M.J. Owens, N.U. Crooker, N.A. Schwadron, H.E. Spence and W.J. Hughes
EMMREM Predicted Dose Rates for CRaTER N. Schwadron, L. Townsend, K. Kozarev, H. Spence, M....
-
Upload
janessa-crute -
Category
Documents
-
view
218 -
download
0
Transcript of EMMREM Predicted Dose Rates for CRaTER N. Schwadron, L. Townsend, K. Kozarev, H. Spence, M....
EMMREM Predicted Dose Rates for CRaTER
N. Schwadron, L. Townsend, K. Kozarev, H. Spence, M. Golightly et al.
Motivator ..1957
1958
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
1999
2001
2003
2005
2007
2009
3000
3250
3500
3750
4000
4250
4500
4750
5000
0
10
20
30
40
50
60
70
80
90
100
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