New Terbium Isotope,Tb152

Abstract

A careful examination of photon and electron spectra from cyclotron-produced mixtures of light terbium isotopes has led to the identification of a new isotope, Tb 152 , with an 18.5-hr half-life. The 344.1-kev transition from first excited state to ground in daughter Gd 152 has been identified and shown to be identical in energy to a transition associated with the beta decay of 9.3-hr Eu 152w to the same daughter nucleus. Gamma transitions of 180 and 265 kev are also assigned to the decay of Tb 152 .T ERBIUM-152 has not been previously reported despite the fact that Tb 151 , Tb 153 , and Tb 154 have been known for some time. In this study Tb 152 has been produced and given a mass assignment in a series of bombardments using alpha particles accelerated in the Berkeley 60-inch cyclotron. The half-life has been found to be 18.5 ±0.5 hr. The similarity of the half-lives of two neighboring isotopes, Tb 151 (19 hr) and Tb 164 (17 hr), Gamma energy (kev) FIG. 1. Gamma spectra of terbium isotopes by alpha-particle bombardment of enriched europium isotopes. (A) 37-Mev alphas on Eu 1S3 , 3X3-inch Nal(Tl) detector; (B) 37-Mev alphas on Eu lw , 3X3-inch detector; and (C) 48-Mev alphas on Eu 151 , 1.5X 1-inch detector. f This work was performed under the auspices of the U. S. Atomic Energy Commission. * Present address: University Institute for Theoretical Physics Copenhagen, Denmark. makes it clear why this isotope has been previously overlooked. A series of bombardments was undertaken using the enriched isotopes, Eu 151 (91.9% Eu 151 , 8.1% Eu 153 ) and Eu 163 (5.0% Eu 151 , 95.0% Eu 153 ), with bombarding energies of 48 Mev and 37 Mev. At the higher energy the most probable-reaction is (a ,4^), while the lower energy is below the threshold for this reaction and produced mostly (a,3n).After bombardment the elements were chemically separated by means of a cation-exchange method described elsewhere. 1 Gamma rays emitted by the terbium isotopes were studied using 3X3-inch and lXlJ-inch Nal(Tl) crystal scintillation counters in conjunction with a 100-channel pulse-height analyzer. Accurate gamma-ray energies were obtained from conversion electron spectra taken in 180-degree-focusing permanentmagnet electron spectrographs described by Smith and Hollander. 2 In Fig. 1, curve A shows the gamma spectrum of the chemically separated terbium isotopes following 37-Mev alpha-particle bombardment of Eu 153 . This sample should consist mostly of Tb 154 with smaller amounts of Tb 155 and very little Tb 153 and Tb 152 . The three peaks have energies (determined precisely by conversion electron measurements) of 123.2, 248.1, and 347.1 kev and have previously been ascribed to Tb 154 decay. 3 -4 Curve B of Fig. 1 shows the gamma spectrum following 37-Mev alpha-particle bombardment of Eu 151 . Here the majority of product should be Tb 152 with smaller amounts of Tb 153 and Tb 154 . Again a peak is seen at 340 kev and its rate of decay as obtained from a series of spectra taken at various times after bombardment indicates a half-life nearly...

Discovery of samarium, europium, gadolinium, and terbium isotopes

“…[22]. An enriched 112 Sn target was bombarded with a 190 MeV 32 S beam from the Dubna U-300 cyclotron. The reaction products were identified with the on-line BEMS-2 mass separator and by measuring X-and γ-rays.…”

“…In 1985 Ollivier et al reported the discovery of 145 Tb in "Identification and decay of 12s 143 Tb" [103]. A 191 MeV 35 Cl beam from the Grenoble SARA accelerator bombarded an enriched 112 Sn target and 143 Tb was produced in the fusion-evaporation reaction 112 Sn( 35 Cl,2p2n). Gamma-ray coincidences were measured with intrinsic Ge detectors in combination with a He-jet system.…”

“…Very neutron deficient isotopes of samarium and europium" by Nowicki et al reported the observation of 140 Eu[22]. An enriched112 Sn target was bombarded with a 190 MeV 32 S beam from the Dubna U-300 cyclotron. The reaction products were identified with the on-line BEMS-2 mass separator and by measuring X-and γ-rays.…”

“…described the first observation of 141 Gd in the 1986 paper "Exotic neutron-deficient nuclei near N=82"[25]. Targets of112 Sn were bombarded with beams of35 Cl and 32 S beams from the Grenoble SARA accelerator. The residues were separated with an on-line mass separator and a He-jet system.…”

“…A50 Cr beam from the Daresbury Laboratory Van de Graaff accelerator was incident on a94 Mo target at 230 MeV. Gamma rays, 32 S + 112 Sn and in35 Cl +112 Sn reactions but with a minor intensity in the latter one." This half-life agrees with the currently accepted value of 24.5(5) s. Gd was identified in 1986 by Lunardi et al in "First observation of yrast γ-rays in the N =78 nuclei 142 Gd and 141 Eu"[84].…”