E. Runte

Beta- and gamma-decay studies of neutron-rich chromium, manganese, cobalt and nickel isotopes including the new isotopes 60Cr and 60gMn

Abstract A 36 mg cm 2 thick natW target was irradiated with 11.5 MeV/u 76Ge of 15 to 20 particle-nA beam intensity. On-line mass-separated samples of projectile-like neutron-rich products from multi-nucleon transfer-reactions were investigated in the region of mass 58–69 by β and γ-ray spectroscopy. The new isotope 60Cr was identified with a half-life of 0.57 (6) s and for the 60Mn ground state a half-life value of 51 (6) s was obtained. Decay schemes were constructed for 58Cr, 58Mn ( t 1 2 = 3 s ), 65,66,67Co and 69Ni. One new γ-ray was found in the decay of 59Cr. The Qβ value of 66Co was measured yielding 9.7 (5) MeV. The comparison of the measured new β half-life of 60Cr with the most recent predictions gave again an enhancement of the experimental value.

Investigation of neutron-rich rare-earth nuclei including the new isotopes 177Tm and 184Lu☆

Abstract Decays of neutron-rich isotopes in the rare-earth region were studied by means of on-line mass separation and β − γ spectroscopy using multinucleon-transfer reactions between beams of 136 Xe (9 and 11.7 MeV/u), 186 W (11.7 and 15 MeV/u) and 238 U (11.4 MeV/u) and targets of nat W and Ta. The higher beam energies appear to be advantageous for the production of such isotopes. Two new isotopes were identified: 177 Tm with a half-life T 1 2 = 85 −15 +10 s , and 185 Lu with T 1 2 ≈ 18 s . A new 47 s activity found at A = 171 is tentatively assigned to the decay of the new isotope 171 Ho. The properties of the ground and excited states of neutron-rich lanthanide isotopes are interpreted within the shell model using the deformed Woods-Saxon potential. A change of the ground-state configuration for odd-mass neutron-rich lutetium isotopes from π 7 2 + [404] to π 9 2 − [514] is suggested, this change being due to the influence of a large hexadecapole deformation. The role of the possible isomeric state in 180 Lu for the nucleosynthesis of 180m Ta is discussed.

Spectroscopic investigation of 164,168Ta, 166,W and 164,165Hf

Abstract Using reactions induced by beams of 36 Ar and 40 Ar in targets of 133 CsCI and 136 BaF 2 , the half-lives of 164,168 Ta, 166 W, and 164,165 Hf were measured to be 14.9 (2) s, 2.0 (l) min, 18.8 (4) s, 111 (8) s, and 76 (4) s, respectively. The β-decay of 166 W is reported for the first time, yielding an α-decay branch of 0.03 (1)%. Decay schemes were derived and are discussed by comparison with nuclear structure calculations.

Decay energies of the low-spin states of147Tb and148Tb

Using112Cd(40Ar,pxn) reactions andγ-ray spectroscopy, the EC/β+ and EC(K)/β+ probability ratios were determined for individualβ-transitions in the147Tb(1.6 h)→147Gd and148Tb(60 min)→148Gd decays. Under assumption of applicability of theoretical ratios for allowedβ-decays on the first-forbidden nonunique transitions studied here, the experimental ratios were converted into information on decay energies. Combining the results with the known masses of147,148Gd andQα values of neutron-deficient holmium-to-lutetium isotopes, mass excesses could be determined for147Tb,148Tb, low-spin151Ho, low-spin152Ho,155Tm,156Tm and159Lu.

Investigation of neutron-deficient tungsten isotopes168−174W

The decays of168−174W were observed in the reactions of36Ar and40Ar beams with enriched targets of136BaF2 and138BaF2. The measured half-lives are 53(2) s, 76(6) s, 2.42(4) min, 2.38(4) min, 6.6(9) min, 6.3(4) min, and 35.3 (5) min, respectively. Decay schemes were derived from theγ− and X-ray coincidence data. Spin assignments of ground- and excited states are discussed within experimental level systematics and compared with the results of microscopic-macroscopic model calculations. Excitation energies of modeled one-quasiparticle states were found in reasonable agreement with the experimental data. Allowed unhindered beta decay from the 5/2− [523] to the 7/2− [523] configuration was identified in171W and this transition is also proposed for the decays of the even-even isotopes168, 170W.

The decay of the new isotope180Yb and the search for ther-Process path to180mTa

IrradiatingnatW/Ta targets with186W, the decay of the new isotope180Yb was observed and its half-life determined to be 2.4(5) min. Based on the measuredβ-,γ- and X-ray data, ther-process production of180mTa and the role of a possible isomer180mLu in this context are discussed.

Beta-delayed gammas and QEC-values in the decays of150m,152mHo and149Dy

Abstract150m, 152mHo, and149Dy were produced by fusion-evaporation reactions of40Ar with targets of natural indium and114Cd. Theβ-decays of the isotopes were reinvestigated with emphasis on high-excitation daughter states. The decay energies for selectedβ-transitions were measured from electron-capture to positron-decay ratios. Corrections forγ-feeding from higher-lying states were taken into account. The following QEC-values were derived for150mHo,152mHo, and149mDy of 6819 (−100+117, 6263 (−80+89), and 3914 (−52+76) keV, respectively.

Decay of the new isotope167W

Theα- and β-decay of the new isotope167W were observed in the reaction of 191 MeV36Ar with136Ba using a helium-jet and a fast tape-transport system. The identification is based on coincidences with tantalum X-rays and excitation function measurements. The measured half-life is 19.9(5) s. A decay scheme comprising 12 levels was constructed from γγ-coincidences. The β-decay is discussed within experimental and calculated level systematics. Alpha-rays with energy 4.55(2) MeV were assigned to167W.

The decay of the new isotope171Re

Irradiating LaF3-targets with36Ar, the decay of the new isotope171Re was observed for the first time and its half-life determined to be 15.2(4) s. Based on the measuredγ- and X-ray data, a decay scheme could be constructed.

Completion of α-decay chains: The α-decays of162Ta and163Ta

Using the reactions35Cl(130Ba;4,5n) and36Ar(133Cs;6,7n), the half-lives of160,161Ta were measured to be 1.2(3) and 2.7(2) s, respectively, and theα-lines observed at 4.88(1) and 4.63(1) MeV were assigned to162Ta and163Ta, respectively. Theα-decay branch of162Ta was determined to be 0.065(14)%.