analysis-NAA) [41], [52], [78], [79], [103]
Phuang phiip phan tich kfch hoat natron dua tren su bfin phii chiim nótron vao mfiu phan tfch. Qua trinh luang lac ciia natron vdi trudng hiU nhan ciia cac
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nguyen ui cd trong mfiu; cac phan ling (n,y); (n,P); (n,a)...xay ra, tiio thiuih Ciic đng vi phdng Xiị Nhung đng vi nay phan ra vdi chu ki biin ra xac dinh va ciic biic xa CO nang lugng diic trung dugc ghi bfing cac loiii detector thfch hgp. Cac ngudn nolron thudng dung: Id phan ling hiit nhan, ngudn natron đng vi, ngudn natron tií miiy gia tdc.
127J (j^^^) 12«j
Do hoiU tfnh ciia '^**I trong mfiu phan lich rdi so sanh vdi mfiu chuan va tfnh ket qua tu ti le cac hoiil tfnh ciia mfiu chuan. Ham lugng idt trong mfiu dugc tfnh
theo cong ihiíc: C, = C3 ^ ' e>^(^2.-h.) ^ ^ . jj-^^g ^^5.
' A 3 W , ( 1 - e - ^ ' - ) ' ^ C^, C, : ham lugng idt trong mfiu va chuan tuang iíng
Â, A, : dien tfch dinh quan lam trong mfiu va chuiin tuang liiig W^, W,: khdi lugng mau va chuan luang ling
t2x, t2.s • ll^di gian ra ciia mfiu va chuan tuang ling t3x, 13^ : thdi gian do ciia mfiu va chuan tuang ling
X : hang sd phan ra ciia hiit nhan dugc kfch hoat
Su cd mat ciia brom va clo trong mfiu se can trd phuang phap xiic dinh nen can phai uich cluing trudc khi phan tich; cd the hap thu idt tren nhua anionit AG 1x8 diing NO3", s'lu đ dong gdi mfiu nhua va chieu trong Id phan ling. Gidi hiin dinh lugng ciia phuang phap la 2,4-r5 pg/dl.
Cd nhieu loai phan tfch NAA, tren day la phuang phap phan tfch kfch hoat notion cd xií If mfiu (radiochemiciil neutron activation analysis-RNAA); ngoai ra, ngudi la cdn diing phuang phap plmn tfch kich hoiil natron dung cu (instrument neutron iictivation analysis-INAA), la phuang phap phan tfch kliong can xii" If mfiu; nguyen tfic ciia phuang phap INAA nliu sau: Diing mgl chát chuan cd phd y tdt, phan liug (n,y) & T]/2 thfch hgp. Ngudi ta chieu đng thdi chat chuan va mfiu can phan tfch; tfnh he sd K(, tiii ciic diem cliieu, tfnh cac he rieng ciia chuan va chiit so siinh theo cong thiic:
KI -f r \ / \ SI
A3^ = (0„.a + ^ e p i l o ) ^ va: K,, = ^ ; Trong do :
Agp va Agp: hoiit do rieng ciia chuiin va chill so siinh tuang ling c]),^ va cpgpi: thong lugng neutron nhiel va tren nhiel
N.,: híuig sd Avogadro = 6,023x10^^ £ : hieu suat ghi ciia thiet bi
0 : do phd bien đng vi
f : hieu sufil phat ciia dinh ghi nhan a : liel dien phan iíng (barn)
M : nguyen lii* lugng ciia nguyen td cfin phan tfch
Thiel lap bang cac he sd Ko đi vdi cac nguyen td tai kenh chieu chufin
trong Id phan ling da biel ti sd F = 0^^/(l>^p^.
Hiim lugng C,^ ciia mfiu phan tfch dugc tfnh theo cong ihiic :
[Fana, + ( — ) ] [ F . e , + ( - ' M * ]
Sp a
Q = ., : . , Kong do K,„„ = f i^ K
Vanal + ( ) Jl'~ref
Phuong phiip nay cdn dugc ggi phuang phap chuan hda K-zerọ
Vi phuang phap NAA đi hdi thiet bi hiem (Id phan iíng hiit nhan, may gia tdc...), do đ phuang phap phan tfch nay khd thuc hien rgng rai, tuy nhien day la
phuong phap cd do chfnh xac cao, non ngudi ta thudng diing phuang phiip NAA
lam chuan de diinh giii do diing ciia cac phuang phap khac. Ngudi la da su dung phuong phiip NAA de Xiic dinh idt trong: tdc, mdng, sua, nude lieu, nude sinh hoat, dugc pham...