lawrence livermore national laboratory nicholas scielzo lawrence fellow physics division, physical...
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Lawrence Livermore National Laboratory
Nicholas ScielzoLawrence Fellow
Physics Division, Physical Sciences
LLNL-PRES-408002
Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Precise neutrino and neutron spectroscopy using trapped radioactive ions
August 8, 2009
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Ion traps
Efficiently collect any isotope nearly at rest, suspended only by electromagnetic fields
Recoil nucleus momentum available for study
<1mm3 volume
Combine ion-trapping techniques with modern detector technology to perform -decay and -delayed neutron decay measurements with unprecedented precision
Entire decay kinematics reconstructed to determine energy/momenta of:
(1)Neutrinos in beta decay
(2)Neutrons in beta-delayed neutron emission
Neutrino
escapes
detection!
Neutron emission
n
Spectroscopy of “invisible” and difficult-to-detect particles
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Scientific goalsScientific goals
Nuclear beta-decay correlations Beta-delayed neutron emission
Improved decay spectroscopy can address many interesting questions:
Existence of new particles influences the correlation between momenta of emitted beta and neutrino particles
Large Hadron Collider at CERN
8.6 km
ion trap for beta-decay
86 cmTable-top device sensitive to physics at TeV energies!
Are there massive particles that have never been observed?
Measurements of beta-delayed neutron emission branching ratios and energies are needed to better understand:
• the distribution of stable nuclei produced by the rapid-neutron capture process (r process) when the exotic nuclei produced decayed back to stability
• the evolution of nuclear structure in neutron-rich nuclei
• fission reactor performance
SN1987A supernova: r-process site
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Nuclear decay
dddEEEEpEZFdW eeeeee2
00 ,
d
u
W
Compare experimental values to SM predictions
Put limits on terms “forbidden” by SM
...1 D
EE
ppB
E
pA
E
pJb
E
ma
EE
ppdWdW
e
e
e
e
e
e
e
eo
Hint 21 CSe C Se5 21 CVe
C Ve5
122 1 CTe
C Te5
251 CAe5 C Ae
251 CPe5 C Pe Coupling constants:
CS, CV, CA, CT
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The angular correlation
Neutrino too difficult to detect – correlation must be inferred from nuclear recoil
Sensitive to detector thresholds and resolution
Correlation easily perturbed by scattering
Nuclear recoil
Neutrino escapes detection!
nu
mber
of
eve
nts
(arb
. u
nit
s)200150100500
Recoiling Nucleus Energy (eV)
a = 0
a = 1
Example Recoil Energy Spectrum (21Na)
a > 0 leads to larger average recoil energy
Direct detection – acceleration of daughters
Energy shift in subsequent particle emission
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8Li decay
8Li
8Be
t1/2=0.84 s
MeV
100%
Q=16.003 MeV
In most beta decays there are 5 degrees of freedom:
3 × 3 - 4 = 5
Of course, 8Li (and 8B) decays are not like most beta decays – the excitation energy of the 8Be daughter is broad, leading to another degree of freedom – the beta-decay Q value.
Even still, we can overconstrain the system – by measuring 7 degrees of freedom!
• energy, , •energy sum the Q value • energy difference recoil energy, r r
energy/momentum of beta, neutrino, nucleus
conservation of energy/momentum
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Beta-neutrino correlation in 8Li
DSSD Plastic scintillator
8Li+
8Li 8Be*
Neutrino momentum/energy can be determined from and recoiling 8Be momentum/energy
momentum/energy measured from DSSD and plastic scintillator detector
8Be momentum/energy determined from particle break-up… with no recoil, particles would have same energy and would be back-to-back. With recoil, energy difference can be up to 730 keV and the angle can deviate by as much as ±70
Low mass of 8Li and Q ≈ 13 MeV lead to large recoil energies of 12 keV which makes the correlation easier to measure. Other correlation measurements have had to deal with recoil energies of only 0.2-1.4 keV.
Beta-neutrino correlation measurement takes advantage of 1 mm3 trapped ion sample and position and energy resolution of double-sided silicon strip detectors to precisely reconstruct momentum vectors of all emitted particles (including neutrino!)
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Beta-delayed neutron emission
Plastic scintillator
Plastic
scintillator
n
94Sr
95Rb+
95Rb 95Sr* 94Sr* n
• 1-mm3 trapped-ion sample and 1-ns timing resolution of detectors determines neutron momentum/energy to ~1% from time-of-flight of recoiling daughter ion
• intrinsic efficiency for MCP detectors can be ~100%
• many fission fragments available from the newly-developed CARIBU facility (an intense source of fission-fragment beams) at ANL
Novel approach: determine neutron energies and branching ratios by detecting beta particles and recoil ions that emerge from ion trapProvide reliable data for: r-process nucleosynthesis, nuclear structure, nuclear reactor performance, modeling of environments where fission fragments are produced
MCP ion detector
ExampleQ = 4.9 MeVt1/2 = 0.378 secPn ≈ 9%