Physics-Based Modeling Robert Reedy (UNM), Kyeong Kim (U. Ariz 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 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.

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.

Work on Codes Compare codes Fine tune parameters in 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

Code Work – Compare fluxes Neutron fluxes using MCNPX and LCS

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

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

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

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]

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

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

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

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

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)

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

NEUTRON-INDUCED CROSS 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).

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

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

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)

Fast and thermal neutron fluxes

Changes due to water (snow)

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