Lower Isomeric Purity (#2)

RIKEN Accel. Prog. Rep. 51 (2018)

High

Medium Isomeric Purity (#1)Ⅱ-1. Nuclear Physics

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Al proton resonant elastic scattering with CRIB
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D. Kahl,∗1 H. Shimizu,∗2 H. Yamaguchi,∗2 K. Abe,∗2 O. Beliuskina,∗2 S. M. Cha,∗3 K. Y. Chae,∗3 A. A. Chen,∗4Z. Ge,∗5 S. Hayakawa,∗2 N. Imai,∗2 N. Iwasa,∗6 A. Kim,∗7 D. H. Kim,∗7 M. J. Kim,∗3 S. Kubono,∗5M. S. Kwag,∗3 J. Liang,∗4 J. Y. Moon,∗8,∗9 S. Nishimura,∗5 S. Oka,∗10 S. Y. Park,∗7 A. Psaltis,∗4T. Teranishi,∗10 Y. Ueno,∗10 and L. Yang∗2800200600400100200500226

Al is known as the ﬁrst speciﬁc radioactivity discovered with extraterrestrial origins.1) The observed
spatial and velocity proﬁles of galactic 26 Al provide
insights to nucleosynthesis and galactic chemical evolution. In this context, the stellar nuclear reactions
which produce and destroy 26 Al should be suﬃciently
constrained by experimental data when possible, in order to reduce the uncertainties on the ejected mass of26
Al calculated in various stellar models. Knowledgeof the reaction rate of radiative proton capture on thelow-lying isomeric state 26m Al(p, γ) is still lacking, particularly at higher excitation energies when the twospecies 26g,m Al are expected to be in thermal equilibrium (> 1 GK).
We performed the ﬁrst measurement of mixed26g,mAl proton elastic scattering at the CNS lowenergy RI beam separator (CRIB)2) to search for lowspin states with large Γp which may inﬂuence the26mAl(p, γ) rate. Considering the isomer’s excitationenergy of 228 keV, the typical operating resolution ofCRIB ( ∆pp ∼ 1%) is insuﬃcient to distinguish the two
26Al species event by event. To make the measurement
tractable, we considered that the 26 Mg(p, n)26 Al reaction cross section shows anticorrelated yield for 26g,m Al
depending on Ec.m. 3) as well as that the previous measurement of 26g Al(p, p) showed only Rutherford scattering over the measured energy range.4)
We produced the cocktail beam inﬂight via the26Mg(p, n)26 Al reaction in inverse kinematics. A primary beam of 26 Mg8+ was extracted from the HyperECR ion source, accelerated up to 6.65 MeV/u by theAVF cyclotron, and delivered to CRIB with typicalintensities of 25–50 pnA. The 26 Mg beam impinged
on the CRIB cryogenic production target, which contained H2 at 130–290 Torr at an eﬀective temperatureof 90 K over 8 cm (0.4 to 0.8 mg cm−2 ). By varying theH2 gas pressure as well as a removable Havar energy degrader foil upstream of the production target, we couldcontrol Ec.m. and hence the isomeric purity of the cocktail beam. We regularly monitored the isomeric purity
using β-decay measurements in a beam pulsing mode.

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11Fig. 1. Example laboratory residual proton energy spectraobtained near 0◦ . The isomeric purity of (b) is higher
than (a).

The decay measurements were interpreted with the assistance of Geant4 simulations, and we found the isomeric purity was approximately 40–60% depending on
the experimental conditions. The 26 Al cocktail beams
had an average intensity of 1.5 × 105 pps, 93% purity,and on-target energies of 68, 83, and 93 MeV
To measure the physics of interest, the 26 Al beam
was tracked with two PPACs before fully stopping in a
7.5 mg cm−2 CH2 foil which served as a proton target.
Scattered protons were measured at forward laboratory angles with ∆E–E silicon telescopes. Backgroundcontributions from carbon in the polyethylene target
were evaluated by intermittently exchanging the CH2foil with a 10.6 mg cm−2 carbon foil. Examples ofthe preliminary laboratory proton energy spectra areshown in Fig. 1. The background contribution fromcarbon (scaled to the number of incident 26 Al ions)looks smooth, and hints of some peak-like structures
seem to emerge when the isomeric purity is higher.
These preliminary results look promising for our future
analysis, where we will add all the kinematic conditions
including all energy losses to obtain the proton scattering excitation function in the center-of-mass frame.
Finally, we plan to extract resonance parameters with
an R-matrix analysis.

∗1

School of Physics & Astronomy, University of Edinburgh
Center for Nuclear Study, University of Tokyo∗3 Department of Physics, Sungkyunkwan University∗4 Department of Physics & Astronomy, McMaster University∗5 RIKEN Nishina Center∗6 Department of Physics, Tohoku University∗7 Department of Physics, Ewha Womans University∗8 Institute for Basic Science∗9 Wako Nuclear Science Center∗10 Department of Physics, Kyushu University∗2References
1) W. A. Mahoney, J. C. Ling, A. S. Jacobson, R. E. Lingenfelter, Astrophys. J. 262, 742 (1982).
2) Y. Yanagisawa et al., Nucl. Instrum. Methods Phys.
Res. A 539, 74 (2005).
3) R. T. Skelton et al., Phys. Rev. C 35, 45 (1987).
4) S. T. Pittman et al., Phys. Rev. C 85, 065804 (2012).

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