79Se—AMS测量样品的化学形式选择及其制备方法

中国原子能科学研究院的AMS小组在原蒋菘生、何明等对79Se—AMS测量的基础上,发展了基于SeO2-分子负离子引出形式的79Se—AMS测量方法,测量灵敏度由原来的3．0×10^-9提高到好于1．0×10^-12。     

利用加速器质谱学中的入射离子X射线方法测定79Se的半衰期

利用加速器质谱学中的入射离子X射线方法(PX-AMS)对79Se的半衰期进行了测定.用这一直接测量79Se原子数的方法得到新的79Se半衰期为(2.80±0.36)×105a.利用同样的方法也测定了75Se的半衰期,75Se半衰期的测定结果显示利用PX-AMS方法对79Se半衰期的测定结果是可靠的.     

79Se-AMS示踪研究亚毒性剂量亚硒酸钠摄入的硒代谢

长寿命放射性核素79Se的半衰期长达2．8×10^5a，其放射性比活度（单个原子的活度）约1×10^-14Bq。79Se衰变时仅放射出能量为150．7keY纯β射线，对生物组织甚至细胞的辐射损伤远小于75Se，而79Se的加速器质谱测量方法（795e—AMS）具有灵敏度高、相对测量准确性高以及测量精度高等特点，因而适合于长周期、无损伤的生物示踪研究。     

中国原子能科学研究院的AMS测量与应用研究

AMS作为一种超高灵敏的核素测量手段,目前在国际上成为一种十分活跃的研究领域。到2002年底,国际上有近50个AMS装置开展测量与应用研究工作。中国原子能科学研究院基于HI-13串列加速器的AMS装置1989年在我国首次建成。可进行~(10)Be、~(36)Cl、~(26)Al、~(129)I、~(79)Se等核素的测量与应用研究。目前有研究项目与合作研究项目十余个,国际国内的合作伙伴有十多家。研究内容主要集中在AMS测量技术与应用研究两个方面。     

79Se的AMS测量方法研究

测定⁷⁹Se时由于⁷⁹Se尚无标准样品,需要建立⁷⁹Se/Se（⁷⁹Se、Se原子个数比,余同）的AMS测量方法。在⁷⁹Se/Se的绝对测定中,为尽可能避免测量Se的同位素之间的差异,通常利用探测器测量⁷⁹Se离子,本文用法拉第筒对⁷⁸Se和⁸⁰Se进行测量,但这造成两个测量系统之间的系统误差。为避免这种系统误差,利用同一探测器测定⁷⁹Se、⁷⁸Se和⁸⁰Se。考虑到⁷⁸Se和⁸⁰Se的计数率非常高,在CIAE-AMS系统中的静电分析器前和靶室内安装衰减片以降低⁷⁸Se和⁸⁰Se的计数率。实验结果表明：通过两个衰减片的衰减作用,能将⁷⁸Se和⁸⁰Se的束流降低到半导体探测器的检测范围内,实现了样品中⁷⁹Se/Se的绝对测定,得到⁷⁹Se/Se为(2.08±0.10)×10^-7,为准确测定⁷⁹Se半衰期奠定了基础。     

放化分析高放废液1AW中的~(78)Se

应用以溴化硒蒸馏和元素硒沉淀为主要步骤的放化流程,从高放废液1AW中分离出纯的~(79)Se。应用低本底液闪谱仪测量~(79)Se,得到了1AW中~(79)Se的含量。     

Se在北山花岗岩地下水中的化学形态及浓度控制分析

利用地球化学模拟软件GWB(Geochemist’s Workbench),研究了Se在我国高放废物预选场址北山花岗岩地下水中的化学形态及浓度控制因素。结果表明,Eh和pH对Se的化学形态影响较大,在处于弱碱性的北山花岗岩地下水中,溶解态的Se主要以SeO32-、HSeO3-和HSe-的形式存在。北山花岗岩地下水属于高矿化水,在保持地下水组分不变的情况下,当固定Eh为0mV,pH在5～12之间变化时,Se浓度主要受Se(0)、CuSe2、Cu3Se2或CuSe等矿物的沉淀所控制;当固定pH为7.56,硒浓度随Eh变化则主要受FeSe2、Se(0)、CuSe2、Cu3Se2或CuSe等矿物的沉淀所控制。与Fe2+相比,Cu2+更易与Se反应形成沉淀。从本文的模拟结果来看,由于Se在北山花岗岩地下水中易形成硒-矿物沉淀,使得溶液中的Se浓度能维持在较低水平,因此有利于阻滞对氧化还原条件敏感的核素79Se的迁移。     

晕核体系~6He+~(64)Zn的光学势的能量相依性

正在近垒能区测量了单质子转移反应~(63)Cu(~7Li,~6 He)~(64)Zn的角分布,以抽取并研究晕核缚体系~6 He+~(64)Zn光学势的性质。由于受放射性束流强度和品质的限制,很难通过直接的弹性散射测量来抽取晕核体系的光学势。因此,采用转移反应作为间接的方法研究晕核体系的光学势。实验在中国原子能科学研究院的HI-13串列加速器上完成,束流7Li的能量分别为E_(lab)(~7Li)=12.67、15.21、16.33、23.30、27.30以及30.96 MeV。对测量得到的~(63)Cu(~7Li,~6 He)~(64)Zn转移反应角分布     

HI-13串列加速器离子源环境中K本底初探

加速器离子源环境中的K本底是影响AMS测量40K灵敏度的关键因素。实验采用高纯Cu(99.9999%,K含量低于8×10-9)对HI-13串列加速器离子源中的K本底进行了初步调查。在实验中,离子源靶锥由高纯Cu直接制成。靶锥表面经过1h的离子源Cs束溅射后,在加速器低能端和AMS终端分别测量63Cu的     

Determination of ^129I in IAEA-375 Reference Material

^79Se是一长寿命、纯β裂变产物核素，β能量为0．151MeV。^79Se半衰期已被测量过5次，每次测得数据间在误差范围内不吻合。随着新的测量手段的不断涌现，对^79Se半衰期重新进行测量很有必要。     

Measurement of 79Se by accelerator mass spectrometry using projectile X-ray technique

1IntroductionInacceleratormassspectrometry(AMS)measurementsoflong-livedradioisotopes,stableisobarsarethedominantbackground.FortheradioisotopesofatomicnumberZ520,theisobarsbackgroundcanbeeliminatedbymeansofthedifferentenergylossofisobarinmatterduetotherateofenergylossisafunctionofZ.Butwithincreasingatomicnumber,theenergystragglingincreasesrelativetotheenergylossdifference,sothatisobarseparationbecomesprogressivelylesseffective.Inordertoseparatetheisobarswithhigheratomicnumberstheionenergyhast…     

Absolute determination of 79Se/80Se with AMS

Selenium-79 measurement with accelerator mass spectrometry (AMS) is increasingly being used for the determinations of ⁷⁹Se relevant nuclear data. Furthermore, ⁷⁹Se was deemed to be an ideal tracer nuclide for long-period and non-intrusive biological studies on selenium. An ultra-sensitive AMS measurement method of ⁷⁹Se has been established at the CIAE-AMS system. For further applications of ⁷⁹Se-AMS, reference standards were requested. ⁷⁹Se can be derived from the ⁷⁸Se(n, γ)⁷⁹Se reaction but cannot be accurately quantified by theoretical calculation owing to the small and dubious cross section and other relevant parameters. In this paper, an AMS method has been developed for the absolute determination of the ⁷⁹Se/⁸⁰Se ratio in a ⁷⁹Se sample with relatively high ⁷⁹Se content. The relative standard uncertainty of ⁷⁹Se/⁸⁰Se ratio is 4.7% and a reference standard is thus acquired. The results are favourable for further applications of ⁷⁹Se-AMS.     

Isobaric identification techniques of AMS at CIAE

Some long-lived nuclides, such as ³⁶Cl, ⁴¹Ca, ⁵³Mn, ⁷⁹Se, etc., are very interested in life science, environment science, geo- and cosmo-sciences, nuclear wastes management, and other fields. Taking the advantages in high sensitivity and the strong ability to reduce the interferences from molecular ions and isobars, AMS has been one of the most promising methods for the measurement of these nuclides. However, the sensitivity of AMS is often unsatisfactory due to the interferences of stable isobars especially for medium and heavy radioisotopes. Gas-filled time of flight (GF-TOF), Gas-filled Magnet with a time of flight (GFM-TOF), Bragg Curve detector and energy loss (ΔE) combined with a Q3D magnetic spectrometer (ΔE-Q3D) are among the techniques used or being developed in AMS lab of China Institute of Atomic Energy, in an attempt to further reduce the interferences from isobars. These techniques will be tested in our AMS measurement of ⁵³Mn, ⁷⁹Se, ⁹³Zr, ⁹⁹Tc, etc., for identifying isobaric interferences.     

重核离子束成分的加速器质谱分析

为拓展加速器质量技术测量范围及测量放射性核束成分,建立了利用入射离子发射特征Ｘ射线鉴别同量异位素的方法,开展了利用ＡＭＳ测量重核离子束成分的工作。     

Nuclear Data Sheets for A=75

The experimental nuclear data for mass=75 have been reviewed, superceding 1981 evaluation by Ekstrom (81Ek02). Detailed level and decay schemes together with summary (adopted), arguments for Jπ assignments and experimental data of the known nuclei (Cu, Zn, Ga, Ge, As, Se, Br, Kr, Rb) are presented. ⁷⁵Cu has been identified as a β⁻ delayed neutron emission precursor while ⁷⁵Ga has been studied in detail in ⁷⁵Zn β⁻ decay recently. In ⁷⁵Ge, there are quite a few new data available, specially on particle-transfer reactions. Not much new information is known for ⁷⁵As except for a particle transfer reaction and ⁷⁵Se ε decay. The same is true for ⁷⁵Se except for a neutron capture study. New data have been reported for ⁷⁵Kr and ⁷⁵Br.     

Measurement of the 77Se(γ, n) cross section and uncertainty evaluation of the 79Se(n, γ) cross section

The ⁷⁷Se (γ, n) cross section was measured for the energy range from 7.6 to 13.8 MeV by using quasi-monochromatic laser-Compton scattering γ-rays. The advanced method to deduce γ-ray strength functions from (γ, n) cross section was developed. By utilizing the method, the γ-ray strength functions of ^{77, 78, 80}Se were deduced so as to reproduce the ^{77, 78, 80}Se (γ, n) cross sections measured in this work and previous systematic measurements. The inverse (n, γ) cross sections for ^{76, 77, 79}Se isotopes were calculated using the statistical model calculation code CCONE with the deduced γ-ray strength functions. The uncertainty of the calculated ⁷⁹Se(n, γ)⁸⁰Se cross section was evaluated by comparing the calculations and the experimental data on ^{76, 77}Se (n, γ) cross sections.     

裂片核素在岩石中的迁移研究 Ⅰ.核素~(75)Se在花岗岩和石灰岩中的扩散行为

高水平放射性废物处置的主要方法是深埋在地质岩石中。在研究放射性核素随地下水穿过岩石缝隙网的迁移中,扩散法起着重要的作用。本文测定了~(75)SeO_3~(2-)在花岗岩和石灰岩(取自北京郊区)中的扩散系数,并详细叙述了实验技术和分析方法。     

The 63Cu(n,2n)62Cu and 65Cu(n,2n)64Cu cross sections at 14.8 MeV

Measurements have been made of the ⁶³Cu(n,2n)⁶²Cu and ⁶⁵Cu(n,2n)⁶⁴Cu cross sections. Separated isotope targets were irradiated with 14.8 MeV neutrons and the resulting ⁶²Cu and ⁶⁴Cu activities were measured using both 4πβ-γ coincidence counting and by counting in coincidence the annihilation radiation produced following the β⁺-decay of ⁶²Cu and ⁶⁴Cu. The variation in the neutron flux and the neutron energy were measured during each single irradiation. Good agreement was obtained for the cross-section values using the two methods. However, the standard deviation of the mean of the ⁶⁵Cu(n,2n)⁶⁴Cu cross-section measurements was significantly greater when the 4πβ-γ coincidence method was used. The measurements were made relative to the ⁵⁶Fe(n,p)⁵⁶Mn cross section. Values of 549 ± 11 and 968 ± 20 mbarn were obtained using a value of 108.5 mbarn for the Fe cross section at 14.8 MeV.     

79Se半衰期计算

介绍了用log ft系统学计算⁷⁹Se半衰期的方法。根据系统学计算和与实验测量数据的比较，推荐了⁷⁹Se的半衰期。给出了⁷⁹Se衰变纲图并计算得到了⁷⁹Se辐射数据。 