Nuclear nonproliferation is of critical importance for global security.Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect.Active interrogation ...Nuclear nonproliferation is of critical importance for global security.Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect.Active interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal neutrons.Also,most conventional portal monitoring systems rely on ^(3)He,which has a finite and continually decreasing supply.By designing a highly segmented array of organic scintillators,we posit that we can accurately and quickly identify fissile materials,including weapons-grade plutonium and highly enriched uranium,being smuggled.We propose a new design for a fast-neutron detector that overcomes the limitations of the current generation of portal monitors.MCNP6 simulations have been performed in conjunction with the UMPBT statistical model to determine the sensitivity limitations of the proposed detector.Results suggest that the proposed detector may be 10 times more efficient than current-generation thermal neutron detectors and may be able to positively identify a 81 mg 235U source in as little as 192 seconds utilizing active interrogation techniques.展开更多
在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物...在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。由于角动量守恒,白矮星可能在一次爆发之后被踢开,接着在演化过程中由于引力辐射再次充满洛希瓣,实现再次爆发。这种情况下,快速射电暴的周期对应于双星轨道周期P_(orb),而它与两次质量转移时间间隔Δt之间的关系是能否显现周期性行为的关键因素。很明显,Δt≈P_(orb)或者Δt<P_(orb)是周期性行为显现的必要条件。反之,如果Δt>>P_(orb),周期性将很难观测到。结果表明,只有相对较长周期的快速射电暴才能显示周期性行为,这表明目前仅有的两个周期性快速射电暴都对应于较长的周期是合理的。展开更多
为应对3He短缺情况,采用更加低价、易获取的液闪来探测中子,并推广应用中子多重性技术,研制了一种基于EJ309的液闪快中子探测器,自主开发了中子伽玛甄别电路,采用电荷积分法进行中子伽玛信号甄别,并通过实验验证了该中子探测器在能量阈...为应对3He短缺情况,采用更加低价、易获取的液闪来探测中子,并推广应用中子多重性技术,研制了一种基于EJ309的液闪快中子探测器,自主开发了中子伽玛甄别电路,采用电荷积分法进行中子伽玛信号甄别,并通过实验验证了该中子探测器在能量阈值为100 keVee(ee—等效能)时,中子伽玛甄别性能参数FOM(Figure of Merit)大于1;在多重性数据分析过程中,为了解决散射中子对多重性符合计数带来的影响,引入散射串扰因子对传统多重性方程进行了修正;为降低测量腔内探测效率的非均匀性对测量结果的影响,通过蒙特卡洛模拟设计了一套球形快中子多重性测量装置,并通过实验验证了其探测效率的均匀性以及测量结果的相对偏差,结果表明:其探测效率的均匀性以及测量结果的相对偏差均好于5%,该工作为快中子多重性测量技术的实际应用奠定了基础。展开更多
基金supported by the National Nuclear Security Administration(NNSA)through the Center for Excellence in Nuclear Training and University Based Research(CENTAUR)under Award No.DE-NA0003841by the U.S.Department of Energy,Office of Science,Office of Nuclear Physics,under Award No.DE-FG02-93ER40773the College of Science at Texas A&M University through Strategic Transformative Research Program(CoS STRP).
文摘Nuclear nonproliferation is of critical importance for global security.Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect.Active interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal neutrons.Also,most conventional portal monitoring systems rely on ^(3)He,which has a finite and continually decreasing supply.By designing a highly segmented array of organic scintillators,we posit that we can accurately and quickly identify fissile materials,including weapons-grade plutonium and highly enriched uranium,being smuggled.We propose a new design for a fast-neutron detector that overcomes the limitations of the current generation of portal monitors.MCNP6 simulations have been performed in conjunction with the UMPBT statistical model to determine the sensitivity limitations of the proposed detector.Results suggest that the proposed detector may be 10 times more efficient than current-generation thermal neutron detectors and may be able to positively identify a 81 mg 235U source in as little as 192 seconds utilizing active interrogation techniques.
文摘在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。由于角动量守恒,白矮星可能在一次爆发之后被踢开,接着在演化过程中由于引力辐射再次充满洛希瓣,实现再次爆发。这种情况下,快速射电暴的周期对应于双星轨道周期P_(orb),而它与两次质量转移时间间隔Δt之间的关系是能否显现周期性行为的关键因素。很明显,Δt≈P_(orb)或者Δt<P_(orb)是周期性行为显现的必要条件。反之,如果Δt>>P_(orb),周期性将很难观测到。结果表明,只有相对较长周期的快速射电暴才能显示周期性行为,这表明目前仅有的两个周期性快速射电暴都对应于较长的周期是合理的。
文摘为应对3He短缺情况,采用更加低价、易获取的液闪来探测中子,并推广应用中子多重性技术,研制了一种基于EJ309的液闪快中子探测器,自主开发了中子伽玛甄别电路,采用电荷积分法进行中子伽玛信号甄别,并通过实验验证了该中子探测器在能量阈值为100 keVee(ee—等效能)时,中子伽玛甄别性能参数FOM(Figure of Merit)大于1;在多重性数据分析过程中,为了解决散射中子对多重性符合计数带来的影响,引入散射串扰因子对传统多重性方程进行了修正;为降低测量腔内探测效率的非均匀性对测量结果的影响,通过蒙特卡洛模拟设计了一套球形快中子多重性测量装置,并通过实验验证了其探测效率的均匀性以及测量结果的相对偏差,结果表明:其探测效率的均匀性以及测量结果的相对偏差均好于5%,该工作为快中子多重性测量技术的实际应用奠定了基础。
