A. Helal | Searcharxiv

arXiv2023

Creation of super-high-flux photo-neutrons and gamma-rays > 8 MeV using a petawatt laser to irradiate high-Z solid targets

We report the creation of super-high-flux gamma-rays with energy >8 MeV and photo-neutrons via the (g,n) reaction near giant dipole resonance energies (8 - 20 MeV), using the ~130 J Texas Petawatt laser to irradiate high-Z (Au, Pt, Re, W) targets of mm - cm thickness, at laser intensities up to ~5x1021W/cm2. We detected up to ~ several x 1012 gamma-rays > 8 MeV (~3% of incident laser energy) and ~ 1010 photo-neutrons per shot. Due to the short pulse and narrow gamma-ray cone (~17o half-width) around laser forward, the peak emergent gamma-ray flux >8 MeV reached ~1027 gammas/cm2/sec, and the peak emergent neutron flux reached ~1020 neutrons/cm2/sec. Such intense gamma-ray and neutron fluxes are among the highest achieved for short-pulse laser experiments. They will facilitate the study of nuclear reactions requiring super-high-flux of gamma-rays or neutrons, such as the creation of r-process elements. These results may also have far-reaching applications for nuclear energy, such as the transmutation of nuclear waste, isotope production and inertial fusion.

physics.app-ph↗

arXiv2020

Explosion Dynamics of Methane Clusters Irradiated by 38 nm XUV Laser Pulses

We have studied the explosion dynamics of methane clusters irradiated by intense, femtosecond, 38 nm (32.6 eV) XUV laser pulses. The ion time-of-flight spectrum measured with a Wiley-McLaren-type time-of-flight spectrometer reveals undissociated molecular $\textrm{CH}_4^+$ ions, fragments which are missing hydrogen atoms due to the breakage of one or more C-H bonds $(\textrm{CH}_3^+, \textrm{CH}_2^+ \ \textrm{and}\ \textrm{CH}^+)$ and the recombination product $\textrm{CH}_5^+$. Also visible on the time-of-flight traces are atomic and molecular hydrogen ions $(\textrm{H}^+ \textrm{and}\ \textrm{H}_2^+)$, carbon ions, and larger hydrocarbons such as $\textrm{C}_2 \textrm{H}_2^+$ and $\textrm{C}_2\textrm{H}_3^+$. No doubly-charged parent ions $(\textrm{CH}_4^{2+})$ were detected. The time-of-flight results show that total and relative ion yields depend strongly on cluster size. The absolute yields of $\textrm{CH}^+_5$ and $\textrm{H}^+$ scale linearly with the yields of the other generated fragments up to a cluster size of $\langle\textrm{N}\rangle=70,000 \ \textrm{molecules}$, then begin to decrease, whereas the yields of the $\textrm{CH}_n^+(n=1-4) $ fragments plateau at this cluster size. The behavior of $\textrm{H}^+$ may be understood through the electron recombination rate, which depends on the electron temperature and the cluster average charge. Moreover, the $\textrm{CH}_5^+$ behavior is explained by the depletion of both $\textrm{CH}_4^+$ and $\textrm{H}^+$ via electron-ion recombination in the expanding nanoplasma.

physics.atm-clus↗