Theoretical approach to the study of vibrational effects on strong field ionization of molecules with alignment-dependent tunneling ionization rates

The tunneling ionization rates of vibrationally excited N2 molecules at the ground electronic state are calculated using molecular orbital Ammosov–Delone–Krainov theory considering R-dependence. The results show that molecular alignment significantly affects the ionization rate, as the rate is mainly determined by the electron density distribution of the highest occupied molecular orbital. The present work indicates that the ratios of alignment-dependent rates of different vibrational levels to that of the vibrational ground level increase for the aligned N2 at the angle θ = 0？, and suggests that the alignment-dependent tunneling ionization rates can be used as a diagnostics for the influence of vibrational excitation on the strong field ionization of molecules.

Theoretical research on the transport and ionization rate coefficients in glow discharge dusty plasma

The electron kinetic model for investigating the transport and ionization rate coefficients of argon glow discharge dusty plasma is developed from the Boltzmann equation.Both of the electron-neutral and electron-dust collisions are considered as collision terms in the kinetic equation.The kinetic equation is simplified by employing the local approximation and nonlocal approach under the same discharge conditions,and the corresponding simplified kinetic equations are known as local and nonlocal kinetic equations respectively.Then the electron energy distribution function(EEDF)is obtained by numerically solving the local and nonlocal kinetic equations and the dust charging equations simultaneously.Based on the obtained EEDFs,the effective electron temperature,electron mobility,electron diffusion coefficient and ionization rate coefficient are calculated for different discharge conditions.It is shown that the EEDFs calculated from the local kinetic model clearly differ from the nonlocal EEDFs and both the local and nonlocal EEDFs are also clearly different with Maxwellian distributions.The appearance of dust particles results in an obvious decrease of high energy electrons and increase of low energy electrons when axial electric field is low.With the increase of axial electric field,the influence of dust particles on the EEDFs becomes smaller.The electron mobility and diffusion coefficients calculated on the basis of local and nonlocal EEDFs do not differ greatly to the dust-free ones.While,when dust density nd=10^6 cm^?3,the electron mobility increases obviously compared with the dust-free results at low axial electric field and decreases with the increasing axial electric field until they are close to the dust-free ones.Meanwhile,electron diffusion coefficients for dusty case become smaller and decrease with the increasing axial electric field.The ionization rate coefficients decrease when dust particles are introduced and they approach the dust-free results gradually with the increasing axial electric field.

Absorbed Dose to Water Rate in a Cyberknife VSI System Reference Field Using Ionization Chambers and Gafchromic Films

This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welhöfer Scanditronix with different serial numbers. The correction factor,, was studied using a Varian iX linac and the Cyberknife system. The measurements in the Varian iX were performed in a 10 × 10 cm2 field, 10 cm depth in liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm2 field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the Cyberknife system, measurements were performed using ionization chambers and both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference field. The results indicate that ?is independent of the dosimeters and the evaluation methods. Maximum differences of 0.22% - 0.55% (combined uncertainties of 1.22% - 1.98%, k = 1) are obtained on ?using Varian iX, whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement between detectors and the combined standard uncertainties, the data from Varian iX could be considered the most accurate and consequently a weighted average factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference field. Within measurement uncertainties, the absorbed dose rate measured in the Cyberknife VSI system reference field was found to be independent of the dosimeters used. These results suggest that the absorbed dose measured at a point within a given field size should be the same, regardless the dosimeter used, if their dosimetric characteristics are well known. This highlighted the importance of performing dosimetry by controlling all parameters that could affect the dosimeter response. One can conclude that radiochromic film dosimetry can be considered as an appropriate alternative for measuring absorbed dose to water rate.

Electron Ionization Cross Sections of PF₃Molecule

Partial single and double differential cross sections with their sums through direct and dissociative ionization of PF3 have been evaluated at fixed electron energies 100 and 200 eV, by using modified Jain-Khare semi-empirical approach. To the best of my knowledge no other data of differential cross sections are available for the comparison. I have also calculated integral ionization cross sections with their ionization rate coefficients by using M-B distribution. No other data of partial ionization cross section are available till now. The sum/or total of evaluated partial cross sections reveal good agreement with available theoretical data.

Ionization in an intense field considering Coulomb correction

We derive a simple ionization rate formula for the ground state of a hydrogen atom in the velocity gauge under the conditions：ω〈〈1 a.u.（a.u.is short for atomic unit） and γ〈〈1（ω is the laser frequency and y is the Keldysh parameter）.Comparisons are made among the different versions of the Keldysh-Faisal-Reiss（KFR） theory.The numerical study shows that with considering the quasi-classical（WKB） Coulomb correction in the final state of the ionized electron,the photoionization rate is enhanced compared with without considering the Coulomb correction,and the Reiss theory with the WKB Coulomb correction gives the correct result in the tunneling regime.Our concise formula of the ionization rate may provide an insight into the ionization mechanism for the ground state of a hydrogen atom.

Effect of Magnetic Field on the Ionization Potential of the Atoms and Ions

The authors found the effect of magnetic field on the ionization of atoms and ions and shown that the magnetic field affected the rate of ionization and electron emission at angle of 60°, 120°, 240° and 300°. It is shown that the calculation must take into account the ionization potential of the magnetic field.

Estimation of enhanced low dose rate sensitivity mechanisms using temperature switching irradiation on gate-controlled lateral PNP transistor

The mechanisms occurring when the switched temperature technique is applied,as an accelerated enhanced low dose rate sensitivity(ELDRS)test technique,are investigated in terms of a specially designed gate-controlled lateral PNP transistor(GLPNP)that used to extract the interface traps(Nit)and oxide trapped charges(Not).Electrical characteristics in GLPNP transistors induced by ^(60)Co gamma irradiation are measured in situ as a function of total dose,showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP.Based on the analysis of the variations of Nit and Not,with switching the temperature,the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation.Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup.In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP,which provides us with a new insight into the test technique for ELDRS.

Measurement of niobium reaction rate for material surveillance tests in fast reactors

A highly accurate and precise technique for measurement of the 93 Nb(n,n’)93m Nb reaction rate was established for the material surveillance tests,etc.in fast reactors.The self-absorption effect on the measurement of the characteristic X-rays emitted by 93m Nb was decreased by the dissolution and evaporation to dryness of niobium dosimeter.A highly precise count of the number of 93 Nb atoms was obtained by measuring the niobium solution concentration using inductively coupled plasma mass spectrometry.X-rays of 93m Nb were measured accurately by means of comparing the X-ray intensity of irradiated niobium solution with that of the solution in which stable 93 Nb was added.The difference between both intensities indicates the effect of 182 Ta,which is generated from an impurity tantalum,and the intensity of X-rays from 93m Nb was evaluated.Measurement error of the 93 Nb(n,n’)93m Nb reaction rate was reduced to be less than 4%,which was equivalent to the other reaction rate errors of dosimeters used for Joyo dosimetry.In addition,an advanced technique using Resonance Ionization Mass Spectrometry was proposed for the precise measurement of 93m Nb yield,and 93m Nb will be resonance-ionized selectively by discriminating the hyperfine splitting of the atomic energy levels between 93 Nb and 93m Nb at high resolution.

Dose-rate effects of low-dropout voltage regulator at various biases

A low-dropout voltage regulator,LM2941,was irradiated by ^(60)Coγ-rays at various dose rates and biases for investigating the total dose and dose rate effects.The radiation responses show that the key electrical parameters, including its output and dropout voltage,and the maximum output current,are sensitive to total dose and dose rates, and are significantly degraded at low dose rate and zero bias.The integrated circuits damage change with the dose rates and biases,and the dose-rate effects are relative to its electric field.

重复频率微波脉冲大气击穿延时与电离率

针对高功率微波在大气传输中可能出现的击穿现象,研究了脉冲序列中首次脉冲击穿延时和后续脉冲击穿延时,研究结果发现首次脉冲击穿延时在脉宽范围内大致均匀分布,后续脉冲击穿延时波动性较小。根据击穿延时数据对电离率进行了分析,指出在重复频率条件下,初始电子密度较高,电子密度分布不适用指数分布,无法用延时数据标准差对电离率进行估计。提出了一种用重复频率脉冲击穿延时数据计算电离率的方法,并将计算结果与仿真结果进行了对比,结果显示,二者有较好的对应关系。

环境自动监测站固定式辐射监测仪性能测试与评价

参考计量技术规范《固定式环境γ辐射空气比释动能(率)仪现场校准规范》(JJF 1733—2018),对辐射环境空气自动监测站78台高气压电离室开展辐射特性测试。现场校准方面,仅88%的电离室满足1±0.2的响应范围要求;78台电离室的重复性均不超过1%,响应的非线性均不超过6.5%,符合规范要求。针对电离室开展辐射性能测试,发现电离室在9.0×10^(-2)~1.0×10^(9)μGy/h范围内的响应均不超过1±0.2;电离室对164 keV以上的光子的能量响应趋于1.0,对60 keV以下的光子无响应能力,而当光子能量在60~164 keV范围内时,响应曲线会因γ光子与电离室内部惰性气体的光电效应出现“鼓包”;电离室不具备对核临界事故脉冲辐射的监测与警示能力;电离室能够在2 s内给出测量范围内的准确示值,但在分段电压的交界处,响应时间会延长至180~360 s;电离室的响应受环境温度、湿度变化的影响大小不足±0.01,表明电离室的环境适应性优良。

252名医疗放射工作人员的血象及淋巴细胞微核率检测

目的对贵州省252名放射工作医务人员的血象及淋巴细胞微核率进行检测,并分析可能的影响因素。方法选取接受职业健康体检的252名从事医疗放射工作人员为研究对象,根据其工种分为诊断放射学组(n=68)、介入放射学组(n=15)及其他放射工作组(n=169);使用全自动生化分析仪检测外周血象常规指标,采用微量全血培养法检测其外周血淋巴细胞微核率,并根据不同工种、年龄以及接害工龄分组对结果进行Kruskal-Wallis H秩和检验与χ^(2)检验,采用Spearman秩相关进行相关性分析。结果252名放射工作医务人员的外周血象结果均在正常范围内,不同工种、年龄组被检者白细胞、红细胞、血红蛋白及血小板计数比较,差异无统计学意义(P>0.05);不同接害工龄被检者的白细胞、红细胞、血红蛋白比较,差异无统计学意义(P>0.05);不同接害工龄被检者的血小板计数比较、差异有统计学意义(P<0.05),血小板数与接害工龄呈负相关关系(r=-0.170,P=0.007);微核率分析显示,不同工种被检者外周血淋巴细胞微核率、微核率异常率比较,差异无统计学意义(P>0.05);不同年龄组被检者的微核率、微核率异常率比较,差异有统计学意义(P<0.05),微核率与年龄呈正相关关系(r=0.179,P=0.004);不同接害工龄被检者微核率比较、差异无统计学意义(P>0.05),但微核率异常率比较、差异有统计学意义(P<0.05)。结论医疗放射工作人员的接害工龄与血小板负相关,年龄与淋巴细胞微核率、微核异常率正相关,且工龄增加、微核异常率也增加。

PTW Detector7293种剂量验证方法在调强放射治疗中的对比研究

目的 :对比PTW Detector729 3种验证方法在调强放射治疗(intensity modulated radiation therapy,IMRT)剂量验证中的差异。方法:回顾性选取2022年1—12月于某院完成放射治疗的鼻咽癌、肺癌、乳腺癌、宫颈癌和全脑放射治疗患者共50例,使用PTW Detector729二维电离室矩阵配合PTW RW3固体水与PTW Ocavius 4D旋转模体对50例患者的IMRT计划分别进行归零机架角2D剂量验证、实际机架角2D剂量验证和实际机架角3D剂量验证。将剂量评估阈值设为10%,统计3种验证方法在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种评估标准下的γ通过率。采用SPSS 22.0统计学软件进行数据分析。结果:在10%剂量评估阈值标准下,归零机架角2D剂量验证的γ通过率最高,差异有统计学意义(P<0.05);实际机架角2D剂量验证的γ通过率高于实际机架角3D剂量验证,差异有统计学意义(P<0.05)。3种验证方法的γ通过率在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种标准下逐渐升高,且在3%/2 mm标准下均超过90%,结果满足临床放射治疗要求。结论:3种验证方法的验证结果均能达到IMRT剂量验证实践指南要求,根据IMRT开展情况选择合适的验证方法,对确保治疗方案安全、有效实施具有重要意义。

双极晶体管空间辐射效应的研究进展

双极晶体管具有电流驱动能力强、噪声低、线性度高等优点,已成为航天飞行器中常用的电子元器件。然而,在空间辐射环境下服役时,双极晶体管容易发生性能退化,进而危及航天设备的运行。因此,本文综述了双极晶体管在空间辐射环境中产生的损伤效应,主要包含电离损伤效应、位移损伤效应以及电离/位移损伤协同效应,并分析了双极晶体管的性能退化规律以及损伤机理,从而为双极晶体管的抗辐射研究提供一定的参考。

重复频率高功率微波脉冲的大气击穿

理论研究了重复频率高功率微波脉冲在大气中的传输特性,推导了n个高功率微波脉冲之后空间某点的电子密度,数值模拟并给出了在不同微波频率、大气压强、脉冲宽度以及脉冲间隔的条件下,大气击穿时,透射过去的脉冲个数与微波功率的关系。模拟结果表明:当微波脉冲参数一定时,压强越小,透射过去的脉冲个数越少,大气越容易发生击穿;当压强一定时,脉宽越宽,微波频率越小,透射过去的脉冲个数越少,大气越容易发生击穿。

双极晶体管的低剂量率电离辐射效应

通过对 npn管和 pnp管进行不同剂量率的电离辐射实验 ,研究了双极晶体管的低剂量率辐射效应 .结果表明 ,双极晶体管在低剂量率辐照下电流增益下降更为显著 ,这是由于低剂量率辐照在氧化层中感生了更多的净氧化物正电荷浓度 ,致使低剂量率下过量基极电流明显增大 .而辐照后 npn管比 pnp管具有更大的有效表面复合面积 ,致使前者比后者有更大的表面复合电流 ,从而导致了在各种剂量率辐照下 ,npn管比 pnp管对电离辐射都更为敏感 .

低剂量电离辐射对人体健康状况的影响

目的 了解射线对放射工作者健康的影响 ,为放射防护管理工作提供科学依据。方法 以 5 47名放射工作者作为调查对象 ,对其分别进行了受照剂量临床查体、实验室检查。结果 个人年受照有效剂量约为 :4 5～ 15mSv。血象异常检出率以医用同位素应用者的血细胞效应最为明显。白细胞总数、血红蛋白、红细胞、血小板均有随放射工龄的延长而降低的趋势 ,但与对照组相比 ,差异无显著性 (P >0 0 5 )。免疫球蛋白IgG、IgA相对升高。外周血淋巴细胞染色体畸变、微核率均明显高于对照组。结论 长期小剂量的电离辐射照射可使机体受到一定的辐射损伤。

空心阴极电子束对多弧离子镀TiAlN薄膜组织形貌及摩擦学性能的影响

采用空心阴极电子束辅助多弧离子镀的方式在WC基体上制备了TiAlN薄膜,讨论了电子束能量的大小对膜层组织形貌及摩擦学性能的影响。利用X射线衍射仪、扫描电子显微镜、表面轮廓测试仪及材料表面微纳米力学测试系统对薄膜的相组成、微观结构、三维形貌及摩擦学性能进行了检测和分析。结果表明:在未施加空心阴极电子束作用时薄膜具有明显的(112)择优取向,随着空心阴极电流的提高,薄膜逐渐朝着多晶面生长,择优取向减弱。电子束对膜层的形貌及摩擦学性能有显著影响,随着电子束能量的提高,膜层逐渐变得致密、平整,表面粗糙度和摩擦系数均降低,抗磨损性能提高。

不同剂量率下偏置对双极晶体管电离辐照效应的影响

对双极晶体管进行了不同剂量率、不同偏置的电离辐照实验。结果表明,对于不同偏置条件,晶体管在低剂量率辐照下,电流增益都有更为明显的衰降;各种剂量率辐照下,电流增益在发射结反向偏置时比浮空偏置时有更为显著的下降。文章对相关机理进行了探讨。

高功率脉冲磁控溅射技术的发展与研究

高功率脉冲磁控溅射技术(HPPMS)作为一种溅射粒子离化率高、可以沉积致密、高性能薄膜的新技术已经在国外广泛研究,但在国内尚未见研究报道。本文介绍了近十年来HPPMS技术在电源、脉冲形式、放电行为和薄膜沉积等方面的研究进展。在HPPMS过程中,粒子随脉冲开关通过电子冲击和电荷交换电离,并按照双极扩散理论向基体附近传输,离子能量分布随工作气压的不同而呈现不同的分布特征。这些放电特征有利于获得更宽的工艺范围和优异的膜层性能,最后介绍了我们实验室在HPPMS方面的研究工作。