E1106 calibration reaction

The reaction of interest is 17O (beam energy 3.45 MeV) + p (gas pressure 10 Torr) --> α + 14N, via a resonance in 18F of 183 keV lab resonance energy and width Γ=0.3 eV. The candidate calibration reaction is 18O+p-->15N + α via a 151 keV resonance in 19F with width Γ=0.3 keV.

kinematic curves for both reactions (the legend is wrong because I am a numpty: the residuals are obviously N isotopes not O isotopes)


cross sections for both reactions, as a function of position in the gas cell


Cross section as a function of position, for coincidence events


Residual (14N or 15N) hitting S2 detector: for coincidence events


alphas hitting barrel detector: for the same coincidence events

Darren's Louvain experiment revisited

Here's an annotated copy of the detector configuration paper from Darren's thesis. Dimensions of the detectors and their positions are indicated.

Orsay data: theta calibration?

In this post, I simulated the elastic scattering events that are coincidences between dets 1 and 4. Here are the results for some data.
sort routine: require exactly one good det 1 event and one good quad event. (A good event in det 1 means that both ends of one strip fire. A good event in det 4 means that both ends of one strip fire, and the corresponding strip in det 3 does not fire.) Also require that strip number 6 in det 1 is always the one to fire. (Having a single strip in det 1 simplifies the energy gain matching: the gain-match parameters have not been selected at all so it would be surprising if the energies of all strips of det 1 were even similar.) The hits in det 1 look like this (all strips, E vs p):



and the hits in det 4 look like this (all strips, E vs p):



Distribution of theta hits in det 1 strip 6: theta conversion used is theta = 15-9*position



Distribution of theta hits in det 4 all strips: theta conversion used is theta = 63-14*position



Theta for det 4 all strips vs theta for det 1 strip 6:



I was hoping that, as I messed around like this with the data, some patterns would appear and/or start making sense. But I still don't know...

• why the det 1 E vs p loci seems to slope up to the right. Does that mean that right (= large position) = small theta, or just that the gainmatching is bad?
  
• why the det 1 E vs p loci don't extend all the way across the detectors. Does this mean that left (= small position) = small theta = high intensity, or just that there's some kind of threshold/triggering problem?
  
• what all the blobs in det 4 correspond to...it looks like there are several distinct things happening, but I have no idea what any of them are.

I'm going to select one region in strip 6 of det 4 and see what patterns emerge in its data. Here's the region:



and here are the corresponding events in strip 6 of det 1: Now we're onto something!



Here are the blobs from det 4 strip 6 (on the right; the one used for gating) and det 1 strip 6 (on the left; the resultant).



For completeness, try gating on the other three evident blobs in det 4 strip 6:




For comparison/orientation, here's the ungated data for det 1 (top) and det 4 (bottom):

Orsay data: selecting different strips in detector 4

require a good event in strip 3 of detector 4: here are the coincident events in det 1:

same for strip 7 of det 4:

same for strip 11 of det 4:

same for strip 15 of det 4:


As the strip number in det 4 increases, more events come in lower strip numbers in det 1. (This is eyeballing it, because I can't remember how to take the area of a 2d spectrum in Midas.)

Orsay: relative energy distribution for alpha coincidences

Alex's suggestion: calculate relative energy for (simulated) two-alpha events, see if there's a spectrum.
Results: see figure: there's a clear peak, with a fwhm of about 250 keV.



To duplicate this in the data, need some kind of position-to-theta mapping. If the position is linear in theta, then the mapping should be as follows:
detectors 2 and 3: θ = 96 - 14 p or 96 - 14(1-p)
detectors 4 and 5: θ = 63 - 14 p or 63 - 14(1-p)
where p goes from -1 to 1, and the two options account for the two possible orientations of the strips (low p = low theta or the opposite).

18F(p,α): update

Don Tomas el Sabio wrote:

The detector energy resolution for alpha particles and oxygen ions
is ~10keV and ~80keV FWHM respectively plus (in quadrature) the dead
layer energy straggling.

If we consider 1H(18F,4He) at E_lab=6.5MeV (say) the beam energy
loss in a 50ug (CH2)n target is ~0.8MeV or E_CM = 0.300 - 0.345MeV.
Can you allow the beam to interact at random depths within the 50ug
and 100ug (CH2)n targets at the energy appropriate to that depth
(E_beam - dE) and, including the various effects on resolution, plot
the beam's actual interaction energy versus the sum of the 15O+alpha
energies (for given angles)?

Here's an update. This simulation is done using energy straggling parameters derived from SRIM, so more accurate (though at least for the alphas not much different) than what I had before. The interaction position is randomly chosen within the target (flat probability distribution). The beam loss/straggling is calculated up to that point. From then on, only straggling of the outgoing particles is taken into account--that is, I assume we can somehow correct for the average energy loss. There is also angular straggling included, which for the ¹⁵O is fairly large. The detector is an S2 at 100 or 500 mm downstream. The beam energy at the time of the reaction is reconstructed using the measured particle energy and angle (θ).
The simulations were done for two CH₂ target thicknesses (50 and 100 μg/cm^/2) with beam energies chosen to get 6.27 MeV in the centre of the target (6.7 and 7.1 MeV respectively).
Here's a plot of how the standard deviation of the reconstructed beam energy changes with different degrading factors (click for a larger version):

What this implies is that the (corrected, particle-dependent) energy resolution of the detector is by far the dominant factor in the resolution of the final measurement, if you're using a 50 μg/cm² target. The beam straggling through the thicker target can have an additional degrading effect, but everything else gets washed out.

Revised Update: try plotting the actual beam interaction energy as a function of the sum of E_α + E_15O, for a narrow range of alpha angles (choose 19-20'). (I tried making a similar plot for 5-7' and it was virtually identical.)



Same thing, 16-18', thick target: