LaBr3(Ce)元件破损在线监测关键核素确定及效率校准

常用的元件破损在线监测方法受外在因素影响较大，以γ能谱中关键裂变产物核素比活度进行在线定量分析是一种可靠的元件破损监测方法。针对新型LaBr₃(Ce)元件破损监测仪，设计了元件破损模拟实验，对逸出的裂变产物采用HPGe和LaBr₃(Ce)探测器进行了对比测量。通过不同冷却时间γ能谱的核素分析，确定了¹³⁵Xe，⁸⁸Kr，¹³⁸Xe，⁸⁸Rb，¹³⁸Cs等可作为LaBr₃(Ce)元件破损γ能谱监测的关键核素。同时，制备了覆盖能量范围(250～2 400)keV，含⁶⁰Co，¹³⁷Cs，¹³³Ba；²⁴¹Am，¹⁵²Eu；¹⁰⁹Cd，⁸⁸Y，⁵⁷Co及²⁴Na的4组放射性标准溶液，在建立的效率校准系统上，校准了LaBr₃(Ce)在线监测仪的效率。在反应堆一次异常情况分析中，已校准的LaBr₃(Ce)元件破损监测仪对关键核素的现场分析结果与HPGe的取样分析结果一致，表明效率校准结果准确，校准方法可靠。     

LaBr3(Ce)元件破损在线监测关键核素确定及效率校准

常用的元件破损在线监测方法受外在因素影响较大，以γ能谱中关键裂变产物核素比活度进行在线定量分析是一种可靠的元件破损监测方法。针对新型LaBr₃(Ce)元件破损监测仪，设计了元件破损模拟实验，对逸出的裂变产物采用HPGe和LaBr₃(Ce)探测器进行了对比测量。通过不同冷却时间γ能谱的核素分析，确定了¹³⁵Xe，⁸⁸Kr，¹³⁸Xe，⁸⁸Rb，¹³⁸Cs等可作为LaBr₃(Ce)元件破损γ能谱监测的关键核素。同时，制备了覆盖能量范围(250～2 400)keV，含⁶⁰Co，¹³⁷Cs，¹³³Ba；²⁴¹Am，¹⁵²Eu；¹⁰⁹Cd，⁸⁸Y，⁵⁷Co及²⁴Na的4组放射性标准溶液，在建立的效率校准系统上，校准了LaBr₃(Ce)在线监测仪的效率。在反应堆一次异常情况分析中，已校准的LaBr₃(Ce)元件破损监测仪对关键核素的现场分析结果与HPGe的取样分析结果一致，表明效率校准结果准确，校准方法可靠。     

Solar radiation variability in the last 1400 years recorded in the carbon isotope ratio of a mediterranean sea core

We present measurements and data analysis of the carbon stable isotopes (δ¹³C) in the planktonic Globigerinoides ruber extracted from the GT90/3 shallow water Ionian sea core, dated with high precision. It is commonly accepted that δ¹³C variations in symbiontic foraminifera mainly record the effects of productivity and of photosynthetic activity, varying with the ambient light level. Therefore from this time series we can deduce information on the sea surface illumination at the time of the planktonic foraminifera growth. The profile (359 points) covers the period 590–1979 AD, with a resolution of 3.87 years and it is an extension of the time series (215 points) previously published in this journal. The spectral analysis of the longer time series confirms the presence of the 11 y signal, with amplitude 0.08‰ (peak-to-trough), found in the shorter time series in phase with the sunspot solar cycle; furthermore it shows the presence of two centennial cycles of 100 and 200 years, with amplitude 0.08‰ and 0.02‰ respectively. These components are identified at high significance level by Monte Carlo singular spectrum analysis (MC-SSA). A comparison between the δ¹³C profile and the historical aurorae series (600–1500 AD) shows that the long-term δ¹³C variations are at least partially generated by the solar activity modulation and in phase with the solar output, as represented by the solar wind interaction with the magnetosphere.     

The 2.5 to 5 microns spectrum of comet Halley from the IKS instrument of Vega

Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H₂O and CO₂ molecules have been detected with production rates of 10³⁰ s⁻¹ and 1.5 10²⁸ s⁻¹ respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H₂O 0.2. OH emission and H₂O - ice absorption might also be present in the spectra.     

Hot atoms in cosmic chemistry

High energy chemical reactions and atom molecule interactions might be important for cosmic chemistry with respect to the accelerated species in solar wind, cosmic rays, colliding gas and dust clouds and secondary knock-on particles in solids. “Hot” atoms with energies ranging from a few eV to some MeV can be generated via nuclear reactions and consequent recoil processes. The chemical fate of the radioactive atoms can be followed by radiochemical methods (radio GC or HPLC). Hot atom chemistry may serve for laboratory simulation of the reactions of energetic species with gaseous or solid interstellar matter. Due to the effective measurement of 10⁸–10¹⁰ atoms only it covers a low to medium dose regime and may add to the studies of ion implantation which due to the optical methods applied are necessarily in the high dose regime.

Experimental results are given for the systems: C/H₂O (gas), C/H₂O (solid, 77 K), N/CH₄ (solid, 77K) and C/NH₃ (solid, 77 K). Nuclear reactions used for the generation of 2 to 3 MeV atoms are: ¹⁴N(p, ) ¹¹C, ¹⁶O(p, pn) ¹¹C and ¹²C(d,n) ¹³N with 8 to 45 MeV protons or deuterons from a cyclotron. Typical reactions products are: CO, CO₂, CH₄, CH₂O, CH₃OH, HCOOH, NH₃, CH₃NH₂, cyanamide, formamidine, guanidine etc. Products of hot reactions in solids are more complex than in corresponding gaseous systems, which underlines the importance of solid state reactions for the build-up of precursors for biomolecules in space. As one of the major mechanisms for product formation, the simultaneous or fast consecutive reactions of a hot carbon with two target molecules (reaction complex) is discussed.     

Diurnal variations of ion flux intensity on a synchronous orbit

The data from the synchronous-orbit satellites of the Gorizont series are used to study the dependences of the ion flux variation amplitudes in the synchronous altitude region (the diurnal behaviour) on particle energies and on the form and rigidity of the particle energy spectrum. The proton fluxes were measured in the energy range E 60–120 keV, and the [N,0]²⁺ and [C,N,0]⁴⁺ ion fluxes in the energy range E 60–70 keV/e.

The ratio of the diurnal variation amplitudes of the studied ions is shown to correspond to the similarity of their energy spectra in the E/Q representation. The magnetically-quiet time gradient of the distribution function F(μ,J,L) in the synchronous-orbit region is shown to be (∂F/∂L)=0 for the H⁺ and [N,0]²⁺ ions and (∂F/∂L) > 0 for the [C,N,0]⁴⁺ ions (at the values of μ corresponding to the examined energy ranges). During magnetically-disturbed periods the inner boundary of the (∂F/∂L)=0 region shifts to lower L and (∂ F/∂L) = O in the synchronous altitude region must be also for the [C,N,O]⁴⁺ ions.     

Effect of track structure and radioprotectors on the induction of oncogenic transformation in murine fibroblasts by heavy ions

The oncogenic potential of high-energy ⁵⁶Fe particles (1 GeV/nucleon) accelerated with the Alternating Gradient Synchrotron at the Brookhaven National Laboratory was examined utilizing the mouse C3H 10T1/2 cell model. The dose-averaged LET for high-energy ⁵⁶Fe is estimated to be 143 keV/μm with the exposure conditions used in this study. For ⁵⁶Fe ions, the maximum relative biological effectiveness (RBE_max) values for cell survival and oncogenic transformation were 7.71 and 16.5 respectively. Compared to 150 keV/μm ⁴He nuclei, high-energy ⁵⁶Fe nuclei were significantly less effective in cell killing and oncogenic induction. The prostaglandin E₁ analog misoprostol, an effective oncoprotector of C3H 10T1/2 cells exposed to X rays, was evaluated for its potential as a radioprotector of oncogenic transformation with high-energy ⁵⁶Fe. Exposure of cells to misoprostol did not alter ⁵⁶Fe cytotoxicity or the rate of ⁵⁶Fe-induced oncogenic transformation.     

金刚石13 C核子定位用参数可调动态解耦序列

针对金刚石内¹³C核自旋的逐个定位,提出了一种非均匀分布周期内对称的动态解耦序列--可调动态解耦（APDD）序列。针对该序列,进行了理论推导和仿真分析;并就¹³C核自旋定位精度指标,与目前金刚石内原子量子态操控使用最为广泛的CPMG （Carr-Purcell-Meiboom-Gill）脉冲序列和XY4序列进行了比较。结果表明,相比于CPMG序列与XY4序列,APDD序列可将单个¹³C核自旋的定位精度提高6.27倍。进一步研究表明,在单个周期内比值τ₁/τ介于0.51~0.58范围为APDD序列核子定位最优工作条件。因此,APDD序列能被用于控制毗邻金刚石中NV^-色心的核自旋,并且在量子信息和量子探测器领域有着重要的应用。     

Possible radio JETS in GX 1+4

GX 1+4 is an X-ray pulsar with a nominal period of 2 or 4 min. and has the highest of 0.22 yr⁻¹ among the X-ray pulsars. The source is identified with an optical counterpart V2116 Oph, however no binary period has been reported so far. There are several features of the source like , variable pulse shape, period history and the spectral changes which do not fit well with our present understanding of the source.

The radio observation of the galactic center region were made using Molonglo observatory Synthesis Telescope operating at a frequency of 843 MHz. A 12 hr observation was made with the field center at the position coordinates of the optical counterpart. No significant radio emission was seen corresponding to the center position.

The synthesis map however, showed the presence of two regions of radio enhancements almost equidistant from the optical source in the diametrically opposite directions/1/. The data is interpreted as due to synchrotron emission produced by the expanding jets of GX 1+4, similar to the radio jets observed in galaxies. Radio jets have been inferred for three galactic X-ray binary sources namely, Sco X-1, Cyg X-3, and SS 433. However, for all these sources no X-ray pulsation has been detected so far. The present observations if confirmed will be the first case of radio jets in a stellar system containing an X-ray pulsar.     

LMXB luminosity function and connection to globular cluster in early type galaxies

We derive bias-corrected X-ray luminosity functions (XLFs) of LMXBs detected in 14 E and S0 galaxies observed with Chandra. After correcting for incompleteness, the individual XLFs are statistically consistent with a single power-law. A break at or near L_X,Eddington , as previously reported, is not required in any individual case. The combined XLF with a reduced error, however, suggests a possible break at L_X = 5 × 10³⁸ erg s⁻¹, which may be consistent with the Eddington luminosity of neutron stars with the largest possible mass (3 M), or of He-enriched neutron star binaries. We confirm that the total X-ray luminosity of LMXBs is correlated with the the near-IR luminosities, but the scatter exceeds that expected from measurement errors. The scatter in L_X(LMXB)/L_K appears to be correlated with the specific frequency of globular clusters, as reported earlier.

We cross-correlate X-ray binaries with globular clusters determined by ground-based optical and HST observations in 6 giant elliptical galaxies. With the largest sample reported so far (300 GC LMXBs with a 5:2 ratio between red and blue GCs), we compare their X-ray properties, such as X-ray hardness, XLF and L_X/L_B and find no statistically significance difference between different groups of LMXBs. Regardless of their association with GCs, both GC and field LMXBs appear to follow the radial profile of the optical halo light, rather than that of more extended GCs. This suggests that while metallicity is a primary factor in the formation of LMXBs in GCs, there may be a secondary factor (e.g., encounter rate) playing a non-negligible role.     

Compact X-ray binaries in and out of core collapsed globulars

We review new Chandra and HST observations of the core collapsed cluster NGC 6397 as a guide to understanding the compact binary (CB) populations in core collapse globulars. New cataclysmic variables (CVs) and main sequence chromospherically active binaries (ABs) have been identified, enabling a larger sample for comparison of the L_x, F_x/F_V and X-ray vs. optical color distributions. Comparison of the numbers of CBs with L_x  10³¹ erg s⁻¹ in 4 core collapse vs. 12 King model clusters reveals that the specific frequency S_X (number of CBs per unit cluster mass) is enhanced in core collapse clusters, even when normalized for their stellar encounter rate. Although core collapse is halted by the dynamical heating due to stellar (and binary) interaction with CBs in the core, we conclude that production of the hardest CBs – especially CVs – is enhanced during core collapse. NGC 6397 has its most luminous CVs nearest the cluster center, with two newly discovered very low luminosity (old, quiescent) CVs far from the core. The active binaries as well as neutron star systems (MSP and qLMXB) surround the central core. The overall CB population appears to be asymmetric about the cluster center, as in several other core collapse clusters observed with Chandra, suggesting still poorly understood scattering processes.     

Biological modulation of the terrestrial carbon cycle: Isotope clues to early organic evolution

The characteristic difference of some 20 to 30 ‰ in the ¹³C/¹²C rations of reduced (organic) and oxidized (carbonate) carbon as observed in the contemporary environment can be traced back over 3.5 (if not 3.8) Ga of recorded Earth history. There is little doubt that the enrichment of isotopically light carbon in fossil organic matter ultimately derives from the bias in favor of ¹²C during photosynthetic carbon fixation (notably the RuBP carboxylase reaction of the Calvin cycle). Accordingly, the mainstream of the sedimentary δ ¹³C_org record can be most reasonably explained as geochemical evidence of the isotope-discriminating properties of the principal CO₂-fixing enzymatic reaction of the assimilatory pathway, thus giving eloquent testimony to an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation.     

Energetic particles in the comet Halley environment

An overview is presented of electrons, protons and heavier ions (E > 20 keV) recorded by the energetic particle detector EPONA in the Comet Halley environment, 12–15 March, 1986. Pick-up ions were detected at distances of up to at least 7.5 × 10⁶ km from the nucleus. Estimates of the energies that typical cometary ions may be expected to acquire from the solar wind pertaining at Encounter show that the pick-up process is insufficient to account for the energies of the particles detected. An additional mechanism must thus be postulated to account for the observed particle signatures. Preliminary correlations with magnetic and plasma wave data from other instruments suggest that the presence of MHD turbulence at several million kilometers upstream of the bowshock may have contributed to the acceleration of the first pick-up ions observed. The bowshock boundary (inbound) does not appear to have constituted a location where particle acceleration to high energies took place. Downstream of the shock boundary, hardening of the energy spectrum and the development of less anisotropic particle streaming was observed to occur when the spacecraft was in a turbulent environment 1 × 10⁶ km from the nucleus. The waxing influence of mass loading as a mechanism for reducing energetic particle fluxes as well as the depletion of energetic ions due to their escape along open field lines and to charge exchange collision with neutrals in a progressively more stagnant solar wind, may be inferred in a regime (seen on the magnetometer data to be largely non-turbulent) traversed by the spacecraft from 5 × 10⁵ km from the nucleus to within the magnetic pile-up region. A major burst of ions and electrons (not yet established to be of cometary origin) occurred when the spacecraft was close to the Contact Surface. A population of high energy electrons (from 180 keV to at least 300 keV) was detected for about one hour before Closest Approach and for several hours thereafter. Also an energetic beam of electrons was identified exiting from a location at about 1 × 10⁶ km from the nucleus (outbound). Finally, differences between inbound and outbound particle signatures are described.     

电离层效应的测时误差及其修正

电磁波经过电离层传播时会受到电离层折射的影响而产生延迟, 星载接收机探测到的时间是信号延迟之后的到达时间. 某次实验数据显示, 一些波段的瞬态电测辐射信号的群时延之差可达105ns数量级, 这在对信号源进行时差定位时是不能直接运用的. 为有效消除电离层延迟的影响, 将双频修正法应用于某项工程中, 利用接收到的实验数据求解出电离层的TEC(电离层总电子含量), 并在此基础上对信号到达星载接收机的时间进行修正. 最后,对修正结果进行了验证, 给出了误差来源.      

The structure of the IC443 supernova remnant complex derived from ROSAT and Ginga observations

Radio observations have shown that the emission from IC443 can be attributed to three, partially incomplete shells. The two smaller diameter shells are bright in X-rays, whereas the X-ray extent of the largest one has been discovered only recently in the ROSAT All-Sky-Survey. This new X-ray shell — G189.6+3.3 — is well explained by a separate old ( 10⁵yr) supernova remnant (SNR), in contrast to the IC443 proper SNR, the age of which has been estimated to 10³yr. Spatial structure of the X-ray absorption observed with ROSAT suggests that G189.6+3.3 is located in front of a molecular cloud while the two smaller subshells previously known as IC443 are behind it. This geometry is confirmed by the observation of an additional absorption ridge across IC443, which is produced by a shell of cool and dense matter associated with G189.6+3.3.     

纳秒脉冲电子束冲击强化金属表面的研究

讨论了纳秒强脉冲电子束(功率密度为10⁹W/cm²)辐射金属表面后产生的强化作用.纳秒脉冲电子束瞬间在材料表面局部区域注入巨大能量,使金属表面微区瞬间产生高温高压和冲击作用,并产生骤热急冷过程,使材料表面硬度、耐腐蚀性和其他物化性能发生明显变化.文中讨论了脉冲电子束导致快速熔凝的热传导过程,并分析了从扫描电镜照片观察到的金属急冷过程的显微结构.纳秒强脉冲电子束注入是金属材料表面改性的新手段.     

Rocket observation of the ultraviolet spectrum of comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on 26 February 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 × 10²⁹ s⁻¹ and the volume mixing ratio of CO to H₂O is 21%. The predicted brightness distribution from a radial outflow model with H₂O and CO as parent molecules are in accordance with the measured spatial profiles of OI and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker CI emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3% of the water production rate is included in the model.     

An archival study of extended X-ray emission from classical and recurrent novae

I discuss morphology and spectrum of the first resolved and detected classical nova shell in the X-rays – the remnant of GK Persei (1901). The existence of such a nebulosity brings about the possibility of other nova remnants emitting X-rays. I calculate that the X-ray luminosity should be about 10²⁶–10³³ ergs s⁻¹ on the onset of cooling for nova remnants. I have done an archival search on 250 classical and recurrent nova candidates using Chandra, XMM-Newton, ROSAT and ASCA databases. There is no significant extended emission detected which places an upper limit of F_x < × 10⁻¹² erg s⁻¹ cm⁻² (unabsorbed). Only exceptions are GK Per, RR Pic and DQ Her (all observed by Chandra ACIS-S and GK Per also by ROSAT HRI) where the latter two show marginal extended emission in the X-rays associated with emission knots (DQ Her) or an equatorial ring (RR Pic).     

High-velocity impact experiments needed to improve our understanding of the asteroids

The lifetime of almost all the asteroids against catastrophic impact events is less than the age of the solar system, implying that the asteroids can be considered as outcomes of catastrophic collisions. Therefore to understand their physical properties (structure, shape, rotation, regolith development) and their family memberships (since families are generated by the escape of breakup fragments), a systematic knowledge of the outcomes of catastrophic impacts under a variety of conditions seems needed. In particular, interesting fields to be explored by laboratory experiments are: the dependence of the critical energy densities associated with various degrees of fragmentation on the target's size and composition; the velocity distribution of the fragments and the inelasticity of the process in different cases; the shape of the fragments and its possible correlation with other quantities; the way a dust- or regolith-covered target affects the collisional outcomes; the angular momentum partitioning and the rotation of the fragments. On this latter problem very few experimental results are presently available; on the other hand, the rotation of small asteroids presents several intriguing “anomalies”.

A significant progress of our understanding of asteroid collisional evolution and related phenomena can be provided by new laboratory experiments of collisional breakup. The targets should have spherical and/or irregular shape (up to axial ratios of the order of 2), and should be made of (possibly different) geological materials. The interesting projectile velocities are of the order of the relative velocities commonly found among asteroids, i.e., in the range 1 to 10 Kms⁻¹. In order to get catastrophic collisions, the ratio of the projectile kinetic energy to the target mass (≡E/M) has to be chosen within a “critical” range (for basalt targets, from 10⁶ to 10⁸ erg/g). In some particular cases, this kind of experiments has been already performed in past (Gault and Wedekind [10]; Fujiwara et al. [7]; Fujiwara and Tsukamoto [9]); however the generalization of the results to a wide range of experimental conditions is lacking, and many problems of outstanding importance to model asteroid evolution are still completely open.