S- and P-wave neutron spectroscopy. XII. Higher resolution techniques in the keV region with windowless gas targets

Beard, Percy Morris; Parks, P. B.; Bilpuch, E.G.; Newson, H.W.

doi:10.1016/0003-4916(69)90169-9

Cited by 16 publications

(9 citation statements)

References 21 publications

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“…The use of the 18 O(p, n) 18 F reaction to generate the medical radioisotope 18 F and as a neutron source means that it has been studied in great detail using both activation techniques [23] and direct measurement of the neutron flux [17,[24][25][26]. The study of Beard et al [17] provides probably the most complete spectroscopy of the 18 O(p, n) 18 F reaction in the region of the neutron threshold. However, care must be taken when considering the excitation energies determined therein.…”

Section: Ex [Mev]mentioning

confidence: 99%

“…Some direct reactions have been performed populating states in 19 F via a number of different routes, e.g. 18 F(d, p) 19 F [10], 16 O( 6 Li,t) 19 F [11] etc. ; these direct reactions tend to have much poorer energy resolution than the resonance reactions and it is sometimes difficult to firmly identify which states populated in the direct reactions correspond to those observed in resonance reactions.…”

Section: Existing 19 F Nuclear Datamentioning

confidence: 99%

“…Energy levels which likely correspond to the levels listed in ENSDF [12] are listed in the column corresponding to that measurement. The excitation energies from Carlson et al [13], Gorodetzky et al [14,15] and Beard et al [16] are recalculated using the proton energies listed in those papers and recent mass values [17]. The uncertainties are also recalculated, and are dominated by the uncertainties in the proton bombarding energies.…”

Section: Existing 19 F Nuclear Datamentioning

confidence: 99%

“…Data were also taken using a 28 SiO 2 target (nominally 40 µg/cm 2 on 5 µg/cm 2 carbon) for the purpose both of calibration and quantification of the 16 O background [32], and a natural carbon foil (nominally 55 µg/cm 2 ) to characterise the background resulting from the 12 C backing of the LiF target.…”

Section: Munich Q3dmentioning

confidence: 99%

“…The location of the contaminating E x = 10.356-MeV state of 16 O (Γ = 26 keV) was determined by using the 28 SiO 2 target. In this case, the spectrum -including any overlapping 28 Si states -was fitted with a linear combination of one exponentially tailed Gaussian function for the 16 O state, and one exponentially tailed Gaussian function for each 28 Si state. This allowed the location and shape of the 16 O state to be described.…”

Section: B Data Analysismentioning

confidence: 99%

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Charged-particle branching ratios above the neutron threshold in F19 : Constraining N15 production in core-collapse supern

Adsley¹,

Hammache²,

Séréville³

et al. 2021

Phys. Rev. C

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Background: Spatially-correlated overabundances of 15 N and 18 O observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of 15 N and 18 O are 18 F(n, α) 15 N and 18 F(n, p) 18 O.Purpose: The relative strengths of the 18 F(n, α) 15 N and 18 F(n, p) 18 O reactions depend sensitively on the relative α0 and p0 decay branches from states above the neutron threshold in 19 F in addition to other properties such as the spins and parities, and the neutron widths. However, experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent.Method: Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain the properties of levels in 19 F. A second experiment using the Orsay Split-Pole spectrograph and an array of silicon detectors was performed in order to measure the charged-particle decays of neutron-unbound levels in 19 F.Results: A number of levels in 19 F have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of 18 O lies 68 keV (Ex = 10.5 MeV) above the neutron threshold. The α-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays. Conclusion:Neutron-unbound levels in 19 F are observed to decay predominantly by α-particle emission, supporting the role of 18 F(n, α) 15 N in the production of 15 N in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately. I. ASTROPHYSICAL BACKGROUND *

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