Studies	  of	  X-­‐Ray	  Burst	  αp-­‐process	  Wai6ng	  Points	  using	  Radioac6ve	  Ion	  Beams	  at	  ATLAS	  Catherine	  M.	  Deibel	  Louisiana	  State	  University	  ARIS	  2014	  	  1	  TypetoI X-RayBursts(XRBs)
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Neutron stars:
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– Second level• Third level– Fourth level» Fifth level

Accretion rate ~ 10-8/10-10 Mo/year
Peak x-ray burst temperature ~ 1.5 GK
Recurrence rate ~ hours to days
Burst duration of 10 – 100 s
Observed x-ray outburst ~1039 – 1040 ergs
ARIS

June 1 – 6, 2014

2TokyoD.K. Galloway et al., ApJ 601 466
2 (2004).

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X-Ray Burst Nucleosynthesis• Pre-burst hot CNO cycle– burns H into He– results in persistent thermal Xray spectrum• Triple-α reaction ignites burst– 3α à 12C– T ~108 K• Nucleosynthesis proceeds up
proton-rich side of stability:– rp (rapid proton capture) process• (p,γ) reactions and β decays‒ αp process• (α,p) and (p,γ) reactions– peak temperatures of 1 – 2 GK
H. Schatz, K. E. Rehm, NPA 777, 601 (2006)

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June 1 – 6, 2014

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αp-process waiting points• Nuclei with low Qpγ values andlong (~ 1 s) β–decay half lives:– 22Mg, 26Si, 30S and 34Ar•(p,γ)-(γ,p) equilibrium isreached and nucleosynthesis
stalls awaiting β decay or
breaks out via (α,p) reaction• Effects of waiting points:– final elemental abundances– energy output of XRB– luminosity profiles (multipeaked structure)
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June 1 – 6, 2014

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Nuclear Structure Information•{Gamowwindow

30S + α à 34Ar

compound nucleus• At T ~ 1 GK (peak temperature)– Gamow peak located at 8.61 MeV– only one known level in window• Similar situations for otherwaiting point nuclei• Indirect studies at RCNP, Osakaand Notre Dame have been
completed to determine levelstructure[e.g. O’Brien AIP Conf. Proc. 101 288(2009), S. Almaraz-Calderon PRC 86065805 (2012)]

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June 1 – 6, 2014

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Studying (α,p) Waiting Points via (p,α)
Reactions

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June 1 – 6, 2014

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Radioactive Ion Beams at ATLASIn-flight facility

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June 1 – 6, 2014

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Radioactive Ion Beams (RIBs) at ATLAS
36Ar
stable primary andradioactive beam
to experiment•RIBs produced via 1 or 2 nucleon transfer reactions:
24Mg
28Si
32S
36Ar

•
•

37K(d,n)

25Al

37K
36Ar

29P
33Cl
37K

Result is cocktail beam of RIB and primary beam
RF sweeper reduced background from stable beam component
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June 1 – 6, 2014

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Experimental Setup•

RIB produced via in-flight method enters target chamber– energy degraded by Au foils– impinges on 650 µg/cm2 CH2 target•α-particles detected in double-sided Si strip detector (DSSD) segmented in θlab•

Heavy reaction products separated from beam by Enge Split-Pole SpectrographSPS):– SPS run in gas-filled mode
– detected at focal plane by Parallel Grid Avalanche (PGAC) counter and Ionization Chamber (IC)Heavy reaction
products to SPS

ARISJune 1 – 6, 2014

Tokyo9Results: 33Cl(p,α)30S
Monte Carlo Simulation

Data• Coincidence detection between
30S heavy recoils and α‘s• Yield normalized to beam current
and target thickness• Normalized yield corrected for
efficiencies determined via Monte
Carlo simulations!!"!#$%!&'()*+!,-.-/!
!!"!#$%!0,-!/123-/+!,-.-/• Resulting cross sections up to afactor of four greater than NONSMOKER calculations– theoretical calculations valid forthese reactions?
– experimental determinationnecessary
C.M. Deibel et al, PRC 84, 045802 (2011).

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June 1 – 6, 2014

Tokyo10• Similar setup to 33Cl(p,α)30S
study!lab (degrees)

Results: 37K(p,α)34Ar• Preliminary results showcross sections lower thanNON-SMOKER calculations• Publication to be submitted
Summer 2014

cross section (mb)

• SSB monitor added for third
method of normalization

PRELIMINARY!!!
Ecm (MeV)

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June 1 – 6, 2014

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Results: 29P(p,α)26Si and 25Al(p,α)22Mg• Similar setup to 33Cl(p,α)30S and 37K(p,α)34Ar studies• Analysis in progress for both experimental runs
PRELIMINARY!!!
29P(p,!)26Si!"##$+##'

25Al(p,!)22Mg!"##$%#!'!"##$%#*'! (barns)/0/1203$4'$56"'!"##$%#)'!"##$%#('PRELIMINARY!!!

!"##$%#&','-'.'!#'!!'Ecm (MeV)

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June 1 – 6, 2014

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Future . . . Direct (α,p) Studies with HELIOS• HELIcal Orbit Spectrometer (HELIOS)

Prototype
Si array– 2.85 T repurposed MRI magnet– allows improved inverse kinematics studies:• high geometrical efficiency• better resolution (alleviates kinematiccompression)• unique particle ID via time-of-flight

Beam

Target fan

RecoilDetector• Upgrades to HELIOS for (α,p) studies:– cryogenic gas target• commissioned Spring 2013

– high-rate ionization chamber• commissioned Spring 2013

– new Si array

Si ArrayBeam• under construction

Gas targetRecoildetector•30S beam development underway
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June 1 – 6, 2014

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Studying (α,p) reactions withANASEN•

Array for Nuclear Astrophysics andStructure with Exotic Nuclei (ANASEN)

pRIBrecoil(via window)– posters: PS1-A059 J. Blackmon; PS1-A056
G. Rogachev•

Extended active gas target/detector– Proportional Counter (PC) gas acts as target– PC plus Si detector coverage allow for eventby event reconstruction– active gas target allows maximum efficiencywith low intensity RIBs•

Successful runs with both stable andradioactive beams at Florida StateUniversity––•14N(α,p)17O
18Ne(α,p)21Na

First experimental run with reaccelerated
RIB from ReA3 at NSCL: 37K(p,p) 37K
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June 1 – 6, 2014

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Summary• Time-inverse (p,α) measurements have been completed
for all four candidate αp process waiting-point nuclei– 25Al(p,α)22Mg– 29P(p,α)26Si– 33Cl(p,α)30S– 37K(p,α)34Ar• Significant deviations from theoretical calculations havebeen found• Next steps:– examining effects of new cross sections on XRBs
– direct (α,p) measurements with devices such as HELIOS andANASEN

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June 1 – 6, 2014

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Thank You!!

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June 1 – 6, 2014

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