Low background gamma spectrometry was used to measure the radionuclides activity of <sup>238</sup>U, <sup>232</sup>Th, and <sup>235</sup>U series as well as <sup>40</sup>...Low background gamma spectrometry was used to measure the radionuclides activity of <sup>238</sup>U, <sup>232</sup>Th, and <sup>235</sup>U series as well as <sup>40</sup>K and <sup>137</sup>Cs in a sediment sample. The goal of the study was to measure the <sup>238</sup>U (63.3 keV peak of <sup>234</sup>Th;1001 keV peak of <sup>234m</sup>Pa) and <sup>235</sup>U (143.76 keV, 163.33 keV, and 205.31 keV peaks) activity by low background gamma spectrometry in sediment sample. <sup>235</sup>U activity in environmental samples is difficult to accurately measure by gamma spectrometry due to its low abundance in nature and low gamma line intensities at 143.76 keV, 163.33 keV, and 205.31 keV. We have shown that by using low background gamma spectrometry, it is possible to accurately measure the <sup>235</sup>U activity in sediment samples. The <sup>235</sup>U activity was measured without using the major peak of 185.7 keV (I<sub>γ</sub> = 57.2%) which requires interference correction from 186.21 keV of <sup>226</sup>Ra. <sup>226</sup>Ra activity was determined by measuring <sup>222</sup>Rn daughters (<sup>214</sup>Pb and <sup>214</sup>Bi). The precision and accuracy of the gamma activity measurement in the sediment sample were verified by using the HPGe detectors with Certified Reference Material (CRM) Irish Sea Sediment (IAEA-385). The results obtained for the 63.33 keV energy line of <sup>234</sup>Th are compared with the 1001 keV energy line of <sup>234m</sup>Pa. The values of <sup>238</sup>U and <sup>235</sup>U activities, as well as <sup>40</sup>K, <sup>137</sup>Cs, and <sup>226</sup>Ra, agreed with the certificate values of CRM. The results show that the <sup>238</sup>U is in equilibrium with its daughters (<sup>234</sup>Th, <sup>234m</sup>Pa, and <sup>210</sup>Pb). <sup>232</sup>Th is also in equilibrium with its daughters (<sup>228</sup>Ra, <sup>212</sup>Pb, <sup>212</sup>Bi and <sup>208</sup>Tl). <sup>235</sup>U/<sup>238</sup>U activity ratio of 0.046 ± 0.007 in the sediment is constant in nature but fluctuates due to geological processes. A value of 0.055 ± 0.008 was found in our sediment sample.展开更多
A low-background neutron detector array was developed to measure the cross section of the ^(13)C(a,n)^(16)O reaction,which is the neutron source for the s-process in AGB stars,in the Gamow window(E_(c.m.)=190±40 ...A low-background neutron detector array was developed to measure the cross section of the ^(13)C(a,n)^(16)O reaction,which is the neutron source for the s-process in AGB stars,in the Gamow window(E_(c.m.)=190±40 keV)at the China Jinping Underground Laboratory(CJPL).The detector array consists of 24^(3)He proportional counters embedded in a polyethylene cube.Owing to the deep underground location and a borated polyethylene shield around the detector array,a low background of 4.5(2)/h was achieved.The ^(51)V(p,n)^(51)Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energies E_(n)<1 MeV.Geant4 simulations are shown to effectively reproduce the experimental results.They were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the ^(13)C(α,n)^(16)O reaction.The theoretical angular distributions of the ^(13)C(α,n)^(16)O reaction were shown to be important in the estimation of the uncertainties of the detection efficiency.展开更多
Highly oriented pyrolytic graphite (HOPG) is frequently adopted as the reaction target in12C+12C fusion reaction experiments owing to its superior purity.In this study,we investigate the reaction yield dependence on t...Highly oriented pyrolytic graphite (HOPG) is frequently adopted as the reaction target in12C+12C fusion reaction experiments owing to its superior purity.In this study,we investigate the reaction yield dependence on the accumulated beam dose on HOPG target using a novel detection system consisting of a time-projection chamber and silicon array.The reaction yields are significantly reduced under intense beam bombardment owing to radiation damage to the HOPG surface.The α_(0) and p_(0,1) yields decrease by 51.5% and 25%,respectively,when the ^(12)C^(2+) beam dose accumulates at 5 C.Using the novel detection system and HOPG target,the α0yield is determined to be 2.68_(-1.69)^(+4.69)×10^(-17/12) C after correcting for the yield loss due to radiation damage.Our result represents the highest sensitivity achieved to date in direct measurements of ^(12)C(12C,α_(0))^(20)Ne.展开更多
光伏新能源发电系统的电能产出受到多种外部条件的影响,包括光照强度、环境温度变化以及局部阴影的遮挡效应,容易导致其MPP(Maximum Power Point,最大功率点)发生漂移,从而难以快速准确地跟踪功率点变化。在低碳背景下,计算发电系统Boos...光伏新能源发电系统的电能产出受到多种外部条件的影响,包括光照强度、环境温度变化以及局部阴影的遮挡效应,容易导致其MPP(Maximum Power Point,最大功率点)发生漂移,从而难以快速准确地跟踪功率点变化。在低碳背景下,计算发电系统Boost电路中的占空比、输出负载、电感和电容参数,引入蚁群算法对Boost电路参数进行优化,增强搜索过程的多样性和探索性。采用随机化步长,通过模糊控制器,实现对最大功率点跟踪控制。仿真结果表明,当直流母线电压存在扰动时,所提方法可以迅速作出反应,并将电压恢复到正常水平;当光照强度骤减后,仅需要0.9 s左右的时间就可以稳定在最大功率点附近。展开更多
根据掺杂稀土离子固体材料激光冷却四能级理论模型,冷却样品的背景吸收系数是影响样品激光冷却性能的关键参数.为了探究冷却样品(以Yb^(3+):LuLiF_(4)(LLF)为例)中背景吸收系数与温度的函数关系,设计了在低温条件下获取冷却晶体背景吸...根据掺杂稀土离子固体材料激光冷却四能级理论模型,冷却样品的背景吸收系数是影响样品激光冷却性能的关键参数.为了探究冷却样品(以Yb^(3+):LuLiF_(4)(LLF)为例)中背景吸收系数与温度的函数关系,设计了在低温条件下获取冷却晶体背景吸收系数的低温-激光诱导温度调制光谱(laser-induced temperature modulation spectrum,LITMoS)实验方案.依据热负载理论推导了低温条件下冷却效率的实验计算公式,并对热负载来源进行理论分析.分析结果表明,接触传导热负载是低温-LITMoS实验样品热负载的主要来源.实验方案中采用液氮低温恒温器和特殊设计的冷指结构去控制晶体的温度,利用时间阀门-差分荧光光谱测温法对晶体进行非接触式测温获得晶体的温降,并对实验设计方案进行了可行性分析,计算了对应波长下的样品冷却效率.结果表明,在低温条件下实验设计方案可以测量样品背景吸收系数与温度之间的函数关系,制冷效率的测试结果符合光学制冷理论模型的预测.展开更多
文摘Low background gamma spectrometry was used to measure the radionuclides activity of <sup>238</sup>U, <sup>232</sup>Th, and <sup>235</sup>U series as well as <sup>40</sup>K and <sup>137</sup>Cs in a sediment sample. The goal of the study was to measure the <sup>238</sup>U (63.3 keV peak of <sup>234</sup>Th;1001 keV peak of <sup>234m</sup>Pa) and <sup>235</sup>U (143.76 keV, 163.33 keV, and 205.31 keV peaks) activity by low background gamma spectrometry in sediment sample. <sup>235</sup>U activity in environmental samples is difficult to accurately measure by gamma spectrometry due to its low abundance in nature and low gamma line intensities at 143.76 keV, 163.33 keV, and 205.31 keV. We have shown that by using low background gamma spectrometry, it is possible to accurately measure the <sup>235</sup>U activity in sediment samples. The <sup>235</sup>U activity was measured without using the major peak of 185.7 keV (I<sub>γ</sub> = 57.2%) which requires interference correction from 186.21 keV of <sup>226</sup>Ra. <sup>226</sup>Ra activity was determined by measuring <sup>222</sup>Rn daughters (<sup>214</sup>Pb and <sup>214</sup>Bi). The precision and accuracy of the gamma activity measurement in the sediment sample were verified by using the HPGe detectors with Certified Reference Material (CRM) Irish Sea Sediment (IAEA-385). The results obtained for the 63.33 keV energy line of <sup>234</sup>Th are compared with the 1001 keV energy line of <sup>234m</sup>Pa. The values of <sup>238</sup>U and <sup>235</sup>U activities, as well as <sup>40</sup>K, <sup>137</sup>Cs, and <sup>226</sup>Ra, agreed with the certificate values of CRM. The results show that the <sup>238</sup>U is in equilibrium with its daughters (<sup>234</sup>Th, <sup>234m</sup>Pa, and <sup>210</sup>Pb). <sup>232</sup>Th is also in equilibrium with its daughters (<sup>228</sup>Ra, <sup>212</sup>Pb, <sup>212</sup>Bi and <sup>208</sup>Tl). <sup>235</sup>U/<sup>238</sup>U activity ratio of 0.046 ± 0.007 in the sediment is constant in nature but fluctuates due to geological processes. A value of 0.055 ± 0.008 was found in our sediment sample.
基金supported by the National Natural Science Foundation of China(Nos.11490564 and 11805138).
文摘A low-background neutron detector array was developed to measure the cross section of the ^(13)C(a,n)^(16)O reaction,which is the neutron source for the s-process in AGB stars,in the Gamow window(E_(c.m.)=190±40 keV)at the China Jinping Underground Laboratory(CJPL).The detector array consists of 24^(3)He proportional counters embedded in a polyethylene cube.Owing to the deep underground location and a borated polyethylene shield around the detector array,a low background of 4.5(2)/h was achieved.The ^(51)V(p,n)^(51)Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energies E_(n)<1 MeV.Geant4 simulations are shown to effectively reproduce the experimental results.They were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the ^(13)C(α,n)^(16)O reaction.The theoretical angular distributions of the ^(13)C(α,n)^(16)O reaction were shown to be important in the estimation of the uncertainties of the detection efficiency.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB34020200)National Key Research and Development Program(MOST 2022YFA1602304)+1 种基金Scientific Research Instrument and Equipment Development Program of the Chinese Academy of Sciences(No.GJJSTD20210007)National Natural Science Foundation of China(Nos.12175156,U1632142).
文摘Highly oriented pyrolytic graphite (HOPG) is frequently adopted as the reaction target in12C+12C fusion reaction experiments owing to its superior purity.In this study,we investigate the reaction yield dependence on the accumulated beam dose on HOPG target using a novel detection system consisting of a time-projection chamber and silicon array.The reaction yields are significantly reduced under intense beam bombardment owing to radiation damage to the HOPG surface.The α_(0) and p_(0,1) yields decrease by 51.5% and 25%,respectively,when the ^(12)C^(2+) beam dose accumulates at 5 C.Using the novel detection system and HOPG target,the α0yield is determined to be 2.68_(-1.69)^(+4.69)×10^(-17/12) C after correcting for the yield loss due to radiation damage.Our result represents the highest sensitivity achieved to date in direct measurements of ^(12)C(12C,α_(0))^(20)Ne.
文摘光伏新能源发电系统的电能产出受到多种外部条件的影响,包括光照强度、环境温度变化以及局部阴影的遮挡效应,容易导致其MPP(Maximum Power Point,最大功率点)发生漂移,从而难以快速准确地跟踪功率点变化。在低碳背景下,计算发电系统Boost电路中的占空比、输出负载、电感和电容参数,引入蚁群算法对Boost电路参数进行优化,增强搜索过程的多样性和探索性。采用随机化步长,通过模糊控制器,实现对最大功率点跟踪控制。仿真结果表明,当直流母线电压存在扰动时,所提方法可以迅速作出反应,并将电压恢复到正常水平;当光照强度骤减后,仅需要0.9 s左右的时间就可以稳定在最大功率点附近。
文摘根据掺杂稀土离子固体材料激光冷却四能级理论模型,冷却样品的背景吸收系数是影响样品激光冷却性能的关键参数.为了探究冷却样品(以Yb^(3+):LuLiF_(4)(LLF)为例)中背景吸收系数与温度的函数关系,设计了在低温条件下获取冷却晶体背景吸收系数的低温-激光诱导温度调制光谱(laser-induced temperature modulation spectrum,LITMoS)实验方案.依据热负载理论推导了低温条件下冷却效率的实验计算公式,并对热负载来源进行理论分析.分析结果表明,接触传导热负载是低温-LITMoS实验样品热负载的主要来源.实验方案中采用液氮低温恒温器和特殊设计的冷指结构去控制晶体的温度,利用时间阀门-差分荧光光谱测温法对晶体进行非接触式测温获得晶体的温降,并对实验设计方案进行了可行性分析,计算了对应波长下的样品冷却效率.结果表明,在低温条件下实验设计方案可以测量样品背景吸收系数与温度之间的函数关系,制冷效率的测试结果符合光学制冷理论模型的预测.
