Magnetic dipole contribution to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> spectrum from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>d</mml:mi><mml:mtext>−</mml:mtext><mml:mi>t</mml

One in about a few <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mn>10</a:mn><a:mn>5</a:mn></a:msup></a:math> sub-Coulomb <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>d</b:mi><b:mtext>−</b:mtext><b:mi>t</b:mi></b:math> collisions is accompanied by the emission of a <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>γ</c:mi></c:math> photon. The <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>γ</d:mi></d:math> spectrum from these collisions is dominated by a 16.7 MeV peak, corresponding to the population of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mi>p</e:mi></e:math>-wave <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mn>3</f:mn><f:mo>/</f:mo><f:msup><f:mn>2</f:mn><f:mo>−</f:mo></f:msup></f:mrow></f:math> <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mi>α</g:mi><g:mtext>−</g:mtext><g:mi>n</g:mi></g:math> ground-state resonance in the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>E</h:mi><h:mn>1</h:mn></h:mrow></h:math> transition from an intermediate <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mi>d</i:mi></i:math>-wave <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mi>α</j:mi><j:mtext>−</j:mtext><j:mi>n</j:mi></j:math> state, corresponding to the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mmultiscripts><k:mi>He</k:mi><k:mprescripts/><k:none/><k:mn>5</k:mn></k:mmultiscripts></k:math> excited state around 16.7 MeV. The strength of this spectrum at the large <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:mi>γ</l:mi></l:math>-energy endpoint decreases fast both due to kinematic factors and due to centrifugal repulsion between neutron and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mi>α</m:mi></m:math> particle at near-zero relative energies. However, no centrifugal repulsion would occur if <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mi>s</n:mi></n:math>-wave <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:mi>α</o:mi><o:mtext>−</o:mtext><o:mi>n</o:mi></o:math> states were populated in a magnetic dipole transition. Therefore, one can expect that close to the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:mi>γ</p:mi></p:math>-spectrum endpoint around 17.5 MeV the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mrow><q:mi>M</q:mi><q:mn>1</q:mn></q:mrow></q:math> transition could dominate, leading to additional counts in experimental spectra which could be easily misinterpreted as a background. This work presents calculations of the <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:mrow><r:mi>M</r:mi><r:mn>1</r:mn></r:mrow></r:math> contribution to the <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:mrow><s:mi>d</s:mi><s:mo>+</s:mo><s:mi>t</s:mi><s:mo>→</s:mo><s:mi>α</s:mi><s:mo>+</s:mo><s:mi>n</s:mi><s:mo>+</s:mo><s:mi>γ</s:mi></s:mrow></s:math> cross section caused both by convection and magnetization currents. While the first contribution was found to be negligible, the one from magnetization depends strongly on the choice of the model for the <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mi>d</t:mi><t:mtext>−</t:mtext><t:mi>t</t:mi></t:math> channel scattering wave function. Using <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:mi>d</u:mi><u:mtext>−</u:mtext><u:mi>t</u:mi></u:math> interaction models from the literature, represented either by a gaussian of by a square well, resulted in unrealistically strong <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:mrow><v:mi>M</v:mi><v:mn>1</v:mn></v:mrow></v:math> contribution. Withoptical folding potential constructed in the present work, correctly representing the sizes of deuteron and triton, the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>M</w:mi><w:mn>1</w:mn></w:mrow></w:math> contribution near the endpoint is reduced to about <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mn>2</x:mn><x:mo>%</x:mo></x:math> of the 16.7-MeV <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:mrow><y:mi>E</y:mi><y:mn>1</y:mn></y:mrow></y:math> peak. Arguments in favor of more detailed calculations, that could potentially change this number, are put forward. Published by the American Physical Society 2024