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Helium-2 (diproton)
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accumulation 2015-4-3 14:57
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Helium-2 (diproton) Helium-2 or 2 He , also known as a diproton, is an extremely unstable isotope of helium that consists of two protons without any neutrons . According to theoretical calculations it would have been much more stable (although still beta decaying to deuterium ) had the strong force been 2% greater. Its instability is due to spin-spin interactions in the nuclear force, and the Pauli exclusion principle , which forces the two protons to have anti-aligned spins and gives the diproton a negative binding energy . There may have been observations of 2 He . In 2000, physicists first observed a new type of radioactive decay in which a nucleus emits two protons at once—perhaps a 2 He nucleus. The team led by Alfredo Galindo-Uribarri of the Oak Ridge National Laboratory announced that the discovery will help scientists understand the strong nuclear force and provide fresh insights into the creation of elements inside stars . Galindo-Uribarri and co-workers chose an isotope of neon with an energy structure that prevents it from emitting protons one at a time. This means that the two protons are ejected simultaneously. The team fired a beam of fluorine ions at a proton-rich target to produce 18 Ne , which then decayed into oxygen and two protons. Any protons ejected from the target itself were identified by their characteristic energies. There are two ways in which the two-proton emission may proceed. The neon nucleus might eject a 'diproton'—a pair of protons bound together as a 2 He nucleus—which then decays into separate protons. Alternatively, the protons may be emitted separately but at the same time—so-called 'democratic decay'. The experiment was not sensitive enough to establish which of these two processes was taking place. More evidence of 2 He was found in 2008 at the Istituto Nazionale di Fisica Nucleare , in Italy. A beam of 20 Ne ions was directed at a target of beryllium foil. This collision converted some of the heavier neon nuclei in the beam into 18 Ne nuclei. These nuclei then collided with a foil of lead. The second collision had the effect of exciting the 18 Ne nucleus into a highly unstable condition. As in the earlier experiment at Oak Ridge, the 18 Ne nucleus decayed into an 16 O nucleus, plus two protons detected exiting from the same direction. The new experiment showed that the two protons were initially ejected together, correlated in a quasibound 1 S configuration, before decaying into separate protons much less than a billionth of a second later. Further evidence comes from RIKEN in Japan and JINR in Dubna , Russia, where beams of 6 He nuclei were directed at a cryogenic hydrogen target to produce 5 He . It was discovered that the 6 He nucleus can donate all four of its neutrons to the hydrogen. The two remaining protons could be simultaneously ejected from the target as a 2 He nucleus, which quickly decayed into two protons. A similar reaction has also been observed from 8 He nuclei colliding with hydrogen. 2 He is an intermediate in the first step of the proton-proton chain reaction . The first step of the proton-proton chain reaction is a two-stage process; first, two protons fuse to form a diproton: 1 1 H + 1 1 H → 2 2 He followed by the immediate beta-plus decay of the diproton to deuterium: 2 2 He → 2 1 D + e + + ν e with the overall formula: 1 1 H + 1 1 H → 2 1 D + e + + ν e + 0.42 MeV R. A. W. Bradford has considered the hypothetical effect of this isotope on Big Bang and stellar nucleosynthesis.
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个人分类: 原子核物理|0 个评论
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Compare And Contrast: Public Vs Private Retiree Underfunding In One Chart
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insight 2013-8-17 20:57
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Compare And Contrast: Public Vs Private Retiree Underfunding In One Chart Submitted by Tyler Durden on 08/16/2013 12:05 -0400 The chart below explains, in the simplest possible terms, why there are many more "Detroits" on deck. It shows the underfunded status of public vs private retiree healthcare plans. It needs no commentary, although it may deserve one question: what happens when all those public servants who have been promised over a trillion in healthcare benefits upon retirement, realize it was all a lie? And then come... the pensions. Average: 4.875 Your rating: None Average: 4.9 ( 16 votes)
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个人分类: inequality|16 次阅读|0 个评论
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Can The Fed Ever Exit?
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insight 2012-10-7 17:15
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Can The Fed Ever Exit? Submitted by Tyler Durden on 10/06/2012 17:38 -0400 We have extensively discussed the size ( here - must read! ) and growth ( here ) of the Fed's largesse in soaking up massive amounts of the primary and second Treasury (and now MBS) markets with the ongoing theme of 'what about the exit strategy?' among other things. The onset of QEternity likely means the Fed's balance sheet will grow to over $4 trillion within the next year and, as UBS notes, although the Fed has suggested that it will not begin an exit strategy until 2015, the magnitude of the excess balance sheet argues for considering whether the Fed has the ability to unwind their balance sheet . We, like UBS, believe that the Fed will find it far more difficult to exit than they have found it to enter given the limitations of the exit tools frequently cited . There are three main tools for reducing the Fed’s balance sheet: asset sales/maturation (bad signaling), reverse repurchase agreements (size constraints), and interest on reserves (inflationary). Via UBS: Asset sales/maturation. The portfolio shift to a longer average maturity means that the Fed is unable to reduce its balance sheet only by letting securities mature . There would be no material reduction until at least 2016 and even then the reduction would likely be under $250bn. Outright sales face a different problem – expectations. Unlike purchases where announcing a certain amount of purchases reinforces the Fed’s goal of lowering rates via expectations, any sales would likely result in the market pricing in a fully normalized balance sheet . As such, an initial sale program of just $200bn would not be credible as the expectation would be that the sale announcement signals a desire to return to normality requiring an addition $2.5tn in sales at some point. Reverse repurchase agreements. This tool is swamped by the magnitude of the drain required . At present money fund assets are roughly $2.5 trillion, $200 billion less than the excess balance sheet we anticipate by the end of 2013. However, this statistic does not tell the full story as reverse repurchase agreements only make up just over 20% of money fund assets, or just $500 billion . The other primary counterparty the Fed would rely on, the Primary Dealer community, are unlikely to be able to participate in anything close to that size. While these figures do not prevent the Fed from using this tool, they do suggest it can only be a part of the overall solution. Interest on reserves. Although interest on reserves theoretically creates a floor on rates in the interbank market, it does not prevent banks from using funds to make loans. Loans eventually end up as deposits somewhere and, as such, the overall level of deposits at the Fed provide little guidance as to whether the funds are circulating in the economy. The only way to prevent lending would be for the Fed to raise this rate sufficiently to make banks prefer depositing the money at the Fed to lending to their client base . QE3 and QE4, if enacted and continued until the end of 2013, will leave the Fed with excess balance sheet of roughly $2.7 trillion. Fed Treasury holdings by coupon maturity date (2013-2042) expected at the end of Operation Twist at the end of 2012. Money fund assets have been falling and the total amount of repos done by money funds does not appear sufficient to allow the Fed to rely solely on reverse repos from this financial segment to drain liquidity. Average: 4.5 Your rating: None Average: 4.5 ( 6 votes) Tweet Login or register to post comments 6281 reads Printer-friendly version Send to friend Similar Articles You Might Enjoy: Guest Post: The War Between Credit And Resources Fed Balance Sheet Composition Update For Italy, It Is Game Theory Over Evidence QE3 is Working, and Other Lies Guest Post: The Economics Of Breaking Bad
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