Calibration of CN and CR-39 track detectors for measurements of fast deuterons and nitrogen ions

The paper reports on the analysis of responses of CN-type films and CR39-plastic nuclear track detectors (NTDs) to fast deutrons and nitrogen ions emitted from high-current Plasma-Focus (PF) facilities, as operated at SINS and INFIP. In order to separate the deutrons and nitrogen ions of different energy, the use was made of a Thomson-type mass-spectrometer adapted to measurements within dense plasma streams. Deutron and ion parabolaen were registered the CN-80 and CN-LR115 films as well as with the CR39 plastic NTDs, which were undergone routine etching procedures. On the basisof known characteristics of the spectrometer applied energy- and mass-scales for the obtained ion paraboale were determined. Using an optical microscope, a detailed analysis of track dimensions was performed in chosen points along the registered parabolae, and the calibration diagrams (i.e. a track diameter for the chosen ion energy and different etching times) were determined. Results of the calibration procedure, after comparing with other calibration data obtained with conventional particle accelerators, may be applicable for measurements of fast deutrons (i.g., in nuclear fusion experiments) and energetic nitrogen ions (i.g., in some plasma- and ion-facilities used for technological applications).     

Effect of high energy ion irradiation on silicon substrate in a pulsed plasma device

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si(1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are reported. In particular, it has been found that with silicon targets, the application of PF carbon ion beams results in the formation of a surface layer of hexagonal (6H) silicon carbide, with embedded self-organized step/terrace structures.     

On the mechanism of cluster emission in sputtering

The intensity and the energy distribution of Si⁺_n cluster ions emitted from clean silicon have been measured for different target orientations as a function of the primary ion energy (3–30 keV) and the projectile mass (noble gas ion bombardment). The results favour the idea that clusters are emitted as such rather than being produced by vacuum recombination of individually emitted atoms and ions.     

Nitrogen ion spectrum from a low energy plasma focus device

The nitrogen ion spectrum generated from a low energy Mather-type Plasma Focus device is reported. The main species of ions present are N ⁺¹, N⁺², and N⁺³. It is found that its relative concentrations at a distance of several cm from the ion source are in agreement with those predicted for an equilibrium charge-state of the beam, and hence the spectrum of the neutral nitrogen is also derived. By taking into account the lateral spread of the beam due to multiple elastic scattering with the background gas, the derivation of absolute values for the total ion spectrum within the investigated energy range (>170 keV), the total number and total energy of the fast particles has been obtained     

Track measurements of fast particle streams in pulsed discharge explosive plasma

This paper reports results of track registration for fast particles from the hot spot sparked inside a metal target. CR-39 track detectors placed in the ion pinhole camera, a magnetic analyzer, and Thomson-type mass-spectrometer in order were used to obtain images of the hot spot and to determine spectra of the fast particles. Using track detectors in the pinhole camera, we have obtained specific split images. The “average etch rate ratio versus track length” locus for track sample groups is depicted by means of squared diameters asymptotic method. Our analysis shows the majority of tracks belong to hydrogen nuclei. The track loci for the detectors from the pinhole or analyzers turn out to be split into two parallel streaks that have been interpreted as a proton–deuteron doublet. Data obtained using the Thomson analyzer clearly demonstrate the equal numbers of protons and deuterons for some parallel parabola sections.     

Low-energy ion measurements by means of CR-39 nuclear track detectors

The paper presents an additional acceleration system, used to shift up an ion energy spectrum by 20 keV, and some examples of the ion parabolas registered by means of a Thomson-type spectrometer within the rod plasma injector (RPI-60) facility, designed for plasma physics and application studies. The use of the described acceleration system and CR-39 track detectors has enabled the registration of ions of energy above 20 keV to be performed. It made possible to measure the ion (e.g. deuteron) energy spectrum more exactly in the low-energy range, what is important for the determination of ion emission characteristics.     

The16O(d,n)17F reaction at deuteron energies from 2.5 to 5.5 MeV

The¹⁶O(d, n)¹⁷F transitions to the ground state and to the first excited state were studied in the deuteron energy range 2.5–5.5 MeV. Time-of-flight techniques and gas targets were used. Differential cross sections in the angular range 0–160? at deuteron energies from 3.0 to 5.5 MeV in steps of 0.5 MeV were recorded as well as yield curves at 0 and 30? from 2.5 to 5.5 MeV in steps of 100 keV. DWBA calculations using seven different deuteron optical potentials were performed. It is found that the spectroscopic factors depend strongly on the choice of deuteron optical potential. The ratio between the spectroscopic factors for the ground state and for the first excited state varies between 0.9 and 1.7 for various choices. The most straightforward choice gives the ratio 1.4. Similar studies at higher deuteron energies have yielded ratios close to unity.     

Proposal of the experiment on the investigation of the (d, p) reaction at the extracted deuteron beam of the U-70 accelerator

The experiment on the investigation of the A(d, p)X reaction at the extracted deuteron beam created at the Serpukhov U-70 accelerator is proposed. Precise measurements of the momentum spectra of protons emitted in the (d, p) reaction at an initial deuteron momenta of 20–40 GeV/c can give unique information on the deuteron short-range structure. A manifestation of contribution of nonnucleonic degrees of freedom in the deuteron is entirely possible over this energy range. The text was submitted by the authors in English.     

Excitation of Doubly‐Charged Ion Emission Lines from a Grimm‐Style Glow Discharge Plasma—Comparison Between Yttrium and Zirconium

Spectra of yttrium and zirconium emitted from a Grimm‐style glow discharge plasma were investigated to elucidate the excitation mechanism of doubly‐charged ionic lines when using argon–helium mixed gas as well as argon gas alone. The energy sum for exciting doubly‐charged ion species of yttrium is slightly smaller compared to the case of zirconium, which yields an interesting correlation in the excitation energy between their ionic species and excited species of helium or argon. The Y III emission lines which were assigned to the 4p⁶5p–4p⁶5s(4p⁶4d) transitions could be observed in the argon–helium mixed gas plasma, but those were hardly excited with argon gas only. The Zr III emission lines did not appear in the spectra emitted by the argon gas plasma nor by the mixed gas plasma. A possible explanation for these phenomena is that the excitation of these ionic species is caused principally by collisional energy transfer from helium species to the analyte atoms.     

Study of spatial structure and energy spectrum of ion beams by means of LR 115A and PM-355 nuclear track detectors

The paper reports on measurements of pulsed plasma-ion streams, as performed with the selected solid-state nuclear track detectors (SSNTD). The ion-beams were produced by an experimental device (RPI-IBIS) equipped with coaxial electrodes (each made of molybdenum rods) and a fast-acting gas valve. The device was operated at 30 kV/44 kJ, with puffing of pure hydrogen or deuterium. The spatial structure of the ion beams was studied with pinhole cameras equipped with replaceable detectors, and ion mass- and energy-spectra were measured with a Thomson spectrometer. To analyse low-energy ions (below the energy thresholds of LR 115A and PM-355 SSNTD) an additional accelerating system was applied. It was observed that ions of energy are emitted in bunches, and the ion flux amounts to at a distance of 30 cm from the electrodes outlet. Energy spectra of protons and deuterons ranged from about 30 keV to about 400 keV. The ion distributions, as recorded by means of the PM-355 and LR 115A detectors, are similar.     

SINGLET DEUTERON INTERMEDIATE STATE IN d-d FOUR-BODY BREAKUP REACTION (Ⅱ)

At C.M. angles 90°and 64°two-dimensional spectra of protons emitted from singlet deuterons were measured under such geometry where the kinematic ambiguty was small. From the data it is obtained that the breakup energy E_B of the singlet deuteron state is (52+21)keV.     

Generation of neutrons at the relaxation of fast deuterons in deuterium matter

We analyze the fusion process involving two deuterium nuclei in the case of deceleration of a fast deuteron with an energy of approximately 100 keV located in a deuterium target. We calculate the probability ω _fus(ε) of generating a neutron by a fast deuteron with an initial kinetic energy ε during its deceleration. The mean free path of fast deuterons with respect to their relaxation is found for various deuterium targets. The data are analyzed for neutron generation in deuterium cluster beams under laser irradiation. The method of neutron generation in the collision of two deuterium cluster beams is suggested. The text was submitted by the author in English.     

Emission of helium nuclei in heavy ion interactions at energies ≧ 100 MeV/nucleon

The energy and angular distributions of helium particles emitted in interactions between nuclei in the cosmic radiation and nuclei in photoemulsions at energies ≧ 100 MeV/nucleon have been studied. The data obtained is impossible to interpret on the basis of a statistical decay of excited nuclei. For example, it is found that more than 28% of the helium nuclei are emitted in processes different from simple evaporation. The differential energy distribution of the helium nuclei in the energy interval (40–200) MeV can be represented by the relationN(E)dE=constE ^?a dE, wherea≈1.2. The large spread in angles and energies of the fast helium particles emitted in heavy ion interactions can to a certain degree be understood, if it is assumed that interactions between nucleons and clusters of nucleons occur.     

氘核与聚变中子耦合输运方法及应用

对加速器驱动中子发生器的数值模拟包括离子输运、聚变反应、中子输运等。由于核反应截面远低于带电粒子输运的库仑截面,且核反应平均自由程远大于靶厚度,直接蒙卡抽样难以抽到聚变反应。在MCNPX程序基础上,采用“强迫”聚变方法,即每个入射氘核必发生一次聚变反应,聚变反应处氘核的真实状态(位置、能量和方向)以抽样产生,并以此状态来确定聚变中子的出射状态,实现了氘核与聚变中子的耦合输运模拟计算。研究结果表明,该方法能够给出氘核输运对聚变中子能谱和角分布的影响,中子产额计算结果符合预期。     

Continuous proton spectra emitted in 3He and deuteron induced reactions

A study of the energy and angular distributions of protons emitted in ³He induced reactions was undertaken at an incident energy of 25.6 MeV. An analysis in the framework of the pre-equilibrium hybrid model did not succeed in explaining the overall behaviour of proton spectra; a contribution due to a break-up or a double stripping of the incident particle has to be taken into account. An attempt was made to account for these processes by performing a phase space calculation. This formulation was firstly tried in the case of deuteron induced reactions for which a break-up mechanism has already been confirmed in continuous proton spectra. The calculation extended to the case of ³He induced reactions showed that a double stripping mechanism could explain the observed distribution.     

Fast neutron emission from partial fusion heavy ion reactions

The Boltzmann master equation theory which succesfully reproduces the spectra of fast nucleons emitted in fusion and quasi-fusion heavy ion reactions is used to predict the spectra of fast nucleons in coincidence with a projectile-like fragment in the interaction of 35 MeV/ nucleon¹⁴N with¹⁶⁵Ho. In particular it is shown that the spectra of neutrons in coincidence with a high energy projectile-like fragment emitted at a very forward angle with energy corresponding to the beam velocity may be reproduced satisfactorily assuming an elastic breakup of the projectile followed by fusion of one of the fragments with the target nucleus.     

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：     

CLUSTER EFFECTS IN DEUTERIUM CLUSTER ION IMPLANTATION ON SOLIDS

Atomic and nuclear cluster effects of (D⁺₃) were studied by alternative implantation of deuterium cluster ion beam and isolated deuteron (D⁺) beam on metal targets. The beam energy was adjusted from 10keV/d to 100keV/d in experiment. The atomic cluster effect was shown by the enhancement of X-ray emission induced by cluster deuterion. The average ratio of X-ray intensity induced by each cluster deuteron to that induced by each isolated deuteron is about 2.6 in the experimental energy region. The nuclear cluster effect is shown by the difference of D-D fusion rates induced by two kinds of deuterons under the same experimental conditions. The ratio of the D-D fusion rates induced by the two kinds of deuterons is energy dependent.     

Multi-spike structure of ion pulses generated by plasma focus discharges

Space- and time-resolved studies of high-energy (> 50 keV) deuteron beams emitted from 3 different Mather-type plasma focus facilities of energy capacity ranging from about 10 kJ to above 200 kJ are presented. In deuteron beams space-resolved with a pinhole camera a spike structure is observed. In quasi-monoenergetic, e.g. 305±20 keV deuterons chosen from a Thomson-spectrograph image there appear up to 3 separate pulses of 8–10 ns FWHM, separated by 30–40 ns intervals. Some pulses demonstrate a fine spike structure with FWHM < 2 ns.     

Secondary particle emission from a ferromagnetic binary compound

Secondary ion emission from an ion-bombarded binary compound in the ferro- and paramagnetic states has been studied using experimental methods and molecular dynamics simulations. The experiments were performed with a widely used NiPd binary compound, which was bombarded by obliquely incident 10-keV Ar ions. It is established that the intensity of Ni⁺ and Pd⁺ ion emission from a polycrystalline NiPd sample decreases significantly when it passes from the ferromagnetic to paramagnetic state. This effect is explained by a change in the surface binding energy and density of surface states at the Fermi level and by a cumulative process related to sputtering. The energies and directions of emission of secondary particles from poly- and single-crystalline NiPd samples in the ferromagnetic state have been jointly studied. It is established that the maximum of the polar angular distribution of secondary particles deviates toward the normal to the irradiated surface with a decrease in their energy. A difference in the azimuthal distribution of emitted Ni and Pd particles has been observed during the bombardment of a (001)NiPd crystal face and explained by specific features of correlated collisions. The best agreement of experimental data with the results of molecular dynamics simulations is obtained if the calculations are performed with allowance for an experimentally established modified composition of the three uppermost surface layers [39].