Science

Studies of the charge state distribution of low energy (<1.5 MeV/u), low Z (<13) heavy ions passing through hydrogen and helium gas of varying target pressure have been performed using separate windowless gas target systems at TRIUMF and the University of Naples. Semi-empirical relationships have been deduced to estimate the equilibrium charge state distributions as a function of beam energy. From these distributions, cross-sections for the relevant charge changing reactions have been deduced.

wenjie.pdf

Author: Liu, W. et al.

Journal: Nuclear Instruments and Methods in Physics Research A

A facility for measuring cross-sections (resonance strengths) for reactions of astrophysical importance involving short-lived, radioactive reactants has been designed, built and installed at the new TRIUMF-ISAC Radioactive Beams Laboratory in Canada. Named DRAGON (Detector of Recoils And Gammas of Nuclear reactions), it has been successfully commissioned with stable and radioactive heavy ion beams from ISAC. This report presents the main components of the facility, namely, the windowless gas target, the surrounding ϒ detector array, the subsequent electromagnetic recoil mass separator, the focal plane detectors for recoils, the detection system for elastics, and the modular electronics and computer software used for the data acquisition. Examples of the operation of the facility for both stable beam reactions and the first radioactive beam reaction study, ²¹Na(ρ,ϒ)²²Mg are also presented, along with future plans for the program.

hutcheon.pdf

Author: Hutcheon, D. A. et al.

Journal: Nuclear Instruments and Methods in Physics Research A

The new DRAGON facility (detector of recoils and gammas of nuclear reactions), located at the TRIUMF-ISAC Radioactive Beams facility in Vancouver, Canada, is now operational. This facility is used to study radiative proton capture reactions in inverse kinematics (heavy ion beam onta a light gaseous target) with both stable beams and radioactive beams of mass A=13-26 in the energy range 0.15-1.5 MeV/u. A double sided silicon strip detector (DSSSD) has been used to detect recoil ions. Tests have been performed to determine the performance of this DSSSD.

emiswrede.pdf

Author: Wrede, C.; Hussein, A; Rogers, J. G.; D'Auria, J

Journal: Nuclear Instruments and Methods in Physics Research B

The DRAGON (detector of recoils and gamma-rays of nuclear reactions) setup at the ISAC radioactive ion beam facility of TRIUMF, Vancouver, was used to measure the energy loss of stable neon and magnesium as well as of radioactive sodium ions (energy range 200-1150 keV/u) in hydrogen gas. Stopping power values were determined and (as no previous experimental data around the stopping power maximum existed) compared to the available semi-empirical codes SRIM 2003, ATIMA and MSTRAR. The experimental data seems to favor the new SRIM 2003 approach and will hopefully provide input to a further improvement of the parameter set.

greife_nimb2004_energyloss_in_h.pdf

Author: Greife, U. et al.

Journal: Nuclear Instruments and Methods in Physics Research B

We present new measurements of the charge-state distributions (CSD) of a 1.068 MeV/u C beam in He, and of the 6+ : 5+ charge-state population ratio in the recoils of the ¹²C(α,ϒ)¹⁶O reaction, noth measured at the DRAGON recoil mass spectrometer. A computer simulation to model the CSD of both beam and recoil particles in inverse-kinematics experiments is compared to data from this work and from previous work at ERNA. The simulation provides good agreement with both data sets. The results suggest that, for this fusion reaction on the J^π=4+ resonance at E_beam=1.064 MeV/u, immediately after fusion, the recoil ions contain only the nucleons and not the electrons of the target He atom.

csd.pdf

Author: Zylberberg, J. et al.

Journal: Elsevier Preprint

The performance of the DRAGON recoil spectrometer at TRIUMF-ISAC has been studied using the radiative capture reactions with stable beams of 12C, 20Ne, 21Ne, 23Na, 24Mg, and 26Mg. Calibration of the deflection magnet measuring the beam energy was established and the beam suppression factors of the separator were investigated. Yields from six narrow resonances were measured and compared with previous results. For the 1112.6 keV resonance in 20Ne(ρ,ϒ)21Na, our result is in disagreement with the NACRE database assignment but agrees with one other previous result.

engel_commiss.pdf

Author: Engel, S. et al.

Journal:

The radionuclide Na22 is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the Na22(p,γ)Mg23 reaction. We have measured the strengths of low-energy Na22(p,γ)Mg23 resonances directly and absolutely using a radioactive Na22 target. We find the strengths of resonances at E_p=213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4-3.2, and we exclude important contributions to the rate from proposed resonances at E_p=198, 209, and 232 keV. The Na22 abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.

physrevlett.105.152501.pdf

Author: Sallaska, A. L.; Wrede, C.; García, A.; Storm, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K. A.; Ottewell, D. F.; Buchmann, L.; Vockenhuber, C.; Hutcheon, D. A.; Caggiano, J. A.

Journal: Physical Review Letters, vol. 105, Issue 15, id. 152501 (2010)

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide Na22 produced in novae. Previously published uncertainties in the dominant destructive reaction, Na22(p,γ)Mg23, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the Na22 implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~20 C bombardment as a result of protective layers. We avoided the need to know the absolute stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for E_p=213, 288, 454, and 610 keV are stronger by factors of 2.4-3.2 than previously reported. Upper limits have been placed on proposed resonances at 198, 209, and 232 keV. These substantially reduce the uncertainty in the reaction rate. We have re-evaluated the Na22(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to Na22 destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of Na22 ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion.

physrevc.83.034611.pdf

Author: Sallaska, A. L.; Wrede, C.; García, A.; Storm, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K. A.; Ottewell, D. F.; Buchmann, L.; Vockenhuber, C.; Hutcheon, D. A.; Caggiano, J. A.; José, J.

Journal: Physical Review C, vol. 83, Issue 3, id. 034611 (2011)

The ¹⁸F(p,α)¹⁵O reaction rate is crucial for understanding the final abundance of ¹⁸F predicted by nova models. The γ-ray emission in the first few hours after a nova outburst is expected to be dominated by 511 keV annihilation photons from the decay of ¹⁸F, and so understanding its production can provide important constraints on the conditions during the outburst when compared with observations. Results are presented from the lowest-energy direct measurement to date, performed at the Isotope Separator and Accelerator radioactive beam facility at the TRIUMF laboratory, Canada. Cross section measurements at center-of-mass energies of 250, 330, 453, and 673 keV are obtained and the results compared to previous data and R-matrix calculations. The implications for the overall reaction rate in the context of nova explosions have been discussed.

physrevc.83.042801_2.pdf

Author: C. E. Beer, A. M. Laird, A. St. J. Murphy, M. A. Bentley, L. Buchman, B. Davids, T. Davinson, C. A. Diget, S. P. Fox, B. R. Fulton, U. Hager, D. Howell, L. Martin, C. Ruiz, G. Ruprecht, P. Salter, C. Vockenhuber, and P. Walden

Journal: Phys. Rev. C 83, 042801(R) (2011) [4 pages]