Io volcano observer (IVO) integrated approach to optimizing system design for radiation challenges

One of the major challenges for a mission to the Jovian system is the radiation tolerance of the spacecraft (S/C) and the payload. Moreover, being able to achieve science observations with high signal to noise ratios (SNR), while passing through the high flux radiation zones, requires additional ingenuity on the part of the instrument provider. Consequently, the radiation mitigation is closely intertwined with the payload, spacecraft and trajectory design, and requires a systems-level approach. This paper presents a design for the Io Volcano Observer (IVO), a Discovery mission concept that makes multiple close encounters with Io while orbiting Jupiter. The mission aims to answer key outstanding questions about Io, especially the nature of its intense active volcanism and the internal processes that drive it. The payload includes narrow-angle and wide-angle cameras (NAC and WAC), dual fluxgate magnetometers (FGM), a thermal mapper (ThM), dual ion and neutral mass spectrometers (INMS), and dual plasma ion analyzers (PIA). The radiation mitigation is implemented by drawing upon experiences from designs and studies for missions such as the Radiation Belt Storm Probes (RBSP) and Jupiter Europa Orbiter (JEO). At the core of the radiation mitigation is IVO's inclined and highly elliptical orbit, which leads to rapid passes through the most intense radiation near Io, minimizing the total ionizing dose (177 krads behind 100 mils of Aluminum with radiation design margin (RDM) of 2 after 7 encounters). The payload and the spacecraft are designed specifically to accommodate the fast flyby velocities (e.g. the spacecraft is radioisotope powered, remaining small and agile without any flexible appendages). The science instruments, which collect the majority of the high-priority data when close to Io and thus near the peak flux, also have to mitigate transient noise in their detectors. The cameras use a combination of shielding and CMOS detectors with extremely fast readout to mi- imize noise. INMS microchannel plate detectors and PIA channel electron multipliers require additional shielding. The FGM is not sensitive to noise induced by energetic particles and the ThM microbolometer detector is nearly insensitive. Detailed SNR calculations are presented. To facilitate targeting agility, all of the spacecraft components are shielded separately since this approach is more mass efficient than using a radiation vault. IVO uses proven radiation-hardened parts (rated at 100 krad behind equivalent shielding of 280 mils of Aluminum with RDM of 2) and is expected to have ample mass margin to increase shielding if needed.

[Radiation exposure in (90)Y-Zevalin therapy: results of a prospective multicentre trial]

AIM of this study was the assessment of the radiation exposure from preparation and application of (90)Y-Zevalin, the measurement of the dose rate at the patient, the exposure of family members as well as the determination of the activity concentration in urine of patients. METHODS: Overall data from 31 therapeutic administrations carried out in four institutions were evaluated. During preparation and application of (90)Y-Zevalin the finger exposures of radiochemists, technicians, and physicians were measured. The dose rate of the patient was measured immediately after radioimmunotherapy. In patients treated in a nuclear medicine therapy unit, urine was collected over a two day period and the corresponding activity was determined. Family members of outpatients were asked to wear a dosimeter over a seven day period. RESULTS: During the preparation we found a maximum skin dose of 6 mSv at the average, and during application of 3 mSv, respectively. After administration of (90)Y the dose rate was 0.4 +/- 0.1 microSv/h at 2 m distance. Urine measurements yielded a cumulated 24 h excretion of 3.9 +/- 1.4% and 4.4 +/- 1.4% within 48 h, respectively, that is equivalent to 43 +/- 18 and 50 +/- 20 MBq of (90)Y, respectively. Family members received a radiation exposure of 40 +/- 14 microSv over seven days. CONCLUSION: During preparation and application of (90)Y-Zevalin appropriate radiation shielding is necessary. For family members as well as nursing staff no additional special radiation protection measures beyond those being common for other nuclear medicine procedures are necessary.

Radiation exposure to the surgeon during fluoroscopically assisted percutaneous vertebroplasty: a prospective study

STUDY DESIGN: A prospective case control study design was conducted. OBJECTIVES: The purpose of the current study was to determine the intraoperative radiation hazard to spine surgeons by occupational radiation exposure during percutaneous vertebroplasty and possible consequences with respect to radiation protection. SUMMARY OF BACKGROUND DATA: The development of minimally invasive surgery techniques has led to an increasing number of fluoroscopically guided procedures being done percutaneously such as vertebroplasty, which is the percutaneous cement augmentation of vertebral bodies. METHODS: Three months of occupational dose data for two spine surgeons was evaluated measuring the radiation doses to the thyroid gland, the upper extremities, and the eyes during vertebroplasty. RESULTS: The annual risk of developing a fatal cancer of the thyroid is 0.0025%, which means a very small to small risk. The annual morbidity (the risk of developing a cancer including nonfatal ones) is 0.025%, which already means a small to medium risk. The dose for the eye lens was about 8% of the threshold dose to develop a radiation induced cataract (150 mSv); therefore, the risk is very low but not negligible. The doses measured for the skin are 10% of the annual effective dose limit (500 mSv) recommended by the ICRP (International Commission on Radiologic Protection); therefore, the annual risk for developing a fatal skin cancer is very low. CONCLUSION: While performing percutaneous vertebroplasty, the surgeon is exposed to a significant amount of radiation. Proper surgical technique and shielding devices to decrease potentially high morbidity are mandatory. Training in radiation protection should be an integral part of the education for all surgeons using minimally invasive radiologic-guided interventional techniques.

Martian sub-surface ionising radiation: biosignature and geology

The surface of Mars, unshielded by thick atmosphere or global magnetic field, is exposed to high levels of cosmic radiation. This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation is of prime astrobiological interest. Here, we present modelling results of the absorbed radiation dose as a function of depth through the Martian subsurface, suitable for calculation of biomarker persistence. A second major implementation of this dose accumulation rate data is in application of the optically stimulated luminescence technique for dating Martian sediments. We present calculations of the dose-depth profile in the Martian subsurface for various scenarios: variations of surface composition (dry regolith, ice, layered permafrost), solar minimum and maximum conditions, locations of different elevation (Olympus Mons, Hellas basin, datum altitude), and increasing atmospheric thickness over geological history. We also model the changing composition of the subsurface radiation field with depth compared between Martian locations with different shielding material, determine the relative dose contributions from primaries of different energies, and discuss particle deflection by the crustal magnetic fields.

Effect of Nontronite Smectite Clay on the Chemical Evolution of Several Organic Molecules under Simulated Martian Surface Ultraviolet Radiation Conditions

Most of the phyllosilicates detected at the surface of Mars today are probably remnants of ancient environments that sustained long-term bodies of liquid water at the surface or subsurface and were possibly favorable for the emergence of life. Consequently, phyllosilicates have become the main mineral target in the search for organics on Mars. But are phyllosilicates efficient at preserving organic molecules under current environmental conditions at the surface of Mars? We monitored the qualitative and quantitative evolutions of glycine, urea, and adenine in interaction with the Fe3+-smectite clay nontronite, one of the most abundant phyllosilicates present at the surface of Mars, under simulated martian surface ultraviolet light (190-400 nm), mean temperature (218 +/- 2 K), and pressure (6 +/- 1 mbar) in a laboratory simulation setup. We tested organic-rich samples that were representative of the evaporation of a small, warm pond of liquid water containing a high concentration of organics. For each molecule, we observed how the nontronite influences its quantum efficiency of photodecomposition and the nature of its solid evolution products. The results reveal a pronounced photoprotective effect of nontronite on the evolution of glycine and adenine; their efficiencies of photodecomposition were reduced by a factor of 5 when mixed at a concentration of 2.6x10(-2) mol of molecules per gram of nontronite. Moreover, when the amount of nontronite in the sample of glycine was increased by a factor of 2, the gain of photoprotection was multiplied by a factor of 5. This indicates that the photoprotection provided by the nontronite is not a purely mechanical shielding effect but is also due to stabilizing interactions. No new evolution product was firmly identified, but the results obtained with urea suggest a particular reactivity in the presence of nontronite, leading to an increase of its dissociation rate. Key Words: Martian surface-Organic chemistry-Photochemistry-Astrochemistry-Nontronite-Phyllosilicates. Astrobiology 15, 221-237.