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%