An experimental study of $^{256}$Rf spontaneous fission following the fusion reaction of $^{50}$Ti+$^{208}$Pb was performed using the velocity filter SHELS of the Flerov laboratory at JINR. The average number of neutrons of <math><mover><mrow><mi>ν</mi></mrow><mo>‾</mo></mover><mspace width="0.25em"></mspace><mo>=</mo><mspace width="0.25em"></mspace><mn>4.30</mn><mo>±</mo><mn>0.17</mn></math> and variance of <math><msubsup><mrow><mi>σ</mi></mrow><mrow><mi>ν</mi></mrow><mrow><mn>2</mn></mrow></msubsup><mspace width="0.25em"></mspace><mo>=</mo><mspace width="0.25em"></mspace><mn>3.2</mn></math> from the prompt neutron multiplicity distribution were obtained. The alpha decay branching ratio of <math><msub><mrow><mi>b</mi></mrow><mrow><mi>α</mi></mrow></msub><mspace width="0.25em"></mspace><mo>=</mo><mspace width="0.25em"></mspace><msubsup><mrow><mn>0.003</mn></mrow><mrow><mo>−</mo><mn>0.003</mn></mrow><mrow><mo>+</mo><mn>0.005</mn></mrow></msubsup></math> and the half-life of <math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub><mspace width="0.25em"></mspace><mo>=</mo><mspace width="0.25em"></mspace><mo>(</mo><mn>6.7</mn><mo>±</mo><mn>0.2</mn></math>) ms of the isotope were determined. For the first time, our neutron detector system allowed us to extend investigation of the prompt neutron multiplicity study to the superheavy element region.

JINR

A.V. Isaev

R.S. Mukhin

A.V. Andreev

France

Z. Asfari

M.L. Chelnokov

V.I. Chepigin

H.M. Devaraja

O. Dorvaux

B. Gall

K. Hauschild

I.N. Izosimov

A.A. Kuznetsova

A. Lopez-Martens

Russia

O.N. Malyshev

A.G. Popeko

Yu.A. Popov

A. Rahmatinejad

Kazakhstan

B. Sailaubekov

T.M. Shneidman

E.A. Sokol

A.I. Svirikhin

M.S. Tezekbayeva

A.V. Yeremin

N.I. Zamyatin

Structure of the prompt neutron multiplicity distribution in the spontaneous fission of Rf

The probabilities of xn-, pxn-, and αxn-evaporation channels in excited superheavy nuclei were evaluated using the Monte Carlo method. The calculations utilized microscopically determined nuclear level densities and were compared with results obtained from the phenomenological Jackson formula. Effective temperatures derived from the microscopic approach were incorporated into the Jackson formula for different evaporation channels at low and moderate excitation energies. Additionally, an analytical formula was introduced to estimate the average kinetic energy of emitted particles in multi-step processes.

G.G. Adamian

N.V. Antonenko

Poland

P. Jachimowicz

M. Kowal

Multi-step particle emission probabilities in superheavy nuclei at moderate excitation energies

Half-lives of the low-lying yrast states of $^{212}$Po have been measured using the delayed coincidence fast-timing method. We report on the first measurement of the <math><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> half-life, as well as a new measurement of the <math><msubsup><mrow><mn>6</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> half-life with improved accuracy compared to previous studies. The extracted lifetime of the <math><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> and <math><msubsup><mrow><mn>6</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> state have been determined to be 100(14) ps and 1.66(28) ns respectively. With these measurements, precise values are now available for the reduced transition strengths B(E2) of all ground state band levels in $^{212}$Po up to the first <math><msup><mrow><mn>8</mn></mrow><mrow><mo>+</mo></mrow></msup></math> state, in particular B(E2; <math><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math>) = 9.4(13) W.u. and B(E2;<math><msubsup><mrow><mn>6</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math>) = 8.7(15) W.u. Comparison of the new available data with an α-clustering model calculation provides evidence that the inclusion of the α-cluster degree of freedom significantly improves agreement with experimental data compared to earlier shell model calculations.

Germany

Ma. von Tresckow

M. Rudigier

Th. Kröll

Romania

M. Boromiza

C. Clisu

C. Costache

D. Filipescu

N.M. Florea

I. Gheorghe

Bulgaria

K. Gladnishki

A. Ionescu

D. Kocheva

R. Lică

N. Mărginean

R. Mărginean

United Kingdom

Canada

K.R. Mashtakov

C. Mihai

R.E. Mihai

A. Negret

C.R. Nita

A. Olacel

A. Oprea

S. Pascu

G. Rainovski

T. Sava

M. Scheck

P. Spagnoletti

C. Sotty

L. Stan

I. Stiru

S. Toma

A. Turturică

S. Ujeniuc

New evidence for alpha clustering structure in the ground state band of Po

We discuss a supersymmetric model with discrete flavor symmetry . The additional scalar fields which contribute masses of leptons in the Yukawa terms are introduced in this model. We analyze their scalar potential and find that they have various vacuum structures. We show the relations among 24 different vacua and classify them into two types. We derive expressions of the lepton mixing angles, Dirac CP violating phase and Majorana phases for the two types. The model parameters which are allowed by the experimental data of the lepton mixing angles are different for each type. We also study the constraints on the model parameters which are related to Majorana phases. The different allowed regions of the model parameters for the two types are shown numerically for a given region of two combinations of the CP violating phases.

Japan

Takuya Morozumi

Hideaki Okane

Hiroki Sakamoto

Yusuke Shimizu

Kenta Takagi

Hiroyuki Umeeda

Phenomenological aspects of possible vacua of a neutrino flavor modelSupported by JSPS KAKENHI Grant Number JP17K05418 (T.M.). This work is also supported in part by Grants-in-Aid for Scientific Research [No. 16J05332 (Y.S.), Nos. 24540272, 26247038, 15H01037, 16H00871, and 16H02189 (H.U.)] from the Ministry of Education, Culture, Sports, Science and Technology in Japan. H.O. is also supported by Hiroshima Univ. Alumni Association