DEMON consists of 100 individual large size NE213 liquid scintillator cells. Each cell is 20 cm long, has a diameter of 16 cm and contains 4.5 litres of liquid rich in Hydrogen. A neutron coming into the scintillator interacts mainly with the protons which results in the ionization of the atoms of the scintillator. The subsequent deexcitation induces a light emission which has two components: a fast one and a slow one.

The outcoming light is transformed into an electrical signal by a specially designed XP4512B photomultiplier tube. The shape analysis of this pulse allows the discrimination between incident neutrons and s which have different slow components.

The signal is analysed by an electronic chain which has been developed in the VXI standard.

Scheme of a DEMON cell equiped with its SYREP scintillator.

SYREP: Proton Rejection System

DEMON operates in the atmosphere. Therefore slow charged particles don't reach the scintillators.

To avoid the contamination of the neutron spectra by very energetic protons which may reach the neutron detectors, DEMON disposes of 24 NE102 scintillators (3 mm thin) coupled to photomultipliers which can be mounted in front of the DEMON cells. These plastic scintillators are nearly 100% efficient to the protons and less than 0.5% to the neutrons. Thus the protons can be rejected in the analysis of the data by an anti-coincidence between the two signals delivered by the two photomultipliers.

Forward and backward views of DEMON cells equiped with SYREP scintillators

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