裂变产额差异法测量~(235)U丰度

利用裂变产额差异法,从裂变产额质量分布曲线,选取位于双驼峰曲线两翼的裂变产物的产额随可裂变核素的不同有很大变化的核素88Rb、104Tc和92Sr作为测量对象,选择平均裂变产额比88Rb Y/104Tc Y、92Sr Y/104Tc Y为监测对象,研究了平均产额比与铀丰度之间的关系曲线,获得了平均产额比/i j Y Y随丰度H0变化的关系式Y1/Y2-f(H0)。利用两条关系曲线分别对72.2%的模拟样品测量5次,RSD均优于2%。将样品分析结果与无源γ射线法的结果相比较,两种方法在规定的误差范围内结果是一致的。     

中子活化法测定~(232)Th裂变产物产额

采用中子活化法测量了~(232)Th的裂变产物及其累积产额。利用加速器T(d,n)~4He反应产生的14.9 MeV高注量中子长时间照射ThO_2样品,用高纯锗γ谱仪测量其特征γ谱,求得较长半衰期核素~(99)Mo、~(141)Ce、~(143)Ce、~(131)I、~(140)Ba等的裂变产额,实验结果的典型误差为4%。其中,利用MCNP程序对中子的多次散射效应和自屏蔽效应进行修正,同时考虑了中子注量波动及γ射线在样品中的自吸收影响。     

0.57、1.0和1.5MeV中子诱发~(235)U裂变时~(95)Zr、~(140)Ba和~(147)Nd产额的绝对测量

用HPGeγ能谱法绝对测量0.57、1.0和1.5 MeV中子诱发235U裂变的裂变产物95Zr、140Ba和147Nd的产额。P型同轴HPGe探测器的体积为110 cm3,对60Co 1 332.5 keVγ射线的分辨率为1.8 keV。使用双裂变电离室监测裂变率,应用SPAN程序解析γ谱。对影响产额测量的主要因素进行了分析,并用MCNPIVB程序模拟计算了非主中子的影响。实验测得0.57 MeV中子诱发时,95Zr、140Ba、147Nd的产额分别为(6.64±0.21)%、(6.37±0.22)%、(2.37±0.08)%;1.0 MeV中子诱发时,95Zr、140Ba、147Nd的产额分别为(6.49±0.19)%、(6.35±0.18)%、(2.25±0.07)%;1.5 MeV中子诱发时,95Zr、140Ba、147Nd的产额分别为(6.59±0.19)%、(6.25±0.18)%、(2.37±0.07)%。对95Zr、140Ba、147Nd的产额随入射中子能量的变化趋势作了简要分析与讨论。     

强度平衡法测定138Csγ射线发射概率

短寿命裂变产物138Cs是测量裂变燃耗的重要核素,其半衰期为33.41min,经β-衰变到138Ba,共发射88条γ射线.根据母核衰变到子核基态上各种射线强度之和等于母核衰变活度的强度平衡法原理,用已标定好的峰效率曲线的HPGeγ谱仪准确测定了138Cs的γ射线发射概率,Pγ(1435.86keV)的测定结果为0.7599±0.0032.     

~(142)La活度及主要γ射线发射几率实验测量

利用数字符合方法对短寿命核素142La的活度和641 keV的γ射线绝对发射几率进行了实验测量。142La活度测量结果的合成标准不确定度小于0.46%,641.285 keV的γ射线发射几率测量结果为0.473±0.005(k=1),与《同位素表》第8版推荐数据0.474±0.005的相对偏差为-0.24%。此外,还依据γ射线发射几率测量工作中获取的数据,得到了142La的半衰期为(91.0±0.7)min,与《同位素表》第8版推荐数据(91.1±0.5)min的相对偏差小于0.2%。     

~(252)Cf自发裂变中子诱发~(235)U裂变时几个核素裂变产额的绝对测定

引言 在燃耗测量工作中,常应用质量产额曲线峰上的裂变产物核素作为监测体。一般说来,这些核素的裂变产额随入射中子能量的变化不灵敏。但是~(99)Mo的情况比较复杂。文献中~(235)U热中子裂变的产额数据相互符合得较好,但是裂变谱或快堆谱诱发裂变时,数据比较混乱,     

3MeV中子诱发~(238)U裂变的质量分布

本文叙述了用放化法和Ge(Li)直接γ能谱法测量3MeV中子诱发~(238)U裂变的裂变产额。测得了38个核素的产额值,其中9个核素的产额尚未见文献报道。用实验值描绘出的质量-产额曲线下的总产额为200.2％。在重峰A=134处存在精细结构峰,在轻峰A=101-103处观测到一小峰。     

燃料元件中~(235)U丰度的快中子诱发裂变测量方法研究

铀同位素丰度分析是确保核燃料元件在堆中安全可靠运行非常重要的质量控制环节。本文从裂变产额质量分布曲线图中,选取位于双驼峰曲线两翼的、裂变产物的产额随可裂变核素的不同有较大的变化的核素~(88)Rb、~(107)Rh、~(135)I作为测量对象,绘制了平均裂变产额比Y_((88 Rb))/Y_((107 Rh)、Y_(88 Rb)/Y_(135 I)与铀丰度之间的关系曲线。利用两条工作曲线对不同堆型元件的模拟样品进行了分析,并就元件包壳对分析结果的影响进行了理论和实验研究。为了验证方法的准确性,分别对3.03%的模拟样品测量了各5次,相对标准偏差(RSD)均小于5%。     

101Mo半衰期的测定

101Mo是测定核燃料裂变燃耗用的重要核素,但其半衰期文献值差异很大.详细阐述了用双HPGe探测器位置接续法测定101Mo半衰期的原理和过程,最后101Mo半衰期的测定结果为(14.86±0.02)min.     

142La半衰期的测定

142La是核燃料裂变燃耗测定用的重要核素,但其半衰期的文献值差异很大.本文详细阐述了用阱式HPGe探测器质量接续法和同轴型HPGe探测器连续跟踪法测定142La半衰期的原理和过程,测定结果为(90.78±0.16)min.     

低浓缩铀靶辐照后裂变核素产量的理论研究

用低浓缩铀靶代替高浓缩铀靶辐照进行⁹⁹Mo、¹³¹I等医用放射性核素生产是一个必然的趋势。本文利用输运计算程序DRAGON研究了靶件²³⁵U富集度、中子注量率、辐照时间对⁹⁹Mo、¹³¹I、⁹⁰Sr、⁹⁵Zr、²³⁹Pu等核素比活度变化的影响,以及不同²³⁵U富集度下裂变体系组成和总比活度的变化规律。计算结果表明,本文考察的10余种核素比活度的变化随辐照时间的不同而有所不同,其中⁹⁹Mo、¹³¹I、¹⁴⁷Nd和¹³³Xe等核素的比活度可快速达到饱和,⁸⁹Sr、¹⁰³Ru、⁹⁵Zr和¹⁴¹Ce等缓慢达到饱和,而⁹⁹Tc、⁸⁵Kr和⁹⁰Sr、²³⁹Pu在计算时间内达不到饱和,但所有核素的比活度随时间的变化趋势与靶件²³⁵U富集度无关;⁹⁹Mo、¹³¹I、⁹⁰Sr、⁹⁵Zr等核素的比活度均随靶件²³⁵U富集度提高而增加,而²³⁹Pu比活度则随着靶件富集度的减少而显著增加,提示改用低浓缩铀靶进行⁹⁹Mo、¹³¹I等医用放射性核素生产时应特别关注²³⁹Pu带来的影响;核素比活度随中子注量率的增加而线性增加,且斜率基本相同;靶件辐照时间的改变不会明显影响裂变体系的组成,在低浓缩铀（²³⁵U含量≤20%）区域,靶件²³⁵U富集度对裂变体系的组成影响很小。     

Analyses with latest major nuclear data libraries of the fission rate ratios for several TRU nuclides in the FCA-IX experiments

In the 1980s, a series of integral experiments was conducted in FCA-IX assemblies with systematically changed neutron spectra covering from the intermediate to fast ones. The experiments provide systematic data of central fission rates for TRU nuclides containing minor actinides, ²³⁷Np, ²³⁸Pu, ²³⁹Pu, ²⁴²Pu, ²⁴¹Am, ²⁴³Am, and ²⁴⁴Cm. Regarding the fission rate ratios relative to ²³⁹Pu, benchmark models had been recently developed for validation of nuclear data for the TRU's fission cross sections. In this paper, the latest major nuclear data libraries, JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2, are compared on the benchmark models. For the libraries, the analyses by a Monte Carlo calculation code show obvious overestimations particularly for the fission rate ratios of ²⁴⁴Cm to ²³⁹Pu. Additionally, a large discrepancy about by 20% between the libraries is revealed for the fission rate ratio of ²³⁸Pu to ²³⁹Pu measured in the intermediate neutron spectrum. The causes of discrepancies are furthermore clarified by sensitivity analyses.     

热中子诱发239Pu裂变初级裂变产物质量分布测量

原子核裂变是最复杂的物理过程之一,至今仍缺乏可以统一描述裂变前和裂变后过程的理论。中子诱发239Pu裂变产额数据是重要的核数据,完整的初级裂变产物质量分布数据有助于完善裂变理论模型并提高产额评价数据的质量。本文研制了初级裂变产物鉴别谱仪（FFIS）,通过屏栅电离室和微通道板时间探测器分别测量裂变碎片的动能和飞行时间,基于动能 速度关联的方法直接获得碎片放中子后的质量分布,在BNCT医院中子照射器（IHNI 1）上开展了热中子诱发239Pu裂变初级裂变产物的质量分布测量。测量结果表明,对轻峰碎片质量分辨约为1 amu,对重峰碎片质量分辨约为15 amu。239Pu(nth,f)初级裂变产物质量分布的精确测量可为裂变产额理论计算和评价提供重要的实验数据。     

Energy Dependence of Plutonium Fission-Product Yields

A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured ²⁴⁰Pu spontaneous fission and thermal-neutron-induced fission of ²³⁹Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + ²³⁹Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.     

Estimation of 239Pu independent and cumulative fission product yields from the chain yield data using a Bayesian technique

The independent and cumulative fission product yields (FPYs) are obtained by using the Bayesian technique based on the evaluated mass chain yield, where required constraints such as the normalization can be straightforwardly included. We apply this technique to the ²³⁹Pu FPY data at neutron incident energies of 0.5, 2.0, and 14 MeV, where the most updated mass chain yield ENDF/B-VII.1 data are available. The obtained yield data are compared with the evaluated values by England and Rider in ENDF/B-VI, and differences from their values are investigated. We show that the modern decay data used, such as branching ratios to ground and metastable states, cause differences in the evaluated individual and cumulative fission yields.     

Gamma-ray energy release in the decay of fission products

Total disintegration rate, gamma-ray energy release rate and energy spectrum of the fission products of ²³⁵U, ²³⁹Pu, ²⁴¹Pu, and ²³³U by thermal neutrons, and ²³⁵U, ²³⁸U, ²³⁹Pu and ²³²Th by fission spectrum neutrons have been reevaluated as a function of reactor operating times from 10² to 10⁸ sec after shutdown. Decay scheme data were taken mainly from the Table of Isotopes [1] and fission yields from Meek and Rider's 1972 recommendations [2]. Gamma energy releases do not depend strongly on the incident neutron energy, and those for ²³⁹Pu and ²⁴¹Pu are much different from that for ²³⁵U. Soon after fission, the present values for burst fission are lower than those of Perkins [3], but agree after 10⁴ sec and agree better with the experimental results of Sugarman et al. [4] and Borst [5]. The calculated data are tabulated in detail to facilitate interpolation.     

Fission-product yields from neutron-induced fission

Exsting experimental thermal, fast, and 14-MeV neutron-induced fission-product cumulative and independent yieds have been compiled, corrected to common reference values, and listed in tabular form for the following fissile nuclides:Thermal-neutron fission: cumulative yields for ²²⁷Th, ²²⁹Th, ²³³U, ²³⁵U, ²³⁹Pu, ²⁴¹Pu, ²⁴¹Am, ²⁴²Am, ²⁴⁵Cm, ²⁴⁹Cf, ²⁵¹Cf, ²⁵⁴Es, and ²⁵⁵Fm; independent yieds for ²³³U, ²³⁵U, ²³⁷Np, ²³⁸U, and ²³⁹Pu.Fast-neutron fission: cumulativ yields for ²²⁷Ac, ²³¹Pa, ²³²Th, ²³³U, ²³⁵U, ²³⁷Np, ²³⁸U, and ²³⁹Pu; independent yields for ²³⁵U and ²³⁸U.14-MeV-neutron fission: cumulative yields for ²³¹Pa, ²³²Th, ²³³U, ²³⁵U, ²³⁷Np, ²³⁸U, and ²³⁹Pu; independent yields for ²³²Th, ²³³U, ²³⁵U, ²³⁸U, and ²³⁹Pu.11-MeV-neutron fission: cumulative yields for ²³²Th.3-MeV-neutron fission: cumulative yields for ²³¹Pa, ²³²Th, and ²³⁸U.1.1-MeV-neutron fission: cumulative yields for ²³⁷Np.From these experimental values the unknown independent yields are deduced empirically for thermal-neutron fission of ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu; the fast fission of ²³²Th, ²³³U, ²³⁵U, ²³⁸U, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu (the chain yields for ²⁴⁰Pu and ²⁴¹Pu used at this energy being predictions); and the 14-MeV-neutron fission of ²³²Th, ²³³U, ²³⁵U, and ²³⁸U.Finally, by the fitting of the preceding information to condition equations derived from the conservation laws, adjusted sets of chain and independent yields are calculated for thermal fission of ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu; fast fission of ²³²Th, ²³³U, ²³⁵U, ²³⁸U, ²³⁹Pu, and ²⁴¹Pu; and 14-MeV fission of ²³²Th, ²³³U, ²³⁵U, and ²³⁸U. The literature search is probably complete to the end of 1975; some 1976 results are included.This paper replaces and makes obsolete the following UKAEA reports: AERE-R7209, AERE-R7394, AERE-R7680, and AERE-R8152.     

能谱变化对239Pu裂变室测量快中子注量的影响

热中子和共振区的中子在快中子临界装置中所占的份额很小,但是由于其相对大的截面,在慢化物存在的情况下,热中子和共振中子份额的微小变化,对^239Pu裂变室测量中子注量的结果影响很大。通过测量^239Pu裂变电离室在包镉和包硼、周围有无慢化物等情况下的反应率,Au、In活化片的镉比,S活化片在能谱变化下与^239。Pu的反应率比等,分析了快中子临界装置中热中子和共振区中子的分布,讨论了中子能谱变化对^239Pu裂变室测量快中子注量的影响及解决办法。     

Radioactivity of fission product and heavy nuclides deposited on soil in Fukushima Dai-Ichi Nuclear Power Plant accident

Based on periodically performed radioactivity measurements on soil samples in the site of Fukushima Dai-Ichi Nuclear Power Station, activity ratios to ¹³⁷Cs of fission product and heavy nuclides were obtained for Sr, Nb, Mo, Tc, Ru, Ag, Te, I, Ba, La, Pu, Am, and Cm isotopes. By exponentially fitting or averaging, the activity ratios at the core shutdown were estimated. Using correlations of activity ratios of ¹³⁴Cs to ¹³⁷Cs, and ²³⁸Pu to the sum of ²³⁹Pu and ²⁴⁰Pu against fuel burnup, burnup of the fuel sourcing the deposited activity of the soil was estimated. The activity ratios to ¹³⁷Cs of each nuclide on the deposited activity were divided by those calculated on the fuel at the shutdown to obtain the deposited activity fraction of each nuclide as a relative value to ¹³⁷Cs, which also corresponds to the deposited fraction of each element as a relative value to Cs. The obtained deposited fractions relative to Cs are the orders of 10^?4 to 10^?2 for Sr, 10^?5 to 10^?3 for Nb, 10^?2 to 10^?1 for Mo, 1 to 10 for I, 10^?3 to 10^?2 for Ba, 10^?2 for La, 10^?6 to 10^?3 for Pu, 10^?6 to 10^?4 for Am, and 10^?7 to 10^?5 for Cm. The deposited fractions for Tc, Ag, and Te were not estimated due to the lack of the calculated inventories in the fuel for the relevant measured radioactive nuclides.