Reaction rates in the Laboratory

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Reaction rates in the Laboratory
Example I 14N(p,g)15O

• slowest reaction in the CNO cycle
• Controls duration of hydrogen burning
• Determines main sequence turnoff glob. cluster
  ages

• stable target ? can be measured directly

g-ray detectors
Accelerator
vacuum beam line
N-target
Proton beam

• but cross sections are extremely low
• ? Measure as low an energy as possible
  then extrapolate
  to Gamow window

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Calculating experimental event rates and yields
beam of particles
hits target at rest
area A
j,v
thickness d
assume thin target (unattenuated beam intensity
throughout target)
Reaction rate (per target nucleus)
Total reaction rate (reactions per second)
with nT number density of target nuclei
I jA beam number current (number of
particles per second hitting the target)
note dnT is number of target nuclei per cm2.
Often the target thickness is specified
in these terms.
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Events detected in experiment per second Rdet
e is the detection efficiency and can accounts
for

• detector efficiency (fraction of
  particles hitting a detector that produce
  a signal that is registered)
• solid angle limitations
• absorption losses in materials
• energy losses that cause particles energies to
  slide below a detection threshold

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14N(p,g) level scheme
Gamow window0.1 GK 91-97 keV
g-signature of resonance6791 keV
g0
Direct gs capture7297 keV Ep
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LUNALaboratory Underground for Nuclear
Astrophysics(Transparencies F. Strieder
http//www.jinaweb.org/events/tucson/Talk_Strieder
.pdf)
Gran Sasso Mountain scheme
11 Mio cosmic ray suppression
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Spectra above and under ground
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Beschleuniger bild
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Setup picture
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Spectrum overall
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Spectrum blowup
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Results
GamowWindow
Formicola et al. PLB 591 (2004) 61
New S(0)1.7 - 0.2 keVb (NACRE 3.2 - 0.8)
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New Resonance ?
Resonance claim and TUNL disproof
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Effect that speculative resonance would have had
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• Age of oldest globular clusters Increases by
  0.7-1 Gyr with new data (mainly reevaluation
  of subthreshold resonance influence)

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Example II 21Na(p,g)22Mg
problem 21Na is unstable (half-life 22.5 s)
solution radioactive beam experiment in inverse
kinematics 21Na p ? 22Mg g
thick 21Na production target
hydrogen target
22Mg products
Accelerator I
Accelerator 2
p beam
21Na beam
g-detectors
ionsource
particleidentification
difficulty beam intensity typically 107-11 1/s
(compare with 100 mA protons 6x1014/s)
? so far only succeeded in 2 cases 13N(p,g) at
Louvain la Neuve and 21Na(p,g) in
TRIUMF (for capture reaction)
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DRAGON _at_ TRIUMF
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Results
Result for 206 keV resonance
S. Bishop et al. Phys. Rev. Lett. 90 (2003) 2501
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Example III 32Cl(p,g)33Ar
Shell model calculations Herndl et al. Phys. Rev.
C 52(1995)1078
? proton width strongly energy dependent? rate
strongly resonance energy dependent
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NSCL Coupled Cyclotron Facility
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Installation of D4 steel, Jul/2000
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Fast radioactive beams at the NSCL

• low beam intensities
• Impure, mixed beams
• high energies (80-100 MeV per nucleon)
  (astrophysical rates at 1-2 MeV per nucleon)

? great for indirect techniques

• Coulomb breakup
• Transfer reactions
• Decay studies

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Setup
Focal planeidentify 33Ar
S800 Spectrometer at NSCL
34Ar
Beamblocker
33Ar
33Arexcited
34Ar
d
Plastic
People
Plastictarget
34Ar
D. Bazin R. Clement A. Cole A. Gade T.
Glasmacher B. Lynch W. Mueller H. Schatz B.
Sherrill M. VanGoethem M. Wallace
Radioactive 34Ar beam84 MeV/u T1/2844 ms(from
150 MeV/u 36Ar)
SEGAGe array(18 Detectors)
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S800 Spectrometer
SEGA Ge-array
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New 32Cl(p,g)33Ar rate Clement et al. PRL 92
(2004) 2502
Doppler corrected g-rays in coincidence with
33Ar in S800 focal plane
g-rays from predicted 3.97 MeV state
stellar reaction rate
reaction rate (cm3/s/mole)
33Ar level energies measured 3819(4) keV (150
keV below SM) 3456(6) keV (104 keV below SM)
temperature (GK)
Typical X-ray burst temperatures