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The LH2 target built for npdγ experiment contains 20l more than 99.8% liquid para-hydrogen at 15~17K.

What's Done
The hardware is at Indiana University Cyclotron Facility Jun 03 2008
What's Next
Modify the main vacuum body of target
Build new target vessel
Ship the all target package to SNS




Design Goals

The physics goals of the experiment coupled with the known properties of cold neutron and MeV gamma interactions with materials, the properties of hydrogen, and the need for the target system to be consistent with the other subsystems of the experiment implicitly define the following design goals for the target: (a) The target must absorb as much of the polarized cold neutron beam flux as possible without depolarizing the neutron beam before capture. The need to prevent neutron depolarization requires the target to consist of para-hydrogen at a temperature no higher than 17 K (Fig 2). (b) The target must possess negligible attenuation for the 2.2 MeV γ-rays from neutron capture. This requires the use of low Z materials in the target vessel and associated radiation shields as well as the vacuum vessel. (c) To ensure that the statistical accuracy of the measurement is not compromised by extra noise due to density fluctuations in the target, we require a liquid target in which bubbles are suppressed to acceptable levels and in which fluctuations in the pressure and temperature of the target are held to acceptable levels. (d) To ensure that no false effects are introduced by γs produced by polarized slow neutron capture on target materials other than para-hydrogen, we must use target engineering materials with sufficiently low PV γ-asymmetries. (e) To ensure that the interaction of circularly polarized γs produces negligible systematic effects and that the magnetic field in the target can be maintained with sufficient uniformity, the target materials in the vicinity of the neutron beam must be nonmagnetic (relative magnetic permeability less than μγ < 1.02). Any magnetic components in the target system must result in negligible magnetic field gradients.


Gas Handling System

Venting System

Warning and Alarm System



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