137Ba Double Gamma Decay Measurement with GAMMASPHERE

The study of the electromagnetic moments (EM), and decay probability, provides detailed information about nuclear wave functions. The well-know properties of EM interactions are good for extracting information about the motion of nucleons. Higher order EM processes always occur, but are usually too weak to be measured. In the case of a 0+ → 0+ transitions, where a single gamma transition is forbidden, the simultaneous emission of two γ-rays has been studied. An interesting opportunity to further investigate 2-photon emission phenomena is by using a standard 137Cs source populating, via β-decay, the Jπ = 11/2- isomeric state at 662 keV in 137Ba. In this case, two photon process can have contributions from quadrupole-quadrupole or dipole-octupole multipolarities in direct competition with the high multipolarity M4 decay. Since the yield of the double gamma decay is around six orders of magnitude less than the first order transition, very good statistics are needed in order to observe the phenomena and great care must be taken to suppress the first-order decay. The Gammasphere array is ideal since its configuration allows a good coverage of the angular distribution and the Compton events can be suppressed. Nevertheless the process to understand and eliminate the Compton backgroundmore » is a challenge. Geant4 simulations were carried out to help understand and correct for those factors.« less


2-photon decay
One of a family of second order electromagnetic processes.
They are sensitive to the initial and final state wave functions.
On the probability of a collaboration of two light quanta in an elementary process M. Goppert. Natureweiss 17 932 (1929) A total of 68 Compton suppresed HpGe were used.
Detector selection.
Total time (dead time).
Factor of 2 accounting for symmetrized matrix.  (12) The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.
E. Merchan (UMass Lowell) 20 / 20 The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.
E. Merchan (UMass Lowell) 20 / 20 The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.
E. Merchan (UMass Lowell) 20 / 20 The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.
E. Merchan (UMass Lowell) 20 / 20 The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.
E. Merchan (UMass Lowell) 20 / 20 The branch of the 137 Ba cascade of two photons has been measured.
The calculated branching ratio is of 1.12 ± 0.9 × 10 −7 The intensity of the 378 keV transition has been measured to be 1.06(9) × 10 −5 The cascade is about two orders of magnitude less than the expected double gamma decay. A distribution for the double gamma decay has been observed, its angular distribution must be carefully studied. Compton correction is ongoing by using the GS simulation. Thanks.