Astrophysically important 19Ne states studied with the 2H(18F, α+15 O)n reaction

The nuclear structure of 19Ne near the proton threshold is of interest for understanding the rates of proton-induced reactions on 18F in novae. Analogues for several states in the mirror nucleus 19F have not yet been identified in 19Ne indicating the level structure of 19Ne in this region is incomplete. The 18F(d,n)19Ne and 18F(d, p)19F reactions have been measured simultaneously at Ec.m. = 14.9 MeV. The experiments were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL) by bombarding a 720-μg/cm2 CD2 target with a radioactive 18F beam. The 19Ne states of interest near the proton threshold decay by breakup into a and 15O particles. These decay products were detected in coincidence with position-sensitive E-ΔE silicon telescopes. The α and 15N particles from the break up of the mirror nucleus 19F were also measured with these detectors. Particle identification, coincidence, and Q-value requirements enable us to distinguish the reaction of interest from other reactions. The reconstruction of relative energy of the detected particles reveals the excited states of 19Ne and 19F which are populated. The neutron (proton) angular distributions for states in 19Ne (19F) were extracted using momentum conservation. The observed states in 19Ne and 19F will be presented

Neutron-upscattering enhancement of the triple-alpha process

The neutron inelastic scattering of carbon-12, populating the Hoyle state, is a reaction of interest for the triple-alpha process. The inverse process (neutron upscattering) can enhance the Hoyle state’s decay rate to the bound states of 12C, effectively increasing the overall triple-alpha reaction rate. The cross section of this reaction is impossible to measure experimentally but has been determined here at astrophysically-relevant energies using detailed balance. Using a highly-collimated monoenergetic beam, here we measure neutrons incident on the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas, we measure the 3α-particles (arising from the decay of the Hoyle state following inelastic scattering) and a cross section is extracted. Here we show the neutron-upscattering enhancement is observed to be much smaller than previously expected. The importance of the neutron-upscattering enhancement may therefore not be significant aside from in very particular astrophysical sites (e.g. neutron star mergers)

A high precision n-p scattering measurement at 14.9 MeV

The n-p scattering angular distribution was measured with 14.9 MeV incident neutrons using the traditional time-of-flight technique with neutron-gamma discrimination. The scattering angle varied from 20o to 65o (laboratory system) in 5o incremental steps. The efficiency of the neutron detectors was measured in the energy range 2–9 MeV relative to the 252Cf-standard, and was calculated using Monte Carlo methods in the 2–14 MeV energy range. Two methods of analysis were applied for experimental and simulated data: a traditional approach with a fixed threshold, and a dynamic threshold approach. The present data agree with the ENDF/B-VII evaluation for the shape of n-p angular distribution within about 1.5%

The low-energy M1 γ-strength from radiative proton capture experiment

The multipolarity of the low-energy (< 3 MeV) γ–strength function has been experimentally studied with the 55Mn(p,2γ)56Fe reaction at 1.65 MeV proton beam energy. The spectrum of two-step γ–cascades populating the ground state of 56Fe has been measured and compared with calculations assuming that E1 or M1 multipolarities dominate in the low-energy region. It was found that experimental data points are reproduced only if the assumption on dominance of the M1 multipolarity is used

The low-energy M1

The multipolarity of the low-energy (< 3 MeV) γ–strength function has been experimentally studied with the 55Mn(p,2γ)56Fe reaction at 1.65 MeV proton beam energy. The spectrum of two-step γ–cascades populating the ground state of 56Fe has been measured and compared with calculations assuming that E1 or M1 multipolarities dominate in the low-energy region. It was found that experimental data points are reproduced only if the assumption on dominance of the M1 multipolarity is used

The 3H(d,γ)5He Reaction for Ec.m. ≤ 300 keV

The 3H(d, γ)5He reaction has been measured using a 500-keV pulsed deuteron beam incident on a stopping titanium tritide target at Ohio University’s Edwards Accelerator Laboratory. The time-of-flight (TOF) technique has been used to distinguish the γ-rays from neutrons detected in the bismuth germinate (BGO) γ-ray detector. A stilbene scintillator and an NE-213 scintillator have been used to detect the neutrons from the 3H(d, n)4He reaction using both the pulse-shape discrimination and TOF techniques. A newly-designed target holder with a silicon surface barrier detector to simultaneously measure α-particles to normalize the neutron count was incorporated for subsequent measurements. The γ-rays have been measured at laboratory angles of 0°, 45°, 90°, and 135°. Information about the γ-ray energy distribution for the unbound ground state and first excited state of 5He can be obtained experimentally by comparing the BGO data to Monte Carlo simulations. The 3H(d, γ)/3H(d, n) branching ratio has also been determined

The

The 3H(d, γ)5He reaction has been measured using a 500-keV pulsed deuteron beam incident on a stopping titanium tritide target at Ohio University’s Edwards Accelerator Laboratory. The time-of-flight (TOF) technique has been used to distinguish the γ-rays from neutrons detected in the bismuth germinate (BGO) γ-ray detector. A stilbene scintillator and an NE-213 scintillator have been used to detect the neutrons from the 3H(d, n)4He reaction using both the pulse-shape discrimination and TOF techniques. A newly-designed target holder with a silicon surface barrier detector to simultaneously measure α-particles to normalize the neutron count was incorporated for subsequent measurements. The γ-rays have been measured at laboratory angles of 0°, 45°, 90°, and 135°. Information about the γ-ray energy distribution for the unbound ground state and first excited state of 5He can be obtained experimentally by comparing the BGO data to Monte Carlo simulations. The 3H(d, γ)/3H(d, n) branching ratio has also been determined

Band structures in Be 12 experimental results

The structure of the neutron rich isotope 12Be has been studied using different transfer reactions, which populate distinct structures in 12Be. This concerns two neutron and three neutron stripping reactions and two proton pick up reactions at incident energies of 15 20 MeV u. Band structures of positive and negative parity are discussed