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PubMed1994

Overview of the space environmental effects observed on the retrieved Long Duration Exposure Facility (LDEF).

The Long Duration Exposure Facility (LDEF), which encompassed 57 experiments with more than 10,000 test specimens, spent 69 months in low Earth orbit (LEO) before it was retrieved by the Space Shuttle in January 1990. Hundreds of LDEF investigators, after studying for over two years these retrieved test specimens and the onboard recorded data and systems hardware, have generated a unique first-hand view of the long term synergistic effects that the LEO environment can have on spacecraft. These studies have also contributed significantly toward more accurate models of the LEO radiation, meteoroid, manmade debris and atomic oxygen environments. This paper provides an overview of some of the many LDEF observations and the implications these can have on future spacecraft such as Space Station Freedom.

Aluminum↗
PubMed1994

Comparison of model predictions with LDEF satellite radiation measurements.

Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.

Cosmic Radiation↗
PubMed1994

Anatomical models for space radiation applications: an overview.

Extremely detailed computerized anatomical male (CAM) and female (CAF) models that have been developed for use in space radiation analyses are discussed and reviewed. Recognizing that the level of detail may currently be inadequate for certain radiological applications, one of the purposes of this paper is to elicit specific model improvements or requirements from the scientific user-community. Methods and rationale are presented which describe the approach used in the Space Shuttle program to extrapolate dosimetry measurements (skin doses) to realistic astronaut body organ doses. Several mission scenarios are presented which demonstrate the utility of the anatomical models for obtaining specific body organ exposure estimates and can be used for establishing cancer morbidity and mortality risk assessments. These exposure estimates are based on the trapped Van Allen belt and galactic cosmic radiation environment models and data from the major historical solar particle events.

Computer Simulation↗
PubMed1994

Angular distributions of energetic charged particles observed with HELIOS-1 and -2 between 0.3 amd 1 AU and their relevance to manned interplanetary space missions.

The University of Kiel Cosmic Ray Instrument on board the solar probes HELIOS-1 and -2 measured angular distributions of electrons, protons, and heavier nuclei between 0.3 and 1 AU over one complete solar cycle between 1974 and 1986. Anisotropies are observed mainly during the rising phase of solar particle events or close to the passage of certain interplanetary shocks. The anisotropies are presented as proton data of energies between 27 and 37 MeV. The dependence of the anisotropies on particle energy and distance from the sun is provided based on diffusive propagation in interplanetary space. Strong anisotropies could provide a chance of efficient shielding of the passenger compartment by moving heavier parts of the spacecraft structure into the direction of the highest flux. A reduction of the total radiation dose by less than a factor of 2 might be achievable, however, selection of quiet times for the mission reduces the radiation hazard much more.

Anisotropy↗
PubMed1994

Dosimetric investigations on Mars-96 mission.

The dosimetric experiments Dose-M and Liulin as part of the more complex French-German-Bulgarian-Russian experiments for the investigation of the radiation environment for Mars-96 mission are described. The experiments will be realized with dosemeter-radiometer instruments, measuring absorbed dose in semiconductor detectors and the particle flux. Two detectors will be mounted on board the Mars-96 orbiter. Another detector will be on the guiderope of the Mars-96 Aerostate station. The scientific aims of Dose-M and Liulin experiments are: Analysis of the absorbed dose and the flux on the path and around Mars behind different shielding. Study of the shielding characteristics of the Martian atmosphere from galactic and solar cosmic rays including solar proton events. Together with the French gamma-spectrometer and the German neutron detectors the investigation of the radiation environment on the surface of Mars and in the atmosphere up to 4000 m altitude will be conducted.

Cosmic Radiation↗
PubMed1994

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.

Aluminum↗
PubMed1994

Inactivation of individual Bacillus subtilis spores in dependence on their distance to single cosmic heavy ions.

For radiobiological experiments in space, designed to investigate biological effects of the heavy ions of the cosmic radiation field, a mandatory requirement is the possibility to spatially correlate the observed biological response of individual test organisms to the passage of single heavy ions. Among several undertakings towards this goal, the BIOSTACK experiments in the Apollo missions achieved the highest precision and therefore the most detailed information on this question. Spores of Bacillus subtilis as a highly radiation resistant and microscopically small test organism yielded these quantitative results. This paper will focus on experimental and procedural details, which must be included for an interpretation and a discussion of these findings in comparison to control experiments with accelerated heavy ions.

Bacillus subtilis↗
PubMed1995

Dosimetric results on EURECA.

Detector packages were exposed on the European Retrievable Carrier (EURECA) as part of the Biostack experiment inside the Exobiology and Radiation Assembly (ERA) and at several locations around EURECA. The packages consist of different plastic nuclear track detectors, nuclear emulsions and thermoluminescence dosimeters (TLDs). Evaluation of these detectors yields data on absorbed dose and particle and linear energy transfer (LET) spectra. Behind a shielding thickness in front of the detectors of 0.09g cm-2 the doses range between 21.26 Gy and 0.87 Gy depending on the location of the dosimeter. Not all measurement can be explained by calculations.

Cosmic Radiation↗
PubMed1996

LET spectra of trapped anomalous cosmic rays in low-Earth orbit.

Observations aboard Cosmos satellites discovered trapped anomalous cosmic rays (ACRs), tracked the variation in their intensity in 1986-1988, and measured their fluence, spectrum, and composition at solar minimum in the previous solar cycle. The MAST instrument aboard the SAMPEX satellite has observed trapped anomalous cosmic rays in the present solar cycle, confirmed the general features of the Cosmos data, and provided the first detailed observations of trapped ACRs. In this paper we apply theoretical modeling of trapped ACRs, which is shown to provide a reasonably good description of both the Cosmos and SAMPEX data, to calculate the integral linear-energy-transfer (LET) spectra due to trapped ACRs in typical low-Earth orbits. We compare these calculations with the LET spectra produced by galactic cosmic rays (GCRs) and non-trapped ACRs in order to assess the relative radiation hazard posed by trapped ACRs.

Cosmic Radiation↗
PubMed1993

Radiation risk to patients from percutaneous transluminal coronary angioplasty.

OBJECTIVES: This retrospective study sought to estimate patient radiation exposure during percutaneous transluminal coronary angioplasty, the corresponding organ doses and the resulting cancer mortality risk. Patient demographic data were also examined. BACKGROUND: Coronary angioplasty is commonly used as an intervention for coronary atherosclerosis, and repeated application in the same patient is now common. The combined use of fluoroscopy and cineradiography in this complicated, delicate and, hence, lengthy procedure induced us to investigate the patient radiation exposures and resulting risks. METHODS: All complete records for angioplasty procedures performed over a 3-year period were entered into a data base. The data comprised 1,893 procedures performed in a total of 1,503 patients, of whom 21% had two or more procedures in the 3-year period. Fluoroscopy time was converted to entrance exposures, assuming a rate of 520 muC kg-1 min-1 (2.0 R min-1). Cineradiographic film lengths were determined for a smaller number of procedures (200) and converted to exposures at 7.7 muC kg-1 frame-1 (30 mR frame-1). In addition, fluoroscopy and cineradiographic times and, hence, exposures for 91 diagnostic angiograms performed in these patients were obtained. Exposures were converted to organ doses using the Monte Carlo results of the Rosenstein group and then to cancer mortality risks using the latest rates of the International Commission on Radiological Protection. RESULTS: The mean age was 56.0 years; men constituted 77.5% of the patients. Radiation doses varied considerably owing to a large spread in exposure times (e.g., fluoroscopy time per angioplasty case averaged 19 min but for some cases exceeded 1 h). The average patient skin entrance exposure per angioplasty procedure was 32.0 mC kg-1 (124 R), of which 69.7% was from cineradiography. The resulting cancer mortality risk per angioplasty procedure is approximately 8 x 10(-4). CONCLUSIONS: The skin exposures estimated for angioplasty are on average higher than for other X-ray procedures. The cancer mortality risk does not exceed the mortality risk of bypass surgery. Good professional practice requires maximization of the benefit/risk ratio through quality assurance in all aspects of the procedure.

Adult↗
PubMed1994

Radiation exposure from cervical spine radiographs.

Radiation exposure to hospital personnel during 41 cervical spine radiographs of 30 multiply injured patients was prospectively evaluated. A digital dosimeter was attached to the exposed torso of personnel applying upper extremity traction or managing the airway. Radiation exposure was measured during each radiograph. Any exposure of one or more milliroentgen was detectable. No radiograph resulted in a measurable radiation exposure. Multiple radiographs (up to five exposures) also did not register even the minimum recordable exposure, demonstrating that exposure is less than 1.0 mR per radiograph (P < .05). We conclude that hospital personnel, even those applying traction or managing the airway, are not at risk of significant radiation exposure at the time of cervical spine radiographs.

Cervical Vertebrae↗
PubMed1992

Radionuclide monitoring in environmental water body using an in situ gamma probe.

An HPGe gamma probe designed to monitor radioactive nuclides in environmental water in situ is described. The probe is equipped with a 15% HPGe detector and an associated spectrum analyzer. Laboratory tests were performed to evaluate its operating depth, detecting sensitivity, detecting volume and the detection limits of radionuclides. A field operation was conducted to measure in situ radionuclide concentrations in a nuclear reactor pool, and the feasibility as well as the disadvantages of this rapid survey are discussed.

Environmental Monitoring↗
PubMed1988

Procedures for radioactive I-131.

Details of the radioactive I-131 administration and radiation safety considerations are presented. Topics covered include patient survey, radioactive labelling, levels in patients containing radioactivity, hospital discharge of radioactive patients, and nursing procedures.

Brachytherapy↗
PubMed1995

A study of the radiation environment on board the Space Shuttle flight STS-57.

A joint NASA-Russian study of the radiation environment inside a SPACEHAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5 degrees inclination and 462 km altitude. The locker carried a charged particle spectrometer, a tissue equivalent proportional counter (TEPC), and two area passive detectors consisting of combined NASA plastic nuclear track detectors (PNTDs) and thermoluminescent detectors (TLDs), and Russian nuclear emulsions, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil technique. The results show good agreement between the integral LET spectrum of the combined galactic and trapped particles using the tissue equivalent proportional counter and track detectors between about 15 keV/micrometers and 200 keV/micrometers. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading. The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal processing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent calculations. The results of the analysis of the spectrometer data will be reported separately.

Cosmic Radiation↗
PubMed1990

Differential neutron energy spectra measured on spacecraft in low Earth orbit.

Two methods for measuring neutrons in the range from thermal energies to dozens of MeV were used. In the first method, alpha-particles emitted from the 6Li(n,alpha)T reaction are detected with the help of plastic nuclear track detectors, yielding results on thermal and resonance neutrons. Also, fission foils are used to detect fast neutrons. In the second method, fast neutrons are recorded by nuclear photographic emulsions (NPE). The results of measurements on board various satellites are presented. The neutron flux density does not appear to correlate clearly with orbital parameters. Up to 50% of neutrons are due to albedo neutrons from the atmosphere while the fluxes inside the satellites are 15-20% higher than those on the outside. Estimates show that the neutron contribution to the total equivalent radiation dose reaches 20-30%.

Cosmic Radiation↗
PubMed1990

Linear energy transfer (LET) spectra of cosmic radiation in low Earth orbit.

Integral linear energy transfer (LET) spectra of cosmic radiation (CR) particles were measured on five Cosmos series spacecraft in low Earth orbit (LEO). Particular emphasis is placed on results of the Cosmos 1887 biosatellite which carried a set of joint U.S.S.R.-U.S.A. radiation experiments involving passive detectors that included thermoluminescent detectors (TLDs), plastic nuclear track detectors (PNTDs), fission foils, nuclear photo-emulsions, etc. which were located both inside and outside the spacecraft. Measured LET spectra are compared with those theoretically calculated. Results show that there is some dependence of LET spectra on orbital parameters. The results are used to estimate the CR quality factor (QF) for the Cosmos 1887 mission.

Cosmic Radiation↗
PubMed1992

Radiation shielding estimates for manned Mars space flight.

In the analysis of the required radiation shielding protection of spacecraft during a Mars flight, specific effects of solar activity (SA) on the intensity of galactic and solar cosmic rays were taken into consideration. Three spaceflight periods were considered: (1) maximum SA; (2) minimum SA; and (3) intermediate SA, when intensities of both galactic and solar cosmic rays are moderately high. Scenarios of spaceflights utilizing liquid-propellant rocket engines, low- and intermediate-thrust nuclear electrojet engines, and nuclear rocket engines, all of which have been designed in the Soviet Union, are reviewed. Calculations were performed on the basis of a set of standards for radiation protection approved by the U.S.S.R. State Committee for Standards. It was found that the lowest estimated mass of a Mars spacecraft, including the radiation shielding mass, obtained using a combination of a liquid propellant engine with low and intermediate thrust nuclear electrojet engines, would be 500-550 metric tons.

Cosmic Radiation↗