M.N. Akhtar

Low energy heavy ion detection with the plastic scintillator NE102E

Detection capabilities of low cost plastic scintillation detector NE102E have been explored for slow heavy ions and carbon clusters. The carbon clusters are produced in a graphite hollow cathode based duoplasmatron and the mass analysis performed by a compact E×B velocity filter. The energy of the heavy ion beams of C70+, C60+, C24+, Xe2+, Xe+ and Ar+ is varied between 1 and 10 keV. The experimental data suggests that the scientillation response of NE102E is related to the electronic stopping and after a critical longitudinal range of about 80 A the scintillator’s response becomes linear.

Evolution of clusters in energetic heavy ion bombarded amorphous graphite

A study has been conducted into the mechanisms of evolution of clusters and their subsequent fragmentation under energetic heavy ion bombardment of amorphous graphite. The evolving clusters and their subsequent fragmentation under continuing ion bombardment are revealed by detecting various clusters in the energy spectra of the Direct Recoils emitted as a result of collisions between ions and surface constituents. The successive Direct Recoil spectra reveal that the energetics of Carbon Carbon bond formation as well as any subsequent fragmentation can be related to the processes of energy dissipation in a cylindrical volume of a few Angstrom surrounding the ion path. The dependence of cluster with m carbon atoms formation or its subsequent fragmentation into cluster with m-2 carbon atoms and diatomic carbon C2 is seen to be a function of the ionic stopping powers in this cylindrical volume.

MULTIPLY CHARGED DIRECT RECOIL SPECTRA FROM AR+ AND KR+ BOMBARDED GRAPHITE

Abstract Measurements of the energy spectra of multiply charged positive and negative carbon ions (Cn ±) recoiling from graphite surface under 100 and 150 keV argon and krypton ion bombardment are presented. With the energy spectrometer set at recoil angle of 79.5°, direct recoil (DR) peaks have been observed with singly as well as multiply charged carbon ions Cn ±, where n = 1 to 6. These Cn ± ions have been seen recoiling with the characteristic recoil energy EDR = kE0cos2 θDR, where θDR is the direct recoil angle, k = 4m 1 m 2 (m 1 + m 2 ) 2 , m1 and E0 are projectile mass and energy and m2 is carbon mass. We have observed sharp DR peaks. A collimated projectile beam with divergence ∼ ±0.2° is supplemented with a similar collimation before the energy analyzer to reduce the background of sputtered ions due to scattered projectiles.Measurements of the energy spectra of multiply charged positive and negative carbon ions recoiling from graphite surface under 100 and 150 keV argon and krypton ion bombardment are presented. With the energy spectrometer set at recoil angle of 79.5 degrees, direct recoil (DR) peaks have been observed with singly as well as multiply charged carbon ions , where n = 1 to 6. These monatomic and cluster ions have been observed recoiling with the characteristic recoil energy E(DR) . We have observed sharp DR peaks. A collimated projectile beam with small divergence is supplemented with a similar collimation before the energy analyzer to reduce the background of sputtered ions due to scattered projectiles.

Role of the kinetic and potential sputtering in the regeneration of the soot

We have used the photoemission spectroscopy of the graphite hollow cathode sooting discharge to identify the roles played by the kinetic and potential sputtering, respectively. Our indicators are the relative densities of the sputtered carbon C, the Ne metastable atoms, and the ionized components (Ne+) of the regenerative sooting plasma. We find that the metastable atoms are the main agents for the regeneration of the soot.

Sputtering and formation of C1 and C2 in the regenerative sooting discharge

Photoemission spectroscopy of the regenerative soot in neons glow discharge plasma reveals the contributions from the sputtered atomic and molecular carbon species. We present the pattern of sputtering and the formation of monatomic C1 and diatomic C2 as a function of the discharge current, the support gas pressure and the number densities of the excited and ionized neon as the active constituents of the carbonaceous plasma.Abstract Photoemission spectroscopy of the regenerative soot in neons glow discharge plasma reveals the contributions from the sputtered atomic and molecular carbon species. We present the pattern of sputtering and the formation of monoatomic C 1 and diatomic C 2 as a function of the discharge current, the support gas pressure and the number densities of the excited and ionized neon as the active constituents of the carbonaceous plasma.

A compact, permanent-magnet-based E×B velocity filter for carbon cluster diagnostics

Abstract An E × B velocity filter is described that has been used for the detection and diagnostics of large carbon clusters C m (m≤10 4 ) . The velocity and momentum analyses are compared for our special experimental arrangement. We describe the variability of the resolving power of our compact velocity filter as the main advantage over other comparable mass analysis techniques.An ExB velocity filter is described that has been used for the detection and diagnostics of large carbon clusters Cm (where m is up to ten thousand). The velocity and momentum analyses are compared for our special experimental arrangement. We describe the variability of the resolving power of our compact velocity filter as the main advantage over other comparable mass analysis techniques.