emmrem predicted dose rates for crater

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EMMREM Predicted Dose Rates for CRaTER N. Schwadron, L. Townsend, K. Kozarev, H. Spence, M. Golightly et al.

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EMMREM Predicted Dose Rates for CRaTER. N. Schwadron , L. Townsend, K. Kozarev , H. Spence, M. Golightly et al. . Motivator . Modulation Potential . M odulation potential , Φ = |Z e| φ(r ); barrier to penetrations of CRs - PowerPoint PPT Presentation

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Page 1: EMMREM Predicted Dose Rates for  CRaTER

EMMREM Predicted Dose Rates for CRaTER

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

Page 2: EMMREM Predicted Dose Rates for  CRaTER

Motivator ..1957

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GCR Dose Rate Modulation Near EarthMeasurements Outside Geomagnetosphere Over Four Solar

Cycles

Thu

le N

eutr

on M

onito

r M

onth

ly-A

vera

ged

Cou

nt R

ate

(c/1

00/h

)

Miss

ion-

Ave

rage

s Dos

e R

ate

(mra

d[Si

]/d)

Apo

llo 8

Apo

llo 1

1

Apo

llo 1

5A

pollo

16

Apo

llo 1

7

LRO

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

Apo

llo 1

3

average Biostack tissue dose

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

Cha

ndra

yyan

Thin detector dose ~ 35km x 200 kmThick detector dose ~35 km x 200 kmThin detector dose ~50 km circularThick detector dose ~50 km circular

Page 3: EMMREM Predicted Dose Rates for  CRaTER

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

Page 4: EMMREM Predicted Dose Rates for  CRaTER
Page 5: EMMREM Predicted Dose Rates for  CRaTER
Page 6: EMMREM Predicted Dose Rates for  CRaTER

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+01 Computed GCR LET Spectra in Detector D1CREME-96: 1987.0SPENVIS: 1982.5SPENVIS: 1987CREME-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)

Page 7: EMMREM Predicted Dose Rates for  CRaTER

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?

Page 8: EMMREM Predicted Dose Rates for  CRaTER

Revised Modulation Potential

Page 9: EMMREM Predicted Dose Rates for  CRaTER

Revised Doses using Thule Neutron Monitor Data

Page 10: EMMREM Predicted Dose Rates for  CRaTER

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

Page 11: EMMREM Predicted Dose Rates for  CRaTER

CMEs Add Closed Flux To Heliosphere

Page 12: EMMREM Predicted Dose Rates for  CRaTER

Model for CME Injection of Closed Magnetic Flux

Page 13: EMMREM Predicted Dose Rates for  CRaTER

Correlation Between Field Strenght and Modulation Potential

Page 14: EMMREM Predicted Dose Rates for  CRaTER

-- 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, JGR, 2007

Page 15: EMMREM Predicted Dose Rates for  CRaTER

-- 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

Page 16: EMMREM Predicted Dose Rates for  CRaTER

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

Page 17: EMMREM Predicted Dose Rates for  CRaTER

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

Page 18: EMMREM Predicted Dose Rates for  CRaTER

Takeaway

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