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High-precision branching ratio of Gallium-62 - 2005

date: February 2005


Participants: A. Bey, N. Adimi, B. Blank, G. Canchel, J. Giovinnazo, I. Matea

In collaboration with: JYFL, GANIL, LPC Caen


The β-decay of the heavy (N=Z= 31) Fermi super-allowed emitter 62Ga has been investigated at the IGISOL facility of the Accelerator Laboratory of the University of Jyväskylä. Four very weak intensity (<0.1%) g rays were identified and allowed a partial decay scheme reconstruction in the daughter nucleus 62Zn. The branching ratio of the 0+ -> 0+ super-allowed transition established from this study 99.983(36) % is in agreement with previous measurements. The universal Ft value obtained 3074.59 s agrees well with the other twelve well-known Fermi decays. Furthermore, the upper limit set on the isospin-symmetry-breaking correction is compatible with theoretical predictions.



Super-allowed 0+ -> 0+ beta decay allows to test the weak-interaction standard model [1] with its CVC hypothesis and to determine the Vud matrix element of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. This matrix has to be unitary:

The best determination of the Vud matrix element is achieved with beta decay, where it can be determined from the corrected Ft value. The Ft value itself is a function of the decay Q value, the half-life and the branching ratio of the super-allowed decay. Vud is determined as follows [2,3] :

K is a constant and G’F is the coupling constant for pure leptonic decays determined from the weak decay of the muon.

62Ga is one of the heavier N=Z nuclei for which we contributed to a precise determination of the three quantities:

- Half-life of the emitter (T1/2),

- Masse difference between emitter and daughter nucleus (QEC)

- Super-allowed branching ration for the 0+ -> 0+ decay branch (B.R.)

As follow-up of our half-life measurements [4,5], we determined now the branching ratio [6] with the necessary precision in an experiment performed at the University of Jyväskylä (Finland) in February 2005. 0


Experimental setup

As in our previous experiments, 62Ga was produced by the fusion-evaporation reaction 64Zn(p,3n)62Ga. A primary proton beam at 48 MeV and an intensity of 20\muA impinged on a 3mg/cm2 64Zn target at the entrance of IGISOL. The reaction products were either just selected by the analyzing magnet of IGISOL or by the Penning trap JYFLTRAP, which allowed to have pure 62Ga beams.

Figure 1: Schematic drawing of the experimental setup showing the plastic scintillator to detect the beta particles as well as three Germanium clover detectors for the gamma rays.

The 62Ga was then directed onto a tape situated in the center of a cylindrical plastic scintillator to detect the beta particles, which was itself surrounded by three Germanium clover detectors (« small EXOGAM clovers ») to detect the gamma rays.



We have accumulated 7*107 decays of 62Ga. Examples of decay spectra are presented in figure 2. These spectra together with the number of decays as registered by the plastic scintillator allowed to determine the branching ratios for all observed gamma rays. Figure 3 is the result of the present experiment and gives all branching ratios determined as well as the half-life of 62Ga.

Figure 2: Beta-gamma coincidence spectra showing the gamma rays observed in the present work.
Figure 3: Decay scheme of 62Ga from the present work

Figure 4 presents all Ft value determined with high precision up to now. The value of 62Ga nicely fits in this systematics.

Figure 4: Summary of high-precision Ft value including 62Ga from the present work.



The present study allowed to establish a high-precision value for the super-allowed decay of 62Ga to the ground state of 62Zn of B.R. = 99.893(24)%. This value is in agreement with other results obtained during the present work. The precision value available for the half-life as well as the Q value measured recently [7] allowed to include 62Ga in the systematics of high-precision Ft values.



[1] R. P. Feynman and M. Gell-Mann, Phys. Rev. 109, 193 (1958).

[2] I. S. Towner and J. C. Hardy, Phys. Rev. C 77, 025501 (2008).

[3] I. S. Towner and J. C. Hardy, Phys. Rev. C 66, 035501 (2002).

[4] B. Blank, Eur. Phys. J. A 15, 121 (2002).

[5] G. Canchel et al, Eur. Phys. J. A 23, 409 (2005).

[6] A. Bey et al., Eur. Phys. J. A 36, 121 (2008).

[7] T. Eronen et al., Phys. Lett. B 636, 191 (2006).