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  • NUCLEAR AND HIGH-ENERGY PHYSICS  (1)
  • THERMODYNAMICS AND STATISTICAL PHYSICS  (1)
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  • 1
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    Cosmic ray models for early galactic lithium, beryllium, and boron production (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: To better understand the early galactic production of Li, Be, and B by cosmic ray spallation and fusion reactions, the dependence of these production rates on cosmic ray models and model parameters is examined. The sensitivity of elemental and isotropic production to the cosmic ray pathlength magnitude and energy dependence, source spectrum spallation kinematics, and cross section uncertainties is studied. Changes in these model features, particularly those features related to confinement, are shown to alter the Be- and B-versus-Fe slopes from a naive quadratic relation. The implications of our results for the diffuse gamma-ray background are examined, and the role of chemical evolution and its relation to our results is noted. It is also noted that the unmeasured high energy behavior of alpha + alpha fusion can lead to effects as large as a factor of 2 in the resultant yields. Future data should enable Population II Li, Be, and B abundances to constrain cosmic ray models for the early Galaxy.
    Keywords: NUCLEAR AND HIGH-ENERGY PHYSICS
    Type: NASA-CR-197626 , NAS 1.26:197626 , FERMILAB-PUB-94/010-A
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Big-bang nucleosynthesis revisited (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The homogeneous big-bang nucleosynthesis yields of D, He-3, He-4, and Li-7 are computed taking into account recent measurements of the neutron mean-life as well as updates of several nuclear reaction rates which primarily affect the production of Li-7. The extraction of primordial abundances from observation and the likelihood that the primordial mass fraction of He-4, Y(sub p) is less than or equal to 0.24 are discussed. Using the primordial abundances of D + He-3 and Li-7 we limit the baryon-to-photon ratio (eta in units of 10 exp -10) 2.6 less than or equal to eta(sub 10) less than or equal to 4.3; which we use to argue that baryons contribute between 0.02 and 0.11 to the critical energy density of the universe. An upper limit to Y(sub p) of 0.24 constrains the number of light neutrinos to N(sub nu) less than or equal to 3.4, in excellent agreement with the LEP and SLC collider results. We turn this argument around to show that the collider limit of 3 neutrino species can be used to bound the primordial abundance of He-4: 0.235 less than or equal to Y(sub p) less than or equal to 0.245.
    Keywords: THERMODYNAMICS AND STATISTICAL PHYSICS
    Type: NASA-CR-186256 , NAS 1.26:186256 , FERMILAB-PUB-89/262-A , CFA-89-2985 , UMN-TH-816/89
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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