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8/12/2019 Referat Engleza Terminat

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Contents

!" Characteristics2" Aplications

2"! Military

2"2 Civilian

#" $istory

#"! Pre%descovery use

#"2 &iscovery

#"# Bom's

#"( Contamination and cold )ar le*acy

(" Compounds

("! +,ides

("2 The effects of p$

("# $y'rides-car'ides and nitrides

." /sotopes

."! 0atural concentrations

."2 1nrichment

."# $uman e,posure

."( 1feects

" 3eferences


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Uranium

Uranium is a silvery%)hite metallic chemical element in the actinide series of the

periodic ta'le )ith atomic num'er 42" /t is assi*ned the chemical sym'ol U" A uraniumatom has 42 protons and 42 electrons - of )hich are valence electrons " The uraniumnucleus 'inds 'et)een !(! and !( neutrons - esta'lishin* si, isotopes- the most commonof )hich are U%2#5 6!( neutrons7 and U%2#. 6!(# neutrons7" All isotopes are unsta'leand uranium is )ea8ly radioactive " Uranium has the second hi*hest atomic )ei*ht of thenaturally occurrin* elements- li*hter only than plutonium %2((" /ts density is a'out 9 :hi*her than that of lead- 'ut not as dense as *old or tun*sten " /t occurs naturally in lo)concentrations of a fe) parts per million in soil- roc8 and )ater- and is commerciallye,tracted from uranium%'earin* minerals such as uraninite "

/n nature - uranium is found as uranium%2#5 644"29(2:7- uranium%2#. 6 "92 (:7-and a very small amount of uranium%2#( 6 " .(:7" Uranium decays slo)ly 'y emittin*an alpha particle" The half%life of uranium%2#5 is a'out ("(9 'illion years and that ofuranium%2#. is 9 ( million years- ma8in* them useful in datin* the a*e of the 1arth "

Many contemporary uses of uranium e,ploit its uni;ue nuclear properties"Uranium%2#. has the distinction of 'ein* the only naturally occurrin* fissile isotope "Uranium%2#5 is fissiona'le 'y fast neutrons- and is fertile - meanin* it can 'e transmutedto fissile plutonium%2#4 in a nuclear reactor " Another fissile isotope- uranium%2##- can 'e

produced from natural thorium and is also important in nuclear technolo*y"


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Characteristics


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&epleted uranium is also used as a shieldin* material in some containers used tostore and transport radioactive materials"


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and a'undant" Besides the pottery *la es- uranium tile *la es accounted for the 'ul8 ofthe use- includin* common 'athroom and 8itchen tiles )hich can 'e produced in *reen-yello)- mauve- 'lac8- 'lue- red and other colors"

Uranium )as also used in photo*raphic chemicals 6especially uranium nitrate as atoner 7- in lamp filaments- to improve the appearance of dentures - and in the leather and)ood industries for stains and dyes" Uranium salts are mordants of sil8 or )ool" Uranylacetate and uranyl formate are used as electron%dense IstainsI in transmission electronmicroscopy - to increase the contrast of 'iolo*ical specimens in ultrathin sections and inne*ative stainin* of viruses - isolated cell or*anelles and macromolecules "

History

/n !492 French physicist Francis Perrin discovered fifteen ancient and no lon*eractive natural nuclear fission reactors in three separate ore deposits at the +8lo mine inEa'on -


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discovered metal itself 6in fact- that po)der )as an o,ide of uranium7"$e named thene)ly discovered element after the planet Uranus - )hich had 'een discovered ei*ht yearsearlier 'y


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nuclear proliferation could 'e avoided 'y simply 'uyin* up all 8no)n uranium stoc8s- 'ut )ithin a decade lar*e deposits of it )ere discovered in many places around the )orld"

The mushroom cloud over $iroshima after the droppin* of the uranium%'ased atomic 'om' nic8named @ittle Boy 6!4(.7

Contamination and the Cold ar le!acy

A'ove%*round nuclear tests 'y the Soviet Union and the United States in the!4. s and early !4 s and 'y France into the !49 s and !45 s spread a si*nificantamount of fallout from uranium dau*hter isotopes around the )orld"Additional falloutand pollution occurred from several nuclear accidents "

Uranium miners have a hi*her incidence of cancer " An e,cess ris8 of lun* canceramon* 0ava o uranium miners- for e,ample- has 'een documented and lin8ed to theiroccupation"The 3adiation 1,posure Compensation Act - a !44 la)- re;uired ! - inIcompassion paymentsI to uranium miners dia*nosed )ith cancer or other respiratoryaliment"

&urin* the Cold


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at research and stora*e facilities" Scientific American reported in Fe'ruary 2 thatsome of the facilities security consisted of chain lin8 fences )hich )ere in severe statesof disrepair" Accordin* to an intervie) from the article- one facility had 'een storin*samples of enriched 6)eapons *rade7 uranium in a 'room closet 'efore the improvement

pro ect another had 'een 8eepin* trac8 of its stoc8 of nuclear )arheads usin* inde, cards

8ept in a shoe 'o,"

Compounds

"#ides

The most common forms of uranium o,ide are triuranium octao#ide 6U$" %7 andU" &" Both o,ide forms are solids that have lo) solu'ility in )ater and are relativelysta'le over a )ide ran*e of environmental conditions" Triuranium octao,ide is6dependin* on conditions7 the most sta'le compound of uranium and is the form mostcommonly found in nature" Uranium dio,ide is the form in )hich uranium is mostcommonly used as a nuclear reactor fuel"At am'ient temperatures- U" & )ill *raduallyconvert to U$" %" Because of their sta'ility- uranium o,ides are *enerally considered the

preferred chemical form for stora*e or disposal"

'he e((ect o( pH

The uranium fraction dia*rams in the presence of car'onate illustrate this further)hen the p$ of a uranium6Q/7 solution increases- the uranium is converted to a hydrateduranium o,ide hydro,ide and at hi*h p$s it 'ecomes an anionic hydro,ide comple,"


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Uranium car'ides and uranium nitrides are 'oth relatively inert semimetallic compounds that are minimally solu'le in acids - react )ith )ater- and can i*nite in air toform U #+ 5"Car'ides of uranium include uranium monocar'ide 6U C7- uranium dicar'ide6UC27- and diuranium tricar'ide 6U 2C#7" Both UC and UC 2 are formed 'y addin* car'onto molten uranium or 'y e,posin* the metal to car'on mono,ide at hi*h temperatures"

Sta'le 'elo) !5 RC- U 2C# is prepared 'y su' ectin* a heated mi,ture of UC and UC 2 tomechanical stress"Uranium nitrides o'tained 'y direct e,posure of the metal to nitro*en include uranium mononitride 6U07- uranium dinitride 6U0 27- and diuranium trinitride6U2 0 #7"

Isotopes

Natural concentrations

0atural uranium consists of three ma or isotopes uranium%2#5 644"25: naturala'undance 7- uranium%2#. 6 "9!:7- and uranium%2#( 6 " .(:7" All three areradioactive- emittin* alpha particles - )ith the e,ception that all three of these isotopeshave small pro'a'ilities of under*oin* spontaneous fission - rather than alpha emission "

Uranium%2#5 is the most sta'le isotope of uranium- )ith a half%life of a'out("( 5G! 4 years- rou*hly the a*e of the 1arth " Uranium%2#. has a half%life of a'out9"!#G! 5 years- and uranium%2#( has a half%life of a'out 2"(5G! . years"For naturaluranium- a'out (4: of its alpha rays are emitted 'y each of U%2#5- and also (4: 'y U%2#(U 6since the latter is formed from the former7 and a'out 2" : of them 'y the U%2#."


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Uranium%2#. is important for 'oth nuclear reactors and nuclear )eapons - 'ecauseit is the only uranium isotope e,istin* in nature on 1arth in any si*nificant amount that isfissile " This means it can 'e split into t)o or three fra*ments 6 fission products 7 'ythermal neutrons"

Uranium%2#5 is not fissile- 'ut is a fertile isotope- 'ecause after neutron activation it can produce plutonium%2#4- another fissile isotope" /ndeed- the U%2#5 nucleus cana'sor' one neutron to produce the radioactive isotope uranium%2#4" U%2#4 decays 'y

'eta emission to neptunium %2#4- also a 'eta%emitter- that decays in its turn- )ithin a fe)days into plutonium%2#4" Pu%2#4 )as used as fissile material in the first atomic 'om' detonated in the I Trinity test I on !. Kuly !4(. in 0e) Me,ico "

*nrichment

/sotope separation concentrates 6enriches7 the fissiona'le uranium%2#. for nuclear)eapons and most nuclear po)er plants- e,cept for *as cooled reactors and pressurisedheavy )ater reactors" Most neutrons released 'y a fissionin* atom of uranium%2#. mustimpact other uranium%2#. atoms to sustain the nuclear chain reaction" The concentrationand amount of uranium%2#. needed to achieve this is called a critical mass "

To 'e considered enriched - the uranium%2#. fraction should 'e 'et)een #: and.:"This process produces hu*e ;uantities of uranium that is depleted of uranium%2#. and)ith a correspondin*ly increased fraction of uranium%2#5- called depleted uranium or

&U " To 'e considered depleted - the uranium%2#. isotope concentration should 'e nomore than "#:"The price of uranium has risen since 2 !- so enrichment tailin*scontainin* more than "#.: uranium%2#. are 'ein* considered for re%enrichment- drivin*the price of depleted uranium he,afluoride a'ove !# per 8ilo*ram in Kuly- 2 9 from

. in 2 !"

The *as centrifu*e process- )here *aseous uranium he,afluoride 6UF 7 isseparated 'y the difference in molecular )ei*ht 'et)een 2#. UF and 2#5UF usin* hi*h%speed centrifu*es - is the cheapest and leadin* enrichment process" N2!O The *aseousdiffusion process had 'een the leadin* method for enrichment and )as used in theManhattan Pro ect " /n this process- uranium he,afluoride is repeatedly diffused throu*h asilver % inc mem'rane- and the different isotopes of uranium are separated 'y diffusionrate 6since uranium 2#5 is heavier it diffuses sli*htly slo)er than uranium%2#.7"Themolecular laser isotope separation method employs a laser 'eam of precise ener*y tosever the 'ond 'et)een uranium%2#. and fluorine" This leaves uranium%2#5 'onded tofluorine and allo)s uranium%2#. metal to precipitate from the solution"An alternativelaser method of enrichment is 8no)n as atomic vapor laser isotope separation 6AQ@/S7and employs visi'le tuna'le lasers such as dye lasers "Another method used is li;uidthermal diffusion"
http://en.wikipedia.org/wiki/Nuclear_reactorhttp://en.wikipedia.org/wiki/Nuclear_weaponhttp://en.wikipedia.org/wiki/Fissilehttp://en.wikipedia.org/wiki/Fission_productshttp://en.wikipedia.org/wiki/Neutron_activationhttp://en.wikipedia.org/wiki/Neutron_activationhttp://en.wikipedia.org/wiki/Plutonium-239http://en.wikipedia.org/wiki/Plutonium-239http://en.wikipedia.org/wiki/Uranium-239http://en.wikipedia.org/wiki/Uranium-239http://en.wikipedia.org/wiki/Beta_emissionhttp://en.wikipedia.org/wiki/Neptuniumhttp://en.wikipedia.org/wiki/Atomic_bombhttp://en.wikipedia.org/wiki/Atomic_bombhttp://en.wikipedia.org/wiki/Trinity_testhttp://en.wikipedia.org/wiki/New_Mexicohttp://en.wikipedia.org/wiki/Isotope_separationhttp://en.wikipedia.org/wiki/Gas_cooled_reactorhttp://en.wikipedia.org/wiki/Pressurised_heavy_water_reactorhttp://en.wikipedia.org/wiki/Pressurised_heavy_water_reactorhttp://en.wikipedia.org/wiki/Nuclear_chain_reactionhttp://en.wikipedia.org/wiki/Critical_masshttp://en.wikipedia.org/wiki/Gas_centrifugehttp://en.wikipedia.org/wiki/Gas_centrifugehttp://en.wikipedia.org/wiki/Uranium_hexafluoridehttp://en.wikipedia.org/wiki/Uranium_hexafluoridehttp://en.wikipedia.org/wiki/Uranium_hexafluoridehttp://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Uranium#cite_note-BuildingBlocks478-20http://en.wikipedia.org/wiki/Gaseous_diffusionhttp://en.wikipedia.org/wiki/Gaseous_diffusionhttp://en.wikipedia.org/wiki/Manhattan_Projecthttp://en.wikipedia.org/wiki/Manhattan_Projecthttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Silverhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Molecular_laser_isotope_separationhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Atomic_vapor_laser_isotope_separationhttp://en.wikipedia.org/wiki/Tunable_laserhttp://en.wikipedia.org/wiki/Dye_laserhttp://en.wikipedia.org/wiki/Dye_laserhttp://en.wikipedia.org/wiki/Nuclear_reactorhttp://en.wikipedia.org/wiki/Nuclear_weaponhttp://en.wikipedia.org/wiki/Fissilehttp://en.wikipedia.org/wiki/Fission_productshttp://en.wikipedia.org/wiki/Neutron_activationhttp://en.wikipedia.org/wiki/Plutonium-239http://en.wikipedia.org/wiki/Uranium-239http://en.wikipedia.org/wiki/Beta_emissionhttp://en.wikipedia.org/wiki/Neptuniumhttp://en.wikipedia.org/wiki/Atomic_bombhttp://en.wikipedia.org/wiki/Trinity_testhttp://en.wikipedia.org/wiki/New_Mexicohttp://en.wikipedia.org/wiki/Isotope_separationhttp://en.wikipedia.org/wiki/Gas_cooled_reactorhttp://en.wikipedia.org/wiki/Pressurised_heavy_water_reactorhttp://en.wikipedia.org/wiki/Pressurised_heavy_water_reactorhttp://en.wikipedia.org/wiki/Nuclear_chain_reactionhttp://en.wikipedia.org/wiki/Critical_masshttp://en.wikipedia.org/wiki/Gas_centrifugehttp://en.wikipedia.org/wiki/Uranium_hexafluoridehttp://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Uranium#cite_note-BuildingBlocks478-20http://en.wikipedia.org/wiki/Gaseous_diffusionhttp://en.wikipedia.org/wiki/Gaseous_diffusionhttp://en.wikipedia.org/wiki/Manhattan_Projecthttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Silverhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Molecular_laser_isotope_separationhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Atomic_vapor_laser_isotope_separationhttp://en.wikipedia.org/wiki/Tunable_laserhttp://en.wikipedia.org/wiki/Dye_laser


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Cascades of *as centrifu*es are used to enrich uranium ore to concentrate its fissiona'leisotopes"

Human e#posure

A person can 'e e,posed to uranium 6or its radioactive dau*hters such as radon 7 'y inhalin* dust in air or 'y in*estin* contaminated )ater and food" The amount ofuranium in air is usually very small ho)ever- people )ho )or8 in factories that process

phosphate fertili ers- live near *overnment facilities that made or tested nuclear )eapons-live or )or8 near a modern 'attlefield )here depleted uranium )eapons have 'een used-or live or )or8 near a coal%fired po)er plant- facilities that mine or process uranium ore-or enrich uranium for reactor fuel- may have increased e,posure to uranium"$ouses orstructures that are over uranium deposits 6either natural or man%made sla* deposits7 mayhave an increased incidence of e,posure to radon *as"

Most in*ested uranium is e,creted durin* di*estion " +nly ".: is a'sor'ed )heninsolu'le forms of uranium- such as its o,ide- are in*ested- )hereas a'sorption of themore solu'le uranyl ion can 'e up to .:"$o)ever- solu'le uranium compounds tend to;uic8ly pass throu*h the 'ody )hereas insolu'le uranium compounds- especially )henin*ested 'y )ay of dust into the lun*s- pose a more serious e,posure ha ard" Afterenterin* the 'loodstream- the a'sor'ed uranium tends to 'ioaccumulate and stay formany years in 'one tissue 'ecause of uranium s affinity for phosphates"Uranium is nota'sor'ed throu*h the s8in- and alpha particles released 'y uranium cannot penetrate thes8in"

/ncorporated uranium 'ecomes uranyl ions- )hich accumulate in 'one- liver-8idney- and reproductive tissues" Uranium can 'e decontaminated from steel surfaces anda;uifers "
http://en.wikipedia.org/wiki/Gas_centrifugehttp://en.wikipedia.org/wiki/Radonhttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Weaponshttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Digestionhttp://en.wikipedia.org/wiki/Uranylhttp://en.wikipedia.org/wiki/Lunghttp://en.wikipedia.org/wiki/Bioaccumulationhttp://en.wikipedia.org/wiki/Bonehttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Uranylhttp://en.wikipedia.org/wiki/Aquiferhttp://en.wikipedia.org/wiki/File:Gas_centrifuge_cascade.jpghttp://en.wikipedia.org/wiki/Gas_centrifugehttp://en.wikipedia.org/wiki/Radonhttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Weaponshttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Digestionhttp://en.wikipedia.org/wiki/Uranylhttp://en.wikipedia.org/wiki/Lunghttp://en.wikipedia.org/wiki/Bioaccumulationhttp://en.wikipedia.org/wiki/Bonehttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Uranylhttp://en.wikipedia.org/wiki/Aquifer


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*((ects

0ormal functionin* of the 8idney - 'rain - liver - heart - and other systems can 'eaffected 'y uranium e,posure- 'ecause- 'esides 'ein* )ea8ly radioactive- uranium is ato,ic metal "Uranium is also a reproductive to,icant"3adiolo*ical effects are *enerallylocal 'ecause alpha radiation- the primary form of U%2#5 decay- has a very short ran*e-and )ill not penetrate s8in" Uranyl 6U+ 2 7 ions- such as from uranium trio,ide or uranylnitrate and other he,avalent uranium compounds- have 'een sho)n to cause 'irth defectsand immune system dama*e in la'oratory animals"


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Re(erences

V 1msley- Kohn 62 !7"IUraniumI " Nature's Building Blocks: An A to Z Guide to the Elements "+,ford +,ford University Press " pp" (9 D(52V Sea'or*- Elenn T" 6!4 57" IUraniumI" The Encyclopedia of the Chemical Elements "S8o8ie- /llinois 3einhold Boo8 Corporation" pp" 99#D95
http://en.wikipedia.org/wiki/John_Emsleyhttp://books.google.com/?id=j-Xu07p3cKwC&printsec=frontcoverhttp://en.wikipedia.org/wiki/Oxfordhttp://en.wikipedia.org/wiki/Oxford_University_Presshttp://en.wikipedia.org/wiki/Glenn_T._Seaborghttp://en.wikipedia.org/wiki/Skokie,_Illinoishttp://en.wikipedia.org/wiki/John_Emsleyhttp://books.google.com/?id=j-Xu07p3cKwC&printsec=frontcoverhttp://en.wikipedia.org/wiki/Oxfordhttp://en.wikipedia.org/wiki/Oxford_University_Presshttp://en.wikipedia.org/wiki/Glenn_T._Seaborghttp://en.wikipedia.org/wiki/Skokie,_Illinois


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