Nghiên cứu một số đặc trưng của tương tác bức xạ gamma mềm với vật chất và ứng dụng trong phân tích nguyên tố bằng đêtectơ nhấp nháy

•>"' J'J ^n BO ClAO DUC VA DAO I'AO DAI HOC g u d c CIA MA NOI TRirONCi DAI HOC KHOA H(.)C TU NHIEN BUI VAN LOAT NGHIEN CUrU MOT SO DAG TRUNG CUA TlTONG TAG BUfG XA GAMMA MEM VQfl VAT GHAT VA UfNG DUNG TRONG • • • PHAN TiGH NGUYEN TO B A N G DETEGT0 NHAP NHAY Chuyen ngdnh : Vat ly hat nhan nguyen tu Ma so : 01.02.03 LUAN AN PHO TIEN SI KHOA HQC TO AN LY NgUcri Huong dan khoa hoc : P(JS FTS Fham Quoc Himj^ Ha Noi - 19% MUCLUC Tran Mddau Chuotig Tuong tac ciia hire xa gamma mdm vdi vat chat 13 1.1 Hap thu va tan xa 13 1.2 Ht sd suy giam va nguyen tu sd hi6u dung ciia moi trmVng phuc tap IV 1.3 Nghi^n ciiu xac dinh hing thuc nghiem ht sd suy giam ciia cac chat ddi vdi hue xa gamma m6m Ket luan chuong 24 35 Chuong Kdt qua thuc nghiem nghi(^n cuu mot sd dac trung CO ban cua tuong tac gamma m6m vdi vat chal 2.1 Hi6u ling tu hap thu cua mSu 36 36 2.2 Xac dinh bang thuc nghiem nguyen tu sdhi6u dung cua moi trudng vat chat phuc tap 39 2.3 Nghi^n cuu xac dinh ph^n dong gop ciia phan tan xa Rayleigh phd gamma tan xa Kdt luan chuong 47 61 Chuong Mot sd van A6 co ban ciia phuong phap phan tich ham lugng nguyen id thco hue xa huynh quang X dac trung kich thich hdi gamma 3.1 Ca so" ciia phuang phap 62 62 3.2 Hicu ung chal n6n irong phan lich ham Immg thco phd hue xa huvnh quang X dac iruni: hS 3.3 Nghi6n cuu thuc nghi6m cac ydu td anh huctng d^'n k6t qua phan tich ham luc;mg nguy6n td theo dinh cua vach dac trung K6t luan chuong 79 ^^ Chirong Sir dung hue xa tan xa lam chua'n va phucmg phap ty sdphd 4.1 Phuong phap ty sdphd ^^ XX 4.2 Nghien cihi thuc nghiem chgn nang lugng biic xa tan xa lam chu^n 4.3 Bie^u thiic tinh ham lugng theo phuong phap ty sd phd 9'* 93 4.4 \Su Aiim va pham vi tog dung cua phuang phap ty sdphd 4.5 Nghi6n cthi anh hudng cua cac tap chat nang 96 102 4.6 Nghi6n curu thuc nghi6m khdc phuc anh hudng ciia cac hue xa nhiSu co nang lugng gSn vdi nang lugng vach phan tich lOX K6t luan chuong 109 Phan ke't luan 116 Tai lieu tham khao 119 M0DAU Nghi^n cufu cac dac trung ciia tuong tac btrc xa hat nhan vdi vat chat la CO sd vat ly Ai ap dung c6 hi6u qua ky thuat hat nhan cac linh vuc khac Trong ph^n tich ham lugng nguyen td theo hue xa huynh quang X dac trung, kich thich bdi gamma phat tir cac ngudn ddng vi phdng xa, ca hire xa dac trung dugc chgn phan tich va hue xa gamma kich thich A6u co nang lugng thap Nghi^n cuu cac dac trung cua tuong tac hire xa gamma m6m vdi vat chat la can thi^'t d^ nang cao chat lugng ciia phep phan tich Khai ni6m hire xa gamma m6m su dung luan an dugc hi6^u la cac biic xa gamma c6 nang lugng nam vimg nang lugng ion hoa cua cac nguyen td co Bang he thdng tu^n hoan Nang lugng ciia cac birc xa dac trung cua cac nguyen td co tu nhi^n va ca cac nguyen td nhan tao d cudi Bang he thdng tuin hoan d6u nhd hon 150 keV Vi vay d^^ kich thich c6 hi6u qua cac hue xa dac trung ciia cac nguyen td c^n phan tich, thuc t^' ngudi ta sir dung hue xa gamma m6m Cac hire xa gamma m6m tuong tac vdi vat chat thd hicn nhiJng tinh chat ri^ng hi6t ciia minh: Rat nhay ddi vdi su thay ddi cua phan boa hoc ciia moi trmVng, ht sd suy giam co linh nhay hac nang luang cua hue xa gamma di qua hi^n hap thu ciia mdi Idp vd ciia nguyen tu Dt nang cao chinh xac ciia phep phan tich vice nghicn cuu cac dac trung tuong tac ciia hue xa gamma nang lucmg thap vdi val chat la can thi^'t V6 mat ly thuydt, tuong tac ciia hue xa gamma vdi vat chat dugc dac trung hang iiti Aitn tuong tac ciia hue xa gamma tr^n mgl nguyen tu Trong thuc nghiem, he sd suy giam la mot nhirng dai lU(tng dac trung cho tuong tac ciia hire xa gamma vdi vat chat Cac hire xa dac trung cac nguyen td cd mau phat tham gia vao tuong tac vdi cac nguyen td cd mSu trudc no di ve detecto Chinh mSu da "tu" hap thu cac hire xa dac trung no phat Su tu hap thu ciia mSu phu thugc vao b6 day khdi ciia mSu va he sd suy giam cua mSu ddi vdi hiic xa can phan tich Khi phan tich ham lugng ciia cac nguyen td theo hue xa dac trung nang lugng thap theo phuong phap tuong ddi, su sai khac ve phan hoa hoc cung nhu hi day ciia mSu phan tich va mSu chuan se gay nen mot sai sd Idn.Trong cac hai toan phan tich c6 yeu cau chinh xac cao, can phai hieu chinh su sai khac tren De^ tie'n hanh cac hieu chinh tren, can phai hie't dugc he sd suy giam ciia mlu chuan va mSu phan tich ddi vdi hire xa can phan tich Ngoai qui trinh phan tich cac mau day ciia cac phuong phap phan tich khac chang ban nhu phuong phap PIXE, de hieu chmh su tu hap thu ciia mau can phai hie't su phu thuoc ciia he sd suy giam vao nang lugng ciia hire xa gamma va nguyen tu sd ciia moi trucVngI 151 Mac du su phu thugc ciia he sd suy giam vao nang lucrng ciia hire xa gamma mdm ra'l phirc tap, nhung nhidu tac gia da dua cong thirc [x{z) mo ta su phu thugc vao nang lugng cua he sd suy giam ddi vdi moi nguyen td Cac thdng sd c6ng thirc |a(e) dugc chgn hang each lam khdp c6ng thiirc vdi cac sd lieu thuc nghiem ve he sd suy giam ciia mdi nguyen td ddi vdi cac hire xa gamma nang lugng xac dinh D6 lam dugc dieu tren ddi vdi mdi nguyen td can phai cd nhieu sd lieu thuc nghiem ve he sd suy giam khdi cua no ddi vdi hire xa gamma nang lugng khac Sd lieu thuc nghiem ve dac trung suy giam ciia cac chal ddi vdi cac gamma mem it Viec xac dinh he sd suy giam ciia cac nguyen td ddi vdi cac gamma mem cd y ngbla qua trinh lam khdp tren cung nhu qua trinh xac dinh hieu sua't ghi ciia detecto han dSn Si(li) d vung gamma nang lugng thap Cung vdi su tie'n ho cua khoa hoc c5ng nghe, cac thie't hi va phuang phap phan tich phd huynh quang X dac trung cang dugc hoan thien Ngay phuang phap phan tich phd huynh quang X dac trung kh6ng nhung chi cd ung dung phan tich phan nguyen td ma cang cd nhirng ung dung cac ITnh vuc khac nhau: Trong viec kie^m tra cha't lugng san pham, y te' [18, 20,- 22], linh vuc kie^m tra nhiem ban [13, 42,45] cua moi trudng Su tie'n ho ciia ky thuat ludng cac hire xa hat nhan da cho phep sir dung cac detecto han dSn cd kha nang phan giai nang lucrng cao, kich thich hue xa dac trung hang cac hat tich dien gia tdc hoac hang tia X tao tir cac thiet hi dien tu Cho ddn da xua'l hicn cac detecto han dan loai Si (Li) khong cd cua sd Vice xua't hien cac detecto da cho phep met rong viing phan lich ve phia cac nguyen id nhc Ngoai |14| da xual hien nhung loai detecto han dan cd kich thudc nhc\ cd phan giai nang lugng cao, cd kha nang lam viec d nhiet phdng Vice xual hicn loai detecto loai cho phep tie'n hanh phan tich ham luc^ng nguyen id theo phuang phap huynh quang X dac trung, ngoai hicn truong, vdi chinh xac cao Phuang phap phan tich thco hue xa huynh quang X dac trung cang hoan thien va dugc sir dung rgng rai de phan tich ham lugng ciia nguyen td cac mSu vat cac loai khac Cung vdi su phat tri^n cua cac thie't hi kich thich va detecto ghi nhan hire xa dac trung, cac chuong trinh xir ly phd gamma va tia X cang hoan thien Trong cac he phan tich deu cai dat cac chuong trinh cho phep xac dinh ham lugng cac nguyen td cac mau vat dang khac vdi chinh xac cao Tuy detecto nhap nhay cd phan giai nang lugng khong cao hang detecto ban dSn, nhung nd cd im viet hon so vdi detecto han dSn dd la: Hieu sua't ghi cao, cd the^ lam viec ca vdi nhiet ngoai trdi, thuan tien qua trinh van chuyen phan tich da ngoai Chinh vi nhung uu diem tren, hien tren the'gidi detecto nhap nhay van dugc sir dung rgng rai nha't la ITnh vuc dia vat ly hat nhan Cung vdi cac ddng vi phdng xa, vice sir dung cac phd ke gamma nhap nhay van cho phep giai quye't cd hieu qua mot sd yeu cau ciia hai loan thuc te dal ra: Phan tich ham lugng nguyen td nang tren ntn cac cha't nhe, tim kie'm tham dd mo khoang san tai hicn trucmg xac dinh nhanh ham lugng ciia nguyen td irong cac qua irinh cong nghc Trong cac phep phan tich ham lugng cac nguyen id thco phd hire xa dac irung X vdi vice sir dung cac ddng vi phdng xa \'a deiccur nhap nha)' ihic'l hi gon, don gian khong can phai lam viec d nhiei Nito long, thai gian can cho mgt phep nhd, gia phan tich re Trong phan tich ham lugng cac nguyen td thco phd huynh quang X dac trung kich thich bdi gamma, ke'l qua phan tich chiu anh hmrng ciia nhieu ye'u td nhu su thay ddi phan boa hoc ciia chat nen, su thay ddi cua mat A6 mau, su khong dn dinh cua hinh bgc va thiet hi De khac phuc cac ye'u td anh hudng tren va nang cao chinh xac ciia phep phan tich, nhieu tac gia da dua [16, 31, 33, 34, 44] phuang phap ty sd phd Phuong phap ty sd phd da dugc su dung nhi6u cac hai toan khac nhu: Trong phuong phap gamma - gamma mat do, phuong phap gamma - gamma Igc lua va phuong phap phan tich ham lugng nguyen td theo phd huynh quang X dac trung Thuc cha't ciia phuang phap ty sd phd la su dung chinh cac hire xa tan xa tir mSu lam chuan de^ han che' anh hudng cua cac ye'u td den ke't qua phan tich Cac phuong phap chuan thong thudng dugc su dung [8,11,31] de^ hieu chinh anh hudng cua cac ye'u td de'n ke't qua phan tich hang each dua them vao mSu mot lugng xac dinh ddng vi phat hue xa cd nang lugng gan vdi nang lugng cua nguyen td can phan tich Can cir vao dien tich hai dinh dac trung ciia nguyen td can phan tich va nguyen tddugc dua them vao hie't dugc ham lugng cha't can phan tich Trong phuong phap ty sd phd, ham lucrng ciia nguyen td can phan tich dugc xac dinh thong qua ty sd ciia sd de'm vimg nang luctng dac trung cho nguyen tdcan phan tich va sdde'm viing nang lucmg ung vcri cac hue xa tan xa tir mau Su thay ddi ciia cac ydu td ke' ircn sc anh hudng c6 dang nhu len toan ho phd ciia hue xa thir cap vi \'ay ma dai luctng ty si) phd sc hi anh hudng il di Ap dung phucmg phap ty sd phd phan tich ham lucmg thco phd huynh quang X dac trung, nghien ciru xac dinh hang thuc nghiem mot sd dac trung cua tuong tac hire xa gamma mtm vdi val chal da dugc tie'n hanh tai ho m5n Vat ly Hat nhan trucVng Dai h()c Khoa hoc Tu nhien thugc Dai hoc Qudc gia Ha Ngi Ke't qua nghien cuu theo cac hudng tren da cong hd tren mgl so Tap chi va Hoi nghi chuyen nganh Ban luan an vdi ten ggi: "Nghien cihi mot so dac trung ciia tuong tdc bite xa gamma mem v&i vat chat vd ijcng dung phan tich nguyen to bdng detectanhdp nhdy*' la cong trinh he thdng va phat trien cac ke't qua tren thai gian tir 1982 de'n Muc dich cua luan an: Ban luan an cd muc dich nghien cu"u va xac dinh hang thuc nghiem mgt sd dac trung co han tuong tac cua hire xa gamma mem vcVi vat cha't, ap dung phuong phap ty sd phd de^ nang cao cha't lucTng phan tich ham lugng nguyen td theo phd hue xa huynh quang X dac trung tren phd ke'gamma nha'p nhay Cac nhiem vu chinh ciia ban luan an la: - Xac dinh hang thuc nghiem moi sd dac trung quan irgng ciia lucrng tac hire xa gamma mdm vcri vat chal tren phd ke' gamma nhap nhay: - Xac dinh he si) suy giam cua mgl sd chat dc')i vc'ri gamma m6m - Kie'm chirng hang thuc nghiem tinh nhay tucmg tac ciia gamma mdm vcri val chat, dc'ii vcri su thay ddi phan hoa hoc cua val cha'l va tinh chal phu thugc nhay hac cua he sc')' suy giam kh(')i vao nang lucrng cua hue xa gamma va nguyen lu sc')' hieu dung cua mc')i trucrng 2- Nghien cu*u hang thuc nghiem nhung ye'u td anh hudng de'n ke't qua xac dinh ham hxgng nguyen td dua vao dien tich vach dac trung cua nguyen tdcan phan tich 3- Nghien ciru va ap dung phuong phap ty sd phd phan tich ham lugng nguyen td theo phd huynh quang X dac trung tren phd ke' gamma nha'p nhay, dap irng dugc yeu cau ciia mot sd hai toan thuc te' dal Tinh khoa hoc va mdi cua luan an: 1- Da nghien cuu mot each cd he thdng cac va'n de cd lien quan tdi phuong phap phan tich nguyen td theo hire xa huynh quang X dac trung va dua dugc nhiing hien phap nham nang cao chat lucrng phan tich nguyen tdhang detecto nhap nhay 2- Da de xual mot sd phuang phap ngoai suy xac dinh he sd suy giam ciia mot so chat dc'ii vc'ri hue xa gamma mem dua vao quy lual ham e mu mo ta su suy giam cudng hire xa gamma val chal va phucrng phap danh gia phan tan xa Rayleigh irong phd lan xa cua gamma mdm 57 W^\ 120^^ nang lugng tucmg irng vdi cue dai cua tan xa Complon mgl lan la 58 kcV,56,7 keV,53,7 keV va 51 kcV Cac dinh hap thu U)an phan tucrng irng vdi cac nang lugng tren lan lucri cd dang: y = yo cxp f- 0,0100 (s- 58)^ ] (2.9h) y = yo exp [- 0,0104 (£- 56,7)=^] (2.9c) y = y^ exp [- 0,0108 (s- 53,7)-] (2.9d) y = yo exp [-0,0112(8-51)^] (2.9e) Can cir vao cac sd lieu thuc nghiem cua phd gamma tan xa va cac c6ng thirc m6 ta dang ciia dinh ha'p thu loan phan cua hue xa true tie'p va hire xa tan xa tren cac gdc tan xa tuemg irng, theo phuang phap hinh phuemg tdi thie^u da xac dinh dugc phan ddng gdp cua gamma tan xa Rayleigh chiim gamma tan xa chung tren cac cha'l va gdc tan xa khac Ke't qua thuc nghiem dugc cho hang 2.9 Trong hang 2.9 cQng dua cac ke't qua tinh loan theo cong thirc (2.3 ) va phucmg phap hai phd chuan Cac ke't qua thuc nghiem xac dinh ddng gdp tuemg ddi cua hire xa gamma tan xa Rayleigh phd gamma tan xa theo phuemg phap ti sd bien cue dai phii hgp vdi ke't qua tinh theo cong thirc (2.3) hern phuemg phap so sanh hai phd chuan Tuy nhien, ddi vdi ehi ke'l qua thuc nghiem thu dugc theo phuemg phap hien van nhc) hem 20% so vdi kei qua tinh theo cong thirc (2.5) Tir cac so lieu bang sd 2.9 nhan tha'y rang, phan ddng gdp cua tan xa Rayleigh thu dugc theo phuemg phap so sanh pht') chuan luc)n nhd hem gia tri thuc nghiem thu dugc tii' phuong phap hicn di) cue dai su sai lech giira kei qua thuc nghiem thco phucmg phap cang ion gi)c tan xa nhc) va nguyen tu sd cha'l tan xa lim 58 Bam: sd2.9: Ddng gdp tuo'ng ddi (^/c) ciia gamma tdn xg Ravicigh phd gamma xg tdn xg tren mdt sd chat tdn xg vd gdc tdn xg khac ddi vrri l?uc xg gamma 60 keV Chal Goc Phucmg phap Phuang phap Gia Iri 1)' lan xa lan xa phd chua'n (%) bien cue dai Ihuye'l (%) (%) Nhom 90O 3,5 ±0,5 5.5 ± 0,5 4,8 sai - 13,8 ±1,2 16,5 ± 1,8 17,2 • Dong - 16,8 ±1,5 19,5 ± 1,9 20.3 Chi - 22,4 ± 2,5 48,5 ±2.5 62.2 450 25,2 ± 2,5 42 ± 2,3 52 6OO 21,5 ±2,2 32,0 ± 2,0 36 90O 16,8 ±1,5 19.5 ±1,9 20 1200 6,8 ±1,2 12.2 ±0.8 lO.X Dong Die'm khac can han eiia phuemg phap ty se") hien cue dai so vdi phuemg phap so sanh hai phd chuan la d chd : phucrng phap ty se^' hien cue dai da tinh de'n ddng ge)p ciia hire xa tan xa Rayleigh vao sd de'm tai cac kenh chua'n va cac kenh trudc nd Ngoai Irong phuemg phap so sanh hai phd chuan, coi phan giai ciia detcctcr diii viri nang lucmg cua hire xa tan xa Complon moi lan va hire xa scr cap la khcmg ddi ccm phuang phap ty sd hien cue dai cd tinh de'n ca su iha)' ddi ciia phan giai thco nang lucmg Vi vay ke'l qua thuc nghiem thu ducrc tir phuong phap li sd hicn cue dai phu hcrp vdi cong ihiic (2.3) hern so viri phuong phap so sanh hai phd chuan hoa 59 Cac ke't qua thuc nghiem"^ ciia Liman [34] cung da chi 66\ viri cha't tan xa cd nguyen tir sd nhd, gia tri ly thuye't tinh theo ci)ng thirc han thuc nghiem (2.3) va gia tri thu dugc tir thuc nghiem phii hcrp viri Khi cha't tan xa cd nguyen tir sd 1cm ket qua thuc nghiem luon nhd hem nhieu so vdi ke't qua tinh theo c6ng thuc ban thuc nghiem Cd the' giai thich su sai khac giii'a sd lieu thuc nghiem so vdi gia tri tinh theo cong thirc (2.3) la c6ng thu*c (2.3) dugc xay dung dua tren ly thuye't tan xa Compton va tan xa Rayleigh Trong tinh tie't dien ciia tuong tac Compton, d^u coi dien tu trudc tan xa la tu do, dong nang ciia nd trudc tucmg tac bang khong Dieu chi dung nang lugng gamma tdi ra't Idn so vdi nang lugng lien ke't cua dien tu Ddi vdi hue xa gamma 60 keV nhd hon the' nang ion boa lop K ciia ' chi, vi vay cac c6ng thirc tinh he sd hap thu can phai hieu chinh nang lucrng lien ke't ciia cac dien tir 80 De' minh dugc uu di^m cua bien cue dai dugc xay dung luan ca phd tren T—'—I—•—r 70 - Phi/ang phap ty so bien dp - Gia tri ly thuyet 60 a: X an vdi phucmg phap sanh 1—'—I—'—r - Theo phi/ang phap so sanh phucmg phap ty sd so -I—I—.—r hga 50 40 30 a 20 Hinh 2.6 dua dd thi mi) ta su phu thugc ciia (3 vao nguyen tir si) eiia cha't tan xa Do 10 0^, 10 20 _3p 40 50 60 70 80 90 Nguyen tu so cua nha't tan xa thi irng vdi cac sd Hinh , , 2.6: , Su phu , thudc , vdo nguyen tu sd hicu dung dong gop cua tan \g Rayleigh lieu thuc nghiem thu gamma tdn xa TOO 60 dugc theo phuong phap so sanh hai phd chuan hoa luon nam dudi dd thi va dd thi Dd thi ung vdi cac sd lieu thuc nghiem thu dugc theo phuong phap ty sd bien cue dai va dd thi irng vdi cac sd lieu tinh theo cong thirc (2.3).khi Z khong Idn pham vi sai sd cua thuc nghiem dd thi va dd thi triing Khi Z tang dd thi cang cd xu hudng nhd dan so voi dd thi Nhu vay, ddi vdi cha't tan xa cd nguyen tu sd nhd va trung binh, cac sd lieu thuc nghiem theo phuong phap ty sd bien phii hgp vdi sd lieu tinh theo cong thuc ban thuc nghiem (2.3) hon so vdi phuang phap so sanh phd chuan CT3- X U a o 6Q eo 100 120 40 Goc tan xa (do) Hinh 2.7: Su phu thuoc vao gdc cua ddng gdp tuong ddi cua tan xa Rayleigh Hinh 2.7 Bie'u dien su phu thugc vao gdc cua phan ddng gdp tuong ddi ciia tan xa Rayleigh phd gamma tan xa Tii' dd thi nhan tha'y su ddng gdp tuong ddi ciia hire xa tan xa Rayleigh phd gamma tan xa giam nhanh theo gdc tan xa Dang cua dd thi khong khac so vdi dang ciia ham sd O (0) cong thirc (1.9h) Do thi Hinh 2.7 da kiem chirng tinh chat uu tien ve phia trudc cua tan xa Rayleigh 61 Ket luan chuotig Trong chuong da trinh bay cac ket qua nghien cu'u mc)l sc')' dac trung CO ban cua tuemg tac hire xa gamma mdm vdi vat cha't Bang thuc nghiem da khang dinh tinh cha't nhay cua hire xa gamma mem viri sir thay ddi ph^n hda hgc cua vat cha't, tinh phu thugc nhay hac eiia he sd suy giam nang lugng hire xa gamma di qua bien ha'p thu ciia mdi lop dien tir cua nguyen td Phuemg phap hien cue dai, dugc xay dung luan an, cho phep danh gia ddng gdp cua phan tan xa Reyleigh phd gamma tan xa tren cac gdc tan xa nhd va cha't tan xa nang Da xay dung dugc dd thi p.(Z) mo ta mdi lien he giira he sc)' suy giam khdi va nguyen tir sd hieu dung cua moi trudng vat cha't phuc tap Can cir vao dd thi |i(Z) irng vdi hire xa gamma 122 keV da xac dinh nguyen tu sd hieu dung ciia cac mSu phdng xa chuan Qudc gia dc'ii viri cac birc xa gamma cd nang lu