Editing Nuclear thermal rocket (section)

=== Israel ===
In 1987, Ronen & Leibson<ref name=Ronen1987>Ronen, Yigal, and Melvin J. Leibson; "An example for the potential applications of americium-242m as a nuclear fuel" Trans. Israel Nucl. Soc. 14 (1987): V-42</ref><ref name="Ronen1988">{{cite journal |last1=Ronen |first1=Yigal |last2=Leibson |first2=Melvin J. |title=Potential Applications of 242m Am as a Nuclear Fuel |journal=Nuclear Science and Engineering |date=July 1988 |volume=99 |issue=3 |pages=278–284 |doi=10.13182/NSE88-A28998 |bibcode=1988NSE....99..278R }}</ref> published a study on applications of <sup>242m</sup>Am (one of the [[isotopes of americium]]) as nuclear fuel to [[Nuclear power in space|space nuclear reactors]], noting its extremely high [[Neutron cross section|thermal cross section]] and [[energy density]]. Nuclear systems powered by <sup>242m</sup>Am require less fuel by a factor of 2 to 100 compared to conventional [[nuclear fuel]]s.{{fact|date=March 2025}}

[[Fission-fragment rocket]] using <sup>242m</sup>Am was proposed by [[George Chapline Jr.|George Chapline]]<ref name=Chapline1988>{{cite journal |last1=Chapline |first1=George |title=Fission fragment rocket concept |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |date=August 1988 |volume=271 |issue=1 |pages=207–208 |doi=10.1016/0168-9002(88)91148-5 |bibcode=1988NIMPA.271..207C }}</ref> at [[Lawrence Livermore National Laboratory]] (LLNL) in 1988, who suggested propulsion based on the direct heating of a propellant gas by fission fragments generated by a fissile material. Ronen et al.<ref name=Ronen/> demonstrate that <sup>242m</sup>Am can maintain sustained nuclear fission as an extremely thin metallic film, less than 1/1000 of a millimeter thick. <sup>242m</sup>Am requires only 1% of the mass of <sup>235</sup>U or <sup>239</sup>Pu to reach its critical state. Ronen's group at the [[Ben-Gurion University of the Negev]] further showed that nuclear fuel based on <sup>242m</sup>Am could speed space vehicles from Earth to Mars in as little as two weeks.<ref>{{cite press release |url=https://www.sciencedaily.com/releases/2001/01/010103073253.htm|title=Extremely Efficient Nuclear Fuel Could Take Man To Mars in Just Two Weeks|date=28 December 2000|publisher=Ben-Gurion University of the Negev}}</ref>

The <sup>242m</sup>Am as a nuclear fuel is derived from the fact that it has the highest thermal fission cross section (thousands of [[Barn (unit)|barns]]), about 10x the next highest cross section across all known isotopes. The <sup>242m</sup>Am is [[fissile]] (because it has an odd number of [[neutron]]s) and has a low [[critical mass]], comparable to that of [[plutonium-239|<sup>239</sup>Pu]].<ref>{{cite web |title=Critical Mass Calculations for <sup>241</sup>Am, <sup>242m</sup>Am and <sup>243</sup>Am|url=http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf|archive-url=https://web.archive.org/web/20110722105207/http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf|archive-date=22 July 2011|access-date=3 February 2011}}</ref><ref>{{cite journal |last1=Ludewig |first1=H.|display-authors=etal |title=Design of particle bed reactors for the space nuclear thermal propulsion program |journal=Progress in Nuclear Energy |date=January 1996 |volume=30 |issue=1 |pages=1–65 |doi=10.1016/0149-1970(95)00080-4|bibcode=1996PNuE...30....1L }}</ref>

It has a very high [[Nuclear cross section|cross section]] for fission, and if in a nuclear reactor is destroyed relatively quickly. Another report claims that <sup>242m</sup>Am can sustain a chain reaction even as a thin film, and could be used for a novel type of [[nuclear rocket]].<ref name=Ronen>{{cite journal|last1=Ronen|first1=Yigal|last2=Shwageraus|first2=E.|title=Ultra-thin 241mAm fuel elements in nuclear reactors|journal=Nuclear Instruments and Methods in Physics Research A|date=2000|volume=455|issue=2|pages=442–451|doi=10.1016/s0168-9002(00)00506-4 |bibcode=2000NIMPA.455..442R}}</ref><ref name="Ronen2">{{cite journal |last1=Ronen |first1=Y |last2=Raitses |first2=G |title=Ultra-thin 242mAm fuel elements in nuclear reactors. II |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |date=April 2004 |volume=522 |issue=3 |pages=558–567 |doi=10.1016/j.nima.2003.11.421}}</ref><ref name="Ronen2000">{{cite journal |last1=Ronen |first1=Yigal |last2=Aboudy |first2=Menashe |last3=Regev |first3=Dror |title=A Novel Method for Energy Production Using 242 m Am as a Nuclear Fuel |journal=Nuclear Technology |date=March 2000 |volume=129 |issue=3 |pages=407–417 |doi=10.13182/NT00-A3071 |bibcode=2000NucTe.129..407R }}</ref><ref name="Ronen2006">{{cite journal |last1=Ronen |first1=Y. |last2=Fridman |first2=E. |last3=Shwageraus |first3=E. |title=The Smallest Thermal Nuclear Reactor |journal=Nuclear Science and Engineering |date=May 2006 |volume=153 |issue=1 |pages=90–92 |doi=10.13182/NSE06-A2597 |bibcode=2006NSE...153...90R }}</ref>

Since the thermal [[absorption cross section]] of <sup>242m</sup>Am is very high, the best way to obtain <sup>242m</sup>Am is by the capture of [[Neutron temperature#Fast|fast]] or [[Neutron temperature#Epithermal|epithermal]] neutrons in [[Americium-241]] irradiated in a [[Fast-neutron reactor|fast reactor]]. However, [[Fast neutron reactor|fast spectrum reactors]] are not readily available. Detailed analysis of <sup>242m</sup>Am breeding in existing [[pressurized water reactor]]s (PWRs) was provided.<ref>{{cite journal |last1=Golyand |first1=Leonid |last2=Ronen |first2=Yigal |last3=Shwageraus |first3=Eugene |title=Detailed Design of 242 m Am Breeding in Pressurized Water Reactors |journal=Nuclear Science and Engineering |date=May 2011 |volume=168 |issue=1 |pages=23–36 |doi=10.13182/NSE09-43 |bibcode=2011NSE...168...23G }}</ref> [[Treaty on the Non-Proliferation of Nuclear Weapons|Proliferation]] resistance of <sup>242m</sup>Am was reported by the [[Karlsruhe Institute of Technology]] 2008 study.<ref>{{cite journal |last1=Kessler |first1=G. |title=Proliferation Resistance of Americium Originating from Spent Irradiated Reactor Fuel of Pressurized Water Reactors, Fast Reactors, and Accelerator-Driven Systems with Different Fuel Cycle Options |journal=Nuclear Science and Engineering |date=May 2008 |volume=159 |issue=1 |pages=56–82 |doi=10.13182/NSE159-56 |bibcode=2008NSE...159...56K }}</ref>