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Tetra 1


4 Pi neutrons detector

Tetra 5
TETRA is a 3He-based detector which are the only neutron detector having no energy threshold. Furthermore they allow practically 4pi coverage thus providing excellent detection efficiency (over 60%) for beta-delayed neutrons (low energy, reduced production rate). These kinds of devices are then the most suited detectors for delayed neutron emission probability measurements.
TETRA detector
Tetra 1

CAD view of TETRA

The detector counts 90 tubes, 500 mm long, filled with 3He gas, each one coupled to photomultiplier tube. They are then embedded in a polyethylene bloc HDPE 1000 (about 9 200 000 g/mol) and, in turn, wrapped in a shielding of 150 mm-thick 5%-boron doped polyethylene.

On the TETRA installation there are as well implemented a movable tape aluminum collector and a HPGe detector along the beam axis, and a plastic scintillator 4pi beta detector orthogonal to the beam. This one is clamped in the polyethylene plates’ assembly, which represents the core of the detector, and can be opened in two separate segments to allow access to the 4pi beta detector. At present, a new PARRNe version of the movable tape is in fabrication and, in the meanwhile the TETRA set-up will make use of the movable tape from IPHC.

TETRA with BEDO beam line
Tetra 2


Tetra 3

Tetra on BEDO 2

TETRA was originally placed on the BEDO, and so its installation required demounting the HPGe detectors, the plastic and the BGO scintillators as well as the BEDO beta detector. The present permanent installation of the Tetra detector results then really convenient as it considerably minimizes the manipulations of the small clovers installed on BEDO which are particularly fragile.


TETRA beam line
  Tetra 4

TETRA 1 implantation

Tetra 5

TETRA 1 beam line

Tetra will be installed next by the PARRNe separator, on the beam line at 45deg, in a straight line through the 60 deg deflector. In this configuration, it can be used at any time, with always the same optimized settings, without beamtime loss. During the same experience, it will be then possible to measure, at the same time, the beta-gamma decay of the sources as well as the beta-delayed neutron emission.
International context
 The Tetra detector belongs to FLNR Dubna. It has been made available for the ALTO facility in the framework of a long-lasting collaboration between IPNO and FLRN, which has been continuously supported for the last 6 years by the PICS and by the IN2P3-JINR collaboration. The Tetra detector will be installed at ALTO until the delivery of DESIR (Désintégration, Excitation et Stockage d’Ions Radioactifs - disintegration, excitation and radioactive ion storage) at SPIRAL2.

Contact  : L. Vatrinet

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Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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