Objective is to advance the state-of-the-art of solid-state microdosimeters (SSMD) to design, develop, and test a flight-qualifiable engineering model by Dec 2012. This 4 year project started in 1 Jan 2009 with this report concluding the 2nd year. Aims include:

1.1 Develop a benchtop system to advance the state-of-the-art of SSDM incorporating proven advancements into the flight engineering model

1.2 Develop a flight engineering model suitable as a personal SSDM

1.3 Develop improved SSDM sensors

1.4 Utilize computer modeling to support instrument development and compare with observations

1.5 Explore opportunities to transition to a flight program

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 ~0.3keV/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 MIcroDosimeter iNstrument (MIDN)-II (MIDN-II). We have designed an improved version, MIDN-III, reducing size and mass with an expanded set of remote commands that should be available by the end of 2010. MIDN-II tests showed good agreement with the benchtop system observations, radiation codes, and tissue equivalent proportional counter (TEPC) results used as references. Its noise cutoffs is ~ 1keV/micron. Continued development of our unique optical calibration system and applied for a patent in Sept 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. A 3rd generation sensor has been designed and fabricated; preliminary tests look promising with more testing to continue in year 3.

2.4 Modeling - Several versions of the Geant4 radiation code are employed to compare to our SSMD observations. Collaboration has produced detailed SSMD distributions for each particle type and energy, critical for interpreting observations, especially since individual components can be measured with the dose equivalent (DE) coincidence system. We obtain acceptable agreement between our observations and radiation transport codes. We also employ the SolidWorks tool to develop test fixtures and housings and Electronic Workbench tool to model electrical circuits.

2.5 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 declined a flight opportunity for a potential launch in 2012 due to insufficient funds and impact to the MIDN project.

3. IMPACTS

Noise measurements with the bench-top system established that SSMDs are able to be operated with noise levels as good as or better than those obtained previously by TEPCs in space. This establishes the feasibility of building space qualifiable systems with sufficiently low noise so that complete SSMD spectra for high energy protons will be able to be obtained even in the lower-lineal energy region not detected previously with space-qualified systems, a major goal of this research project. Recent measurements of SSMD spectra with high-energy neutrons (~15 MeV), considered to be the most damaging particles in space, show that SSMD can operate in high-dose radiation fields for long time periods without failures. This establishes the radiation resistance of our SSDMs, a major goal of this project. Recent measurements with SSDM systems at the NSRL facility at Brookhaven National Laboratory (BNL) establish the practicality of using our new capability of identifying particle species, energy, and charge-to-mass ratio responsible for specific individual events. These 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. Development of an end-to-end system test and calibration of a personal SSMD while operational without the need for an ionizing radiation source is a critical achievement. The development and test of the MIDN-II and the design of the MIDN-III that are early versions of a flight qualifiable personal SSMD are important accomplishments.

4.0 RESEARCH PLAN for 2011

4.1 Benchtop System - Having established the feasibility of particle identification with our SSMDs we shall:

a. build a new prototype with smaller DE detectors with lower noise characteristics to reduce the number of random events.

b. obtain data with protons and iron to investigate contributions from low-energy delta rays, typically responsible for 20-30% of the physical dose not seen by typical TEPCs.

c. compare new sensor with the previous and with silicon sensors of the same thicknesses of a few microns but with larger cross-sectional areas.

4.2 Flight Engineering Model - Complete development of our flight engineering model, MIDN-III, and carry out radiation tests at the U.S. Naval Academy (USNA) and at NSRL. The remote command capability will be expanded. Further the optical calibration technique.

4.3 Sensor Development - Carry out detailed testing of 3rd generation SSMD sensors anticipating additional improved sensors from our collaborators.

4.4 Modeling - Add to our radiation transport codes by integrating the newly available GRAS (generally recognized as safe) module into our transport code suite.

4.5 Flight Opportunity - Continue to work with the DoD Space Test Program Office to obtain a future flight opportunity.

With sufficient investment in very-large-scale integration (VLSI) technology the solid-state microdosimeter can be integrated into a cell-phone sized instrument. Since microdosimetry provides the regulatory risks from radiation exposure in real time, it can be beneficially used by first responders in emergency situations when there is uncertainty in the radiation risk. The microdosimeter can be used in nuclear power plants and other facilities with radioactive materials to provide risk due to exposure. It can also be used to detected contraband radioactive material; because of its compact size and potentially relatively low cost, it can be used in situations where large numbers of sensitive detectors are needed.

Development of Silicon on Insulator (SOI) microdosimeters has a potentially significant impact on applications to monitor the dose equivalent during proton therapy to reduce the possibility of secondary cancers generated in normal tissue by the radiation.

Development of our calibration technique that does not use an ionizing radiation source will reduce the exposure of handlers of the microdosimeter. It will also eliminate the cost of satisfying the regulations on certification of users and on the handling, shipping, and facilities.

The benchtop instrument continues to be used to develop and investigate improvements to the state-of-the-art of SSMDs. This past year the focus has been on development of improved preamplifiers. Radiation sources available at the USNA have been used to carry out the test protocols.

The benchtop system has been expanded to obtain and analyze microdosimetric spectra for incident NSRL beams of both protons and heavy ions with identification of particle types in the beam, their energies, and their mass-to-charge ratios and those produced by intervening materials.

We carried out tests of our bench-top system with a neutron beam generated in the Nucleonics Laboratory at the USNA with favorable results.

An improved version of the flight engineering model, MIDN-III, has been designed and is nearing completion. It has a reduced footprint and mass and expanded remote command capability. It will be available for test by the end of 2010.

We processed data sets obtained at the NSRL/BNL from our benchtop system, flight engineering model MIDN-II, and two Far West HAWK tissue equivalent proportional counters. Inter-comparisons of the observations agreed well and also agreed with Geant4 simulations. These spectra have been added to our past data sets to update our extensive library of microdosimetric spectra.

We continued development our unique optical calibration system for a SSMD that permits continual end-to-end system test and calibration while the instrument is operational deployed. This is an alternative to using a radiation source that is problematic in a personal dosimeter and eliminates handling and shipping restrictions and personnel and facility certifications required by international, federal, and local regulations. Our provisional patent application was superseded by a patent application in Sep 2010.

We have tested our second generation microdosimeter sensors with our bench-top and flight engineering instruments and compared our results favorably with those obtained at the University of Wollongong.

We received a sample of our third generation solid-state microdosimeter sensors in November and will begin testing at the beginning of the year.

We completed an initial conceptual design of our instrument to fit within a NanoRacks configuration for deployment on the International Space Station through the auspices of the DoD Space Test Program. The NanoRacks configuration is modeled after the design of a cubesat. Our configuration would be 10cm x 10cm x 15cm with the majority of the volume dedicated to a rechargeable battery power supply.

[Ed. note 2/29/2012: PI Vincent Pisacane retired and end date changed to 9/30/2011; James Ziegler is new PI effective 10/1/2011 and project continues through 3/31/2013, per NSBRI. See Ziegler for FY2012 and later reports]

FINDINGS: In the first 10 months we have designed and developed a preliminary working version of the flight prototype and performed initial pulser and radiation tests at the USNA. We also carried out two sets of radiation beam tests at the Brookhaven's NSRL. In June 2009 we measured NSRL proton microdosimetric spectra at 0.1 and 1 GeV/n. In October 2009 we measured NSRL iron microdosimetric spectra at 0.6 and 1 GeV/n. Analysis of these data is in progress, but our preliminary noise cutoff for energy deposition delE/delx in tissue is about 1 keV/um. We have compared our experimental results favorably with simulations of the radiation transport code GEANT4 and two Hawk tissue equivalent proportional counters (TEPCs) placed in the beam with our solid-state instruments.

The bench-top instrument uses a sensor identical to that in the flight prototype. It was used this year at both the USNA and NSRL to obtain microdosimetric spectra of protons and iron ions at energies between 0.050 - 1 GeV/n. At NSRL, with about 200 feet of cable between the beam and the experimental rooms this system had a lower limit for delE/delx energy deposition in silicon of about 0.3 keV/um (corresponding to a delE/delx in tissue of approximately 0.2 keV/um) with no upper limit. This is significantly better than that available using the HAWK TEPC system and comparable or better than those being obtained with systems under development using other TEPC detection systems; however, these values are still insufficient to obtain that portion of the microdosimetric spectra below the modal value for high-energy protons of typically 0.2 to 0.3 keV/um in tissue, with protons responsible for the majority of the physical dose and a major contributor to the dose equivalent.

High-energy protons and the low lineal-energy portion of the spectra for heavy ions account for 20-30% of the heavy ion dose. We have built and are testing a new type preamplifier. Initial noise measurements of this new design are promising. The recent spectra obtained at NSRL were added to our comprehensive data library used for comparisons with data from the flight unit, theoretical calculations, and spectra from commercial TEPCs. With previous spectra collected by Dr. Dicello over a period of 40 years with walled and wall-less TE and silicon detectors for energetic heavy ions and protons as well as x-rays down to 0.2 keV, gamma rays, pions, and muons, we have one of the most extensive microdosimetric data bases.

When collecting NSRL spectra with our two solid-state instruments, we routinely collect spectra with two Far West Hawk TEPCs to compare with the spectra we obtain in silicon. These are used along with spectra from radiation transport codes to interpret and evaluate the performance of the two solid-state instruments.

Another objective satisfied, is the development of a rechargeable battery power supply to reduce noise on the power lines, a major problem observed in a previous flight.

Since the microdosimeter is to be used to monitor astronaut health and determine future flight eligibility, remote operational calibrations and end-to-end system level tests are critical. We have conceived and developed a means, without using an ionizing radiation source, to remotely carry out recalibrations and end-to-end system level tests to assure the sensor and electronics continue to perform as anticipated. A provisional patent application has been submitted. This technique eliminates the many handling and shipping constraints imposed by regulations on ionized radiation sources.

We have obtained from our contractor at the University of Wollongong proprietary second generation silicon microdosimetric sensors of a new design and have carried out preliminary pulser, Am-241 radiation sources, and iron ions beam tests.

IMPACT: We are ahead of schedule and have not uncovered any significant limitations. We have established a delE/delx energy deposition of about 0.2 keV/um tissue-equivalent with no upper limit for our bench-top instrument.

RESEARCH for 2010: Our plan includes the following objectives:

1. Flight Breadboard

a. Finalize the design and development of a non-ionizing radiation source for in-orbit end-to-end system testing and

b. Carry out evaluation of new silicon microdosimetric sensors with both the benchtop and flight systems

c. Upgrade the MIDN flight prototype to mod2 breadboard

d. Carry out radiation beam tests at NSRL in the Summer 2010 and compare results with radiation transport codes and HAWk TEPCs

2. Bench-Top System

a. Test the newly designed preamplifier to match impedances to that of the old and new detectors to further reduce noise

b. Evaluate new silicon microdosimeter sensors,

c. Carry out radiation beam tests at NSRL in the Summer 2010 and compare results with radiation transport codes and HAWK TEPCs

d. Use experimental results to develop a protocol for obtaining regulatory risk from measured spectra

3. Built-In Remote Tester

a. Finalize design and test of in-orbit calibration and end-to-end system test

Development of SOI microdosimeters has a potentially significant impact on applications to monitor the dose equivalent during proton therapy, for instance in treating cancer, to reduce the possibility of secondary cancers generated in normal tissue by the radiation.

Development of a calibration technique that does not use an ionizing radiation source will reduce the exposure of handlers of the microdosimeter. It will also eliminate the cost of satisfying the regulations on certification of users and on the handling, shipping, and facilities.

Our project consists of the development of two instruments, a benchtop instrument and a breadboard flight instrument. The bench-top instrument is used to advance the state of the art of solid-state microdosimetry for ultimate inclusion in a flight system and consequently is not limited by power and mass and selection of components. The breadboard flight prototype is necessarily constrained by mass, power, and limited to use of components with radiation hardened analogs.

The bench-top instrument has used as its primary sensor the same sensor that has been incorporated into the present version of the flight system, although sensor and components are relatively easy to change. It has been used at both the Naval Academy and the NSRL BNL to obtain microdosimetric spectra. We have designed and developed a preliminary version of the breadboard flight prototype and have carried out preliminary pulser and radiation-source tests at the Naval Academy. We have also carried out radiation beam tests of both instruments at the NSRL at BNL) in June and October 2009. We are still processing the data and comparing our experimental results with simulations using the radiation transport code GEANT4 and with additional experimentat results obtained with two Far West HAWK tissue equivalent proportional counters that were in the same beams. The preliminary comparisons are promising. These spectra have been added to our past data sets to update our extensive library of microdosimetric spectra.

Another objective satisfied this year was the development a rechargeable battery power supply to reduce noise on the power lines. This subsystem provides a low noise ±5 volts source from a external power supply with any input voltage ±5 volts. The power supply consists of 4 batteries of which each has its own recharging circuits so that while any two are providing power either one or both of the other two batteries can be recharged. This provides flexibility when the external supply power is limited or too noisy.

Since the microdosimeter is to be used to monitor astronaut health, periodic remote operational calibration and remote operational end-to-to end system level tests are critical. To this end we have conceived and developed a means that does not use an ionizing radiation source to assure that the entire instrument continues to perform as anticipated. A provisional patent application has been submitted. This eliminates the onerous regulations imposed by international and federal regulations on the use of ionizing radiation sources.

We have begun preliminary tests of our custom proprietary Mod-2 sensors at the Naval Academy and NSRL with pulser tests, Am-241 radiation sources, and the NSRL iron ion beam.

The NASA Bioastronautics Roadmap identifies four radiation risks for space missions acute radiation risks, acute and late central nervous system risks, chronic and degenerative tissue risks, and carcinogenesis. Consequently, prevention, protection, management and treatment of radiation exposure are critical to the performance, health and survivability of humans.

Measurements at skin-equivalent and organ-equivalent depths provide the physical absorbed dose, average radiation quality, dose equivalent, gray equivalent, and their rates. To make these measurements, the instrument consists of three, proprietary solid-state sensors a skin-dose equivalent dosimeter (Hp(0.07)), deep-dose equivalent dosimeter (Hp(10)), and microdosimeter. This instrument will provide dose equivalents to assess stochastic risks and gray equivalents to assess deterministic risks. The rates will be made available to the astronaut and mission control in real time, so action can be taken to reduce exposures.

The proposed MIDN instrument will be suitable for portable application, including spacesuits, rovers and extravehicular tool boxes. MIDN will be based on the heritage of the MIDN microdosimeter launched on the MidSTAR spacecraft in March 2007.

The research project has five elements:

Work with collaborators at NASA Johnson Space Center, especially the new lunar spacesuit development, to assure compatibility;

Develop ground-based instrumentation to further the state of the art of solid-state microdosimetry;

Develop a proto-flight instrument;

Assess performance by radiation source and beam tests and by comparison with the GEANT4, MCNPX, and proprietary Zaider-developed microdosimetric radiation transport codes; and

Develop radiation sensors with improved signal-to-noise ratio.