# Presentation: 126580

## Space Radiation Dosimetry forHuman Exploration Missions...so far

- Eric Benton
- Department of Physics
- Oklahoma State University
- Stillwater, OK 74074

## Overview of Presentation

- Overview of the Space Radiation Environment
- Summary of extant dosimetric measurements of relevance to Exploration Missions
- Important areas in Space Crew Dosimetry
- Effect of Shielding
- SPE Dosimetry
- EVA Dosimetry
- Measurement of Neutrons
- Current dosimetry capabilities and their limitations with respect to Exploration Missions
- Conclusions

## Space Radiation Environmentinside Habitable Volume of Spacecraft

## Dosimetric Measurements relevant to Exploration Missions

- Dosimetry from Apollo Missions;
- Dosimetry Experiments on High Altitude (~5 g/cm2) Polar Balloons;
- Charge (Z) and Energy Spectrum measurements on various interplanetary probes, e.g. MARIE on Mars Odyssey, CRIS on ACE.

## Dosimetric Results from Apollo

## LET Spectra Measurements from Plastic Nuclear Track Detector (PNTD)

## LET Spectra Measurements from Plastic Nuclear Track Detector (PNTD)

## Apollo Dosimetry compared toLEO and Polar Balloon Dosimetry

- Apollo Dosimetry compared toLEO and Polar Balloon Dosimetry

## Summary of Exploration Dosimetry

- Dose Eq. data from TLD+Nuclear Emulsion not comparable to more recent TLD+CR-39 PNTD and TEPC Dose Eq. data.
- No LET Spectra measurements from Apollo below ~200 keV/m (CR-39 PNTD & TEPC not yet developed)
- High altitude, polar balloons (e.g. DSTB) provide cost effective way to obtain dosimetry measurements from interplanetary space.
- LEO Dosimetry results can also be extremely useful, e.g. ISS as platform for testing of new instruments
- Measurements from Space Probes tend not to be in form useful for dosimetry, e.g. dose and dose equivalent to tissue.

## Effect of Shielding

## Dose Rate in 7LiF TLD as a function of Shielding Depth on the exterior of the Mir Orbital Station

## Integral LET Flux Spectra in CR-39 PNTD measured on the Exterior of the Mir Orbital Station in 1997

- Under ~0 g/cm2 shielding

- 0.1 to 1.5 g/cm2 shielding

- Inside the Mir
- 5-40 g/cm2 shielding

## Dose & Dose Equivalent Rates as functions of Shielding Depth on the Exterior of Mir Orbital Station

## Summary of Shielding Effects

- Differences of 33% in Dose and 25% in Dose Equivalent measured throughout ISS during Expedition 2 in 2001.
- Differences in Dose measured throughout Russian Mir Orbital Station of up to 50%.

## Solar Particle Events

## Dose Rate on Mir during the 10/89 SPE

- -Dachev et al. 1996

## MARIE on 2001 Mars Odyssey

- 6-element silicon spectrometer includes 4 counters:
- A1, proton E > 20 MeV
- A2, E > 30 MeV
- B2, E > 50 MeV
- B4, E > 70 MeV (4 g cm-2 shielding above)
- Operated from March 2002 to October 2003.

- -C. Zeitlin, 2005

## MARIE Counter Data – Small SPE on May 31, 2003

- -C. Zeitlin, 2005

## MARIE Dose Measurementsfrom 5/31/2003 SPE

| Detector | A1 | A2 | B1 | B4 |
| --- | --- | --- | --- | --- |
| Shielding above detector (g/cm2) | 0.35 | 0.78 | 1.17 | 4.67 |
| Quiet time dose rate (Gy/hr) before SPE | 11.3 | 11.3 | 7.1 | 5.6 |
| Dose rate, days 151+152 (Gy/hr) | 102.1 | 39.6 | 14.2 | 7.1 |
| Proton Ethresh (MeV) | 20 | 30 | 35 | 70 |

-  A1 and A2 doses include spacecraft-induced (background) contribution.
-  GCR dose from B1 is probably most reliable.
-  All doses have  25% normalization uncertainty.

- -C. Zeitlin, 2005

## MARIE vs. GOES Oct. 2002

**10****1**

**1.0**

**10****-1**

**Particles/cm****2**** sec sr**

**10****2**

**Dose Rate (mrads/day)**

**1**

**6**

**11**

**16**

**21**

**26**

**31**

**GOES 8**

**MARIE**

**10****1**

**10****2**

**10****3**

**10****4**

**Sun**

**Mars**

**Earth**

**October 15,  2002**

**(146 degrees)**

**Sun**

**Mars**

**Earth**

**October 1,  2002**

**(153 degrees)**

**Sun**

**Mars**

**Earth**

**October 31,  2002**

**(137 degrees)**

- -C. Zeitlin, 2005

## Summary of SPE Dosimetry

- SPE dosimetry in LEO is of little use in extrapolating SPE doses outside the magnetosphere.
- Some SPE dose results from MARIE on Mars Odyssey, still being processed for other SPEs.
- Detectors on GOES, Mars Odyssey, etc., generally don’t go to high enough energy. Should be at least 200 MeV (GOES is only up to 100 MeV).

## EVA Dosimetry

## EVA Dosimetry

- Measured with Pille portable TLD System,
- -S. Deme, KFKI AERI, Budapest, 2005

## Summary of EVA Dosimetry

- Only data if from Hungarian Pille portable TLD system (absorbed dose) on Mir & ISS.
- 3 to 12x increase in dose rate seen outside vs. inside spacecraft during EVA.
- EVA doses primarily from electrons encountered at high latitudes. EVAs were not performed during passes through the SAA.

## Neutron Energy Spectra on Mir & ISS

## Neutron Dosimetry

- Bonner Ball Neutron Detector (BBND) on STS-89 (Jan. 1998): 4.4 Sv/hr average, 8.1 Sv/hr from GCR.
- BBND experiment on ISS Expedition 2 (2001):
- 1st location: 3.5 Sv/hr average, 2.5 Sv/hr from GCR;
- 2nd location: 4.5 Sv/hr average, 3.3 Sv/hr from GCR;
- at 1st location, estimate that 26.6% of total Dose Eq. from neutrons, based on comparison with CR-39/TLD measurements.
- Measurements in Nuclear Emulsion on several 28.5STS missions found neutrons made a 15% to 60% contribution to total Dose Equivalent.

- -BBND data: Koshiishi, 2004
- -Emulsion data: Dudkin, 2001

## Current NASA Dosimetry Instrumentation

- Crew Passive Dosimeter (CPD) & Radiation Area Monitor (RAM):
- TLD – absorbed dose (primarily low-LET);
- CR-39 PNTD – LET spectra, Dose, Dose eq. 10 keV/m;
- TLD & CR-39 PNTD combined to yield total Dose and Dose Eq.
- Tissue Equivalent Proportional Counter (TEPC):
- Time resolved lineal energy (y) spectra from 1 to 1250 keV/m;
- Dose & Dose Eq. in real time.
- Charged Particle Directional Spectrometer (CPDS):
- Multi-element Si telescope (similar to MARIE);
- Insenstive to high LET or Z > 10.

## Slide 28

## Other Current Dosimetry Instrumentation

- R-16 Dosimeter (SRSS):
- 2 ionization chambers, 1 bare & 1 covered with 3 g/cm2;
- Dose and Dose Rate in real time.
- Si Spectrometers & Telescopes:
- DOSTEL (Kiel U. & DLR);
- Alteino/Altea (INFN & Rome U.);
- RRMD-III (Waseda U. & JAXA);
- Liulin-4 & -5 (STILBAS).
- Bonner Ball Neutron Detector (JAXA)
- Pille Portable TLD System (KFKI AERI)

## ICCHIBANInterComparison of Cosmic Rays with Heavy Ion Beams at NIRS

- C, O

- Ne, Si

- Ar, Fe

## Differential LET/y Spectra from Active Detectors(ICCHIBAN-3 at HIMAC, Feb. 2003)

## Some Concluding Remarks

- Dearth of Dosimetry Measurements made outside Earth’s Magnetosphere. Need to identify what we need for predicting/planning Exploration Missions.
- Difficult to Interpret Measurements from Spectrometers on Space Probes in terms of Tissue Dose and Dose Equivalent.
- No Single Detector/Dosimeter is likely to provide all the required data.
- Imperative that we heed the Lessons Learned from past experience in designing the next generation of instruments.

## Acknowledgements

- Cary Zeitlin of Lawrence Berkeley National Laboratory for MARIE data;
- Sandor Deme of KFKI Atomic Energy Research Institute for EVA data;
- Eddie Semones and Dazhaung Zhou of the Space Radiation Analysis Group, NASA JSC for the STS-114 LET spectra;
- H. Koshiishi of JAXA for the BBND data from ISS Expedition 2.
- Tsvetan Dachev of STILBAS for the 10/89 SPE measurements on Mir.