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Nuclear data is also an important ingredient in the interpretation of new observations made by ground-based observatories such as the Keck and European Southern Observatory ESO Very Large Telescopes, by space-borne observatories such as the Hubble Space Telescope and the Chandra X-Ray Observatory, and by large subterranean detectors such as the Sudbury Neutrino Observatory and Super-Kamiokande. More complete and precise nuclear physics measurements are therefore needed to improve astrophysical models and to decipher the latest observations [1].

Because radioactive nuclei play an influential, and in some cases the dominant, role in many cosmic phenomena, information on these nuclei is particularly important to improve our understanding of the processes that shape our universe. In the explosive environments of novae and X-ray bursts, hydrogen and helium react violently with heavier seed nuclei to produce extremely proton-rich nuclei via hot-CNO burning and the a p - and rp -processes.

Neutron-induced nucleosynthesis may occur in the neutrino-wind driven shock front of supernova explosions initiating the r -process and producing extremely neutron-rich nuclei. These cataclysmic stellar explosions produce reaction flows through nuclei far from the valley of beta stability. To understand and interpret observations of these events we must understand the nuclear reactions, the nuclear structure, and the decay mechanisms for unstable nuclei.

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Because the lifetimes of most of the nuclei of interest are too short for use as targets in experiments, the required information can best be obtained by producing energetic beams of radioactive ions. The atoms diffusing from the target material are ionized and extracted by a close-coupled ion source.

After undergoing two stages of mass analysis, the radioactive ions are then injected into the 25 MV tandem accelerator, accelerated to the appropriate energy for the experiment, and delivered to the experimental station. At the HRIBF, a full suite of developed beams is available including radioactive beams and 79 beams of stable species [3].

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Available radioactive beams include proton-rich species such as 7 Be and 17,18 F and neutron-rich beams such as 82 Ge and doubly-magic Sn. These studies were performed as part of the RIBENS collaboration [4] and involved 13 distinct measurements of nuclear properties or cross sections. The 17 F p , g 18 Ne [5,6] and 14 O a , p 17 F [7] reaction rates were studied with 17 F beams, while 18 F beams were used to determine the stellar rates of the 18 F p , a 15 O [8,9] and 18 F p , g 19 Ne [10] reactions.

While the availability of radioactive beams provides great opportunities for the better understanding of nuclei and nuclear reactions far from stability, there are also great challenges that most be overcome to utilize such beams. High-efficiency large solid-angle detector arrays have been developed to deal with low beam intensity measurements. Another challenge is that radioactive beams are frequently contaminated with an unwanted isobar. While this contaminant can sometimes be removed with chemical techniques at the ion source or by fully stripping the beam, a general solution does not exist and many times an isobarically mixed beam will be delivered to the experimenter.

A detector system with high selectivity is many times the best solution to the problem. Kinematically-complete measurements utilizing coincidence techniques is one method to identify the events of interest.


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We have frequently detected the beam-like recoil from a reaction in a gas-filled ionization counter, identifying the proton number Z of the recoil, and thus determining the reaction channel. While direct measurements of the reaction of interest are extremely important, it is not generally possible or even desirable to measure the reaction cross section at all of the energies required to completely determine the stellar reaction rate.


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  • It is important to have complimentary measurements which may not directly determine the reaction rate but do help to elucidate the structure of the nuclei involved. A good understanding of the properties of states in the compound nuclei can be used to calculate the stellar reaction rate over a large range of astrophysical temperatures. Direct measurements of reaction cross sections should thus be complimented with other studies such as single-nucleon transfer reactions populating states of interest or particle-decay branching ratio studies from stable beam measurements.

    These points are discussed further in the next section discussing the 18 F p , a 15 O reaction. The decay of 18 F is thought to provide the most prolific source of gamma rays during the first several hours after a nova explosion. Orbital gamma-ray telescopes are probing and will continue to probe nova remnants searching for this signature of radioisotope decay [15]. To interpret these expected observations, we must understand the destruction rate of 18 F in the nova environment and, in particular, we must know the rate of the 18 F p , a 15 O reaction as it is the main destruction path for 18 F at high temperatures.

    Unfortunately, recent evaluations found that the amount of 18 F that is produced in nova models in uncertain by a factor of just due to uncertainties in the 18 F p , a 15 O reaction rate [16]. It was critical that more and better studies of the reaction rate be performed. The mixed beam was used to bombard a polypropylene CH 2 target as shown in Fig. By plotting the a energy versus the heavy recoil energy, the 1 H 18 F, a 15 O events were cleanly distinguished from the contaminant 1 H 18 O, a 15 N events.

    The yield of the 1 H 18 F, p 18 F reaction was measured simultaneously. Protons elastically scattered from 18 F were detected in the SIDAR and distinguished from 18 O induced events by requiring coincidence with recoil 18 F ions detected in a gas ionization counter. Excitation functions for the 1 H 18 F, a 15 O and 1 H 18 F, p 18 F reactions were produced by measuring the yields of these reactions as a function of beam energy Fig.

    Precise resonance parameters were obtained from a simultaneous fit of the data sets [9]. Use of this method allowed the strengths of two important 18 F p , a 15 O resonances at E c. It was found, however, that other low energy resonances may also make important contributions to the 18 F p , a 15 O rate especially at low temperatures [16]. The cross sections populating these state were too low to be measured in the laboratory so other methods were necessary to constrain their strengths. An alternative measurement involved populating the mirrors of the 19 Ne levels of interest via the 18 F d,p 19 F reaction.

    The idea was that by measuring the single-particle neutron spectroscopic factors of states in 19 F, one could then use isospin symmetry to constrain the proton partial widths and thus the strengths of the mirror levels in 19 Ne. This experiment was recently performed at the HRIBF, and while the analysis is still preliminary, it looks likely that important constraints will be placed on the strengths of several resonances in 19 Ne [17].

    The r -process produces roughly half of the elements heavier than iron via a series of neutron captures and beta decays flowing through extremely neutron-rich nuclei. The path and abundances produced are uncertain, however, because of the lack of information on the properties and structure of extremely neutron-rich nuclei. Recently accelerated beams of many neutron-rich nuclei have become available at the HRIBF opening some of the first studies of many nuclei thought to be on the r -process path.

    The most critical piece of information that is needed to understand r -process nucleosynthesis is the masses of nuclei along the path. The masses used in calculations are currently based almost entirely upon extrapolations.

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    It is critical that mass models be benchmarked in this mass region with actual measurements. To better constrain these mass models, mass measurements were performed on a number of short-lived neutron-rich fission products at the HRIBF. The measurements were performed using a simple setup consisting of a position-sensitive microchannel plate and an ion counter mounted near the focus of the energy-analyzing magnet of the MV tandem accelerator [18].

    The idea of the measurements was that two isobars of different mass passing through the tandem simultaneously will have the same energy but different momenta, and thus will be bent to different locations at the focus of the energy-analyzing magnet. By measuring an unknown mass difference relative to a known mass difference, it is not necessary to known the magnet radius. About this book This volume is the first of its kind on focusing gamma-ray telescopes.

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    Show all. Annihilation of positrons in the Galaxy Pages Sazonov, S. Non-thermal cosmic backgrounds and prospects for future high-energy observations of blazars Pages Giommi, P. Focusing supernova gamma rays Pages Leising, M. Nucleosynthesis in nova explosions: Prospects for its observation with focusing telescopes Pages Hernanz, M.

    Puzzles and potential for gamma-ray line observations of solar flare ion acceleration Pages Smith, David M. Replicated nickel optics for the hard-x-ray region Pages Ramsey, Brian D. Progress toward light weight high angular resolution multilayer coated optics Pages Ulmer, M.

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    Laue diffraction lenses for astrophysics: Theoretical concepts Pages Halloin, Hubert et al. Laue diffraction lenses for astrophysics: From theory to experiments Pages Halloin, Hubert. Copper mosaic crystals for Laue lenses Pages Courtois, P.

    Nuclear Astrophysics

    High diffraction efficiency, broadband, diffraction crystals for use in crystal diffraction lenses Pages Smither, Robert K. Development of a new photon diffraction imaging system for diagnostic nuclear medicine Pages Roa, D. Gamma ray Fresnel lenses — why not? Pages Skinner, G.

    Development of ground-testable phase fresnel lenses in silicon Pages Krizmanic, John et al. Multiwavelength focusing with the Sun as gravitational lens Pages Koechlin, Laurent et al.

    Bibliographic Information

    New scintillators for focal plane detectors in gamma-ray missions Pages Buis, Ernst-Jan et al. A focal plane detector design for a wide-band Laue-lens telescope Pages Caroli, Ezio et al. Distributed space segment for high energy astrophysics: Similarities and specificites Pages Hinglais, Emmanuel. Formation flying for a Fresnel lens observatory mission Pages Krizmanic, John et al. Show next xx. Read this book on SpringerLink.