Experiment Proposal - opera - Infn

entry : 85
RMS: 0.060
15
10
5
0
0
deviation ( micron )
Figure 29: Position residuals of the grain center with respect to a fitting straight line.
Usually the distortion becomes larger near the edge of the film. In the case of industrial emulsion
films, the distortion is lower than ∼ 1 µm up to 1 mm from the film edge. At ≤ 500 µm from the
film border, track recognition by eye is still rather easy. This means that by using a proper distortion
correction, tracks can be well recognised by automatic systems even at this position. Only at about
100 µm from the edge the film is completely damaged, due to black stripes caused by the pressure
applied at the film cutting. Fig. 31 displays some measurements of edge distortions. The data show that
these effects are negligible up to ∼ 200 µm from the film edge.
The fading and aging features of the industrial emulsion films have been investigated. Fading is
the loss of the latent image occurring prior to development. Aging is the degradation of the emulsion
sensitivity during the exposure.
Fading is not a severe problem for this experiment, since we plan to extract the selected brick and
develop the emulsions within one week after the event occurred. Within about one month, possible extra
bricks required for further analysis (candidate events) are extracted and developed. Moreover, one can
take advantage of the existence of some fading, which contributes to erase unwanted cosmic ray tracks
accumulated during film production and transportation before the run, as described in the next Section.
This feature is beneficial to suppress the degradation of the electron identification efficiency and obtain
an adequate energy resolution for cascade showers. In principle, the fading time constant depends on
the environmental temperature, humidity and on the oxygen density. One example of these properties is
shown in Fig. 32. According to the film producer, fading properties are well under control.
In order to check the features of the Fuji emulsion in maintaining their sensitivity with age we have
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