View source for Alpha particle X-ray spectrometer

{{Use dmy dates|date=September 2021}}
:''APXS is also an abbreviation for '''AP'''ache e'''X'''ten'''S'''ion tool, an extension for [[Apache HTTP Server|Apache]] web servers.''

{{multiple image|perrow = 2|total_width=300
| image1 = MER APXS PIA05113.jpg
| image2 = Back of Sojourner and its Alpha Proton X-Ray Spectrometer.png
| image3 = MSL - Alpha Particle X-ray Spectrometer (APXS).jpg
| footer = Alpha particle X-ray spectrometer ''(top left)'', APXS at the back of the Mars Pathfinder [[Sojourner rover|''Sojourner'' rover]] ''(top right)'', MSL [[Curiosity (rover)|''Curiosity'']]'s alpha particle X-ray spectrometer, with a ruler ''(bottom)''.
}}

An '''alpha particle X-ray spectrometer''' ('''APXS''') is a [[spectrometer]] that analyses the chemical element composition of a sample from scattered [[alpha particle]]s and fluorescent [[X-ray]]s after a sample is irradiated with alpha particles and X-rays from radioactive sources.<ref>
{{cite journal
 |title=The Alpha-Scattering Technique of Chemical Analysis
 |author=Economou, T.E. 
 |author2=Turkevich, A.L. 
 |author3=Sowinski, K.P. 
 |author4=Patterson, J.H. 
 |author5=Franzgrote, E.J.
 |journal=Journal of Geophysical Research 
 |date=1970
 |volume=75
 |issue=32
 |doi=10.1029/JB075i032p06514| pages = 6514
 |bibcode=1970JGR....75.6514E
}}
</ref> This method of analysing the elemental composition of a sample is most often used on space missions, which require low weight, small size, and minimal power consumption. Other methods (e.g. [[mass spectrometry]]) are faster, and do not require the use of radioactive materials, but require larger equipment with greater power requirements. A variation is the '''alpha proton X-ray spectrometer''', such as on the [[Mars Pathfinder|Pathfinder mission]], which also detects [[protons]].

Over the years several modified versions of this type of instrument such as APS (without X-ray spectrometer) or APXS have been flown: [[Surveyor program|Surveyor 5-7]],<ref>
{{cite journal
 |title=Alpha-scattering experiment on Surveyor 7 – Comparison with Surveyors 5 and 6
 |author=Patterson, J.H. 
 |author2=Franzgrote, E.J. 
 |author3=Turkevich, A.L. 
 |author4=Anderson, W.A. 
 |author5=Economou, T.E. 
 |author6=Griffin, H.E. 
 |author7=Grotch, S.L. 
 |author8=Sowinski, K.P.
 |journal=Journal of Geophysical Research 
 |date=1969
 |volume=74
 |issue=25 
 |pages=6120–48
 |doi=10.1029/JB074i025p06120
 |bibcode=1969JGR....74.6120P
}}
</ref> [[Mars Pathfinder]],<ref>
{{cite journal
 |title=Determination of the chemical composition of Martian soil and rocks:The alpha proton X ray spectrometer
 |author=R. Rieder
 |author2=H. Wänke
 |author3=T. Economou
 |author4=A. Turkevich
 |journal=Journal of Geophysical Research
 |date=1997
 |volume=102
 |issue=E2 
 |pages=4027–4044
 |doi=10.1029/96JE03918
 |bibcode=1997JGR...102.4027R|doi-access=free
 }}
</ref> [[Mars 96]],<ref>
{{cite journal
 |title=An Alpha Proton X-Ray Spectrometer for Mars-96 and Mars Pathfinder
 |author=Rieder, R.
 |author2=Wanke, H.
 |author3=Economou, T.
 |journal=American Astronomical Society
 |date=1997
 |volume=28 
 |pages=1062
 |bibcode=1996DPS....28.0221R
 }}</ref> [[Mars Exploration Rover]],<ref>
{{cite journal
 |title =The new Athena alpha particle X-ray spectrometer for the Mars Exploration Rovers
 |author = R. Rieder
 |author2 = R. Gellert
 |author3 = J. Brückner
 |author4 = G. Klingelhöfer
 |author5 = G. Dreibus
 |author6 =  A. Yen
 |author7 = S. W. Squyres
 |journal = Journal of Geophysical Research
 |date = 2003
 |volume = 108
 |issue =E12
 |pages = 8066
 |doi = 10.1029/2003JE002150
 |bibcode=2003JGRE..108.8066R
|doi-access = free
 }}</ref> [[Phobos program|Phobos]],<ref name=phobos>
{{cite journal
 |title=In-Situ Measurement of the Surface Composition of the Mars Moon Phobos: The Alpha-X Experiment on the Phobos Mission
 |journal=Abstracts of the Lunar and Planetary Science Conference
 |date=1988
 |volume=19
 |pages=511
 |bibcode=1988LPI....19..511H
 |last1=Hovestadt
 |first1=D.
 |last2=Andreichikov
 |first2=B.
 |last3=Bruckner
 |first3=J.
 |last4=Economou
 |first4=T.
 |last5=Klecker
 |first5=B.
 |last6=Kunneth
 |first6=E.
 |last7=Laeverenz
 |first7=P.
 |last8=Mukhin
 |first8=L.
 |last9=Prilutskii
 |first9= A.
 |display-authors=8
}}</ref> [[Mars Science Laboratory]] and the [[Philae (spacecraft)|Philae comet lander]].<ref name="philae-jgu" /><ref name=Philae>
{{cite web
 |title=Alpha Proton X-ray Spectrometer (APXS) – Mission Name: Philae
 |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=2004-006C-03
 |publisher=[[NASA]]
 |date= 26 August 2014
}}</ref> APS/APXS devices will be included on several upcoming missions including the [[Chandrayaan-2]] [[lunar rover]].<ref>
{{cite web
 |title=Payloads for Chandrayaan-2 Mission Finalised 
 |url=http://www.isro.gov.in/pressrelease/scripts/pressreleasein.aspx?Aug30_2010 
 |date=2010-08-30 
 |accessdate=2012-08-07 
 |work=isro.gov.in 
 |publisher=[[Indian Space Research Organisation]] 
 |url-status=dead 
 |archiveurl=https://web.archive.org/web/20121015032050/http://isro.gov.in/pressrelease/scripts/pressreleasein.aspx?Aug30_2010 
 |archivedate=15 October 2012 
}}</ref>

== Sources ==

Several forms of radiation are used in APXS. They include [[alpha particles]], [[protons]], and [[X-ray]]s. Alpha particles, protons, and X-rays are emitted during the radioactive decay of unstable atoms. A common source of alpha particles is [[curium-244]]. It emits particles with an energy of 5.8 [[MeV]]. X-rays of 14 and 18 keV are emitted in the decay of [[plutonium-240]]. The [[Mars Exploration Rover]]s' Athena payload uses curium-244 with a source strength of approximately {{convert|30|mCi|GBq|lk=on}}.<ref>{{cite web |url=http://athena.cornell.edu/pdf/tb_apxs.pdf |title=Alpha Particle X-Ray Spectrometer (APXS) (2 pages) |author=unknown}}</ref>

== Alpha particles ==
[[File:Pathfinder01.jpg|thumb|''[[Sojourner (rover)|Sojourner]]'' takes its APXS measurement of the [[Yogi Rock]].]]

Some of the alpha particles of a defined energy are backscattered to the detector if they collide with an atomic nucleus. The physical laws for [[Rutherford backscattering]] in an angle close to 180° are [[conservation of energy]] and conservation of [[linear momentum]]. This makes it possible to calculate the mass of the nucleus hit by the alpha particle.

Light elements absorb more energy of the alpha particle, while alpha particles are reflected by heavy nuclei nearly with the same energy. The energy spectrum of the scattered alpha particle shows peaks from 25% up to nearly 100% of the initial alpha particles. This spectrum makes it possible to determine the composition of the sample, especially for the lighter elements. The low backscattering rate makes prolonged irradiation necessary, approximately 10 hours.

== Protons ==

Some of the alpha particles are absorbed by the atomic nuclei. The [alpha,proton] process produces protons of a defined energy which are detected. [[Sodium]], [[magnesium]], [[silicon]], [[aluminium]] and [[sulfur]] can be detected by this method. This method was only used in the Mars Pathfinder APXS. For the [[Mars Exploration Rover]]s the proton detector was replaced by a second alpha particle sensor. So it is also called alpha particle X-ray spectrometer.

== X-ray ==

The alpha particles are also able to eject electrons from the inner shell (K- and L-shell) of an atom. These vacancies are filled by electrons from outer shells, which results in the emission of a characteristic X-ray. This process is termed [[particle-induced X-ray emission]] and is relatively easy to detect and has its best sensitivity and resolution for the heavier elements.

== Specific instruments ==

*''Alpha-X'', for DAS lander on Phobos 1 and Phobos 2.<ref name=phobos/><ref>[https://web.archive.org/web/20111015141115/http://space.jpl.nasa.gov/msl/QuickLooks/phobosQL.html JPL QuickLook – Phobos 1, 2]</ref>
*''ALPHA'', for Mars 96 landers. Collaboration between Germany, Russia, and USA.<ref>[http://www.iki.rssi.ru/mars96/08_mars_e.htm#%D0%90%D0%9B%D0%AC%D0%A4%D0%90 SMALL AUTONOMOUS STATIONS – Mars 96]</ref>
*''Alpha Proton X-Ray Spectrometer'', for [[Mars Pathfinder]] by the [[Max Planck Institute]] and the [[University of Chicago]].<ref name=mpf>[http://mars.jpl.nasa.gov/MPF/mpf/sci_desc.html Mars Pathfinder Instrument Descriptions – NASA]</ref>
*''Alpha Particle X-ray Spectrometer'', for ''Spirit'' (MER-A) and ''Opportunity'' (MER-B) [[Mars Exploration Rovers]].<ref>[http://athena.cornell.edu/the_mission/ins_apxs.html ATHENA – Cornell University]</ref><ref name=jpl-apxs>{{cite web|url=http://marsrovers.jpl.nasa.gov/mission/spacecraft_instru_apxs.html|title=Mars Exploration Rovers: Spacecraft: Surface Operations: Instruments: Alpha Particle X-Ray Spectrometer (APXS)|publisher=[[NASA JPL]]}}</ref>
*''Alpha Particle X-ray Spectrometer'', for ''Curiosity'' (MSL). The principal investigator for ''Curiosity''{{'}}s APXS is [[Ralf Gellert]], a physicist at the [[University of Guelph]] in [[Ontario]], Canada. It was developed and funded by the [[Canadian Space Agency]], with operations also supported by Guelph and United States' space administration.<ref>[https://web.archive.org/web/20090320125136/http://msl-scicorner.jpl.nasa.gov/Instruments/APXS/ NASA – Alpha Particle X-ray Spectrometer (APXS)]</ref>
*''Alpha Particle X-ray Spectrometer'', for [[Philae (spacecraft)|Philae]], the [[European Space Agency]]'s lander attached to [[Rosetta (spacecraft)|''Rosetta'']], to study the comet [[67P/Churyumov–Gerasimenko]].<ref name="philae-jgu">http://www.uni-mainz.de/, Johannes Gutenberg Universität Mainz, [http://www.uni-mainz.de/presse/17491_ENG_HTML.php Alpha particle x-ray spectrometer developed in Mainz to be used on comet Churyumov–Gerasimenko], 10 April 2014</ref>

== Gallery ==

<gallery>
Image:PIA18602-MarsCuriosityRover-BonanzaKingRock-20140817.jpg|"[[List of rocks on Mars#Curiosity|Bonanza King]]" rock on Mars – cleaned with "[[Curiosity (rover)#Dust Removal Tool (DRT)|Dust Removal Tool]]" (17 August 2014).
Image:PIA18477-MarsCuriosityRover-BonanzaKingRock-Drill-20140911.jpg|"[[List of rocks on Mars#Curiosity|Bonanza King]]" rock on Mars – [[:File:PIA18602-MarsCuriosityRover-BonanzaKingRock-20140817.jpg|dusted]] and initially drilled (11 September 2014).
Image:PIA18478-MarsCuriosityRover-Bonanz-KingRock-Drill-LightColorVein-20140911.jpg|"[[List of rocks on Mars#Curiosity|Bonanza King]]" rock on Mars – drilling stopped due to loose rock (11 September 2014).
Image:PIA18479-MarsCuriosityRover-BonanzaKingRock-APXS-Graph-20140911.png|"[[List of rocks on Mars#Curiosity|Bonanza King]]" rock on Mars – [[APXS|APXS analysis]] (''[[Curiosity (rover)|Curiosity]]'' rover; 11 September 2014).
</gallery>

== References ==
{{Reflist}}

== External links ==
{{Wiktionary|APXS}}
* {{Commons category-inline}} 
* {{cite journal|title= Chemical Composition of Rocks and Soils at the Pathfinder Site |author=H. Wänke |author2=J. Brückner |author3=G. Dreibus|author4=R. Rieder |author5=I. Ryabchikov|journal= Space Science Reviews| volume= 96|issue= 1/4|pages= 317–330| date= 2001|doi=10.1023/A:1011961725645|bibcode=2001SSRv...96..317W }}

{{Mars Pathfinder}}
{{NASAMER}}
{{MSL}}
{{Mars}}

{{DEFAULTSORT:Alpha Particle X-Ray Spectrometer}}
[[Category:Mars Pathfinder]]
[[Category:Mars Science Laboratory instruments]]
[[Category:Science and technology in Canada]]
[[Category:Canadian inventions]]
[[Category:Space program of Canada]]
[[Category:Mars Exploration Rover mission]]
[[Category:X-ray spectroscopy]]
[[Category:Spacecraft instruments]]
[[Category:University of Guelph]]
[[Category:Space science experiments]]