Experiment Proposal - opera - Infn

Figure 22: A photograph of an ECC brick with origami packing.
Due to the thin aluminum layer and to thermo-sealing, the inner pressure and humidity are kept
stable. The inner pressure is less than 0.1 atmosphere. This can be achieved by conventional vacuum
packing techniques. The hermeticity of the packing has been checked over long periods, as demonstrated
by existing samples packed more than ten years ago.
The vacuum packing also helps mantaining the brick mechanical stability. Under the atmospheric
pressure, the sandwich structure can well resist external mechanical constraints, because of the friction
between plates. In addition, slipping between plates due to the difference of the thermal expansion
coefficients between emulsion films and lead plates is suppressed by the vacuum packing.
The maximum tolerable temperature variation (∆T ) can be expressed as follows
∆T max =
2 · F
E · A · ∆k
where F is the friction force between the lead plate and the film, E is the Young’s modulus of the
film (3 × 10 4 kgf/cm 2 ), A is the thickness of the film and ∆k is the difference of the thermal expansion
coefficient between the lead plate and the film (k(lead) ∼ 30 × 10 −6 , k(film) ∼ 50 × 10 −6 ). Here F
is expressed as µ × N, µ is the friction coefficient and N is the force supplied by the vacuum packing.
The friction coefficient is measured to be 0.31 − 0.34 at N =0.2 kgf/cm 2 inthecaseofleadplates
and emulsion films.
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