电感耦合等离子体质谱(ICP-MS)法测定谷类产品中8种重金属元素

为建立大批量谷类产品中重金属元素的快速检测方法,采用快速消解法,样品于聚丙烯刻度离心管中经硝酸消解,用电感耦合等离子体质谱仪同时检测Pb、Cd、Cr、Cu、Zn、Ni、As、Hg等8种重金属元素含量。研究了消解酸用量及消解时间对结果的影响,并优化了仪器工作参数。研究结果表明,样品在120℃消解1 h后直接定容测定,各元素在实验浓度范围内线性良好,相对标准偏差RSD值1.1%～7.2%,Pb、Cd、Cr、Cu、Zn、Ni、As、Hg各元素的方法检出限分别为0.02、0.000 3、0.03、0.02、0.08、0.01、0.002和0.000 4 mg/kg。试剂用量少、简便、快捷、准确性好,适用于电感耦合等离子体质谱法定量检测稻米、小麦、玉米等谷类产品中重金属元素的含量。     

Quasi-free electron scattering from 12C using Hartree-Fock wave functions

The energy spectrum and the angular correlation distributions for the reaction ¹²C(e, e'p)¹¹B are calculated within the framework of DWBA using spherical Hartree-Fock wave functions. A comparison with experiment and some of the earlier calculations is made. It is observed that a large spatial extent of the wave functions significantly improves the agreement.     

1MeV Si+衬底加温注入Al0.3Ga0.7As/GaAs超晶格和GaAs的晶格损伤研究

用卢瑟福背散射／沟道技术研究了１ＭｅＶＳｉ⁺在衬底加温和室温下以不同剂量注入Ａｌ_0.3Ｇ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ后的晶格损伤。在衬底加温下，观察到Ａｌ_0.3Ｇａ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ都存在一个动态退火速率与缺陷产生速率相平衡的剂量范围，以及两种速率失去平衡的临界剂量。超晶格比ＧａＡｓ更难以损伤，并且它的两种速率失去平衡的临界剂量也大于ＧａＡｓ中的相应临界剂量，用热尖峰与碰撞模型解释了晶格损伤积累与注入剂量和衬底温度的关系。用ＣＮＤＯ／２量子化学方法计算了ＧａＡｓ和Ａｌ_xＧａ_1-xＡｓ中化学键的相对强度，并根据计算结果解释了注入过程中Ａｌ_0.3Ｇａ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ中晶格损伤程度的差别。 关键词：     

Neutron moderation in a bulk sample and its effects on PGNAA setup geometry

In a prompt gamma ray neutron activation analysis (PGNAA) setup, the neutron moderation in the bulk sample also plays a key role. This can even dominate the thermalization effects of the external moderator in some cases. In order to study the neutron moderation effect in the bulk sample, moderators with two different sizes of the sample were tested at the King Fahd University of Petroleum & Minerals (KFUPM) PGNAA facility. In these tests, the thermal neutron relative intensity and prompt gamma ray yield from the two moderators were measured using nuclear track detectors (NTDs) and NaI detector, respectively. As predicted by Monte Carlo simulations, the measured intensity of thermal neutron inside the large sample cavity due to the external moderator was smaller than that from the smaller sample cavity. Due to its larger size, additional thermalization of neutrons will take place in the larger sample. In spite of smaller thermal neutron yield from the external moderator at the large sample location, higher yield of the prompt gamma ray was observed as compared to that from the smaller sample. This confirms the significance of neutron moderation effects in the bulk sample and can thereby affect the PGNAA geometry size. This allows larger samples in conjunction with smaller moderators in the PGNAA setup.     

PSORALEN-PHOTOSENSITIZED DAMAGE OF RAT PERITONEAL EXUDATE CELLS

Psoralen-sensitized photodamage (PUVA) of rat peritoneal exudate cells was investigated. Quartz-activated luminol-dependent chemiluminescence (ChL) was registered and the amount of trypan-positive cells was determined. Irradiation of peritoneal exudate cells in the presence of psoralen resulted in a dose-dependent monotonous inhibition of ChL. The reciprocity law of irradiation intensity and duration of irradiation was not valid for the observed inhibition of ChL: the inhibition increased with higher intensity. When psoralen previously photooxidized in ethanol (POP) was added to peritoneal exudate cell suspension, a double-phase response depending on psoralen irradiation dose was obtained: ChL activation was observed at low doses of UVA, ChL inhibition at high doses. Chemiluminescence inhibition correlated well with the increase in the number of trypan-positive cells. It may be supposed that the observed effects of PUVA or POP treatment are caused by cell cytoplasmic membrane damage.     

State selective laser photodissociation of Tl2 at 337.1 nm by optogalvanic spectroscopy

This paper reports the first time achievement of laser photolysis of thallium dimers by single photon absorption of N₂-laser light at 337.1 nm resulting in a large population inversion of thallium 7 ²S excited state with respect to 6 ²P state. The photodissociation nitrogen laser pulse is spatially and temporally overlapped with the tunable dye laser pulse that is used for confirming the production of selectively excited thallium atoms. The dye laser excites the thallium atoms from 7 ²S state to high lying Rydberg states that collisionally ionize giving an ion-current signal which is subsequently processed by a box-car average/integrator and recorded on the chart recorder. The photodissociation of Tl₂ to Tl(7 ²S ) state demonstrates the existence of the molecular dissociative state 1g that is correlated with Tl 7 ²S +6 ²P states. A complete absence of 6 ²P state population among the photolysis products indicates a 100% prompt population inversion between 7 ²S and 6 ²P atomic states.     

An241Am−Be source based thermal neutron activation analysis facility at KFUPM

An instrumental thermal neutron activation analysis facility based, on a 16 Ci²⁴¹ Am–Be source, a high resolution -ray spectrometry setup and a PC-based data acquisition system at KFUPM is described. The thermal neutron flux distribution was determined from the induced activities of high purity indium foils. The absolute thermal neutron flux was calculated from the activities of bare and cadmium-covered gold foils at a position of 3 cm from the soource at which the flux reaches a maximum. The facility tests were carried out with the determination of manganese concentrations in six types of industrially important steel samples. The result of 1.33% manganese in SS-304 steel sample was in excellent agreement with the literature value. The method is nondestructive, economical and ideal for bulk analysis.     

Measurements of sub-nanosecond lifetimes by means of nanosecond laser pulses

It is shown that the lifetimes of excited states of molecules which give a reasonably strong absorption (molar decadic extinction coefficient ∈ > 10⁴M^?1cm^?1) at the frequency of the ruby laser can be determined from the saturation of the optical transitions. This is illustrated for DDI (1,1'-diethyl-2,2'-dicarbocyanine iodide) in glycerol, which appears to have a lowest excited state with a lifetime of 110 psec. This value agrees fairly well with that calculated from the formula for the rate of internal conversion derived from Siebrand's work. Under favourable conditions lifetimes as short as 10 psec can be measured.