D. L. Guo

A machine learning method to separate cosmic ray electrons from protons from 10 to 100 GeV using DAMPE data

DArk Matter Particle Explorer (DAMPE) is a general purpose high energy cosmic ray and gamma ray observatory, aiming to detect high energy electrons and gammas in the energy range 5 GeV to 10 TeV and hundreds of TeV for nuclei. This paper provides a method using machine learning to identify electrons and separate them from gammas,protons,helium and heavy nuclei with the DAMPE data from 2016 January 1 to 2017 June 30, in energy range from 10 to 100 GeV.

Investigation of fragmentation dynamics of nitrogen dimers by collisions with highly charged ions

Synopsis The fragmentation dynamics of nitrogen molecule dimers have been studied by using highly charged Ne8+ ions at impact energy of 1.0 MeV. For its three-body fragmentation, three fragmentation mechanisms have been identified by analyzing Dalitz plot and Newton diagram of the momenta of three fragment ions. The sequential dissociation of covalent first breakdown is quite surprising in contrast to the fragmentation of triatomic molecule.

Forward-angle electron spectroscopy in heavy-ion atom collisions studied at the ESR

The collision system U88+ + N2 at a low-relativistic projectile energy of 90 MeV/u has been analyzed experimentally and theoretically with respect to fast electrons emitted with a velocity ve close to the projectile velocity, vp ≈ ve, at an observation angle of e ≈ 0°, i.e., in the direction of the projectile beam. Three distinct processes are identified, where each of the underlying charge-transfer mechanisms leads to a characteristic feature in the asymmetry of the observed electron energy distribution. The experimental results for each of the three processes are compared to the corresponding theoretical models.

The nucleus-nucleus scattering in transfer ionization of helium by He2+ impact

We have performed kinematically complete measurement on transfer ionization of He by 50 keV/u He2+ impact. The data were analyzed in terms of Dalitz spectrum. We evaluated the role of three particles interactions and found that the main momentum exchange occurs between the projectile and the recoil ion. This result indicate that the nucleus-nucleus high order interaction could not be overlooked in transfer ionization collision dynamics of atom by intermediate energy ion impact.

The fragmentation of neon dimer induced by low energy O6+ ions

We have investigated the fragmentation channels Ne+-Ne+ and Ne2+-Ne+ from Ne2 dimer induced by O6+ ions at impact energy of 15 keV/u. The Ne+-Ne+ fragmentation channel mainly results from three pathways: the interatomic coulombic decay of Ne2+(2p4)-Ne initial state, the direct columbic explosion and the radiation charge transfer. Nevertheless, the fragmentation channel Ne2+-Ne+ is predominant by the direct coulombic explosion.

Experimental investigation of state selective single-electron capture in 120 keV Ar8+ - He collisions

The longitudinal and the transversal momentum of recoil ions were measured for single electron capture in 120 keV Ar8+ - He collisions, using the reaction microscope techniques. The characteristics of the radial and the rotational coupling were identified for 1s to 4s and 1s to 4p sub-state selectivity.

Electron emission spectra of U28+-ions colliding with gaseous targets

The electron-loss to continuum has been studied experimentally and theoretically for the collision systems U28+ + H2 at a collision energy of 50 MeV/u, U28+ + N2 at 30 MeV/u, and U28+ + Xe at 50 MeV/u.

Projectile charge state effects on electron emission in transfer ionization processes

Electron emissions in transfer ionization processes were studied for 75 keV u−1 He2+, and 80 keV u−1 Ne8+on He collisions, using the well-developed reaction microscope techniques. Momentum distributions in the scattering plane, doubly differential distributions as a function of longitudinal momentum and emission angles of the ejected electrons were obtained. An apparent enhancement of electrons distributed around the projectile in the scattering plane was found for the Ne8+ incident case. Furthermore, we report the ratio of doubly differential distributions at the emission angle of 0° between these two transfer ionization processes, in which an abrupt rise is found at and above the electron capture to the continuum peak. This rise qualitatively agrees with the prediction within the framework of Dettmann’s theory. We conclude that this kind of enhancement was caused by the charge state effect of the projectile.

Metal vapor target for precise studies of ion-atom collisions

Although different ion-atom collisions have been studied in various contexts, precise values of cross-sections for many atomic processes were seldom obtained. One of the main uncertainties originates from the value of target densities. In this paper, we describe a unique method to measure a target density precisely with a combination of physical vapor deposition and inductively coupled plasma optical emission spectrometry. This method is preliminarily applied to a charge transfer cross-section measurement in collisions between highly charged ions and magnesium vapor. The final relative uncertainty of the target density is less than 2.5%. This enables the precise studies of atomic processes in ion-atom collisions, even though in the trial test the deduction of precise capture cross-sections was limited by other systematic errors.

An experimental investigation of the dissociative ionization process of argon cluster ions induced by electron impact

Utilizing the Cold Target Recoil Ions Momentum Spectrometer (COLTRIMS), dissociative ionization of argon cluster was experimentally investigated by electron impact. The recoil ions produced both in the pure ionization process and the dissociative ionization channels are measured with collision energies from 100 and 1000 eV. The ratios of the dimer ions from pure ionization (Ar2P+) and the dimer ions from small cluster dissociation (Ar+2D) to the atomic argon ion (Ar+) in different stagnation pressures were obtained.