Radioactive ion beams — hot stellar reactions in the laboratory

doi:10.1016/0168-583X(85)90269-1

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volumes 10–11, Part 1, 15 May 1985, Pages 361-365

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Abstract

Following our initial production of beams of ⁷Be and ¹³N, we have improved the purity and intensity of these beams. In addition we have generated beams of ¹⁵O (at 30 MeV) and ⁸Li (at 22 MeV). These beams are intended for cross-section measurements of proton and alpha-particle capture reactions on unstable species that are important in hot stellar environments. We have begun studies aimed towards measuring the ¹H(⁷Be, ⁸B)γ cross-section. As part of the developmental work, we attempted to remeasure the ²H(⁷Be, ⁸B)n cross-section with a different technique that pointed out the importance of background ⁸Li. We measured the ²H(⁷Li, ⁸Li)¹H cross-section to be 155 ± 20 mb at 12.2 ± 1.3 MeV.

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High intensity targets for ISOL, historical and practical perspectives
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Citation Excerpt :
Active interest in nuclear astrophysics reaction studies using accelerated RIB coincided with the award of the 1983 Nobel Prize in Physics to William A. Fowler “for his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe” [3]. In the 1980s, some astrophysical reaction studies were already being performed with radioactive beams produced by projectile fragmentation [4–7], however, the existing facilities could not meet the intensity requirements of many potential experiments. The requirement for higher intensity radioactive beams soon resulted in a proliferation of workshops [8–11], design studies [12,13] and facility proposals [14,15] based on using intense primary beams irradiating thick ISOL targets to produce intense RIB that could subsequently be accelerated using a second dedicated accelerator.
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The feasibility of inclusive neutron production measurements in reactions induced by low-intensity radioactive beams using a 4π thermalization counter is studied. The time response of the detector is investigated experimentally by a technique that results in an enhanced sensitivity to weak components with long capture times. Complementary Monte Carlo simulations are presented. The capture time response is found to be independent on the neutron energy above 0.1 MeV. The capability of the capture time information in the unambiguous identification of neutron signals correlated to the projectile arrival on the target even in the presence of an intense background contamination is shown. As an application case, the ⁸Li(⁴He,n)¹¹B reaction at the Big-Bang temperature is commented.
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The in flight production of a secondary ⁸Li radioactive beam using the existing beam transport lines at the SMP13 Tandem accelerator of the Laboratori Nazionali del Sud in Catania is studied. The method consists in the momentum filtering by a switching magnet of the ⁸Li ions emitted backward in the centre of mass of the ²H(⁷Li,p)⁸Li reaction, followed by a time-of-flight tagging of the deflected ions. Details of the experimental procedures and preliminary results of the ⁸Li(⁴He,n)¹¹B reaction study relevant for pregalactic nucleosynthesis are presented and discussed.
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A two-stage method for generating a radioactive ¹⁸F ion beam has been developed. ¹⁸F is produced with a medical cyclotron by 11 MeV proton activation of [¹⁸O]water, then chemically processed off-line for use in a tandem accelerator ion source. Azeotropic distillation reduces the ¹⁸O component by 10⁵, with a resulting ¹⁸O to ¹⁸F beam ratio of about 10³. The average ¹⁸F⁻ beam intensity per synthesis is 1 ppA over 120 min from a cesium vapor, sputter negative ion source (SNICS), with a peak intensity of 4.5 ppA.
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Experimental efforts by the LLNL/Ohio State radioactive ion beam collaboration are described. We are presently focusing on some reactions which are of great importance in the newly proposed inhomogeneous big bang cosmological models [G.M. Fuller, G.J. Mathews and C.R. Alcock, in: Origin and Distribution of the Elements, ed. G.J. Mathews (World Scientific, Singapore, 1987)]. Specifically we are using our system to make beams of ⁸Li for measurements of the ⁸Li(d, n)⁹Be and ⁸Li(a, n)¹¹B cross sections. These are the key reactions which determine the production of heavy (A > 12) elements during the era of big bang nucleosynthesis, and thus the initial composition of stars and subsequent stellar isotope production. Plans for future experiments, including the measurement of the ⁷Be(p, γ)⁸B cross section will be discussed.

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Radioactive ion beams — hot stellar reactions in the laboratory

Abstract

Nucl. Instr. and Meth.

Rev. Mod. Phys.

IEEE Trans. Nucl. Sci.