A new proton-unbound isotope 204Ac was produced in the fusion-evaporation reaction <math altimg='si1.svg'><mmultiscripts><mrow><mi mathvariant='normal'>Tm</mi><mo stretchy='false'>(</mo><msup><mrow /><mrow><mn mathvariant='normal'>40</mn></mrow></msup></mrow><mprescripts /><none /><mrow><mn>169</mn></mrow></mmultiscripts><mrow><mi mathvariant='normal'>Ca</mi></mrow><mo>,</mo><msup><mrow><mn mathvariant='normal'>5n</mn><mo stretchy='false'>)</mo></mrow><mrow><mn mathvariant='normal'>204</mn></mrow></msup><mrow><mi mathvariant='normal'>Ac</mi></mrow></math> and identified via the recoil- <italic>&#945;</italic> correlation at the gas-filled recoiled separators SHANS2 and SHANS. The excitation function for producing 204Ac was measured and the optimal beam energy was evaluated to be 212 MeV. Nineteen ER - <math altimg='si2.svg'><msub><mrow><mi>&#945;</mi></mrow><mrow><mn mathvariant='normal'>1</mn></mrow></msub></math> - <math altimg='si3.svg'><msub><mrow><mi>&#945;</mi></mrow><mrow><mn mathvariant='normal'>2</mn></mrow></msub></math> - <math altimg='si4.svg'><msub><mrow><mi>&#945;</mi></mrow><mrow><mn mathvariant='normal'>3</mn></mrow></msub></math> decay chains were observed for this isotope. Based on these chains, the <italic>&#945;</italic>-particle energy and half-life of 204Ac were determined to be 7948(15) keV and 7.4 <math altimg='si5.svg'><msubsup><mrow /><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>1.4</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>2.2</mn></mrow></msubsup></math> ms, respectively. Both are consistent with the theoretical prediction. The reduced <italic>&#945;</italic>-decay width was deduced to be 49 <math altimg='si6.svg'><msubsup><mrow /><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>15</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>10</mn></mrow></msubsup></math> keV, which indicates a favored <italic>&#945;</italic> decay for 204Ac. In addition, more precise decay properties of <math altimg='si32.svg'><msub><mrow><mi>E</mi></mrow><mrow><mi>&#945;</mi></mrow></msub></math> = 7883(15) keV and <math altimg='si8.svg'><msub><mrow><mi>T</mi></mrow><mrow><mn mathvariant='normal'>1</mn><mo stretchy='false'>/</mo><mn mathvariant='normal'>2</mn></mrow></msub></math> = 7.7 <math altimg='si9.svg'><msubsup><mrow /><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>1.6</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>2.7</mn></mrow></msubsup></math> ms were obtained for 205Ac.

China

M.H. Huang

Z.G. Gan

Z.Y. Zhang

L. Ma

J.G. Wang

M.M. Zhang

H.B. Yang

C.L. Yang

X.Y. Huang

Z. Zhao

S.Y. Xu

L.X. Chen

X.J. Wen

Y.F. Niu

C.X. Yuan

Y.L. Tian

Y.S. Wang

J.Y. Wang

M.L. Liu

Y.H. Qiang

W.Q. Yang

H.B. Zhang

Z.W. Lu

S. Guo

W.X. Huang

Y. He

Z.Z. Ren

S.G. Zhou

X.H. Zhou

H.S. Xu

Russia

V.K. Utyonkov

A.A. Voinov

Yu.S. Tsyganov

A.N. Polyakov

<italic>&#945;</italic> decay of the new isotope 204Ac

A new isotope $^{203}$Ac was produced in the reaction $^{40}$Ca + $^{169}$Tm at beam energy of 226 MeV. One correlated α-decay chain was attributed to $^{203}$Ac. The α-particle energy and half-life were determined to be 8217(16) keV and <math><msubsup><mrow><mn>56</mn></mrow><mrow><mo>−</mo><mn>26</mn></mrow><mrow><mo>+</mo><mn>269</mn></mrow></msubsup></math> μs, respectively. The reduced α-decay width (<math><msup><mrow><mi>δ</mi></mrow><mrow><mn>2</mn></mrow></msup></math>) of $^{203}$Ac was deduced to be <math><msubsup><mrow><mn>1096</mn></mrow><mrow><mo>−</mo><mn>906</mn></mrow><mrow><mo>+</mo><mn>921</mn></mrow></msubsup></math> keV, which indicates a favored α decay. The systematics of <math><msup><mrow><mi>δ</mi></mrow><mrow><mn>2</mn></mrow></msup></math> and single-particle energy levels indicate that the new state probably arises from the intruder <math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></math> configuration, which shows an onset of deformation in Ac isotopes. The proton separation energy <math><msub><mrow><mi>S</mi></mrow><mrow><mi>p</mi></mrow></msub></math> of $^{203}$Ac was extracted as <math><mo>−</mo><mn>1214</mn><mo>(</mo><mn>22</mn><mo>)</mo></math> keV and the systematics of <math><msub><mrow><mi>S</mi></mrow><mrow><mi>p</mi></mrow></msub></math> for odd-A isotopes beyond proton drip line were discussed.

Z.C. Li

L.C. Sun

H. Zhou

X. Zhang

X.L. Wu

JINR

-decay Properties of new Neutron-deficient Isotope Ac

In recent years, interest has grown in alternative strategies for the search for New Physics beyond the Standard Model. One envisaged solution lies in the development of anomaly detection algorithms based on unsupervised machine learning techniques. In this paper, we propose a new Generative Adversarial Network-based auto-encoder model that allows both anomaly detection and model-independent background modeling. This algorithm can be integrated with other model-independent tools in a complete heavy resonance search strategy. The proposed strategy has been tested on the LHC Olympics 2020 dataset with promising results.

France

Louis Vaslin

Vincent Barra

Julien Donini

GAN-AE: an anomaly detection algorithm for New Physics search in LHC data

We study single-image super-resolution algorithms for photons at collider experiments based on generative adversarial networks. We treat the energy depositions of simulated electromagnetic showers of photons and neutral-pion decays in a toy electromagnetic calorimeter as 2D images and we train super-resolution networks to generate images with an artificially increased resolution by a factor of four in each dimension. The generated images are able to reproduce features of the electromagnetic showers that are not obvious from the images at nominal resolution. Using the artificially-enhanced images for the reconstruction of shower-shape variables and of the position of the shower center results in significant improvements. We additionally investigate the utilization of the generated images as a pre-processing step for deep-learning photon-identification algorithms and observe improvements in the case of training samples of small size.

Germany

Johannes Erdmann

Aaron Graaf

Florian Mausolf

Olaf Nackenhorst

SR-GAN for SR-gamma: super resolution of photon calorimeter images at collider experiments

The precession of an atomic nucleus can be approximately described as wobbling motion, arising from the coupling of a rotation and a harmonic vibration. Recently, a number of wobbling bands were reported at low spin, which violate the wobbling approximation that can be valid only at high spin. In the present work, we explore the nature of the reported low-spin wobbling bands. Via a new experiment including both angular correlation and linear polarization measurements, we demonstrate that one such band in $^{187}$Au is generated by dominant single-particle excitation rather than by the excitation of a wobbling phonon. Assessing the experimental proofs and discussions to assign the reported low-spin wobbling bands, we further point out that the imperfect research paradigm used previously would lead to unreliable identification of low-spin wobbling bands.

C.M. Petrache

South Africa

E.A. Lawrie

S.H. Mthembu

Y.D. Fang

H.Y. Wu

H.L. Wang

H.Y. Meng

G.S. Li

Y. Zheng

B. Ding

W.Q. Zhang

A. Rohilla

K.R. Muhki

Y.Y. Yang

H.J. Ong

J.B. Ma

S.W. Xu

Z. Bai

H.L. Fan

J.F. Huang

J.H. Li

J.H. Xu

B.F. Lv

W. Hua

Y.H. Zhang

Probing the nature of the conjectured low-spin wobbling bands in atomic nuclei

The decay of $^{218}$Pa was investigated by means of α and γ spectroscopy. The nucleus was produced in the fusion reaction $^{40}$Ar+$^{182}$W and separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The known α decays of $^{218}$Pa were measured with improved precision and newly assigned to be originating from the ground state, which clarified the ambiguities in their previous assignments. In addition, a new isomeric state in $^{218}$Pa decaying with α-particle energies of 9691(15) keV, 9595(21) keV and a half-life of <math><msubsup><mrow><mn>135</mn></mrow><mrow><mo>−</mo><mn>32</mn></mrow><mrow><mo>+</mo><mn>62</mn></mrow></msubsup></math> μs was identified. The spins and parities of the involved states were tentatively assigned on the basis of the systematic α-decay properties of the odd-proton <math><mi>N</mi><mo>=</mo><mn>127</mn></math> isotones and shell model calculations.

H.B. Zhou

S. Huang

X.T. He

S.Y. Wang

W.Z. Xu

H.W. Li

X.X. Xu

H.R. Yang

L.M. Duan

M.V. Shumeiko

A new isomeric state in Pa

Fine structure in the α decay of $^{223}$U was observed in the fusion-evaporation reaction $^{187}$Re($^{40}$Ar, p3n) by using fast digital pulse processing technique. Two α-decay branches of $^{223}$U feeding the ground state and 244 keV excited state of $^{219}$Th were identified by establishing the decay chain $^{223}$U <math><mover><mrow><mo>→</mo></mrow><mrow><msub><mrow><mi>α</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></mover></math> $^{219}$Th <math><mover><mrow><mo>→</mo></mrow><mrow><msub><mrow><mi>α</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></mover></math> $^{215}$Ra <math><mover><mrow><mo>→</mo></mrow><mrow><msub><mrow><mi>α</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></mover></math> $^{211}$Rn. The α-particle energy for the ground-state to ground-state transition of $^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62<math><msubsup><mrow></mrow><mrow><mo>−</mo><mn>10</mn></mrow><mrow><mo>+</mo><mn>14</mn></mrow></msubsup></math> μs. Evolution of nuclear structure for N = 131 even-Z isotones from Po to U was discussed in the frameworks of nuclear mass and reduced α-decay width, a weakening octupole deformation in the ground state of $^{223}$U relative to its lighter isotones $^{219}$Ra and $^{221}$Th was suggested.

M.D. Sun

Z. Liu

T.H. Huang

United Kingdom

Japan

A.N. Andreyev

X.Y. Liu

H.Y. Lu

D.S. Hou

L. Yu

J. Jiang

K.L. Wang

Z.H. Li

J. Li

X. Wang

A.H. Feng

C.J. Lin

L.J. Sun

N.R. Ma

W. Zuo

G.Q. Xiao

Sweden

C. Qi

F.S. Zhang

Fine structure in the Decay of U

The semi-magic nucleus $^{219}$Np was produced in the fusion reaction $^{187}$Re($^{36}$Ar, 4n)$^{219}$Np at the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). A fast electronics system based on waveform digitizers was used in the data acquisition and the sampled pulses were processed by digital algorithms. The reaction products were identified using spatial and time correlations between the implants and subsequent α decays. According to the observed α-decay chain, an energy of <math><msub><mrow><mi>E</mi></mrow><mrow><mi>α</mi></mrow></msub><mo>=</mo><mn>9039</mn><mo>(</mo><mn>40</mn><mo>)</mo><mtext> </mtext><mtext>keV</mtext></math> and a half-life of <math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>=</mo><msup><mrow><msub><mrow><mn>0.15</mn></mrow><mrow><mo>−</mo><mn>0.07</mn></mrow></msub></mrow><mrow><mo>+</mo><mn>0.72</mn></mrow></msup><mtext> </mtext><mtext>ms</mtext></math> were determined for $^{219}$Np. The deduced proton binding energy of $^{219}$Np fits well into the systematics, which gives another evidence of that there is no sub-shell closure at <math><mi>Z</mi><mo>=</mo><mn>92</mn></math>. The influence of the <math><mi>N</mi><mo>=</mo><mn>126</mn></math> shell closure on the stability of Np isotopes is discussed within the framework of α-decay reduced widths.

Alpha decay properties of the semi-magic nucleus Np

The <math><mi>N</mi><mo>=</mo><mn>130</mn></math> short-lived isotope 223Np was produced as evaporation residue (ER) in the fusion reaction 40Ar + 187Re at the gas-filled recoil separator Spectrometer for Heavy Atom and Nuclear Structure (SHANS). It was identified through temporal and spatial correlations with α decays of 215Ac and/or 211Fr, the third and fourth members of the α-decay chain starting from 223Np. The pileup signals of ER(223Np)–α(223Np)–α(219Pa) were resolved by using the digital pulse processing technique. An α decay with half-life of <math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>=</mo><mn>2.15</mn><mo>(</mo><mmultiscripts><mrow></mrow><mprescripts></mprescripts><mrow><mn>52</mn></mrow><mrow><mn>100</mn></mrow></mmultiscripts><mo>)</mo></math> μs and energy of <math><msub><mrow><mi>E</mi></mrow><mrow><mi>α</mi></mrow></msub><mo>=</mo><mn>9477</mn><mo>(</mo><mn>44</mn><mo>)</mo><mspace width="0.25em"></mspace><mtext>keV</mtext></math> was attributed to 223Np. Spin and parity of <math><mn>9</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>−</mo></mrow></msup></math> were tentatively proposed for the ground state of 223Np by combining the reduced α-decay width and large-scale shell-model calculations. This assignment together with the proton separation energy disprove the existence of a <math><mi>Z</mi><mo>=</mo><mn>92</mn></math> subshell closure.

New short-lived isotope Np and the absence of the = 92 Subshell Closure Near = 126

In deeply inelastic heavy-ion collisions, the quadrupole deformations of both fragments are taken as stochastic independent dynamical variables governed by the Fokker–Planck equation (FPE) under the corresponding driving potential. The mean values, variances and covariance of the fragments are analytically expressed by solving the FPE in head on collisions. The characteristics and mechanism of the deformation are discussed. It is found that both the internal structures and interactions of the colliding partners are critical for the deformation relaxation in deeply inelastic collisions.

H.F. Zhang

J.Q. Li

Deformation relaxation in heavy-ion collisions