J.K. Bair

Neutron Yields from Alpha-Particle Bombardment

Thick-target (α,n) neutron yields have been measured for 6,7,NATLi, 9Be,10,11,NATB, Pb19F2 and Zn19F2, NATMg, 27Al, NATSi, and 28SiNATO2. From the Pb19F2 and Zn19F2 data, we have extracted the neut...

Neutrons from the proton bombardment of Li6, Li7, Be9, B11 and O18

Abstract The total neutron yield from proton bombardment has been measured for Li 6 from threshold to 14 MeV; for Li 7 , Be 9 and B 11 from 4 to 14 MeV; and for O 18 from 3.5 to 10 MeV. The Li 6 (p, n)Be 6 reaction Q value measured in this experiment is −5.05±0.05 MeV, giving a Be 6 mass excess of 18.36±0.05 MeV. The neutron yield from Li 7 at higher energies cannot be explained on the basis of the (p, n) reaction alone and is ascribed in part to multi-particle breakup. An anomaly in the Be 9 +p neutron yield curve is ascribed to a threshold for production of neutrons by a state in B 9 at 4.04 MeV. The B 11 (p, n)C 11 reaction results confirm previous level structure in C 12 and a new “level” at E p = 11.85 MeV (energy of excitation in C 12 of 26.81 MeV.) The O 18 +p neutron yield shows 21 “resonant” peaks (energy of excitation 11.4 to 16.8 MeV).

Evaluation of carbon stripper foils for heavy-ion accelerators

Abstract Carbon foils of thickness 2–10 μg/cm 2 were produced by vapor deposition and by dc glow discharge cracking of hydrocarbon gas. Their lifetimes to mechanical failure, under bombardment with 10 MeV 35 Cl ions, were determined. Foils produced by the glow discharge technique have lifetimes ranging from 5 to over 20 times longer than those produced by vapor deposition. The glow discharge foils are also found to exhibit a strong correlation between lifetime and thickness. Changes in foil thickness with increasing fluence are examined and evidence for sputtering is obtained from beam-scanning.

The 18O(α, p) reaction and the beta decay of 21F

Abstract The 18O(α, p)21F reaction has been studied in the bombarding energy range 7.78 to 9.95 MeV by observing, with approximately 2π geometry, the beta particles following the 21F decay. Prominent peaks in the yield curve occur at incident particle laboratory energies of about 7.86, 8.36, 8.61, 8.71, 8.83, 8.94, 9.16, 9.28, 9.43 and 9.82 MeV. The observed width of the peaks exceeds the experimental resolution of about 20 KeV. A half-life of 4.35±0.04 sec was determined for the 21F beta decay.

The energy levels of 21Na

Abstract The energy levels of 21Na are investigated with the 20Ne(p, γ)21Na and 20Ne(d, n)21 Na reactions. From the γ-ray energy measurements the excitation energies in 21Na are found to be 331 ± 3, 1717 ± 3, 2426 ± 2, 2800 ± 4, 3545 ± 3, 3679 ± 4, 3867 ± 4, 4117 ± 11 and 4297 ± 4 keV. A 20Ne(p, γ)21Na Q-value of 2434 ± 2 keV is deduced. Branching ratios are determined for the upper five levels. Direct non-resonant capture is observed to the 0.33 and 2.43 MeV states. Angular distributions for the 20Ne(d, n)21Na reaction are presented for all of these levels and for levels at 4453 ± 12 keV and 5009 ± 12 keV for incident deuteron energies of 3.60, 4.88, 5.57 and 5.94 MeV. The unbound 4.12 MeV state has a stripping pattern consistent with l = 1. Its lab width from the γ-ray work is 125 keV. The combined evidence of the branching ratios, reduced widths and stripping patterns show that the 4.12 keV level is the mirror of the 4.73 MeV level in 21Ne.

A search for interference effects between nuclear resonance and Coulomb excitation in the Na23(p, p′) reaction

Abstract The narrow, isolated resonance in the Na23(p, p′) reaction at 873 keV, situated upon a continuum due to Coulomb excitation, would appear to be a favourable case for observing interference effects between compound nucleus inelastic scattering and Coulomb excitation. The yield of 439 keV gamma radiation emitted from the first-excited state of Na23 was measured from 828 to 1100 keV incident proton bombarding energy. To within the accuracy of the experimental data, about ±8%, the non-interfering compound nucleus and Coulomb excitation contributions adequately account for the resonance shape, although the presence of an interference effect cannot be definitely excluded.

Some experimental techniques used in a precision charged particle absolute cross section measurement

Abstract In the course of a recent precision cross-section measurement utilizing solid-state detectors in a gaseous target scattering chamber, many effects which determine the shape and character of observed spectra were investigated experimentally. Data are presented on (1) slit edge scattering, (2) gas target scattering compensation processes, (3) detector efficiency, (4) gas scattering spectrum shape, (5) solid state detector response, and (6) incoming beam energy degradation.

Thresholds for /sup 116/Sn(p,n) and /sup 118/Sn(p,n)

The /sup 116/Sn(p,n) and /sup 118/Sn(p,n) thick-target integrated cross sections were measured up to about 100 keV above the thresholds and fitted by the Hauser--Feshbach statistical theory. It is shown for these nuclei that the familiar plot of the thick-target yield to the two-thirds power is not valid, except for an impractical region very near threshold. It is also shown that ..gamma..-ray emission dominates over neutron and proton emission for more than 100 keV above each threshold. The deduced thresholds are 5531 +- 6 keV for /sup 116/Sn and 4477 +- 3 keV for /sup 118/Sn. The corresponding Q values, 5483 +- 6 keV and 4439 +- 3 keV, disagree with values from the literature.

Thresholds for Sn 116 ( p , n ) and Sn 118 ( p , n )

The /sup 116/Sn(p,n) and /sup 118/Sn(p,n) thick-target integrated cross sections were measured up to about 100 keV above the thresholds and fitted by the Hauser--Feshbach statistical theory. It is shown for these nuclei that the familiar plot of the thick-target yield to the two-thirds power is not valid, except for an impractical region very near threshold. It is also shown that ..gamma..-ray emission dominates over neutron and proton emission for more than 100 keV above each threshold. The deduced thresholds are 5531 +- 6 keV for /sup 116/Sn and 4477 +- 3 keV for /sup 118/Sn. The corresponding Q values, 5483 +- 6 keV and 4439 +- 3 keV, disagree with values from the literature.

High-spin states of 26Mg populated in the 12C(18O, α) reaction

Abstract The structure of 26 Mg has been investigated by means of the 12 C( 18 O, α) reaction. Several previously unknown states were populated between excitation energies of 0 to 16 MeV. Excitation functions were measured for 126 states for bombarding energies between 43.2 and 45.9 MeV in 300 keV steps at a lab angle of 7°. The experimental energy averaged differential cross sections were compared with statistical model calculations and good agreement was obtained for the states whose spins and parities were previously established. The statistical model calculations were used to suggest the spins and parities for the rest of the states. In particular, candidates for 6 + and 8 + states were interpreted as members of three rotational bands in 26 Mg: the ground-state band, the K = 2 + band based on the 2.938 MeV 2 + state, and a K = 0 + band based on the 3.588 MeV 0 + state. Back bending of the yrast band is observed and it is suggested that it may be due to band crossing of the ground-state and first excited K = 0 + bands.