EMMREM Predicted Dose Rates for CRaTER

N. Schwadron, L. Townsend, K. Kozarev, H. Spence, M. Golightly et al.

Motivator ..1957

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3000

3250

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4750

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0

10

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GCR Dose Rate Modulation Near EarthMeasurements Outside Geomagnetosphere Over Four Solar

Cycles

Th

ule

Neu

tron

Mon

itor

Mon

thly

-Ave

rage

d C

oun

t R

ate

(c/1

00/h

)

Mis

sion

-Ave

rage

s D

ose

Rat

e (m

rad

[Si]

/d)

Ap

oll

o 8

Ap

oll

o 1

1

Ap

oll

o 1

5A

po

llo

16

Ap

oll

o 1

7

LR

O

average crew skin dose average VABD skin dose average VABD depth dose

Ap

oll

o 1

3

average Biostack tissue dose

mean CRaTER dosimeter IP doseaverage Chandrayyan/RADOM IP doseaverage Chandrayyan/RADOM100 km circular orbit dose

Ch

an

dra

yy

anThin detector dose ~ 35km x 200 km

Thick detector dose ~35 km x 200 kmThin detector dose ~50 km circularThick detector dose ~50 km circular

Modulation Potential

• Modulation potential, Φ = |Z e|φ(r); barrier to penetrations of CRs• Integral in (1) extends from the inner boundary at radius r to the outer

modulation boundary Rb,

• Solar wind speed is V (x) and 1(x) is related to the radial diffusion coefficient,

• based on fit to observed spectrum over time and species [O’Neil and Badhwar, 2006]: = 1(r) P β where P is the rigidity in GV, β is the particle speed over the speed of light, 1(r) 1 + (r/r0)2 and r0 = 4 AU

• Reductions in modulation potential are caused by enhanced diffusion, allowing greater access and therefore higher fluxes of GCRs in the inner heliosphere

Predictions for LRO CRaTER

0.1 1 10 100 1000 100001E-09

1E-08

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E+01Computed GCR LET Spectra in Detector D1

CREME-96: 1987.0

SPENVIS: 1982.5

SPENVIS: 1987

CREME-96: 1982.5

LETSi (keV/μm)

J (#

/s-s

r-cm

2-(k

eV/μ

m))

CREME-96 GCR Flux Model and Particle TransportZ = 1 to 26No SPE contributionEmin = 0.1 MeV/nuc, LETmin = 0.466 keV/μmFlux transported through D1 endcap (0.8128 mm Al)GF = 29.97 cm2-sr (D1 coincidence)

SPENVIS GCR Flux Model and Particle TransportLinear Energy Transfer spectrum (CREME-86)Target material stopping power: Sil (CREME) GCR model: MSU model (ISO-15390)Z = 1 to 26Flux transported through D1 endcap (0.8 mm Al)GF = 29.97 cm2-sr (D1 coincidence)

Revisions to Original Predictions

• The extended solar minimum shows lowest field strengths through space age; but why isn’t the modulation potential at a minimum?– Base modulation potential on ACE and Thule

Neutrons ..• Characterize modulation potential in terms of field

strength (extensions back to Maunder Minimum and before)

• Is there an effect of the shrinking heliopshere in the extended solar minimum?

Revised Modulation Potential

Revised Doses using Thule Neutron Monitor Data

Modulation Potential

• Modulation potential, Φ, should scale with some power of the field strength or radial field strength

• Motivated by recent work on the Closed flux ejected by CMEs over the solar cycle

CMEs Add Closed Flux To Heliosphere

Model for CME Injection of Closed Magnetic Flux

Correlation Between Field Strenght and Modulation Potential

-- Annual 10Be data (1428–1930) averaged with binomial filter; the other data are annual averages. -- Line Cnm(LIS) estimated pseudo-Climax counting rate in the absence of any solar modulation -- Heavy lines indicate the levels of “residual modulation” during the four Gleissberg maxima. -- Arrows between 1533 and 1686 are at 22-year intervals -- Removed Effects of long-term change in geo dipole, and prod. of 10Be by solar cosmic rays

McCracken and Beer, JG

R, 2007

-- Estimated annual average heliospheric magnetic field strength near Earth, 1428–2005-- heavy lines are estimates of the heliomagnetic floor values for the several Gleissberg cycles

McCracken, JGR, 2007

Derived from Cosmic Ray Record

Modulation Potential Paleo Record

• Field strengths reduced by 5-10 from historical record

• Implications modulation potentials of 6-20 (as opposed to 400 currently)

• Need to run much smaller modulation potentials to know how bad the environment can get

Is there an Effect of the Shrinking Heliosphere?

• Reduction in modulation potential more than adequately accounted for by changes in field strength

• The effect of a reduction in size of heliosphere remains elusive

Takeaway

• We have a story to tell with dose rate comparison– But we are missing the comparison part