Recombination of U89+ ions with free electrons at the ESR

After an extended upgrading period at the Experimental Storage Ring (ESR) of the GSI in Darmstadt, an experiment on recombination of lithium-like uranium has been carried out. A 107.1 MeV/u U⁸⁹⁺ beam with up to 500 μA effective current was stored and cooled. In addition to measurements of radiative recombination (RR) and dielectronic recombination (DR) with high energy resolution in the range of 0–90 eV, the diagnostic properties of DR have been utilized to characterize the new cooler setup. Preliminary experimental results for the 1s²2p_3/25ℓj(j=3/2,5/2) resonance manifolds are presented and compared with theoretical predictions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Recombination of U 92 + ions with electrons

Recombination of fully stripped U⁹²⁺ ions with electrons has been investigated at the Experimental Storage Ring (ESR) in Darmstadt. Absolute recombination rate coefficients have been measured for relative energies from 0 to 33 eV. For energies greater than 20 meV the experimental result is well described by the theory for radiative recombination (RR). Below 20 meV the experimental rate increasingly exceeds the RR calculation as observed previously in the recombination of light bare ions as well as of Bi⁸³⁺. This low-energy rate enhancement is shown to scale as Z^2.6 for bare ions, where Z is the atomic number of the ion. The U⁹²⁺ recombination rate enhancement is insensitive to changes of the electron density. Variation of the magnetic guiding field strength from 80 mT to 120 mT resulted in oscillations of the recombination rate at 0 eV. The oscillations are partly attributed to changes of the transverse electron temperature accompanying the change of the magnetic guiding field strength; partly they may be caused by uncompensated small changes of the interaction angle between the two beams. Received 1st March 2001 and Received in final form 20 April 2001     

Recombination of Au25+ with free electrons at low energies

The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown. We investigated the recombination of Au²⁵⁺ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E _rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the electron density by a factor of 10 had not much influence on the measured rate coefficient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Recombination of lithium-like bismuth and uranium ions with free electrons at the ESR

In two separate experiments at the ESR recombination of 230 MeV/u Bi⁸⁰⁺ and 170 MeV/u U⁸⁹⁺ ions was studied. The analysis of these experiments has been carried on in order to extract information about radiative recombination (RR) of very highly charged ions exposed to electrons with a density of few 10⁶ cm^-3. In the light of the recombination rate enhancement seen in almost all recent experiments at a relative energy E_rel = 0 eV, a surprising result is found for the very highly charged ions, which could add some confusion to an already puzzling picture: in spite of the high charge state of the investigated ions there is no evidence of enhanced recombination beyond the expected RR rate. This observation appears to be supported by other experimental findings at the ESR as well. We suspect, however, that this is a consequence of excessive transverse magnetic field components in the ESR cooler (which have meanwhile been corrected for) causing variable degrees of angular mismatch between the ion beam and the electron beam occurring when the ring settings are tuned for optimum cooling. This revised version was published online in August 2006 with corrections to the Cover Date.     

Recombination channels of molecular ions He 2 + and electrons

The dependence of the intensities of atomic lines and molecular bands emitted in the afterglow of a helium discharge on the electron temperature is used to identify the processes in which states of He and He ₂ ^* are populated. It is established that the formation of He^* atoms (n = 3, 4) in decaying helium plasma occurs principally on account of the associative recombination of vibrationally excited He ₂ ⁺ ions and electrons. Analysis of the experimental reuslts leads to the conclusion that the distribution of the molecular ions He ₂ ⁺ over vibrational states is strongly nonequilibrium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 67–72, February, 1984.It remains to thank N. P. Penkin for discussions and for his interest in the work.     

Recombination of electrons with highly charged heavy ions at very low energies

Recombination of highly charged ions with free electrons is studied in merged-beams experiments at the UNILAC accelerator in Darmstadt and at the heavy-ion storage ring TSR in Heidelberg. Unexpected high recombination rates are observed for a number of ions at very low energiesE _cm in the electron-ion center-of-mass frame. In particular, theoretical estimates for radiative recombination are dramatically exceeded by the experimental recombination rates of U²⁸⁺ ions nearE _cm=0 eV. The observations point to a general phenomenon in electron ion recombination depending onE _cm, on the ion charge state, and possibly also on electron density, electron beam temperature, and strength of external magnetic fields.     

Recombination processes in lanthanum beryllate single crystals doped with Ce3+ and Pr3+ ions

The paper presents experimental results on recombination processes in lanthanum beryllate (BLO) single crystals (undoped BLO, and doped with 0.5 at % by Ce³⁺ and Pr³⁺ ions) obtained using XRL-spectroscopy at T = 8, 80 and 290 K and thermoluminescence technique in the temperature range of 8–650 K. The paper discusses spectra of the steady-state XRL-luminescence recorded in the energy range from 1.5 to 6.2 eV at different temperatures between 8 and 290 K; temperature dependences of XRL intensity recorded in the temperature range from 8 to 650 K; thermoluminescence glow curves recorded in spectral-integrated regime after X-ray exposure at T₀ = 8 or 290 K.     

Dissociation of 14N2+ ions induced by slow electrons

The cross sections and thermal rate coefficients for the dissociative recombination (DR) of the molecular nitrogen ions initially in the first four vibrational levels of the ground electronic state have been computed in the framework of the multichannel quantum defect theory. An energy range of 0.001–1 eV has been considered. The contribution of the indirect DR mechanism involving Rydberg states associated with the first excited ion core has also been investigated.     

Cross sections of 43Sc, 44Sc, 46Sc isotopes formed in the 45Sc + 3He reaction

Reactions ⁴⁵Sc(³He, αn)⁴³Sc, ⁴⁵Sc(³He, α)⁴⁴Sc and ⁴⁵Sc(³He, 2p)⁴⁶Sc in the ³He energy range of 5 to 24 MeV are investigated in experiments performed with a ³He ion beam during the irradiation of U-120M cyclotron scandium targets. Activation is used to determine the yield of nascent Sc isotopes. The γ activity induced in targets is measured using a high-resolution HPGe detector. The character of the excitation function changes during the formation of these ions and differs from the excitation functions for deuterons, despite the low bond energy of ³He and the positive values of the Q reactions leading to the formation of ⁴⁴Sc and ⁴⁶Sc isotopes. The cross sections of ⁴⁴Sc formation reach their maximum value at the Coulomb barrier of the reaction, due to the stable ⁴He nucleus that accompanies the formation of ⁴⁴Sc. The contribution from different reaction mechanisms to the cross sections of ⁴³Sc, ⁴⁴Sc, and ⁴⁶Sc isotope formation are considered.     

Photoluminescence of LiNbO3 crystals doped with Er3+ and Yb3+ ions

Results of cooperative phenomena investigations in the impurity subsystem of lithium niobate crystals doped with Er³⁺ and co-doped with Yb³⁺ impurity ions under continuous wave and pulsed excitation at 975 nm and 1064 nm wavelengths are presented. Dependences of some spectroscopic characteristics on the intensity of laser pumping are studied. Based on the pair centers model the analysis of the cooperative luminescence behavior in LiNbO₃:Yb³⁺+Er³⁺ crystals is performed.     

Spectroscopic study of dissociative recombination between Ar2 + ions and electrons

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 3, pp. 407–412, September, 1988.     

Three-body recombination of atomic ions with slow electrons

Using the time-dependent wave-packets method, we have quantum mechanically investigated the three-body recombination process for electron energies varying from 10 to 0.01 eV. The classical "bottleneck" prediction on the probable population was confirmed by our S-wave quantum calculations for electron kinetic energies (K(E)) as low as 0.1 eV. But for K(E)<0.1 eV, the quantum three-body recombination tends to populate lower n levels than the classical theory predicted. We also find that, in the same n level, the recombination tends to populate higher angular-momentum states with K(E) decreasing. These results may shed light on the intrinsic dynamics of both ultracold plasmas and frozen Rydberg gases.     

Si5++He相互作用时双活跃电子势能的计算

利用附加电子转移因子和开关函数的半经典近似和量子分子轨道方法,在0.3～3.0 KeV能区和2.0～20.0(a.u.)核间距的条件下,对Si5+离子与He原子相互作用过程中5个singlet 态和5个triplet态的双电子捕获势能进行了理论计算.通过参数优化,在比较了基通道电子转移势能和实验值之后,研究了主通道的电子转移势能.其结果说明了这一动力学过程中的避交叉(avoided crossings)性质,给出了双电子容易被捕获的不同核间距离点.     

Cross sections for production of 43Sc, 44Sc, and 46Sc isotopes in the 45Sc + 3He reaction

Reactions ⁴⁵Sc(³He, αn)⁴³Sc, ⁴⁵Sc(³He, α)⁴⁴Sc, and ⁴⁵Sc(³He, 2p)⁴⁶Sc, resulting from the irradiation of scandium targets with a beam of ³He ions with energy from 5 to 24 MeV, are investigated in experiments on the U120M cyclotron of the Nuclear Physics Institute (Rez, Czech Republic). The activation technique is used to find the yield of the produced Sc isotopes. The induced γ activity in the targets is measured using a high-resolution HPGe detector. Despite the low binding energy of ³He and positive reaction Q values, which leads to formation of the ⁴⁴Sc and ⁴⁶Sc isotopes, the behavior of the excitation functions for the formation of these isotopes differs from the behavior of the excitation function for deuterons. Scandium-44 formation cross sections reach their maximum at the reaction Coulomb barrier. This is because not only ⁴⁴Sc but also a stable ⁴He nucleus is formed in the reaction.     

Three-body recombination of ions with electrons in cooler-storage rings

Three-body recombination (TBR) of bare ions with free electrons of anisotropic velocity distribution is discussed in the context of recombination experiments in cooler-storage rings. The recombination rates are derived from the electron impact ionization rates using the modified Saha equation. Analytical expressions for the TBR rates and new scaling rules with main quantum number n, atomic number Z, and both transverse and longitudinal electron temperatures are derived for the low n-states regime probed in experiments in cooler-storage rings. In this context, the discrepancies found between measured rates and predictions for radiative recombination for the e + Ne¹⁰⁺ system [Gao et al., Phys. Rev. Lett. 75 (1995) 4381] are discussed. Present results show that TBR rates for the flattened electron beam velocity distribution cannot account for the recombination enhancement observed at very low relative energies. This revised version was published online in August 2006 with corrections to the Cover Date.     

H3+团簇离子与固体相互作用

报道了H3+团簇通过碳膜对产生的各种产物的测量结果.分析讨论了三原子离子团簇与固体相互作用中的电荷交换过程.证明在产物的形成中,电荷交换过程起关键作用.分析研究了H3+团簇与固体作用中的团簇效应和尾流效应. 关键词： H3+团簇 电荷交换 团簇效应 尾流效应