Further Analysis of Neutron Double-Differential Cross Section of n ＋ ^16O at 14.1 MeV and 18 MeV

By using a new reaction model for light nuclei, the double-differential cross section of total outgoing neutron with LUNF code for n＋^16O reactions at En=14.1 MeV and 18 MeV have been calculated and analyzed. In this paper the opened reaction channels, which have contribution to emitting the neutrons, are listed in detail. To improve the fitting results the direct inelastic scattering mechanism is involved. The calculating results agree fairly well with the experimental data at E,~ = 14.1 MeV and the deviation from calculated results and experimental data in low energy region at En= 18 MeV has been analyzed. Since the possibility of 5He has been affirmed theoretically [J.S. Zhang, Sci. Chin. G 47 （2004） 137], so 5He emission from n＋ ^16O reaction is taken into account, which plays an important role at the region of the outgoing neutron energy εn〈3 MeV in total outgoing neutron energy-angular spectrum. The calculated results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil effect in light nuclear reactions is essentially important.     

Analysis of Neutron Double-Differential Cross Sections for n ＋ ^12 C Reaction Below 30 MeV

Based on the light nucleus reaction model （Nucl. Sci. Eng. 133 （1999） 218）, four aspects （neutron incident energy region, reaction channel analysis, the renewed level schemes and the optical model parameters） of n＋ ^12 C reaction are improved to calculate total outgoing neutron double-dilferential cross sections with modified LUNF code below 30 MeV. The calculated results agree fairly well with the experimental data at En = 14.1 MeV and 18 MeV. The analysis shows that the pre-equilibrium mechanism, which is exactly considered the conservation of energy, momentum and parity, dominates the whole reaction process. The contribution of the neutron emission from 5He to total energy- angular spectra is also considered properly. This modified LUNF code will be a useful tool to set up the file of neutron double-differential crass sections below 30 Me V in the neutron evaluation nuclear data library.     

Elastic and charge exchange scattering of pions from He

Elastic and charge exchange scattering of pions from ³He is studied using an optical potential in the momentum representation, which includes the second-order effect as well as the nucleon binding correction. These corrections are found to be appreciable but still not enough to resolve the discrepancy between theoretical calculations and recent experimental data on the reaction ³He(π⁻, π⁰)³H.     

Analysis of Neutron Double-Differential Cross Section of n＋^14N at 14.2 MeV

Abstract By using a new reaction model for light nuclei, the double-differential cross section of n ^14N reactions at En=14.2 MeV has been analyzed. In the case of n ^14N reactions, the reaction mechanism is very complex, there are over one hundred opened partial reaction channels even at incident energy En=14.2 MeV. In this paper the opened reaction channels are listed in detail. With LUNF code the model calculation is performed to analyze the doubledifferential cross sections of total outgoing neutron. The calculated results agree fairly with the experimental data. The results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil egect in light nuclear reactions is essentially important. 5He emission has been considered, but it is only a small contribution to thedouble-differential cross section at incident energy En=14.2 MeV.     

Determination of r Factor of Kalbach-Mann Systematics for Energy Balance

Kalbach-Mann systematics is a very useful formula to discrete the double-differential cross sections of emitted particles. However, the energy balance by using this systematics is still a task to be studied. In the form of Legendre polynomial expansion the energy balance has been proved analytically. In terms of this approach, the formula to determine the pre-equilibrium fraction r factor of Kalbach-Mann systematics has been obtained for keeping energy balance strictly. This formula could be straightforwardly applied for describing the double-differential cross sections of all projectile types in the continuum spectrum emissions. It indicates that Legendre expansion coefficient with l=1 is the key term in the energy balance.     

Measurements of interaction cross sections and radii of He isotopes

Secondary beams of ³He, ⁴He, ⁶He, and ⁸He were produced through the projectile fragmentation of an 800 MeV/nucleon ¹¹B primary beam. Interaction cross sections (σ_I) of all He isotopes of 790 MeV/nucleon on Be, C, and Al targets were measured by a transmission-type experiment. The interaction nuclear radii of He isotopes R_I(He) = (σ_I/π)^1/2 − R _I(T) where R_I(T) is the radius of the target nucleus, have been deduced to be R_I(³He) = 1.59 ± 0.06 fm, R_I(⁴He) = 1.40 ± 0.05 fm, R_I(⁶He) = 2.21 ± 0.06 fm, and R_I(⁸He) = 2.52 ± 0.06 fm.     

A Method for Calculating Double Differential Cross Sections of α Particle Emissions

On the basis of the successful studies on pick-up mechanism of composite particle emission and the angular distribution of single nucleon emissions, a theoretical method for calculating double differential cross sections of α particle emissions is propoLed. As an example, the double differential cross sections of α particles in the neutron induced reaction ⁵⁶Fe(n, xα) have been calculated at E_n = 14.5 MeV. The theoretical results reproduce the experimental data successfully.     

Medium effects in coherent pion photo- and electroproduction on He and C

Coherent π⁰ photo- and electroproduction on ⁴He and ¹²C nuclei is investigated in the framework of a distorted wave impulse approximation in momentum space. The elementary process is described by the recently developed unitary isobar model. Medium effects are considered by introducing a phenomenological Δ self-energy. Recent experimental data for ⁴He and ¹²C can be well described over a wide range of energies and emission angles by the assumption that the Δ–nuclear interaction saturates.     

极化3He系统核磁共振FID信号的激光探测

极化率测量装置是极化³He系统的重要组成部分之一.本文介绍了一套在极化³He系统上搭建的激光探测自由感应衰减核磁共振（FID NMR）信号的实验装置,该装置有望为³He极化率的高精度实时测量提供新的途径.激光探测法的原理是法拉第旋光效应,该方法使用一束线偏振光探测极化³He磁矩绕主磁场进动的FID信号,实验结果表明相较于拾波线圈探测方法,激光探测方法的信噪比提高了106%,对³He的极化率测量更精确.该探测方法有望替代传统的拾波线圈,广泛地应用于³He极化系统的极化率测量或精密测量实验中.     

Binding and pauli principle corrections in subthreshold pion-nucleus scattering

In this investigation I develop a three-body model for the single scattering optical potential in which the nucleon binding and the Pauli principle are accounted for. A unitarity pole approximation is used for the nucleon-core interaction. Calculations are presented for the π−⁴He elastic scattering cross sections at energies below the inelastic threshold and for the real part of the π−⁴He scattering length by solving the three-body equations. Off-shell kinematics and the Pauli principle are carefully taken into account.

The binding correction and the Pauli principle correction each have an important effect on the differential cross sections and the scattering length. However, large cancellations occur between these two effects. I find an increase in the π−⁴He scattering length by 100%; an increase in the cross sections by 20–30% and shift of the minimum in π−⁴He scattering to forward angles by 10°.     

Decay Analysis of Ge Isotopes Formed in Reactions Induced by Tightly and Loosely Bound Projectiles

The dynamical cluster-decay model (DCM) is employed to investigate the decay of ^68,70Ge^* compound nuclei formed respectively via tightly (⁴He) and loosely (⁶He) bound projectiles, using ⁶⁴Zn target. The study is carried out over a wide energy range (E_c.m.~5 MeV to 16 MeV) by including the quadrupole deformations (β2i) and optimum orientations (θ_i^opt) of the decaying fragments. The fusion cross-sections, obtained by adding various evaporation channels show nice agreement with the experimental data for ⁴He+⁶⁴Zn reaction. The contribution from competing compound inelastic scattering channel is also analyzed particularly for ⁶⁸Ge^* nucleus at above barrier energies. On the other hand, the decrement in the fusion cross-sections of ⁷⁰Ge^* nuclear system is addressed by presuming that ⁶⁵Zn ER is formed via two different modes:(i) the αn evaporation of ⁷⁰Ge^* nucleus, and (ii) 1n-evaporation of ⁶⁶Zn^* nuclear system, formed via breakup and 2n-transfer channels due to halo structure of the ⁶He projectile. Besides this, the suppression in 2np evaporation cross-sections suggests the contribution of another breakup and transfer process of ⁶He i.e. ⁴He+⁶⁴Zn. The contribution of breakup+transfer channels for ⁶He+⁶⁴Zn reaction is duly addressed by applying relevant energy corrections due to the breakup of " ⁶He" projectile into 2n and ⁴He. In addition to this, the barrier lowering, angular momentum and energy dependence effects are also explored in view of the dynamics of chosen reactions.     

Er，Yb和Hf同位素的基态占有率（英文）

应用严格求解的Nilsson 平均场加推广对力模型,在同时考虑质子-质子和中子-中子间对力相互作用的情况下,对稀土区的152-164Er,154-166Yb 和156-168Hf 核素的结合能、奇偶能差、低激发态转动惯量等基态性质进行系统的统一描述。通过计算结果与实验数值比较分析显示,对力相互作用在阐明以上核素能谱的基态性质中起到了关键的作用。应用拟合上述物理量所确定的模型参数,对156-162Yb 核素基态中价核子配成角动量J = 0,1,… ,12的价核子对占有率的计算结果显示,配成角动量为偶数价核子对的占有率远远高于配成角动量为奇数价核子对的占有率,其数值结果揭示了配成角动量为S,D和G的价核子对在所考虑的核素基态性质中占主导地位。The Nilsson mean-field plus extended-pairing model for deformed nuclei is applied to describe the ground-state properties of selected rare-earth nuclei. Binding energies, even-odd mass differences, moments of inertia for the ground-state band of 152-164Er, 154-166Yb, and 156-168Hf are calculated systematically in the model employing both proton-proton and neutron-neutron pairing interactions. In comparison with the corresponding experimental data, it is shown that for these rare-earth nuclei, pairing interaction is crucial in elucidating the properties of the ground state. With model parameters determined by fitting the energies of these states, ground-state occupation probabilities of valence nucleon pairs with angular momentum J =0,1, …,12 for even-even 156-162Yb are calculated. It is inferred that the occupation probabilities of valence nucleon pairs with even angular momenta are much higher than those of valence nucleon pairs with odd angular momenta. The results clearly indicate that S, D, and G valence nucleon pairs dominate in the ground state of these nuclei.     

Current conservation, meson-exchange currents, and magnetic form factors of He and H

The effect of the requirement of current conservation for meson-exchange currents containing the πNN form factor is investigated for the magnetic form factors of ³He and ³H. The effect is substantial for the pionic current contribution but is small for the total contribution to the momentum transfer, Q 5 fm⁻¹.     

Muon capture by He: the hyperfine effect

The hypertine effect for muon capture by ³He is calculated in a modified closure approximation as a function of g_p, the nucleon pseudoscalar form factor. It is found to be very sensitive to g_p.     

光泵抽运3He极化程度监控系统的设计与实现

极化³He的一项重要应用是中子的极化.中国绵阳研究堆（CMRR）已建立国内首个自旋交换光学泵浦（SEOP）极化³He中子极化系统.为了监测³He的极化率随时间的相对变化情况,本文首先设计了基于核磁共振（NMR）技术的³He相对极化率测量系统,通过Matlab控制程序实现了对³He相对极化率的定时检测.然后对拾波线圈的构形和信噪比（SNR）进行了优化.结果表明当绕线长度一样时,Brooks构形的线圈有利于提高SNR;当线圈的平均半径为（a₀+d）/√2（a₀为³He气室的半径,d为拾波线圈与气室之间的距离）时,其SNR最高.最后对该系统的本底噪声进行了测量,发现其主要来源于环境噪声（0.27 μV/√Hz）和数据采集（DAQ）卡的噪声（0.40 μV/√Hz）,系统的总噪声功率谱密度约为√0.16+0.073G² μV/√Hz（G为放大器的增益倍数）.     

Center of mass spuriosity effects on the charge form factor in many-body theories

The effect of c.m. spuriosity on the charge form factor of the nuclei ⁴He and ¹⁶O is studied by assuming 0747 Saxon-Wood wave functions as selfconsistent wave functions. It is found that this effect is quite large at high momentum transfer.     

Pionic K X-rays in liquid He

Energies and lorentzian widths of pionic K X-ray transitions have been measured in liquid ³He with improved accuracy. The strong interaction on the π³He 1s level is found to be attractive and to produce an increase in the K transition energies of 34 ± 4 eV; the measured lorentzian width is 36 ±7 eV. Measured values are also presented for K X-ray energies in liquid π⁴He and μ⁴He, the lorentzian width of the 1s level in π⁴He, and relative intensities of K X-ray transitions in π³He, π⁴He and μ⁴He. The measurements are compared with those of others and with recent theoretical calculations.     

Spectroscopy of molecules in helium droplets

The work reviewed in the talk explores the possibilities of using molecules immersed in liquid helium as probes to study superfluidity on the microscopic level. For this purpose liquid ⁴He, ³He and mixed ⁴He/³He droplets consisting of 10³–10⁵ atoms have been doped with single molecules or a small defined number of molecules which form clusters in the droplet interior. The dopants were investigated with high-resolution optical spectroscopy. The electronic and rovibrational spectra show unusually sharp spectral lines and unexpected features such as a distinct gap between the zero phonon line and the phonon wing as well as the free rotations of single molecules. Both are not observed in colder nonsuperfluid ³He droplets and therefore are considered to be new microscopic manifestations of superfluidity. Spectroscopic studies of small p-H₂ and o-D₂ clusters surrounding a single chromophore molecule formed in the interior of the He droplets are also reported.     

Elastic photoproduction of charged pions on He and H in the Δ(1232) resonance region

Photoproduction of charged pions on ³He and ³H has been measured in the Δ(1232)-resonance region. Differential cross sections are presented as functions of the photon energy at fixed momentum transfer and compared to experimental data and theoretical calculations.     

Adsorption of He on He crystal surfaces

We have compared the surface properties of crystals respectively grown from normal ⁴He containing 130 ppb of ³He and from ultrapure ⁴He (0.4 ppb). Below 0.4 K, ³He impurities are found to decrease both the surface tension and the step energy. Our results are consistent with the existence of two-dimensional bound states for ³He atoms at the solid-liquid interface. Quantitative agreement with the data is found with a binding energy _s ≈ 4.3 K and a ³He density saturating around 0.4 monolayer. The presence of steps is found to increase the binding energy by about 10 mK.