[Crater-team] Status of follow-up on last week's discussion [was: Re: CRaTER mtg today]

[Mark D Looper]

Hello--

	Last week I kind of hogged the telecon time based on having had about 15 minutes to look over the slides that were attached to the email below.  I figured if I was going to say anything else, I should put in more time than that thinking them over; however, I have not finished what I had hoped to send to the group within the week, as demands from other projects intervened.  Below are the calculations I am in the middle of; I attach two figures, to which I will refer briefly in (3).

1) I am in the middle of stripping the mission-long dataset into a D2/D4/D6 cube of PHA channels, so that I can slice and dice it both to replicate the plots on the attached slides and to see if this gives any additional insight into the origin of the particle-event populations under discussion.

2) You will recall that I expressed concern as to how directional the response identified as albedo MIPs would actually be.  That is, if we see a big D6 pulse height and a D4/D2 pair consistent with an upward-going proton penetrating both of them, can we be sure that the primary particle apparently striking D6 came from below?  To address this, I am preparing a simulation of a simplified lower-half of CRaTER, with D6, the TEP, and the surrounding aluminum (approximated as cylinders), so that I can illuminate this from all directions with GeV protons and see how collimated are the subset of these that result in modest-energy protons coming out the other end of the TEP within the D4/D2 acceptance cone.

3) You will also recall that we had some discussion as to how many albedo MIP protons would actually be present, given that the albedo spectrum is falling at energies above the D4/D6 doubles energy range and we already don't see any distinct population of D2/D4/D6 albedo triples at the lowest possible energies for those.  If I understood last Wednesday's discussion correctly, the assertion was that the source would be energetic fragments from He and heavier GCR nuclei that scatter in the regolith and come back out.  Also if I understood correctly, the simulations being used in this discussion do not produce many albedo protons from GCR protons, but only from GCR He and heavier, which is why the source is identified as being from such fragments.  I did not understand why GCR protons should not scatter up as well as any fragments of heavier nuclei.  Moreover, my own simulations produce albedo protons from GCR H, He, and heavies roughly in proportion to their primary intensities, i.e., 100:10:1; this and the fairly isotropic upward-going distribution of protons (and other albedo species) suggests that the source of most albedo particles in my simulations is isotropic disintegration of regolith nuclei after being struck by a GCR primary, regardless of species.  With regard to scattering, I attach energy-angle plots of all simulated albedo protons, and of the subset of these that are due to primary GCR protons that scatter back out.  Comparing the two, my simulations assert that scattering is very much focused toward shallow angles; when one looks leftward in the scattered-primaries plot, toward upward-going rather than surface-grazing albedo trajectories, the intensity and the energy fall off very rapidly.  Either I need to be shown what I am misunderstanding in the simulations being discussed in last week's slides, or we should try to understand why our results are so different.  I thought that some time ago Larry Townsend, after dissecting the Geant4 "Shielding" physics list and throwing the appropriate switches in his codes to use the same models, was able to get results similar to mine; if our results really differ as much as last week's discussion led me to believe that they do, we should figure out which set of assumptions/models is more representative of the actual processes, by comparing predicted albedo spectra with observations.  I did a preliminary (no GCRs heavier than He) version of this in the 2013 Space Weather paper, and if I ever get around to finishing the two papers that I'm trying to get out the door, I should include an update; Joe Mazur already did a comparison with whole-moon gamma and neutron observations from other spacecraft, getting pretty good agreement with the simulations.

4) Sorry, that was pretty darn long.  If (1) and (2) do not persuasively identify the particle population in question, I can slice and dice the results of my simulations of the sensor-head response to see what kind of particles (species, energy, incidence direction) are predicted to produce a signature like that being discussed in last week's slides.  I'll send out another PPTX when I get (1) and (2) done, and if necessary (4).

Let me know if we have a telecon tomorrow/today--
--Mark

Mark D. Looper
Space Sciences Department
The Aerospace Corporation
M/S M2-260
P.O. Box 92957
Los Angeles, CA 90009-2957
Mobile: 310-529-3406
Voicemail: 310-336-6302

On 7/10/19, 7:29 AM, "Crater-team on behalf of Andrew Jordan" <crater-team-bounces at lists.sr.unh.edu on behalf of ajordan at guero.sr.unh.edu> wrote:

    Hi folks,
    
    Attached are some slides I can talk about. They're about how to get 
    directional information from some minimum-ionizing protons in CRaTER.
    
    Andrew
    
    
    On 7/10/19 11:33 AM, Sonya wrote:
    > Team,  sorry about the late notice, but if anyone is available we will go ahead and have a call at 2pm today.
    >
    > Usually call in #.
    >
    > Sonya
    >
    > _______________________________________________
    > Crater-team mailing list
    > Crater-team at lists.sr.unh.edu
    > https://lists.sr.unh.edu/mailman/listinfo/crater-team
    >
    
    

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