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A. Ariga et al.
change in the detector design philosophy occurred: emulsions became a highresolution tracking detector with three-dimensional reconstruction capabilities,
rather than a visual and volume detector. This is obtained by sandwiching emulsion
films or plates with passive material layers, usually made of plastic or metal plates.
Today, we would call such a detector a very finely subdivided sampling-calorimeter,
by means of which all charged tracks originating from the shower are reconstructed
in space with high resolution. In the ECC, emulsion films are placed perpendicular
to the incoming particles, so acting as a tracking detector featuring high spatial
resolution (up to 1 μm).
The first design of the ECC consisted of a sandwich of brass plates and thin
emulsion films. This type of detector was first developed by Kaplon and used
to study heavy primaries in cosmic-ray interactions [19]. ECC detectors were
applied to the study of the cosmic-ray spectrum and to very-high energy interaction
processes. Nishimura, in particular, proposed the cascade shower analysis method to
measure the energy of interacting γ -rays and predicted the capability of this detector
to regulate the development of electron showers by selecting passive material plates
on purpose [20].
Niu developed double-sided emulsion plates in which the sensitive emulsion
layer is deposited on either side of a plastic substrate (see e.g. [21]). For this
purpose FUJI developed a special 800 μm thick plastic base to allow gel pouring
on both sides of the layer. The emulsion layers were 50 μm thick. With this new
film design, two problems had to be solved: the availability of a plastic base with
optical properties compatible with that of nuclear emulsions, and of a high-power
objective lens with a working distance longer than 1 mm. The first problem was
overcome with meta-acrylic (lucite) plates, the second was solved thanks to the
efforts of Tiyoda Optical Co. The use of a plastic base between the two emulsion
layers allows a precise measurement of the track angle by connecting those grains
closest to the base. These points indeed are not affected by distortions. The long
lever arm available with such a thick base improves the angular resolution up to
1 mrad.
The ECC opened the way to a series of important experiments of large size,
thanks to the use of the dense metal plates allowing the realization of large-mass
detectors with unprecedented space resolution. For the study of high-energy cosmicrays (10 TeV) and the determination of their power law spectrum, we mention in
particular the Chacaltaya experiment [22] that allowed the study of the central
core of air showers, and the relatively large-size Mt. Fuji experiment [23]. For
even higher cosmic-ray energies (1000 TeV and more), the RUNJOB [24] and
JACEE [25] experiments studied the spectrum of primary heavy ions.
As said above, the analysis methods of ECC events are based on the reconstruction of all tracks produced following a primary interaction, likely occurring in the
dense passive material. Space angles are measured for all track segments. Shower
reconstruction and identification (electromagnetic or hadronic) can be performed
on the basis of the topological features of the shower. In the same way, one can
also reconstruct particle decays. In addition to the topological studies, powerful
kinematical analyses can be conducted with ECC detectors by exploiting Multiple
A. Ariga et al.
change in the detector design philosophy occurred: emulsions became a highresolution tracking detector with three-dimensional reconstruction capabilities,
rather than a visual and volume detector. This is obtained by sandwiching emulsion
films or plates with passive material layers, usually made of plastic or metal plates.
Today, we would call such a detector a very finely subdivided sampling-calorimeter,
by means of which all charged tracks originating from the shower are reconstructed
in space with high resolution. In the ECC, emulsion films are placed perpendicular
to the incoming particles, so acting as a tracking detector featuring high spatial
resolution (up to 1 μm).
The first design of the ECC consisted of a sandwich of brass plates and thin
emulsion films. This type of detector was first developed by Kaplon and used
to study heavy primaries in cosmic-ray interactions [19]. ECC detectors were
applied to the study of the cosmic-ray spectrum and to very-high energy interaction
processes. Nishimura, in particular, proposed the cascade shower analysis method to
measure the energy of interacting γ -rays and predicted the capability of this detector
to regulate the development of electron showers by selecting passive material plates
on purpose [20].
Niu developed double-sided emulsion plates in which the sensitive emulsion
layer is deposited on either side of a plastic substrate (see e.g. [21]). For this
purpose FUJI developed a special 800 μm thick plastic base to allow gel pouring
on both sides of the layer. The emulsion layers were 50 μm thick. With this new
film design, two problems had to be solved: the availability of a plastic base with
optical properties compatible with that of nuclear emulsions, and of a high-power
objective lens with a working distance longer than 1 mm. The first problem was
overcome with meta-acrylic (lucite) plates, the second was solved thanks to the
efforts of Tiyoda Optical Co. The use of a plastic base between the two emulsion
layers allows a precise measurement of the track angle by connecting those grains
closest to the base. These points indeed are not affected by distortions. The long
lever arm available with such a thick base improves the angular resolution up to
1 mrad.
The ECC opened the way to a series of important experiments of large size,
thanks to the use of the dense metal plates allowing the realization of large-mass
detectors with unprecedented space resolution. For the study of high-energy cosmicrays (10 TeV) and the determination of their power law spectrum, we mention in
particular the Chacaltaya experiment [22] that allowed the study of the central
core of air showers, and the relatively large-size Mt. Fuji experiment [23]. For
even higher cosmic-ray energies (1000 TeV and more), the RUNJOB [24] and
JACEE [25] experiments studied the spectrum of primary heavy ions.
As said above, the analysis methods of ECC events are based on the reconstruction of all tracks produced following a primary interaction, likely occurring in the
dense passive material. Space angles are measured for all track segments. Shower
reconstruction and identification (electromagnetic or hadronic) can be performed
on the basis of the topological features of the shower. In the same way, one can
also reconstruct particle decays. In addition to the topological studies, powerful
kinematical analyses can be conducted with ECC detectors by exploiting Multiple