 independent pixelated scintillator detectors that can simultaneously obtain the gamma spectrum. The prototype has two LaBr_3 scintillator modules for gamma ray spectrum measurement with good performance in terms of energy resolution and one BGO module with high efficiency in high-energy detection. Therefore, in this study, a compound advanced imaging device based on energy spectrum detection was designed, assembled, and tested with radioactive sources. This device is called a pixelated prompt gamma imaging detector system (PPGID). The PPGID can correctly measure the source position as predicted by the FOV mathematical model. Both LaBr_3 and BGO can reproduce the gamma spectrum of the radioactive source. The tested energy response of LaBr_3 is 0.03–2.6 MeV, and that of BGO is 1–2.6 MeV with ^22Na and ^232Th . Dedicated data acquisition software was developed for energy calibration and gamma count histogram distribution. The gamma count histogram can be transformed into a thermal map which is the basis of the image.

The excited states of 93Zr have been investigated using the heavy-ion fusion-evaporation reaction 82Se(18O, alpha 3n) 93Zr at the beam energies of 82 and 88 MeV. Particle-gamma-gamma and gamma-gamma coincidence measurements using CsI and HPGe arrays are employed to gain selectivity to Zr isotopic products. The level scheme of 93Zr was extended up to E approximate to 12.5 Mev and I pi= (47/2-) with twenty-six new gamma-ray transitions. The observation of gamma rays with approximate to 2 Mev and the associated fragmentation of the gamma-ray flux into many competing pathways provide a clear experimental signature for the breaking core. Level structures in 93Zr were interpreted in the framework of the spherical shell model in a model space including the proton orbitals (1 f5/2, 2p3/2, 2p1/2, 1g9/2) and neutron orbits (1g9/2, 1g7/2, 2d5/2, 1h11/2). A possible reduction of the Z = 38 subshell spacing gap in 93Zr is discussed.

Objective. A scintillator is a luminescent material that converts high-energy photons into visible light and is widely used in medical imaging. Different scintillators are applied to gamma imaging in proton therapy and boron neutron capture therapy (BNCT). A pixelated scintillator is suitable for position measurement. The energy resolution, detection efficiency and position measurement of pixelated scintillators coupled to a SiPM were investigated via two kinds of detectors. The goal of this manuscript was to accurately measure the gamma source position through spectrum analysis in selection of energy windows for characteristic gamma lines. Approach. Scintillators were effectively manufactured and encapsulated before testing, especially for the easily deliquescent LaBr3. The compact front-end electronic prototype modules with 2 x 2 array SiPMs in stacked form and 1 x 10 array SiPMs in parallel form were developed for gamma ray energy resolution and efficiency measurements with a radioactive source of 22Na, which had two energy gamma lines at 511 keV and 1274 keV. Energy calibration was used for accurate energy window selection when measuring the position of the gamma source. Main results. Evident inconsistencies were present between different pixels of the same type of scintillator. Thus, an energy calibration method was needed. LaBr3 was the first candidate scintillator for the gamma ray spectrum measurement since it exhibited the best performance with an energy resolution of similar to 5%. The recommended size of LaBr3 was 5 x 5 mm2, which had a higher efficiency than the 3 x 3 mm2 size. The gamma count of the multiple mode of the 2 x 2 array was much higher than that of the single mode, while the energy resolution was poorer. Thus, multiple mode was not suitable for gamma ray detection. The 1 x 10 array detector had the potential to measure the gamma ray source position and could be used for proton therapy and BNCT. A small deviation of 0.22 cm was observed in the measurement of the source center position with Energy Window 1 for 511 keV and Energy Window 2 for 1274 keV before the energy calibration. No deviation was observed after energy calibration. Thus, to achieve a higher accuracy position measurement, automatic energy calibration algorithm was coded into data acquisition software. Significance. The characteristic gamma lines produced by particle therapy are abundant and useful for imaging technology. Our developed compact pixelated scintillator detector coupled with SiPMs could measure the gamma spectrum with high resolution. The energy calibration and window selection method could measure the position of the source with high accuracy. Therefore, an advanced imaging device based on the energy spectrum for particle therapy could be potentially attainable.

Excited states of Rn-2 have been studied via the Au-1(N-1, 5n) Rn-2 fusion reaction at a beam energy of 78 MeV. A number of transitions and levels are identified by the gamma-gamma coincidence measurement, further enriching the level scheme of Rn-2. Both the full configuration shell model and the nucleon-pair approximation (NPA) were utilized to investigate the single-particle configurations and seniority structures in Rn-2. The results of these two calculations suggest that the 2(1) and 4(1) states exhibit only a 50% component of a seniority-two state associated with a broken neutron pair. The collectivity of these two states primarily arises from configuration mixing due to residual proton-neutron interactions. The 6(1) and 8(1) states are predominantly characterized by a seniority-two state marked by a broken proton pair.

Objective. Non-primary radiation doses to normal tissues from proton therapy may be associated with an increased risk of secondary malignancies, particularly in long-term survivors. Thus, a systematic method to evaluate if the dose level of non-primary radiation meets the IEC standard requirements is needed.Approach. Different from the traditional photon radiation therapy system, proton therapy systems are composed of several subsystems in a thick bunker. These subsystems are all possible sources of non-primary radiation threatening the patient. As a case study, 7 sources in the P-Cure synchrotron-based proton therapy system are modeled in Monte Carlo (MC) code: tandem injector, injection, synchrotron ring, extraction, beam transport line, scanning nozzle and concrete reflection/scattering. To accurately evaluate the synchrotron beam loss and non-primary dose, a new model called the torus source model is developed. Its parametric equations define the position and direction of the off-orbit particle bombardment on the torus pipe shell in the Cartesian coordinate system. Non-primary doses are finally calculated by several FLUKA simulations.Main results. The ratios of summarized non-primary doses from different sources to the planned dose of 2 Gy are all much smaller than the IEC requirements in both the 15-50 cm and 50-200 cm regions. Thus, the P-Cure synchrotron-based proton therapy system is clean and patient-friendly, and there is no need an inner shielding concrete between the accelerator and patient.Significance. Non-primary radiation dose level is a very important indicator to evaluate the quality of a PT system. This manuscript provides a feasible MC procedure for synchrotron-based proton therapy with new beam loss model. Which could help people figure out precisely whether this level complies with the IEC standard before the system put into clinical treatment. What' more, the torus source model could be widely used for bending magnets in gantries and synchrotrons to evaluate non-primary doses or other radiation doses.

As medical facilities are usually built at urban areas, special concrete aggregates and evaluation methods are needed to optimize the design of concrete walls by balancing density, thickness, material composition, cost, and other factors. Carbon treatment rooms require a high radiation shielding requirement, as the neutron yield from carbon therapy is much higher than the neutron yield of protons. In this case study, the maximum carbon energy is 430 MeV/u and the maximum current is 0.27 nA from a hybrid particle therapy system. Hospital or facility construction should consider this requirement to design a special heavy concrete. In this work, magnetite is adopted as the major aggregate. Density is determined mainly by the major aggregate content of magnetite, and a heavy concrete test block was constructed for structural tests. The compressive strength is 35.7 MPa. The density ranges from 3.65 g/cm3 to 4.14 g/cm3, and the iron mass content ranges from 53.78% to 60.38% from the 12 cored sample measurements. It was found that there is a linear relationship between density and iron content, and mixing impurities should be the major reason leading to the nonuniform element and density distribution. The effect of this nonuniformity on radiation shielding properties for a carbon treatment room is investigated by three groups of Monte Carlo simulations. Higher density dominates to reduce shielding thickness. However, a higher content of high-Z elements will weaken the shielding strength, especially at a lower dose rate threshold and vice versa. The weakened side effect of a high iron content on the shielding property is obvious at 2.5 μSv/h. Therefore, we should not blindly pursue high Z content in engineering. If the thickness is constrained to 2 m, then the density can be reduced to 3.3 g/cm3, which will save cost by reducing the magnetite composition with 50.44% iron content. If a higher density of 3.9 g/cm3 with 57.65% iron content is selected for construction, then the thickness of the wall can be reduced to 174.2 cm, which will save space for equipment installation.

Prompt gamma ray in proton therapy is the product of a nuclear reaction between a proton and a target. The characteristic energies and intensities of prompt gamma lines can be used to determine the types of elements and their amounts in the target. In several previous experiments, it was demonstrated that no matter how complex the reaction cross-section is, once the energy of the incident proton and the irradiated element are determined, there is a definite linear relationship between the element concentration and the number of gamma-ray photons. However, this linear relationship is difficult to apply to medical imaging, and the nonlinear behavior of hydrogen has not been investigated so far. In this study, this linear relationship is extended to mixed elemental materials including a nonlinear case such as hydrogen, and a universal mathematical form, which is referred to as the prompt gamma spectroscopy retrieval algorithm (PGSRA), is developed. The basic assumption of the PGSRA is that the PGS of the sample material has a relationship with the molar gamma lines of the elements. For carbon and oxygen, this relationship is linear, while for hydrogen, this relationship is nonlinear. As the 2.23 MeV gamma line originates from neutron absorption radiation, the behavior of hydrogen is carefully investigated. The linear and nonlinear relationships are verified using Monte Carlo simulations with different combinations of carbon, oxygen, and hydrogen, such as PMMA, pentanediol, and ethanediol. The PGSRA developed in this work could be the first bridge between PGS and medical imaging.

目的:评估质子治疗中扫描治疗头对束流品质的影响.方法:通过扫描治疗头的蒙特卡罗模型研究深度剂量曲线的变化,计算射程移位器对束斑截面的影响以及分析扫描磁场对单质子束的偏转情况.结果:随着能量的增加,质子在水中的射程增加,同时散射也越严重,最终布拉格峰变宽,尾端变胖.相比于直接入射水模,通过治疗头后质子在水中的射程缩短了约0.6 cm,但布拉格峰形基本保持不变;将4 cm厚度聚乙烯射程移位器放置于距离水模表面0、10、20、30、40和50 cm分别进行独立计算,发现与水模距离越远,质子的散射越大,因此治疗过程中射程移位器应尽量靠近患者;当扫描磁铁加载磁场后,束斑将偏离束流中心.设置纵向扫描磁场Bx=0.1 T,横向扫描磁场By=0.3 T,180 MeV质子束在Y方向偏离了2.693 cm,横向扫描磁场使质子在-X方向上偏离了8.427 cm.当束流有偏转的时候,要求射程移位器横截面足够大以满足宽扫描场的需要.结论:扫描治疗头的蒙特卡罗模型将有助于理解质子治疗这一新兴的放疗方法以及熟悉扫描治疗的束流特性,在调试和质量保证中提供参考.

目的:提供一种权重适配的布拉格峰展宽(SOBP)方法,得到平滑的展宽布拉格峰.方法:通过重新拟合质子能量-射程的关系(盖格法则),找出适配函数的函数形式,并对权重进行重新适配,通过求敏感参数k,得到平滑的SOBP,最后用蒙特卡洛程序FLUKA进行验证.结果:SOBP的形状对参数k比参数P更加敏感,拟合得到4～32 cm的SOBP,中间平坦区偏差不超过±2％,并解决中间区坍塌的问题.结论:蒙特卡洛模拟检验了权重适配的SOBP方法的有效性.

A synchrotron-based proton therapy(PT) facility that conforms with the requirement of future development trend in compact PT can be operated without an energy selection system. This article demonstrates a novel radiation shielding design for this purpose. Various FLUKA-based Monte Carlo simulations have been performed to validate its feasibility. In this design, two different shielding scenarios(3-m-thick concrete and 2-m-thick iron–concrete) are proved able to reduce the public annual dose to the limit of 0.1 mSv/year. The calculation result shows that the non-primary radiation from a PT system without an inner shielding wall complies with the IEC60601-2-64 international standard, making a single room a reality. Moreover, the H/D value of this design decreases from 2.14 to 0.32 mSv/Gy when the distance ranges from 50 to 150 cm from the isocenter, which is consistent with the previous result from another study. By establishing a typical time schedule and procedures in a treatment day for a single room in the simulation, a non-urgent machine maintenance time of 10 min after treatment is recommended, and the residual radiation level in most areas can be reduced to 2.5μSv/h. The annual dose for radiation therapists coming from the residual radiation is 1 mSv,which is 20% of the target design. In general, this shielding design ensures a low cost and compact facility compared with the cyclotron-based PT system.

Increased accuracy of proton beam delivery provides additional benefits to the patients undergo the treatment. A prompt gamma imaging detector can provide additional information during the treatment, as the prompt gammas produced by the interactions between protons and human tissues are related to the range and profile of the beam in the patient. This paper makes a Monte Carlo feasibility study for a pixelated prompt gamma imaging detector which can not only measure the proton range but also merge the beam profile and 3D beam image inside the patient. FLUKA simulation result shows that this detector can reduce background noise and measure the range and beam profile by using of grated shielding material, vertical gammas selection and a 5 MeV energy window.

Electron-induced electrostatic discharge on spacecraft can lead to severe anomalies, especially for some scientific instruments, such as space environment detection system. The ground simulation can help to figure out the mechanism of the discharge's impacts on these detectors, and thus some mitigation methods were put forward and the experiments proved them to be valid. A novel simulation apparatus combined with an electron gun and seven radioactive sources was developed for such tests. This simulation method can also be applied to other electronics system to diagnose problems caused by electron-induced charge and discharge.

The vacuum outgassing of nonmetallic materials used for satellite may have a significant impact on the dielectric properties of the materials, thus increase the ESD risk of a long-term service satellite at a later stage. In this paper, the commonly-used non-metallic material (polyimide) is selected as the research object. The influence of outgassing on the surface potential of the polyimide samples is studied through the accelerated ground simulation test by a 90Sr-90Y radiation source, and the dielectric conductivity is calculated by curve fitting. It is found that in a high temperature vacuum environment under the 5 pA/cm2 electron irradiation, the samples that have experienced longer time of degassing exhibit lower conductivity, about half of its original value at a total mass loss of 0.5%. The related physical mechanism is analyzed. The result may provide some guidance to the ESD protection design for long-lifetime satellites.