IOP

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TACTICDirect measurements of nuclear
astrophysics reactions
Alison Laird
7/04/09
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IOP
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Overview

• Nuclear Astrophysics Why? What? How?
• Case study - 8Li(a,n)11B
• TACTIC design
• Beam tests
• Current challenges
• Future plans

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Nuclear Astrophysics What?
http//ie.lbl.gov/systematics/chart2000g.pdf
What reactions are important in stars and stellar
explosions? What are the conditions? What are
the reaction rates? What impact do they have?
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Nuclear Astrophysics Why?
BIG QUESTIONS! How are the elements in the
Universe formed? Why does the chart of the
abundances look like it does? What are the sites
of nucleosynthesis? What can primordial
nucleosynthesis tell us about the Big Bang?
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Nuclear Astrophysics How?

• Direct or Indirect?
• Indirect use nuclear physics techniques to
  determine parameters
• (energy states, spin/parity, widths, etc) to
  enable us
• to calculate the reaction rate
• (typically) uses existing beams and techniques
• high cross sections
• but requires significant interpretation
• Direct study the reaction as it actually happens
  in the star!
• (little (nuclear) model interpretation required)
• but technically very challenging

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Explosive Nucleosynthesis

• Explosive astrophysical environments
• Supernovae
• core collapse - massive stars
• thermonuclear binary system
• Novae and X-ray bursters
• thermonuclear binary system
• Conditions
• high temperatures
• high densities
• short timescales
• (high neutron flux)
• Nuclear processes
• r, rp, ap, p,..

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Reaction rates
Courtesy of M.Aliotta
So reaction dominated by small energy region
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Typical Gamow peak energies
Quiescent nucleosynthesis p p - 5 keV
(helium burning) 14N(p,g)15O - 25 keV (hydrogen
burning) Explosive nucleosynthesis 14N(p,g)15O
- 170 keV (novae) 18F(p,a)15O 250 keV
(novae) 18Ne(a,p)21Na 1300 keV (x-ray
bursts) 44Ti(a,g)48Cr 3700 keV (supernovae)
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Direct Techniques Experimental Nuclear
Astrophysics at low energies

• Studying directly key nuclear reactions for
  nucleosynthesis and energy generation in
  explosive sites novae, supernovae and X-ray
  bursters
• Experimental conditions
• Beam energies about 0.1 2 MeV/u ( up to few
  109 K )
• Charged particle energies of few MeV down to
  100 keV
• Radioactive beams high background, low
  intensity
• Cross sections can be low - lt mbarn
• Hydrogen or helium target
• Need low detection threshold
• Need high rate capability
• Gas target

TACTIC!
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Case study
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Case study r-process
rapid-neutron capture process thought to be
responsible for 50 -70 of elements heavier than
iron. Sequence of neutron captures and b-decays
far from stability in high neutron flux
environment (favoured site - supernova).
But.
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Case study r-process seed nuclei
.. To understand r-process abundances need to
understand production of seed nuclei.
a(t,g)7Li(n,g)8Li(a,n)11B
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Case study 8Li(a,n)11B
Significant discrepancies between existing data
sets. Possible resonances. Lowest (most
important) energies not covered by existing data.
H. Ishiyama et al. 2006
23/09/08
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STFC PRD - Laird
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TACTIC Design
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TACTIC TRIUMF Annular Chamber for Tracking and
Identification of Charged particles
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Key design features
Cylindrical design maximise beam
intensity Radial drift field maximise event
rate without pile up GEM amplification lowering
detection threshold Flash ADC readout full
pulse shape analysis
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Cathode cage
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Initial beam tests
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ISAC radioactive beam facility at TRIUMF
11B and 14N beams from OLIS Systematic studies
at a variety of pressures and voltages
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Initial TACTIC tests
Online track reconstruction
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TACTIC Tests
SIM.
DATA
DATA
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13 MeV 11B, 403 mbar
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Recoil sims
4He
16O
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3.5 MeV 14N, 121 mbar
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3.5 MeV 14N, 66 mbar
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Pulse shapes alpha source
3.5 MeV a source 1017 mbar lt 500 keV deposited
per pad Clear peaks, good timing and track
reconstruction.
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Pulse shapes 14N beam, 66 mbar
Signalnoise 4 gt poor timing gt poor track
reconstruction BUT detection of signals with
energy deposited per pad approx. 70 keV NEXT
STEPS reduce noise and improve PSA algorithms
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Current challenges
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• Energy calibration
• a designing automated rig to calibrate each pad
• position dependence of GEM response
• Tracking techniques
• Missing energy reconstruction of energy lost
  within cage
• Timing drift field
• Anode pitch
• Triggering
• Firmware issues
• Crossing between modules
• Stability
• Strange things in the data.

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The future

• April 09
• Firmware tests
• Gamma coincidences
• June 09
• First radioactive tests
• New cathode cage arrangement
• GEM readout
• Ongoing
• Calibration techniques
• Firmware development
• Simulation and analysis software development
• Analysis of tests at Notre Dame
• Future plans
• Second GEM lower energies, smaller pads?
• Silicon detector

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Experimental programme
First experiment 8Li(a,n)11B Beam already
available at required intensity. 7Be(p,p)
pp-chains approved (L. Buchmann) Will require
development of hydrogen target 18Ne(a,p)21Na
breakout from HCNO cycles in X-ray bursts Will
require auxilliary silicon detectors 13N(a,p)16O
X-ray bursts 12C12C hydrostatic and
explosive hydrogen burning Will require
windowless target region and solid cathode
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Thank you for your attention

• The TACTIC collaboration
• A. M. Laird, S. P. Fox, P. Mumby-Croft, B. Hide
• University of York, U.K.
• P. Amaudruz, L. Buchmann, U. Hager, L. Martin, P.
  Machule,
• R. Openshaw, G. Ruprecht, A. Shotter, P. Walden
• TRIUMF, Canada