Short Note

The Study of Short-Lived Nuclei in the Region Z= 59-68

G.D. Alkhazov, K.A. Mezilev, and Yu.N. Novikov
Leningrad Nuclear Physics Institute, Leningrad, USSR

N. Ganbaatar, K.Ya. Gromov, V.G. Kalinnikov, A. Potempa, E. Sieniawski, and F. Tarkanyi
Joint Institute for Nuclear Research, Head Post Office, P.O. Box 79, 101000 Moscow, USSR

Received January 19, 1983
 

Abstract
b+ -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. Q _EC values have been obtained and new isomeric states have been identified for the first time.
 

Knowledge of accurate atomic masses is both of fundamental and practical importance. Mass determination for nuclides far from the stability line requires mass differences derived from b -endpoint measurements.
At the IRIS on-line mass-separator facility [1] using Ge(HP) technique systematic investigation of b + -endpoint energies were undertaken for neutron deficient RE isotopes.
The nuclei were produced in spallation reaction on Ta target with 1 GeV proton beam from synchrocyclotron. The b +, g , X spectra of mass separated samples were recorded parallely using Ge(HP) and Ge(Li) detectors, which allowed to analyse the isotopic composition of the isobars in the samples and to check possible contamination of other (A ± 1, A-16) masses. For isotopic identification of the components of b + spectra the decay characteristics (time dynamic) of the spectrum were followed. The details of sample production, measurement techniques, identification principles and data analysis were very similar to those employed in our previous studies [2]. The principles of data analysis of continous positron spectra will be published elsewhere.
The experimental b + -endpoint energy values and the derived total decay energies Q _EC are summarized in Table 1.

The Q _EC values for ^138mPm , ^146mTb and ^147mDy isomers are based on the following new experimental results [3] :
- Via b + and X , g measurements a new long-lived isomeric state has been identified in ¹³⁸Pm (T _1/2 = 10 ± 2 s).
- Our experimental results from b + and conversion electron studies on A=146 isobar confirm the results of Munchen group [4] concerning the half-life and spin-parity assignments of ^146mTb (1⁺) isomer.

From our investigation of the decay scheme of ^147m+g Dy isomers, the half-life of ¹⁴⁷Dy ground state (T _1/2 = 75 ± 4 s, Ip = 1/2 ) and the sequence of low lying levels of ¹⁴⁷Tb have been found: 0 keV (11/2- g.s.), 50 keV (1/2+), 303 keV (3/2+), 404 keV (5/2+), 769 keV (7/2+).

The analysis of the data is in progress, and more complete results will be published.

REFERENCES

1. E.Ye.Berlovich et al., Proc. 8th Int.EMIS Conf. Skovde, Sweden, 1973, p.349.

2. E.Ye.Berlovich et al., Acta Phys.Polonica, Bl1, 1980, p. 455.

3. G.D. Alkhazov et al., Proc. of 9th EPS Nuclear Physic Division Conference, Amsterdam, 1982, v.1, p.264.

4. E.Nolte et al., Z.Phys., A306, 1982, p. 223.