Error bars for the He3 cross section?

[SimonHeybrock]

          Do we have an error bar for the `2966`? Then we could include it in the propagation of uncertainties.

Originally posted by @SimonHeybrock in #26 (comment)

[astellhorn]

Sigma_0 is measured very precisely, I would need to search deeply in literature to find an error bar - as far as I know it hasnt been measured/evaluated for neutrons with parallel spin to the He state (basically 0). It will be overwhelmed by any other error. Literature on the value of sigma_0 will follow
(As discussed in slack #polarization on 26th January)

[astellhorn]

V. McLane, C.L. Dunford, P.F. Rose, "Neutron Cross. Sections, Vol. 2, Neutron Cross Section Curves", Academic. Press Inc., New York (1988).

I will also add it in the documentary.

[astellhorn]

Also for other workflows: (citation Hal) 2966 barn at 1 Å is the unpolarised neutron cross-section. For polarised neutrons, 5933 bar at 1 Å for anti-parallel spin sigma and we usually use 0 for parallel spin sigma.