A novel nuclear emulsion detector for measurement of quantum states of ultracold neutrons in the Earth's gravitational field - Archive ouverte HAL
Article Dans Une Revue Journal of Instrumentation Année : 2022

A novel nuclear emulsion detector for measurement of quantum states of ultracold neutrons in the Earth's gravitational field

Naoto Muto
  • Fonction : Auteur
Hartmut Abele
  • Fonction : Auteur
Tomoko Ariga
  • Fonction : Auteur
Masahiro Hino
  • Fonction : Auteur
Katsuya Hirota
  • Fonction : Auteur
Go Ichikawa
  • Fonction : Auteur
Hiroaki Kawahara
  • Fonction : Auteur
Shinsuke Kawasaki
  • Fonction : Auteur
Masaaki Kitaguchi
  • Fonction : Auteur
Kenji Mishima
  • Fonction : Auteur
Naotaka Naganawa
  • Fonction : Auteur
Mitsuhiro Nakamura
  • Fonction : Auteur
Stéphanie Roccia
  • Fonction : Auteur
  • PersonId : 865412
Osamu Sato
  • Fonction : Auteur
René I.P. Sedmik
  • Fonction : Auteur
Yoshichika Seki
  • Fonction : Auteur
Hirohiko M. Shimizu
  • Fonction : Auteur
Satomi Tada
  • Fonction : Auteur
Atsuhiro Umemoto
  • Fonction : Auteur

Résumé

Hypothetical short-range interactions could be detected by measuring the wavefunctions of gravitationally bound ultracold neutrons (UCNs) on a mirror in the Earth's gravitational field. Searches for them with higher sensitivity require detectors with higher spatial resolution. We developed and have been improving an UCN detector with a high spatial resolution, which consists of a Si substrate, a thin converter layer including $^{10}$B$_{4}$C, and a layer of fine-grained nuclear emulsion. Its resolution was estimated to be less than 100 nm by fitting tracks of either $^{7}$Li nuclei or α-particles, which were created when neutrons interacted with the $^{10}$B$_{4}$C layer. For actual measurements of the spatial distributions, the following two improvements were made. The first improvement was to establish a method to align microscopic images with high accuracy within a wide region of 65 mm × 0.2 mm. We created reference marks of 1 μm and 5 μm diameter with an interval of 50 μm and 500 μm, respectively, on the Si substrate by electron beam lithography and realized a position accuracy of less than 30 nm. The second improvement was to build a holder for the detector that could maintain the atmospheric pressure around the nuclear emulsion to utilize it under a vacuum during exposure to UCNs. The intrinsic resolution of the improved detector was estimated to be better than 0.56(8) μm by evaluating the blur of a transmission image of a gadolinium grating taken by cold neutrons. The evaluation included the precision of the gadolinium grating. A test exposure was conducted to obtain the spatial distribution of UCNs in the quantized states on a mirror in the Earth's gravitational field. The distribution was obtained, fitted with the theoretical curve, and turned out to be reasonable for UCNs in quantized states when we considered a blurring of 6.9 μm. The blurring was well explained as a result of neutron refraction due to the large surface roughness on the upstream side of the Si substrate. By using a double-side-polished Si substrate, a resolution of less than 0.56 μm is expected to be achieved for UCNs.

Dates et versions

hal-03547098 , version 1 (28-01-2022)

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Citer

Naoto Muto, Hartmut Abele, Tomoko Ariga, Joachim Bosina, Masahiro Hino, et al.. A novel nuclear emulsion detector for measurement of quantum states of ultracold neutrons in the Earth's gravitational field. Journal of Instrumentation, 2022, 17 (07), pp.P07014. ⟨10.1088/1748-0221/17/07/P07014⟩. ⟨hal-03547098⟩
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