9 Nuclear Emulsions
413
the dependence of crystal sensitivity on its size. This study was motivated by the
interest to understand the phenomenology of the latent image formation, which
predicts that the quantum sensitivity can be better at such a crystal size. Further
studies are in progress with the aim of developing emulsions with higher sensitivity.
The conditions of chemical sensitisation and development were optimised for each
crystal size in the range of 200–800 nm. The increase in the crystal sensitivity
depending on the crystal size was confirmed for crystals of 350–800 nm [127].
These R&D activities form the base for a broad range of future applications.
9.6.2 Projects in Fundamental Physics
9.6.2.1 Balloon Experiments
Balloon experiments employing emulsion detectors were reported in [128]. The use
of emulsion technique for cosmic-ray physics experiments has recently attracted
research interest after the significant technological advances in the last decades.
In 2004, a balloon experiment using emulsions was performed to observe primary
cosmic-ray electrons [129]. Various innovations such as the industrial emulsion
films, the refreshing technique, the automated emulsion read-out system and the
off-line analysis methods were introduced. In addition, a dedicated device was
developed to distinguish between particles passing through a chamber at the balloon
level altitude and those recorded during other periods. The mechanism of this device
is such that it causes intentional shift of the upper block of the chamber with respect
to the lower block, when the balloon reaches float altitude and again when the
flight at float altitude is terminated. The working principle of the technique was
successfully demonstrated.
Based on these techniques, a balloon-borne emulsion γ -ray telescope was proposed [130] and the Gamma-ray Astro-Imager with Nuclear Emulsion (GRAINE)
project was developed for the observation of γ -rays in the energy range of 10 MeV–
100 GeV. A precise, polarisation-sensitive, large-aperture-area emulsion telescope
with repetitive long-duration balloon flights was employed. The electron and
positron angles at the pair creation point can be measured in emulsions and the
angular resolution for γ -rays (10 MeV–10 GeV) is about one order of magnitude
higher than that of the Fermi Large Area Telescope (Fermi-LAT) (Fig. 9.19). The
polarisation sensitivity of an emulsion-based telescope was demonstrated using a
polarised γ -ray beam at SPring-8/LEPS [131].
An emulsion multi-stage shifter was used to develop an innovative solution capable of providing the event time-stamp and hence the γ -ray absolute direction [135].
The relative alignment between the automatically sliding emulsion films, each
moving with a known different speed, provides the required time association of the
event. This technique allows γ -ray detection with low energy threshold, minimising
the electric power and also limiting the overall detector mass.
413
the dependence of crystal sensitivity on its size. This study was motivated by the
interest to understand the phenomenology of the latent image formation, which
predicts that the quantum sensitivity can be better at such a crystal size. Further
studies are in progress with the aim of developing emulsions with higher sensitivity.
The conditions of chemical sensitisation and development were optimised for each
crystal size in the range of 200–800 nm. The increase in the crystal sensitivity
depending on the crystal size was confirmed for crystals of 350–800 nm [127].
These R&D activities form the base for a broad range of future applications.
9.6.2 Projects in Fundamental Physics
9.6.2.1 Balloon Experiments
Balloon experiments employing emulsion detectors were reported in [128]. The use
of emulsion technique for cosmic-ray physics experiments has recently attracted
research interest after the significant technological advances in the last decades.
In 2004, a balloon experiment using emulsions was performed to observe primary
cosmic-ray electrons [129]. Various innovations such as the industrial emulsion
films, the refreshing technique, the automated emulsion read-out system and the
off-line analysis methods were introduced. In addition, a dedicated device was
developed to distinguish between particles passing through a chamber at the balloon
level altitude and those recorded during other periods. The mechanism of this device
is such that it causes intentional shift of the upper block of the chamber with respect
to the lower block, when the balloon reaches float altitude and again when the
flight at float altitude is terminated. The working principle of the technique was
successfully demonstrated.
Based on these techniques, a balloon-borne emulsion γ -ray telescope was proposed [130] and the Gamma-ray Astro-Imager with Nuclear Emulsion (GRAINE)
project was developed for the observation of γ -rays in the energy range of 10 MeV–
100 GeV. A precise, polarisation-sensitive, large-aperture-area emulsion telescope
with repetitive long-duration balloon flights was employed. The electron and
positron angles at the pair creation point can be measured in emulsions and the
angular resolution for γ -rays (10 MeV–10 GeV) is about one order of magnitude
higher than that of the Fermi Large Area Telescope (Fermi-LAT) (Fig. 9.19). The
polarisation sensitivity of an emulsion-based telescope was demonstrated using a
polarised γ -ray beam at SPring-8/LEPS [131].
An emulsion multi-stage shifter was used to develop an innovative solution capable of providing the event time-stamp and hence the γ -ray absolute direction [135].
The relative alignment between the automatically sliding emulsion films, each
moving with a known different speed, provides the required time association of the
event. This technique allows γ -ray detection with low energy threshold, minimising
the electric power and also limiting the overall detector mass.