Exploding Stars in the Lab Nuclear Astrophysics with TUDA and DRAGON

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Exploding Stars in the Lab!Nuclear Astrophysics
with TUDA and DRAGON

• Dr. Alison Laird
• TRIUMF

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Outline

• Nuclear astrophysics what and why?
• Explosive astrophysical sites
• Nuclear reaction processes
• Experimental nuclear astrophysics
• The TUDA facility
• The DRAGON facility

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Aims of Nuclear Astrophysics

• Understand the origin and evolution of the
  chemical elements

• Understand the nuclear processes responsible for
  energy generation

HEAO light curve of X-ray burst MXB 1728-34
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Brief Overview of Stellar Evolution
Hertzsprung-Russell diagram Temperature vs
Luminosity
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Explosive Astrophysical Sites

• Novae, X-ray bursters, supernovae type 1a
• Binary system compact object
• and main sequence or red giant star
• Accretion of hydrogen rich
• material
• Thermonuclear runaway lots of energy
• High temperatures and short timescales
• Radioactive nuclei important

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Thermonuclear runaway

• Accreted material under degenerate conditions
• Velocity distribution described by Fermi-Dirac
  statistics not Maxwell-Boltzmann
• Pressure and temperature are decoupled and so
  cannot respond to increases in temperature by
  expanding to cool so get positive feedback
  thermonuclear runaway
• Eventually degeneracy lifted
• Explosion

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Novae

• White dwarf with companion star
• Temperatures of up to 3 x 108K
• Time 100-1000s to eject layer
• Light curve increases to max in hours but can
  take decades to decline
• Absolute magnitude can increase by up to 11
  magnitudes
• Can be recurrent

Nova Herculis 1934 AAT
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X-ray bursters

• Neutron star
• Temperatures up to 2 x 109K
• Time 1-10s to lift degeneracy and eject layer
• Ejecta little net ejecta due to gravitational
  field

X-ray burster in NGC 6624 HST
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Supernovae Type 1a

• White dwarf
• Accreted material builds up until Chandrasekhar
  mass limit reached
• Electron degeneracy pressure no longer supports
  star
• Carbon ignited explosively in the centre
• Resulting explosion destroys star
• Used as standard candles

SN1999BE CGCG 089-013 One week after outburst
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Observations vs. Models
Accretion parameters, reaction rates, mixing,
Models
Improve input/physics
Predictions
Observations
Light curves Spectroscopy
Peak temperatures Timescales Abundances
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Relevant Parameters for modelsto understand
these scenarios need

• From astrophysics
• Temperatures energy available for reactions
• Abundances types of nuclei available for
  reactions

• From nuclear physics
• Reaction rates

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Nuclear Reaction Rates (I)

• Maxwell-Boltzmann distribution of velocities
• Penetration probability through Coulomb barrier
• Gamow peak reaction rate only significant in
  this region

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Nuclear Reaction Rates (II)

• Direct capture smooth component that drops off
  sharply with energy below the Coulomb barrier
• Enhancement in cross section if resonances exist
  in compound system

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The CNO and hot CNO cycles

• Hydrogen burning
• Above T 2 x 107K, carbon-nitrogen-oxygen cycle
  dominates
• Above 108K, proton capture on 13N supersedes
  b-decay
• Change to hot CNO cycle
• Material builds up as 14O and 15O
• Sites novae
• 4 protons 4He energy

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Advanced HCNO cycle and breakout

• Above 4 x 108K, 14O(a,p)17F supersedes b-decay of
  14O
• Build up of material in 15O and 18Ne
• Breakout reactions 15O(a,g)19Ne and 18Ne(a,p)21Na
  control subsequent energy generation
• Sites XRB and possibly novae

20Na
21Na
18Ne
19Ne
17F
18F
15O
14O
16O
13N
14N
15N
12C
13C
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NeNa and MgAl cycles

• For temperatures exceeding 3 x 107K
• Sites ONeMg novae
• Important for synthesising 22Na
• Decay of 22Na leads to a g which is ideal
  observable for a nova event
• INTEGRAL satellite aims to detect these signatures

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The rp-process

• Temperatures up to 3 x 109K
• Follows breakout from hot CNO cycles or uses
  pre-existing seed nuclei
• Increase in energy generation by a factor of 100
  over hot CNO cycles
• Energy generation rate limited by waiting points

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Experimental Nuclear AstrophysicsWhat can we
measure in the lab?
Want to measure nuclear reaction rates
Can do this directly by measuring
or if yields too low, indirectly by measuring

• Cross sections
• Resonance strengths

• Energies
• Spins and parities
• Widths
• Partial widths, branching ratios

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The story so far.

• Trying to understand explosive scenarios
• To model these, need nuclear reaction rates
• So need data on relevant nuclear parameters
• However, temperatures are high enough for nuclear
  reactions to compete with decay processes and so
  many important reactions involve radioactive
  nuclei
• Many of these radioactive nuclei have short
  lifetimes cannot make targets
• Need radioactive ion beams

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ISAC _at_ TRIUMF

• Worlds largest cyclotron and then RFQ and DTL
• Beam energies between 0.15 and 1.5 MeV/u
• Extension to ISAC II beam energies up to 6.5MeV/u

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Nuclear Astrophysics at ISAC the TUDA and
DRAGON facilities
DRAGON
TUDA
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TUDAthe TRIUMF UK Detector Array

• Studying charged particle reactions
• e.g (p,p)
• (a,p)
• (d,p)

using both direct and indirect techniques
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TUDA Layout

• 4-vane beam monitor
• Anti-scatter collimator
• Upstream detector/s
• Preamplifiers
• Target
• Downstream detector/s
• Preamplifiers
• 4-vane beam monitor
• Beam dump FC

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Detectors LEDA Louvain Edinburgh Detector Array

• Large area, highly segmented silicon strip array

Can be used in various configurations to cover
the required angular range
CD detector (double sided)
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Silicon Detectors

• Reverse biased semiconductor junction
• Charged particle loses energy in the silicon by
  creating electron-ion pairs
• Bias voltage sweeps out electrons
• Collected charge proportional to energy lost by
  particle

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TUDA Electronics

• To reduce noise, all electronics from amplifiers
  onwards are in TUDA Copper Shack
• Copper Shack acts as Faraday cage

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TUDA Targets

• Solid targets
• CH2
• CD2
• Gold foils
• Carbon foils
• Gas target
• Helium filled cell

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Recent measurement with TUDA20Na(p,p)

• Connects hot CNO breakout to rp-process
• Also important for understanding energy
  generation in NeNa cycles
• Studied states in 21Mg via resonant elastic
  scattering
• 20Na beam impinging on CH2 target
• Proton spectrum exhibits resonant features

Courtesy of A. Murphy
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Direct measurement with TUDA18Ne(a,p)21Na

• Breakout from HCNO cycle
• Reaction rate dominated by resonances in compound
  system
• Reaction protons detected in CD/LEDA dE/E
  telescope
• Trajectory reconstructed to determine position of
  reaction in gas cell
• Centre of mass energy of reaction (function of
  distance through gas cell)
• Proton yield due to each resonance
• Reaction rate for each resonance

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Indirect measurement with TUDA18Ne(d,p)19Ne(a)15
O
p

• HCNO breakout reaction
• Reaction rate dominated by resonances
• Populate excited states in 19Ne by neutron
  transfer
• Proton tags excited state and coincident a and
  15O identify decay
• Measure a-branching ratios to determine reaction
  rate

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Future measurements at TUDA
Reaction
Motivation

• 18Ne(a,p)21Na
• 18Ne(d,p)19Ne
• 17,18Ne(3He,p)
• 14O(a,p)
• 8Li(a,n)11B
• 15O(6Li,d)

• HCNO breakout
• HCNO breakout
• HCNO breakout
• HCNO advanced
• r-process
• HCNO breakout

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DRAGON Detector of Recoils and Gammas of Nuclear
Reactions

• For radiative capture reactions, (p,g), (a,g)
• Recoil mass separator
• Windowless gas target
• Gamma array
• End detectors silicon strip detector or ion
  chamber

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DRAGON Gas Target

• Windowless gas target
• Extensive pumping system
• H or He

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DRAGON Gamma Array

• 30 BGO Gamma detectors surrounding gas target

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DRAGON Separator

• Two stage separator
• Each stage consists of a magnetic dipole and an
  electric dipole plus focusing elements
• Magnetic dipole separates according to charge
  state
• Electric dipole separates according to mass
• Repetition of separation stages improves
  suppression

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DRAGON End detectors

• Choice of end detectors depending on requirements
  of reaction being studied
• Silicon strip detector (DSSSD)
• - yield, timing, position, energy
• Ion chamber (IC)
• - particle i.d., energy, timing
• Micro-channel plate (MCP)
• - local timing (with DSSSD)

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Recent measurements with DRAGON 21Na(p,g)22Mg

• Important for the production of 22Na in ONeMg
  novae
• 21Na beam on hydrogen target
• Determined resonance strengths for several states
  in 22Mg

Courtesy of S. Engel
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Upcoming measurements at DRAGON

• Reaction
• 19Ne(p,g)
• 13N(p,g)
• 12C(a,g)
• 17F(p,g)
• 25Al(p,g)

• Motivation
• HCNO breakout
• CNO/HCNO
• Carbon burning
• 18F abundance
• 26Al abundance

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TUDA vs. DRAGON
TUDA
DRAGON

• Charged particle detector array
• Direct and indirect techniques
• Flexible configuration
• Solid/gas target
• Limited beam intensity

• Recoil mass separator
• Direct technique
• Fixed configuration (variable end detector)
• Solid/gas target
• Limited reaction kinematics

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And finally..

• Study of nuclei and their reactions plays a vital
  role in our understanding of the structure and
  evolution of the universe.
• Radioactive beam facilities are necessary to
  study explosive astrophysical phenomena
• Nuclear astrophysics is a dynamic field which
  continues to advance as new facilities come
  online and better observational data becomes
  available

TUDA and DRAGON are world class,
complementary facilities for studying, directly
and indirectly, the reactions vital for our
understanding of explosive stellar environments.
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Many thanks to..

• The TUDA collaboration
• The DRAGON collaboration