Polarization Measurement for Npdgamma at the SNS M. Jon Dadras

Outline My previous proposal My previous proposal Why we can’t use this method for p n Why we can’t use this method for p n My new proposal to determine p n My new proposal to determine p n Basics of a 3 He cells Basics of a 3 He cells Using my previous method to determine the ε SF Using my previous method to determine the ε SF Simulation results Simulation results

My old method to determine p n What is the count-rate for spin-up/down neutrons when an un-polarized beam impinges on a 3 He analyzer? What is the analyzing power of the analyzer, i.e. what is the polarization of an un-polarized beam after passage through the 3 He cell? What is the transmission of a polarized beam after passing through the 3 He cell? Suppose we flip the polarization with a given efficiency (epsilon), what is the transmission?

New method to determine p n Again What is the transmission of a polarized beam after passing through the 3 He cell? Now we flip the polarization of the 3 He cell (P  -P), what is the transmission? The uncertainty of the opacity will be dominated by the unceratinty in the 3 He polarization (about 5%). Thus from the above, the opacity must be at least 1.1 But we cannot use the previous method because we must also measure the SF efficiency in situ (I will come back to this). We can use a different measurement for the neutron beam polarization.

How is 3 He Polarized Circularly polarized light impinges on an alkali- metal (Rb) resonant with gs  1 st exc. transition Circularly polarized light impinges on an alkali- metal (Rb) resonant with gs  1 st exc. transition Light spin-polarizes the electrons Light spin-polarizes the electrons Spin-exchange occurs through binary collisions Spin-exchange occurs through binary collisions Meaning there’s a spin-spin interaction between the nucleus of the noble gas ( 3 He) and the spin-polarized electron Meaning there’s a spin-spin interaction between the nucleus of the noble gas ( 3 He) and the spin-polarized electron Courtesy of 3

How to Perform the Measurement Empty cell transmission Empty cell transmission Filled cell P=0, T=e -σnd Filled cell P=0, T=e -σnd Finally we use AFP-NMR to monitor the 3 He polarization Finally we use AFP-NMR to monitor the 3 He polarization What is AFP-NMR? What is AFP-NMR? n + 3 He  p + 3 H

AFP-NMR AFP Courtesy of 4 Helmholtz coils will provide the RF field A pick-up coil is used to measure the magnetization of the cell (Rb) which depends on the polarization of 3 He.

The old method and ε We may still use Zimmer’s method to find the spin-flipper efficiency. We may still use Zimmer’s method to find the spin-flipper efficiency.

Neutron Spectrum

Numerical Results

Flipping Ratio

References Zimmer et al, Spin Filters and Supermirrors..., 2000 Zimmer et al, Spin Filters and Supermirrors..., 2000 Zimmer et al, High Precision Neutron Polarization..., 1999 Zimmer et al, High Precision Neutron Polarization..., 1999 Walker et al, Spin-exchange optical pumping of noble-gas nuclei, 1997 Walker et al, Spin-exchange optical pumping of noble-gas nuclei, 1997 Ino et al, A compact solenoid 3 He neutron spin filter..., 2005 Ino et al, A compact solenoid 3 He neutron spin filter..., 2005 Babcock et al, AFP flipper devices:..., 2007 Babcock et al, AFP flipper devices:..., 2007 Shankar, Principles of Quantum Mechanics, 1994 Shankar, Principles of Quantum Mechanics, 1994