Guoqing Xiao

Energy dissipation of fast heavy ions in matter

Abstract The energy dissipation due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to material modifications. Starting from a discussion of the initial electronic energy-deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is presented. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different materials.

Measurement of reaction cross section for proton-rich nuclei ( A< 30) at intermediate energies

Radioactive ion beams were produced through the projectile fragmentation induced by 69 MeV/nucleon Ar-36 primary beam on a Be-9\ target. Measurements of reaction cross sections (sigma(R)s) for 44 nuclei with A < 30 (mostly proton-rich), on carbon were performed on RIBLL (Radioactive Ion Beam Line in Lanzhou) of HIRFL (Heavy Ion Research Facility in Lanzhou) at intermediate energies around 30 MeV/nucleon by a transmission method. The experimental sigma(R) values for Al-23 and P-27 are abnormally large compared with their neighboring nuclei. Together with the previous experimental facts such as the binding energy and ground state data, it suggests anomalously large matter root-mean-square radii and proton halo structure in Al-23 and in P-27. There is an enhancement for the sigma(R) of F-17 + C-12 compared with the neighboring isotopes. Considering that the ground state of F-17 is 1d(5/2), this can indicate that there is a proton skin in F-17. The calculation of relativistic density-dependent Hartree model (RDDH) shows that the nuclei Al-23 and P-27 may have proton-halo structure and F-17 may have proton-skin structure. The significance of these measurements is discussed

Mass Measurement of 45Cr and Its Impact on the Ca-Sc Cycle in X-Ray Bursts

Masses of neutron-deficient 58Ni projectile fragments have been measured at the HIRFL-CSR facility in Lanzhou, China employing the isochronous mass spectrometry technique. Masses of a series of short-lived Tz = –3/2 nuclides including the 45Cr nucleus have been measured with a relative uncertainty of about 10–6-10–7. The new 45Cr mass turned out to be essential for modeling the astrophysical rp-process. In particular, we find that the formation of the predicted Ca-Sc cycle in X-ray bursts can be excluded.

Auger electrons from ion tracks

Abstract The target KVV Auger electron emission has been investigated experimentally and theoretically for heavy-ion irradiation of amorphous carbon at an ion velocity of 14.1 a.u. (5 MeV/u). We extend previous investigations of multiple ionization and electronic nuclear-track temperatures to a large variety of charged projectiles, covering electrons to uranium ions. Experimental data are compared with non-pertubative calculations of multiple ionization and with results of two thermal-spike models.

An experimental determination of electron temperatures in the center of nuclear tracks in amorphous carbon

Abstract In this work we present carbon K-Auger electron spectra from amorphous carbon foils induced by fast heavy ions and by electrons. The high-energy tail of the experimentally determined Auger structure shows a clear projectile-charge dependence. Model electron-spectra for the Auger decay of the K vacancy, calculated from the known density of states, are in good agreement with electron induced Auger spectra. The experimental data for heavy ions could be fitted with the model results by using the mean electron temperature in the track center as the only free parameter. These temperatures are presented and discussed in comparison with theoretical estimates for the electron temperature in the thermal spike.

Observation of the Superheavy Nuclide 271 Ds

With the recent commissioning of a gas-filled recoil separator at Institute of Modern Physics (IMP) in Lanzhou, the decay properties of (271)Ds (Z = 110) were studied via the Pb-208(Ni-64, n) reaction at a beam energy of 313.3MeV. Based on the separator coupled with a position sensitive silicon strip detector, we carried out the energy-position-time correlation measurements for the implanted nucleus and its subsequent decay alphas. One alpha-decay chain for (271)Ds was established. The.. energy and decay time of the (271)Ds nucleus were measured to be 10.644 MeV and 96.8 ms, which are consistent with the values reported in the literature.

Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe22+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface.

Trends in heavy ion interaction with plasma

In this work, we review current trends in China to investigate beam plasma interaction phenomena. Recent progresses in China on low energy heavy ions and plasma interaction, ion beam-plasma interactions under the influences of magnetic fields, high energy heavy ion radiography through marginal range method, energy deposition of highly charged ions on surfaces and Raman spectroscopy of surfaces after irradiation of highly charged ions are presented.

Results of carbon ion radiotherapy for skin carcinomas in 45 patients

Background  Heavy ions represent the best tool for external radiotherapy (RT) of inoperable tumours. Heavy ion RT has been used in the treatment of various tumours, especially for radioresistant tumours mediated by hypoxia, localized near organs at risk. Most of these treatments are concentrated in deep‐seated tumours such as those of the brain, head, lung, liver, rectum and urogenital organs, and treatment of skin carcinomas is limited.

Charge exchange and ionization cross sections of H+ + H collision in dense quantum plasmas

The plasma screening effects of dense quantum plasmas on H+ + H charge exchange and ionization cross sections are calculated by the classical trajectory Monte Carlo method. For charge exchange cross sections, it is found that the screening effects reduce cross sections slightly in weak screening conditions. However, cross sections are reduced substantially in strong screening conditions. For ionization cross sections, with the increase of screening effects, cross sections for low energies increase more rapidly than those for high energies. When the screening effects are strong enough, it is found that ionization cross sections decrease with the increase of incident H+ energy. In addition, the cross sections have been compared with those in weakly coupled plasmas. It is found that in weak screening conditions, plasma screening effects in the two plasmas are approximately the same, while in strong screening conditions, screening effects of dense quantum plasmas are stronger than those of weakly coupled plasmas.