A nonlinear thermal spike model for pyrolytic graphite under irradiation with 86Kr and 209Bi high-energy heavy ions

The temperature dependences of the specific heat capacity and thermal conductivity are introduced for a highly oriented pyrolytic graphite; i.e., the nonlinear model of a thermal spike is considered and a comparative analysis of the obtained results and those for the linear model of a thermal spike is performed. The temperature effects observed in the highly oriented pyrolytic graphite with a change in the electron-phonon interaction coefficient g are investigated in detail. It is shown that, under irradiation of the highly oriented pyrolytic graphite by bismuth ions with an energy of 710 MeV, the temperature on the surface of the target within the framework of the nonlinear model can exceed the sublimation temperature, whereas the temperature on the surface of the target under irradiation by krypton ions with an energy of 253 MeV does not exceed the sublimation temperature. The characteristic range of variations in the electron-phonon interaction coefficient g is evaluated. For values of g in this range, the thermal spike model explains the experimental data on the presence of structures in the form of hillocks with craters at their centers on the surface of the highly oriented pyrolytic graphite exposed to irradiation by ²⁰⁹Bi ions and on the absence of such structures in the case of irradiation by ⁸⁶Kr ions.     

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with ⁸⁶Kr (253 MeV) and ¹⁹⁷Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift ⁸⁶Kr ions. The small crystalline objects are detected on the InP surface irradiated with ⁸⁶Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.     

Statistical fluctuations in dissipative heavy-ion collisions

We investigate statistical fluctuations in the relative motion of colliding heavy ions as well as in the nucleon transport. Approximate analytical expressions for the fluctuations in energy loss, scattering angle, and fragment charge number are derived from a Fokker-Planck equation and evaluated at the scission point using previously determined mean interaction times. In a detailed comparison with the data for¹³⁶Xe +²⁰⁹Bi and⁸⁶Kr +¹⁶⁶Er we can account for the observed multidifferential cross sections except at low energy loss where the calculated fluctuations in scattering angle are too small.     

STM and AFM observations of damage produced by swift Ne and Kr ions in graphite

Radiation damage of highly oriented pyrolitic graphite (HOPG) samples have been investigated following irradiation with 215 MeV Ne and 209 MeV Kr ions, available at U-400 cyclotron, Dubna. A freshly cleaved HOPG surface was irradiated perpendicularly to the sample surface (c plane). A low ion irradiation dose was used (10¹² ions/cm²) in order to avoid damage overlap. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are useful methods allowing direct observation of surface defects. The observations were made after irradiation without any further sample preparation. The experimental results are compared to computer simulations (TRIM code) and primary knonked-on atomic spectrum calculations (LET code). Clear distinction can be made between surface features attributed to nuclear stopping effects and defects owing to electronic stopping mechanisms.     

Evidence of new isotopes:169, 170Ir,166, 167, 168Re

At the Darmstadt UNILAC newα-emitting nuclei were produced in the bombardment of⁸⁹Y and⁹³Nb targets using⁸⁴Kr ions with energies in the range of 5.1 to 5.5 MeV/u, and 5.8 to 6.4 MeV/u, and using⁸⁶Kr ions with energies in the range of 5.6 to 6.0 MeV/u. Reaction recoils emitted from the targets were stopped and transported with argon to a collection site. Using three alpha detectors and spectrum multiscaling, energies and half-lives were measured. Ir and Re isotopes were identified by cross bombardments, excitation function data andα-systematics. The decay characteristics of the new species are as follows: Estimates onα-branching ratios have been obtained for^{169, 170}Os and^{166, 167, 168}Re.     

Probabilistic model for deep inelastic reactions

Due to transport phenomena in the interaction region, the dynamical variables in deep inelastic collision do not have sharp values at the end of the interaction. In the present model, they are considered as random variables with Gaussian probabilities centered on the classical results, while the Coulomb dynamics outside the interaction domain is treated exactly. Very simple formulas are obtained for multiple-differential cross-sections. Numerical results applied to the “quasi-fission” products of the reaction⁸⁴Kr(525 MeV)+²⁰⁹Bi agree fairly well with experimental data.     

Evidence from inelastic proton scattering for a giant quadrupole vibration in spherical nuclei

A systematic study of inelastic proton continuum spectra produced at small angles by bombardment of ²⁷Al, ⁵⁴Fe, ¹²⁰Sn and ²⁰⁹Bi with 62 MeV protons suggests the existence of a collective region in the continuum with properties of a giant quadrupole vibration.     

Scattemng of 14.1 MeV neutrons from 209Bi

Differential cross sections for the elastic and inelastic scattering of 14.1 MeV neutrons from ²⁰⁹Bi have been measured with a time-of-flight system which had an energy resolution of 650 keV. For elastic scattering from ²⁰⁹Bi, an optical-model analysis gave the best-fit potential parameters. The absolute cross sections for excitation of collective (2.66 and 4.36 MeV) states are reproduced by the results of distorted-wave calculations under the assumption of a core (²⁰⁸Pb) excitation model using deformation parameters obtained from (p, p') reactions.     

Search for coulomb fission induced by 84Kr ions on 238U

We have searched for Coulomb fission induced by ⁸⁴Kr ions on a ²³⁸U target at energies ranging from the interaction barrier down to 37 MeV below (408–458 MeV lab). No event attributed to Coulomb fission was detected; it was deduced that the cross section for this reaction is lower than 0.3 mb/sr near the interaction barrier. This value was compared to theoretical predictions. However, fission events originating from transfer reactions at the interaction barrier have been detected.     

Study of Ternary Fission Produced in 12C Bombarding 209Bi Target with Medium Energy

Alternative layers of target material,which were prepared by evaporating ²⁰⁹Bi on the surface of mica foils,were irradiated with ¹²C ions.Ternary fission events in which three fragments of comparable mass were produced in 2525－47.5MeV/A ¹²C+²⁰⁹Bi reaction,were recorded by the mica detectors with 2π geometry.The observed probability ratio of ternary fission relative to binary fission in 2π geometry was modified to 4π geometry spatial in terms of the Monte Carlo method.The values of ratioes increase with the bombarding energy,and are compared with the calculation result of the cascade fission model.     

A DYNAMICAL METHOD IN DEEP IN ELASTIC COLLISION OF HEAVY IONS

A method correlating the dynamical equations with the diffusion equations is developed in this paper to explain the dissipations and fluctuations of heavy ion collisions. Considering the degrees of freedom about the relative motion, rotation and asymmetric mass, the relation between the frictional and diffusion tensors is obtained.
Some imformations of deep inelastic collisions in three reaction systems are obtained by solving coupling equations numerically. The calculated results show that there are orbiting effects in the reaction systems of ⁸⁶Kr(8.18MeV/A)+¹⁶⁶Er and ⁸⁴Kr(8.5MeV/A)+¹⁶⁵Ho and there is strong focusing effect in the reaction system of ¹³⁶Xe(8.31MeV/A)+²⁰⁹Bi. But the calculated results are in agreement with the experimental data only for larger partial waves. The nuclear force and diffusion coefficients must be studied further.     

Experimental study of excitation functions and isomer ratios for 211, 212Po

Excitation functions have been measured for ground states and isomers populated in the ²⁰⁸Pb(α, n)²¹¹Po, ²⁰⁹Bi(α, np)²¹¹Po, ²⁰⁹Bi(α, p)²¹²Po and ²⁰⁹Bi(α, n)²¹²At reactions for α-beams ranging from 45 MeV to 172.5 MeV. The experimental results have been compared with theoretical calculations assuming direct and preequilibrium reaction mechanisms, respectively. It is found that the experimental excitation functions can be reproduced satisfactorily by calculations in the framework of the preequilibrium model. Isomer ratios have been extracted from the data as well. Their energy dependence can be reproduced by an optical-model calculation for beam energies larger than about 60 MeV.     

ANGULAR DISTRIBUTIONS OF FISSION FRAGMENTS AND THE SHAPES OF THE SADDLE POINT OF COMPOUND NUCLEI

We have measured the angular distributions of fission fragments for a series of compound nuclei formed in the bombardment of ¹⁶⁹Tm, ¹⁷⁵Lu, ¹⁸¹Ta, ¹⁹⁷Au, ²⁰⁹Bi, ²³²Th and ²³⁸U by 78 MeV ¹²C ions and in the bombardment of natural lead by 96.6, 92.2, 88.1, 79.0 and 75.6 MeV ¹⁴N ions with mica track detectors. All the measured angular distributions can be fitted by the theoretical formula given by Halpern and Strutinski. The effective moments of inertia of the fissioning nuclei at the saddle point are derived from the angular distribution anisotropies. A comparison is made for the shapes of experimental saddle point with the theoretical predictions by the liquid drop model.     

Comparative Study of Electrodeposited and Ion Beam Mixed Fe-Ni-Cr Alloys

Electrodeposited Fe-Ni-Cr alloys irradiated with 209 MeV energy ⁸⁴Kr ions were investigated by conversion electron Mössbauer spectroscopy, X-ray diffraction and electron microprobe analysis. Significant dose dependent changes were found between Mössbauer spectra of the irradiated and non-irradiated deposits. These changes reflect the dose dependent transformation of the metastable ferromagnetic phase to the paramagnetic one.     

Reactions on 209Bi induced by intermediate energy protons and the effect of direct reactions

Excitation functions and ranges of recoil nuclei in the ²⁰⁹Bi(p, 3n)²⁰⁷Po, ²⁰⁹Bi(p, 4n) ²⁰⁶Po and ²⁰⁹Bi(p, p3n)²⁰⁶Bi reactions have been measured for incident energies from 18 MeV up to 52 MeV. It has been found that the recoil ranges in (p, p3n) reactions are rather shorter than those in (p, 4n), and that beyond E_p = 40 MeV the high energy tail of the excitation function for (p, p3n) is roughly flat, in contrast to the decreasing tail for (p, 4n). A theoretical analysis of the excitation functions and of the nuclear recoil ranges has been made. It has been found that in (p, p3n) reactions the direct process plays a very important part in the reaction mechanism. It is also found that the reaction mechanisms of (p, 3n) and (p, 4n) reactions should be interpreted by means of an admixture of the equilibrium compound process and the pre-equilibrium decay process at bombarding energies up to 40 MeV and 50 MeV, respectively, and that the direct process seems to appear at bombarding energies higher than these respective energies.     

Correlation between strain and defects in Bi implanted Si

The strain in Si containing group-V impurities is a topical subject of study due to its potential applications in quantum computing. In this paper we study ²⁰⁹Bi implanted Si concerning the correlation between the strain produced by stopped Bi ions and trapping characteristics of the defects resulted from implantation. The depths distributions of stopped ions and primary defects are simulated and the distributions of permanent defects are modelled for Si implanted with low fluence ²⁰⁹Bi ions of 28 MeV kinetic energy. For comparison, these depths distributions were similarly calculated for ¹²⁷I ions with the same fluence and energy, implanted in Si. The results are compared with each other and correlated with the characteristics of traps in these systems, previously obtained. We demonstrate that the intensity of the strain field is the most important factor in changing of trap parameters, while the superposition between the region with strain and the region where defects are located is a second order effect.     

Effects of Heavy Ion Irradiation on Short-Range Order of Fe–Cr–P–C Amorphous Alloys Investigated by Mössbauer and DSC Measurements

Rapidly quenched Fe–Cr–P–C amorphous alloys irradiated with 209 MeV energy ⁸⁴Kr ions were investigated by Mössbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry measurements. Significant changes were found between Mössbauer spectra of the irradiated and non-irradiated amorphous alloys. The changes were analysed by the hyperfine field distribution method, too. The crystallisation temperature as well as the phase composition at a certain stage of crystallisation were found to be different in the non-irradiated and irradiated samples. These results reflect the changes in the short-range ordering due to the irradiation with energetic heavy ions.     

MEASUREMENT OF FISSION FRAGMENT ANGULAR DISTRIBUTION IN HEAVY-IONS INDUCED REACTION

The angular distributions of fission fragments for a series of compound nuclei formed in the bombardment of ¹⁸¹Ta,¹⁹⁷Au Pb and ²⁰⁹Bi by ¹²C ions and in the bombardment of natural lead by ¹⁴N ions were measu ed with mica track detectors and gold surface barrier detectors.It is shown that all experimental data for the fission fragment angular distributions can be fitted by the statistical scission model of fission fragment angular distribution.     

Observation of the Damage on HOPG Surface Induced by Ar+8 Ions

Highly oriented pyrolytic graphite (HOPG) samples were bombarded by Ar+8 ions with energy range from 10.1 to 112MeV. After bombardment the sample surfaces were observed using a STM and NanoScope. The resultS show that the energetic ion could cause observable praotrusionlike damage on the HOPG surface.The relationship betWeen damage and energy loss, and the possible mechanism of damage process are discussed.     

Ar+8轰击石墨表面损伤的扫描隧道显微镜观测研究

报道了用10—112MeV能量的Ar+8离子轰击高定向石墨造成损伤的原子水平观测结果,给出了损伤形貌、损伤大小和损伤数密度.讨论了损伤与表面核能损的关系及损伤过程的可能机制.