Nuclear emulsions for the detection of micrometric-scale fringe patterns: an application to positron interferometry

Abstract

Nuclear emulsions are capable of very high position resolution in the detection of ionizing particles. This feature can be exploited to directly resolve the micrometric-scale fringe pattern produced by a matter-wave interferometer for low energy positrons (in the 10-20 keV range). We have tested the performance of emulsion films in this specific scenario. Exploiting silicon nitride diffraction gratings as absorption masks, we produced periodic patterns with features comparable to the expected interferometer signal. Test samples with periodicities of 6, 7 and 20 µm were exposed to the positron beam, and the patterns clearly reconstructed. Our results support the feasibility of matter-wave interferometry experiments with positrons.

First demonstration of antimatter wave interferometry

“…A monochromatic and continuous beam is thus formed with an energy spread less than 0.1%, limited by the stability of the power supplies. The positron rate is (5 ± 1) × 10 3 e + /s, and beam focusing can be tuned to reach a spot size of the order of several millimeters of full width at half maximum (FWHM), an approximately Gaussian intensity profile ( 23 ) and an angular divergence at the level of a few milliradians ( 24 ). A suitable model ( 25 ) of grating-based interferometry with a partially coherent beam exploits the analogy with Gaussian Schell-model beams of classical optics (Materials and Methods).…”

“…1) is revealed by a nuclear emulsion detector. Nuclear emulsions ( 28 ) offer submicrometer-level position resolution in the detection of ionizing particles ( 24 , 29 ). They work as photographic films by exploiting the properties of silver bromide crystals embedded in a 50-μm-thick gelatin matrix.…”

“…For this experiment, we developed a glass-supported emulsion detector (fig. S1) and experimentally demonstrated its capability to resolve periodic patterns at the micrometric scale even with low signal contrast and on large areas ( 24 ).…”

“…To ensure uniform working conditions throughout the explored energy range, we used nuclear emulsions prepared without the standard surface protective gelatin layer. The presence of even a micrometric layer would have introduced detection efficiency ( 23 ) and positron trajectory smearing ( 24 ) that are both energy dependent. Thermally induced grains are the dominant source of background noise in emulsion detectors.…”

First Demonstration of Antimatter Quantum Interferometry

“…suitable for anti-electrons (positrons) in the 5-18 keV energy range. This development is part of the QUPLAS (QUantum interferometry and gravitation with Positrons and LASers) research program[17][18][19][20] . Sketch of the setup: the beam, prepared by two 2-mm-wide collimators, reaches the gratings and the emulsion detector.…”