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 -decay β β probability over the daughter-nucleus levels provides information of relevance for the understanding of the structure of nuclei or for other fields as astrophysics or reactor technology � ± Fermi / Gamow-Teller • Basic process: simple � �� ± ± and sensitive to the Ψ τ στ Ψ � � wave function �� ± • In general the bulk of the strength lies outside the Q β β window β β Exception: • β β +/EC for A ∼ β β ∼ 150, ∼ ∼ A ∼ ∼ 100, N ∼ ∼ ∼ ∼ Z ∼ ∼
β + side Previous work at the β β β π ����� π π π π ������ π π π στ + Gamow-Teller στ στ στ resonance ν ����� ν ν ν 64 ν ����� ν ν ν Odd-Odd N=83 nuclei 82 above 146Gd ��� ���� � ��� ���� � ���� ���� ���� ��� ���� � ��� ���� � ���� ���� ���� ��� ���� � ��� ���� � ���� ���� ����
Oblate-prolate 2 /4 π ) competition ������������ �� %� � ∗ � 5 Σ B(GT) (g A ����������� 4 �������� !"����#����$� ������ 3 0 g [413]7/2 9/2 2 / (MeV) 1 ] [301]3/2 1 0 3 Oblate [ 42 40 [404]9/2 p 2 [422]5/2 1/2 [303]5/2 38 [ 4 [440]1/2 3 38 1 36 f ] 3 / 2 5/2 -5 34 [312]3/2 p 32 [321]1/2 [310]1/2 3/2 30 28 28 1 2 Prolate 7 / 3 ] 0 3 [ f -10 [312]5/2 7/2 [321]3/2 Q EC [ 3 3 0 ] 1 20 / 2 [211]1/2 [200]1/2 [202]3/2 s 0 1 2 3 4 5 6 7 1/2 -15 d 3/2 Energy (MeV) -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 � ∗ � ������������ ���������������������� N ∼ Z nuclei with A ∼ 70-80 & ' β + side Previous work at the β β β
Neutron capture is the source β - side Future work at the β β β of elements heavier than iron The interplay A Z+1 β - -decay between β β -decay β β β β β and (n, γ γ ) γ γ determine the A Z A+1 Z isotopic abundances (n, γ γ ) γ γ • For the s-process (close to stability) the relevant quantity (except at branching points) is σ σ (n, γ σ σ γ ) (experimental) γ γ • For the r-process (very far from stability) the relevant quantity is T 1/2 (theoretical) ✦ trimming of the codes to ✦ ✦ ✦ reproduce S β β may help to β β improve their predictive power
Example: 104 Tc Example: Ni isotopes QRPA: P. Möller & K.L. Kratz (taken from A. Lisetskiy) T1/2=2.7 min (Exp: 18.3 min) Quenching for GT operator: up to q=0.37! (Standard value is 0.70-0.75) P. T. Hosmer et al., PRL 94, 112501 (2005) Anomalous quenching or wrong S β distribution?
The TAS technique • Total absorption gamma-ray spectroscopy is the best technique to measure the β β -decay strength distribution over the entire β β energy window in particular for nuclei far from the stability. • Total absorption spectroscopy, using large 4 π π scintillation detectors , π π 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. β -decay β β β
The Pandemonium effect in 150 Ho decay: CLUSTER-CUBE: 6 EUROBALL ε T Clusters in cubic geometry ε P CLUSTER: Efficiency 7 Ge detectors, CLUSTER-CUBE at GSI 60% each HR S � = 0.4 TAS S � 1064 γ γ -rays γ γ 295 levels Algora et al PRC50(2002)
An ideal TAS (100% peak efficiency) provides directly S β but • How do we extract the β β -strength from real TAS β β spectra? Statement of the problem: β -decay β β β � Relation between � � = β -strength S β and � � � � � � � − � � � β β -intensity I β : Relation between TAS data and the β -intensity distribution: � R ij � � � = � � � � � � � = ✦ ✦ � ✦ ✦ � �� � � 3 2 Response R ij : probability that for decay to level j we 1 register a count in channel i � � − � ! � * ! = ⊗ ) �� )( ( 0 � � =
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 Exp. background close to MC the end point (Cano et al. NIMA430, p.488) 2. Demonstration of the accuracy of Monte Carlo simulations to Pile-up obtain the spectrometer response ( Cano et al. NIMA430, p.333)
3. Investigation of the adequacy of several ✦ algorithms for the solution of the TAS inverse problem (Tain et al., NIMA submitted) LINEAR REGULARIZATION ✬ ✬ ✬ ✬ MAXIMUM ENTROPY ✪ ✪ ✪ ✪ EXPECTATION-MAXIMIZATION ✪ ✪ ✪ ✪ : stat. mod. b.r. : “flat” b.r. : reference 4. Investigation of the dependency of the result on ✥ the assumption about the cascade branching ratios (Tain et al., NIMA accepted)
Existing β β -decay TAS: β β St. Petersburg INEL TAS LBL TAS @ GSI Lucrecia @ ISOLDE TAS @ JYFL 38 35 30 30 15 15 10 7.7 7.5 20 4.6 5.7 11 25 10 35 5 15 38 1 MeV 5 MeV Size TAS Material (cm) ε P ε T ε P ε T ε ε ε ε ε ε ε ε ε ε ε ε St. Pt. NaI(Tl) 0.47 0.87 0.25 0.71 20 × × × 30 × INEL NaI(Tl) 25 × × × 30 × 0.65 0.90 0.45 0.76 LBL NaI(Tl) 35 × × 35 0.65 0.97 0.52 0.89 × × Lucrecia NaI(Tl) 38 × × 38 × × 0.62 0.89 0.44 0.79
TAS for ALTO ? 25 BaF 2 : Surrey-Valencia TAS (Rocinante) 5 25 12 Crystals ε P ε T ε ε ε ε ε ε 1 MeV 0.70 0.89 5 MeV 0.43 0.79 • Efficiency compares favorably with Lucrecia Ancillary detectors: • Small sensitivity to very low • X-ray/ γ γ γ γ -ray detectors energy neutrons • β β β β -detectors • Very good timing resolution • n-detectors?
TAS measurements at the neutron rich side Challenge: β -delayed neutrons and the subsequently emitted γ -rays may become a source of contamination End-nucleus γ γ γ -rays are γ prompt with the β β β β -decay: γ γ γ γ they must be measured with Ge + n-detectors and subtracted (anyhow needed to obtain the complete S β β ) β β n cross-sections Neutrons interact through: Neutrons are strongly dependent on • elastic scattering energy and • inelastic scattering → → γ γ - γ -rays rays → → γ γ γ γ γ isotopic • capture → → γ → → γ γ γ - γ -rays rays γ γ γ composition • other: (n,p), (n, α α )… → α α → → → γ γ γ γ γ - -rays rays γ γ γ → → → → MC simulation
Geant4 MC simulation (Using nuclear statistical model) 87 Br β β β -decay: β Q β β = 6.85 MeV β β Rejection of n-induced S n = 5.52 MeV signals by timing ε ε neut = 1% ε ε P n = 2.6 % 5 ns 147 Cs β β -decay: β β Q β β = 9.2 MeV β β S n = 4.45 MeV ε β β n- γ γ = 24% ε β β γ γ ε ε P n = 27.5 % ε neut = 11% ε ε ε
Conclusions: Conclusions: • The TAS technique is the most powerful technique to The TAS technique is the most powerful technique to • investigate the β β - -strength strength distribution far from stability, distribution far from stability, investigate the 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
St. Petersburg TAS vs. LBL TAS @GSI 156 Tm β β β β -decay
γ ) ! TAC @ FZK and n_TOF for (n, γ γ γ ε P ε T ε ε ε ε ε ε 15 1 MeV 0.90 0.98 5 MeV 0.80 0.91 20 spherical BaF 2 , 42 Crystals
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