Constraining calculations of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>Pu</mml:mi><mml:mprescripts/><mml:none/><mml:mn>239</mml:mn></mml:mmultiscripts><mml:mo>(</mml:mo><mml:mi>n</mml:mi><mml:mo>,</

Measurements of multistep cascade gamma-ray spectra from several low-lying <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mn>1</a:mn><a:mo>+</a:mo></a:msup></a:math> resonances in the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mmultiscripts><b:mi>Pu</b:mi><b:mprescripts/><b:none/><b:mn>239</b:mn></b:mmultiscripts><b:mo>(</b:mo><b:mi>n</b:mi><b:mo>,</b:mo><b:mi>γ</b:mi><b:mo>)</b:mo></b:mrow></b:math> reaction were made using the DANCE detector. The measured spectra are compared to spectra simulated using several models for the photon strength function and the nuclear level density, representing the first analysis of this nature on a fissile nucleus. In general, models of the photon strength function that included a strong <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>M</c:mi><c:mn>1</c:mn></c:mrow></c:math> “scissors mode” contribution coupled with a Gilbert-Cameron nuclear level density provided a reasonable description of the spectra. Simulations using photon strength functions and nuclear level densities specifically for <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mmultiscripts><d:mi>Pu</d:mi><d:mprescripts/><d:none/><d:mrow><d:mn>240</d:mn></d:mrow></d:mmultiscripts></d:mrow></d:math>, extracted by the Oslo method, resulted in a very good representation of the measured spectra. Neutron-capture cross section calculations that included the scissors mode provided a good estimate of the previously measured values, without additional normalization. However, the scissors-mode energy that produced the best description of the multistep cascade spectra was different from the value that best reproduced the capture cross section. In addition, the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mo>〈</e:mo><e:msub><e:mi mathvariant="normal">Γ</e:mi><e:mi>γ</e:mi></e:msub><e:mo>〉</e:mo></e:mrow></e:math> inferred from the multistep cascade calculations was somewhat less than the tabulated value, which was determined from resonance analysis.