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The α-decay of the nucleides 188–192Pb, 180Hg, and 176Pt has been studied after on line mass separation of spallation products from reactions with 600 MeV protons. For the lead isotopes, the K X-ray/α ratios were determined, and from these partial α half-lives were deduced. In the decay of 6 sec 176Pt, a 1.4% α-branch was found to the 228 keV 2+ level of 172Os, while for 180Hg an upper limit of 10−3 (relative to the ground-state α-branch) could be put on the intensity of an assumed rotational fine-structure component. The systematics of reduced s-wave (0+ → 0+) α-widths is discussed. The lead isotopes show a surprising trend: the reduced s-widths vary from a very small value for 186Pb (deduced from the heavy-ion cross sections of Gauvin et al.) to a quite large value for 192Pb. The systematics of d-wave (0+ → 2+) hindrance factors (relative to the ground-state branch) shows that these range from 1 to 4 for the actinides, while for platinum and mercury one finds 8 and ≈ 50, respectively.

Large-angle light particle correlations in 12C + 12C and 12C + 197Au collisions at 85A MeV are observed. An excess of pp correlations in the particle-particle scattering plane is observed for both reactions whereas for dd correlations it exists only for 12C + 12C reactions. Quasi-elastic scattering and emission from a sequentially recoiling thermal source explain the gross structure — but hardly all details - of the pp correlation functions.

Two gamma -rays of 129.2 and 288.4 keV observed in the beta -decay of 55 ms /sup 100/Rb are interpreted as representing the two lowest transitions in the /sup 100/Sr ground-state rotational band. The energy ratio of the two levels, 3.23, approaches the value for a rigid rotator. The half-life of the 2/sup +/ state is 5.15+or-0.20 ns corresponding to a deformation parameter epsilon of 0.29. The theoretical implications of these results are discussed on the basis of a Nilsson-Strutinsky calculation. (10 refs).

22h Pa228 was produced by (p, 5n) reactions on Th232. The decay was studied by means of a double-focusing high-resolution β-spectrometer, a six-gap high-transmission β-spectrometer, scintillation spectrometers, and coincidence techniques. More than 200 conversion lines were found. Of these, 153 were ascribed to the Pa228 decay on the basis of their half-lives and assigned to 72 γ-transitions in Th228. Numerous coincidence relations between conversion lines and γ-rays were measured. A decay scheme comprising 22 excited states, ranging from 57.5 keV to 1943 keV, is presented and discussed with respect to the quantum numbers (K,I,π). In addition to the ground-state rotational band, the level structure indicates the presence of 3 or 4 rotational bands, built on intrinsically excited states. The possible collective vibrational character of the lower lying intrinsic states is discussed. Theoretical branching ratios and selection rules associated with the quantum number K are compared with experiment and discussed.

The conversion electron spectrum, electron-gamma and β + -gamma coincidence spectra are investigated, and the gamma-ray spectrum is studied in two Ge(Li) semiconductor spectrometers. A decay scheme 152 Tb → 152 Gd is suggested, including many new levels among which two 0 + states at 1484.0 and 2720.7 keV. Relative intensities at 0.2 : 0.3 : 1 are found for positon branches from 152 Tb to the 615.6 keV (0 + ), 344.4 keV (2 + ) and to the ground state of 152 Gd. Spin 1 − is ascribed to the ground state of 152 Tb. Spin assignments are being made for the following excited levels: 755.6 keV 4 + , 1109.8 keV 2 + , 1123.8 keV 3 − , 1606.1 keV 2 + , 1643.9 keV 1 − , 1862.3 keV 2 + and 1942.5 keV 2 + .

Coincidences have been detected between γ-rays and β-delayed protons emitted after the decay of very neutron-deficient nuclei. In the three cases studied the decay proceeds to the ground state with branches to the first excited (2 + ) state of the even daughter nucleus of (58±7) % ( 115 Xe to 709 keV in 114 Te), (14±3) % ( 117 Xe to 679 keV in 116 Te), and (50±10) % ( 181 Hg to 158 keV in 180 Pt). Upper limits of 2 and 6 % can be placed on the branches to the 4 + states of 114 Te and 180 Pt. For the cases of 115,117 Xe, coincidences with annihilation radiation were also observed; the measured positon/proton ratio determines the difference Q — B p , between the energy available for electron capture and the proton separation energy for the daughter. For 115 Xe the result is 6.20±0.13 MeV, for 117 Xe 4.10±0.20 MeV.

The levels in Hf/sup 1//sup 7//sup 8/ populated by the allowed positron and electron capture decays of 9.3 min Ta/sup 1//sup 7//sup 8/ are investigated with a six-gap spectrometer. Conversion-electron spec trum and beta-gamma coincidence measurements establish the spin and parities of levels in Hf/sup 1// sup 7//sup 8/ with energies of 1483(2+) kev, and possibly a level at 1550 kev. (Double parentheses indicate that the spin is not definitely established.) Intrinsic configuration assignments for the excited states are discussed in terms of theoretical developments. The half life of the 93 kev level is found to be (1.25 plus or minus 0.08) x 10/sup -//sup 9/ sec. The beta /sup +//K capture ratio measured for the allowed decay to ground is within experimental error of theory. Reduced E0/E2 transition probability ratios for the transitions depopulating the 1197 and 1440 kev 0+ levels are calculated from the observed K- conversion line intensities of the E0 and E2 transitions depopulating the levels. (auth)

Measurements on internal conversion lines of Bi214 confirm that the experimental M1 internal conversion coefficients for heavy elements are considerably smaller than the values calculated for a point nucleus. The results are in approximate agreement with the finite size corrected values of Sliv and Band 1). A number of transitions in Po214 with ΔI = 0 or 1 were found to be mainly Ml according to conversion coefficients corrected for finite size effects. The tables of uncorrected conversion coefficients 2, 3) would have indicated the systematic occurrence of large E2 admixtures. The K/L ratio for the 115 keV Ml transition in Bi212 was found to agree with the theoretical value, which is not sensitive to the finite size effect. This ratio was earlier thought to be abnormally low4).

Approximate beta strength functions have been derived from measurements of the electroncapture beta feed to the high-lying excited states in about 40 neutron-deficient nuclei. These nuclei, available at the ISOLDE on-line facility at CERN, ranged from isotopes of iridium ( Z = 77) to those of radon ( Z = 86). The beta feed was determined from the gamma spectra by a total absorption spectrometry technique involving two 15 cm diam. × 10 cm height NaI (T1) crystals. Two sum spectra, one with and one without a coincidence demand, were recorded simultaneously for each isotope. An average multiplicity of three to four high-energy γ-rays per cascade was deduced from the ratio of these two spectra. In general, the strength functions vary smoothly with energy as well as with the neutron number N and the proton number Z . Strong peaks appear in the energy region 1.5–3.5 MeV. Relatively little strength is found below an excitation energy in the daughter nucleus corresponding approximately to the energy required for forming a (pn) pair. This overall behaviour can be understood by assuming that the main part of the strength is associated with transitions that excite protons that are initially in paired orbits. An average value S β of the beta strength function for a given isotope may be calculated if the Q -value and the gross electron-capture half-life are known. It was found that S β varies strongly but systematically with N and Z ; from the light Pt isotopes with N ≈ 100 to isotopes just below the 126-neutron closed shell, it decreases by a factor of about 300. Fine structure in this dependence may be evidence for Subshell effects in deformed nuclei. The results are discussed in terms of the shell model.

One possible explanation for the anomalous isotope shifts of 183,185Hg is the sudden occurrence of permanent quadrupole deformations. The α-particle decay of 25 s 188Pb, however, does not show any rotational fine structure. It is interesting to consider the possibility that the nuclei 183–185Hg have “bubble” shape.

Quantitative e- gamma coincidence measurements showed that all strong transitions were coincident with 3 to 5 others. Estimates of the conversion coefficients show predominant M1 multipole order. Existence of at least two rotational cascades involving three or more levels is indicated. The about the same intensity. The energy ratios correspond to transitions between rotational levels having spins of 7/2, 9/2, 11/2 -and 13/2. The e- gamma coincidence relations support this interpretation and suggest the 282-kev transition as a cross over, whereas a 180-kev gamma in the coincident spectra possibly represents a transition from a 15/2 level. The coincidence measurements also seem to indicate coincidence with the 113- and 208-kev transitions; this is inconsistent with the spin 9/2 for the 321-kev level in Lu/sup 177/. The 123and 149-kev transitions with a 175-kev gamma possibly form a similar cascade built on a level at 412 kev. (L.N.N.)