Deuterium burning

Even before the advent of Apollo samples, for example, it was noted that He/ He in the solar wind, as observed in solar-gas-rich meteorites, was of order 4 X 10 ". This is several-fold lower than it would be just from deuterium burning if primordial D/H were close to the terrestrial (seawater) value, 1.6 X 10 ". This contrast provided the first solid argument that primordial D/H must have been several-fold lower than the seawater value (Geiss and Reeves, 1972). 

Models of planetary evolution assume that at the time of planetary formation the solar system had a single universal and well-mixed composition from which aU parts of the solar system were derived (see Podosek, 1978). Information as to the elemental and isotopic characteristics of this primordial composition is presently available from the Sun, meteorites, and the atmospheres of the giant planets (Wider, 2002). In the case of the Sun, distinction is usually made between the present-day composition, which is available via spectral analysis of the solar atmosphere and capture of the solar wind, either directly in space or by using metallic foU targets, and the proto-Sun (the composition at the time of planetary accretion) whereby the lunar regolith and/or meteorites are utilized as archives of ancient solar wind. As discussed below, the distinction is only really important for helium due to production of He by deuterium burning. 

Hydrogen was the most abundant element in the solar nebula. The D/H ratio of the solar nebula has not been preserved in the Sun due to deuterium burning to He, but has been deduced from the solar He/ He and He/H ratios to be 5D = -880%o (Geiss and Gloeckler, 1998). A large range of values has been measured in meteorites due to fractionation between chemical... 

Fig. 4. Isotopic variations of hydrogen in the Solar System (adapted from Robert et al. 2000). The deuterium/ hydrogen ratio of different components is normalized to the D/H ratio of the Sun (as it was before deuterium burning), which is thought to represent H2 in the protosolar nebula. Numbers along the y-axis represent the numbers of cases. Terrestrial hydrogen is enriched in deuterium by a factor of about six relative to solar. Among Solar System objects analysed so far, carbonaceous chondrites, Antarctic micrometeorites (Engrand Maurette 1998) and chondruies from LL3 chondrites present a distribution of D/H values that centre around the terrestrial D/H ratio. Notably, comets analysed so far (Halley, Hale Bopp and Hyakutake, references given by Dauphas et al. (2000)) present D/H values about two times higher than the terrestrial value.

As contraction continues, the core continues to heat until Tc exceeds the critical value for the ignition of deuterium burning (the second reaction in the p-p I chain). Providing the star is sufficiently massive, this will be followed by the p-p reaction and/or the CNO-cycle and full hydrogen burning will be established. At this point the star has reached the zero-age main sequence (ZAMS). 

The reactions comprising the rest of the (three) pp-chains start out with the predominant product of deuterium burning 3He (manufactured from d+p... 

Fig. 1. Luminosity evolution of tracks of 0.5 M0 starting at different central temperature, labelled in the figure. At the bottom we sketch the energy liberated per gram due to the deuterium fusion with protons. The tracks of logT > 6.0 start in the middle of D-burning.

Defensive Compounds. All developmental stages of oedemerid beetles contain and produce cantharidin as a defensive substance. The total amount of the terpenoid anhydride increases in successive instars [306]. Moreover, by using deuterium-labelled cantharidin it was found that males of Oedemerafemorata transfer no or only very small amounts of cantharidin 48 to females during copulation. False blister beetles cause a severe dermatitis, i.e. blisters with burning and itching sensation a few hours after contact with oedemerid haemo-lymph [307]. 

The seemingly simple reaction between deuterium and tritium produces 1.7 X 10 J of energy for each mole of deuterium. This is about 10 times fewer joules of energy than are produced by the fission of one mole of uranium. It is still, however, 500 000 times more energy than is produced by burning one mole of coal. 

Hamuro Y., Burns L.L., Canaves J.M., Hoffman R.C., Taylor S.S., Woods V.L. Jr domain organization of D-AKAP2 revealed by enhanced deuterium exchange-mass spectrometry (DXMS). J. Mol. Biol. 

Burns-Hamuro L., Hamuro Y, Kim J., Sigala P., Fayos R., Stranz D., Jennings P., Taylor S., Woods V.L. Jr Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/ deuterium exchange. Protein Sci. 

Deuterium may be analyzed from density measurements of waters. A confirmation method recommended here is GC mass spectrometry. Deuterium is burned in oxygen (or air) to form D2O which may be separated with helium on a GC column (of intermediate polarity) and identified from its mass spectra. The mass to charge ratio of the molecular ion is 20. Additionally, deuterated products obtained by exchange reactions with hydrogen containing substances (other than those containing C—H bonds) may be separated on a capillary GC column and identified by mass spectrometry. 

Tracks followed by 1,3, and 5 M pre-main sequence stars as they evolve toward the main sequence are shown on an H-R diagram. Pre-main sequence stars shine primarily by conversion of gravitational potential energy to heat, although energy released by burning of deuterium and other elements also plays a role. 

The nuclear reaction that finally stabilizes the structure of the protostar is the fusion of two protons to form a deuterium atom, a positron, and a neutrino (1 H(p,p+v)2D). This reaction becomes important at a temperature of a few million degrees. The newly produced deuterium then bums to 3He, which in turn bums to 4He in the proton-proton chain. The proton-proton chain is the main source of nuclear energy in the Sun. With the initiation of hydrogen burning... 

Tile first iwo equations represent tlie fact that the D-D reaction can follow either of Iwo paths, producing tritium and one proton or helium-3 and one neutron, wirli equal probability. The products of the first two reactions form the fuel for the third and fourth reactions, and they are burned with additional deuterium. The net reaction consists of the conversion of six deuterium nuclei into two helium nuclei, two hydrogen nuclei, and two neutrons along with a net energy release of 43.1 MeV. The reaciion products—helium, hydrogen, and neutrons—are harmless as... 

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