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