Development of Thick-foil and Fine-pitch GEMs with a Laser Etching Technique

We have produced thick-foil and fine-pitch gas electron multipliers (GEMs) using a laser etching technique. To improve production yield we have employed a new material, Liquid Crystal Polymer, instead of polyimide as an insulator layer. The effective gain of the thick-foil GEM with a hole pitch of 140 um, a hole diameter of 70 um, and a thickness of 100 um reached a value of 10^4 at an applied voltage of 720 V. The measured effective gain of the thick-foil and fine-pitch GEM (80 um pitch, 40 um diameter, and 100 um thick) was similar to that of the thick-foil GEM. The gain stability was measured for the thick-foil and fine-pitch GEM, showing no significant increase or decrease as a function of elapsed time from applying the high voltage. The gain stability over 3 h of operation was about 0.5%. Gain mapping across the GEM showed a good uniformity with a standard deviation of about 4%. The distribution of hole diameters across the GEM was homogeneous with a standard deviation of about 3%. There was no clear correlation between the gain and hole diameter maps.Comment: 21 pages, 9 figure

Mass, Spectroscopy, and Two-Neutron Decay of Be 16

The structure and decay of the most neutron-rich beryllium isotope, Be16, has been investigated following proton knockout from a high-energy B17 beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground (Jπ=0+) and first excited (2+) state, with Ex=1.31(6) MeV. The mass excess of Be16 was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2+ level presents a far more diffuse neutron-neutron distribution

Quasifree Neutron Knockout Reaction Reveals a Small s-Orbital Component in the Borromean Nucleus 17B

International audienceA kinematically complete quasifree (p,pn) experiment in inverse kinematics was performed to study the structure of the Borromean nucleus B17, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 1s1/2 and 0d5/2 orbitals, and a surprisingly small percentage of 9(2)% was determined for 1s1/2. Our finding of such a small 1s1/2 component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B17. The present work gives the smallest s- or p-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of s or p orbitals is not a prerequisite for the occurrence of a neutron halo

Nanosecond laser ablation and deposition of silicon

Nanosecond-pulsed KrF (248 nm, 25 ns) and Nd:YAG (1064 nm, 532 nm, 355 nm, 5 ns) lasers were used to ablate a polycrystalline Si target in a background pressure of < 10(-4) Pa. Si films were deposited on Si and GaAs substrates at room temperature. The surface morphology of the films was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Round droplets from 20 nm to 5 mu m were detected on the deposited films. Raman Spectroscopy indicated that the micron-sized droplets were crystalline and the films were amorphous. The dependence of the properties of the films on laser wavelengths and fluence is discussed