A slow neutron detector , comprising: a slow neutron converter ; a cathode plate , disposed at one end of the slow neutron converter ; an electron multiplier , disposed at another end of the slow neutron converter ; and an anode plate , disposed opposite to the electron multiplier , an electric field being formed between the cathode plate and the anode plate , wherein the slow neutron converter comprises: a substrate , comprising a plurality of holes extending along a first direction; and a boron layer , at least covering an exposed surface of the plurality of holes ; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter , characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage . a slow neutron converter ; a cathode plate , disposed at one end of the slow neutron converter ; an electron multiplier , disposed at another end of the slow neutron converter ; and an anode plate , disposed opposite to the electron multiplier , an electric field being formed between the cathode plate and the anode plate , wherein the slow neutron converter comprises: a substrate , comprising a plurality of holes extending along a first direction; and a boron layer , at least covering an exposed surface of the plurality of holes ; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter , characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage . a substrate , comprising a plurality of holes extending along a first direction; and a boron layer , at least covering an exposed surface of the plurality of holes ; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter , characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage . <EOS>