Lunar EVA Dosimetry: Microdosimeter-Dosimeter Instrument (PI Ziegler)

1. AIMS. Cosmic radiation is the prime limiting factor of astronaut survivability. The objective of this research is to develop a radiation monitor for an astronaut's suit, which will determine radiation in real time, with an instant warning alarm in the space helmet, and with remote telemetry in the ship for real time advanced analysis. This new monitor will use radiation detectors about the size of the most sensitive human radiation cells, and also cell components such as the nucleolus (~6 µm). This will be accomplished using new semiconductor micro-dosimeters (SMD). The goal is to evaluate in detail the use of microdosimeters for various NASA radiation applications. This project started in 1 Jan. 2009, with Dr. Vincent Pisacane as the Principal Investigator (PI), and this report concludes the final year. Objective is to advance the state-of-the-art of solid-state microdosimeters (SSMD) to design, develop, and test an engineering model by September, 2013.

Aims include: 1.1 - Develop a bench-top system to advance the state-of-the-art of Silicon micro-dosimeters (SMDs) to incorporate proven advancements into the flight engineering model. 1.2 - Use the most advanced integrated-circuit technologies to make the most sensitive SMDs possible, allowing the measurement of the lowest energy radiation with high accuracy. 1.3 – Test the new micro-dosimeters with a wide variety of ion and neutron beams to evaluate their accuracy in a complex space environment. 1.4 – Evaluate the accuracy and advantage of microdosimeters designed to replicate human cells and cell components. Compare these results with those of more standard radiation dosimeters.

2. KEY FINDINGS. 2.1 Benchtop System – Obtained and analyzed SSMD spectra for NASA Space Radiation Laboratory (NSRL) beams (protons & heavy ions) to identify particle types, energies, and mass-to-charge ratios in the beams and produced by intervening materials. Reduced instrument noise levels near a factor of 10 during our National Space Biomedical Research Institute (NSBRI) funding period. Best noise measurements at NSRL with 200 feet of cable is ~0.3 keV/micron (~0.2 keV/micron-tissue). Compared SSMD spectra from our 1st generation sensors with silicon surface barrier detectors and also obtained spectra for neutrons, the most damaging particles. 2.2 Flight Engineering Model – The instrument developed in year 1 is called MIcroDosimeter iNstrument (MIDN)-II (MIDN-II) MIDN-II. We have designed an improved version, MIDN-III, reducing size and mass with an expanded set of remote commands. Its noise cutoffs is ~1 keV/micron. Continued development of our unique optical calibration system and applied for a patent in 2010. This provides a continuous end-to-end test and confirms the calibration or recalibrates the SSMD while in operation accomplished without a problematic radiation source. 2.3 Sensor Development – Prior observations were with the 1st generation SSMD sensors. A 2nd generation SSMD sensor was produced and tests confirmed performance using the benchtop and flight engineering instruments. 3rd and 4th generation sensors are now completed and extend the sensitivity of the microdosimeters by an order of magnitude. 2.4 Flight Opportunity – Completed a conceptual design to fit a NanoRacks configuration for the International Space Station (ISS) through the auspices of the Department of Defense (DoD) Space Test Program. Our system has been approved annually for several years for inclusion on DoD space missions. We were forced to decline a flight opportunity for a potential launch due to insufficient funds.

3. IMPACTS. Silicon micro-dosimeters (SMDs) have been shown to have noise levels better than that obtained with tissue equivalent proportional counters (TEPC) in space. SMD spectra for space protons will be able to obtain very low-lineal energy detection, a major goal of this research project. This was achieved by incorporating new integrated circuit technologies, not available in any past efforts. Recent measurements of SMD spectra with intense high-energy neutrons (~14 MeV), considered to be the most damaging particles in space, show that SMD can also operate in high-dose radiation fields for long time periods without failures. This establishes the radiation resistance of our SDMs, a major goal of this project. Recent measurements with SDM systems at the NSRL facility at Brookhaven National Laboratory (BNL) establish the practicality of using our new capability of identifying particle species: i.e., energy and charge-to-mass ratio responsible for specific individual events. Such measurements provide more stringent data for establishing quality factors and the accuracy of the transport codes and theoretical calculations, a major aim of this project. Recent measurements with SMD in a plastic phantom on a Heavy Ion Medical Accelerator in Chiba (HIMAC) beamline (in Japan) demonstrated the success of MIDN-III sensors for deep space missions by showing equivalent performance to TEPC instruments. Development of an end-to-end system test and calibration of an astronaut's personal SMD without the need for an ionizing radiation source is an important achievement. The final testing of MIDN-II sensors, and the design and highly-successful early testing of the MIDN-III sensors (probably final flight qualifiable personal SMDs) are important accomplishments. Development of WiFi communication and control of remote extravehicular activity (EVA) radiation sensor systems has been demonstrated, with real-time evaluation of radiation hazards.

4.0 RESEARCH PLAN - n/a (this was the final year of research).

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