Photo-transmutation Of Long-lived Nuclear Waste By Laser-plasma Driven Electron Source

The disposal of nuclear waste is a key issue to be solved in development of nuclear power.Exploring novel transmutation principle,physicalscheme or approachto deal with the highly toxic and long-lived fission products is of paramount importance.Based on the laser-plasma drivenelectron source,collimated high-flux?-rays can be generated through bremsstrahlung and then the nuclear transmutation can be induced byphotonuclear reactions.With rapid development of ultraintenseandultrashortlasertechnology,laserplasma interactionenables exploring and even revisiting photo-transmutation of nuclear waste initiated by laser-based electron source.Currently two main physical mechanisms,namely laser ponderomotive acceleration?LPA?and laser wake-field acceleration?LWFA?,have been proposed for electron acceleration in relativistic laser-plasma interactions.A photo-transmutation model taking the LPAelectron beam?e-beam?characteristicsinto account,is implemented into the Monte Carlo?MC?Geant4 toolkit to study the photo-transmutation of long-lived radionuclides(for example,¹³⁵Cs).High-energy electron andbremsstrahlung radiation generation,and the following photonuclear reaction are investigatedat four different laser intensities:10²⁰,5×10²⁰,10²¹ and 5×10²¹ W/cm².The transmutation efficiency depends on the laser intensity and the geometry of both the convertor and the cesium target.Optimum laser intensity,namely 10²¹ W/cm²,isfound,with which the photonuclear reaction yield can exceed 10⁸ per Joule of the laser energy.Furthermore,we proposed the hybrid acceleration mechanism consistingLPAandLWFAtosignificantlyenhancethe photo-transmutation efficiency.Considering two kinds of isotopes samples,i.e.single¹²⁶Snisotopeand multiple ⁹³Zr,¹⁰⁷Pd,¹²⁶Sn and ¹³⁵Cs isotopes,nuclear waste transmutation driven by laser-hybrid-accelerated relativistic e-beam have been investigated through particle-in-cell?PIC?and MC simulations.It is shown that collimated relativistice-beam with a high charge of approximately 100 nC,produced by high-intensity laser irradiating near-critical-density?NCD?plasma,can generate high-flux(10¹¹ per laser shot)bremsstrahlung?-rays in the GDR energy region.The transmutation yield obtained is the order of 10⁹ per laser shot,which is two orders of magnitude higher than achievedin previous studies.It is also found that tightly focused lasers impinging on longer NCD plasmas at lower densities helpto enhance the transmutation yield.This study providessome guidance for possible photo-transmutation experiments with desktop laser plasma accelerator,and may offer potential physical scheme for nuclear wastetransmutation.