Y.K. Agarwal

Fusion of 28Si + 68Zn, 32S + 64Ni, 37Cl + 59Co and 45Sc + 51V in the vicinity of the Coulomb barrier

Abstract Results of the measurements of fusion excitation functions and average angular momenta are presented for 37 Cl + 59 Co, 28 Si + 68 Zn, 32 S + 64 Ni and 45 Sc + 51 V, for centre-of-mass energies ranging from ∼5 MeV below to ∼10 MeV above the Coulomb barrier. These results are discussed in terms of the simplified coupled-channel model and the neutron-flow model due to Stelson. It is pointed out that simplified coupled-channel calculations including collective inelastic excitations alone do not reproduce the observed sub-barrier fusion cross section in most of the cases and that there is a need to include couplings to other channels, like transfer, in order to explain the observations. An analysis of 32 S + 64 Ni fusion excitation data has been performed to derive an empirical barrier distribution in order to investigate the relationship between the simplified coupled-channel model and the neutron-flow model. A simultaneous analysis of the fusion excitation function and average angular momentum seems to indicate that these two quantities are related to each other, as was pointed out by Balantekin and Reimer.

Measurements of the g-factors of 2+ states in even nuclei utilizing hyperfine fields in iron lattice (I). The 316 keV state in 192Pt and 328 and 622 keV states in 194Pt

The g-factors of the first excited 2+ state in 192Pt and the first and second excited 2+ states in 194Pt have been measured by the integral gamma-gamma angular correlation method utilizing the hyperfine magnetic fields at Pt nuclei in dilute Ir-Fe alloys. The following values have been obtained: 316 keV state in 192Pt, g=0.33±0.05, 328 keV state in 194Pt, g=0.24±0.03, 622 keV state in 194Pt, g=0.15±0.05,

A plunger set-up for measuring picosecond nuclear half-lives

A plunger set-up has been designed and constructed to measure picosecond nuclear half-lives using recoil distance method (RDM). The system has been used to measure the half-lives of nuclear states in35Cl,37,38Ar and40K. The shortest half-life measured with the system isT1/2=0.36(14) ps for the 4366 keV (8+) state and the longest half-life isT1/2=1.10(7) ns for the 2543 keV (7+) state in40K.

Measurement of magnetic moments of excited states in Ta181 and Cs133

Abstract The magnetic moments of the 482 keV ( 5 2 ) level in Ta181 and the 80 keV ( 5 2 ) level in Cs133 have been measured by the azimuthal shift method. The results obtained are μ = 3.23±0.05 n.m. and μ = 3.25±0.15 n.m. for the 482 keV level in Ta181 and the 80 keV level in Cs133, respectively.

Spectral shapes and a beta-gamma directional correlation in the beta decay of 172Tm(Jπ = 2−)

Abstract The isotope 172Tm populates the 0+, 2+ and 4+ states of the 172Yb ground-state rotational band directly in beta decay. The shapes and intensities of the three beta groups have been measured by means of a six-gap magnetic spectrometer operated in coincidence with a NaI(Tl) crystal. The experimental shape factor plots are taken relative to the 90Y shape factor measured in the same circumstances, and it is concluded that on this basis the shapes of all three 172Tm beta groups agree with the theoretical shape for a first-forbidden unique transition. The directional correlation for the 2−(β)2+(γ)0+ cascade has been measured at six energies from 1010 to 1550 keV and these results too are consistent with the assumption that the 2− → 2+ beta transition is purely of tensor rank 2. The data for the 2− → 2+ transition are analysed on the basis of the modified Bij approximation, which defines parameters X and Y corresponding to the relative contributions of tensor ranks 0 and 1 respectively. The shape measurement provides the limit X2+Y2 ≦ 0.10, whereas the angular correlation measurement gives Y = 1.64X+(0.02±0.03). The reduced transition probabilities (ƒ 1 t) − can therefore be compared with the theoretical intensity rules for λ = 2, which predict the ratios 0.70 : 1 : 0.05 for the branches to the 0+, 2+ and 4+ states. The experimental result is (0.63±0.19) : 1 : (0.046±0.007).

Levels in La140 from the beta decay of Ba140

Abstract Some properties of the low-lying levels in the odd-nucleus La 140 as populated by the beta decay of Ba 140 have been studied by beta-gamma and gamma-gamma directional correlation experiments. The multipole orders and the E2/M1 mixing ratios of the promiment gamma-rays have thus been measured. On the basis of these measurements the following spin assignments to the La 140 levels have been made: 30 keV (2 − ), 162 keV (2 − ) , 466 keV (1 − ) and 566 keV (1 − ). The 162 keV gamma ray is predominantly of E2 character with the reduced transition probability at least 90 times that of a single-particle transition.

Particle parameters for conversion electrons in 152Sm, 152Gd and 160Dy

Abstract The internal conversion-electron particle parameters for several low-lying E2 transitions in 152 Sm, 152 Gd and 160 Dy have been determined by making e − - γ and γ − γ directional correlation measurements on the same source. In several of these cases both b 2 (E2, K) and b 4 (E2, K) have been measured. The results are: (i) 122 keV transition in 152 Sm: b 2 (K) = 1.82±0.05, b 4 (K) = −1.06±0.14 and b 2 (L) = 1.30±0.07, (ii) 344 keV transition in 152 Gd: b 2 (K) = 1.62±0.13, (iii) 87 keV transition in 160 Dy: b 2 (K) = 1.90±0.07, b 4 (K) = −1.25±0.18 and b 2 (L)= 1.37±0.18. The measured values of b 4 (K) have also been used in determining b 2 (K). In all the cases measured, no deviations from the theoretical values have been observed within the experimental errors.

Magnetic moment of the 160 keV state in Cs133

The magnetic moment of the 160 keV state in Cs133 has been measured to be μ = 3.3±0.8 n.m. by perturbing the observed angular correlation pattern of the 276 keV-160 keV gamma-gamma cascade in an external magnetic field. Our directional correlation results on this cascade confirm the spin of the 160 keV state to be 52.

Nuclear matrix elements in the 2.14 MeV beta group in 139Ba

Abstract The spectral shape and beta-gamma directional correlation of the 2.14 MeV ( 7 2 − → 5 2 + ) beta-group in the decay of 139Ba have been studied. The spectral shape measured in coincidence with the 166 keV γ-ray shows a large deviation from a statistical shape. The beta-gamma directional correlation coefficient A2 varies from 0.01 to 0.06 in the energy region 0.5 to 2.0 MeV. The ratios of relevant nuclear matrix elements have been obtained from these two measurements. The absolute values of the matrix elements involved have been calculated from the known ft value. The matrix element ∫ i r has been found to be 3.9 × 10−3 (in natural units) as compared to a value of 7.1 × 10−3 calculated on the basis of the single-particle shell model. The structure of the 5 2 + state in 139La is discussed on the basis of these results.

Properties of low-lying levels in 59Co

Abstract The half-life and the magnetic dipole moment of the 1290 keV ( 3 2 − ) state in 59Co have been measured to be T 1 2 = 0.59±0.02 ns and μ = 1.90±0.35 n.m. respectively. These and other properties of the 1100 and 1290 keV levels in 59Co have been explained by assigning a mixture of p 3 2 and { f 7 2 , 2 + ; 3 2 − } configurations to these levels.