abstract

Separable charge independent nucleon-nucleon potentials containing an attraction and a hard shell repulsion in the \(^1S_0\) state and the Yamaguchi tensor interaction in the \(^3S_1\)+\(^3D_1\) state are used to calculate the \(^3\)H ground state energy, \(E_T\), and the \(n\)–\(d\) doublet scattering length, \(^2a\). For the potential which gives the best fit to the nucleon–nucleon data we get: \(E_T= -8.81\) MeV, \(^2a=0.58\) fm. All our results fall on the Phillips line. The paper contains also a derivation of the system of coupled integral equations for the bound state and for the scattering problem for an arbitrary rank potential acting in the \(^1S_0\) and \(^3S_1\)+\(^3D_1\), states.

abstract

Magnetic and semiconductor (Ge and Si) spectrometers were used to study the \(^{232}\)Pa \(\to ^{232}\)U decay scheme. The following \(\gamma \) lines, new with respect to the earlier data reported by Bjørnholm et al. , were observed: 922.7, 1003.3, 1016.4, 1051.4, 1055.4, 1085.4, 1125.1, 1132.7 and 1164.5 keV. Conversion coefficients and multipolarity assignments were determined for several of these transitions. Due to the \(e\)–\(\gamma \) coincidence studies it was possible to show that the 1125.1 and 1055.4 keV \(E\)l transitions feed respectively the \(2^+\) and 4\(^+\) levels of \(^{232}\)U ground-state band. This indicates the existence of the new \(^{232}\)U levels at 1172.8 and 1212.1 keV which are interpreted as 2\(^-\) and 3\(^-\) members of the \(K^{\pi }= 1^-\) octupole band. Another new level is proposed at 1132.9 keV. The 10164 keV \(M\)2 transition is believed to connect the band-head state of the \(K^{\pi }= 2^-\) octupole band with the ground state; the 1051.4 keV transition may possibly be an analogous \(E\)3 transition from the 3\(^-\) state of this band. As deduced from the \(\beta \)–\(\gamma \) coincidence experiments, the \(\beta ^-\) decay energy of \(^{232}\)Pa is equal to \(1337 \pm 10\) keV. The discussion of experimental data in terms of nuclear models is concentrated on the octupole bands and their Coriolis interaction.

abstract

The relative \(K\)-capture probability, \(P_K\), for the unique first forbidden decay of \(^{145}\)Sm to the 492.3 keV level in \(^{145}\)Pm was measured by the coincidence method to be \(P_K = 0.27 \pm 0.03\). This is compared with the theoretical values \(P_K\)(allowed) \(= 0.70 \pm 0.03\) and \(P_K\)(unique forb.) \(=0.19^{+0.06}_{-0.05}\) calculated using the experimental decay energy \(Q = 115 \pm 10\) keV.

abstract

The \(^{230}\)Pa decay to levels of \(^{230}\)Th and \(^{230}\)U is investigated using Si(Li) and Ge(Li) spectrometers for singles-spectra measurements, and a Ge(Li) spectrometer combined with a six-gap \(\beta \) spectrometer or with a NaI(Tl) detector for coincidence measurements. The decay scheme is proposed which accounts for all but one of the 50 transitions observed in the present investigation. The following bands of the \(^{230}\)Th excited states are established or proposed (in parentheses: level energies in keV, spin values and parities of the levels): the ground-state band (53.19, 2\(^+\) and 174.12, 4\(^+\)), the quadrupole bands (\(\beta \): 634.7, 0\(^+\) and 677.8, 2\(^+\); \(\gamma \): 781.4, 2\(^+\) and 825.4, 3\(^+\); \(\beta +\gamma \) (?): 1009.61, 2\(^+\) and 1052.6, 3\(^+\)) and the octupole bands (\(K^{\pi }=0^-\): 508.20, 1\(^-\) and 571.71, 3\(^-\); \(K^{\pi }\)=1\(^-\): 951.91, 1\(^-\); 971.70, 2\(^-\) and 1012.2, 3\(^-\); \(K^{\pi }=2^-\): 1079.20, 2\(^-\) and 1127.85, 3\(^-\)). The \(^{230}\)Pa \(\to ^{230}\)Th decay energy, \(Q\), is deduced from the measured relative probabilities of the \(K\) capture transitions to several excited states in \(^{230}\)Th: \(Q=1315^{+15}_{-10}\) keV. For \(^{230}\)U, the first excited 2\(^+\) state is observed at 51.72 keV and the bandhead state of the \(K^{\pi }=0^-\) octupole band is proposed at 366.5 keV. The experimental data are discussed in terms of nuclear models, with emphasis on the band-mixing effects.

abstract

Angular distributions and total cross-sections for \(^9\)Be\((d,\alpha _0)^7\)Li (ground state) and \(^8\)Be\((d,\alpha _1)^7\)Li (470 keV) reactions have been measured over the angular range from 15\(^{\circ }\) to 165\(^{\circ }\) lab.) in 100 keV steps. A detailed description of the experimental technique is given. The observed behaviour of angular distributions does not allow to determine univocally the dominating reaction mechanism. The revealed features of the reactions in question indicate that these reactions may proceed through overlapping levels of the compound nucleus \(^{11}\)B, which possess opposite parities, and one of them is probably centered at the excitation energy \(E_k\approx 17.3\) MeV. However, direct pick-up and heavy particle stripping may be responsible as well.

abstract

Spectra of photons from the \((n,\gamma )\) reaction have been measured for the \(^{115}\)In, Sb, \(^{127}\)I, \(^{133}\)Cs, \(^{159}\)Tb, \(^{165}\)Ho, \(^{181}\)Ta, \(^{197}\)Au, Tl, and \(^{238}\)U nuclei at neutron energies of about 400 keV. The dependence of the cross-sections for high energy \(\gamma \)-rays emission on neutron energy in the range 0.03 to 1.4 MeV was investigated for \(^{115}\)In, \(^{181}\)Ta, and \(^{197}\)Au. Furthermore, \(\gamma \)-ray spectra for the \((p,\gamma )\) reaction were measured and compared with those for the \((n,\gamma )\) reaction. The experimental results are compared with the results of calculation based on the compound nucleus model under the assumption that the probability of emission of \(\gamma \)-rays with energy of about 6 MeV is increased.

abstract

The results of measurements of total and differential cross-section and of neutron polarization have been analysed in terms of compound nucleus contribution. The analysis performed seems to point to existence in \(^5\)He of a positive parity state 5/2\(^+\) at an excitation energy of about 20 MeV.

abstract

In our paper we give an analysis of the polarization of protons from the reaction \(^9\)Be\((d,p)^{10}\)Be. It is shown that the predictions based on the invariance of the density matrix under the exchange of distorted waves (when \(p_dr_d=p_pr_p\)) are in qualitative agreement with the experimental data. The usefulness of the DWBA for the describing of the polarization in the energy range 2–10 MeV is also discussed.

abstract

The energy spectra of alpha particles from \((n,\alpha )\) reactions on \(^{122}\)Te, \(^{139}\)La, \(^{159}\)Tb, \(^{160}\)Dy, \(^{161}\)Dy, \(^{163}\)Dy, \(^{164}\)Dy, \(^{166}\)Er, \(^{168}\)Er and \(^{169}\)Tm induced by 14.2 MeV neutrons have been measured using the semiconductor detector technique. The analysis of the energy spectra leads to results which imply that the evaporation theory is inadequate to describe the investigated reactions. The shapes of the experimental spectra suggest the presence of strong direct effects.

abstract

Excitation curves for the \(^{89}\)Y\((n,n')^{89m}\)Y reaction were measured in the neutron energy range 3–18 MeV and for the \(^{89}\)Y\((n,2n)^{88}\)Y reaction in the energy range 13–18 MeV. The results obtained were interpreted in terms of the statistical nuclear reaction model. The problem of the competition between electromagnetic radiation emission acd neutron emission from the highly excited compound nucleus states is discussed.

abstract

The spontaneous fission and alpha decay half-lives of even superheavy nuclei are calculated microscopically. The calculations are based on the single-particle Nilsson scheme with the parameters fitted to the scheme obtained in the Woods–Saxon potential at zero deformation. The largest total half-lives of the order of 10\(^{10}\) years are obtained for the nuclei with \(Z=108\)–110 and \(N=184\). The strength of the pairing forces used is smaller than in previous investigations. The use of a larger strength would lead to half-lives smaller by a few orders. The sensitivity of the half-lives to different factors, in particular to the pairing forces strength, is discussed.

abstract

Activation cross-sections of \(^{84m}\)Rb, \(^{86m}\)Rb, \(^{89m}\)Y, \(^{107m}\)Pd, \(^{109m}\)Pd, \(^{111m}\)Cd, \(^{185m}\)W, \(^{190m}\)Os and \(^{203}\)Pb for 14.8 MeV neutrons were measured using Ge(Li) and NaI(Tl) detectors. The following values (in millibarns) were obtained: \(^{85}\)Rb\((n,2n)^{84m}\)Rb(20.5 min) 412\(\pm \)40; \(^{87}\)Rb\((n,2n)^{86m}\)Rb(1 min) 432\(\pm \)45; \(^{89}\)Y\((n,n'\gamma )^{89m}\)Y(16.5 s) 438\(\pm \)44; \(^{107}\)Pd\((n,2n)^{107m}\)Pd(21 s) 590\(\pm \)60; \(^{110m}\)Pd\((n,2n)^{109m}\)Pd(4.8 min) 554\(\pm \)55; \(^{112}\)Cd\((n,2n)^{111m}\)Cd(48 min) 812\(\pm \)80; \(^{111}\)Cd\((n,n'\gamma )^{111m}\)Cd (48 min) 167\(\pm \)17; \(^{186}\)W\((n,22n)^{185m}\)(1.7 min) 1152\(\pm \)110; \(^{190}\)0s\((n,n'\gamma )^{190m}\)Os(10 min) 15\(\pm \)1.5; \(^{204}\)Pb\((n,2n)^{203m}\)Pb(6.1 s) 1020\(\pm \)100. Experimental results for isomeric ratios in \((n,2n)\) reaction were compared with statistical theory predictions.