Development and test of neutron activation simulation program based on JMCT software
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摘要: 中子活化产物和辐射特征的数值模拟程序是研究材料活化效应的重要工具。在JMCT软件的基础上开发了具备材料中子活化效应模拟能力的数值模拟程序，并将其命名为“中子活化数值模拟程序”，旨在将其应用于军控核查、核安全等领域的研究中。对该程序在核弹头内部中子输运和活化计算的准确性进行了验证，发现该程序对核弹头内部中子输运和活化的计算精度优良。利用该程序研究了混凝土地面核素在裂变核材料的裂变中子辐照下的活化效应，计算结果进一步验证了中子活化数值模拟程序的功能。Abstract: The numerical simulation program of neutron activation products and their radiation characteristics is an important tool to study the activation effect of materials. A numerical simulation program capable of simulating the neutron activation effect of materials was developed through the secondary development of the JMCT software, and it was named “neutron activation simulation program”, which is expected to be applied to the research of arms control verification and nuclear security. The correctness of the neutron activation simulation program in calculating the neutron transport and activation inside nuclear warheads was tested, and the calculation results are accurate. The activation effect of concrete floors under the irradiation of the fission neutrons from fissile materials was studied based on the neutron activation simulation program, and the calculation results furthermore prove the functions of the neutron activation simulation program.
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图 2 放射性核素半衰期数据库和放射性核素γ衰变数据库
Figure 2. Databases of half-lives and γ-decay of radionuclides
图 3 中子活化数值模拟程序的核素数目计算的结果文件
Figure 3. Output file of radionuclide numbers of neutron activation simulation program
图 6 七种活化核素的数目与材料闲置时长的关系曲线
Figure 6. Relationship curves between numbers of 7 radionuclides and idle time
图 7 不同中子辐照时长和材料闲置时长下进入高纯锗探测器的γ射线的能谱
Figure 7. Spectra of γ rays entering HPGe detector under different neutron irradiation time and idle time
表 1 核弹头模型中各结构的尺寸、质量和成分参数
Table 1. Size, mass and ingredient parameters of structures in nuclear warhead model
structure outer radius/cm mass/kg ingredient parameters hole 5.77 0.0 vacuum fissile core 7.0 12.0 weapons-grade uranium (234U(1%), 235U(93.3%), 238U(5.5%), O(0.2%)) reflector 9.0 3.0 natural beryllium tamper 12.0 79.0 Model 1: depleted uranium (235U(0.3%), 238U(99.7%)); Model 2: Natural tungsten explosive 22.0 71.0 explosive (atom number ratio is H:C:N:O=2:1:2:2) shell 23.0 17.0 natural aluminium 
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表 2 裂变材料的中子产额
Table 2. Neutron fields of fissile materials
material nuclide portion neutron yield/neutrons∙s−1 (α, n) reaction spontaneous fission weapon-grade uranium 234U 1% 50 5.546 235U 93.3% 0.012 0.299 238U 5.5% 0.001 13.57 O 0.2% 0 0 depleted uranium 235U 0.3% 0 0.299 238U 99.7% 0 13.57
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表 3 从核弹头模型中出射的中子的数目
Table 3. Numbers of neutrons emitted from nuclear warhead model
simulation software contribution of fission core to neutron
leakage from shell (neutrons/s)contribution of tamper to neutron
leakage from shell (neutrons/s)total neutron leakage
(neutrons/s)Model 1 neutron activation
simulation program18 718 736 MCNP5 18 720 738 Model 2 neutron activation
simulation program13 0 13 MCNP5 13 0 13
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表 4 核弹头模型中的放射性核素
Table 4. Radionuclides in nuclear warhead model
radionuclide nuclear reaction half-life decay type 16N 16O(n,p)16N 7.130 s β−, γ 15O 16O(n,2n)15O 122.240 s β+ 13N 14N(n,2n)13N 9.970 min β+, β−, γ 11C 12C(n,2n)11C 20.48 min β+, β−, γ 14C 14N(n,p)14C 5730 a β−
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表 5 炸药中放射性核素的产生情况
Table 5. Production of radionuclides in explosive
simulation
softwareneutrons
simulatedequivalent
measuring timenumber of radionuclide 16N 15O 13N 11C 14C Model 1 neutron activation
simulation program107 9.19×103 s 47 0 4 0 5.56×106 GEANT4 107 9.19×103 s 61 0 5 0 5.72×106 Model 2 neutron activation
simulation program107 5.23×105 s 35 0 2 0 5.93×106 GEANT4 107 5.23×105 s 36 0 9 0 6.07×106
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表 6 混凝土地面模型的元素组分
Table 6. Element composition of concrete floor model
element atom proportion/% nuclide H 13.3 1H/2H O 73.7 16O/17O Na 1.8 23Na Mg 0.3 24Mg/25Mg/26Mg Al 4.2 27Al Si 0.3 28Si/29Si/30Si K 1.2 39K/40K/41K Ca 4.8 40Ca/42Ca/43Ca/44Ca/46Ca/48Ca Fe 0.4 54Fe/56Fe/57Fe/58Fe
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表 7 混凝土地面模型中核素活化产生的放射性核素的信息
Table 7. Information of activation products of concrete floor model
radionuclide half-life decay type yield/s−1 activation reaction 14C 5715 a β− 1.59 17O(n,α) 16N 7.13 s β−,γ 0.613 16O(n,p) 20F 11.0 s β−,γ 0.432 23Na(n,α) 23Ne 37.2 s β−,γ 1.05 23Na(n,p) 24Na 14.96 h β−,γ 14.8 23Na(n,γ), 24Mg(n,p), 27Al(n,α) 27Mg 9.45 min β−,γ 7.05 27Al(n,p) 28Al 2.25 min β−,γ 15.6 27Al(n,γ), 28Si(n,p) 36Cl 3.01×105 a β+,β−,EC 20.1 39K(n,α) 37Ar 35.0 d EC 82.7 40Ca(n,α) 39Ar 268 a β− 61.6 39K(n,p), 42Ca(n,α) 41Ar 1.82 h β−,γ 0.0700 41K(n,p) 40K 1.26×109 a β+,β−,EC,γ 261 39K(n,γ), 40Ca(n,p) 42K 12.36 h β−,γ 2.04 41K(n,γ), 42Ca(n,p) 41Ca 1.02×105 a EC 29.4 40Ca(n,γ) 45Ca 162.7 d β− 1.18 44Ca(n,γ) 49Ca 8.72 min β− 0.134 48Ca(n,γ) 54Mn 312 d EC,γ 0.835 54Fe(n,p) 56Mn 2.579 h β−,γ 0.141 56Fe(n,p) 55Fe 2.73 a EC 0.798 54Fe(n,γ)
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