Non-characteristic X-ray Research Articles

Characteristic and non-characteristic X-ray yields produced from thick Ti element by sub-relativistic electrons

Measurements are performed to study the electron impact energy dependence of doubly differential bremsstrahlung yields (DDBY) and of characteristic Ti Kα line yields produced from sub-relativistic electrons (10–25keV) colliding with a thick Ti (Z=22) target. The emitted radiation is detected by a Si-PIN photo-diode detector with energy resolution (FWHM) of 180eV at 5.9keV. The measured data of DDBY are compared with the results predicted by Monte-Carlo (MC) simulations using the general purpose PENELOPE code. A reasonable agreement is found between experimental and simulation results within the experimental uncertainty of measurements of 12%. Characteristic Ti Kα yields are obtained for the considered impact energy range and they are compared with the existing theoretical results. A good agreement is found between the present measurements and the theoretical calculations. Furthermore, data are presented for impact energy dependence of the ratio Kα/(Kα+Kβ) of a thick Ti target under impact of 10–25keV electrons. The ratio shows a very weak dependence on impact energy in the studied range. The average value of the ratio is found to be 0.881±0.003.

Development of a new experimental setup for studying collisions of keV-electrons with thick and thin targets

Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering, innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0 keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based 8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design, fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray spectrum are illustrated to exhibit the satisfactory performance of the developed setup.

Characteristic and non-characteristic X-ray emission from SF $_6$ and SO $_2$ molecules by electron impact

Cross sections for K-shell ionization of sulphur in collisions of electrons with kinetic energies of 3.5–14.0 keV with SF6 and SO2 gases have been measured. In addition, the impact energy dependence of the bremsstrahlung radiation emitted at different photon energies was investigated. The experimental results are compared with theoretical calculations in plane wave Born approximation and with the available semi-empirical models.

Characteristic and non-characteristic X-ray emission by lepton impact

Recent progress of characteristic and non-characteristic X-ray emission in collisions of leptons (electrons, positrons) with target atoms is reviewed. We discuss, in particular, i) the differences between electron and positron impact in the ionization of inner atomic shells, ii) the two-photon bremsstrahlung emitted in collisions of electrons with heavy atoms, and iii) the role played by stimulated emission and absorption of photons during electron collisions in a strong laser field.

Periodic Anisotropy Fluctuations in Quasimolecular X-Ray Emission

We have found striking periodic intensity fluctuations in the anisotropy of noncharacteristic x-ray radiation emitted in Ca-Ca, Fe-Fe, and Ni-Ni collisions. It is shown that the properties of this new effect can be interpreted as quasimolecular transitions in a rotating two-center system.

Non-characteristic X-ray emission in NeAl collisions

Al Kα characteristic and non-characteristic X-ray production cross sections in Ne impacting on Al-foils have been investigated for projectile energies 0.4–20 MeV and foil thicknesses 2–400 μg/cm 2. Thin foils were supported on C-substrates. Three effects were found: The Al Kα characteristic X-ray cross section (1) increases with target thickness and (2) increases for a given Al + C foil upon turning the carbon side to the beam. (3) The X-ray spectral contribution from the C-substrate is less intense by a factor 5 than from a lone C-foil of the same thickness. Al(recoil)→Al contributions to the characteristic X-ray are estimated to be 10 2 less intense than Ne→Al contributions.

Characteristic and noncharacteristic x rays produced during 1-MeV argon bombardment of silicon

This work reports the first detailed examination of the noncharacteristic x-ray distribution produced during 1-MeV Ar bombardment of silicon. A crystal spectrometer was used to observe the characteristic and noncharacteristic x rays. It is shown that to within 5 eV the noncharacteristic x-ray band is continuous and tails off in the region of 1.4 keV, as required by the molecular x-ray interpretation. We have obtained the true shape of the noncharacteristic x-ray band in the energy range 675-1550 keV by using a rubidium acid phthalate crystal spectrometer calibrated for its relative efficiency. The observation of a broadened argon $L$ line spectrum and multiple satellite line in the Si $K$ spectrum shows that a high degree of excitation is produced in the $L$ shells of both argon and silicon during the collision.

Investigation of the Noncharacteristic X-Radiation Band Observed in Ar Bombardment of Various Targets

The noncharacteristic X-ray band produced by Ar bombardment of various targets has been investigated with a high-transmission window, gas-flow proportional counter, and Si(Li) detectors. We find (i) that the Ar bombardment of Si produces a continuum with monotonically decreasing intensity for increasing energy, extending from \ensuremath{\lesssim}250 eV to \ensuremath{\sim}1.2 keV; (ii) Ar-target interactions and Ar-Ar interactions produce distinctly different spectra; (iii) the band observed in the Ar-C system is inconsistent with a simple quasimolecular picture. The bearing of these results on the quasimolecular description is discussed.

Noncharacteristic X-Ray Bands Produced in Targets of C, Al, Si, and Solid Ar by Argon Ions at keV Energies

The energy, width, and yield of noncharacteristic x-rays are reported from collisions of argon ions at energies from 25 to 200 keV with targets of C, Al, Si, and solid Ar. The x-ray band has a peak at \ensuremath{\sim} 1160 eV with a full width at half-maximum of \ensuremath{\sim} 700 eV for solid Ar targets and a peak at \ensuremath{\sim} 900 eV with a full width at half-maximum of \ensuremath{\sim} 300 eV for the other targets. The yield increases with ion energy and decreases with the target $Z$.