1,130 research outputs found
Can the Equivalent Sphere Model Approximate Organ Doses in Space Radiation Environments?
In space radiation calculations it is often useful to calculate the dose or dose equivalent in blood-forming organs (BFO). the skin or the eye. It has been customary to use a 5cm equivalent sphere to approximate the BFO dose. However previous studies have shown that a 5cm sphere gives conservative dose values for BFO. In this study we use a deterministic radiation transport with the Computerized Anatomical Man model to investigate whether the equivalent sphere model can approximate organ doses in space radiation environments. We find that for galactic cosmic rays environments the equivalent sphere model with an organ-specific constant radius parameter works well for the BFO dose equivalent and marginally well for the BFO dose and the dose equivalent of the eye or the skin. For solar particle events the radius parameters for the organ dose equivalent increase with the shielding thickness, and the model works marginally for BFO but is unacceptable for the eye or the skin The ranges of the radius parameters are also shown and the BFO radius parameters are found to be significantly larger than 5 cm in all eases
Nuclear Fragmentation Processes Relevant for Human Space Radiation Protection
Space radiation from cosmic ray particles is one of the main challenges for human space explorations such-as a moon base or a trip to Mars. Models have been developed in order to predict the radiation exposure to astronauts and to evaluate the effectiveness of different shielding materials, and a key ingredient in these models is the physics of nuclear fragmentations. We have developed a semi-analytical method to determine which partial cross sections of nuclear fragmentations most affect the radiation dose behind shielding materials due to exposure to galactic cosmic rays. The cross sections thus determined will require more theoretical and/or experimental studies in order for us to better predict, reduce and mitigate the radiation exposure in human space explorations
Can the Equivalent Sphere Model Approximate Organ Doses in Space?
For space radiation protection it is often useful to calculate dose or dose,equivalent in blood forming organs (BFO). It has been customary to use a 5cm equivalent sphere to. simulate the BFO dose. However, many previous studies have concluded that a 5cm sphere gives very different dose values from the exact BFO values. One study [1] . concludes that a 9 cm sphere is a reasonable approximation for BFO'doses in solar particle event environments. In this study we use a deterministic radiation transport [2] to investigate the reason behind these observations and to extend earlier studies. We take different space radiation environments, including seven galactic cosmic ray environments and six large solar particle events, and calculate the dose and dose equivalent in the skin, eyes and BFO using their thickness distribution functions from the CAM (Computerized Anatomical Man) model [3] The organ doses have been evaluated with a water or aluminum shielding of an areal density from 0 to 20 g/sq cm. We then compare with results from the equivalent sphere model and determine in which cases and at what radius parameters the equivalent sphere model is a reasonable approximation. Furthermore, we address why the equivalent sphere model is not a good approximation in some cases. For solar particle events, we find that the radius parameters for the organ dose equivalent increase significantly with the shielding thickness, and the model works marginally for BFO but is unacceptable for the eye or the skin. For galactic cosmic rays environments, the equivalent sphere model with an organ-specific constant radius parameter works well for the BFO dose equivalent, marginally well for the BFO dose and the dose equivalent of the eye or the skin, but is unacceptable for the dose of the eye or the skin. The ranges of the radius parameters are also being investigated, and the BFO radius parameters are found to be significantly, larger than 5 cm in all cases, consistent with the conclusion of an earlier study [I]. The radius parameters for the dose equivalent in GCR environments are approximately between 10 and I I cm for the BFO, 3.7 to 4.8 cm for the eye, and 3.5 to 5.6 cm for the skin; while the radius parameters are between 10 and 13 cm for the BFO dose
Determination of Important Nuclear Fragmentation Processes for Human Space Radiation Protection
We present a semi-analytical method to determine which partial cross sections of nuclear fragmentations most affect the shielded dose equivalent due to exposure to galactic cosmic rays. The cross sections thus determined will require more theoretical and/or experimental studies in order for us to better predict, reduce and mitigate the radiation exposure in human space explorations
Deuteron production and elliptic flow in relativistic heavy ion collisions
The hadronic transport model \textsc{art} is extended to include the
production and annihilation of deuterons via the reactions , where and stand for baryons and mesons, respectively, as well as
their elastic scattering with mesons and baryons in the hadronic matter. This
new hadronic transport model is then used to study the transverse momentum
spectrum and elliptic flow of deuterons in relativistic heavy ion collisions,
with the initial hadron distributions after hadronization of produced
quark-gluon plasma taken from a blast wave model. The results are compared with
those measured by the PHENIX and STAR Collaborations for Au+Au collisions at
GeV, and also with those obtained from the coalescence
model based on freeze-out nucleons in the transport model.Comment: 9 pages, 10 figures, REVTeX, version to be published in Phys. Rev.
Multiplicity, average transverse momentum and azimuthal anisotropy in U+U collisions at = 200 GeV using AMPT model
Using a multi-phase transport (AMPT) model that includes the implementation
of deformed Uranium nuclei, we have studied the centrality dependence of the
charged particle multiplicity, , eccentricity (e2), triangularity (e3),
their fluctuations, elliptic flow (v2) and triangular flow (v3) for different
configurations of U+U collisions at midrapidity for \sqrt(s_NN)=200 GeV. The
results are compared to the corresponding observations from Au+Au collisions.
We find that for the U+U collisions the dNch/d\eta at midrapidity is enhanced
by about 15-40% depending on the collision and model configuration chosen,
compared to Au+Au collisions. The tip-to-tip collisions leads to the largest
values of Nch,transverse energy (ET) and . The and its fluctuation
shows a rich centrality dependence, whereas not much variations are observed
for and its fluctuations. The U+U side-on-side collision configuration
provides maximum values of and minimum values of eccentricity
fluctuations, whereas for peripheral collisions and mid-central collisions
minimum values of and maximum value of eccentricity fluctuations are
observed for body-to-body configuration and the tip-to-tip configuration has
minimum value of and maximum value of eccentricity fluctuations for
central collisions. The calculated v2 closely correlates with the eccentricity
in the model. It is smallest for the body-to-body configuration in peripheral
and mid-central collisions while it is minimum for tip-to-tip configuration in
central collisions. For peripheral collisions the v2 in U+U can be about 40%
larger than in Au+Au whereas for central collisions it can be a factor 2 higher
depending on the collision configuration. It is also observed that the v3(pT)
is higher for tip-to-tip and body-to-body configurations compared to other
systems for the collision centrality studied.Comment: 10 pages and 29 figures. Accepted for publication in Physical Review
Quark Coalescence with Quark Number Conservation and the Effect on Quark-Hadron Scaling
We develop a new formulation of the quark coalescence model by including the
quark number conservation in order to describe the hadronization of the bulk of
the quark-gluon plasma. The scalings between hadron and quark phase space
distributions are shown to depend on the transverse momentum. For hard quarks,
our general scalings reproduce the usual quadratic scaling relation for mesons
and the cubic scaling relation for baryons. For softer quarks, however, the
inclusion of the quark number conservation leads to a linear scaling for the
hadron species that dominates the quark number of each flavor, while the
scalings of non-dominant hadrons depend on the coalescence dynamics. For charm
mesons, we find that the distribution of soft mesons does not depend on the
light quark distribution but the distribution of soft mesons is
inversely correlated to the light quark distribution.Comment: Added 6 more equations to explain the derivations; added discussions;
final published versio
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