Activation Induced by Laser-Plasma Electrons

In some experiments, the same solid target acted for both accelerator and radiator. 

Let us first review some experiments in which the laser-driven acceleration of electrons has been obtained in laser-solid interactions. 

Schwoerer et al. used tantalum for both accelerator and radiator but in two separate targets and the Jena 15 TW laser system at an intensity of 102°Wcm-2. A 5() pm first foil employed for the accelerator and a second slab of 1mm that acted as radiator [89]. As a result, 104 fission events per Joule of laser energy of 232Th and 238U, placed behind the second tantalum layer, were obtained with a reaction rate of the order of 1 event per laser shot. 

A critical point in the retrieving of the number of nuclear reactions in laser-solid experiments is that there is no control on the spectrum of the electrons accelerated in the interaction, as well as the acceleration mechanism is uncertain and difficult to fit in a predictable scheme. In most cases, the electron energy distribution is assumed to be Boltzmann-like and deconvolutions are performed starting from this assumption. 

A better control on the electron spectrum can be obtained in experiments that employ gas-jets as target for laser interaction. Experiments performed with gas-jets enable the generation of electron bunches with a higher energy and a lower angular spread. 

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