Sử dụng phần mềm Gupix để tính toán hàm lượng các nguyên tố có mặt trong mẫu dày

7/24/2019 S dng phn mm Gupix tnh ton hm lng cc nguyn t c mt trong mu dy

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Bi thc tp 3: Tm hiu phng php phn tch nguyn tda vonguyn l kch thch pht tia X bng proton (PIXE)

Mn : Thc tp my gia tc 1

I. MC CH

Lm quen vi phng php PIXE : chun nng lng, xc nh cc nguyn tc mt trongmu chun mng v mu mng.

Lm quen vi phn mm xl GUPIXII. GII THIU CHUNG

Phng php phn tch nguyn t da vo nguyn l kch thch pht tia X bngproton (tn ting anh: Proton Induce X-Ray Emission, vit tt: PIXE) l mt trong ccphng php phn tch khng ph hy mu tin tin, c ng dng rng ri trong nhiu lnhvc nh y hc, kho c, mi trng Cc u im ni bt ca phng php ny l:

- C thphn tch ng thi nhiu nguyn ttrong di in tch nguyn tZ rng.- nhy phn tch cao, cppm.- Thi gian phn tch ngn (chcn vi pht).- Khnng xc nh phn btrn bmt bng kthut PIXE, khnng phn tch trc

tip ngoi mi trng chn khng.Nguyn l c bn ca phng php PIXE da trn s to thnh tia X c trng khi chm

ht ion bn vo bia, c nng lng c trng cho mi nguyn t. to ra tia X c trng,ht tch in (proton) bn vo bia sion ha cc nguyn t bng tng tc Coulomb. Cc

proton ny s to ra cc l trng cc lp in t nm su bn trong nguyn t. Mtht electron tlp ngoi snhy vo lp ltrng y.

Hnh 1. a) Minh ha qu trnh to tia X c trng bng ngun kch thch bn ngoi (chmht proton ). b) Minh ha qu trnh pht electron Auger.

Trong khong thi gian rt ngn nguyn tbkch thch skhkch thch trvtrngthi c bn bng cch pht ra mt photon vi nng lng nht nh hoc gin tip

bng cch truyn nng lng cho mt electron (gi l electron Auger). Nng lng catia X pht ra bng vi hiu nng lng lin kt gia lp cha electron trc khi nhy vochim chv lp cha ltrng m electron chim ch.

Da vo cu trc cc lp, phn lp electron trong nguyn t, ngi ta quy c gi tn ccvch tia X c trng pht ra khi in t nhy n cc lp K, L, M (lp trong cng) canguyn t l tn ca cc lp tng ng. Ngoi ra ngi ta cn phn bit cc vch ph

tng ng bng cch gn thm ch ci hy lp , , v mt ch stheo sau ,


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nhng k hiu ny thng phn nh cng tng i ca mi vch, v d vch 1ccng mnh nht trong dy. V dvcch k hiu ny: K1, L2.

Hnh 2. S ngun gc cc vch tia X c trng

Hnh 3.PhPIXE ca mu a chtPhPIXE bao gm 2 thnh phn: Cc nh tng ng vi tia X c trng nm trn nn

bc xhm lin tc (Nh cc nh thp c xy trn sn i).Mi nguyn tspht ra ccvch tia X vi nng lng hon ton xc nh c trng cho nguyn t.Tcng ca


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cc vch tia X c trng(din tch nh ph trphng),ta c thxc nh c hm lngcc nguyn tc trong mu.

III.

Cc loi mu v hng phn tch

Trong phn tch PIXE, c thphn tch cc loi mu sau:

- Mu dy (Thick target), mu ny c chia lm 2 loi:

+ Bit ma trn mu, cn tm hm lng cc nguyn tvt: Ma trn mu to thnh tnhng nguyn tchnh m tng hm lng ca chng > 99.9 %.

+Khng bit ma trn mu, dng cho nhng mu dy hon ton khng bit thng tin.

- Mu mng.(Thin target): i vi loi mu ny hiu ng ma trn c thbqua.

- Mu va (Intermediate target): Mu khng stop hon ton chm tia, nhng vnlm suy gim nng lng chm tia, tng tcng c hai trng hp nh mu dy

- Mu lp (thng t khi sdng)

- Hiu ng ma trn mu lin quan n: Smt mt nng lng ca chm ion, v ssuygim ca tia X trong mu.

3.1. Mu "mng"

Vi nhng mu mng n mc nng lng hao ph ca chm tia ti v ssuy gim ca tiaX sinh ra trong mu l khng ng k, khng c hiu ng ma trn mu v cc i lng Iz

phthuc tuyn tnh vi Cz. C thchun mt ho PIXE bng cch sdng cc mu chun"mng ". chnh xc chcn phthuc vo chnh xc ca cc hm lng mu chun vca vic khp ph. mu cng phi mng v c thc cc tp cht ty ; cc phoi lm

bng polycarbonate vi dy vi micron l mt loi tt c dng. Phng php phn tch

mu mng ny c ng dng rng ri trong phn tch son kh (aerosol) bng phng phpPIXE.

Xt mt trng hp n gin trong phn tch PIXE, khi chm proton c gia tc bnvo bia c dy sao cho nng lng ca chm tia mt mt khng ng kkhi i qua

bia. i vi mu loi ny, ngi ta thng quan tm n hm lng nguyn ttrn mt

n vdin tch(cn gi l mt mt),n vthng l 2/g cm hay snguyn t/cm2.

i vi mt nguyn tc shiu nguyn tZ trn bia, ta c:

- Xc sut ion ha ca chm proton i vi tng lp(K,L,M..) c trng bi tit dinion ha(n v barn) ph thuc vo nng lng chm proton ti E0, s s kin ion ha

c to ra bi Np ht proton trn bia c mt mt Nt (snguyn t/cm2) l:

Yion ha 0( )z

p tN E N

- Xt theo n vmt mt 2/g cm , cng thc trn c thvit thnh:

Yionization 0( )

( ) AV Ap z

z

N M ZN E

A

AVN l s Avogadro.

( )AM Z l khi lng ca nguyn ttrn mt n vdin tch( 2/g cm ).

zA l khi lng nguyn tca nguyn tZ trn mu.


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Xc sut s kin ion ha th gy ra qu trnh pht tia X c trng cho tng lp

in t(K,L,M) gi l hiu sut hunh quangz

, sskin dn n pht tia X c trng l:

Yfluorescense= Yionization z

Gi bz l hst lvcng c trng cho mt vch tia X xc nh trn ton bstia X c pht ra tmt lp (V dtlgia stia X c trng Kpht ra trn tng stiaX c trng pht ra tlp K).Khi stia X c trng pht ra tng ng vi mt vch tia Xxc nh l:

Ycharacteristic= Yfluorescensebz- Cc tia X c trng pht ra c ghi nhn bi detector o tia X,thng s dng

detector Si(Li),detector HpGe hay Silicon drift detector (SDD). Mi loi detector c mt

hiu sut ghi ni xc nhint rinsic :

int rinsic =

Sbc xghi nhn c trn phPIXE chnh l din tch nh phtia X ( trphng) S.Ngoi ra, tng ng vi mi hnh hc o xc nh mt gi trgc c (n vsteradian)

tng ng vi "gc nhn" tim pht bc x(trong trng hp khong cch xa, c thcoil ngun im) ti vng nhy ca detector.

2

DetS

R

SDet:Din tch tinh thca Detector.

R:Khong cch tmu ti Detector.

khong gia bia v detector, ngi ta thng t vo m t tm foil mng ngnkhng cho cc ht proton tn xtbia i n detector (v c thlm hng detector hoc gyra nhiu khng mong mun).Tm foil mng ny sgy ra ssuy gim vcng tia X tidetector. Gi T l hssuy gim. Kt hp hai iu kin ktrn:

Sbc xti vng nhy ca detector= Ycharacteristic4

T

Trong I=I0.T vi I0l cng tia X trc khi i qua foil, v I l cng tia X saukhi i qua foil. i vi tm foil lm bng vt liu Mylar, gi tr T c xc nh gn ng

bi cng thc:2.9897

470.168x

ET e

Vi E nng lng ca tia X tng ng (n vKeV); x l bdy ca foil (n vmm).- Kt hp cc cng thc trn,ta thu c cng thc xc nh hm lng ca mt nguyn

tZ trn mu mng da vo din tch nh phtng ng S nh sau:

0 int

4( )

( )

zA

p z AV z z rinsic

A SHM z

N E N b T

y ta thm vo hshiu chnh H lin quan n sai shthng ca ho.


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Cng chm ion tch in +q trong hmy gia tc thng c o bi bm intch, tgi trin tch Q (n vC) thu c mi php o, sht proton ti bia c tnh

bi:

p

Q

N eq

Trong e=1.60217646 10-19C l gi trin tch nguyn t.

IV. Phn mm GUPIXGUPIX l chng trnh khp bnh phng ti thiu phi tuyn i vi phPIXE v sau

chuyn i din tch cc nh thnh hm lng nguyn tca tia X trong ph.-Sdng phn mm GUPIX phn tch hm lng nguyn ttrong mu mng:Bc 1: khi ng phn mm GUPIX bng cch click vo biu tng GUPIX trn mn

hnh desktopBc 2: mphcn phn tch v ci t cc thng sClick file => New project => mfile .PIX.Click setup => solution type => chn Fixed Matrix solution i vi mu mng

hoc mu dy bit ma trn mu v chn interated Matrix solution i vi mu dy chabit ma trn mu

Click setup => setup v ci t cc thng sth nghimClick Fit => spectrum Details v ci t cc thng sClick sample => sample Structure => chn loi mu cn phn tchClick sample => chn cc gii php tng ng v in cc nguyn tBc 3 : Chy chng trnh

Click Gupix => runKt quc lu trong cc file Data ca GUPIX

V. Thc nghim:Quan st phPIXE trn mu chun,thc hin php chun nnglng cho ho.

Dng cth nghim:- My gia tc tnh in Tandem 5SDH-2, nng lng cc i 3.4 MeV i vi ion c

in tch bng 1.- Ho ph tia X bao gm: Detector Silicon Drift (SDD), phn gii nng lng

138 eV ti nh 5.9 KeV ca Mn, hcompact gm thnui, tin khuch i, khuch i, bphn tch a knh (MCA), my tnh thu thp dliu.

- Detector c t gc 32.8 so vi hng chm tia.- Bia sdng:

Mu chun mng cha NaCl c mt mt 45.8 2/g cm c cy trn b

mt Mylar dy 3.5 m .

Mt mu mng do sinh vin tchun b( mu git nc)


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Cc bc tin hnh:

1. Thit lp ho nh hnh v, kim tra cc kt ni.2. Khi ng hmy gia tc, gia tc chm tia vi cc thng ssau:

Loi chm tia: H+

Nng lng: 2591 KeV

Cng chm tia: 5 nA,

3. iu chnh vtr ca detector SDD thch hp (theo chdn ca g.v hng dn),ghi lithng svgc khi tng ng vi vtr .

4. Ghi li thng sbdy ca foil Mylar (c t sn).5. Bt nt ngun ca bcompact ca detector SDD ln.6. a mu NaCl v mu o xl vo bung chiu mu (theo chdn ca GVHD).7. Khi ng chng trnhthu thp dliu RC43:

Tmn hnh chnh,click chn chng trnh RC43, 2 ca ssxut hin sau .

Chn ca s NEC RC43 ANALYTICAL DATA COLLECTION, vo mc

DATA COLLECTION, chn Collect data. Ca s Full Energy Data Collection s xut hin, b chn phn MCAs

displayed 3 la chn RBG, RBS v NRA.

Thc hin cc thao tc sau i vi 2 mu o:

8. iu chnh cng chm tia theo cc gi tryu cu tng ng vi mi mu.9. Sdng ca sManipulator tin hnh iu chnh vtr ca mu sao cho vtr chm

tia c nh du trn mn hnh nm trn mu v gc gia chm tia v php tuynmt phng mu =0 (theo chdn ca g.v hng dn).

10. t trc gi tr tng in tch ghp ca chm ht trn ca s Full Energy Data

Collection, charge uC. t tn file dliu ty Filename.


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11. Kim tra li mt ln na cc thng scn thit tin hnh th nghim.12. Trn ca sFull Energy Data Collection, click vo nt Manual collect bt

u cho chm proton chiu vo mu. Quan st phPIXE thu c, chra vng nnlin tc v cc nh tia X c trng.

13.

Khi gi trbn phi trong Charge uC v0, php o kt thc, chng trnh stnglu li file c cha phPIXE mt th mc nht nh.

Ghi nhn li cc thng sca th nghim v phPIXE thu c.Sdng phn mm phn tch Gupix phn tch sliu va thu c.Thc hin ln lt i vi mu chun NaCl v mu o

Bi tp

1. T ph PIXE thu c ca mu NaCl, thc hin php chun nng lngcho h o s dng cc vch ph ca Na; Vch ca Cl . Nng lng ca tng vchc th c tra cu trong bng gi km ti liu ny.

2. T gi tr chun nng lng va tm c, xc nh(nh tnh) cc nguyn t cth c mt trn ph PIXE thu c ca mu o, ngoi ra xc nh cc nguyn t cn li(contamination) trn ph PIXE thu c ca mu NaCl.

3. So snh gi trhm lng thu c vi gi trthc tca mu NaCl

Cu hi

1. Nu c chpht bc xhm to nn nn lin tc trong phPIXE.

2. Trnh by c chhm ca tia X trong vt liu (lin quan trc tip n bi ton sdng foil Mylar).

3. Trnh by cc qu trnh xy ra khi s dng bia l mu dy (Gi : Nng lngchm proton khi i su vo trong mu sthay i).

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Sử dụng phần mềm Gupix để tính toán hàm lượng các nguyên tố có mặt trong mẫu dày