Measuring the magnetic moments of short-lived particles using channeling in bent crystals

A recent demonstration of spin precession using channeling in a bent crystal offers the interesting possibility of a technique to measure magnetic moments of short-lived charm baryons. There are significant differences among theoretical models of these moments. Accumulating experimental evidence indicates the tools used for hyperon magnetic moment measurements, polarized production and decay asymmetries, may also be available with heavier baryons. Useful measurements may be possible using the channeling technique but they will require challenging beam conditions.     

Ionoluminescence decay measured with single ions

A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino.     

Gas-driven hydrogen permeation in the surface-limited regime

Gas-driven permeation of hydrogen through metal membranes in the surface-limited regime (SLR) is analyzed. An analytical solution for the concentration and permeation flux as a function of time is given for permeation through the asymmetric membrane having different conditions on the inlet and outlet sides. The features of the steady state and transient permeation are discussed. Comparison of calculations with an experiment on deuterium permeation through vanadium, which is available from literature, is performed. It has been demonstrated that the parameters, extracted from the measurements of the permeation rate in SLR are very uncertain. Even the calculations with opposite asymmetries can be equally well adjusted to the experiment. Non-zero initial conditions in SLR experiments are additional source of uncertainty. Measurements of the accumulation in a closed volume instead of the permeation rate can seriously mislead in the interpretation of the experiment. Complementary experiments on permeation in two opposite directions and measurements of permeation decay could increase the reliability of the data obtained.     

Prompt alpha and reactivity measurements on fast metal assemblies

This paper summarizes and reviews the methods of reactivity determination and measurement of the prompt-neutron decay, briefly describes the equipment requirements for such measurements for unmoderated metal assemblies, and presents experimental results to illustrate the methods. These assemblies include fast metal critical assemblies and fast pulsed reactors. The primary reactivity determination methods used have been: (1) stable reactor period measurements which are usually used near delayed criticality to obtain the reactivity or to calibrate the reactivity prior to burst initiation; (2) prompt reactor period measurements which are useful to determine the reactivity early in superprompt critical excursions; (3) inverse kinetics rod drop measurements which obtain the reactivity as a function of time after a rod or reactor component is removed from a delayed critical assembly, and (4) prompt neutron decay constant measurements from which the reactivity can be obtained if corrections are made for changes in the neutron lifetime. Inverse kinetics and decay constant measurements are usually used below delayed criticality, although decay constant measurements have been performed above delayed critical.The decay constant is usually obtained by the traditional pulsed-neutron method, using a pulsed neutron source such as a Cockcroft-Walton accelerator, or by the Rossi-α method. The recent use of ²⁵²Cf has resulted in some new techniques for determining the decay constant and reactivity; this method has some unique advantages over the traditional methods. The theory of these new measurements is reviewed, and some recent results are presented.     

Study of ion beam induced mixing during sputter depth profiling of thin films by LEIS

Ion beam induced mixing during sputter depth profiling was studied for tantalum and lead marker layers in silicon with 5 keV neon by low energy ion scattering spectroscopy (LEIS). The diffusion approximation was used to calculate mixing efficiency values (D/JF_d) from decay length measurements. The mixing efficiency values are shown to be sensitive to the preferential sputtering which takes place during ion bombardment. TRIM simulations for Ta/Si are shown to agree with the experimentally determined value for preferential sputtering. Depth profiling at high temperature is shown to separate some of the interrelated mixing mechanisms of radiation enhanced diffusion (RED) and radiation induced segregation (RIS). For the Ta/Si system the mixing efficiency value is observed to remain constant regardless of the 5 keV inert gas ion beam used for depth profiling.     

Charge transfer and excitation in high-energy ion-atom collisions

Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K-shell of Ca ions and the L-shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture.     

(ε+β+)衰变的γ射线强度归一化因子计算

文章涉及根据伴随(ε+β+)衰变的β+、湮没辐射和X射线等的强度测量计算其γ射线绝对强度归一化因子的计算方法。文中给出了计算实例，并进行了简要讨论。     

Apparatus for Precise Measurement of Scintillator Decay Times

A digital system has been built for making precise measurements of scintillator decay times. The approach used is similar to the one developed by Bollinger and Thomas. Time intervals between the start of a gamma-induced scintillation and the detection of a single light photon are measured with a time-to-height converter and stored in a pulse height analyzer. The apparatus has a time resolution of less than 2 nanoseconds, a dynamic range of greater than four decades, and is able to detect both prompt and slow decay components in plastic and liquid scintillators. For all fast scintillators studied, the decay of light intensity over the first decade is approximately exponential; however, measured decay times are shorter than those generally quoted. Results of measurements made on several commercially available scintillators will be presented, including NE 102, Pilot B, Pilot A, and MEL-150C.     

Relativistic, QED and nuclear effects in highly charged ions revealed by resonant electron-ion recombination in storage rings

Dielectronic recombination (DR) of few-electron ions has evolved into a sensitive spectroscopic tool for highly charged ions. This is due to technological advances in electron-beam preparation and ion beam cooling techniques at heavy-ion storage rings. Recent experiments prove unambiguously that DR collision spectroscopy has become sensitive to 2nd order QED and to nuclear effects. This review discusses the most recent developments in high-resolution spectroscopy of low-energy DR resonances, experimental studies of KLL DR of very heavy hydrogen like ions, isotope shift measurements of DR resonances, and the experimental determination of hyperfine induced decay rates in divalent ions utilizing DR.     

放射性核素电离空气电子离子对产生率计算

α衰变核素和β衰变核素发射的射线具有电离空气能力而被广泛应用于工业生产中。为研究α或β衰变核素对空气电离能力的大小,本研究采用蒙特卡洛方法模拟理想放射源发出带电粒子在空气中的能量沉积,并结合空气电离理论,计算放射源表面不同距离处电子离子对产生率。利用此计算方法,研究放射源形状、粒子能量、活度和粒子能量分布对电子离子对产生率的影响。结果表明,放射源表面空气中电子离子对产生率的大小主要受放射源活度的影响,而粒子能量及能谱分布等主要影响电离空气范围及电子离子对产生率衰减速率; 3.7×10⁶ Bq/cm²的α放射源最大电子离子对产生率可达10¹¹~10¹² cm^-3•s^-1量级, 3.7×10⁶ Bq/cm²的β放射源最大电子离子对产生率可达10⁹~10¹⁰ cm^-3•s^-1量级。研究结果可提供数据支持,为新的放射性同位素应用技术开发提供理论指导。     

The decay of autoionizing states in electric field formed during collisions of multiply charged ions with metal surface

When a multicharged ion approaches the metal surface, a strong electric field occurs due to interaction between the ion and the charge induced in the metal. During ion-surface scattering, double excited autoionizing states can be formed, and their decay occurs in the presence of strong electric field. The Auger transition rates for such states are higher than those in the absence of the electric field; this is connected with the increase in the wave functions overlap and also with mixing of states with different orbital momentums. This effect changes our view on the population scheme of states with the lowest principal quantum numbers for the collisions considered.     

Environmental Influences on K X-Rays from Highly Stripped Sulfur Ions Teavelng in Solids

As a fast heavy-ion passes through a material medium, it undergoes multiple collisions in which electrons are continuously lost and recaptured by the ion, and as a result, an equilibrium distribution of excited states is quickly established. The high density of electrons in a solid state environment enables these collisional excitation and decay processes to compete with x-ray and Auger decay. As a result, the widths of the x-ray lines exhibit a dependence on electron density due to collisional broadening. In addition, the potential of the ion is modified by the polarization of loosely bound electrons of the medium. In effect, these electrons act to screen the ion potential, thereby causing the core electron binding energies of the ion to decrease. As a result of this "dynamic screening" effect, the x-ray transition energies inside the medium differ from those in vacuum.     

Ion beam characterization of advanced luminescent materials for application in radiation effects microscopy

The ion photon emission microscope (IPEM) is a technique developed at Sandia National Laboratories (SNL) to study radiation effects in integrated circuits with high energy, heavy ions, such as those produced by the 88” cyclotron at Lawrence Berkeley National Laboratory (LBNL). In this method, an ion-luminescent film is used to produce photons from the point of ion impact. The photons emitted due to an ion impact are imaged on a position-sensitive detector to determine the location of a single event effect (SEE). Due to stringent resolution, intensity, wavelength, decay time, and radiation tolerance demands, an engineered material with very specific properties is required to act as the luminescent film. The requirements for this material are extensive. It must produce a high enough induced luminescent intensity so at least one photon is detected per ion hit. The emission wavelength must match the sensitivity of the detector used, and the luminescent decay time must be short enough to limit accidental coincidences. In addition, the material must be easy to handle and its luminescent properties must be tolerant to radiation damage. Materials studied for this application include plastic scintillators, GaN and GaN/InGaN quantum well structures, and lanthanide-activated ceramic phosphors. Results from characterization studies on these materials will be presented; including photoluminescence, cathodoluminescence, ion beam induced luminescence, luminescent decay times, and radiation damage. Results indicate that the ceramic phosphors are currently proving to be the ideal material for IPEM investigations.     

SCALE analysis of CLAB decay heat measurements for LWR spent fuel assemblies

A set of decay heat measurements for spent fuel assemblies recently carried out at the Swedish central interim storage facility for spent fuel, CLAB, was analyzed with the SCALE code system. The measurements include a variety of light water reactor assemblies that cover a large burnup range – up to 51 GWd/MTU – and a cooling time domain of interest to spent fuel storage and transportation applications. The results of the analysis show a good agreement between measured and predicted decay heat, with the calculated decay heat in general within the range of the uncertainty of the measured value. The effect of various assembly data on the calculated decay heat is analyzed and discussed. Uncertainties that may arise from various approaches and assumptions in the computational model are identified and examined.     

Evaluation of decay data of 213Bi

213Bi disintegrates (97.91±0.03) % by β- emission to the levels in 213po, and (2.09±0.03) % through α decay to 209Tl. The evaluation of the complete decay scheme and data of 213Bi including the recent new measurements are presented in this report. The Limitation of Relative Statistical Weight Method (LWM) was applied to average numbers throughout the evaluation. The uncertainty assigned to the average value was always greater than or equal to the smallest uncertainty of the values used to calculate the average. The half-life is determined to be 45.59±0.06 minutes. All known measured gamma-ray relative emission probabilities have been examined. And the gamma-ray emission probability of the reference γ line of 440.44keV is recommended to be (26.1±0.3) %. The calculated internal conversion coefficients and their uncertainties have been used to obtain the complete decay intensity balance. The other decay characteristics are calculated using the ENSDF analysis program. Finally the new 213Bi decay scheme was re-built.     

Ion beam induced luminescence of polyethylene terephthalate foils under MeV H and He ion bombardment

The evolution of the ion beam induced luminescence (IBIL) of the polyethylene terephthalate (PET) foils was studied under the irradiation of H and He ions of MeV energy. The optical and chemical changes of the samples were also examined by photo-stimulated luminescence and optical absorption measurements after the irradiation. A prominent broad emission peak of IBIL appeared at around 380 nm, and its intensity monotonically decreased during the ion irradiation. The decay curves of the emission intensity were quantitatively explained as a function of the electronic energy deposition of the incident H and He ions. On the contrary, to the decrease of the main emission peak, a growth of new peaks was observed in the wavelengths between 500 and 600 nm.     

中国的核衰变数据工作

介绍核衰变数据的计算机评价系统、数据评价及更新、结合评价为澄清各家数据间分歧进行的针对性实验测量、国际交流和合作，以及在中国核数据中心建立的含３００多个放射性核素的衰变数据库及其库管理程序系统等。     

Nuclear data sheets for A = 159

Nuclear data based upon reaction and radioactivity studies of mass 159 nuclei are presented.For A = 159 all nuclei with 63 ?Z?72 with the exception of Yb and Lu have been reported; but not much is known for Eu, Er, Tm, and Hf isobars other than their ground-state properties. The only stable nucleus with A = 159 is ¹⁵⁹Tb, and it has been studied in considerable detail both by nuclear reactions and radioactive decay of its neighboring isobars. Because of ambiguity in beta branching in ¹⁵⁹Eu decay and since the beta branch to ¹⁵⁹Tb g.s. in ¹⁵⁹Gd decay is known only approximately, the normalizations in these radioactive decays are rather uncertain.For brevity some of the older data have been omitted or referenced as other measurements.It has been attempted to include all available data prior to February 1, 1973.     

Study of delayed neutron decay curves from thermal neutron induced fission of U and Pu

The results of measurements of the delayed neutron decay curves obtained from the thermal neutron induced fission of ²³⁵U and ²³⁹Pu are presented. The data were obtained by the periodical irradiation method on the pulsed reactor IBR-2 during the time interval 5 to 730 msec following irradiation. A comparison of these newly measured decay curves with the curves calculated using several standard delayed neutron sets was then performed. Based on these measurements, a new 7-group delayed neutron model is proposed.     

Nuclear data sheets for A = 206

Nuclear structure data available through July 1978 for nuclei with mass number 206 are compiled and evaluated. A summary of the information obtained in reaction and decay measurements is presented with the bulk of the data being presented pictorially for easy comparison. Adopted level and decay properties are given. Any additions or corrections should be addressed to the evaluators for maintenance and updating of the data file.