Helium primordial

Helium is the second most abundant element in the universe (76% H, 23% He) as a result of its synthesis from hydrogen (p. 9) but, being too light to be retained by the earth s gravitational field, all primordial helium has been lost and terrestrial helium, like argon, is the result of radioactive decay ( He from a-decay of heavier elements, " °Ar from electron capture by... 

Abstract. New results of the Primordial Helium abundance (Yp) measurement by radio recombination line (RRL) observations from five galactic HII regions are presented. The RRL observations were carried out with two telescopes RT32 (22.4 and 8.3 GHz, Medicina, Italy) and RT22 (36.5 and 22.4 GHz, Pushchino, Russia). The results of the first run of the low frequency RRL observations (408 MHz) with the Croce del Nord radiotelescope (Medicina Observatory, Italy) are also presented. 

Apart from improved calculations of the primordial helium abundance by Alpher, Follin and Herman (1953) and in a prescient paper by Hoyle and Tayler (1964). 

The final outcome of these reactions, as a function of rj or equivalently Slboh2, is shown in Fig. 4.3. The primordial helium mass fraction TP, shown on a large scale, is not very sensitive to r), since this parameter only affects the time for neutron decay before nucleosynthesis sets in, and it can be fitted by the relation FP = 0.226 + 0.025log 0 + 0.0075(g - 10.75) + 0.014(r1/2( ) - 10.3 min). 

Table 4.3. Estimates of primordial helium mass fraction...

The two error terms refer to Yp and the regression slope respectively. In contrast to some earlier work, based on less homogeneous data sets and apparently affected by underlying absorption lines, notably in I Zw 18, this result, together with a similar one by Peimbert, Luridiana and Peimbert (2007), gives a primordial helium abundance in excellent agreement with the one predicted theoretically on the basis of the microwave background fluctuations and the lower estimates of deuterium abundance (see Fig. 4.3), a comparatively small value of about 2 for AT/AZ and no... 

Although Peebles had himself recently completed a calculation of primordial element synthesis including helium (Peebles 1966). 

Estimates of primordial helium and deuterium abundance with Big Bang nucleosynthesis theory limit number of light neutrino families to 4 or less (Schramm et al). 

Zindler A, Hart S (1986) Helium Problematical primordial signals. Earth Planet Sci I tt 79 1-8... 

Alpha (a) particles Helium nuclei (2 He). A common by-product of the radioactive decay of primordial radionuclides. 

Primordial nucleosynthesis really puts the Big Bang cosmology to the test. One might call it a baptism of fire. From these brief but brilliant and fertile beginnings arose a series of light nuclei that are today found everywhere in nature above all hydrogen, followed by helium, which between them amount to 98% of the total mass of atomic matter in the Universe. 

The crucial species in primordial nucleosynthesis of the light elements is helium. There are two reasons ... 

Fig. A1.3. Comparison between observed abundances and abundances predicted by the theory of primordial nucleosynthesis. The horizontal axis shows the ratio r between the number of baryons and the number of photons. The vertical axis shows the mass fraction of helium and the numerical ratios D/H, He/H and li/H. Observational data are represented by boxes with height equal to the error bar. In the case of helium and lithium, there are two boxes, indicating the divergence between different observers. Deuterium holds the key to the mystery, but it is difficult to measure. The region of agreement is shown as a shaded vertical ribbon (after Buries Tytler 1997). A higher level of deuterium would lead to a lower baryonic density, of the order of 2%. This would agree better with the lithium data, which have been remarkably finely established. This idea is supported by E. Vangioni-Flam and shared by myself. (From Tytler 1997.)...

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