Buchinger, F

Caggiano, J A

Clark, J A

Crawford, J E

Deibel, C

Greene, J P

Gulick, S

Hardy, J C

Hecht, A A

Lee, J K P

Levand, A F

Lewis, R

Lundgren, B F

Parikh, A

Parker, P D

Savard, G

Scielzo, N D

Sharma, K S

Tanihata, I

Trimble, W

Wang, J C

Wang, Y

Wrede, C

Zhou, Z

CERN Document Server

PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p, t)reactions and Penning trapsJ. A. Clark1,2,3, A. Parikh1, F. Buchinger4, J. A. Caggiano1, J. E. Crawford4, C.Deibel1, J. P. Greene3, S. Gulick4, J. C. Hardy5, A. A. Hecht3,6, J. K. P. Lee4, A. F.Levand3, R. Lewis1, B. F. Lundgren3, P. D. Parker1, G. Savard3, N. D. Scielzo3, K. S.Sharma2, I. Tanihata3, W. Trimble3, J. C. Wang2,3, Y. Wang2,3, C. Wrede1, and Z.Zhou31Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520, USA2Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada3Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA4 Department of Physics, McGill University, Montreal, PQ H3A 2T8, Canada5Cyclotron Institute, Texas A&M University, College Station, TX 77843-3366, USA6Department of Chemistry, University of Maryland, College Park, MD 20742, USAModels of astronomical phenomena require a number of nuclear physics inputs to characterizethe contribution of these events to the production of the observed elements. Masses and the exci-tation energy levels, spins, and partial and total decay widths of states are particularly important.Reported here are the mass measurements of 22Mg and 26Si which are required to understand thecontribution of novae to the observed (or unobserved) galactic abundances of 26Al and 22Na. Adescription of the Canadian Penning trap mass spectrometer and Yale spectrograph which wereused to determine these masses is presented and is followed by a brief description of the astro-physical consequences.International Symposium on Nuclear Astrophysics — Nuclei in the Cosmos — IXJune 25-30 2006CERN, Geneva, Switzerland© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p,t) reactions and Penning traps1. IntroductionThe success of models used to describe astronomical phenomena such as novae, x-ray bursts,and supernovae is determined by their ability to replicate the observational signatures of theseevents. Two examples of such observables are the abundances of the isotopes 26Al and 22Na whichare detected by the β -delayed 1.809 MeV (26Al, t1/2=7.2×105 yr) and 1.275 MeV (22Na, t1/2=2.6yr) γ rays from the decay of these isotopes [1]. The dominant nuclear uncertainties in the contri-bution of novae to the abundances of these nuclides stem from uncertainties in the 25Al(p,γ)26Siand 21Na(p,γ)22Mg reaction rates [2, 3, 4]. Since the resonant components of the reaction ratesdepend exponentially on the resonance energy, ER = Ex−Qo, either the direct determination of theresonance energy or the indirect determination through measurements of the excitation energy, Ex,and ground-state Qo values is necessary. We report here the measurements made of the masses of22Mg and 26Si which are used to improve the precision of the required Qo values.The current mass evaluation (AME) [5], used two measurements published in 1974 [6, 7]to arrive at -397.0(13) keV for the mass excess of 22Mg. Since the AME was published, a directmeasurement [8] of the resonance energy of the 2+ state had suggested that the mass excess of 22Mgwas 6 keV less than the value published in the AME. In addition, one of the measurements usedin the evaluation [6] had been revised to account for the change in the Q value of the 16O(p, t)14Oreaction [9] which was used as a calibration Q value during the original measurement [10]. Thenet effect was a decrease in the mass excess of 22Mg by 3 keV which was insufficient to resolvethe 6 keV difference noted in Ref. [8] and prompted independent measurements of the 22Mg massand the energy of the 2+ state. As for 26Si, only one measurement of its mass [6] was consideredin the latest AME. Since recent studies of the structure of 26Si above the 25Al + p threshold havebeen made [11, 12, 13] and a measurement has been proposed at the ISAC facility at TRIUMF todirectly study the 25Al(p,γ)26Si reaction [14], a remeasurement of the 26Si mass is warranted.2. The Canadian Penning trap mass spectrometerThe Canadian Penning Trap (CPT) mass spectrometer [15, 16] makes precise mass measure-ments of nuclides created through fusion-evaporation reactions using beams from the ATLAS fa-cility at Argonne National Laboratory. Ions of 22Mg were created with a 3.5 MeV/nucleon 20Nebeam incident upon a cryogenic 3He target held at 700 mbar with entrance and exit windows of 1.3mg cm−2 Ti. The 22Mg ions produced in the reaction were focused and separated from the primarybeam with a combination of a magnetic triplet, a velocity filter, and an Enge split-pole magneticspectrograph [17]. A tuneable degrader, positioned at the focal plane of the spectrograph, reducedthe energy of the ions before they entered a gas catcher [18] where the ions were thermalized in 200mbar of purified helium gas. The ions were extracted from the gas catcher via a combination of gasflow and electric fields and were guided through an ion cooler towards an isotope separator as thehelium was pumped away. Before they entered the isotope separator, the ions were accumulatedwithin a small trapping potential and were periodically ejected. In this way the continuous ion beamwas converted into a pulsed ion beam. The ion bunches were then captured in the isotope separator,a gas-filled Penning trap (B ∼ 1 T), where they were subjected to a mass selective cooling process[19] before they were transferred efficiently to a linear RF quadrupole (RFQ) ion trap with standard2PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p,t) reactions and Penning traps-2 -1 0 1 258606264666870727476TOF (arbitrary units)Frequency applied - 4110820.5 HzFigure 1: TOF spectrum of 22Mg+ obtained with the Canadian Penning trap mass spectrometer.ion optics. During transport, a fast voltage pulse, applied to one of the beam transport elements,efficiently suppressed isotopes outside a restricted range of masses before they were transmitted tothe RFQ. The RFQ was used to accumulate several bunches of ions and cool the ions prior to theirinjection into the precision Penning trap (B ∼ 5.9 T) for the mass measurement. The mass, m, ofthe ions in the Penning trap was determined by measuring their cyclotron frequency, ωc = qB/m,where q is the charge of the trapped ion. The magnetic field strength, B, was periodically calibratedby measuring the cyclotron frequencies of 20Ne+, 21Ne+, 22Ne+ and H3O+, whose masses are wellknown. The cyclotron frequency itself is measured by using the time of flight (TOF) method [20].The mass excess of 22Mg, as determined with measurements using the CPT [21], is -399.73(67)keV. A spectrum consisting of a subset of the data is shown in Fig. 1. Although this precise massmeasurement agrees well with the recent results from an independent Penning trap apparatus [22],only 3 keV of the 6 keV discrepancy suggested by Ref. [8] is accounted for. The remaining 3 keVwas removed following a more accurate measurement of the 2+ energy level [23]. All the recentmeasurements now yield consistent results, including those conducted with the Yale spectrograph[∆M = -400.5(1.0) keV] [24] discussed below.3. The Yale spectrographThe Yale spectrograph sits at the end of a beamline in the tandem Van de Graaff acceleratorfacility of the Wright Nuclear Structure Laboratory at Yale University. Located at the focal plane ofthe Enge split-pole spectrograph [17] is a position-sensitive gas ionization drift chamber followedby a scintillator. The drift chamber is filled with typically 200 mbar of isobutane which is containedwith two 0.25-mil aluminized-mylar windows. A uniform electric field is provided by a series of10 equally spaced wires which form a voltage divider between a 0.25-inch aluminum plate (thecathode) held at negative potential and a grounded Frisch grid. High voltage (about 1500 V) is3PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p,t) reactions and Penning trapsapplied to two sets of three wires each which lie above the Frisch grid to draw the electrons fromthe detector volume. The position of the ions passing through the detector volume is determinedwith 0.09”-wide by 1.4”-long lead-coated copper pick-up pads which lie above the high-voltagewires. A total of 220 pads are in series along the length of the wires and are separated by delaychips providing a delay of 5 ns between adjacent pads. As ions pass through the detector volume,the energy loss is detected by the cathode and the position of the ion along the focal plane detectoris determined by the relative delay between the signals detected at opposite ends of the series ofpick-up pads. These signals, in addition to the residual energy deposited in the scintillator, providea means to select the particles of interest. Further detail is provided in Ref. [25].Measurements of the mass of 22Mg and 26Si were made by studying (p, t) reactions betweena 33 MeV proton beam and targets of 28SiO (65 ug/cm2 with a gold flash) and 24MgO (67 ug/cm2on a 15 ug/cm2 carbon backing). The energies of the tritons corresponding to the ground states of26Si, 22Mg, and 14O were used in conjunction with the beam energy and scattering angle to obtainQo values of the reactions after performing a momentum calibration of the focal plane with (p,d)reactions from both a 360 ug/cm2 25MgO and a 140 ug/cm2 Al target.The top left spectrum in Fig. 2 shows the triton momenta corresponding to different states of22Mg from the 24Mg(p, t) reaction with the Enge spectrograph set at 25°. For the same spectrographangle, the states of 26Si are seen in the bottom left of the same figure. The data shown represent 20hours (top) and 13 hours (bottom) of collection with a proton beam intensity averaging 20 nA. Inthe case of the ground state of 22Mg, a resolution of 10 keV was achieved.Agreement between the 22Mg results obtained with the Yale spectrograph and the compilationof recent measurements provides confidence in the 26Si mass determined by the Yale apparatus.The result [∆M = -7139.5(1.0) keV], however, is in disagreement with the only measurement usedin the AME [∆M = -7145(3) keV] [6], even after it was corrected for changes in the calibrationreaction resulting in a mass excess ∆M = -7145.5(30) keV [26].With the mass of 26Si as determined using the Yale spectrograph, the contributions to the totalreaction rate of 25Al(p,γ)26Si at nova temperatures is shown in top right panel of Fig. 2 and isdominated by the 1+ and 3+ states. The bottom right panel shows the ratio of the resonant ratecontributions determined with the 26Si mass presented here to the rates calculated with the massreported in the AME. More details are given in Ref. [24]. A reduction in the rate by as much as 30%for T > 0.2 GK is possible if the 26Si mass reported in the AME is replaced by the results obtainedwith the Yale spectrograph. These results would be strengthened with additional measurementsof 26Si states above the 25Al + p threshold and experimental determinations for the γ and protonpartial decay widths of these states. An independent confirmation of the 26Si mass is also desirable.This work was supported by the U. S. Department of Energy, Nuclear Physics Division, underContract W-31-109-ENG-38, and by the Natural Sciences and Engineering Research Council ofCanada.References[1] M. Hernanz and J. José, New Astronomy Reviews 48, 35 (2004).[2] J. José et al., Astrophys. J. 520, 347 (1999).[3] C. Iliadis et al., Astrophys. J. Suppl. Ser. 134, 151 (2001).4PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p,t) reactions and Penning traps4003002001000Counts/channel100806040200Counts/channel200015001000500channel number28Si(p,t)26 Si(g.s.)28Si(p,t)26 Si(1.796)16O(p,t)14 O(g.s.)12C(p,t)10C(g.s.)12C(p,t)10C(g.s.)16O(p,t)14 O(g.s.)24Mg(p,t)22 Mg(1.246)24Mg(p,t)22 Mg(g.s.)1new resonant rate/old resonant rate0.01 0.1 1T (GK)10-29  10-26  10-23  10-20  10-17  10-14  10-11  10-8  10-5  10-2  101  104NA<σν> (s-1 mol-1cm3 )0.012 3 4 5 6 7 8 90.12 3 4 5 6 7 8 91   ER=159 keV, 1+   ER=403 keV, 0+   ER=434 keV, 3+   direct captureFigure 2: The left figure shows the triton momentum spectra at the focal plane of the Yale spectrograph forthe 24Mg(p,t)22Mg reaction (top) and the 28Si(p,t)26Si reaction (bottom). Also note the peaks resulting from(p,t) reactions on the carbon and oxygen present in the targets. The top right figure shows the contributionsto the total reaction rate of 25Al(p,γ)26Si with the 26Si mass determined by the Yale spectrograph. Thebottom right figure is a comparison, in terms of a ratio, between the total contribution to the resonant rate ascalculated with the 26Si mass determined with the Yale spectrograph to that determined with the 26Si massfrom the AME.[4] C. Iliadis et al., Astrophys. J. Suppl. Ser. 142, 105 (2002).[5] G. Audi et al., Nucl. Phys. A729, 337 (2003).[6] J. C. Hardy et al., Phys. Rev. C 9, 252 (1974).[7] J. A. Nolen et al., Nucl. Instrum. Methods 115, 189 (1974).[8] S. Bishop et al., Phys. Rev. Lett. 90, 162501 (2003).[9] G. Audi and A. H. Wapstra, Nucl. Phys. A595, 409 (1995).[10] J. C. Hardy et al., Phys. Rev. Lett. 91, 082501 (2003).[11] J. A. Caggiano et al., Phys. Rev. C 65, 055801 (2002).[12] D. W. Bardayan et al., Phys. Rev. C 65, 032801 (2002).[13] Y. Parpottas et al., Phys. Rev. C 70, 065805 (2004).[14] A. A. Chen et al. (E922, proposal accepted by TRIUMF EEC).[15] G. Savard et al., Nucl. Phys. A626, 353 (1997).[16] J. Clark et al., Nucl. Instrum. Methods Phys. Res. B 204, 487 (2003).5PoS(NIC-IX)081Mass measurements of 22Mg and 26Si via (p,t) reactions and Penning traps[17] J. E. Spencer and H. A. Enge, Nucl. Instrum. Methods 49, 181 (1967).[18] G. Savard et al., Nucl. Instrum. Methods Phys. Res. B 204, 582 (2003).[19] G. Savard et al., Phys. Lett. A 158, 247 (1991).[20] G. Gräff et al., Z. Phys. A 297, 35 (1980).[21] G. Savard et al., Phys. Rev. C 70, 042501 (2004).[22] M. Mukherjee et al., Phys. Rev. Lett. 93, 150801 (2004).[23] D. Seweryniak et al., Phys. Rev. Lett. 94, 032501 (2005).[24] A. Parikh et al., Phys. Rev. C 71, 055804 (2005).[25] A. Parikh, Ph.D. thesis, Yale University (2006).[26] J. C. Hardy and I. S. Towner, Phys. Rev. C 71, 055501 (2005).6

Mass measurements of $^{22}Mg$ and $^{26}Si$ via (p,t) reactions and Penning traps

Mass measurements of $^{22}Mg$ and $^{26}Si$ via (p,t) reactions and Penning traps

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Mass measurements of 22Mg^{22}Mg22Mg and 26Si^{26}Si26Si via (p,t) reactions and Penning traps

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Mass measurements of $^{22}Mg$ and $^{26}Si$ via (p,t) reactions and Penning traps