Investigation of a superconducting beam splitter for atlas

The device which is being investigated for use as a beam splitter consists of a dipole bending magnet in which a superconducting flux shield (supertube) is placed. The supertube produces a field free region for one of the charge states while the second charge state enters the magnetic field produced by the dipole magnet and is directed toward the remainder of the ATLAS accelerator. This type of device is appealing because of its simplicity and because the two beam regions are decoupled. The superconducting flux shield is a passive device requiring only that it be cooled below the superconducting transition point for proper operation

ATLAS positive-ion injector proposal

The ATLAS facility will provide beams of heavy-ions through approximately mass 130. Energies provided will range from over 20 MeV/A for lighter ions down to approximately 5 MeV/A for mass 130. In discussions with our user group concerning future program needs, two major areas of focus emerged. The first was a desire to increase the beam intensities available by approximately a factor of ten beyond what is possible from our present negative-ion source and tandem injector for all ion species. The second was to obtain beams of at least 10 MeV/A energy for all possible masses through uranium. These features were desired without compromising the presnt qualities of the ATLAS facility: good beam quality, ease of operation, and continuous (DC) operation. The facility which has been proposed to address these goals consists of replacing the negative-ion injector and FN tandem with a positive-ion source and a superconducting linac of a new design which makes use of the high field gradients possible with superconducting structures. The positive-ion source proposed is an electron cyclotron resonance source mounted on a high-voltage platform, providing a 350-kV potential for preacceleration of the ions. This will produce, for example, uranium ions of 7 MeV with a velocity of .008c, assuming a charge state of 20/sup +/. The ions will be bunched in a two stage bunching system providing a pulsed beam with a time width of better than 0.4 ns for injection into the linac

ATLAS with CARIBU: A Laboratory Portrait

The Argonne Tandem Linac Accelerator System (ATLAS) is the world's first superconducting accelerator for projectiles heavier than the electron. This unique system is a U.S. Department of Energy (DOE) national user research facility open to scientists from all over the world. It is located within the Physics Division at Argonne National Laboratory and is one of five large scientific user facilities located at the laboratory

Production of radioactive ion beams using the in-flight technique

Reactions with a heavy projectile incident on a light target can be used for the efficient in-flight production of secondary radioactive beams. An overview of this technique is given using data on 17F beams produced via the p(17O, 17F)n and d(16O, 17F)n reactions. With primary 16,17O beam currents of 100 pnA, intensities of up to 2×106 17F/s on target were achieved. Using this beam, the p(17F, α) 14O reaction was measured

Experimental study of the astrophysically important Na 23 (α,p) Mg 26 and Na 23 (α,n) Al 26 reactions

The Na23(α,p)Mg26 and Na23(α,n)Al26 reactions are important for our understanding of the Al26 abundance in massive stars. The aim of this work is to report on a direct and simultaneous measurement of these astrophysically important reactions using an active target system. The reactions were investigated in inverse kinematics using He4 as the active target gas in the detector. We measured the excitation functions in the energy range of about 2 to 6 MeV in the center of mass. We have found that the cross sections of the Na23(α,p)Mg26 and the Na23(α,n)Al26 reactions are in good agreement with previous experiments and with statistical-model calculations. The astrophysical reaction rate of the Na23(α,n)Al26 reaction has been reevaluated and it was found to be larger than the recommended rate

Fusion Cross Sections for the Proton Drip Line Nucleus 17F at energies below the coulomb barrier

The fusion-fission cross section for the system 17F + 208Pb involving the drip line nucleus 17F has been measured at energies in the vicinity of the Coulomb barrier. No enhancement of the fusion-fission yields due to breakup or to a large interaction radius was observed

Reaction rate for carbon burning in massive stars

Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5-4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate

Branching ratio Γα/Γγ of the 4.033 MeV 3/2+ state in 19Ne

The branching ratio Γα/Γγ of the 4.033 MeV 3/2+ state in 19Ne plays a crucial role in the breakout from the hot CNO cycle into the rapid proton capture process. This ratio has been studied by making use of the advantages of inverse kinematics. The state was populated via the 3He(20Ne,α) 19Ne* reaction and its decay via γ or α emission was measured by detecting the heavy reaction products (19Ne or 15O) in coincidence in a magnetic spectrograph. An upper limit Γα/Γγ≤6×10-4 has been obtained. With these results, the astrophysical reaction rate for the 15O (α, γ) 19Ne reaction has been calculated. Its influence on the breakout at various astrophysical sites, novas, x-ray bursts, and supermassive stars, is discussed

Fusion measurements of 12C+12C at energies of astrophysical interest

The cross section of the 12C+12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of 12C+12C were successfully carried out with the γ and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for 12C+12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques

Determination of the 8B Neutrino Spectrum

The total energy of the alpha particles, which resulted from the decay of 8B, was measured. A beam of 8B ions was implanted near the midplane of a planar Si detector. This eliminated α-particle energy loss in insensitive regions and allowed the sum energy of the two α particles to be observed with a single detector. The measurement of the 8B β-delayed α apectrum provided direct determination of the 8B neutrino spectrum