Hidetsugu Ikegami

Structure of platinum nuclei (I) new decay scheme of Au196

Abstract Nuclear structure of Pt 196 has been investigated from the decay of the 6.2 d Au 196 . New weak gamma rays of 312, 444, 522, 568, 644, 757, 762 and 1090 keV were found in the analysis of conversion electron spectra by the use of a sector-type double focusing beta ray spectrometer. These new gamma rays were all coincident with the 356 keV gamma transition between the first and ground state of Pt 196 . From the ratio of electron capture to positon emission rate ϵ K.L.M. / β + = 2.0±0.4 × 10 6 , the electron capture decay energy of the 6.2 d Au 196 is estimated as 1480 −12 +8 keV. Directional correlation measurements of 1090-356, 760-340, 530-340 and 333-356 keV gamma ray cascades were also performed. The level scheme of Pt 196 is proposed as folows: 1446 keV, 3 − : (1316 keV, 3 + , 2 + ): 1117 keV, 2 + ; 1002 keV, 3 + : 877 keV, 4 + ; 689 keV 2 + ; 356 keV, 2 + . The 1446 keV 3 − state is assigned as the lowest octupole vibrational state. Almost all these levels are compared with ones determined from the measurement of the Pt 195 (d, p)Pt 196 reaction. The large excitation of the 3 − state by the stripping process seem to be difficult to understand on the basis of any of the usual theories. The extremely low value of the 689 keV cross over transition from the second excited 2 + state, 689 K/356 K = 1.0±1.0 × 10 −5 is discussed in terms of intrinsic nucleonic excitations.

Second‐Order Properties of Double‐Focusing Spectrometer with Nonuniform Magnetic Field

Second‐order focusing properties are considered for a nonuniform magnetic field with arbitrary circular boundaries in the case of normal entry and exit. The formula obtained here agrees with that obtained by Hintenberger for the special case α=β=0. It is also shown that the double and second‐order focusing can be achieved simultaneously. The numerical results are represented graphically for a symmetrical double‐focusing spectrometer with an arbitrary deflection angle.

Nuclear structure of Hg200

Abstract The decay of Tl 200 was investigated by the use of sector-type double-focussing beta-ray spectrometers for the measurements of the conversion spectrum and by means of gamma-gamma and electron-gamma coincidence and directional correlation measurements; 86 electron lines were observed and 63 gamma rays were identified as belonging to Hg 200 . Eleven new levels were proposed at 1028.6 (2 + ), 1254.6 (2 + ), 1643.2, 1846, 1970 (1 + ), 2085 (1 + ) 2112, 2267, 2286, 2358, 2380 (1 + ) keV besides the known 368.0 (2 + ), 947.4 (4 + ), 1574.8 (2 + ), 1595.0 (1 + ), 1733.0 (3 + ), 1776 (3 + ) and 1885 (2 + ) keV levels. The spin and parity of the 947.4 keV level was uniquely determined as 4 + by electron-gamma directional correlation measurements and the 1028.6 keV level is probably the 2 + member of the two-phonon triplet. The discovery of this level revealed a close analogy with the level scheme of Hg 198 .

The 2′ → 2 electric monopole transition in Hg198

Abstract An electric monopole transition in the 676-keV 2′ → 2 transition in Hg 198 was investigated by means of an electron-gamma angular correlation experiment on the 2 + (676 keV)2 + (412 keV) 0 + gamma-ray cascade following the decay of 5.3 h Tl 198 . The electron analyser was a beta-ray spectrometer especially designed for this type of experiment. The data were analysed by taking into account nuclear structure effects on the M1 internal conversion process. Two values of the strength parameters ϱ were found to be consistent with the experimental results. They are 0.21 ≦ ϱ ≦ 0.42 and −0.42 ≦ ϱ ≦ −0.29 with corresponding λ value of 5 ≦ λ ≦ 26 and 31 ≦ λ ≦ 52, respectively, where λ is defined as the ratio of the penetration matrix element to the normal gamma-ray matrix element. The ϱ values were calculated with the assumption B (E2; 2′ → 2)/ B (E2; 2 → 0) = 2. The large ϱ value may imply a large admixture of particle states in the 2 + levels concerned.

The Decay of 1.25-Min Rb82

Gamma rays accompanying the decay of 25.0-day Sr 82 have been investigated. Single and coincidence spectra taken with scintillation counter have shown the presence of gamma rays with energies of 0.69, 0.78 and 1.41 Mev in the decay of 1.25-min Rb 82 and their relative intensities have been determined. Log ft values have been evaluated on the basis of the proposed decay scheme. The allowed beta transitions from the 1+ ground state of Rb 82 to the ground state and the first and second 2+ states are found to be successively hindered, in accord with Sakais empirical rule. This problem is discussed in connection with the systematic trend of ft values in the neighboring nuclei. The E2/M1 mixing ratio of the 0.69-MeV gamma ray decaying from the second 2+ state to the first 2+ state have been determined from angular correlation pattern of the 0.78–0.69-MeV cascade and found to be -5.8 -22 +5.5 . The negative phase is consistant with the systematic trend of δ in the neighboring nuclei.

On the First and the Second Excited States in Ge74

The first and the second excited states in Ge 74 were studied in detail from the decay of As 74 . The possibility of the presence of 0+ excited level was checked by searching for an internal conversion line corresponding to E0 transition by means of a beta-ray spectrometer, but no detectable peak was observed. From the gamma-gamma coincidence measurements the relative intensity T (2→2)/ T (2→0) was obtained to be 1.7. From the gamma-gamma angular-correlation measurements the spin of the second excited state was assigned to be 2 and the E2/M1 mixing ratio δ in the 2→2 gamma transition was found to be begin{aligned} -left(1 begin{array}{l} +9 -0.5 end{array} right). end{aligned} These results were discussed in view of systematics on the medium-weight even-even nuclei.

SECTOR TYPE DOUBLE FOCUSING BETA RAY SPECTROMETER. PART I. GENERAL PROPERTIES

A small scale beta ray spectrometer was built, making use of the double focusing principle applied to sector-field. The fringing field was found to be easily corrected and not to be serious for conventional purposes. The gathering power of 0.3% was obtained for the resolving power of 0.7%. Since the source can be placed outside of the magnetic field, this type of spectrometer might serve as a powerful tool for coincidence and correlation measurements.

A NEW BETA-RAY SPECTROGONIOMETER FOR ANGULAR CORRELATION MEASUREMENTS

A new beta-ray spectrogoniometer for electron-electron angular correlation measurements was designed and constructed. It consists of two sector- type double-focusing spectrometers. Design of the apparatus and data of performance are described. As an example, an electronelectron directional correlntion function of the /sup 206/Pb gamma-gamma cascade obtained with this instrument is presented. (auth)

New Radioactivity 43-min Yttrium-84

A New 43±2-min yttrium radioactivity has been observed in the natural strontium target irradiated with 57-MeV protons. It is assigned to Y 84 by measuring the excitation function. The 3.7-hr activity previously assigned to Y 84 is identified to Y 85 . Gamma transitions of 0.453 MeV (10%), 0.590-MeV (15%),0.795-MeV (100%, E2), 0.982-MeV (100%, E2), 1.041-MeV (50%, E2 or M1), 1.27-MeV (9%), and 1.47-MeV (6%) are observed in the scintillation and internal conversion spectra of Y 84 . The positron spectrum taken with a beta-ray spectrometer gives maximum energies of 3.50±0.10-MeV and 2.90±0.15-MeV. Gamma-Gamma and positron-gamma coincidence measurements are carried out. A tentative decay scheme is proposed. It involves the following energy levels in Sr 84 : 0.982 or 0.795 MeV (2+), 1.777-MeV (4+), 2.367-MeV, 2.818-MeV, etc. The spin and parity of Y 84 are tentatively assigned as 5-.

Sector Type Double Focusing Beta Ray Spectrometer Part II. Twin Setting Measurement of the Weak Higher Component of Cs137

A twin setting of two sector type double focusing beta ray spectrometers was used for measurement of the weak higher component of Cs 137 in order to remove completely the contributions resulting from the secondary causes. The measured spectrum agreed well with those of the previous results, which were therefore confirmed to provide a reliable basis for the analysis of the coupling constants in beta decay.