Beta decay studies using total absorption gamma spectroscopy technique

A. Algora, M. Csatlós, L. Csige, J. Gulyás, M. Hunyadi, A. KrasznahorkayInstitute of Nuclear Research of the

Hungarian Acad. of SciencesDebrecen, Hungary

For the Valencia, Debrecen, GSI, Warsaw, St. Petersburg, Madrid, Strasbourg, Surrey, Jyväskylä collaboration

22

ik

kkfi 1J21

)GT(B

ZAN Z-1AN+1 + e+ + for +

ZAN Z+1AN-1 + e- + for

+ ZAN

Z-1AN+1

In principle a good description of iand f good B(GT)

ZAN + e- Z-1AN+1 + + xray EC

Basic relations

How to measure the B(GT)

B GTJi

f k kk

i( )

12 1

2 2

Theoretical quantity

S EI E

f Q E T

( )( )

( ) /

1 2

Strength function

Sgg E

B GTA

V E Ei f

f

1

6147 71

2

( )

Relationship

Beta feeding

Half life of parent

Fermi function

The problem of measuring the - feeding

ZAN

•We use Ge detectors to construct the level scheme populated in the decay

•From the intensity balance we deduce the -feeding

•What happens if we miss some gamma intensity???

ZAN

Z-1AN+1 Z-1AN+1

Apparent situation

Real situation

Experimental difficulties: Pandemonium Effect

Introduced by the work of Hardy et al (Phys. Lett 71B (1977) 307). Their study questions the possibility of building correctly a level scheme from a beta decay experiment using conventional techniques.

Several factors can contribute to this problem:

• if the feeding occurs at a place where there is a high density of levels, there is a large fragmentation of the strength among different levels and there is a large number of decay paths, which makes the detection of the weak gamma rays difficult

• we can have gamma rays of high energy, which are hard to detect

Solution

Since the gamma detection is the only reasonable way to solve the problem, we need a highly efficient device:

A TOTAL ABSORTION SPECTROMETER

1

2

NaI

Analysisd = R(B) f

Response (R):

• It is calculated for -s and -s using Monte Carlo techniques (GEANT3,GEANT4)

• Introduce branching ratios (guess, or from statistical nuclear theory)

Possible methods for the solution of the inverse problem:

• Peel off

• Regularization methods

• Bayesian progresive learning

• Maximum entropy method

See: Cano et al. NIM A 430 (1999) 333; 488,Cano PhD thesis, J. L. Tain et al. NIM A 571 (2007) 719, 728

Example of the Pandemonium effect, measurements performed at GSI On-line Mass-separator

Clustercube

6 cluster detectors in close geometry

TAS

The decay of 150Ho 2- isomer High resolution

results (cluster cube)

• No. total of : ~ 1064

• No. total of levels:~295

• Sharp resonance ~ 4.4 MeV

• B(GT) is approx. 47 % of the TAS result.

Algora et al. PRC 68 (2003) 034301

The decay of 150Ho 2- isomer:

comparison with the TAS result

3,2,12/92/112/72/3

02

2/1122/72/3

)h h f d (

GT)h ()f d (

Lucrecia, Total Absorption Gamma Spectrometer at ISOLDE (CERN)

• A large NaI cylindrical crystal 38 cm Ø, 38cm length

• An X-ray detector (Ge)• A detector• Collection point inside the

crystal

The NZ region around mass70

Drastic shape changes depending on the occupancy of orbitals. Oblate to prolate transition and shape coexistence are predicted. [A. Petrovici et al. N P. A708 (2002) 190 and ref. therein].

Free neutron orbitals with same quantum numbers than the valence protons:

Gamow-Teller decay allowed. Large part of the GT strength accesible inside the QEC window

Theoretical calculations predict different B(GT) distributions on the daughter nucleus depending on the shape of the ground state of the parent (oblate, prolate or spherical).

[I. Hamamoto et al., Z. Phys. A353 (1995) 145] [P. Sarriguren et al., Nuc. Phys. A635 (1999) 13]

E. NE. Nácher ácher et al.et al. PRL 92 (2004) PRL 92 (2004) 232501232501

The 76Sr and 74Kr β-decays

Ground state of Ground state of 7676Sr prolate (Sr prolate (ββ220.4) 0.4) as indicated in Lister et al., PRC 42 as indicated in Lister et al., PRC 42 (1990) R1191 (1990) R1191

E. Poirier et al. PRC 69 (2004) 034307Ground state of 74Kr:(60Ground state of 74Kr:(60±8)% oblate, ±8)% oblate, in agreement with other exp results in agreement with other exp results and with theoretical calculations (and with theoretical calculations (A. A. Petrovici Petrovici et al.et al.) )

IGISOL proposals I77 and I116, study of the beta decay of nuclei that are important contributors to the reactor

decay heat

Studies of the heat (decay heat) in the cool (weather)

Fission: the released energy

• Kinetic energy of fission products (FP) and neutrons

• Prompt radiation from FP and β decay energy through the natural decay of

fission products

Decay heat: definition

)()(

i

i

i

i iii

N

E

tNEtf

Decay energy of the nucleus i (gamma, beta or both)

Number of nuclei i at the cooling time t

Decay constant of the nucleus i

Requirements for the calculations: large databases that contain all the required information (nuclides, lifetimes, mean - and β-energy released in the decay, n-capture cross sections, fission yields, etc, etc …

The main motivation of this work was the study of Yoshida and co-workers (Journ. of Nucl. Sc. and Tech. 36 (1999) 135)See 239Pu example, similar situation for 235,238U

239Pu example ( component of the decay heat )

I77: measurement of the beta decay of 104,105Tc

In their work (detective work) Yoshida et al. identified some nuclei that may be responsible for the under-estimation of the E component.Possible nuclei that may be blamed for the anomaly were 102,104,105TcExplanation: certainly suffer from the Pandemonium effect, their half lives are in the range needed, and their fission yields are also correlated in the way required to solve the discrepancy

Motivations, original plans

Results of the analysis for 104Tc (preliminary)

Impact of the results on the decay heat summations (104,105Tc)

Nuclide EnergyType

ENDF/B VII (& Jeff 3.1)

TASExperiment

104Tc ELP 1595 (75) 915 (35)

EEM 1890 (30) 3263 (65)105Tc ELP 1310 (173) 805 (35)

EEM 668 (19) 1736 (70)

ΔE()= 1373104+1068105= 2441 keV; ΔE(e-)= -680104-505105=-1185 keV

Impact of the results for 239Pu

• Beta-decay still offers a very interesting field of research. The utilization of new devices and recently developed analysis techniques opens new possibilities for the understanding of nuclear structure.• We have discussed here a method to measure the B(GT) in beta decay, which can be considered more reliable. • The limitations on these kind of studies are determined by nature (we can only reach states inside the Q energy window) • The method is Total Absorption Spectroscopy• A very interesting physics programme running, mainly devoted to cases on the proton rich side (ground state shape determination, conf. mixing, p-n pairing,..). We are also involved in studies of neutron rich side which are also important, but for other reasons (decay heat) and that will allow us to gain experience for the future FAIR

Conclusions