<p>The continuum quasiparticle random phase approximation (CQRPA), which includes the Skyrme interaction for both ground- and excited-state calculations, is extended in a more consistent manner in the present work. The emergence, evolution, and origin of pygmy monopole strengths along the even–even Ni isotopes were investigated carefully within consistent Skyrme HF + BCS and CQRPA models. The SLy5 Skyrme interaction and density-dependent zero-range pairing interactions were adopted in the calculations. No pygmy monopole strength was observed in <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq1.gif" Format="GIF" Height="11" Rendition="HTML" Resolution="72" Type="Linedraw" Width="34" /> </InlineMediaObject> <EquationSource Format="TEX">$^{70-78}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mn>70</mn> <mo>-</mo> <mn>78</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>Ni. However, pronounced pygmy monopole strengths are clearly observed in <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq2.gif" Format="GIF" Height="11" Rendition="HTML" Resolution="72" Type="Linedraw" Width="34" /> </InlineMediaObject> <EquationSource Format="TEX">$^{80-84}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mn>80</mn> <mo>-</mo> <mn>84</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>Ni, which are attributed mainly to the neutron excitations from weakly bound orbitals into the continuum. The neutron states involved in the pygmy monopole strength include 1<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">$g_{9/2}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>g</mi> <mrow> <mn>9</mn> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>, 2<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq4.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">$d_{5/2}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mrow> <mn>5</mn> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>, 3<InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq5.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">$s_{1/2}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>s</mi> <mrow> <mn>1</mn> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> and 2<InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1794_Article_IEq6.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">$d_{3/2}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mrow> <mn>3</mn> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>. We suggest that more efforts from experimental investigations of pygmy monopole resonance should be made to confirm or disprove the predictions from models in the future.</p>

Emergence of pygmy monopole strength in neutron-rich nickel isotopes

期刊论文
发表日期：

2025年9月12日

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Shuai Sun,
Ya-Lu Wang,
Miao Qi,
Rong An,
Li-Gang Cao,
Feng-Shou Zhang

摘要

The continuum quasiparticle random phase approximation (CQRPA), which includes the Skyrme interaction for both ground- and excited-state calculations, is extended in a more consistent manner in the present work. The emergence, evolution, and origin of pygmy monopole strengths along the even–even Ni isotopes were investigated carefully within consistent Skyrme HF + BCS and CQRPA models. The SLy5 Skyrme interaction and density-dependent zero-range pairing interactions were adopted in the calculations. No pygmy monopole strength was observed in $^{70-78}$ $^{70 - 78}$ Ni. However, pronounced pygmy monopole strengths are clearly observed in $^{80-84}$ $^{80 - 84}$ Ni, which are attributed mainly to the neutron excitations from weakly bound orbitals into the continuum. The neutron states involved in the pygmy monopole strength include 1 $g_{9/2}$ $g_{9 / 2}$ , 2 $d_{5/2}$ $d_{5 / 2}$ , 3 $s_{1/2}$ $s_{1 / 2}$ and 2 $d_{3/2}$ $d_{3 / 2}$ . We suggest that more efforts from experimental investigations of pygmy monopole resonance should be made to confirm or disprove the predictions from models in the future.