On the possible determination of hyperfine anomalies by trapped ion spectroscopy

Laser-microwave double-resonance techniques in radiofrequency (rf) traps and Penning traps represent a powerful tool to determine hyperfine structure splittings as well as nuclear g factors to high precision. While hyperfine structure constants have been determined in a number of cases below the 10⁻¹⁰ level of precision, electronic g factors have been measured to 10⁻⁷ and there are good prospects of obtaining similar accuracy for g_l. Moreover sensitive techniques have been developed for injection of ions from outside the trap. This opens the possibility to determine hyperfine anomalies at least to the 1% level of precision for chains of unstable isotopes.     

Low temperature epitaxial regrowth of mercury implanted sapphire

Hg ions were implanted into sapphire at room temperature and 80 keV energy to a fluence of 1 × 10¹⁵ Hg⁺ / cm². This fluence was enough to produce an amorphous surface layer. The annealing behaviour was studied combining RBS/channeling and hyperfine interaction techniques. Surprisingly, the RBS/channeling results show there is an epitaxial regrowth of the damaged layer after annealing at 800°C for 20 min. Although some of the implanted Hg segregates to the surface during the epitaxial regrowth, a significant fraction is incorporated into regular sites along the c-axis. The hyperfine interactions results, obtained after implantation of a dose of 5 × 10¹² Hg⁺ / cm², show that a small fraction of Hg is probably bound to oxygen. This result is in agreement with the RBS/channeling measurements which also show that the system formed after annealing is stable even at high temperatures.     

改装元素分析—稳定同位素比值质谱联用仪测定固体样品硫同位素

本文对元素分析—稳定同位素比值质谱联用仪（EA-IRMS）进行改装,并利用其测定不同形态硫同位素标准物质和样品。结果表明,在色谱柱后加装SO₂气体捕集管,可捕集氧化还原产生的SO₂气体,并重复调用作为参考气使用,无需外部引入高纯SO₂气体,减小了其对仪器管路腐蚀和实验室环境危害;硫酸钡进样量约400 μg时,捕集管中的SO₂气体可提供至少20次峰中心聚焦;改装后的EA-IRMS系统测试硫同位素标准物质（IAEA-SO-5、 IAEA-S-2、IAEA-S-3、EMA-P1）,当硫元素进样量为20 μg时,δ³⁴S值测试精度达到0.2‰（n=3）,4种国际标准物质测量值与真实值相关系数良好（R²=1）,表明硫的不同化合物δ³⁴S值可以相互校准,也表明EA-IRMS改装后可以满足硫同位素测试精度的要求。     

Ion traps — recent applications and developments

Paul and Penning traps are now widely applied in chemistry and physics laboratories. They are used as storage devices, as tools for precision spectroscopy and metrology, and as mass spectrometers. Direct mass measurements of short-lived Rb, Sr, Cs, Ba, Fr and Ra isotopes were performed at the on-line mass separator ISOLDE at CERN, Geneva, by means of a tandem Penning trap system. The ions from ISOLDE are captured and cooled in a first trap and trasnferred to a second trap. Here the mass of the trapped ions is determined by measuring their cyclotron frequency. Resolving powers exceeding m/Δm (FWHM) = 10⁶ could be achieved. Mass values of about 60 isotopes have been determined with accuracies of typically δm/m = 10⁻⁷. For the first time in the history of mass spectrometry the isomeric and ground states of a nucleus have been resolved.     

A wire probe as an ion source for an electron beam ion trap

A thin wire probe inserted near the electron beam in an electron beam ion trap provides a source of ions for the trap. The wire can be plated with a small amount of source material permitting the use of rare or expensive materials. Here we present results on tests with probes of various materials to demonstrate the success of the technique. In one case a sample of approximately 100 ng of ²³³U was plated on a platinum wire tip and used to continuously fill the trap for 10 days.     

Isomer separation of Cu and Cu with a resonance ionization laser ion source

Radioactive copper isotopes were ionized with the resonance ionization laser ion source (RILIS) at the on-line isotope separator ISOLDE (CERN). Using the different hyperfine structure in the 3d¹⁰ 4s  ²S_1/2 – 3d¹⁰ 4p  ²P⁰_1/2 transition the low- and high-spin isomers of ⁷⁰Cu were selectively enhanced by tuning the laser wavelength. The light was provided by a narrow-bandwidth dye laser pumped by copper vapor lasers (CVL) and frequency doubled in a BBO crystal. The ground state to isomeric state intensity ratio could be varied by a factor of 30, allowing to assign gamma transitions unambiguously to the decay of the individual isomers. It is shown that the method can also be used to determine magnetic moments. In a first experiment for the 1⁺ ground state of ⁷⁰Cu a magnetic moment of (+)1.8(3) μ_N and for the high-spin isomer of ⁷⁰Cu a magnetic moment of (±)1.2(3) μ_N could be deduced.     

Bayesian inference theory applied to hyperfine parameter distribution extraction in Mössbauer spectroscopy

We present an effective direct extraction method for hyperfine parameter distributions based on Bayesian inference theory with free-form model and give an example of application to quadrupole splitting distribution analysis in an Fe-57 Mössbauer spectrum of an Fe³⁺-chlorite. The technique gives a unique solution to the distribution with arbitrary shape and is not sensitive to the elemental doublet parameters. In addition full error analysis of the distribution is obtained for the first time in Mössbauer spectroscopy.     

基于v-支持向量机的事故工况下反应堆功率预测

针对事故工况下堆芯功率变化的特点和神经网络（ANNs）易陷极小值、收敛速度慢等问题，提出一种基于ν-SVR）的事故工况下堆芯功率预测方法。该方法运用k重交叉验证（k-CV）完成对ν-SVR预测器并将其用于弹棒事故（REA）和落棒事故（RDA）工况下的堆芯功率预测。研究表明，与ANNs相比，该方法具有更高的预测精度和更短的响应时间。      

Collection, cooling and delivery of ISOL beams

The collection of an ISOL beam in a Penning trap using implantation on a surface that is subsequently manipulated so as to become part of an end electrode of a Penning trap and reionization of the implanted material by heat has already been very productive for high-precision nuclear-mass measurements, even though it is limited to elements that are surface ionizable and the collection efficiencies are never better than about 0.1%. More recently, in 1990 a Paul trap system for electric collection of ions was installed at the ISOLDE-3 facility and collection was demonstrated for a 60 kV beam of ¹³²Xe ions. The purpose of this test setup was to determine the relationship between phase space volume of a typical trap and the collection efficiency that could be obtained in direct capture. For the modest trap used, collection efficiencies of up to 0.2% were achieved. A beam of negative bromine ions was collected by simply reversing the polarities of all voltages used. From the experience with this system it appears feasible to build a Paul trap which is about three times as large in linear dimensions as the existing one and which could be driven at up to 10 kV peak at 1 MHz using a modest rf amplifier (300 W). With moderate prebunching of the injected beam at 1 MHz, this system should achieve collection efficiencies approaching 100%. Based on these results, preliminary design work is being carried out on the collection system to be installed at the ISOLDE Booster facility. Suggestions for other uses of a Paul trap collection system for ISOL beams are presented.     

PILIS: post-ISOCELE laser isobar separation; a high efficiency apparatus for laser spectroscopy

A new experimental setup PILIS II has been installed on-line with the ISOCELE isotope separator (IPN, Orsay). The mass-separated ions are slowed from 30 kV to 500 V and implanted on a graphite collecting disk. The atoms are then thermally desorbed at the implantation region by Nd: YAG laser pulses and selectively ionized by three laser beams. The ions created are mass identified by a time-of-flight (TOF) system. Two versions of the TOF system with accelerating voltages of 1.5 and 30 kV were used to carry out hyperfine structure measurements. With the 30 kV system we obtained an overall detection efficiency of 1.4 × 10⁻⁵. First measurements were performed on very light gold and platinum isotopes. It has been shown that PILIS II is well adapted to study very short half-life isotopes ( ).     

Measurement of niobium reaction rate formaterial surveillance tests in fast reactors

A highly accurate and precise technique for measurement of the ⁹³Nb(n,n’)^93mNb reaction rate was established for the material surveillance tests,etc.in fast reactors.The self-absorption effect on the measurement of the characteristic X-rays emitted by ^93mNb was decreased by the dissolution and evaporation to dryness of niobium dosimeter.A highly precise count of the number of ⁹³Nb atoms was obtained by measuring the niobium solution concentration using inductively coupled plasma mass spectrometry.X-rays of ^93mNb were measured accurately by means of comparing the X-ray intensity of irradiated niobium solution with that of the solution in which stable ⁹³Nb was added.The difference between both intensities indicates the effect of ¹⁸²Ta,which is generated from an impurity tantalum,and the intensity of X-rays from ^93mNb was evaluated.Measurement error of the ⁹³Nb(n,n’)^93mNb reaction rate was reduced to be less than 4%,which was equivalent to the other reaction rate errors of dosimeters used for Joyo dosimetry.In addition,an advanced technique using Resonance Ionization Mass Spectrometry was proposed for the precise measurement of ^93mNb yield,and ^93mNb will be resonance-ionized selectively by discriminating the hyperfine splitting of the atomic energy levels between ⁹³Nb and ^93mNb at high resolution.     

High density γ-ray emission and dense positron production via multi-laser driven circular target

A diamond-like carbon circular target is proposed to improve γ-ray emission and pair production with a laser intensity of 8×10²² Wcm⁻² by using 2D particle-in-cell simulations with quantum electrodynamics. It is found that the circular target can enhance the density of γ-photons significantly more than a plane target, when two colliding circularly polarized lasers irradiate the target. By multi-laser irradiating the circular target, the optical trap of lasers can prevent the high energy electrons accelerated by laser radiation pressure from escaping. Hence, γ-photons with a high density of beyond 5000n_c are obtained through nonlinear Compton backscattering. Meanwhile, 2.7×10¹¹ positrons with an average energy of 230 MeV are achieved via the multiphoton Breit–Wheeler process. Such an ultrabright γ-ray source and dense positron source can be useful in many applications. The optimal target radius and laser mismatching deviation parameters are also discussed in detail.     

Time scales of transient enhanced diffusion: free and clustered interstitials

Transient enhanced diffusion (TED) and electrical activation after nonamorphizing Si implantations into lightly B-doped Si multilayers shows two distinct timescales, each related to a different class of interstitial defect. At 700°C, ultrafast TED occurs within the first 15 s with a B diffusivity enhancement of > 2 × 10⁵. Immobile clustered B is present at low concentration levels after the ultrafast transient and persists for an extended period ( 10²–10³ s). The later phase of TED exhibits a near-constant diffusivity enhancement of ≈ 1 × 10⁴, consistent with interstitial injection controlled by dissolving {113} interstitial clusters. The relative contributions of the ultrafast and regular TED regimes to the final diffusive broadening of the B profile depends on the proportion of interstitials that escape capture by {113} clusters growing within the implant damage region upon annealing. Our results explain the ultrafast TED recently observed after medium-dose B implantation. In that case there are enough B atoms to trap a large proportion of interstitials in Si---B clusters, and the remaining interstitials contribute to TED without passing through an intermediate {113} defect stage. The data on the ultrafast TED pulse allows us to extract lower limits for the diffusivities of the Si interstitial (D_I > 2 × 10⁻¹⁰ cm²s⁻¹) and the B interstitial(cy) defect (D_Bi > 2 × 10⁻¹³ cm²s⁻¹) at 700°C.     

Temperature-dependent dose rate effects in CMOS/SOS devices

The measured photocurrent output by the 3392-μm p-channel and 1992-μm n-channel transistors in the output buffer of the Harris 05131A Octal Latch manufactured in the TSOS4 1.25-μm CMOS/SOS process are used to extract the field and temperature-dependent conductivity of the sapphire substrate. The bulk conductivity was found to vary from 2.15×10^-15 Ω^-1/cm/rad(Si)/s at -55°C to 4.16×10^-15 Ω^-1/cm/rad(Si)/s at +125°C. Parasitic transistor action contributed significant photocurrents with the gain of the n-channel increasing from 1.3±0.3 at -55°C to 5.7±3.3 at +125°C. The gain of the p-channel followed the same temperature variation, with 1.6±0.5 at -55°C to 7.0±2.0 at +125°C. The temperature-dependence of both the substrate and parasitic transistor action appeared due to an Arrenhius variation of the carrier lifetime or mobility controlled by a trap 0.05 eV above the quasi-Fermi level     

Time dependence of interface trap formation in MOSFETs followingpulsed irradiation

The time dependence of interference trap (N_it) formation in MOSFETs was studied as a function of gate oxide thickness, oxide growth type, substrate orientation, temperature, and gate bias. Two different N_it formation mechanisms are observed. Most (typically 90%) of the formation, called the late process, occurs slowly at long times (1-10000 s) after the radiation pulse. From a variety of experimental data, it is concluded that the rate of the late process is limited by drift of a radiation-induced positive ion, probably H⁺ , through the gate oxide to the Si-SiO₂ interface where the N_it are formed. A relatively fast, or early, process is responsible for a small percentage of the total N_it formation. The time constant for this process appears to be consistent with hole drift through the oxide     

A systematic study of the initial electrical and radiation hardnessproperties of reoxidized nitrided oxides by rapid thermalprocessing

The initial electrical and radiation hardness properties of MOS capacitors with reoxidized nitrided oxides (RNO) structures are systematically investigated by changing the pressure, temperature, and times of nitridation and reoxidation in rapid thermal processes. It was found that the initial flat-band voltage (V_fb) and midgap interface trap density (D_itm) are strongly dependent on the growth conditions and show concave or convex “turnaround” dependency on some process parameters. This may be explained by the hydrogen evaporation and oxygen passivation mechanisms. The radiation induced flat-band voltage shift (ΔV_fb) and midgap interface trap density shift (ΔD_itm) are also growth-condition dependent and show different “turnaround” dependencies on some process parameters from those observed in initial properties. This may be explained by the variations of the amount of hydrogen-related species such as Si-NH, Si-H, or Si-OH, and nitrogen-related species, such as Si-N, in the oxide bulk and at the Si/SiO₂ interface. Finally, the sample with a reoxidation pressure of 250 torr, a reoxidation temperature of 1050°C, and a reoxidation time of 100 s is suggested to be the most radiation-hard together with good initial properties for RNO devices     

Radiation Effects on GaAs Charge Coupled Devices with High Resistivity Gate Structures

The results of a study on the effects of 1 MeV electrons and 1 MeV neutrons on the operation of high speed GaAs Charge Coupled Devices (CCDs) are presented. Radiation-induced trapping levels are characterized using a linear array CCD structure and the periodic pulse technique. 1 MeV electron irradiation introduced traps at 0.1 eV and 0.39 eV with bulk trap introduction rates of 1 cm-1 and 0.33 cm-1, respectively. The devices were irradiated to a maximum fluence of 9×1014 electrons/cm2. 1 MeV neutron irradiation introduced an electron trap level at 0.64 eV with a bulk trap introduction rate of 0.5 cm-1. Catastrophic device failure occurred at neutron fluences of 6×1013 neutrons/cm2. Device charge transfer efficiency was characterized pre- and post-irradiation over the temperature range of 80°K to 300°K.     

Fission fragment anisotropy for the Am fission isomer by spin exchange pumping with polarized rubidium vapour

The foundations of an experiment have been worked out with which, in principle, the spin, hyperfine constants and the isomer shift of the 14 ms fission isomer ^242mAm can be measured. Such an experiment would be based on the fission fragment anisotropy signal which has actually been observed in this work after spin exchange pumping with polarized rubidium vapour in an optical buffer gas cell. A decrease of the count rate of (12±4)% has been measured at 90% with respect to the quantization axis. From this result it is concluded that the nuclear spin of the ^242mAm fission isomer must be larger than 1. The low-energy fission isomers originating from the ²⁴²Pu(d, 2n)^242mAm reaction have been post-accelerated with the aid of a 6 cm long 100 kV electrostatic accelerator unit in order to implant them through a 0.4 μm thick entrance window into the optical buffer gas cell. A neutralization efficiency of 13% of the americium fission isomers with an energy of about 1 MeV has been determined experimentally.     

Development of Reflux Vapor Trap for Sodium Cooled Fast Breeder Reactor, (I)

With the view of obtaining basic data required for designing durable reflux vapor traps of high performance for use in sodium-cooled FBR's, experiments were conducted to (a) select a suitable packing, and (b) to examine the effect brought on trapping performance by changing the gas flow rate, packing material, packing density and trap outlet temperature. The results indicated that:

(1) As trap packing, plane weave stainless steel mesh proved to ensure lower pressure drop through trap.

(2) Using the plane weave mesh packing, and with the trap outlet temperature kept at 130°C, the reflux vapor trap efficiency was found to exceed 99.6% in the range of vapor trap gas velocity below 1.3 m/s, and packing density below 0.07 g/cc. The efficiency decreased at outlet temperatures above 130°C.     

Analytical expression for the Mössbauer line shape of 57Fe in the presence of mixed hyperfine interactions

A new method is presented for the calculation of Mössbauer line shapes of hyperfine split nuclei. Instead of solving explicitly the hyperfine Hamiltonian for its eigenvalues and eigenvectors this method uses a superoperator formalism to yield closed form expressions for the Mössbauer line shape in the presence of magnetic dipole and electric quadrupole hyperfine interactions. The advantage of this method over the conventional one lies in the fact that averages over hyperfine field orientations may be calculated analytically. This is demonstrated for the case of ⁵⁷Fe with randomly oriented electric field gradients in a uniform oriented magnetic field.