Kr Targets Research Articles

Medium-indused modification of kaons spectra measured in SIDIS at HERMES

The predicted high sensitivity of the nuclear modification factor for K– in SIDIS due to the QCD based effect of medium-induced flavour conversion in the fragmentation function is studied at HERMES experiment. Unlike π+, π– and K+ nuclear modification factor for K– is assumed to increase at high value of Bjorken variable xB and a hadron fraction energy z. The experimental signature of this phenomenon is an enhanced K– nuclear modification factor compared with those of K+ for high xB and z range. The z spectra of nuclear attenuation ratios for charged kaons in different slices of xB extracted on Ne, Kr and Xe targets will be presented and discussed.

Laser plasma vacuum ultraviolet light source using solid rare-gas targets

The laser plasma emission spectra in a broadband from 30 to 200 nm of solid Ar, Kr, and Xe targets are presented for the first time. The spectra are composed of a broadband continuum and lines. A broadband vacuum ultraviolet (VUV) spectrometer that can measure spectra in the wavelength range from 30 to 200 nm is developed and the measured spectra are able to be calibrated over the entire broad band. The spectral intensity integrated from 30 to 200 nm indicates that the VUV average power generated in the wavelength range is 30 mW when the laser energy is 1 J at 1 Hz. The number of photons of monochromatic light after passing through the spectrometer is estimated to be more than 5 × 106 photons/nm/pulse over the wavelength range and is considered to be useful for applications of broadband VUV spectroscopy.

Laser plasma cryogenic target on translating substrate for generation of continuously repetitive EUV and soft X-ray pulses.

To generate continuously repetitive EUV and soft X-ray pulses with various wavelengths from laser-produced plasmas, a one-dimensionally translating substrate system with a closed He gas cryostat that can continuously supply various cryogenic targets for ~10 Hz laser pulses has been developed. The system was successfully operated at a lowest temperature of 15 K and at a maximum up-down speed of 12 mm/s. Solid Ar, Kr, and Xe layers were formed, and their growth rates and the laser crater sizes on them were studied. By optimization of the operational parameters in accordance with our design rule, it was shown that stable output power was achieved continuously from the plasma emission at frequencies of 1-10 Hz. The average soft X-ray and EUV powers obtained were 19 mW at 3.2 nm, 33 mW at 10.0 nm, and 66 mW at 10.8 nm, with 10% bandwidths, from the Ar, Kr, and Xe solid targets, respectively, with a laser power of 1 W. We will be able to achieve higher frequencies using a high beam quality laser that produces smaller craters, and can expect higher powers. Although only Ar, Kr, and Xe gases were tested in this study, the target system achieved a temperature of 15 K and can thus solidify almost all target gases, apart from H and He, and can continuously supply the solid target. The use of various target materials will enable expansion of the EUV and soft X-ray emission wavelength range.

Comparative analysis of stable ultrahigh power-density 248 nm channels formed in Kr and Xe cluster targets

Comparative single-pulse studies of self-trapped plasma channel formation in Xe and Kr cluster targets produced with 1–2 TW femtosecond 248 nm pulses reveal energy efficient channel formation (>90%) and highly robust stability for the channeled propagation in both materials. Images of the channel morphology produced by Thomson scattering from the electron density and direct visualization of the Xe(M) and Kr(L) x-ray emission from radiating ions illustrate the (1) channel formation, (2) the narrow region of confined trapped propagation, (3) the abrupt termination of the channel that occurs at the point the power falls below the critical power Pcr, and, in the case of Xe channels, (4) the presence of saturated absorption of Xe(M) radiation that generates an extended peripheral zone of ionization. The measured rates for energy deposition per unit length are ∼ 1.46 J cm−1 and ∼ 0.82 J cm−1 for Xe and Kr targets, respectively, and the single pulse Xe(M) energy yield is estimated to be > 50 mJ, a value indicating an efficiency >20% for ∼ 1 keV x-ray production from the incident 248 nm pulse.

Energy-loss straggling of 2–10 MeV/u Kr ions in gases

Measurements have been performed on a time-of-flight setup at the Jyvaskyla K130 cyclotron, aiming at energy-loss straggling of heavy ions in gases. Theoretical predictions based on recently developed theory as well as an empirical interpolation formula predict that straggling can be more than ten times higher than Bohr straggling in the MeV/u regime. Our measurements with up to 9.3 MeV/u Kr ions on He, N2, Ne and Kr targets confirm this feature. Our calculations show the relative contributions of linear straggling, bunching including packing, and charge exchange. Our results for stopping cross sections are compatible with values from the literature.

Multiple ionization of atoms including post-collisional contributions

We present a theoretical study on multiple ionization on Ne and Kr by charged ions in the energy range (0.1-10) Mev/amu. We employed the continuum distorted-wave eikonal initial state and a Hartree-Fock description of the dressed-ion, together with photoionization branching ratios to include Auger-type post-collisional contributions. Results are good, especially for Kr targets. Some questions, such as limitations of the independent particle model or influence of the ion charge-state versus the ion nuclear-charge, are analyzed based on the different results for Ne and Kr targets. We found that single ionization is related to the ion charge-state while multiple-ionization shows that the nuclear-charge is weekly screened by the ion outer-electrons.

Ionization of noble gas by impact of hydrogen anions

Relative cross-sections for double ionization and single ionization of targets under the impact of hydrogen anions were measured. Two systems were investigated, H− projectiles with Kr and Xe targets. The energy region was 10–30 keV. Recoil ions originated from target (Kr+, Kr2+, Xe+, Xe2+) were detected in coincidence with projectiles in several final charge states (q = 0 and q = + 1). We compare the present results with the previous results of Ar. The results show that the cross-section ratios, taken between double and single ionization of Ar, Kr and X in the channels of single and double electron loss of H−, become larger and larger with the incident energy increasing, and that the cross-section ratios will cross at some certain energy for the two different electron loss channels. The crossing energy for Xe is about 23 keV.

A molecular beam scattering investigation of methanol–noble gas complexes: Characterization of the isotropic potential and insights into the nature of the interaction

Integral cross section experiments involving rotationally hot CH3OH projectiles and noble gas (Ng=Ne, Ar, Kr and Xe) targets are reported for the first time. Measured data have been exploited to characterize the phenomenological radial interaction in the CH3OH–Ng weakly bound complexes. Potential energy surfaces for all the systems have been formulated on the basis of a pairwise additive multicenter model. The comparison of model predictions with the most relevant experimental findings suggests that in CH3OH–Ng complexes, at variance with the behavior of the analogous complexes involving water or ammonia, the interaction is mainly due to van der Waals and induction components.

Nuclear model calculation on charge particle induced reaction on Rb and Kr targets and targetry for 82Sr production

The 82Sr/82Rb radionuclide generator is used very commonly in positron emission tomography. ALICE/ASH and TALYS 1.0 codes were used to calculate excitation functions for proton, alpha and 3He induced on various targets that lead to produce 82Sr radioisotope using intermediate energy accelerators. Recommended thickness of the targets according to SRIM code was premeditated. The application of those data, particularly in the calculation of integral yields, is discussed and theoretical integral yields for any reaction were computed. To consider precision of TALYS 1.0 code calculations, 85Rb(p,4n)82Sr process was determined as most interesting one due to radionuclide purity. The TALYS 1.0 code predicts a maximum cross-section of about 130 mb at 47 MeV for this reaction. Rubidium chloride deposition on copper substrate was carried out via sedimentation method in order to produce 82Sr. 2.98 g RbCl, 1.043 g ethyl cellulose, 10 mL acetone were used to prepare a layer of enriched rubidium chloride of 11.69 cm2 area and 0.34 g/cm2 thickness.

Charge-Transfer Cross Sections of H+ Ions in Collisions with Noble Gas Atoms in the Energy Range below 4.0 keV

Charge-transfer cross sections in collisions of H+ ions with the ground state He, Ar, Kr, and Xe atoms have been measured in the energy range below 4.0 keV with the initial growth rate method. These observed cross sections are also compared with previously published experimental data and theoretical predictions. In the He and Ar targets, it is found that some previous experimental data deviate significantly from the present observed cross sections as the collision energy decreases. It has been found that in the Kr and Xe targets, the energy dependence of the present observed cross sections behaves as “near-resonant” charge transfer.

Differential cross sections for fragmentation of positronium

Cross sections differential with respect to energy and angle of ejected positrons and electrons for Ps(1s) fragmentation in collision with He, Ne, Ar, Kr and Xe targets are reported. For Ne, Ar, Kr and Xe, only the case where the target is not excited (target elastic collisions) is considered. For He, fragmentation with target excitation/ionization (target inelastic collisions) is also studied. The impulse approximation has been used for target elastic fragmentation, the first Born approximation for target inelastic processes.

Saturation effect in projectile- and target- x-ray production in collisions between 2.5 MeV/u highly charged Cu ions and gaseous targets

L x-ray production cross sections have been measured for highly charged 2.5 MeV/u Cuq+ (q = 20–26) ions colliding with H2, Ne, Ar, Kr and Xe target atoms. The observed Cu L x-rays are due to the excitation and electron-transfer processes. The charge state dependence of the projectile L x-rays has been studied with Ar and Kr targets. We have derived the subshell resolved K-L1, K-L2 and K-L3 electron-transfer cross sections from the measured Ar K x-ray yields as a function of L vacancies in Cu ion. The measured projectile L x-ray production cross sections arising from the excitation and electron capture are found to saturate as target atomic number Zt increases. Similarly, a saturation has also been found in the Ar K-shell ionization cross sections as a function of Zp.

Electron-density scaling of conversion efficiency of laser energy into L-shell X-rays

Laser-produced plasmas at subcritical densities have proven to be efficient sources for X-ray production. In this context, we obtain experimental results from Kr and Xe gas-filled targets that were irradiated by the OMEGA (Laboratory for Laser Energetics, University of Rochester) laser. Nearly 40% of the laser energy was converted into X-rays in the L-shell-photon-energy range ( ⩾ 1.6 keV ) by a Kr-filled target. The conversion efficiency measurements were correlated with time-resolved plasma-temperature measurements done by means of a Thomson-scattering diagnostic. The measured range of temperatures, between 2–3.5 keV, is in good agreement with LASNEX radiation-hydrodynamics simulations. X-ray-cooling rates and charge-state distributions were computed using detailed atomic data from the HULLAC suite of codes. X-ray yields predicted by the cooling-rate calculations are compared to measured spectra, and good agreement is found for predictions made with highly-detailed atomic models. We find that X-ray conversion efficiency in Kr-filled targets is a strong function of temperature, and has an optimum density near 15% of the laser's critical density.

Hadron attenuation in deep inelastic lepton-nucleus scattering

We present a detailed theoretical investigation of hadron attenuation in deep inelastic scattering (DIS) off complex nuclei in the kinematic regime of the HERMES experiment. The analysis is carried out in the framework of a probabilistic coupled-channel transport model based on the Boltzmann-Uehling-Uhlenbeck (BUU) equation, which allows for a treatment of the final-state interactions (FSI) beyond simple absorption mechanisms. Furthermore, our event-by-event simulations account for the kinematic cuts of the experiments as well as the geometrical acceptance of the detectors. We calculate the multiplicity ratios of charged hadrons for various nuclear targets relative to deuterium as a function of the photon energy nu, the hadron energy fraction z_h=E_h/nu and the transverse momentum p_T. We also confront our model results on double-hadron attenuation with recent experimental data. Separately, we compare the attenuation of identified hadrons (pi^\pm, \pi^0, K^\pm, p and pbar) on Ne and Kr targets with the data from the HERMES Collaboration and make predictions for a Xe target. At the end we turn towards hadron attenuation on Cu nuclei at EMC energies. Our studies demonstrate that (pre-)hadronic final-state interactions play a dominant role in the kinematic regime of the HERMES experiment while our present approach overestimates the attenuation at EMC energies.

Hadron formation and attenuation in deep inelastic lepton scattering off nuclei

We investigate hadron formation in deep inelastic lepton scattering on N, Kr and Xe nuclei in the kinematic regime of the HERMES experiment. The elementary electron–nucleon interaction is described within the event generator PYTHIA while a full coupled-channel treatment of the final state interactions is included by means of a BUU transport model. We find a good agreement with the measured charged hadron multiplicity ratio RMh for N and Kr targets by accounting for the deceleration and absorption of the primarily produced particles as well as for the creation of secondary hadrons in the final state interactions.

Hadron production in deep inelastic lepton–nucleus scattering

Predictions for semi-inclusive deep inelastic lepton–nucleus scattering are presented. Both the effects of gluon radiation by the struck quark and the absorption of the produced hadron are considered. The gluon radiation covers a larger window in virtuality Q 2 because of the increased deconfinement of quarks inside nuclei. The absorption of hadrons formed inside the nucleus is described with a flavor dependent cross-section. Calculations for rescaled fragmentation functions and nuclear absorption are compared with the EMC and HERMES data for N, Cu and Kr targets with respect to the deuteron target. Predictions for Ne and Xe targets in the HERMES kinematic regime are given.

Electron capture and ionization of 33-TeV Pb ions in gas targets

We have measured the total cross sections for electron capture by bare ${\mathrm{Pb}}^{82+}$ ions and for the ionization of hydrogenlike ${\mathrm{Pb}}^{81+}(1s)$ ions at $158\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{A},$ $\ensuremath{\gamma}=168,$ in Ar, Kr, and Xe gas targets. At this energy, the total capture cross sections are dominated by electron capture from pair production. The capture measurements are compared with the results of several theoretical calculations and with similar measurements made with solid targets. The ${\mathrm{Pb}}^{81+}(1s)$ ionization cross sections obtained, which are substantially lower than those measured in solids, agree well with recent calculations that predict saturation at high energies from target screening effects.

Simultaneous excitation and ionization of He-like uranium ions in relativistic collisions with gaseous targets

The process of simultaneous excitation and ionization is investigated for He-like uranium $({\mathrm{U}}^{90+})$ ions colliding with Ar, Kr, and Xe targets at an incident energy of 223.2 MeV/u. The two-electron transitions, where one of the ground-state electrons is promoted into the continuum and the other into the L-subshell states of the projectile, are identified by the coincident observation of U Lyman-series radiation and ${\mathrm{U}}^{91+}$ ions. The experimental cross sections are compared to relativistic calculations based on the independent particle approximation and first-order perturbation theory. It is shown, that simultaneous excitation-ionization occurs preferably at small impact parameters, for which the excitation process is dominated by the monopole part of the interaction potential and the perturbation potential is largest. Good agreement is found between experimental data and calculations for the Ar target. For heavier targets the experimental results are generally smaller than predicted pointing to the invalidity of the first-order perturbation theory in this energy--target atomic number domain.

Angular characteristics of processes of electron detachment from negative ions and hydrogen atoms in gases

The results of experimental measurement of spatial-angular distributions of hydrogen particles (H−, H0, H+) obtained in scattering of a collimated ribbon beam of H− ions and H0(1s) atoms in He, Ar, Kr, Xe, H2, O2, and CO2 gas targets for certain values of energy in the range from 0.6 to 15 MeV are reported. The experimental setup and the measurement procedure with an angular resolution of 5×10−6 rad are described. The angular characteristics of measured distributions, i.e., full width at half maximum and standard deviation, were determined. It is shown that the shape of distribution for a beam of hydrogen atoms produced by neutralization of H− ions in a gas target varies with the type and thickness of the target, and the angular spread is smallest for the H2 target. The variations in the shape of distribution are due to the contribution of scattering processes without changing the charge of particles.

Electron loss and single and double capture ofC3+andO5+ions in collisions with noble gases

Cross sections for the processes of projectile electron loss and single and double capture of ${\mathrm{C}}^{3+}$ and ${\mathrm{O}}^{5+}$ projectile ions impinging on He, Ne, Ar, Kr, and Xe targets were measured in the energy range of 1.0--3.5 MeV. The measured cross sections present a strong saturation as the target atomic number increases, for all the systems and collision channels studied. The single-capture data are compared with calculations based on a semiclassical model and on the eikonal approximation, both presenting a good general agreement with the experiment. In the case of electron loss, the observed saturation is in accordance with previous measurements for ${\mathrm{He}}^{+}$ projectiles, and is present in the first-order calculations for the antiscreening contribution but not in those for the screening. This is due to the fact that, for heavy target atoms, the screening mode can be highly nonperturbative. Calculations for the screening contribution to the electron loss, based on the free-collision model, together with first-order results for the antiscreening, are compared with the experimental data, presenting good agreement in most cases. However, this comparison also shows that one has to include other competitive channels in order to give a better description of the collision.