Phan Tich Hat Nhan

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4/30/20121 CC PHNG PHP PHN TCH HT NHN NGUYN T HUNH TRC PHNG Email: htphuong.oarai@gmail.com Mobile: 0908 272 808 4/30/20122 NI DUNG Phn 1: Phng php phn tch hunh quang tia X(X-Ray Fluorescence Analysis, XRFA) Phn 2: Phng php phn tch kch hot neutron(Neutron Activation Analysis, NAA) 4/30/20123 PHN 1 PHNG PHP PHN TCH HUNH QUANG TIA X MT PHNG PHP TNG QUT CHO MC CH PHN TCH CC NGUYN T 4/30/20124 1. Gii thiuHunh quang tia X Hunh quang tia X thc hin nh th no? Cc nguyn t trong mt mu b kch thch v pht ra nhng tia X c trng Nng lng cc tia X c trngloi nguyn t hin din trong mu (nh tnh) S tia X pht ra t mu nng nguyn t (nh lng) 4/30/20125 1. Gii thiuPh hunh quang tia X Ta quan st thy ph hunh quang tia X nh th no? 4/30/20126 1. Gii thiuCc c trng phn tch ca XRF Ti sao v khi no ta dng XRF? K thut phn tch dng c - c kh nng phn tch a nguyn t Phn tch nguyn t trong mu rn, lng X l mu nh Khong nng : ppm n % Khong nguyn t t Bo n U (l thuyt) Qun l qu trnh cng nghip (luyn kim, xi mng, thy tinh, cng nghip) Thm d v khai thc qung m a cht v a ha hc Nghin cu vt liu, phn tch mi trng, kho c. C hn 14,000 thit b XRF trn ton th gii 4/30/20127 2. Tia XBn cht ca tia X TiaXlmtphncaphbcxintnmgia vng bc x t ngoi v tia gamma KhicpnnhiuxchngtaxemtiaXnhl sng in t c bc sng KhimtqutrnhhpthvtnxthtiaXc xem nh l photon c nng lng xc nh E Mi lin h gia nng lng v bc sng hcE =h: hng s Planck, c: vn tc nh sng (1.1) 4/30/20128 2. Tia XTrong ph k tia X Bc sng c n v Angstrom A0 (1A0 = 10-10m) Nng lng c n v kilo-electron volt (keV) 4/30/20129 Tng tc ca tia X vi vt cht Mu nguyn t Bohr ZelectroncnhmtrncclpK,L,M,N,O,P (tng ng vi s lng t chnh n = 1, 2, 3, 4, 5) Mt lp v nguyn t c th cha ti a 2n2 electron Trongmilpv,ccelectroncphnbitbi cc s lng t mmen ng lng (l = 0, 1,..(n-1)), slngtt(m=0,1,2,.l)vslngt spin (s = 1/2). Haielectrontrongmtnguyntkhngthccng b s lng t (nguyn l loi tr Pauli) 4/30/201210 Tng tc ca tia X vi vt cht Selectrontrongnguyntchimytrncc mc nng lng Electron trn lp K lin kt cht ch hn electron lp L Smcnnglng(hocmccon)trn milpv bng s gi tr c php ca j (j l s lng t ton phn), LpKcmt mcnnglng,lpLc3mc(L1, L2, L3), lp M c 5 mc (M1,,M5) 2 / 1 = j4/30/201211 Mc nng lng ca lp K, L v M Lpnl=0,1,..n-1JS e- cc i, 2j+1 K102 L120 (0+1/2)2 L221 (1-1/2)2 L3213/2(1+1/24 M1302 M2312 M3313/24 M4323/24 M5325/26 4/30/201212 Nng lng lin kt ca e- bn trong cng bc ln vi nng lng photon tia X Tia X c th tng tc vi e- thuc lp v trong Mc nng lng ca Cu Mc conKL1L2L3 Nng lng lin kt (keV) 8,9811,1020,9530,933 4/30/201213 Tng tc ca tia X vi electron nguyn t Hp th photon Hp th quang in l tng tc ch yu lm pht ra cc tia X c trng trong mu Tn x photon Nn lin tc c quan st trn ph XRF (Mt phn bc x kch thch b tn x bi mu v xuyn vo detector) 4/30/201214 Hp th quang in Mt photon b hp th hon ton bi nguyn t (lp v bn trong) lm bt ra mt electron Mt phn nng lng photon chuyn thnh nng lng lin kt ca electron, phn nng lng cn li truyn cho electron di dng ng nngHp th quang in ch xy ra nu Ephoton > Eab Sau khi tng tc, nguyn t (thc s l ion) trng thi kch thch Mt l trng c to ra trn mt lp v nguyn t 4/30/201215 Nguyn t dng nh lp tc tr v trng thi bn hn pht ra mt electron Auger hoc photon tia X c trng Xc sut pht ra tia X c trng c gi l hiu sut hunh quang,e Trn hnh ta thy tit din quang in ca Cu l mt hm theo nng lng ca photon tng tc, tph(E) Hp th quang in (tt) 4/30/201216 Ti nng lng cao xc sut gii phng mt electron l kh thp Ti nng lng E gn bng 8,981keV tit din tng tc cao hn Ti nng lng ng bng 8,98 keV c mt s gim t ngt v tit din Cc tia X nng lng thp hn ch c th tng tc vi electron lp v L hay M T s tit din ngay bn trn v bn di cnh hp th c gi l t s nhy vt, J Hp th quang in (tt) ) () (kkkJuu=+ttkkkki iiJE EE=uu~+) () () ( ) () (0 00ttt ttkki kiJJE E1) ( ) (0 0~t t(1.2) (1.3) 4/30/201217 Nng lng cnh hp th ca mt s nguyn t 4/30/201218 Tn x n hi v khng n hi Tn x lm photon thay i hng Tn x n hi (hay tn x Rayleigh) o Nng lng photon trc v sau tn x bng nhau o Xy ra trn cc electron lin kt cht ch o Dng c bn ca nhiu x tia X Tn x khng n hi (hay tn x Compton) o Photon mt mt t nng lng ca n o Xy ra khi photon tia X tng tc vi electron lin kt yu o MtphotonnnglngEtnx khngnhimtgcuscnli nnglngEthamnphngtrnh Compton: 4/30/201219 S suy gim tia X qua vt cht Tia X xuyn qua vt cht c vi photon s b nh hng bi: s hp th quang in s tn x Cng I0 ca mt chm tia X xuyn qua mt lp dy d v mt th cng I cn li tha mn nh lut Lambert-Beer: S photon (cng ) b gim nhng nng lng ca n khng thay i. l h s suy gim khi c th nguyn [cm2/g]. H s suy gim khi ton phn l s ng gp ca hp th quang in, tn x kt hp v khng kt hp (1.4) (1.5) 4/30/201220 Mt th log-log biu din h s suy gim khi ca Al, Fe v Pb i vi tia X c nng lng t 0.1 keV n 50 keV Cnh hp th do hp th quang in nhn thy kh r rng Vt liu Z thp suy gim tia X t hn vt liu c Z cao Nng lng tia X cao (tia X cng) suy gim t hn nng lng tia X thp (tia mm) 4/30/201221 H s suy gim khi ca mt matrix phc tp (hn hp, hay hp kim) c th c tnh nh sau: I l h s suy gim khi ca nguyn t i wi l hm lng (%) ca nguyn t th i 4/30/201222 Pht tia X c trng Saukhihpthquanginnguynttrngthikchthch cao L trng s c lp y bi mt electron chuyn t lp v cao hn khcnhauvnnglnggiahaitrngthiny(ltrng lp K v l trng lp L3) bng nng lng photon tia X pht ra Cc tia X ny c gi l c trng bi v nng lng ca n khcnhauchominguyntkhcnhauvminguyntc cc mc nng lng ring ca n. Vic pht photon tia X c trng phi tun theo qui tc lc la trong c hc lng t 4/30/201223 Cc vch K: Cc vch tia X m bt u t l trng trn lp v K Dch chuyn t L3 K tiaXcnnglng6,404 keV (Fe K-L3 hoc Fe Ko1) Dch chuyn t L2 K Fe K-L2 hoc Fe Ko2 DoKo1vKo2cnnglng gnbngnhaunntagi chung l Ko CcdchchuyntM,N KtagilvchK |,c nng lng ln hn nhng cng nh hn S dch chuyn ca Fe 4/30/201224 Cc vch L v M: Cc vch tia X m bt u t l trng trn lp v L hoc M Cc vch L: cc electron cc tng cao dch chuyn v lp y l trng mt trong 3 lp con L Doc3(L1,L2vL3)lpvcon,nnphvchLphctp hn ph cc vch K Cc vch L dng xc nh cc nguyn t c Z > 45 (Rh) VchL3-M5,4(Lo)lvchthchhpchovicphntchnht. Nu c s giao thoa vch ny th ta dng vch L2-M4 (L|) Cc vch M: cc electron cc tng cao dch chuyn v lp y l trng mt trong 5 lp con M Him khi c dng trong XRF Cc vch M ca cc nguyn t nng (Pb) s giao thoa vi vch K hoc L ca cc nguyn t c Z thp hn (S) 4/30/201225 Hiu sut hunh quang v pht electron Auger Khi electron lp L chuyn v lp l trng lp K th n gii phngnnglng,vnnglngnyschuynchomt electron lp L hoc M KhielectronlpLhocMnhnnnglngsbtra khi nguyn t v electron ny gi l electron Auger Xc sut m mt l trng pht ra tia X c trng c gi l hiu sut hunh quang. V d, vi lp K: eK = (S tia KX pht ra)/(s l trng to ra trn lp K) ) n n n (N1N) n (K 2 K 1 KK Ki i KK | o o+ + == e(1.5) 4/30/201226 Hiu sut hunh quang (tt) Thnghiusuthunhquangkhcnhauivicc nguyn t khc nhau, v trong cng mt nguyn t th hiu suthunhquangcngkhcnhauivicclpkhc nhau, Eugene P. Berlin a ra cng thc: A=1,08 x 106 (i vi lp K), v A ~ 108 (i vi lp L) NhngnguyntcZ