The uniformity of the beam flux has been measured using several different techniques. At large sweep the ratios of the various fluxes quickly converge to unity, allowing us to select a beam rastering that throws away as little current as possible while still giving a very uniform beam.

The rastering and passage of the beam through an aperture and interaction with various target density functions is currently be modelled to further increase our understanding and to provide a more thorough understanding of systematic effects and uncertainties involved.

In addition to measuring the current through various sized apertures we also measured the yield per incident particle as a second test of beam sweep and alignment between the two ends of the flipping arm. For large target distributions or misaligned targets the yield per incident particle does not level off until larger beam sweeps. Larger beam sweeps put less intensity on target, and are therefore undesirable.

It is also important that our estimate of the beam flux from the 3mm diameter aperture agree with the beam flux striking the actual target; i.e. the target must have most or all of its activity within a 3mm radius. To explore and verify this we have taken scans of the target with a beam well focused in one dimension and rastered into a line in the other dimension.

The points with smooth curves through them are actual target scans while the green line is what an idealized target of perfect uniformity and 3mm diameter would look like. One can see from the scans that some small tail of activity leaks outside of the central region. This tail is much worse in some cases than in others and in once case is not even symetric! The striking result of this is that not all targets are within reasonable bounds for carrying out a 5% measurement of the S-factor. Because of this great effort is being made to increase the consistency of our target fabrication.

Many of these beam sweep tests were carried out using a LiF target to allow us a reasonable event rate in our tests. The ⁷Li(d,p)⁸B reaction provides a much higher event rate than ⁷Be(p,g)⁸B as well as the advantage of not working with a radioactive target.

Another advantage of the LiF target is that it allows us to observe the resonance in ¹⁹F(p,ag)¹⁶O at 1.4 MeV. By observing the prompt g-rays from this reaction in a NaI detector and matching them with the position of the beam at the time of the gate we can create an image of the target. This image allows us to examine the alignment between the two ends of our arm, the uniformity of our target, and the physical extent of our sweep at various values of the raster.

All of the equipment necessary to make a measurement of the absolute cross-section is now in place. Currently the effort is to improve and remove systematic uncertainties and hunt down sources of electronic noise in the system in preparation for high grade targets and taking final data later this year.

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