Creating a baseline radiological standard for the waste isolation pilot plant underground

The Waste Isolation Pilot Plant (WIPP) is a deep underground geological repository for defense transuranic wastes. The creation of a full baseline radiological standard for the WIPP underground is essential in order to evaluate and account for the influence of the naturally occurring radioactive materials, and to prepare for any suspected contamination or the very unlikely event of a real accident scenario. In this report, we describe the establishment of the baseline information using the gamma background dose rate measurements and the salt rib smears of surface removable alpha and beta activities throughout the WIPP underground. The average background gamma dose rate in the WIPP underground is 8.27 x 10(-9) +/- 1.65 x 10(-9) Gy/h while the gamma dose rate on the WIPP surface is 3.46 x 10(-8) +/- 1.65 x 10(-9) Gy/h. The overall surface average alpha activity in the underground is 8.52 x 10(-5) +/- 1.22 x 10(-4) Bq/cm2 (at 1sigma level) with the minimum detectable activity (MDA) of 4.81 x 10(-4) Bq/cm2. The overall surface average beta activity is 8.25 x 10(-4) +/- 8.17 x 10(-4) Bq/cm2 (at 1sigma level) with the MDA of 3.19 x 10(-3) Bq/cm2. This baseline standard will be beneficial to the overall WIPP operational facility, ensuring the worker safety and adding to public confidence in the operation of the WIPP.     

Observed mass distribution of spontaneous fission fragments from samples of lime—an SSNTD study

SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements.     

聚变裂变混合堆处理高放超铀废物的研究

提出一个燃烧高放超铀废物的思路,即在外部聚变中子源驱动下,把燃烧超铀锕系元素和钍铀燃料循环相结合.并且设计相应的一维模型,使用开发的燃耗计算程序ONESN_BURN和新制作的数据库对模型进行计算和分析.通过计算,得到锕系元素的放射性,生物潜在危害因子,高放超铀锕系废物的密度和非常深的燃耗深度等.比较聚变裂变混合堆与传统的热堆,发现中子能谱越硬,对燃烧超铀锕系元素越有效.     

Axial Neutron Flux Evaluation in a Tokamak System: a Possible Transmutation Blanket Position for a Fusion–Fission Transmutation System

A sub-critical advanced reactor based on Tokamak technology with a D–T fusion neutron source is an innovative type of nuclear system. Due to the large number of neutrons produced by fusion reactions, such a system could be useful in the transmutation process of transuranic elements (Pu and minor actinides (MAs)). However, to enhance the MA transmutation efficiency, it is necessary to have a large neutron wall loading (high neutron fluence) with a broad energy spectrum in the fast neutron energy region. Therefore, it is necessary to know and define the neutron fluence along the radial axis and its characteristics. In this work, the neutron flux and the interaction frequency along the radial axis are evaluated for various materials used to build the first wall. W alloy, beryllium, and the combination of both were studied, and the regions more suitable to transmutation were determined. The results demonstrated that the best zone in which to place a transmutation blanket is limited by the heat sink and the shield block. Material arrangements of W alloy/W alloy and W alloy/beryllium would be able to meet the requirements of the high fluence and hard spectrum that are needed for transuranic transmutation. The system was simulated using the MCNP code, data from the ITER Final Design Report, 2001, and the Fusion Evaluated Nuclear Data Library/MC-2.1 nuclear data library.     

A new irradiated quartz for beta source calibration

For luminescence dating to be an accurate absolute dating technique it is very important that we are able to deliver absolutely known radiation doses in the laboratory. This is normally done using a radiation source (alpha, beta, X-ray) calibrated against an absolutely known reference source. Many laboratories have used the various different batches of Risø calibration quartz for the calibration of beta and X-ray sources, but these have been largely undescribed. Here we describe in detail the preparation and luminescence characteristics of a new quartz standard, based on a North Sea beach sand collected from south-western Denmark (Rømø). Two grain sizes (4–11 μm and 180–250 μm) have been examined in detail. These were pre-treated (annealed, dosed and annealed again) to sensitise and stabilise the luminescence signals before being given an absolutely known gamma dose from a point ¹³⁷Cs source in scatter-free geometry. The luminescence characteristics are described; the very intense blue-light stimulated signal is dominated by the fast OSL component and the IR-stimulated signal is negligible. The material is shown to be suitable for measurement using SAR, and the dose recovery ratio is indistinguishable from unity with a standard deviation of <2% for multi-grain aliquots. The material is also shown to be suitable for single-grain calibration, with >80% of the grains giving a useful signal. Although there is an unexplained dispersion in our calibration data of ∼3% (which we cannot attribute to instrument variability), we nevertheless conclude that this material is very suitable for transferring absolute known doses from a standardised gamma source to in-built irradiation sources.     

基于4H-SiC的高能量分辨率α粒子探测器

为突破传统半导体核探测器耐高温与抗辐照性能不足的瓶颈,采用4H-SiC宽禁带半导体材料研制了4H-SiC探测器,并研究其构成的探测系统对α粒子的能量分辨率和能量线性度。所研制4H-SiC探测器漏电流低,当外加反向偏压为200V时,其漏电流仅14.92nA/cm2。采用具有5种主要能量α粒子的226 Ra源研究其构成的探测系统对α粒子的能量分辨率,获得4H-SiC探测系统对4.8~7.7 MeV能量范围内α粒子的能量分辨率为0.61%~0.90%,与国际上报道的高分辨4H-SiC探测系统能量分辨率一致。同时,实验结果表明:4H-SiC探测系统对该能量范围内α粒子的能量线性度十分优异,线性相关系数为0.999 99。     

Relativistic corrections to the electric polarizability of compound systems

The widely used relation alpha; = alpha(0)+Deltaalpha for the electric polarizability, where Deltaalpha is proportional to the r.m.s. charge radius of the system, is revisited within a simple model of two spinless particles bound electromagnetically. A complete set of the relativistic corrections to alpha(0) following from the Breit Hamiltonian is obtained. It is shown that these corrections modify the result for alpha; in comparison to that obtained with alpha(0) taken in the nonrelativistic approximation. We propose that the same situation can take place in the more complicated case of hadrons. Special attention is devoted to the correct definition of the center-of-mass coordinates which are found to be very important.     

ICP-MS法对人发标物中超痕量稀土元素的均匀性检验

利用ＣＩＰ－ＭＳ法，对人发标物ＧＢＷ０９１０１中Ｌａ，Ｓｍ，Ｙ进行均匀性检验，采用ｔ检验法和Ｆ检验法的联用统计处理数据，检验结果表明瓶内和瓶间的均值与方差不存在显著性差异，证明样品是均匀的。     

Novel method for the production of spin-aligned RI beams in projectile fragmentation reaction with the dispersion matching technique

For high precision and accuracy in isotopic ratio measurement of transuranic elements using laser ablation assisted resonance ionization mass spectrometry, a dynamic correction method based on correlation of ion signals with energy and timing of each laser pulse was proposed. The feasibility of this dynamic correction method was investigated through the use of a programmable electronics device for fast acquisition of the energy and timing of each laser pulse.     

Probing the medium effect and isospin dependence of the in-medium nucleon--nucleon cross section in heavy ion collisions

Probing in-medium nucleon-nucleon （NN） cross section σ1/NN（α） in heavy ion collisions has been investigated by means of the isospin-dependent quantum molecular dynamics （IQMD） with the isospin- and momentum-dependent interaction （IMDI（T））. It is found that there are the very obvious medium effect and the sensitive isospin-dependence of nuclear stopping R on the in-medium NN cross section α1/NN（α） in the nuclear reactions induced by halo-neutron projectile and the same-mass stable projectile. However, R induced by the neutron-halo projectile is obviously lower than that induced by the corresponding stable projectile. In particular, there is a very obvious dependence of R on the medium effect of σ1/NN（α） in the whole beam energy region for the above two kinds of projectiles. Therefore, the comparison between the results of R＇s in the reactions induced by the neutron-halo projectile and the corresponding same-mass stable projectile is a more favourable probe for extracting the information of σ1/NN（α） because of adding a new judgement.[第一段]     

Intensity dependence of hydrogen Lyman alpha and Balmer alpha lines upon cathode material of an abnormal glow discharge

The results of the hydrogen L _a_{\alpha} 121.567 nm and H _a_{\alpha} 656.280 nm line intensity dependence upon cathode material of an abnormal glow discharge are reported. Under similar experimental conditions systematic variation of the L _a_{\alpha} and H _a_{\alpha} line intensity with the atomic number Z of cathode material (graphite, Ti, Fe, Cu, Zn, Pd, Ag, Pt, Au and Pb) is detected. Shapes of line intensity Z-dependences suggest that, apart from electron impacts, line excitation is related also to the back-scattering of fast hydrogen atoms from cathode and sputtering yield of cathode material. The excitation of H₂ molecular bands is not sensitive to these cathode processes.     

AFM tip gauge by nuclear tracks methodology

Atomic force microscopy (AFM) instrumentation in the different modes of operation is a metrologic system for evaluating some surface properties of solid and semisolid materials. The resolution of this instrument depends strongly on the tip sharpness, which can be changed by contamination of the AFM tip apex due to wearing and/or breaking. In order to assess new and old tips, scanning electron microscopy (SEM) inspection is often used, which is not very convenient due to the availability and demand of SEM services. In the market there are some expensive devices for verification of the tip geometry, and for the particular case of AFM in the tapping mode, a simple proposal has been published based on fiber-like samples. In this work, we present an AFM tip gauge device based on the use of a pattern of etched tracks on CR-39 material. For the preparation of the device, the requirements are a radioactive alpha particle source with specific energy, controlled temperature bath and KOH solution, with all these parameters optimized for the tip evaluation, based on the AFM profilometry image. This work shows another interesting and a very useful application of nuclear tracks methodology (NTM).     

The effect of metallic environment and low temperature on the 253Es α decay rate

In recent publications it has been pointed out that the α decay of transuranic elements in nuclear waste can be considerably speeded up by putting them into metals. The proposed mechanism is based on the effect of electron screening of radioactive nuclei (according to the Debye electron plasma model), which grows enhanced as temperature decreases. To verify the predicted phenomenon, half-lives of ²⁵³Es nuclei implanted in a metallic iron foil were measured at the temperature from 4 K to 50 mK. The results agree with the room-temperature data reported in the literature; no temperature dependence of the half-life was found within the error of ≈2%.     

Strength of the 18F(p,alpha)15O resonance at Ec.m. = 330 keV

Production of the radioisotope 18F in novae is severely constrained by the rate of the 18F(p,alpha)15O reaction. A resonance at E(c.m.)=330 keV may strongly enhance the 18F(p,alpha)15O reaction rate, but its strength has been very uncertain. We have determined the strength of this important resonance by measuring the 18F(p,alpha)15O cross section on and off resonance using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that its resonance strength is 1.48+/-0.46 eV, and that it dominates the 18F(p,alpha)15O reaction rate over a significant range of temperatures characteristic of ONeMg novae.     

OSL and TL in TLD-100 following alpha and beta irradiation: Application to mixed-field radiation dosimetry

The optically stimulated luminescence (OSL) of LiF:Mg,Ti (TLD-100) following irradiation by beta and alpha particles was investigated by measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. The OSL excitation spectra of all the samples following both beta and alpha irradiation are very similar.Identical emission bands with very similar relative intensities following both beta irradiation and alpha particle irradiation have been recorded in the OSL induced in nominally pure LiF mono and TLD-100 polycrystals. The identical excitation and emission bands in the doped and pure crystals are strong evidence indicating that the observed OSL is due to an intrinsic trapping structure. The OSL has indeed been previously attributed to F₂ centers and F₃⁺ centers.The preferential excitation of OSL compared to TL following high ionisation density (HID) alpha irradiation is naturally explained via the identification of OSL with the “two-hit” F₂ or F₃⁺ center, whereas the major component of composite TL glow peak 5 is believed to arise from a “one-hit” complex defect. This discovery allows near-total discrimination between HID radiation and low ionisation density (LID) radiation and may have significant potential in mixed-field radiation dosimetry.     

Strong coupling constant from scaling violations in fragmentation functions

We present a new determination of the strong coupling constant alpha(s) through the scaling violations in the fragmentation functions for charged pions, charged kaons, and protons. In our fit we include the latest e+e- annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and older, yet very precise, data from SLAC PEP at center-of-mass energy sqaure root of s = 29 GeV. At next-to-leading order, we find alpha(s)(5)(M(Z)) = 0.1170+/-0.0073. A new world average of alpha(s) is given.     

Quantum reflection times for attractive potential tails

When a wave packet with a narrow momentum distribution is quantum reflected in a purely attractive potential proportional to -1/r(alpha), alpha>2, it generally experiences a time gain compared to a free particle reflected at r=0; for alpha=3 and very low energies there are large time delays. In quantum reflection of an atomic beam by a surface, such a time gain (delay) represents an apparent plane of reflection which is shifted in front of (behind) the surface. The quantum reflected wave is always delayed with respect to the classical particle accelerated in the attractive potential.     

Backbone-only restraints for fast determination of the protein fold: the role of paramagnetism-based restraints. Cytochrome b562 as an example

CH(alpha) residual dipolar couplings (Deltardc's) were measured for the oxidized cytochrome b562 from Escherichia coli as a result of its partial self-orientation in high magnetic fields due to the anisotropy of the overall magnetic susceptibility tensor. Both the low spin iron (III) heme and the four-helix bundle fold contribute to the magnetic anisotropy tensor. CH(alpha) Deltardc's, which span a larger range than the analogous NH values (already available in the literature) sample large space variations at variance with NH Deltardc's, which are largely isooriented within alpha helices. The whole structure is now significantly refined with the chemical shift index and CH(alpha) Deltardc's. The latter are particularly useful also in defining the molecular magnetic anisotropy parameters. It is shown here that the backbone folding can be conveniently and accurately determined using backbone restraints only, which include NOEs, hydrogen bonds, residual dipolar couplings, pseudocontact shifts, and chemical shift index. All these restraints are easily and quickly determined from the backbone assignment. The calculated backbone structure is comparable to that obtained by using also side chain restraint. Furthermore, the structure obtained with backbone only restraints is, in its whole, very similar to that obtained with the complete set of restraints. The paramagnetism based restraints are shown to be absolutely relevant, especially for Deltardc's.     

A very compact Mach-Zehnder interferometer with left-handed material

A very compact Mach-Zehnder interferometer (MZI) composed of two parallel straight waveguides with left-handed material (LHM) layers is proposed. The operating principle and characteristics of the MZI with electro-optic material (EOM) core are analyzed by using the supermode theory and coupled mode theory. The result shows that regardless of material loss, a very compact MZI of only 0.87 mm × 0.022 mm can be achieved by utilizing EOM with ultrahigh electro-optic coefficient, which means a new way to fulfill a very compact electro-optic modulator or optical switch. The absorption effect of the proposed MZI is also analyzed by perturbation method which is generated by lossy LHM layers.     

Surface modification of Makrofol-DE induced by α-particles

In the present work, Makrofol DE samples were irradiated with different doses of alpha particles. The optical and mechanical modifications in the alpha-irradiated Makrofol samples as a function of alpha irradiation time have been investigated. Different characterization techniques, UV–vis spectroscopy, photoluminescence spectroscopy and Vickers micro hardness tester have been used. UV–vis spectra of bombarded samples reveal that the optical absorption increases with increasing the irradiation time. The direct and indirect optical band gap was found to decrease from 3.4 and 2.81?eV for pristine sample to 3.1 and 2.35?eV for that bombarded with alpha particles at the highest irradiation time (15?h), respectively. The number of carbon atoms per conjugated length (N) and the number of carbon atoms per cluster (M) have been estimated. An increase in both N and M with increasing the irradiation time was noticed. A remarkable decrease in PL intensity with increasing the alpha irradiation time was observed. This decrease is attributed to ion beam-induced change in molecular structure and/or defects in the modified layer. The surface hardness for unmodified and modified polymeric material has been studied.