Abstract
The Monte Carlo code Geant4 is used to demonstrate ultrafast gamma-ray line emission from the 12C +12C reaction driven by laser-accelerated ion beams. With carbon ions of the order of tens of MeV accelerated by laser-bombarding the carbon target, characteristic gamma-ray line emission is generated with durations as short as picoseconds through ultrafast gamma-ray transitions. Because the relative bandwidths of such gamma-ray lines can be reduced to less than 1% and the yield rate of gamma photons is around 10−5 for an incident carbon ion, this gamma-ray line emission can be used as an ultrafast monoenergetic gamma-ray source with a flux of 1.2 × 106 photons/J into 4π. We also show that the bremsstrahlung background induced by electrons accelerated simultaneously with the carbon ions can be mitigated by choosing a proper detection angle and an optimized target thickness.
Highlights
As important compact sources of gamma rays, laser-driven gamma-ray sources have attracted much attention because of their wide applications, such as the radiography of dense objects,[1] gammaray beam transmutation,[2,3] and nondestructively measuring and assaying nuclear material by nuclear resonance fluorescence[4,5] for nuclear security and safeguards.[6]
The full width at half maximum (FWHM) for 440 keV is only 4 keV when we integrate from θ = 80◦ to 100◦, and we reduce the relative bandwidth to 1%
The yield rates of gamma photons for 440 keV and 1,636 keV are around 10−5 per carbon ion, which can be calculated from the gamma spectrum (e.g., Fig. 3(b))
Summary
As important compact sources of gamma rays, laser-driven gamma-ray sources have attracted much attention because of their wide applications, such as the radiography of dense objects,[1] gammaray beam transmutation,[2,3] and nondestructively measuring and assaying nuclear material by nuclear resonance fluorescence[4,5] for nuclear security and safeguards.[6]. Because gamma-ray transitions take place mainly in excited nuclides with half-lives as short as nanoseconds or even picoseconds, we propose using laser-accelerated ultrashort (picosecond) carbon-ion beams to generate ultrafast gamma-ray line emission with pulse width of several picoseconds. These results show that if we use a monoenergetic (quasi-monoenergetic) ion source,[21,32] the gamma line emission is purer and more gamma photons are generated because the nuclear levels can be excited more selectively.
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