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Chuong DONG DIEN KHONG DOI ■ Nhufng khai niem md dau 1.1 Dinh nghla dong dien Trong moi truong dan dien cac dien tich tu luon luon chuyen dong h6n loan Dudi tac dung cua dien trudng ngoai cac dien tich tu do se chuydn dong co huong: dien tfch duong chuyein dong cung chieu dien trudng, dien tfch am chuyen dong nguoc chieu dien trudng Ddng cac hat dien tich chuyen dong cd huong dudi tac dung ciia dien trudng goi la ddng dien Theo quy udc, chieu cua ddng dien la chieu chuyen ddi cua cac hat dien tich duong hay la nguoc chieu vdi chidu chuyen dong cua cac hat dien tich am 1.2 Ban chat dong dien cac moi trudng Ban chat ddng dien cac mdi trudng khac cung khac (hinh 2.1) Thuc vay nhu ta da biet kim loai, cac nguyen tu lien ket chat che vdi tao mang tinh the kim loai Cac ion duong chi dao dong xung quanh nut mang, ddng cac dien tu tu (electron tu do) chuyen dong hdn loan khdng gian giua cac nut mang Dudi tac dung cua dien trudng, chfnh cac dien tu tir chuy6n dong tao ddng dien (hinh 2.1a) E E © -> ©- Hinh 2.1 Trai lai, chat dien phan chua co dien trudng ngoai, cac phan tir chat dien phan tuong tac vdi da tu phan ly ion duong, ion am Dudi 107 tac dung cua dien trudng cac ion chuyen dong tao ddng dien (hinh 2.1.b) Khoi luong m cua chat dupe giai phong d dien cuc binh dien phan dupe tmh theo cdng thuc: / * = -1 —.It Ai m(g) F n do: F la mot hdng so goi la so Faraday: F = 96500C/mol, A la khoi lupng mol nguyen tir cua chat thu dupe d dien cuc Ddi vdi chat khf d trang thai binh thudng, cac phan tir khf hau nhu deu a trang thai trung hoa ve dien Tuy nhien, cd kfch thfch ben ngoai, cac phan tir khf cd the giai phdng dien tir ion duong Cac dien tir dupe giai phdng, mot so d trang thai tu do, mot sd ket hop vdi nguyen tir trung hoa khac ion am Khi cd dien trudng ngoai ca ion duong, ion am, dien tir deu chuydn dong tao ddng dien (hinh 2.1 c) Chan khdng von khdng cd hat mang dien No chi ddn dupe dien dua electron vao Ddng dien chan khdng la ddng chuyen ddi cd hudng ciia cac electron but tir catot bi nung nong tac dung ciia dien trudng Dac diem cua ddng dien chan khdng la no chi chay theo mot chieu nhat dinh tir anot sang catot Ddng dien ban ddn la ddng dich chuyen cd hudng ciia cac electron tu va Id dudi tac dung ciia dien trudng Tuy theo tap chat pha vao ban ddn tinh khiet ma ban ddn thuoc mot hai loai la ban ddn loai n va ban ddn loai p Ddng dien ban ddn loai n chii yeu la ddng electron, ban ddn loai p chu yeu la ddng cac Id 1.3 Tac dung cua dong dien Tuy cd ban chat khac nhung ddng dien bao gid cung cd tac dung dac trung giong nhu tac dung nhiet, tac dung tir, tac dung sinh ly, tac dung co hoc Cac tac dung dupe ung dung nhieu y hoc INIh urng dai luong dac trurng cua dong dien 2.1 Cudng ddng dien Xet mot dien tfch S bat ky n&m mdi trudng cd ddng dien cha\ qua (hinh 2.2) Theo dinh nghla: Cudng ddng dien qua dien tich S la dai luong cd tri so bang dien luong chuyen qua dien tich dy mot don vi thdi gian 108 (1) dt Tir suy dien lupng q di qua dien tfch S thoi gian t se la: t t q= Jdq= Ji.dt (2) Neu i co phuang, chieu, lan khong d6i theo thai gian thi dong dien dupe goi la dong dien khong doi tir (2) neu i = I = const, ta co: t q= Ji.dt=I.t o (3) Hinh 2.2 Trong he SI, dan vi cuang dong dien la Ampe (A), dan vi dien tfch q la Culong (C) Ngoai thuc te dung: Kilo Ampe: lkA = 10? A Mili Ampe: 1mA = 10'3 A Micro Ampe: fj A = 10‘r,A 2.2 Vecta m at dong dien Cuong dong dien chi dac trung cho manh yeu cua dong dien qua mot dien tfch nao do, chua dac trung cho manh yeu cua dong dien tai tung diem moi truang ngoai cuang dong dien chua cho ta biet phuang, chieu cac dong dien Vi vay, ngoai cudng dong dien, ngudi ta dung mot dai lupng vat ly khac de dac trung cho dong dien la vecta mat dong dien 2.2.1 Dinh nghia Vecto’ mat ddng dien j tai mot diem M moi trudng co ddng dien la mot vecto cd goc tai M, cd phuong chieu la phuong chieu ciia dien tich duong chuyen ddng qua diem dd, cd ldn bang cudng ddng dien qua mdt don vi dien tich dat vuong goc vdi phuong chuyen dong dy (hinh 2.3) Ve Ion, ta co: Hinh 2.3 109 dl J (4) dS„ Tir (4) ta suy cuang dong dien qua dien tich vuong goc Sn la: 1=Jdl=Jj.d.S„ (5) Neu tren ca mat Sn ma j = const, ta co: I=jSn De tfnh cuang dong dien qua dien tich S bat ky, ta phai chia dien tfch S nhung phan tir dS, cho tren dS, j khong doi Goi dSn la hinh chieu dS tren phuang vuong goc vai j ; thi ro rang cuang dong dien qua dSn cung bang cucmg qua dS Ta co: Hinh 2.4 dl = j.dSn = j.dS.cosa Vi: j.cosa = j n jn la hinh chieu cua j tren phap tuyen n cua dS nen dung dS la mot vecta co phuang phap tuyen n , cd Ion bang gia tri cua dS Theo toan hoc ta co: dl = j.dS i = Jdl= Jj.dS s (6) s Trong he SI dan vi cua j la: A/m2 2.2.2 Su lien he giua vecta mat ddng dien vd vecta van toe cua cac dien tich chuyen dong Neu goi n0 la mat dien tich tu |qj la lan m6i hat dien tfch, v la lan van toe m6i hat thi j, n0, |q|, v co moi lien he vdi Thuc vay mot dan vi thdi gian sd hat dien tfch di qua dSn se la: dn = n„ v.dS„ 110 Hinh 2.5 Do cudng dl qua dSn se la: dI=n0.v.dSn|q| j = dI II" = n o-|q|-v n Ta co th£ bieu didn dudi dang tong quat nhu sau: j = n0-q-v (7) D6 dang nhan thay (7) dung cho ca hat mang dien tfch duong va dien tfch am That vay: q > —>j cung chieu v q < - » j nguoc chieu v 111 Chuong TU TRUdNG DONG DIEN KHONG DOI ■ Thi nghiem ve titong tac tuT cua dong dien Ta da biet xung quanh mot nam cham xuat hien mot tir trucmg Nho tir truang ma cac nam cham tuang tac duac vai (cac cue cung dau day nhau, khac dau hut nhau) Tuang tac cua nam cham vai goi la tucmg tac tir Cac thi nghiem sau day chung to dong dien cung co tir tfnh nhu nam cham, nghla la xung quanh dong dien cung xuat hien mot tir trudng 1.1.Thi nghiem Dat mot kim nam N cham tu thi kim nam N cham luon luon chi theo (a) (to Hinh 3.1 huong Bdc Nam Cang mot sai day ddn cho phuang cua soi day song song vai true ciia nam cham (hinh 3.1a) Neu cho dong dien khong ddi di qua sai day thi kim nam cham bi quay di goc (hinh 3.1b) 1.2 Thi nghiem Dua nam cham thing vao gan mot ong day ddn cd ddng dien chay thi thay nam cham cd the hut hoac day ong day dd (hinh 3.2) oV ' Hinh 3.2 1.3 Thi nghiem Cd hai day ddn dat song song vdi Neu cho ddng dien chay qua hai day ddn dd cung chieu thi thay hai day ddn dd hut neu ddng dien chav nguoc chieu thi hai day ddn dd day (hinh 3.3) N S a % \ 4V— \ Hinh 3.3 1.4 Ket luan Qua nhieu thf nghiem chting to nam cham tac dung len nam cham cung giong nhu dong dien tac dung len nam cham, hay nam cham tac dung len dong dien hoac dong dien tac dung len dong dien Vay xung quanh nam cham va xung quanh day ddn co dong dien chay qua deu xuat hien mot tti trudng Tuong tac giua nam cham voi nam cham, dong dien voi dong dien, hay giua nam cham vdi ddng dien d6u cd cung ban chat duoc goi la tuong tac tti Djnh lu at Am pe (Amper) ve ttfdng tac ttt cua dong dien 2.1 Phan tu dong dien Tren mot day ddn cd ddng dien I chlay qua neu ta thay mot doan nhd MN, MN coi la thing, thi phan tir ddng dien MN duoc dinh nghla la: I.dl, dd d1la vecto cd dai MN, cd chieu la chieu ddng dien I cllay day ddn (hinh 3.4) 2.2 Dinh luat Ampe 2.2.1 Trong chan khong Gia su chan khdng cd ddng dien I, I() Tren day ddn cd cudng I, tai O ta lay phan tu ddng dien I.dl, tren day ddn cd cudng I() ta lay phdn tti ddng dien I() dl0 tai dieim M Ke vecto r = OM Dung mat phdng P chtia I dl va r Tai M ke phap tuyen n vdi mat phdng P cho thti tu vecto I d l, r , n lap mot tam dien thuan Hinh 3.5 Goi la goc giua I dl va r, 0ola goc giua I0.dl0 va n (hinh 3.5) Qua thuc'nghiem chting to luc tac dung cua phan tu I dl len phan tir I() di^ la mot luc dF0 - Cd phuong vuong goc vdi phan tir I() dl0 va vuong goc vdi n - Cd chi£u cho thti tu ba vecto I() dl0 , n va dF^ lap tam dien thuan 113 - Co ldn: dF()= K I.dl.sin.0.1o.dlo.sin0o r2 K: la he so ty le he SI: K = — 471 H |a0 duoc goi la hang so tu co gia tri: ^i0= 4^.10 7— (henri/met) m Ta co the bieu di6n bang bieu thtic toan hoc tong quat nhu sau: Ro (Ip'd^o) a 4n (I.dl a r) (1) r3 2.2.2 Trong cac moi trudng Thuc nghiem cung chting to, hai phan tti dong dien neu dat moi trudng, cung khoang cach so vdi dat chung chan khdng thi lire tac dung se thay doi lan d F = li.dFg (j dupe goi la tti tham cua mdi trudng Neu (i> thi mdi trudng dd goi la chat thuan tti n < l thi duoc goi la mdi trudng nghich tti Va dinh luat Ampe dupe viet tong quat cho cac mdi trudng la: ^ = (I0 d l j A ( I d I A f ) 471 r3 Nhan xet: Dinh luat Ampe la dinh luat co ban cua tuong tac tti That vay, ddng dien chfnh la tap hop cua cac phan tti ddng dien, dd neu biet tuong tac giua hai phan tti ddng dien ta cd the tfnh dupe tuong tac gitia cac ddng dien cung giong nhu dinh luat Culong la dinh luat co ban cua tuong tac dien tfch Vecto cam ting tuf, vecto ctfbng tit trifbng 3.1 Vecto cam ung tir B Tu dinh luat Ampe, neu ta xet vecto s = 114 M _ O d l^ i 4ti r (3) thi vecta dB chi phu thuoc vao I dl la ph&n tu dong dien gay tir trudngva vi trf cac diem xet, khong phu thuoc vao I0 dl0 dB duac goi la vecta cam ting tti phdn tti dong dien I dl gay tai diem M Bieu thtic (3) duac goi la dinh luat Bio-Sava-Laplat Dinh ly duac phat bieu nhu sau: Vecta cam itng tilt phan tit ddng dien gay tai mot diem tit trudng co: - Phuang vuong goc vdi mat phdng chita phan tit ddng dien vd diem xet (mat phdng chita I d l , r ) Chieu cho thit tit ba vecta I d l, r , dB lap tam dien thuan (chieu ciia r ) - - Cd ldn: dB= M k I dLsin9 4n r2 * Chit y: - Vdi khai niem dB thi dinh luat Ampe cd the bieu di£n: d F = ( I 0.di;)A dB (4) Ro rang so sanh vdi bieu thtic luc tinh dien: F = q.E thi thay dB tuang duang vdi vecta E - Chieu cua vecta dB cd the tim theo quy tac cai dinh dc sau day: Dat cai dinh o'c theo phuang ciia ddng dien vd van dinh dc cho no tien theo chieu ddng dien, thi chieu quay ciia cai dinh dc la chieu ciia vecta d B - Trong he SI, dan vi cam ting tti la Tesla (T) 3.2 Nguyen ly chong chat tir trudng Dua vao dinh luat Ampe, ta cd the tfnh duac vecta cam tingtir cua ca ddng dien hoac n ddngdien gay tai mot diem tir trudng.That vay: - Ddi vdi mot ddng dien: B= j dB (5) cadongdien - Ddi vdi n ddng dien: (6) i= l 115 do, B, la vecto cam ting tijr dong dien thu i gay Bieu thtic (5) va (6) goi la nguyen ly chong chat cua tti truong 3.3 Vecto cudng tti trucmg H Cung giong nhu dien truong, ngoai vecto E , ngudi ta dung vecto D de dac trung cho dien truong Trong tti trudng ngoai vecto B ta dung mot dai lupng vecto cudng tti trudng H dupe dinh nghla: H=- B (7) Ro rang H va B cung phuong chieu chi khac ve ldn, va H khdng phu thuoc vao Trong he SI don vi cua H la Ampe/met (A/m) 3.4 Vecto cam ting tir B va cudng tti trudng H mot vai trudng hop dac biet Dua vao dinh luat Ampe va nguyen ly chong chat ciia tti trudng, ta cd the tfnh dupe vecto cam ting tti B cho cac ddng dien Ta chi xet mot sd trudng hop dac biet sau: I.dl 3.4.1 Ddng dien trdn Gia sir cd mot day dan hinh trdn ban kfnh R, cd ddng dien I chay qua Ta hay tfnh cam ting tti ddng dien gay tai tam O Hinh 3.6 Xet phan tti I dl bat ky, ta thay: a = 90° Ve ldn: dB = M l I-dl.sina _ ^ I.dl 4.7i r2 47t R2 Con phuong, chieu ap dung quy tac cai dinh dc (trong trudng hop nav cd phuang vuong goc vdi mat phang chtia day dan, chieu di vao) (hinh 3.6) Cac phan tir I dl bat ky tren day dan deu gay d O nhung vecta cam ting tti dB cung phuang, cung chieu va cd ldn d6u bang: dB = M l ti Do dd: 16 R2 dung Khoai tay m^m la qua trinh t6 ng hop acid nhan nhung diem sinh trucmg Viec chieu xa co the lam cham qua trinh t6 ng hop lai Doi v6 i triing gay hai, ngoai viec tieu diet ban than trung bang tia xa, nguoi ta muon tao nhung thuoc tinh di truyen bat lpi gay vo sinh cho trung due roi tung chung vao moi trucmg chung sinh song Ky thuat co nhieu lpi ich vi voi lieu khoang 8000R co the la due mat kha nang sinh san, tao nhung trting ung va sau mot thoi gian, ca tap hop trung bi diet vong Tir trudc toi thuftng khir trung dung cu y te, chi kMu, thuoc, vaccin bang hoa chat (thuoc sat trung, tffy rua, ) va nhiet nang (luoc, hap, say, dot, ) Cac cach xir ly khong phai luc nao cung ap dung dupe va co the lam hu hong mot ph^n hoac toan bo san ph^m Tu sau dai chien the gidi thu hai, nguoi ta ap dung rong rai viec dung btic xa ion hoa de tieu diet cac vi sinh vat cac san pham y te da neu tren Ngay nhieu loai thuoc, gang phau thuat, dung cu tiem truyen, dung cu phau thuat dupe xuat xuong sau ap dung viec khu trung bang btic xa ion hoa Thuc viec xac dinh cai chet cua vi sinh vat day rat kho Thong thucmg chi co the kiem tra su “vo trung” cua san pham ma thoi Lay nhung m iu vat cua san ph^m^ u nhiet thuan lpi cho su phat trien cho su phat trien cua vi khucin (30°C, 37°C va 55°C), nuoi cay tiep vao nhung moi trucmg thich hop, neu khong tha'y vi khuan phat trien (moc cac khudn lac hoac lam thay doi moi truefng nuoi cay vi khu^n) thi dupe coi la “vo trung” - Tieu huy hoac kim ham su phat trien cua cac te bao benh nhu te bao ung thu, te bao noi tiet cu5ng nang, phat trien qua manh Du6 i tac dung cua btic xa ion hoa, cac te bao benh bi kim ham sinh san hoac bi pha huy, ltic cac te bao lanh xung quanh it bi hu hai la do nhay cam phong xa cua chung khac va bang cac kl thuat chuyen mon, nguoi ta lam cho lieu hap thu vao cac mo benh nhieu hon mo lanh Co nhieu cach chieu xa dieu tri Do la cac kl thuat dung nguon chieu dat tir ngoai co th£ (teletherapy) hoac dung cac nguon gamma yeu, beta cting ap sat mo benh (brachytherapy) hoac dua cac nguon phong xa ho vao tan mo benh (curietherapy) - Kich thich cay trong, hat giong va gay dot bien gen co lpi de tao giong moi Ket qua nghien ctiu cho thay vcti mot lieu nhat dinh co the tang thu hoach va thuc d^y su phat trien cua cay Co the dieu khien su sinh truong va phat trien cua cay bang cach lira chon chieu xa vao nhung thdi ky phat trien nhat dinh cua cay So di vay la vi btic xa da tac dong len su phan chia te bao cay Chieu nhurng lieu nho vao hat giong tru c gieo co the kich thich sinh truong nhanh, chong gay benh va rut ngSn thoi gian thu hoach 212 Cac ngu6 n phong xa bang “ Co va 137Cs thudng dupe dung vao muc dich Btic xa ion hoa co th£ gay n£n nhung bien d6 i d cac chat lieu di truyen la ADN va RNA, tao cac dot bien Co che gay dot bien ra't phtic tap va thuoc vao btic xa, sua't lieu, lieu lupng Ngudi ta da tien hanh dong loat thi nghiem, chon lay nhung ca the co xuat hien nhung dot bi6'n co lpi, cung co no va nhan len qua nhieu the h6 Tti co th£ tao mot giong mdi n dinh nhung thuoc tfnh mdi Do la nhung cong viec cong phu, keo dai hang chuc nam Bang 5.1 cho ta mot vai vf du da thu dupe Bang 5.1 NhOmg dot bien thu difoc bang chieu xa d mot so cay Chung dot bien Cay Dia diem va thdi gian tao dot bien Uii diem mdi xuat hien Cai dau he Regina Thuy Dien, 1953 Nang suat cao Lua mach miia dong Jutta Dtic, 1953 Chiu ret, nang sua't cao Yen mach Florad Florida, 1960 Khang benh tan lui Lua mach mua xuSn Mari Thuy Dien, 1960 Chin sdrm Lua mi NP 836 An Do, 1960 Dai cuong, chiu han, nang suat cao An toan phong xa Chung ta da tha'y ro tac dung to ldn cua btic xa ion hoa len cac t chtic sinh hoc Vi vay, de ngan ngtia hoac han che dupe tac hai cua cac tia phong xa len co the’ ngudi va tranh lam o nhi6 m moi trudng song, chung ta phai thuc hi6 n nhung cong viec d£ dam bao an toan su dung va tiep xuc vdi cac ngu n phong xa 5.1 NhOmg nguon chieu xa anh hudng den ngudi Co the ngudi co the bi chieu xa tti ben ngoai Do la cac tia co kha nang dam xuyen Ion nhu tia X, tia gamma, chum hat notron, chum tia beta cting Cac dong vi phong xa cung co th£ bang nhieu cach khac lot vao ben co th£ tao nguon chieu xa tti ben co the Cac nguon xa xuat phat tti cac nguon phong xa tu nhien va nguon xa nhan tao (Bang 5.2) Nguon phong xa tu nhien bao gom cac tia vu tru, cac btic xa ion hoa phat tti cac dong vi phong xa da co san tu nhien nhu 40K, 3H, 14C va tti cac dong vi cua dong ho phong xa tu nhien la dong uran - radi, dong thori va dong actini Nguci ta da tfnh toan dupe rang tti cac nguon phong xa tu nhien lieu chieu tren 213 xucmg ngudi khoang 125 mr/nam 122 mr/nam va li£u chieu tren co quan sinh due la Bang 5.2 Lieu chieu trung blnh dung X quang chup y te Ca quan, phu tang chup Dien the bong X quang (kV) Lieu chieu (bang r) Ban va ngon tay 40-50 0,06 Canh tay 55-65 0,7-1 So nao nghieng 60-65 ,8 - 1,2 So nao thang 65-75 ,2 - 1,6 Cot song nghieng 70-85 1,8 - 3,5 Cot song thang 65-75 1,6 - 2,5 Khung chau 70-75 -2 ,5 Phoi 60-75 0,04 - 0,2 Da day 75-90 1,5-3 Than 65-85 1,4-2,5 Rang 50-60 -5 Tim 85-90 -4 Chup thai -8 Nguon phat xa nh&n tao la cac btic xa ion hoa phat tir cac ngu n phat tia X dung y te va cong nghiep, tti su o nhilm moi trufrng nguoi sir dung cac nguon phong xa ho nhu 131I, 32P hoac tit cac can ba cua cac vu no hat nhan thi nghiem nhu 137Cs, 90Sr, 89Sr Lieu luong gay nguon phong xa nhan tao r£t khac nhau, thuoc timg noi, tting ngudi vdi cac nganh nghe va cong viec khac 5.2 Lieu toi da cho phep Mod d&u, sir dung cac tia phong xa, ngufti ta chua co du hieu biet de giu gin an toan phong xa Do da xay cac tai bien chet nguoi, cac benh nghe nghiep btic xa Tuy nhien, khong the tao duoc mot moi trucmg tuyet doi khong co cac btic xa ion hoa chieu vao co the nguoi thuc te Va lai nguoi ta da da hieu dupe r&ng ngucfi tir phat sinh va ton tai den luon luon v^n phai chiu tac dung cua mot lieu chieu phong xa nhat dinh moi luc, moi noi Tuy v^y, loai ngudi vSn ton tai va phat trien ca the luc va tri tue, ca so luong va hlnh thai Vi vely, ngudi ta tin chdc rSng ton tai mot lieu nguong ma 214 khdng phat hien tha'y tac hai cua no Do la lieu toi da cho phep tire la lieu toi da co th£ chap nhan dupe Viec xac dinh gia tri cua lieu ngudng xay rat dai bdi vi trudc nam 1928 ngudi ta chua co khai niem ro ret ve tac hai cua buc xa Nam 1950, Uy ban Quoc te ve An toan Phong xa ICRP (International Committee of Radiation Protection) xac dinh lieu toi da cho phep la 0,2 r/ngay roi ve sau giam xuong 0,1 r/ngay Nhd cac nghien curu thuc nghiem nen tCr nam 1954 xac dinh lai lieu la 0,3r/tuan Nam 1956 tren co sd ve nhung lo lang ve tac dung di truyen,ngudi ta quy dinh mure tha'p han la 0,1 rem/tuan tuc la rem/nam Ngay ngudi ta khdng quan niem curng nhac nhu vay nua ma xuat phat tu nguyen tac la co gang giam lieu xuong cang thap cang tot, thira nhan rang mot lan chieu den 25 rem la khdng co tac hai gi dang lo ngai 5.3 Cac bien phap chu yeu de dam bao an toan phong xa Tac dung sinh hoc cua burc xa ion hoa trudc het phu thuoc vao ban cha't va nang luong tia, lieu luang, suat lieu va nhieu yeu to khac Cac nguon phong xa hd lai co the gay nen su nhidm xa vao ben ca th£ va o nhi6 m mdi trudng Vi vay d£7 dam bao an toan phong xa can co cac bien phap ve ky thuat va to chtic lam viec Muon giam duac lieu dieu kien va trudng hap cu th£ co the thuc hien dong thdi nhieu hoac mot nhung bien phap sau day: 5.3.1 Dieu chinh hoat nguon phong xa Mot nguon phong xa co tdc phan ldn se tao nen lieu chieu ldn Vi vay, can phai sir dung nhung nguon toi thieu can cho nhu cau cong viec Nguon toi thieu a day la nguon co tdc phan phong xa du d£ dat duac muc dich cong viec ma khdng qua ldn Trong y hoc, ngudi ta sir dung nhung nguon co tdc phan hang nghin Ci cua Cs137, Co60 de dieu tri ung thu hoac chi vai (j Ci cac nghien euu te bao va phan tu Cudng va nang luang cua nguon quang tuyen X va cac may gia tdc duac dieu chinh qua cudng dien tir trudng va mat hat duac gia tdc 5.3.2 Dieu chinh trudng chieu, tang khoang cach va giam thdi gian tiep xuc Vdi mot chum tia nhat dinh lieu luang hap thu thuoc vao trudng chieu Neu chieu 500r len toan ca the co the xay tir vong Nhung vdi each phan lieu nho va chieu khu tru lieu dieu tri co the dat den hang ngan r ma t
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