{"id":1672,"date":"2017-10-03T02:00:03","date_gmt":"2017-10-03T02:00:03","guid":{"rendered":"https:\/\/himinn.fjarver.is\/mengunsjavar\/?p=1672"},"modified":"2021-02-18T00:27:25","modified_gmt":"2021-02-18T00:27:25","slug":"6-2-geislun-og-geislavirkni","status":"publish","type":"post","link":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/2017\/10\/03\/6-2-geislun-og-geislavirkni\/","title":{"rendered":"6.2 Geislun og geislavirkni"},"content":{"rendered":"

Frumefni eru efni sem a\u00f0eins eru samsett \u00far einni ger\u00f0 frumeinda (at\u00f3ma). Frumeindir eru ger\u00f0ar \u00far r\u00f3teindum, rafeindum og nifteindum.<\/span>\u00a0R\u00f3teindir og nifteindir eru \u00ed kjarna frumeindanna og er kjarnanum haldi\u00f0 saman af sterkum kjarnakr\u00f6ftum. Rafeindir sveima \u00e1 brautum umhverfis kjarnann. Fj\u00f6ldi r\u00f3teinda segir til um eiginleika hverrar frumeindar. Frumeindir hvers frumefnis hafa alltaf sama fj\u00f6lda r\u00f3teinda en fj\u00f6ldi nifteinda getur hins vegar veri\u00f0 breytilegur. Til d\u00e6mis hefur vetni, sem er einfaldasta frumefni\u00f0, eina r\u00f3teind. Hins vegar eru til \u00ferj\u00e1r mismunandi sams\u00e6tur<\/span> af vetni, \u00fe.e. vetni (1 r\u00f3teind, engin nifteind), d\u00edtr\u00edum (1 r\u00f3teind, 1 nifteind) og tr\u00edt\u00edum (ein r\u00f3teind, 2 nifteindir). Flest frumefni sem finnast \u00ed n\u00e1tt\u00farunni eru blanda af mismunandi sams\u00e6tum.<\/p>\n

92 frumefni finnast \u00ed n\u00e1tt\u00farunni en okkur m\u00f6nnunum hefur tekist a\u00f0 b\u00faa til nokkur efni \u00ed vi\u00f0b\u00f3t. \u00c1kve\u00f0nir frumeindakjarnar sem finnast \u00ed n\u00e1tt\u00farunni eru \u00f3st\u00f6\u00f0ugir, \u00feeir ummyndast sj\u00e1lfkrafa og losa \u00ed lei\u00f0inni gr\u00ed\u00f0armikla orku \u00ed formi geislunar. Sl\u00edk efni eru k\u00f6llu\u00f0 geislavirk<\/em> og kallast ummyndarferli\u00f0 kjarnasundrun<\/em>. Vi\u00f0 kjarnasundrun losna hla\u00f0nar agnir \u00far kjarnanum og orsaka geislun. Til eru \u00ferj\u00e1r tegundir geislunar : \u03b1-geislun, \u03b2-geislun og \u03b3-geislun<\/span>. Geislavirkni er m\u00e6ld me\u00f0 m\u00e6lieiningunni becquerel (Bq) sem er skilgreind sem 1 kjarnasundrun \u00e1 sek\u00fandu.<\/p>\n

\u00deegar alfa-geislun \u00e1 s\u00e9r sta\u00f0 losnar \u00ed raun hel\u00edumkjarni fr\u00e1 kjarnanum, \u00fe.e. \u00f6gn sem samanstendur af tveimur r\u00f3teindum og tveimur nifteindum. \u00deegar beta-geislun \u00e1 s\u00e9r sta\u00f0 losnar rafeind \u00far kjarnanum og \u00feegar gamma-geislun \u00e1 s\u00e9r sta\u00f0 losna gr\u00ed\u00f0arlega orkur\u00edkar lj\u00f3seindir. \u00deegar geislavirkt frumefni sendir fr\u00e1 s\u00e9r alfa- e\u00f0a betageislun breytist frumefni\u00f0 \u00ed anna\u00f0 frumefni (fj\u00f6ldi r\u00f3teinda breytist, f\u00e6kkar e\u00f0a fj\u00f6lgar).<\/p>\n

\u00daran\u00edum-238 (U-238) hefur 92 r\u00f3teindir og 146 nifteindir. \u00deessi \u00faran\u00edum-sams\u00e6ta er geislavirk og sendir fr\u00e1 s\u00e9r alfa-\u00f6gn. Vi\u00f0 \u00fea\u00f0 myndast n\u00fdr kjarni, \u00fe\u00f3r\u00edum (Th-234), me\u00f0 90 r\u00f3teindir.<\/p>\n

238<\/sup>92<\/sub><\/span>U \u2192 4<\/sup>2<\/sub><\/span>\u03b1 + 234<\/sup>90<\/sub><\/span>Th<\/p>\n

\u00de\u00f3r\u00edumkjarninn er l\u00edka \u00f3st\u00f6\u00f0ugur. \u00cd kjarnanum ummyndast ein nifteind \u00ed r\u00f3teind og sendir fr\u00e1 s\u00e9r beta-geislun sem er \u00ed raun h\u00e1hra\u00f0a-rafeind.<\/p>\n

1<\/sup>0<\/sub><\/span>n \u2192 1<\/sup>1<\/sub><\/span>p + \u03b2 –<\/sup><\/p>\n

\u00deetta er svok\u00f6llu\u00f0 beta-geislun. \u00de\u00f3r\u00edum-kjarninn sem mynda\u00f0ist vi\u00f0 alfa-sundrun \u00e1 \u00faran\u00edum-238 sundrast \u00e1fram me\u00f0 beta-geislun og ver\u00f0ur a\u00f0 pr\u00f3takt\u00edn\u00edum (Pa-234).<\/p>\n

234<\/sup>90<\/sub><\/span>Th \u2192 234<\/sup>91<\/sub><\/span>Pa + \u03b2 –<\/sup><\/p>\n

Pr\u00f3takt\u00edn\u00edum er l\u00edka \u00f3st\u00f6\u00f0ugt efni og ummyndast \u00e1fram. Ummyndunin heldur \u00e1fram en \u00e1 endanum myndast bl\u00fd-206 (Pb-206) sem er st\u00f6\u00f0ugt.<\/p>\n

\u00deegar alfa- e\u00f0a betageislun hefur \u00e1tt s\u00e9r sta\u00f0 ver\u00f0ur yfirleitt endurr\u00f6\u00f0un \u00ed kjarnanum en vi\u00f0 \u00fea\u00f0 losnar orka \u00e1 formi gammageislunar. Alfa-\u00f6gn er st\u00f3r \u00ed samhengi kjarnorkunnar og fer\u00f0ast \u00fev\u00ed frekar h\u00e6gt \u00ed gegnum efni. \u00dev\u00ed eru miklar l\u00edkur \u00e1 a\u00f0 \u00f6gnin lendi \u00e1 \u00f6\u00f0rum frumeindum og gefi fr\u00e1 s\u00e9r hluta orkunnar vi\u00f0 hvern \u00e1rekstur. Alfa-agnir missa \u00fev\u00ed orku s\u00edna hratt og geta einungis fer\u00f0ast stuttar vegalengdir. Beta-agnir eru miklu sm\u00e6rri en alfa-agnir og hreyfast miklu hra\u00f0ar. \u00de\u00e6r lenda \u00fev\u00ed mun sjaldnar \u00e1 frumeindum en alfa-agnir mi\u00f0a\u00f0 vi\u00f0 s\u00f6mu vegalengd og geta \u00fev\u00ed fer\u00f0ast mun lengra. Gammageislar tapa orku a\u00f0allega me\u00f0 samverkun vi\u00f0 rafeindir at\u00f3ma. Geislunin fer\u00f0ast mj\u00f6g langar vegalengdir og n\u00e1nast er \u00f3m\u00f6gulegt a\u00f0 fanga og skerma geislunina algerlega.<\/p>\n

Til eru fj\u00f3rar n\u00e1tt\u00farulegar geislavirkar frumefnaser\u00edur (mynd 6.2). Hver ser\u00eda inniheldur h\u00f3p frumefna sem myndast hafa \u00feegar \u00feungir at\u00f3mkjarnar hafa sundrast me\u00f0 r\u00f6\u00f0 af alfa- og betasundrun \u00fear til st\u00f6\u00f0ugur kjarni myndast. Helmingunart\u00edmi nept\u00fan\u00edums er 2 millj\u00f3nir \u00e1ra, sem er stutt mi\u00f0a\u00f0 vi\u00f0 aldur jar\u00f0arinnar og \u00fev\u00ed er sundrun nept\u00fan\u00edum-ser\u00edunnar loki\u00f0 fyrir l\u00f6ngu s\u00ed\u00f0an.<\/p>\n

\"\"<\/a>

Mynd 6.2. N\u00e1tt\u00farulegar geislavirkar frumefnaser\u00edur: \u00fe\u00f3r\u00edum-ser\u00edan, nept\u00fan\u00edum-ser\u00edan, \u00faran\u00edum-ser\u00edan og aktin\u00edum-ser\u00edan.<\/p><\/div>\n

Helmingunart\u00edmi<\/em> geislavirkra efna er s\u00e1 t\u00edmi sem \u00fea\u00f0 tekur helming kjarnanna \u00ed efninu a\u00f0 geisla fr\u00e1 s\u00e9r og ummyndast. \u00deessi t\u00edmi er \u00f3h\u00e1\u00f0ur upphaflegu magni efnisins. Ef vi\u00f0 h\u00f6fum 100 gr\u00f6mm af geislavirku efni me\u00f0 helmingunart\u00edmann 2 sek\u00fandur \u00fe\u00e1 munum vi\u00f0 hafa 50 g af efninu eftir 2 sek\u00fandur, 25 g eftir 4 sek\u00fandur, 12,5 g eftir 6 sek\u00fandur og svo framvegis. Helmingunart\u00edmi geislavirkrar sams\u00e6tu er fasti. \u00deegar miki\u00f0 er af geislavirkri sams\u00e6tu er mikil geislavirkni \u00ed umhverfinu. \u00deegar fleiri og fleiri kjarnar \u00ed s\u00fdninu hafa hr\u00f6rna\u00f0 h\u00e6gir \u00e1 geisluninni, \u00fe.e. minni geislun ver\u00f0ur \u00e1 t\u00edmaeiningu \u00feegar f\u00e6rri geislavirkir kjarnar eru eftir. Eftir 10 helmingunart\u00edma er um 0,1% af upprunalega efninu enn til sta\u00f0ar.<\/p>\n

Geislun er, og hefur alltaf veri\u00f0, hluti af n\u00e1tt\u00farulegu umhverfi \u00e1 j\u00f6r\u00f0inni. S\u00fa n\u00e1tt\u00farlega geislun sem vi\u00f0 ver\u00f0um fyrir er geislun sem berst fr\u00e1 geimnum (geimgeislun), geislun fr\u00e1 geislavirkum efnum \u00ed jar\u00f0vegi og bergi, geislun fr\u00e1 geislavirkum efnum \u00ed l\u00edkama okkar (\u00fe.\u00e1 m. geislavirkt kolefni, C-14, og geislavirkt kal\u00edum, K-40) og geislun fr\u00e1 geislavirkum lofttegundum sem vi\u00f0 \u00f6ndum a\u00f0 okkur (Rn-222). St\u00f3r hluti geislavirkni \u00ed l\u00edkamanum stafar af lofttegundum sem myndast vegna sundrunar \u00ed \u00faran\u00edum-ser\u00edunni annars vegar og \u00fe\u00f3r\u00edum-ser\u00edunni hins vegar. \u00deessar lofttegundir st\u00edga upp \u00far bergi og jar\u00f0vegi, dreifast og eru m\u00e6lanlegar \u00ed andr\u00famsloftinu. Vi\u00f0 \u00f6ndum \u00feeim a\u00f0 okkur, sem og ni\u00f0urbrotsefnum \u00feeirra. Pl\u00f6ntur og d\u00fdr taka einnig upp geislavirk efni og \u00fev\u00ed innihalda flestar f\u00e6\u00f0utegundir geislavirk efni af n\u00e1tt\u00farulegum uppruna. \u00deannig innihalda \u00fdmsar korntegundir nokku\u00f0 h\u00e1tt magn geislavirkra efna en mj\u00f3lkurv\u00f6rur, \u00e1vextir og gr\u00e6nmeti minna. N\u00e1tt\u00faruleg geislavirkni \u00e1 \u00cdslandi er l\u00e1g og mun l\u00e6gri en \u00e1 hinum Nor\u00f0url\u00f6ndunum, \u00fear sem berggrunnurinn h\u00e9rlendis er a\u00f0 mestu ger\u00f0ur \u00far bas\u00edsku eldfjallabergi sem er snautt af geislavirkum efnum.<\/p>\n","protected":false},"excerpt":{"rendered":"

Frumefni eru efni sem a\u00f0eins eru samsett \u00far einni ger\u00f0 frumeinda (at\u00f3ma). Frumeindir eru ger\u00f0ar \u00far \u00a0R\u00f3teindir og nifteindir eru \u00ed kjarna frumeindanna og er kjarnanum haldi\u00f0 saman af sterkum kjarnakr\u00f6ftum. Rafeindir sveima \u00e1 brautum umhverfis kjarnann. Fj\u00f6ldi r\u00f3teinda segir Lesa meira…<\/a><\/p>\n","protected":false},"author":2,"featured_media":1751,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-1672","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-6-geislavirkni"],"_links":{"self":[{"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/posts\/1672","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/comments?post=1672"}],"version-history":[{"count":33,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/posts\/1672\/revisions"}],"predecessor-version":[{"id":3523,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/posts\/1672\/revisions\/3523"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/media\/1751"}],"wp:attachment":[{"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/media?parent=1672"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/categories?post=1672"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/wp-json\/wp\/v2\/tags?post=1672"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}