David Rodríguez González

Test of LAAPDs Coupled to CsI(Tl) Crystals for the CALIFA R3B/FAIR Calorimeter

Several studies with different Large Area Avalanche Photo-Diodes (LAAPDs) coupled to ad-hoc bi-frustum shaped CsI(Tl) crystals have been carried out as a part of the R&D program for the CALIFA R3B/FAIR calorimeter. CALIFA, which is designed for the detection of light charged particles and gamma-rays in a wide energetic domain, has very stringent requirements. We report in this work our studies on the energy resolution for gamma-rays using LAAPDs as photosensors. One of the factors affecting the energy resolution is the matching between the APD active area and the crystal exit face. We present in this paper a procedure for characterizing APDs based on the measurement of their contribution to the energy resolution. The results obtained are very promising and suggest that a solution based on CsI(Tl) crystals coupled to LAAPDs could be suitable for, at least, part of the CALIFA calorimeter.

Optimization of a fast rotating target to produce kHz X-ray pulses from laser-plasma interaction

We report the development of a fast rotating target to produce ultrashort incoherent X-ray pulses from bremsstrahlung. These short X-ray pulses are produced in the laser-plasma interaction of a 35 fs, 1 mJ pulse of a Ti:Sa laser of 1 kHz repetition rate, with a solid metallic target. In this paper, we report our developments to improve the stability of this micron size source of ultrashort X-rays. As the Rayleigh length is very small (<15 micron), wobbling of the rotatory stage can reduce the intensity on target and change the characteristics of the source. We describe the methods we have developed to measure and adjust the stability of the focus on target. These advances are important for the development of sources with high average power and good stability. The X-ray source has a broad Maxwellian-like distribution with temperatures of around 10 - 40 KeV and could be used for advanced X-ray imaging such as absorption or phase contrast tomography.