Neutron Measurements for Radiation Protection in Low Earth Orbit - History and Future

The neutron environment inside spacecraft has been of interest from a scientific and radiation protection perspective since early in the history of manned spaceflight. With 1:.1e exception of a few missions which carried plutonium-fueled radioisotope thermoelectric generators, all of the neutrons inside the spacecraft are secondary radiations resulting from interactions of high-energy charged particles with nuclei in the Earth's atmosphere, spacecraft structural materials, and the astronaut's own bodies. Although of great interest, definitive measurements of the spacecraft neutron field have been difficult due to the wide particle energy range and the limited available volume and power for traditional techniques involving Bonner spheres. A multitude of measurements, however, have been made of the neutron environment inside spacecraft. The majority of measurements were made using passive techniques including metal activation fo ils, fission foils, nuclear photoemulsions, plastic track detectors, and thermoluminescent detectors. Active measurements have utilized proton recoil spectrometers (stilbene), Bonner Spheres eRe proportional counter based), and LiI(Eu)phoswich scintillation detectors. For the International Space Station (ISS), only the plastic track! thermoluminescent detectors are used with any regularity. A monitoring program utilizing a set of active Bonner spheres was carried out in the ISS Lab module from March - December 200l. These measurements provide a very limited look at the crew neutron exposure, both in time coverage and neutron energy coverage. A review of the currently published data from past flights will be made and compared with the more recent results from the ISS. Future measurement efforts using currently available techniques and those in development will be also discussed

The characteristics of railway service disruption: implications for disruption management

Rail disruption management is central to operational continuity and customer satisfaction. Disruption is not a unitary phenomenon - it varies by time, cause, location and complexity of coordination. Effective, user-centred technology for rail disruption must reflect this variety. A repertory grid study was conducted to elicit disruption characteristics. Construct elicitation with a group of experts (n=7) captured 26 characteristics relevant to rail disruption. A larger group of operational staff (n=28) rated 10 types of rail incident against the 26 characteristics. The results revealed distinctions such as business impact and public perception, and the importance of management of the disruption over initial detection. There were clear differences between those events that stop the traffic, as opposed to those that only slow the traffic. The results also demonstrate the utility of repertory grid for capturing the characteristics of complex work domains

Cross-sectional associations between variations in ankle shape by statistical shape modeling, injury history, and race : the Johnston County Osteoarthritis Project

Rheumatology Research Foundation Medical Student Preceptorship Award (Lateef/Nelson), NIAMS K23 AR061406 (Nelson); NIH/NIAMS P60AR064166 and U01DP003206 (Jordan/Renner), NIH/NIAMS R01AR067743 (Golightly). The funders had no role in study design; collection, analysis, or interpretation of data; writing the manuscript or the decision to submit for publication.Peer reviewedPublisher PD

Osteoarthritis and injury in the knee and hip

Context: Osteoarthritis (OA) is one of the most common causes of disability in the United States, but effective interventions for this disease are limited. Difficulty with defining OA, including the lack of sensitive measures of incident OA, hinders the development of successful treatments. Biomarkers of cartilage turnover and inflammation may be important, sensitive indicators of OA, but biomarker levels may be influenced by joint injury. Additionally, previous efforts to examine injury as a risk factor for OA, either with cross-sectional or longitudinal study designs, have resulted in a wide range of estimates. Understanding the association between injury and OA and exploring new, sensitive measures of OA have important clinical implications for patients who have sustained joint injuries, for those seeking treatment for OA, and for identifying participants for clinical trials of OA. Objectives: This research was conducted in a large, community based sample to: 1) determine whether the biomarkers of cartilage oligomeric matrix protein (COMP), hyaluronan (HA), high-sensitivity C-reactive protein (hsCRP), and keratan sulfate (KS) predict incident radiographic OA at the knee and whether their associations vary by lower extremity injury history, 2) examine the hazard of incident OA of the knee and hip by history of injury, and 3) compare prevalence and hazard estimates from cross-sectional and longitudinal designs. Methods: A longitudinal community-based cohort completed baseline (1991-1997) clinical evaluation and identical follow-up assessment (1999-2003; median follow-up time = 5.6 years, range=3.0-13.1 years) for OA. The OA outcomes examined for Objectives 1 were: radiographic OA (Kellgren-Lawrence [K-L] grade of 2 or greater), osteophyte (OST) formation, and joint space narrowing (JSN), and for Objectives 2 and 3 were: radiographic OA (based on K-L grade), chronic joint symptoms, radiographic OA or symptoms, and radiographic OA with symptoms. History of knee injury or hip injury was based on self-report. Baseline serum COMP, HA, hsCRP, and KS were measured for 803 participants. The study groups with injury data comprised 1,570 participants with linked baseline and follow-up knee radiographs and 1,446 participants with linked hip radiographs. Among participants with biomarker data, linked baseline and follow-up radiographs were available for 542 knees at risk for incident OA, 349 knees at risk for incident osteophyte (OST) formation, and 440 knees at risk for incident joint space narrowing (JSN). For biomarker analyses, Cox regression models were used to estimate the hazard ratio (HR) for a 1-unit increase in the natural log of each biomarker, adjusting for age, race, gender, and body mass index and exploring history of lower extremity injury and chronic knee symptoms as potential modifiers. For injury and OA analyses, Cox regression models were used to determine the hazard of incident knee and hip OA outcomes and logistic regression models were use to estimate the prevalence of knee and hip OA outcomes. Results: The hazard of incident knee OA and incident knee OST increased with higher baseline lnCOMP levels, and the hazard of incident knee JSN also increased with higher lnCOMP levels and higher lnHA levels. Higher levels of lnhsCRP and lnKS did not predict the incident knee outcomes. Neither history of lower extremity injury nor chronic knee symptoms was a strong modifier of these associations. The hazard of incident knee radiographic OA and OA or symptoms was higher among participants with knee injury at baseline compared to those without injury. Injury to the knee was associated with incident ipsilateral and contralateral radiographic knee OA. Hip injury also predicted a higher hazard of hip radiographic OA outcomes, although precision was lower for the hip analyses due to small numbers of outcomes. HR and odds ratio (OR) patterns were similar for some knee injury-OA associations, but the OR estimates tended to be higher than the HR estimates. The pattern of HRs and ORs is less clear for the hip due to low numbers for the longitudinal analysis. Conclusions: Higher baseline lnCOMP and lnHA levels predicted incident knee OA, OST, and JSN, but history of lower extremity injury did not modify the association. The hazard of incident radiographic knee and hip OA was higher in those with a history of injury compared to those without injury. Knee injury predicted an increased hazard of incident radiographic knee OA in the ipsilateral joint and the contralateral joint. Estimates calculated from a cross-sectional analysis may provide a fair approximation of the incidence of radiographic knee OA by knee injury status, but further research over a longer follow-up period, particularly for the hip, is needed to help clarify these comparisons

Parameterizations of the linear energy transfer spectrum for the CRaTER instrument during the LRO mission

[1] The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument was launched as part of the Lunar Reconnaissance Orbiter (LRO) spacecraft in June 2009. Its purpose is to measure the linear energy transfer (LET) spectrum in lunar orbit as an aid in determining risks to human crews on future lunar missions. Part of the preparations for the mission involved estimating the LET spectrum for the anticipated environment that the instrument is likely to see during the 1 year operational phase of the LRO mission. Detailed estimates of LET spectra in the six silicon detectors and two tissue equivalent plastic segments were made using the beta version of the HETC-HEDS Monte Carlo transport code. Tables of LET in each detector component, for incident particle elemental species from hydrogen through iron, were carried out at incident particle energies from 20 MeV per nucleon to 3 GeV per nucleon. The LET values in these tables have been parameterized by elemental species and energy for ease in quickly and accurately estimating the LET response for any input solar or galactic cosmic ray spectrum likely to be encountered during the lifetime of the instrument. The parameterized LET values are in excellent agreement with the HETC-HEDS calculations. Typical differences are on the order of a few percent. These parameterizations will also be useful in validation studies of the Earth-Moon-Mars Radiation Environment Module using CRaTER measurements in lunar orbit

The radiation environment near the lunar surface: CRaTER observations and Geant4 simulations

[1] At the start of the Lunar Reconnaissance Orbiter mission in 2009, its Cosmic Ray Telescope for the Effects of Radiation instrument measured the radiation environment near the Moon during the recent deep solar minimum, when galactic cosmic rays (GCRs) were at the highest level observed during the space age. We present observations that show the combined effects of GCR primaries, secondary particles (“albedo”) created by the interaction of GCRs with the lunar surface, and the interactions of these particles in the shielding material overlying the silicon solid-state detectors of the Cosmic Ray Telescope for the Effects of Radiation. We use Geant4 to model the energy and angular distribution of the albedo particles, and to model the response of the sensor to the various particle species reaching the 50 kilometer altitude of the Lunar Reconnaissance Orbiter. Using simulations to gain insight into the observations, we are able to present preliminary energy-deposit spectra for evaluation of the radiation environment\u27s effects on other sensitive materials, whether biological or electronic, that would be exposed to a similar near-lunar environment

New measurements of total ionizing dose in the lunar environment

[1] We report new measurements of solar minimum ionizing radiation dose at the Moon onboard the Lunar Reconnaissance Orbiter (LRO) from June 2009 through May 2010. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument on LRO houses a compact and highly precise microdosimeter whose design allows measurements of dose rates below 1 micro-Rad per second in silicon achieved with minimal resources (20 g, ∼250 milliwatts, and ∼3 bits/second). We envision the use of such a small yet accurate dosimeter in many future spaceflight applications where volume, mass, and power are highly constrained. As this was the first operation of the microdosimeter in a space environment, the goal of this study is to verify its response by using simultaneous measurements of the galactic cosmic ray ionizing environment at LRO, at L1, and with other concurrent dosimeter measurements and model predictions. The microdosimeter measured the same short timescale modulations in the galactic cosmic rays as the other independent measurements, thus verifying its response to a known source of minimum-ionizing particles. The total dose for the LRO mission over the first 333 days was only 12.2 Rads behind ∼130 mils of aluminum because of the delayed rise of solar activity in solar cycle 24 and the corresponding lack of intense solar energetic particle events. The dose rate in a 50 km lunar orbit was about 30 percent lower than the interplanetary rate, as one would expect from lunar obstruction of the visible sky

Earth‐Moon‐Mars Radiation Environment Module framework

[1] We are preparing to return humans to the Moon and setting the stage for exploration to Mars and beyond. However, it is unclear if long missions outside of low-Earth orbit can be accomplished with acceptable risk. The central objective of a new modeling project, the Earth-Moon-Mars Radiation Exposure Module (EMMREM), is to develop and validate a numerical module for characterizing time-dependent radiation exposure in the Earth-Moon-Mars and interplanetary space environments. EMMREM is being designed for broad use by researchers to predict radiation exposure by integrating over almost any incident particle distribution from interplanetary space. We detail here the overall structure of the EMMREM module and study the dose histories of the 2003 Halloween storm event and a June 2004 event. We show both the event histories measured at 1 AU and the evolution of these events at observer locations beyond 1 AU. The results are compared to observations at Ulysses. The model allows us to predict how the radiation environment evolves with radial distance from the Sun. The model comparison also suggests areas in which our understanding of the physics of particle propagation and energization needs to be improved to better forecast the radiation environment. Thus, we introduce the suite of EMMREM tools, which will be used to improve risk assessment models so that future human exploration missions can be adequately planned for

GCR access to the Moon as measured by the CRaTER instrument on LRO

[1] Recent modeling efforts have yielded varying and conflicting results regarding the possibility that Earth\u27s magnetosphere is able to shield energetic particles of \u3e10 MeV at lunar distances. This population of particles consists of galactic cosmic rays as well as energetic particles that are accelerated by solar flares and coronal mass ejections. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) onboard the Lunar Reconnaissance Orbiter is in orbit about the Moon and is thus able to directly test these modeling results. Over the course of a month, CRaTER samples the upstream solar wind as well as various regions of Earth\u27s magnetotail. CRaTER data from multiple lunations demonstrate that Earth\u27s magnetosphere at lunar distances produces no measurable influence on energetic particle flux, even at the lowest energies (\u3e14 MeV protons) where any effect should be maximized. For particles with energies of 14–30 MeV, we calculate an upper limit (determined by counting statistics) on the amount of shielding caused by the magnetosphere of 1.7%. The high energy channel (\u3e500 MeV) provides an upper limit of 3.2%