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Objective: Calculate the best possible production rates for TCNs using:

Physics-Based Modeling Robert Reedy ( UNM ), Kyeong Kim (U. Ariz.), and Jozef Masarik (Komensky Univ.). Objective: Calculate the best possible production rates for TCNs using: computer codes that numerically simulate particle production and transport

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Objective: Calculate the best possible production rates for TCNs using:

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  1. Physics-Based ModelingRobert Reedy (UNM), Kyeong Kim (U. Ariz.), and Jozef Masarik(Komensky Univ.) • Objective: Calculate the best possible production rates for TCNs using: • computer codes that numerically simulate particle production and transport • Monte Carlo N Particle eXtended (MCNPX) [Reedy and Kim]; GEANT & LAHET Code System [Masarik]. • the latest measured or evaluated cross sections • Experimental ones for proton reactions; a few measurements or adjusted fits for neutrons. • 6 nuclides: 10Be, 26Al, then 14C, 36Cl, 21Ne, 3He.

  2. Numerical Simulation Codes • MCNPX, GEANT, and LCS codes • extensively developed for nuclear physics; • well tested with many benchmarks; • often used by us for extraterrestrial problems. • Some results by us for terrestrial in situ (and atmospheric) terrestrial cosmogenic nuclides • Not perfectly accurate, but represent fairly well the basic processes involved in the production and transport of primary and secondary particles • Need fine tuning for TCNs.

  3. Work on Codes • Compare codes • Neutron fluxes • Rates for making cosmogenic nuclides • Fine tune parameters in codes • Input cosmic ray spectra – deep space and for different locations on Earth • “Physics” packages in codes • Test with various measurements

  4. Code Work – Compare fluxes • Neutron fluxes using MCNPX and LCS

  5. Code Work, GCR fluxes • Test various galactic cosmic ray spectra • Castagnoli & Lal (1980), Webber & Higbie (2003), others in space and at Earth • Compare input spectra for protons only and both protons and alpha particles using latest versions of MCNPX. • Test physics parameters in the codes • Done for 2 sets by Kim & Reedy (2004) for spallogenic nuclides in meteorite – similar

  6. Code Work, Input spectra • Work by G. W. McKinney et al. (2006) for neutron densities in the Apollo 17 drill core

  7. Code Work, Physics Inputs • Work by G. W. McKinney et al. (2006) for neutron densities in the Apollo 17 drill core

  8. Input GCR energy cutoffs • 1980 vertical cosmic ray cutoff rigidity data were used to then estimate the primary galactic cosmic ray (GCR) spectrum for various geomagnetic latitudes for our MCNPX calculations. [J. Masarik]

  9. Code Work, Terr. GCR Fluxes • Need good GCR spectra for all locations

  10. Code Work, Terr. GCR Fluxes • Gordon et al. (2004) and MCNPX Calc. [Kim]

  11. Code Work, Terr. GCR Fluxes • Gordon et al. (2004) and other calculations

  12. BASICS OF CALCULATIONS OF PRODUCTION RATES • Calculate fluxes (neutrons, protons) in specified target (geometry, composition) and incident cosmic rays. • Calculate production rate at depth d using target composition (i, e.g., SiO2), calculated spectra Φ for particles (k), and cross sections σ for target-element pair (i,j; e.g., O to Be-10, Si to Al-26): • Pj(d) = i Ni k∫σjik(Ek) Φk(Ek,d) dEk

  13. Update Cross Sections • Evaluate measured cross sections for proton-induced reactions • Adjust cross sections for neutron-induced reactions • Use any measured (n,x) cross sections • Adjust using good CN measurements in extraterrestrial and terrestrial samples and artificial targets (natural & accelerators)

  14. CROSS SECTIONS FOR PRODUCTION OF 10Be & 26Al ON TARGET ELEMENTS BY PROTONS

  15. NEUTRON-INDUCEDCROSS SECTIONS • Neutrons dominate (~90-95%) TCN production. • Early work, still used (~20 yrs. ago!): • Use a few measured neutron cross sections (Ne). • Use proton cross sections (Al-26), • Adjust neutron cross sections to fit ET measurements (Be-10, C-14).

  16. Test Calculations • For now, use existing extraterrestrial and some terrestrial measurements • Use new CRONUS results • Refine codes, their inputs (physics packages, input spectra), and reaction cross sections

  17. Preliminary rates for TCNs • from quartz using LCS and [MCNPX]: • Be-10: 5.7, [5.0] • C-14: 18.7, [22.2] • Al-26: 34.3, [36.4] • Close to old rates from Masarik & Reedy [1995]: 5.97, 18.6, and 36.1

  18. Work this year • Papers presented at AMS-10 on TCNs • by Kim, Reedy, & Masarik • Papers submitted to Proc. AMS-10 • Tests using neutron fluxes and Be-10 measured for many locations in southern hemisphere by I. Graham [Kim et al.] • Calculations for the air/ground interface and effects of snow cover [Masarik et al.] (see next 2 images)

  19. Fast and thermal neutron fluxes

  20. Changes due to water (snow)

  21. Future Work • More tests with GEANT (will probably drop LCS as is incorporated in MCNPX and will not be supported. GEANT is entirely different code from LCS/MCNPX. • Fine tune codes and their inputs • Cross section work • Comparisons to improve calculations • Extraterrestrial and other existing data • Terrestrial, especially using CRONUS data

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