Editing Fission-fragment rocket (section)

===Am-242m as nuclear fuel===

In 1987, Ronen & Leibson <ref name=Ronen1987>{{cite journal |last1=Ronen |first1=Yigal |first2=Melvin J. |last2=Leibson |title=An example for the potential applications of americium-242m as a nuclear fuel |journal=Transactions – the Israel Nuclear Society |volume=14 |year=1987 |page=V-42}}</ref><ref name=Ronen1988>{{cite journal |last1=Ronen |first1=Yigal |first2=Melvin J. |last2=Leibson |title=Potential applications of 242mAm as a nuclear fuel |journal=Nuclear Science and Engineering |volume=99 |issue=3 |year=1988 |pages= 278–284 |doi=10.13182/NSE88-A28998|bibcode=1988NSE....99..278R }}</ref> published a study on applications of {{sup|242m}}Am (an [[isotope 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}}Am require less fuel by a factor of 2 to 100 compared to conventional [[nuclear fuel]]s.

Fission-fragment rocket using {{sup|242m}}Am was proposed by [[George Chapline Jr.|George Chapline]]<ref name=Chapline1988>{{cite journal | last=Chapline |first = George | title= Fission fragment rocket concept |journal= Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | volume=271 |issue=1 |year=1988 |pages= 207–208 |doi=10.1016/0168-9002(88)91148-5|bibcode = 1988NIMPA.271..207C }}</ref> at [[Lawrence Livermore National Laboratory]] 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}}Am can maintain sustained nuclear fission as an extremely thin metallic film, less than a micrometer thick. {{sup|242m}}Am requires only 1% of the mass of {{sup|235}}U or {{sup|239}}Pu to reach its critical state. Ronen's group at [[Ben-Gurion University of the Negev]] further showed that nuclear fuel based on {{sup|242m}}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 |work=Science Daily |date=3 January 2001 |agency=Ben-Gurion University of the Negev}}</ref>

{{sup|242m}}Am's potential as a nuclear fuel comes 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. {{sup|242m}}Am is [[fissile]] and has a low [[critical mass]], comparable to [[plutonium-239|{{sup|239}}Pu]].<ref>{{cite web |title=Critical Mass Calculations for {{sup|241}}Am, {{sup|242m}}Am and {{sup|243}}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 |url-status=dead |archive-date=22 July 2011 |access-date=3 February 2011 |first1=Hemanth |last1=Dias |first2=Nigel |last2=Tancock |last3=Angela |first3=Clayton |publisher=Atomic Weapons Establishment plc |location=Aldermaston, Reading, Berkshire}}</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 |volume=30 |issue=1 |year=1996 |pages=1–65|doi=10.1016/0149-1970(95)00080-4 }}</ref> It has a very high [[Nuclear cross section|cross section]] for fission, and is destroyed relatively quickly in a nuclear reactor. Another report claims that {{sup|242m}}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. |first2=G. |last2=Raitses |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 |volume=522 |issue=3 |year=2004 |pages=558–567 |doi=10.1016/j.nima.2003.11.421}}</ref><ref name=Ronen2000>{{cite journal |last1=Ronen |first1=Yigal |first2=Menashe |last2=Aboudy |first3=Dror |last3=Regev |title=A Novel Method for Energy Production Using 242 m Am as a Nuclear Fuel |journal=Nuclear Technology |volume=129 |issue=3 |year=2000 |pages=407–417|doi=10.13182/NT00-A3071 }}</ref><ref name=Ronen2006>{{cite journal |last1=Ronen |first1=Y. |first2=E. |last2=Fridman |first3=E. |last3=Shwageraus |title=The smallest thermal nuclear reactor |journal=Nuclear Science and Engineering |volume=153 |issue=1 |year=2006 |pages=90–92|doi=10.13182/NSE06-A2597 }}</ref>

Since the thermal [[absorption cross section]] of {{sup|242m}}Am is very high, the best way to obtain {{sup|242m}}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]]s are not readily available. Detailed analysis of {{sup|242m}}Am production in existing [[Pressurized water reactor|PWRs]] was provided in.<ref>{{cite journal |last1=Golyand |first1=Leonid |first2=Yigal |last2=Ronen |first3=Eugene |last3=Shwageraus |title=Detailed Design of 242 m Am Breeding in Pressurized Water Reactors |journal=Nuclear Science and Engineering |volume=168 |issue=1 |year=2011 |pages=23–36|doi=10.13182/NSE09-43 }}</ref> [[Treaty on the Non-Proliferation of Nuclear Weapons|Proliferation]] resistance of {{sup|242m}}Am was reported by [[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 |volume=159 |issue=1 |year=2008 |pages=56–82|doi=10.13182/NSE159-56 }}</ref>

In 2000, [[Carlo Rubbia]] at [[CERN]] further extended the work by Ronen<ref name=Ronen1988/> and [[George Chapline Jr.|Chapline]]<ref name=Chapline1988 /> on fission-fragment rocket using {{sup|242m}}Am as a fuel.<ref name=Rubbia2000>{{cite report |last=Rubbia |first=Carlo |title=Fission fragments heating for space propulsion |id=No. SL-Note-2000-036-EET. CERN-SL-Note-2000-036-EET |year=2000}}</ref> Project 242<ref>{{cite journal |last1=Augelli |first1=M. |first2=G. F. |last2=Bignami |first3=G. |last3=Genta |title=Project 242: Fission fragments direct heating for space propulsion—Programme synthesis and applications to space exploration |journal=Acta Astronautica |volume=82 |issue=2 |year=2013 |pages=153–158|doi=10.1016/j.actaastro.2012.04.007 }}</ref> based on Rubbia design studied a concept of {{sup|242m}}Am based Thin-Film Fission Fragment Heated [[Nuclear thermal rocket|NTR]]<ref>{{cite report |last=Davis |first=Eric W. |title=Advanced propulsion study |publisher=Warp Drive Metrics |year=2004 |url=https://inspirehep.net/literature/1848385}}</ref> by using direct conversion of the kinetic energy of fission fragments into increasing of enthalpy of a propellant gas. Project 242 studied the application of this propulsion system to a crewed mission to Mars.<ref>{{cite journal |last=Cesana |first=Alessandra |display-authors=etal |title=Some Considerations on 242 m Am Production in Thermal Reactors |journal=Nuclear Technology |volume=148 |issue=1 |year=2004 |pages=97–101|doi=10.13182/NT04-A3550 }}</ref> Preliminary results were very satisfactory and it has been observed that a propulsion system with these characteristics could make the mission feasible. Another study focused on production of {{sup|242m}}Am in conventional thermal nuclear reactors.<ref>{{cite journal |last=Benetti |first=P. |display-authors=etal |title=Production of 242mAm |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |volume=564 |issue=1 |year=2006 |pages=48–485|doi=10.1016/j.nima.2006.04.029 }}</ref>