Z. Phys. A - Atoms and Nuclei 310, 247 (1983)

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.

Table 1. Endpoint and Q EC results
Nuclide
T 1/2
Eb+ (keV)
Q EC (keV)
128Cs
3.8 min
2885(40)
3907(40)
136Pm
1.8 min
4732(70)
-
137Pm
2.4 min
4132(+150-115)
-
138Pm
10 s
6070(100)
7090(100)
139Pm
4.2 min
3520(40)
4540(40)
139Sm
10 s
4735(+180-130)
5946
140Pm
9 s
5070(40)
6090(40)
141Sm
10 min
3020(60)
-
141Eu
40 s
4925(40)
5950(40)
142Pm
40 s
3855(80)
4880(80)
142Eu
73 s
4782(50)
8175(50)
143Sm
8.8 min
2415(30)
3437(30)
143Eu
2.6 min
4220(70)
5240(70)
144 Eu
10 s
5310(30)
6330(30)
146 Tb
8 s
7220(150)
8240(150)
147 Dy
59 s
6012(60)
7035(60)
149 Ho
21 s
3930(50)
6040(50)
150Ho
84 s
4555(+150-120)
-
150Ho
24 s
3940(50)
7360(50)
151Ho
36 s
3530(50)
-
152Ho
52 s
3390(100)
-
153Ho
2 min
2835(50)
4153(50)
154 Ho
12 min
4340(80)
5700(80)

 

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.



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