# Presentation: 900014

## OVERVIEW OF SOLAR ENERGETIC PARTICLE EVENT HAZARDS TO HUMAN CREWS

- Lawrence W. Townsend
- University of Tennessee

## OUTLINE

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**OUTLINE**

**Environment**
**GCR Doses and Effects**
**Solar Particle Event Doses and Effects**
**	****- Carrington Flare as a Worst Case Event**
**Mars and Lunar Surface Doses**
**Space Radiation Transport Code Development**
**Concluding Remarks**

## ENVIRONMENT

**Space environment is complex**
**Van Allen belts important for LEO; also GCR important for high-latitudes (ISS)**
**Solar Energetic Particles (SEP) important for missions outside Earth’s magnetosphere**
**Acute and chronic exposures possible**

## ENVIRONMENT (cont.)

**Galactic Cosmic Rays (GCR) important for missions outside Earth’s magnetosphere**
**Chronic exposures are at issue (unique effects?)**
**Acute effects not possible **

## CORONAL MASS EJECTION (SOHO Image)

**CORONAL MASS EJECTION (SOHO Image)**

## Annual GCR Doses

| Al Shield
(g cm-2) | Skin  |  | Bone Marrow |  | Annual Effective Dose (cSv) |
| --- | --- | --- | --- | --- | --- |
|  | Annual Dose
(cGy)  | Annual Dose Equiv.
(cSv)  | Annual Dose
(cGy) | Annual Dose Equiv.
(cSv) 
 |  |
| 1977 Solar Minimum |  |  |  |  |  |
| 1 | 18.4 | 79.8 | 16.4 | 44.5 | 48.8 |
| 5 | 18.3 | 66.9 | 16.3 | 40.5 | 43.7 |
| 10 | 18.0 | 56.2 | 16.1 | 37.0 | 39.3 |

## DEEP SPACE GCR DOSES

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**DEEP SPACE GCR DOSES**

- Annual bone marrow GCR doses will range up to ~ 15 cGy at solar minimum (~ 40 cSv) behind ~ 2cm Al shielding
- Effective dose at solar minimum is ~ 45-50 cSv per annum
- At solar maximum these are  ~ 15-18 cSv
- Secondary neutrons and charged particles are the major sources of radiation exposure in an interplanetary spacecraft

## GCR Risks

**Clearly, annual doses < 20cGy present no acute health hazard to crews on deep space missions**
**Hence only stochastic effects such as cancer induction and mortality or late deterministic effects, such as cataracts or damage to the central nervous system are of concern.  **
**Unfortunately, there are no data for human exposures from these radiations that can be used to estimate risks to crews**
**In fact, it is not clear that the usual methods of estimating risk by calculating dose equivalent are even appropriate for these particles**

## SOLAR PARTICLE EVENT DOSES

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**SOLAR PARTICLE EVENT DOSES**

**Doses can be large in deep space but shielding is possible**
**August 1972 was largest dose event of space era (occurred between two Apollo missions)**

## SKIN DOSE AUGUST 1972 SPE(1 g/cm2 Al shielding)

## AUGUST 1972 SKIN DOSE RATE

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**AUGUST 1972 SKIN DOSE RATE**

## 	EFFECTIVE DOSE AUGUST 1972 SPE

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| Shielding | Effective Dose
(cSv) | Avg. BFO Dose Eq.
(cSv) | 
% Diff.  |
| --- | --- | --- | --- |
| 1 g/cm2 Al | 337.5 | 111.0 | 203.9% |
| 2 g/cm2 Al | 200.2 | 91.3 | 119.3% |
| 5 g/cm2 Al | 88.5 | 56.3 | 57.3% |
| 10 g/cm2 Al | 40.2 | 30.5 | 31.7% |

- 	**EFFECTIVE DOSE AUGUST 1972 SPE**

## POSSIBLE ACUTE EFFECTSAugust 1972 SPE

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**POSSIBLE ACUTE EFFECTS****August 1972 SPE**

**Bone marrow doses ~ 1 Gy delivered in a day may produce hematological responses and vomiting  (not good in a space suit)**
**Skin doses ~15-20 Gy could result in skin erythema and moist desquamation (in some cases)**
**	****- doses inside nominal spacecraft might ****	****limit effects to mild erythema**

## ORGAN DOSE LIMITS (Gy-Eq)NCRP Report 132

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**ORGAN DOSE LIMITS (Gy-Eq)****NCRP Report 132**

|  | Bone Marrow | Eye | Skin |
| --- | --- | --- | --- |
| 
Career | 
--- | 
4.0 | 
6.0 |
| 
1 y | 
0.50 | 
2.0 | 
3.0 |
| 
30 d | 
0.25 | 
1.0 | 
1.5 |

## October 1989 SEP

## SOLAR PARTICLE EVENT DOSES (cont.)

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**SOLAR PARTICLE EVENT DOSES (cont.)**

**Ice core data from the Antarctic indicate that the largest event in past ~ 500 years was probably the Carrington Flare of 1859**
**	****-****	****fluence much larger than Aug 72**
**	****-****	****actual spectrum energy ****	****dependence unavailable, assume ****	****both hard and soft****	**** spectra**

## Carrington Flare Dose Estimates

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**Carrington Flare Dose Estimates**

| Shielding
(g/cm2)  | Soft Spectrum
(8/72)  |  | Hard Spectrum
(9/89) |  |
| --- | --- | --- | --- | --- |
|  | Skin
(cGy) | BFO
(cGy) | Skin
(cGy)  | BFO
(cGy) |
| 1 | 3426 | 141 | 3539 | 281 |
| 2 | 1905 | 105 | 1801 | 244 |
| 5 | 556 | 47 | 665 | 171 |
| 10 | 123 | 15 | 282 | 109 |

## CARRINGTON FLARE DOSES(9/89 Spectrum)

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**CARRINGTON FLARE DOSES****(9/89 Spectrum)**

**Bone marrow doses ~ 1-3 Gy possible inside a spacecraft (life threatening)**
**“****Storm” shelter of about 18 cm Al needed to shield to the applicable deterministic limits (30 d limits of 0.25 Gy-Eq)**
**Major problem for non radiation hardened electronics built with COTS components**
**	****-****	****up to 50 krads  or more of total ****	****ionizing dose**

## CARRINGTON FLARE DOSES(8/72 Spectrum)

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**CARRINGTON FLARE DOSES****(8/72 Spectrum****)**

**Bone marrow doses in spacesuit up to ~1.5 Gy; much lower inside a spacecraft ( not life threatening)**
**“****Storm” shelter of about 10 g cm****-2**** Al needed to shield to the applicable deterministic limits (30 d limits of 0.25 Gy-Eq)**
**Major problem for non radiation hardened electronics built with COTS components unless they are shielded by at least 1 g cm****-2**** Al **
**	****-****	****up to 15 krads  total ionizing dose for 15mils**

## Lunar Surface

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**Lunar Surface**

- Organ Doses and Dose Equivalents are ~ half those in deep space
- 	-	2 shadow shielding provided
- 	-	Some neutron albedo from Lunar 	Surface
- Inside a habitat the exposure is nearly all due to neutrons

## Mars Surface(mainly protons and neutrons)

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**Mars Surface****(mainly protons and neutrons)**

|  | GCR Solar Minimum | GCR Solar Maximum | October 1989 SPE |
| --- | --- | --- | --- |
| Dskin | 5.7 cGy/yr | 2.7 cGy/yr | 3.2 cGy |
| Hskin | 13.2 cSv/yr | 6.7 cSv/yr | 4.8 cSv |
| DBFO | 5.5 cGy/yr | 2.6 cGy/yr | 1.7 cGy |
| HBFO | 11.9 cSv/yr | 6.1 cSv/yr | 2.7 cSv |

## Hypothesis

- 	It has been proposed that
- proton intensities on the stream-limited plateau present a minimal radiation hazard to astronauts
- hazardous intensities occur upon CME-driven shock arrival at the spacecraft

## Methodology - Data

- Used the 5 largest events, in terms of accumulated dose, from years 1996-2001(July 14, 2000; November 8, 2000; September 24, 2001; November 4, 2001; November 22, 2001)
- Differential and integral flux and fluence spectra measured on GOES-8
- Shock arrival times
- ACE list of disturbances/transients (MAG and SWEPAM instruments)
- SOHO/CELIAS solar wind data site
- Discussions with NOAA SEC researchers
- Stream Limited Intensities from Don Reames

## Dose Calculations-July 14, 2000

| Al Shield Thickness (g/cm2) | Dose to BFO @ Shock (cGy) | Total Dose to BFO (cGy) | Dose to Eye @ Shock (cGy) | Total Dose to Eye
 (cGy) | Dose to Skin @ Shock (cGy) | Total Dose to Skin (cGy) |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 34 | 35 | 400 | 434 | 563 | 617 |
| 2 | 24 | 25 | 185 | 197 | 226 | 242 |
| 3 | 18 | 18 | 107 | 112 | 123 | 130 |
| 5 | 11 | 11 | 48 | 49 | 52 | 54 |
| 7 | 7 | 7 | 26 | 26 | 27 | 28 |
| 10 | 4 | 4 | 12 | 12 | 13 | 13 |

## November 4, 2001-Dose to Eye

## September 24, 2001 – Dose to BFO

## Implications for Event-Triggered Forecasting	

- Hazardous radiation levels **do occur **prior to shock arrival for large events for shielding thicknesses on the order of 3 g/cm2 of Al
- This suggests that we should attempt to predict the temporal evolution of dose for the SEP event prior to shock arrival
- The temporal evolution of the SEP event determines the available time for making decisions

## HETC-HEDS Code Development

- HETC has been extended to include the transport of high-energy heavy ions (HZE particles) in a new version now named HETC-HEDS
- HZE particle event generator has been developed and incorporated into the code to provide nuclear interaction data
- Minor revisions to the models and techniques used in the event generator are performed as needed based upon comparisons with laboratory beam data

## HETC-HEDS Results

**  ****Fragment Fluence for 2A GeV  ****56****Fe on 10 g/cm****2**** of Polyethylene (HETC-HEDS vs. PHITS)**

## Status of FLUKA Development

- Current version has the embedded event generators DPMJET
- Four separate efforts on improvements to the event generators:
- 		- rQMD approach based on the constrained 	Hamiltonian formalism of Dirac (E. N. Zapp)
- 		- G. Xu is revisiting the original rQMD code
- 		- "after-burner" to the rQMD codes to 	reassemble the fragments (M. –V. Garzelli)
- 		- "Master Boltzmann Equation" approach 	(<100 MeV/A) (F. Cerutti)

## HZETRN Code Development

- Publicly-released version improved by incorporating better low energy treatment of interaction cross sections and better neutron transport
- Meson and muon transport being incorporated
- Green’s function techniques being developed for 3D transport

## 1 A GeV iron ion beam validation

- NSRL Test Rig

## CONCLUDING REMARKS

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**CONCLUDING REMARKS**

**GCR exposures will be a problem for Mars missions due to large effective doses**
**Organ doses received from large SPEs can be hazardous to crews of vehicles in deep space**
**	****- exposures that are survivable with    ****	****proper medical treatment on Earth ****	****may not be survivable in space**

## CONCLUDING REMARKS (cont.)

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**CONCLUDING REMARKS (cont.)**

**Aside from acute effects, a single large SPE can expose a crewmember to an effective dose that exceeds their career limit**
**Due to their relatively soft energy spectra, most SPE doses can be substantially reduced with adequate shielding (several cm**** ****Al or equivalent)**
**A worst case event similar to the assumed Carrington Flare of 1859 could be catastrophic in deep space depending on spectral hardness and available shielding**

## CONCLUDING REMARKS (cont.)

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**CONCLUDING REMARKS (cont.)**

**Results presented only for aluminum**
**Other materials with low atomic mass numbers are better ******** LH****2**** reduces GCR dose equivalent by ~ one-half**
**In situ materials on lunar or Martian surface can be used to provide shielding (similar to Al in shielding characteristics)**
**Martian atmosphere is a relatively thick shield  for operations on Mars surface **
**	****~ 16-20 g cm****-2**** CO****2**

## QUESTIONS?

## RBE VALUES FOR CONVERTING DOSE TO Gy-Eq (NCRP 132)

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**RBE VALUES FOR CONVERTING DOSE TO Gy-Eq (NCRP 132)**

| Radiation Type | RBE |
| --- | --- |
| 1-5 MeV Neutrons | 6.0 |
| 5-50 MeV Neutrons | 3.5 |
| Heavy Ions (A  4) | 2.5 |
| Protons > 2 MeV | 1.5 |

## LEO DOSES

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**LEO DOSES**

- GCR and SAA protons dominate
- About half and half at ~ 400 km altitude
- Shuttle flights (28.5-62o; 220-615 km)
- 	-	crew doses : 0.02 – 3.2 cGy
- MIR (51.6o; ~ 400 km)
- 	-	crew doses: 2.3 – 8.2 cGy
- ISS (51.6o; ~ 400 km)
- 	-	crew doses:  ~ 5 cGy (solar max)
- Rapid transits limit doses for deep space

## SPE DOSE FORECASTING

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**SPE DOSE FORECASTING**

**At present it is not possible to forecast SPE fluences/doses before they occur**
**We are developing methods to forecast dose buildup over time based on the doses measured early in an SPE – “*****Nowcast”***** (supported by NASA LWS program)**
**	****-****	****Artificial Intelligence: Sliding Time ****	****Delay ****	****	****Neural Network**
**	****-****	****Locally-Weighted Learning**
**	****-****	****Bayesian Inference**

## NOVEMBER 2001 SPE Bayesian Methodology Dose Forecast at 2 hours into event

## NOVEMBER 2001 SPE Bayesian Methodology Dose Forecast at 6 hours into event