Sodium 21

The ²¹Ne(p, γ) reaction has been carried out a few times at the DRAGON facility with the intent of calculating the resonant strength of the reaction. Two known resonant center of mass energies have been used for this reaction, that of 731.5 keV and 258 keV, but only the latter energy will be discussed here. This reaction was analyzed in Sabine Engel’s thesis, but a few problems were discovered that lead to the need to re-examine the data. These problems will be discussed later. This report will begin with the analysis of the most recent runs carried out with this reaction, and then will re-examine some old data that was analyzed in Sabine’s thesis.

kathrynreport1.pdf

Author: Oraas, K.

Journal:

An oxygen-neon nova is presently understood to be the result of a thermonuclear runaway on the surface of an oxygen-neon white dwarf. During this event production, and subsequent ejection into the interstellar medium, of the radioisotope ²²Na can ensue. With a half life of 2.6 years, ²²Na β-decays leading to the emission of a characteristic γ-ray of energy 1.28 MeV. This combination of long half life and characteristic gamma signature makes ²²Na a possible “viewing port” into the nuclear physics of these cataclysmic events, for, γ-rays of this energy are readily detectable with past and current orbiting satellite observatories. To date, no 1.28 MeV γ-signal has been observed from any nova, and this remains an outstanding problem in astrophysics.

Within these environments, production of ²²Na can proceed via isolated, narrow reso- nances in the reaction path: ²⁰Ne(p,γ)²¹Na(p,γ)²²Mg(β+νe)²²Na. As many as three res- onant states in the ²²Mg nucleus can contribute to the total nova ²¹Na(p,γ)²²Mg reaction rate. The strengths of these resonances and, therefore, the ²¹Na(p,γ)²²Mg nuclear reaction rate, were hitherto unknown, creating significant uncertainty in the expected yield of ²²Na from an oxygen-neon nova event.

Thick target yield measurements, using a high intensity (> 10⁸ s⁻¹) radioactive beam of ²¹Na with the DRAGON facility at ISAC, have been performed in inverse kinematics resulting in a direct measurement and limit on two astrophysically important resonance strengths ²¹Na(p,γ)²²Mg. Uncertainty in this reaction rate has been reduced by more than 10-fold for nominal peak nova temperatures ≥ 0.3 GK. A narrow resonance, thick target yield curve has been mapped out for the first time using a radioactive heavy ion beam. From this curve, a new mass excess for the ²²Mg nucleus has been derived of −403.5 ± 2.4 keV, rather than the literature value of -396.8 keV. The implications the results of the present work have on nova ²²Na production are consistent with no observed 1.28 MeV γ-signal.

bishop_phd.pdf

Author: Bishop, S.

Journal:

A multichannel R-matrix formalism was used to fit ²¹Na + p resonant elastic and inelastic scattering data taken at the TRIUMF UK detector array facility at TRIUMF-ISAC. Five resonances were observed corresponding to states in ²²Mg above the proton threshold. Four of these corresponded to states seen in previous transfer reaction studies where firm spin-parity assignments could not be made. One new resonance, previously unobserved in any reaction, was also seen. Where possible, resonance energies, partial widths, and spin-parity values of these resonances were extracted. The correspondence between these states and possible analogs in the mirror nucleus ²²Ne is discussed, as well as the relation to T = 1 states in the nucleus ²²Na.

ruiz_phys_rev.pdf

Author: Ruiz, C. et al.

Journal: Physical Review C

The "Detector of Recoils And Gammas Of Nuclear reactions", DRAGON, is a new facility, especially designed to measure absolute cross sections of radiative proton- and alpha- capture reactions on radioactive nuclei of astrophysical interest. Located at the TRIUMF-ISAC radioactive ion beams laboratory in Vancouver, Canada, the DRAGON performs studies on reactions in inverse kinematics with ion beams in the mass range of 6 to 30 amu impinging on a gas target at energies of 0.15 to 1.5 MeV/u. A BGO detector array to tag the prompt gamma radiation emitted in a reaction surrounds the target, followed by a recoil mass separator and a double sided silicon strip detector which measures position and energy of the recoil at the final focus. Beam suppression of the order of 1011-1015 is needed to fully separate the readioactive beam ions from the much rarer reaction products. Systematic studies of varioius configurations using stable beams along with measurements of well-know resonance reactions were completed for the commissioning of the complete facility and the energy calibration of the new ISAC radioactive beam accelerator. Additionally, the first results of the scientific program, that has been launched with a study on the ²¹Na(ρ,γ)²²Mg reaction at E_cm ≈ 821 keV, will be presented.

sabine_thesis.pdf

Author: Engel, S.

Journal:

The ²¹Na(ρ,γ)²²Mg reaction is expected to play an important role in the synthesis of intermediate mass elements in Oxygen-Neon novae. The first direct measurement of the rate of this reation was completed using the DRAGON recoil mass separator at TRIUMF's ISAC facility. The energy of one resonance important in the reaction was measured to be E_c.m.=728.1 ± 1.2 keV, and its resonance strength was determined to be ωγ= 254 ± 16_stat ± 44_sys meV.

cath_neish_paper.pdf

Author: Neish, C.

Journal:

The ²¹Na(ρ,ϒ)²²Mg recation is expected to play in 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 keV with a resonance strength ωϒ= 1.03 ± 0.16_stat ± 0.14_sys meV.

na21_prl.pdf

Author: Bishop, L. et al.

Journal: Physical Review Letters

A series of astrophysical measurements was recently completed at TRIUMF, related to the unknown total rate of the 21Na(ρ,ϒ)22Mg reaction. With a high intensity 21Na beam from the ISAC facility, the DRAGON recoil mass spectrometer was used to directly measure seven resonances at center of mass energies from E_c.m.=200 to 1135 keV and determine their respective contributions to the 21(ρ,ϒ)22Mg reaction rate in novae and x-ray bursts, as well as their impact on 22Na production in novae. This study also allowed the investigation of different excited states in 22Mg; proposed decays and spin assignments are given for the 6246, 6329, 6609 keV levels.

nic8paper_trinczek.pdf

Author: Trinczek, M. et al.

Journal:

The long-lived radioactive nuclide 22Na (t_1/2=2.6 yr) is an astronomical observable for understanding the physical processes of oxygen-neon novae. Yields of 22Na in these events are sensitive to the unknown total rate of the 21Na(ρ,ϒ)22Mg reation. Using high intensity 21Na beam at the TRIUMF-ISAC facility, the strengths of seven resonances in 22Mg, of potential astrophysical importance, have been directly measured at center of mass energies from E_c.m.=200 to 1103 keV. We report the results obtained for these resonances and their respective contributions to the 21Na(ρ,ϒ)22Mg rate in novae and x-ray bursts, and their impact on 22Na production in novae.

prc65803.pdf

Author: D'Auria, J. M. et al.

Journal: Physical Review C

The breakout of the hot CNO cycle and the onset of the rapid-proton process are of signicant importance to our understanding of the nucleosynthesis of proton-rich nuclei in our universe. In particular 15O(; )19Ne and 21Na(p, )22Mg are both thought to be key reactions for these processes under explosive astrophysical conditions. In this work, an experiment has been carried out at Louvain-la-Neuve, Belgium, in order to test the feasibility of a measurement of the lifetime of the 4.033 MeV state in 19Ne, which is considered extremely important for the 15O(; )19Ne reaction. Also, an elastic-scattering experiment was performed using a newly-developed 21Na beam at the ISAC post-accelerated radioactive beam facility in Vancouver,Canada. The experiment represents the rst scientic result achieved with this facility. A centre-of-mass energy range of  0.4-1.5 MeV was investigated using a thick-target scan technique utilising polyethylene [CH2]n) foils. Data were collected using a silicon charged-particle detector array, enabling the identication of elastic and inelastic resonances in the 21Na+p system. Monte-Carlo simulations were used to estimate the experimental resolution eects present in the experiment. These results were then incorporated into an analysis of the data using a single-channel ` = 0 R-matrix
code. An analysis of the data enabled the identication of four states in22Mg, one of which was previously unobserved. Resonance energies and widths were estimated for each of these states. A comparison of the resultswith states in the T=1 analogue system was made. The eect a detailed knowledge of these resonances would have on the 21Na(p,)22Mg rate under extreme high temperature conditions was also investigated.

related-theses-2003-ruiz_phd.pdf

Author: Chris Ruiz

Journal: