In systems binary stars consisting of a neutron star and a less evolved companion, material rich in hydrogen and helium can be transferred to the surface of the neutron star. There is compressed and heated to extremely high temperatures that facilitate the thermonuclear runaway.
(The runaway is driven by the energy released in nuclear reactions triple-alpha and other nuclear reactions that "explode" from the so-called hot carbon cycle nitrogen-oxygen (CNO) [more information here].) Explosions are known as ] X-ray bursts type I, and throwing a large X-ray flux that are detected as a strong increase in X-ray luminosity, followed by a decay slower.
Most of the energy of the explosion from a series of nuclear reactions that occur after what is called the process of rapid proton capture (or, rp process): The protons are fused with nuclei seed in rapid succession, synthesizing isotopes in a zig-zag path proton fusion and decays inverse beta near the drip line of the protons, are the limits of nuclear existence beyond which the nucleus simply can not wrap to another proton. At the end of the explosion, the nuclei are on track to break and a population of nuclei to the line of stability. Rp process and increases the abundance of specific elements in the ashes of the surface of the neutron star, or even determine some of the observational properties of x-ray bursts, such as size and shape of the luminosity profile time. As the brightness can be linked to the mass of the neutron star, understanding nuclear reactions that contribute to the x-ray bursts is fundamental [see here and here ]. There is another reason to study the rp process: If the material synthesized during a burst of x-ray escape the gravitational field of the neutron star and is flung into the interstellar medium, could potentially be a source of specific chemicals in the galaxy, whose origins are difficult to explain. Examples include a series of proton-rich stable nuclei, such as molybdenum -92 or ruthenium 96.
Efforts to simulate the path of nucleosynthesis in the rp process and understand the production of these isotopes depend heavily on nuclear data, such as the masses, "the half-life , and catch rates of several unstable nuclei. The mass, or more specifically the proton separation energy (the energy required to remove a proton from a nucleus) plays a particularly decisivo.En present uncertainty in the experimentally determined masses of many unstable nuclei are significant ( In contrast, the theoretical predictions for the masses of stable nuclei are very good). However, the improvement of measures for the fences nuclei of proton drip lines, the most important for the rp process is difficult. The simulations of the production of zigzag paths are changed according to the assumed mass (energy separation), the predicted final abundance varies by an order of magnitude between the estimates.
at the top of the image shows an artist's illustration of an accreting neutron star in a binary system, proton-rich isotopes are produced in highly unstable bursts of x rays through a process called rp.Estos subsequently unstable isotopes decay into more stable isotopes could be the source of some rare isotopes earth. on the bottom of the image shows a possible rp process in the region of the nuclear chart where the group conducted its SHIPTRAP mediciones.El balance (between the proton radiative capture (p, γ) where the energy is released and the photodissociation (γ, p) where the energy is absorbed and emitted a proton creates and destroys the Technetium-87 respectively) is highly sensitive to nuclear mass measurements SHIPTRAP involucrada.Las new mass of Technetium-87 and in particular molibdeno86 show that photodissociation is relatively strong enough to prevent the flow of the reaction up and encouraging the disintegration process of beta in the nuclear region with A = 86.Credito: (Top) NASA / Dana Berry, (Bottom).
One of the main objectives of the ion trap SHIPTRAP , located in the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, is to improve mass measurements of unstable nuclei participate in the rp process. In an article appearing in the journal Physical Review Letters [see HERE ], an international team of scientists working in the measurements reported SHIPTRAP mass, some of which are the first proton-rich isotopes in the vicinity of the atomic mass (A) 84 (see bottom Fig.) This region is about 84 molybdenum - a call-out nuclear point because it is a radioactive nucleus, where the proton capture competes with the reverse dissociation reaction, and flow "uphill" in the nuclear table stops in essence, favoring instead a slow process of beta decay . Top mass measurements in this region may help predict the amount of energy produced in certain ways rp process and, in turn, how high a temperature can be achieved in a burst of x-rays. This in turn determines which items could be produced, for example, in a cycle called ZrNb-a cycle that takes an excited nuclear state through a series of arrests and decays back to its starting point and has the effect of inhibition of nucleosynthesis to the highest masses.
The heart of the experiments is a SHIPTRAP ion trap (Penning) a mass spectrometer which is the most precise and accurate instrument for determining the mass of short-lived isotopes. Penning traps are currently the workhorse for the mass measurement accuracy and are used in almost all facilities that produce beams rare. In these traps ions (which was given the Nobel prize in 1989 with Hans Dehmelt and Wolfgang Paul) the cyclotron frequency ν with the charged particles which orbit in a combined electric and magnetic field is measured, and hence their mass is derived (through ν = m / q * B). Penning traps have been technically advanced to allow experiments in nearly all rare isotopes available from short-lived isotopes such as lithium 11, which has a half life of 8 ms [see here ] super heavy elements [see here], produced in tiny amounts of a few ions per minute or less.
SHIPTRAP The team measured the masses of ten neutron-deficient nuclei, which occurred in a fusion-evaporation reaction at the GSI SHIP velocity filter (a single source for relevant nuclei). The filter separated the shooting of the reaction products and other products do not stop at a gas cell. Thereafter, the ions are extracted and delivered to the ion trap system where the masses are determined with a relative accuracy of δ m / m ~ 10 - 7 to 10 - 8 , or about 5 to 15 keV of absolute uncertainty (a atomic mass unit is about 1 GeV). The team finds low energy alpha separation (the energy required to remove the nucleus an alpha particle) compared to what was predicted and had been previously found in these nuclei. And with these exact mass values \u200b\u200bof nuclei, the team is able to conduct a reevaluation of the landscape of mass within a specific region of the nuclear card. Get a coherent picture of the masses, without breaks or gaps are artificial measures of the masses. Based on their data, recalculated rp process similar to what is expected in x-ray burst on a stage star. They find that once their new values \u200b\u200binclude mass production resulting in the mass number A = 86 is changed by a factor 20, the biggest change ever found in the calculation of rp process, once the New experimental results are included. This surprising result underlines the need for high quality nuclear data.
Interestingly, similar mass measurements made in the new Cooler Storage Ring in Research Facility in Lanzhou Heavy Ion, China, shows that the proton separation energy as arsenic-65 differs from the theoretical predictions. The authors also question the expectation that the germanium-64 is a core holding position. Although their measurements are less precise than the methods with the Penning trap made at GSI, the results of this team are also leading to new conclusions about the rp process.
SHIPTRAP The team also observed a change of scenery to the mass proton-rich nuclei in which are more loosely bound proton. Rp process seems to favor this path leads to a change in the abundance of other isotopes with A = 86 and the indirect parent of key isotope molybdenum-94 (10% molybdenum). Moreover, their newfound low-energy alpha separation suggests that the production cycle is favored ZrNb, which will put a limit on the temperature and energy availability in the rp process. To delve into this and put more restrictions on such possibilities, more direct measurements of masses, in particular for zirbonium-80, zirconium-81, niobium-83, and of course the molybdenum-84, are necessary because they perform a key role in understanding the rp process and the scope and limits of the production of items such a scenario.
understand the nucleosynthesis and energy X-ray bursts requires an interdisciplinary approach between astronomical observations, astrophysical models and calculations, and a good understanding of the underlying nuclear physics. This work shows the amazing vision that comes from precision measurements of a few (but key) properties of nuclear physics.
source of information:
http://physics.aps.org/articles/v4/24
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