-Decay Total Absorption Spectroscopy: A Tool for Applied and - - PowerPoint PPT Presentation

β β β β-Decay Total Absorption Spectroscopy: A Tool for Applied and Fundamental Research

J.L. Tain Jose.Luis.Tain@ific.uv.es http://ific.uv.es/gamma/ Instituto de Física Corpuscular C.S.I.C - Univ. Valencia

An accurate knowledge of the distribution of the β β β β-decay probability over the daughter-nucleus levels provides information

• f relevance for the understanding of the structure of nuclei or for
• ther fields as astrophysics or reactor technology
• Basic process: simple

and sensitive to the wave function

• In general the bulk of

the strength lies

• utside the Qβ

β β β window

Exception:

• β

β β β+/EC for A∼ ∼ ∼ ∼150, A∼ ∼ ∼ ∼100, N∼ ∼ ∼ ∼Z

• Ψ

Ψ

± ±

στ τ

±

• ±
• Fermi / Gamow-Teller

π π π π π π π π ν ν ν ν ν ν ν ν

64 82

• Gamow-Teller στ

στ στ στ+ resonance Odd-Odd N=83 nuclei above 146Gd

Previous work at the β β β β+ side

Oblate-prolate competition

• 0.4
• 0.3
• 0.2
• 0.1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 20 28 38 28 30 38 40 32 34 36 42 d s f p f p g

3/2 1/2 7/2 3/2 5/2 1/2 9/2 [404]9/2 [413]7/2 [422]5/2 [ 4 3 1 ] 3 / 2 [440]1/2 [ 3 1 ] 1 / 2 [303]5/2 [312]3/2 [321]1/2 [301]3/2 [310]1/2 [ 3 3 ] 7 / 2 [312]5/2 [321]3/2 [ 3 3 ] 1 / 2 [211]1/2 [202]3/2 [200]1/2

• 15
• 10
• 5

(MeV)

1 2 3 4 5 1 2 3 4 5 6 7

Energy (MeV) ΣB(GT) (gA

2/4π)

Prolate Oblate QEC

• !"#$
• %

∗

∗

&' N∼Z nuclei with A∼70-80

Previous work at the β β β β+ side

AZ A+1Z AZ+1

(n,γ γ γ γ) β β β β- -decay

Neutron capture is the source

• f elements heavier than iron

The interplay between β β β β-decay and (n,γ γ γ γ) determine the isotopic abundances

• For the s-process (close to

stability) the relevant quantity (except at branching points) is σ σ σ σ(n,γ

γ γ γ) (experimental)

• For the r-process (very far

from stability) the relevant quantity is T1/2 (theoretical) ✦ ✦ ✦ ✦ trimming of the codes to reproduce Sβ

β β β may help to

improve their predictive power Future work at the β β β β- side

Example: 104Tc QRPA: P. Möller & K.L. Kratz T1/2=2.7 min (Exp: 18.3 min) Example: Ni isotopes (taken from A. Lisetskiy)

• P. T. Hosmer et al.,

PRL 94, 112501 (2005)

Quenching for GT operator: up to q=0.37! (Standard value is 0.70-0.75)

Anomalous quenching or wrong Sβ distribution?

β β β β-decay

• Total absorption gamma-ray spectroscopy is the best technique

to measure the β β β β-decay strength distribution over the entire energy window in particular for nuclei far from the stability.

• Total absorption spectroscopy, using large 4π

π π π scintillation detectors, aims to detect the full γ γ γ γ-ray cascade rather than individual γ-rays as in high resolution spectroscopy, using Ge detectors.

• Total absorption spectroscopy avoids the “Pandemonium effect”

(misplacement of β-strength) when constructing level schemes in high resolution spectroscopy.

The TAS technique

CLUSTER-CUBE at GSI The Pandemonium effect in 150Ho decay: CLUSTER-CUBE: 6 EUROBALL Clusters in cubic geometry CLUSTER: 7 Ge detectors, 60% each

Efficiency

εP εT

Algora et al PRC50(2002)

1064 γ γ γ γ-rays 295 levels

0.4 S S

TAS

• HR
• =

• How do we extract the β

β β β-strength from real TAS spectra?

Relation between TAS data and the β-intensity distribution:

• =
• −

=

β

Relation between β-strength Sβ and β-intensity Iβ: Statement of the problem:

β β β β-decay

Response Rij: probability that for decay to level j we register a count in channel i

An ideal TAS (100% peak efficiency) provides directly Sβ but

• =
• Rij

✦ ✦ ✦ ✦

1 2 3

( )( )

! * !

• −

=

⊗ =

Solution: “de-convolute” TAS spectrum using the spectrometer “decay” response (inverse problem) Requirements: Requirements:

• Spectrum must be clean

Spectrum must be clean: : → eliminate background and contaminations

• Response must be accurately known

Response must be accurately known: : → response should depend “weakly” on de- excitation branching ratios → high efficiency

• Solution of inverse problem must be stable

Solution of inverse problem must be stable

• Historically there has been some lack of confidence on the

reliability of TAS results

• During the past few years we have undertaken a systematic

investigation of systematic uncertainties associated with the analysis of TAS data:

• 1. Accurate

calculation of pulse pile-up which constitutes an intrinsic background close to the end point (Cano et

• al. NIMA430, p.488)
• 2. Demonstration of

the accuracy of Monte Carlo simulations to

• btain the

spectrometer response (Cano et al.

NIMA430, p.333) Pile-up Exp. MC

• 3. Investigation of the

adequacy of several algorithms for the solution of the TAS inverse problem (Tain et

al., NIMA submitted)

• 4. Investigation of the

dependency of the result on the assumption about the cascade branching ratios

(Tain et al., NIMA accepted) LINEAR REGULARIZATION ✬ ✬ ✬ ✬ MAXIMUM ENTROPY ✪ ✪ ✪ ✪ EXPECTATION-MAXIMIZATION ✪ ✪ ✪ ✪

: stat. mod. b.r. : “flat” b.r. : reference

✦ ✥

Existing β β β β-decay TAS:

30 20 4.6 7.7 10 25 30 11 10 5.7 35 35 15 15 5 38 38 7.5 15

• St. Petersburg

TAS @ JYFL INEL TAS LBL TAS @ GSI Lucrecia @ ISOLDE 5 MeV 1 MeV 0.79 0.44 0.89 0.62 38× × × ×38 NaI(Tl) Lucrecia 0.89 0.52 0.97 0.65 35× × × ×35 NaI(Tl) LBL 0.76 0.45 0.90 0.65 25× × × ×30 NaI(Tl) INEL 0.71 0.25 0.87 0.47 20× × × ×30 NaI(Tl)

• St. Pt.

ε ε ε εT ε ε ε εP ε ε ε εT ε ε ε εP

Size (cm) Material TAS

25 5 25

TAS for ALTO ?

• Efficiency compares

favorably with Lucrecia

• Small sensitivity to very low

energy neutrons

• Very good timing resolution

BaF2: 12 Crystals

Surrey-Valencia TAS (Rocinante)

0.79 0.43 5 MeV 0.89 0.70 1 MeV

ε ε ε εT ε ε ε εP

Ancillary detectors:

• X-ray/γ

γ γ γ-ray detectors

• β

β β β-detectors

• n-detectors?

Challenge: β-delayed neutrons and the subsequently emitted γ-rays may become a source of contamination

γ γ γ γ

TAS measurements at the neutron rich side

End-nucleus γ γ γ γ-rays are prompt with the β β β β-decay: they must be measured with Ge + n-detectors and subtracted (anyhow needed to obtain the complete Sβ

β β β)

Neutrons Neutrons interact through:

• elastic scattering
• inelastic scattering →

→ → → γ γ γ γ γ γ γ γ-

• rays

rays

• capture →

→ → → γ γ γ γ γ γ γ γ-

• rays

rays

• other: (n,p), (n,α

α α α)… → → → → γ γ γ γ γ γ γ γ-

• rays

rays n cross-sections are strongly dependent on energy and isotopic composition → → → → MC simulation

Geant4 MC simulation

Rejection of n-induced signals by timing

87Br β

β β β-decay: Qβ

β β β= 6.85 MeV

Sn= 5.52 MeV Pn= 2.6 %

147Cs β

β β β-decay: Qβ

β β β= 9.2 MeV

Sn= 4.45 MeV Pn= 27.5 % ε ε ε εneut= 1% ε ε ε εβ

β β βn-γ γ γ γ= 24%

ε ε ε εneut= 11%

5 ns

(Using nuclear statistical model)

Conclusions: Conclusions:

• The TAS technique is the most powerful technique to

The TAS technique is the most powerful technique to investigate the investigate the β β-

• strength

strength distribution far from stability, distribution far from stability, supplemented when necessary by delayed particle supplemented when necessary by delayed particle spectroscopy spectroscopy

• Many experimental studies are still possible. ALTO

Many experimental studies are still possible. ALTO seems an ideal place to carry out new measurements seems an ideal place to carry out new measurements at the neutron rich side, not extremely far from stability at the neutron rich side, not extremely far from stability

• Any means to produce clean sources and eliminate

Any means to produce clean sources and eliminate backgrounds will be essential to obtain reliable results backgrounds will be essential to obtain reliable results

The End

156Tm β

β β β-decay

• St. Petersburg TAS vs. LBL TAS @GSI

BaF2, 42 Crystals

TAC @ FZK and n_TOF

20 15

0.91 0.80 5 MeV 0.98 0.90 1 MeV

ε ε ε εT ε ε ε εP

for (n,γ γ γ γ) !

spherical