Space Radiation Dosimetry: Lessons Learned and Recommendations Eric Benton Eril Research, Inc. and Oklahoma State University, Dept. of Physics Slide 2 Primary Objectives of Operational Space Radiation Dosimetry • Accurately monitor astronaut radiation exposures – Operate mission so as to not exceed radiation limits – Implement ALARA Principle • Provide warning of dangerous changes in radiation environment • Document and provide an archival record of each astronaut’s radiation exposure history – Inform astronauts of their risks – Provide evidence that career radiation limits have not been exceeded – Provide data for ongoing and futrue epidemiological assessments of space flight radiation risks • Provide important secondary information related to the interpretation of instrument readings and experimental results. -Adapted from Radiation Dosimetry Working Group Final Report slide 3 What is Needed • Specifications for dosimeters and instruments, building on Radiation Dosimetry Working Final Report. • Also must cover “Exploration” dosimetry requirements. • Suggestion: Make specifications more concrete – SRAG could issue a set of specifications following a mil- spec model, i.e. spell out exactly what is needed what form it should take. Slide 4 Radiation Dosimetry Working Group requirements (partial) Operational Requirements for Internal and External Area Dosimeters 1. Measure the point quantities D, the spectrum D(L), and H to adjacent tissue from radiation environment experienced at surface of astronauts inside a vehicle/module or EMU a. Expected radiation environment i. Protons: ~10 MeV – 10’s of GeV ii. Electrons: ~ 0.5 MeV – 7 MeV iii. HZE (He to Fe): ~ 10 MeV/amu – 10’s of GeV/amu iv. 1n0: Thermal (<0.1 MeV) to 10’s of GeV b. Equivalent depth in tissue i. TBD c. Sensitivity i. Minimum Detectable Dose: 0.1 mGy ii. Maximum dose to be measured: 0.4 Gy iii. Spectrum coverage of D(L): TBD d. Measurement accuracy in H2O or tissue i. D: TBD ii. Spectrum coverage of fluence(L): TBD iii. H: TBD Slide 5 Current Current Instrumentation Passive Detectors • TLD/OSLD (various laboratories including JSC) • CR-39 PNTD (various laboratories including JSC) – TLD/OSLD + CR-39 PNTD make up current CPDs and RAMs • Pille TLD System (KFKI, two systems on ISS) Active Detectors • Tissue Equivalent Proportional Counter (JSC) • IV/EV Charged Particle Directional Spectrometer (JSC) • DOSimetry TELescope (Kiel U./DLR) • Bonner Ball Neutron Detector (JAXA) • RMD-III (Waseda U./JAXA) • Liulin-4/-5 (STIL-BAS) • Altea/Alteino (IFN/Rome U.) • R-16 (IMBP) • DB-8 (IMBP) slide 6 Lessons Learned from Previous Experience, ICCHIBAN, MARIE, etc. • No single instrument (detector) is capable of measuring all the radiation types, energies, and quantities of relevance to the dosimetry of space crews. e.g. – TLD/OSLD or CR-39 PNTD alone aren’t enought... must be used together. – TLD + CR-39 PNTD are good solution for Crew Personal Dosimeter • A single TEPC, Si telescope, or set of TLDs is not adequate for dosimetry inside spacecraft (especially if it is large and of complex geometry) due to differences in shielding throughout the habitable volume of the spacecraft. Slide 7 Lessons Learned Concerning Shielding • The shielding environment inside the habitable volume of a spacecraft is highly variable and extremely dependent on the localized 3-D mass distribution. • Given the differences in localized shielding within a large spacecraft and the current levels of uncertainty in shielding models, radiation transport models, and radiation environment models, multiple measurements by different instruments at various locations should be part of the overall dosimetry strategy. • At least one passive dosimeter should be co-located with each real-time active detector so that results from the different detector types can be reconciled with one another post-mission • Passive detectors add a layer of redundancy and remain operational in the event of a power failure or active detector malfunction. slide 8 The TEPC/CPDS Experience • Both TEPC and CPDS were designed “covertly” by Gautam Badhwar. • “Covert” design has its pluses and minuses. • Minuses: – Design didn’t benefit from input from qualified individuals on the outside. – Documentation regarding the development of these instruments is murky at best. – Routine operation of the instruments has been a constant challenge. – There were a number of design flaws • Major Plus: Without this effort, SRAG currently might not have any active detector. • MegaMinus: These stressful efforts likely hastened the early death of Dr. Badhwar. Slide 9 More Lessons Learned 1. There has to be a better way to design detectors than Badhwar’s “covert” method. Slide 10 The TEPC/CPDS Experience (cont.) • TEPC isn’t (and never was) the do-all perfect instrument to solve all space dosimetry problems. • Parts of TEPC are really great and shouldn’t be abandoned – the TE ion chamber and FET preamplifier is a robust, sound design. The chamber has never leaked. – The TEPC spectrometer is, at best, obsolete. • IV/EV CPDS was probably an overly ambitious and complicated design that tried to do too much with too little resources...and has required heroic efforts to make use of the data. • Budget Constraints meant that no Non-Flight Engineering Units for ground-based testing were ever built. • Neither instrument was really tested at a heavy ion accelerator until the advent ICCHIBAN (2002), Slide 11 Liulin and DOSTEL compared to CPDS • On paper, CPDS is by far the superior instrument: – Position Sensitive Detectors; – Larger Dynamic Range; – Cerenkov Detector. • DOSTEL and Liulin are much more modest detectors...and they work as advertised: – COTS parts; – Simple data format; – fairly inexpensive; – no “heroic” efforts are needed for data analysis. Slide 12 Still More Lessons Learned 1. There has to be a better way to design detectors than Badhwar’s “covert” method. 2. Just because an instrument has problems, don't throw out the whole thing (i.e. design a new spectrometer for TEPC). Slide 13 Still Even More Lessons Learned 1. There has to be a better way to design detectors than Badhwar’s “covert” method. 2. Just because an instrument has problems, don't throw out the whole thing (i.e. design a new spectrometer for TEPC). 3. Make sure the instrument design is realistic, practical, doable, cost effective, etc. rather than trying to do everything (e.g. DOSTEL works, CPDS...well). Slide 14 Etc. 1. There has to be a better way to design detectors than Badhwar’s “covert” method. 2. Just because an instrument has problems, don't throw out the whole thing (i.e. design a new spectrometer for TEPC). 3. Make sure the instrument design is realistic practical, doable, cost effective, etc. rather than trying to do everything (e.g. DOSTEL works, CPDS...well). 4. Include at least one engineering unit for use in ground-testing, troubleshooting, etc. in the program. Slide 15 The Need for Engineering Units High-fidelity flight quality (but not flight-qualified) “engineering unit” versions of each detector should be built. The use of non-flight-qualified engineering units would enable: • Calibration and characterization of the detectors at ground-based accelerator facilities such as NSRL, HIMAC, and Loma Linda; • Platforms on which to reproduce failures in the flight units; • Platforms on which to test modifications (implemented in software) prior to their implementation in flight units; • Environmental testing including radiation hardness. Slide 16 Etc., Etc. 1. There has to be a better way to design detectors than Badhwar’s “covert” method. 2. Just because an instrument has problems, don't throw out the whole thing (i.e. design a new spectrometer for TEPC). 3. Make sure the instrument design is realistic, practical, doable, cost effective, etc. rather than trying to do everything (e.g. DOSTEL works, CPDS...well). 4. Include at least one engineering unit for use in ground-testing, troubleshooting, etc. in the program. 5. Perform extensive ground-based calibration and testing (participate in ICCHIBAN, get your own beam time). Slide 17 DOSTEL ADCDOSTEL during ICCHIBAN-3 diagram and graphs of the DOSTEL during ICCHIBAN-3.Inputs of Trig. SC (Trigger Logic), DSSD (NIM Amp.), DOSTEL (NIM Amp.) - CAMAC Controller Slide 18 Quick ICCHIBAN Update • ICCHIBAN-3/-4 Report nearly finished. • Currently writing two part paper for Radiation Measurements: Part 1-active IC-1/-3, Part 2-passive IC-2/-4. • Next ICCHIBAN will be Space ICCHIBAN for passive detectors: – Up to 12 participating laboratories; – Inside Russian BRADOS container; – Scheduled for launch in December 2006. • Next ground-based ICCHIBAN will probably be in late 2007 at HIMAC or Loma Linda Slide 19 What We Have Done Right • WRMISS • ICCHIBAN • Lots of cooperation in space experiments: STS-114, Matroshka, Expedition-2, BRADOS, etc. • This Meeting!!! Slide 20 What We Have Done Right • WRMISS • ICCHIBAN • Lots of cooperation in space experiments: STS-114, Matroshka, Expedition-2, BRADOS, etc. • This Meeting!!! • No single laboratory (research group or NASA center) possesses the expertise in all the problems inherent in space dosimetry. • Design and implementation of the next generation of space radiation dosimetry system needs to be a collaborative effort making use of the diverse skills of different groups. Slide 21 Space Dosimetry: The Next Generation While this presentation is primarily focused on solving the dosimetry needs within the habitable volume of spacecraft such as: – ISS, – Space Shuttle, and – Crew Exploration Vehicle (CEV), The individual detectors and instrument bus could be designed in such a way that it could be used on – exterior of spacecraft, – satellites, – space probes, and – landers. Slide 22 Space Dosimetry: The Next Generation 1. Tissue Equivalent Proportional Counter: redesign the spectrometer. 2. Silicon Telescope: make use of existing designs (DOSTEL, Alteino/Altea, RRMD-III, etc.). 3. Active Neutron Detector (sensitive to 1 MeV=En=500MeV): BBND only good up to ~15 MeV, possibilities include phoswich detectors, scintillation fiber detectors, larger Bonner spheres. 4. CR-39 PNTD (in both crew and area dosimeters) For long duration exploration missions (permanent Lunar base, trip to Mars), CR-39 PNTD will no longer be adequate for use in CrewPassive Dosimeter. 5. Portable TLD or OSLD system for both crew and area dosimetry (necessary for Exploration Class missions). 6. Portable Si dosimeters (e.g. Liulin-4) for area dosimetry, SPE alarm, and EVA dosimetry. slide 23 Common Data Format/Bus for Active Detectors • Active detectors would share a common “radiation dosimetry server:” – store data from all the instruments; – host telemetry with the ground; – carry out limited analysis of the measured data. • Active detectors would all use a common ADC and bus, common data structures, format and compression. • Spectrometer front-ends to each detector would share as much as possible in common so that parts could be interchangeable. • Instruments would implement most parameters (e.g. gains, offsets, sampling times, trigger thresholds, etc.) in software so that they could easily (and systematically) be changed. • A common instrument bus will permit addition of new detectors or easy replacement of detectors with improved versions. Slide 24 SpaceWire http://www.spacewire.esa.int/tech/spacewire/overview diagram of Instrument to transmitter flow. I/O Module, high capacity memory module, data compression module telemetry formatter/encryption module, control processor module, dedicated processor modules and Routing Matrix are in diagram Slide 25 Image and block diagram of Space Cube by Shimafuji Electric, Inc. Slide 26 Recommendations • Make the most of the Lessons Learned; • Make the most of the Existing Instrumentation...from all laboratories (e.g. Pille, Liulin); • Carefully consider what is needed, what is practical, what is affordable, what is doable...then issue specifications or requirements; • Consider common data format, common hardware, client/server model, etc. for active detectors; Slide 27 Motherhood & Apple Pie • A redefined relationship between SRAG & the rest of the radiation community. • Create an open, transparent process for defining & procuring SRAG’s tools. – Competition is good. • Need clarity in AO/NRA. – An open call can bring in new groups with helpful expertise. • Also o.k. if not competed, provided the team has the needed expertise. • We want to help, in whatever form that takes. Slide 28 diagram of two dinosaurs saying "All I'm saying is now is the time to develop the technology to deflect an asteroid."