Direct evaluation of high neutron density environment using <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi>n</mml:mi><mml:mo>,</mml:mo><mml:mn>2</mml:mn><mml:mi>n</mml:mi></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> reaction induced by laser-driven neutron source
Takato Mori, Akifumi Yogo, Takehito Hayakawa, S. R. Mirfayzi, Zechen Lan, Y. Abe, Yasunobu Arikawa, D. Golovin, Tianyun Wei, Yuki Honoki, M. Nakai, K. Mima, Hiroaki Nishimura, Shinsuke Fujioka, Ryosuke Kodama
Abstract
We demonstrate that $(n,2n)$ reactions are induced by a high-flux pulse of fast neutrons ($\ensuremath{\sim}{10}^{10}$ neutrons in $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{ns}$) provided from a laser-driven neutron source (LDNS). The maximum energy of the broadband neutrons reaches a few tens MeV. Several kinds of metal targets are exposed to the fast neutrons. As a result, unstable isotopes, such as $^{54}\mathrm{Mn}, ^{58}\mathrm{Co}, ^{175}\mathrm{Hf}$, and $^{196}\mathrm{Au}$ are produced by $(n,2n)$ reactions and $^{180}\mathrm{Hf}^{m}, ^{181}\mathrm{Hf}, ^{56}\mathrm{Mn}, ^{198}\mathrm{Au}$, and $^{60}\mathrm{Co}$ are produced by $(n,\ensuremath{\gamma})$ reactions. We evaluate the neutron fluence and energy spectrum using the activation method in conjunction with a time-of-flight measurement. The neutron fluence is determined to be $(4.3\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.16em}{0ex}}\mathrm{neutrons}/\mathrm{c}{\mathrm{m}}^{2}$ in the energy range from approximately 8 to 20 MeV at 8-mm downstream of the neutron source. The present scheme provides a method to evaluate high-density neutrons seen in stellar environments, which are expected to be generated from future LDNSs.