J. Rogers

21Na(p,gamma)22Mg reaction and oxygen-neon novae.

The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in oxygen-neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E(c.m.)=205.7+/-0.5 keV with a resonance strength omegagamma=1.03+/-0.16(stat)+/-0.14(sys) meV.

Elastic proton scattering from 4He in the forward direction at 200, 350 and 500 MeV☆

Abstract The differential cross section for the elastic scattering of protons from 4He has been measured at 200, 350, and 500 MeV over an angular range from 3.5° to 15° in the lab system. In addition, the analyzing power was measured in the same angular range at 350 and 500 MeV. The experiment makes use of a tenuous gas target in which the recoil α-energy is measured with solid-state detectors. The proton scattering angle is measured outside the target by a system of multi-wire proportional counters. The differential cross sections have a nearly exponential dependence on momentum transfer in this kinematic range and grow with increasing energy. The analyzing power shows strong positive asymmetry.

Large angle cross section and analyzing power for proton-4he elastic scattering between 185 and 500 MeV

Abstract The differential cross section for the elastic scattering of protons from 4He has been measured for ten proton energies between 185 and 500 MeV in the angular range 144° to 168° in the lab system. The analyzing power has also been measured for seven energies in the same angular range. The differential cross section does not show the marked backward peaking that has been observed at both lower and higher energies. The possible structure in the 180° excitation function suggested for energies around 240 MeV is not observed. The analyzing power is large and negative, and shows strong dependence on both energy and angle.

A facility for studying radiative capture reactions induced with radioactive beams at ISAC

Abstract The measurement of low energy fusion reactions of importance to nuclear astrophysics scenarios are a prime objective of the physics program of the new ISAC facility, located at TRIUMF in Vancouver, Canada. Intense radioactive beams of 19 Ne, 14,15 O, 20,21 Na, 17,18 F and other low Z species with energies in the range of 0.15 to 1.5 MeV/mass unit will be available to measure cross sections and resonance strengths of alpha and proton induced reactions. An important component of the experimental configuration will be a new Reaction Products Detection Facility (RPDF) consisting of a windowless gas target, surrounded by a gamma array, while the recoils are separated from the intense radioactive beam using a Recoil Mass Spectrometer (RMS). The RMS will be based on a Wien filter. The recoiling reaction products will then be detected using either a Si μ-strip array or a gas filled detector. Using these devices along with coincidence requirements and time of flight conditions a background reduction factor of the order of 10 +15 is the present goal.

A FACILITY FOR STUDYING RADIATIVE CAPTURE REACTIONS INDUCED WITH RADIOACTIVE BEAMS AT ISAC

Abstract The measurement of low energy fusion reactions of importance to nuclear astrophysics scenarios are a prime objective of the physics program of the new ISAC facility, located at TRIUMF in Vancouver, Canada. Intense radioactive beams of 19 Ne, 14,15 O, 20,21 Na, 17,18 F and other low Z species with energies in the range of 0.15 to 1.5 MeV/mass unit will be available to measure cross sections and resonance strengths of alpha and proton induced reactions. An important component of the experimental configuration will be a new Recoil Product Detection Facility (RPDF) consisting of a windowless gas target, surrounded by a gamma array, while the recoils are separated from the intense radioactive beam using a Electro-Magnetic Separator (EMS) employing Wien filters. The recoiling reaction products will then be detected using either a Si μ-strip array or a gas filled detector. Using these devices along with coincidence requirements and time-of-flight conditions a background reduction factor of the order of 10 +15 is the present goal.

Results of 21Na+p experiments at ISAC

Abstract Several resonances in 22 Mg have been observed with a radioactive beam of 21 Na impinging on a hydrogen target at ISAC. Both elastic scattering as well as radiative capture have been investigated. Some results together with the experimental methods used will be reported.

Measurements with DRAGON on resonances in the 21Na(p, γ)22Mg reaction with a radioactive ion beam

Abstract In the modelling of nucleosynthesis in nova explosions, temperature and density are important parameters to describe the hydrodynamics. Those parameters are not easy to observe, but specific gamma-ray emitters produced in the explosion provide constrains on the models, such as 22 Na, produced via 21 Na ( p , γ ) 22 Mg ( β + ) 22 Na . The new DRAGON recoil separator facility, designed and built to measure directly the rates of radiative proton and alpha capture reactions, important for nuclear astrophysics, is now operational. Experiments have been conducted on the 21 Na(p , γ) 22 Mg reaction using a radioactive 21 Na beam incident onto a windowless hydrogen gas target. Yield measurements have been performed detecting the prompt gamma and the reaction recoils at E cm ≈ 821 keV and 204 keV.

Testing the ISAC radioactive ion accelerator beam specifications using the H(15N,αγ)12C reaction

Important ion beam parameters like energy spread and stability of the new isotope separator and accelerator accelerator at TRIUMF were determined during the first beamtime with the detector of recoils and gammas of nuclear gas target and BGO array. For this purpose a variation of the nuclear resonance method, using a geometrical scan over the resonance as placed in an extended gas target cell, as well as time-of-flight correlations were employed.

Measurement of the 21Na(p,γ)22Mg Reaction with the Dragon Facility at TRIUMF-ISAC

The DRAGON recoil separator facility, designed to measure the rates of radiative proton and alpha capture reactions important for nuclear astrophysics, is now operational at the TRIUMF‐ISAC radioactive beam facility in Vancouver, Canada. We report on first measurements of the 21Na(p,γ)22Mg reaction rate with radioactive beams of 21Na.

Quasifree p‐p scattering on 4He at 350 and 500 MeV

The 4He(p,2p)3H reaction was studied in a coplanar symmetric geometry at 350 MeV and 500 MeV using the proton beam of the TRIUMF cyclotron. At both incident energies we measured the energy sharing spectrum at the quasifree equal angles as well as the symmetric angular distribution. Out data resolve the discrepancy between the zero‐recoil cross sections measured at 460 MeV and at 590 MeV in favor of the 590 MeV SREL result. The excess of high‐momentum components in the 590 MeV angular distribution data, as compared to impulse approximation calculations, is confirmed and extrapolated to higher momenta.