The Karlsruhe 4π barium fluoride detector

Wisshak, K.; Guber, K. H.; Käppeler, F.; Krisch, J.; Müller, H.; Rupp, George; Voß, F.

doi:10.1016/0168-9002(90)90179-a

Cited by 113 publications

(72 citation statements)

References 27 publications

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“…The neutron density profiles are shown in the inset. 13 0 phase, which is decreasing due to the later mixing with unprocessed material when the convective helium shell is progressing beyond the 13 0 pocket. The different pattern obtained for the two Gd isotopes results from the temperature-dependence of the preceding branch points.…”

Section: Resultsmentioning

confidence: 99%

“…Since the experimental method has been published in detail [1,2,13,14], only a more general description is given here, complemented with the specific features of the present measurement. Neutrons were produced via the 7 Li(p,n) 7 Be reaction by bombarding metallic Li targets with the pulsed proton beam of the Karlsruhe 3.75 MV Van de Graaff accelerator.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Stellar neutron capture cross sections of the Gd isotopes

Wisshak¹,

Voß²,

Käppeler³

et al. 1995

Phys. Rev. C

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The neutron capture cross sections of 152 Gd, 154 Gd, 155 Gd, 156 Gd, 157 Gd, and 158 Gd were measured in the energy range from 3 to 225 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons were produced via the 7 Li(p,n)1Be reaction by bombarding metallic Li targets with a pulsed protori beam. Capture events were registered with the Karlsruhe 47r Barium Fluoride Detector, which was improved by replacing crystals with high a background and by introducing a pierced crystal at zero degrees with respect to the beam axis. These changes resulted in a significantly increased efficiency for capture events. The main experimental problern was that the samples of the two s-only isotopes 152 Gd and 154 Gd showed only relatively low enrichment, but the spectroscopic quality of the BaF 2 detector allowed to determine the resulting corrections for isotopic impurities reliably. The cross section ratios could be determined with an overall uncertainty of typically 1%, an improvement by factors of five to ten compared to existing data. Severe discrepancies were found with respect to previous results. Maxwellian averaged neutron capture cross sections were calculated forthermal energies between kT = 10 keV and 100 keV. The new stellar cross sections were used for an updated analysis of the s-process reaction flow in the mass region between samarium and gadolinium, which is characterized by branchings at 151 Sm, 154 Eu, and 155 Eu. With the classical approach, the s-process temperature could be constrained corresponding to a range of thermal energies between kT=28 ke V and 33 keV. The 152 Gd production in low mass starswas found to depend strongly on the neutron freeze-out at the end of the heliumshell burning episodes.

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Stellar neutron capture cross sections of the Gd isotopes

Wisshak¹,

Voß²,

Käppeler³

et al. 1995

Phys. Rev. C

Self Cite

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“…Sinee the experimental method has been published in detail [1] [3] [5] [23], only a more general description is given here, complemented with the specific features of the present measurement. Neutrons were produced via the 7 Li(p,n?Be reaction by bombarding metallic Li targets with the pulsed proton beam of the Karlsruhe 3.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The main experimental program performed with the Karlsruhe 411" Barium Fluoride Detector [1) is the aceurate determination of neutron eapture cross sections for neutron eapture nucleosynthesis in s-process scenarios [2). In this eontext, detailed analyses of branchings in the s-process path are of partieular interest, since these branchings ean be analyzed to derive information on the physieal eonditions during helium shell burning in Red Giant stars.…”

Section: Introductionmentioning

confidence: 99%

Stellar neutron capture cross sections of the Ba isotopes

et al. 1994

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The neutron capture cross sections of 134 Ba, 135 Ba, 136 Ba, and 137 Ba were measured in the energy range from 5 to 225 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons were produced via the 7 Li(p,nfBe reaction by bombarding metallic Li targets with a pulsed proton beam. Capture events were registered with the Karlsruhe 47r Barium Fluoride Detector. Several runs have been performed under different experimental conditions to study the systematic uncertainties, which resulted mainly from the large ratios of total to capture cross sections of up to 400. The cross section ratios were determined with an overall uncertainty of "'3%, an improvement by factors of five to eight compared to existing data. Severe discrepancies were found with respect to previous results. Maxwellian averaged neutron capture cross sections were calculated for thermal energies between kT = 10 ke V and 100 ke V. These stellar cross sections were used in an s-process analysis. For the s-only isotopes 134 Ba and 136 Ba the Nsratio was determined to 0.875±0.025. Hence, a significant brauehing of the s-process path at 134 Cs can be claimed for the first time, in cantrast to predictions from the classical approach. This brauehing yields information on the s-process temperature, indicating values araund T 8 = 2. The new cross sections arealso important for the interpretation of barium isotopic anomalies, which were recently discovered in SiC grains of carbonaceous chondrite meteorites. Tagether with the results from previous experiments on tellurium and samarium, a general improvement of the Nssystematics in the mass range A = 120 to 150 is achieved. This allows for a more reliable separation of s-and r-process yields, resulting in an improved assignment of the respective contributions to eiemental barium that is required for comparison with stellar observations. ZUSAMMENFASSUNG

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“…These requirements are best met by the 4π BaF 2 arrays at FZK (14) and LANL (5) with 42 and 162 detector modules, respectively. BaF 2 turned out to be the most suited scintillator material because of the unique combination of fast timing, high efficiency, low neutron sensitivity, and good resolution in γ-ray energy.…”

Section: γ-Detectormentioning

confidence: 99%

Neutron capture measurements at a RIA-type facility

Reifarth

Haight

Heil³

et al. 2004

Nuclear Instruments and Methods in Physics Research Section A:

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Neutron capture cross sections of unstable isotopes are important for neutron induced nucleosynthesis as well as for technological applications. The Rare Isotope Accelerator (RIA) or comparable facilities will be able to produce radioactive ion beams up to 10 12 particles/s and would therefore be a suitable place for (n,γ) studies on radioactive isotopes with half-lives between days and months. We propose a facility for measurements of (n,γ) cross sections of unstable isotopes in the keV range suited for minimal sample masses down to 10 15 atoms, corresponding to minimum half-lives of only 10 d.

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The Karlsruhe 4π barium fluoride detector

Cited by 113 publications

References 27 publications

Stellar neutron capture cross sections of the Gd isotopes

Stellar neutron capture cross sections of the Gd isotopes

Stellar neutron capture cross sections of the Ba isotopes

Neutron capture measurements at a RIA-type facility

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