The Validity of the Straightahead Approximation in Space-Vehicle Shielding Studies—Part II

Alsmiller, R.G.; Irving, D.C.; Moran, H.S.

doi:10.13182/nse68-a18824

Cited by 11 publications

(9 citation statements)

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“…HZETRN utilizes the straight ahead approximation in which all fragments are assumed to propagate in the same direction as the projectile. The assumption is accurate for high energy charged particles but begins to break down for low energy neutrons which are nearly isotropic [Alsmiller et al 1965]. This is significant for heavily shielded space vehicles, surface habitats, and high altitude aircraft where secondary neutron production is important in exposure calculations [Getselev et al 2004].…”

Section: Introductionmentioning

confidence: 99%

Coupled neutron transport for HZETRN

Slaba

Blattnig

Aghara

et al. 2010

Radiation Measurements

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Section: Introductionmentioning

confidence: 99%

Coupled neutron transport for HZETRN

Slaba

Blattnig

Aghara

et al. 2010

Radiation Measurements

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“…where e G is positive provided G o completely encloses G. The most strongly scattered component is the neutron field for which an 0.2 percent error results for semi-infinite media in most practical problems [20,21]. Standard practice in space radiation protection replaces G as required at some point on the boundary and along a given ray by the corresponding G N evaluated for normal incidence on a semi-infinite slab.…”

Section: Transport Solution Methodsmentioning

confidence: 99%

“…The errors in this approximation are second order in the ratio of beam divergence and radius of curvature of the object [20], rarely exceeds a few percent for space radiations, and are always conservative. The replacement of G by G N as a highly accurate approximation [21] for space shielding applications has the added advantages that G N is the natural quantity for comparison with laboratory simulations and has the following properties: If G N is known at a plane a distance x o from the boundary (assumed at the origin), then the value of G N at…”

Section: Transport Solution Methodsmentioning

confidence: 99%

Materials for Shielding Astronauts from the Hazards of Space Radiations

et al. 1998

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One major obstacle to human space exploration is the possible limitations imposed by the adverse effects of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar energetic particle (SEP) events was of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated exposures can be high. Because cancer induction rates increase behind low to rather large thickness of aluminum shielding according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Preliminary studies indicate that materials with high hydrogen content and low atomic number constituents are most efficient in protecting the astronauts. This occurs for two reasons: the hydrogen is efficient in breaking up the heavy GCR ions into smaller less damaging fragments and the light constituents produce few secondary radiations (especially few biologically damaging neutrons). An overview of the materials related issues and their impact on human space exploration will be given.

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“…The lowest order approximation using the straightahead approximation was guided by the nucleon transport studies of Alsmiller et al (1968) using the Monte Carlo methods in which the differential cross sections were approximated as…”

Section: Straightahead Approximationmentioning

confidence: 99%

“…where the second term on the right hand side of equation (12) results from corrections in assuming the velocity of the ion is preserved in the interaction (Curtis andWilkinson, 1972, Wilson 1977) and the third term is error resulting from the straightahead assumption (Alsmiller et al 1968, Wilson 1977. The surprising result is that the velocity conserving assumption is inferior to the straightahead approximation for the nearly isotropic space radiation.…”

Section: Straightahead Approximationmentioning

confidence: 99%

Pre-engineering spaceflight validation of environmental models and the 2005 HZETRN simulation code

Nealy

Cucinotta

Wilson

et al. 2007

Advances in Space Research

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The HZETRN code has been identified by NASA for engineering design in the next phase of space exploration highlighting a return to the Moon in preparation for a Mars mission. In response, a new series of algorithms beginning with 2005 HZETRN, will be issued by correcting some prior limitations and improving control of propagated errors along with established code verification processes. Code validation processes will use new/improved low Earth orbit (LEO) environmental models with a recently improved International Space Station (ISS) shield model to validate computational models and procedures using measured data aboard ISS. These validated models will provide a basis for flight-testing the designs of future space vehicles and systems of the Constellation program in the LEO environment.

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The Validity of the Straightahead Approximation in Space-Vehicle Shielding Studies—Part II

Cited by 11 publications

References 0 publications

Coupled neutron transport for HZETRN

Coupled neutron transport for HZETRN

Materials for Shielding Astronauts from the Hazards of Space Radiations

Pre-engineering spaceflight validation of environmental models and the 2005 HZETRN simulation code

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