The n-³He Experiment at SNS : Components

Three basic ingredients are required to measure the spin-momentum correlation in n + 3He -> p + t are:

1. longitudinally polarized neutrons with quickly alternating spins to cancel out systematics
2. a 3He target, and
3. a detector to measure the direction of the outgoing protons.
   
   

Polarized neutrons are provided by the FnPB. The spins are reversed on a pulse-by-pulse basis by an RF spin rotator. The target and detector are combined into a single 3He ionization chamber with sense wires to detect the forward- and backward-going recoil protons.

The n-3He reuses many components from the currently running NPDGamma experiment, including the supermirror polarizers, neutron beam monitors, shielding, spin flipper electronics, B-field power supply, and support stands. The new components created specifically for this experiment are:

Subpackages

• Beam
  - intensity monitors, X-Y scanners, polarimetry
• Solenoid
  - holding field for longitudinal polarized electrons (NPDGamma had transverse polarization)
• RFSF
  - a new spin rotator which will work with either longitudinal or transverse polarization
• Ion Chamber
  - an integrated 3He target and detector, similar in design to the beam monitors
• Preamps
  - custom preamplifiers for the 144 sense wires, attached directly to the ion chamber
• DAQ
  - four modules of 64 channel, 24 bit, 128 kHz delta-sigma continuously sampling ADCs
• Integration
  - Unistructure to support all components and 3-D model of experiment
• Simulations
  - Simulations of experiment and radiological simulations

Probing The Hadronic Weak Interaction