低能氘团簇离子(d+3)诱发固体靶内D-D核聚变过程中的团簇效应研究

通过对由三个氘原子组成的氘团簇离子(d⁺₃)与三个分立的氘核(3d⁺)在轰击吸氘固体靶时所发生的D-D聚变反应率的差别的研究，进而揭示氘团簇离子在与固体靶中的氘核发生聚变反应时所体现出的团簇效应.实验结果显示，在10—40keV/d能区，每个氘团簇中的氘核(d⁺₃/3)所产生的聚变反应率高于具有相同速度的独立氘核(d⁺)所产生的聚变反应率.反之，在50—100keV/d能区，独立氘核比之于氘团簇中的单个氘核所产生的聚变反应率要高.两者之间的比值具有非常明显的能量相关性.这种团簇特性与团簇离子本身特性及固体靶环境等多方面因素有关.对其作用过程和实验中观测到的现象的实质做了具体讨论. 关键词：     

Total cross-section measurements for the production of nuclear gamma rays from light nuclei by low-energy deuterons

The thick target yields of the reactions ⁶Li, ⁹Be, ¹⁰B(d, nγ) for specific final nucleus γ-rays have been measured between deuteron bombarding energies of 48 and 170 keV. The measured thick target yields are used, together with recently published values of the stopping power of low-energy deuterons in matter, to infer the total reaction cross sections for the production of the specific γ-rays between deuteron energies of 65 and 160 keV. The cross sections are compared to appropriate Coulomb barrier penetration probabilities and the astrophysical functions S(E) are deduced.     

Investigation of the Reaction 9Be(d,t0)8Be in the Deuteron Energy Range 0.9÷2.5 MeV

The reaction ⁹Be (d, t₀) ⁸Be has been investigated in the deuteron energy range 0.9 ÷ 2.5 MeV. The excitation functions were measured at laboratory angles 45° and 120° and showed no sharp resonances. The angular distributions (differential cross sections in mb/sr) were measured in 200 keV intervals. An analysis of the data has been made using the Butler and the distorted wave theories.     

Low-energy nuclear reactions in crystal structures

Results of studying low-energy nuclear reactions at the HELIS facility (LPI) are presented. Investigations of yields from DD reactions in deuterated crystal structures at deuteron energies of 10 to 25 keV show a considerable enhancement effect. It is shown that exposure of the deuterated targets to the Н⁺ (proton) and Ne⁺ beams with energies from 10 to 25 keV and an X-ray beam with the energy of 20 to 30 keV stimulates DD reaction yields. For the CVD diamond target, it is shown that its orientation with respect to the deuteron beam affects the neutron yield. The D⁺ beam is shown to cause much higher heat release in the TiD_x target than the Н⁺ and Ne⁺ beams, and this heat release depends on the deuterium concentration in the target and the current density of the deuteron beam.     

Low-energy cross section for 6Li(d,n)7Be

Cross sections were determined for the ⁶Li(d, n)⁷Be reaction between 100 and 180 keV deuteron energy using the activation method. Different methods of extrapolation were employed and compared down to the energy region of astrophysical interest.     

厚靶D（d,n）^3He反应加速器中子源的产额、能谱和角分布

给出一种计算氘钛厚靶D(d,n)3He反应加速器中子源的产额、能谱和角分布的方法,并发展了一个计算机模拟程序,程序能够计算氘束流能量小于1.0 MeV的中子源的产额、能谱和角分布.计算时使用推荐的D(d,n)3He反应截面数据和来自SRIM-2003程序的氘在氘钛靶中的阻止本领数据.给出一些典型计算结果,包括中子积分产额、中子能谱和角分布.     

Measurement of the astrophysical S factor for the low energy 2H(d,γ)4He reaction

The y-rays and protons from an Ed = 20 keV deuteron beam incident on a D-Ti target were measured. A branching ratio of the 2H(d,T)4He reaction versus the 2H(d,p)aH reaction of F.v/l'p = (1.06+ 0.34) x 10-7 has been obtained, and the astrophysical S factor of the 2H(d,T)aHe reaction at the center of mass energy Ecru ≈ 7 keV of (6.0+2.4) x 10-8 keV.b was deduced.     

DD reaction enhancement and X-ray generation in a high-current pulsed glow discharge in deuterium with titanium cathode at 0.8–2.45 kV

The DD reaction yield (3-MeV protons) and the soft X-ray emission from a titanium (Ti) cathode surface in a periodic pulsed glow discharge in deuterium were studied at a discharge voltage of 0.8–2.45 kV and a discharge current density of 300–600 mA/cm². The electron screening potential U_e = 610 ± 150 eV was estimated in the range of deuteron energies 0.8 keV < E_d < 2.45 keV from an analysis of the DD reaction yield as a function of the accelerating voltage. The obtained data show evidence for a significant enhancement of the DD reaction yield in Ti in comparison to both theoretical estimates (based on the extrapolation of the known DD reaction cross section for E_d ≥ 5 keV to low deuteron energies in the Bosch-Halle approximation) and the results of experiments using accelerators at the deuteron energies E_lab ≥ 2.5 keV and current densities 50–500 μ A/cm². Intense emission of soft X-ray quanta (10¹³–10¹⁴ s^?1 cm^?2) was observed at an average energy of 1.2–1.5 keV. The X-ray emission intensity and the DD reaction yield enhancement strongly depend on the rate of deuterium diffusion in a thin subsurface layer of Ti cathode.     

Polarization of protons from the Be(d,p)Be reaction at Ed = 12.0 MeV

The polarization of protons from the ⁹Be(d,p)¹⁰Be reaction at E_d = 12.0 MeV was measured for the ground state and first excited state transitions. The results obtained are compared with the predictions of DWBA theory. It was found that better fits to the experimental data can be obtained using volume absorption in the distorting potential of the deuteron elastic channel. A comparison of the present polarization data with the vector analysing power for the same reaction and the same incident deuteron energy has also been made.     

Computer simulations of particle flux and energy peaking

A computer simulation of the channeling of 300 keV deuterons in a niobium lattice has been performed. The model calculations included: binary Thomas-Fermi interaction between projectiles and lattice atoms, thermal displacements of the lattice atoms in the transverse plane of particle motion, electron scattering of the deuterons dependent on the local electron density, and electronic energy loss dependent on the local electron density. Flux distributions and mean particle energy distributions of the deuterons were calculated in their development with penetration depth. Flux peaking and energy peaking was found to depend sensitively on the local variation of the electron density in the crystal.     

Experimental determination of the electron screening potential energy for the d(d, n)3He Reaction in ZrD2 and D2O in the ultralow energy region

This work is devoted to measuring of the values of the astrophysical S-factors and electron screening potential energy for a d(d,n)³He reaction occurring at ultralow energies in zirconium deuteride ZrD₂ (3.5–7.0 keV) and heavy water D₂O (2.2–6.0 keV). The experiment was performed on the Hall pulsed plasma accelerator at the TPU Nuclear Physics Institute (Tomsk) with ZrD₂ and D₂O targets produced by the magnetron sputtering of zirconium in a deuterium environment and heavy water freezing-out on a copper support, respectively. A χ ² analysis of the dependence of the neutron yields and astrophysical S-factors for the dd reaction on the deuteron collision energy E revealed that the upper bounds of the electron screening potential energy for interacting deuterons in ZrD₂ and D₂O and of the astrophysical S-factors at the deuteron collision energy E = 0 were U _e (ZrD₂) < 30 eV, U _e (D₂O) < 25 eV, S(0) = (57.2 ± 3.9) keV · b (ZrD₂), S(0) = (58.6 ± 3.6) keV · b (D₂O) at the 90% confidence level.     

Negative pion production by deuterons

Negative pion production by deuterons on light nuclei has been considered in the framework of the Intranuclear Cascade model. Characteristics of secondary particles have been calculated by means of the Internuclear Cascade model for C and Be extended targets. A satisfactory agreement with experimental data for thin and extended targets has been found for different deuteron energies. Dependencies of pion yield on the target size and deuteron energy have been analyzed in detail.     

Features of excitation of the hydrogen (deuterium)-metal system by an electron bunch

We report on the results of mass-spectroscopic analysis of the hydrogen yield from metals saturated with hydrogen under the action of accelerated electrons (with an energy of up to 100 keV and a current density from 3 to 30 μA). It is found that the desorption rate is determined not only by parameters of the electron bunch, but also by the structure of the oxide film. It is discovered that the electronic subsystem of hydrogen-enriched metals enhances their ability to absorb the energy of the external electromagnetic action and to preserve it for a longer time as compared to a pure metal. This facilitates nonequilibrium migration and yield of hydrogen under the action of radiation in the subthreshold range. A theoretical model is proposed and analytic dependences are derived for the intensity of hydrogen yield from metals exposed to an electron bunch. The results of this study can be used for the removal of hydrogen from metals and for obtaining submicrocrystalline materials (e.g., titanium).     

The effects of electron screening and resonances in (p, α) reactions on10B and11B at thermal energies

The fusion reactions¹⁰B(p, α)⁷Be and¹¹B(p, α)⁸Be have been studied over the c.m. energy range E=17 to 134 keV using intense proton beams and thick solid targets. In the case of¹¹B(p, α)⁸Be the low-energy data in terms of the astrophysical S(E) factor show an exponential enhancement (up to a factor of 1.9) due to the effects of electron screening, where the deduced screening potential is larger than expected. In the case of¹⁰B(p, α)⁷Be the low-energy data exhibit an enhancement by more than a factor of 200, which cannot be explained by the effects of electron screening. The enhancement arises here from the high-energy tail of an expecteds-wave resonance at E_R=10 keV. The results offer an improved prospect for this reaction as advanced fuel in future fusion reactors than previously envisioned.     

Be(d,n)反应中子源能谱测量及应用

 利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7～25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。     

Preliminary results of the study of the d(d,n)3He reaction in the astrophysical energy range with the use of a Hall plasma accelerator

The possibility of using a plasma accelerator based on a pulsed Hall ion source to study the characteristics of pd, dd, d³He, ³He, and⁴He reactions in the astrophysical energy range (2–12 keV) has been considered. The preliminary experimental data on measurement of the astrophysical S factor for the dd reaction (dd → ³He + n (2.5 MeV)) at average deuteron collision energies E _col = 4.5 and 4.95 keV and the deuteron beam energy spread FWHM = 18% are reported. The found value of the S factor is in agreement with the results of the experiments carried out by us previously using linear plasma in the inverse Z-pinch configuration.     

氘代乙烷团簇库仑爆炸产生高能氘核和中子的研究

采用简化库仑爆炸模型对强激光脉冲照射氘代乙烷团簇发生的库仑爆炸过程进行数值模拟,研究了氘代乙烷团簇爆炸产生的氘核动能、中子产额与团簇尺寸的关系,且与氘代甲烷团簇产生的氘核动能及中子产额进行了比较.研究表明,尺寸为5 nm的氘代乙烷团簇在发生库仑爆炸后氘核的最大动能为20.96 keV,获得的中子产额为6.31×105,比同尺寸氘代甲烷团簇产生的氘核最大动能及中子产额更大.因此相对于氘代甲烷团簇,大尺寸的氘代乙烷团簇更适合作为激光驱动团簇库仑爆炸获得高额中子的靶材,这与报道的实验推论相一致.     

Effects of confinement on the electron and lattice dynamics in metal nanoparticles

Effects of confinement on the electron-electron (e-e) and electron-phonon (e-ph) thermalization dynamics in noble metal clusters are calculated using simple approaches. The model predictions are compared with femtosecond pump-probe measurements which display an acceleration of the e-e and e-ph relaxation dynamics. The size-effects on the e-e relaxation dynamics are consistent with a model involving the surface-induced reduction of the screening efficiency of the Coulomb e-e interaction. With regard to the e-ph relaxation dynamics, this model yields too large time constants, pointing out deficiencies of the standard modelling of the e-ph energy exchanges in bulk metals. Analysis of these deficiencies shows that the bare e-ion interaction has to be involved in the transition matrix element describing the non-adiabatic e-ph energy exchanges.     

High-resolution study of the 118Sn(d,p)119Sn reaction at 17 MeV

Energy levels in ¹¹⁹Sn up to 4.75 MeV excitation have been studied with the ¹¹⁸Sn(d, p)¹¹⁹Sn reaction at an incident deuteron energy of 17 MeV. The scattered particles were analysed by a magnetic spectrograph and detected in nuclear emulsions with a resolution of ≈ 9 keV. Seventyseven energy levels were identified. Angular distributions were compared to DWBA predictions allowing the identification of transferred angular momenta and the determination of spectroscopic factors for 49 states. The results obtained are compared with pairing theory and the weakcoupling model.     

Level structure of 42K from the 41(n, γ) and 41K(d,p) reactions

The γ-ray spectrum emitted after thermal neutron capture in ⁴¹K has been measured with pair and Ge(Li) spectrometers at the ILL high-flux reactor. About 630 transitions have been assigned to the decay of 133 excited states in ⁴²K. The level energies have been determined with a precison of 20 ppm; the neutron binding energy was determined to be E_B = 7533.82(15) keV. On the basis of the many transitions to known states, several spin-parity assignments have been made. In addition, high-resolution proton spectra of the reaction ⁴¹K(d,p) have been taken at 20MeV deuteron energy with the München Q3D spectrometer. These data have been essential in establishing the newly-found levels and in differentiating between primary and secondary transitions in the (n, γ) work. A statistical analysis of the level density and relative strengths of primary transitions is given.