Khoa S Phm

Khoa S Phm

Vt L Nguyn T V Ht Nhn

Tc gi: Trn Th

Chng I: Cu trc nguyn t theo l thuyt c inMu nguyn t Thomson v th nghim Rutherford v tn x ht a

1. MU NGUYN T THOMSON. Ti th k XIX quan nim v nguyn t l phn t cui cng khng phn li c do mcrt xng t th k th V, trc cng nguyn khng th tn ti c na. Bi v ngay t s kin khm ph ra cc ht electron (1897) cho ngi ta nhn thy rng nguyn t phi c nhng thnh phn v nhng cu trc nht nh.

Nm 1903 nh vt l ngi Anh Tmxn (Thomson) a ra m hnh nguyn t c th u tin. Theo Thomson, nguyn t c dng hnh cu vi kch thc vo bc Angstron (1 = 10-10m). tch in dng di dng mt mi trng ng cht, cn cc elctrron th phn b ri rc v i xng bn trong hnh cu (hnh 1-1).

in tch dng ca mi trng v in tch m ca cc electron bng nhau m bo tnh trung ho v in ca nguyn t. M hnh ny cn c gi l mu nguyn t bnh ht nhn.

Trong thi gian di mu nguyn t ca Tmxn c v nh hp l. Nh sau kim nghim li mu bng cch cho nhng ht i xuyn su vo bn trong ht nhn th kt qu khc so vi on nhn l thuyt theo mu Thomson.

2. TH NGHIM RUDPHO V TN X HT. Cc nh khoa hc dng mt ngun phng x t nhin pht ra chm htanpha () c vn tc ln. Cc ht ny l cc nguyn t Hli mt 2 electron, v vy n c in tch (+2e). S th nghim c b tr nh hnh v (1-2)

Chm ht i qua mt khe hp p vo mt l vng mng, pha sau l vng l mn hunh quang, ph lp Sunfit km n cho ta mt du hiu lo sng khi c ht a p vo.

Theo d on hu ht cc ht a s xuyn qua l vng. Kt qu ny da theo mu nguyn t Tmxn l nguyn t c cc in tch dng phn b u

trong nguyn t. Nh vy cc ht a ch chu tc dng ca in trng rt yu, v coi nh khng chu nh hng g khi i qua l vng, do vy m phng chuyn ng ban u khng thay i. Th nhng kt qu th nghim hon ton khc vi d on.

Kt qu th nghim l: a s cc ht a bay thng, xuyn qua l vng, nhng s t b lch vi nhng gc rt ln, thm ch c ht bay tr li. Kt qu th nghim mu thun vi mu nguyn t Tmxn.

Nh vy gii thch c hin tng ny th phi gi thuyt rng trong nguyn t phi c mt in trng cc mnh mi c th lm cho cc ht a b lch so vi gc ln.

T Rudopho b mu nguyn t Tnxon v co rng cc in tch dng trong nguyn t phi tp trung li trung tm ca nguyn t v c gi l ht nhn ca nguyn t. Nh vy mu nguyn t ca Rudopho c hnh dung gm ht nhn gia ti tp trung ton b in tch dng v gn nh ton b khi lng ca nguyn t, xung quanh c cc electron chuyn ng.

Vi m hnh nh vy c th gii thch c hin tng tn x ca chm hta. V kch thc ht nhn nh hn rt nhiu so vi kch thc nguyn t, nn i b phn cc ht a xuyn qua c v i thng, ch nhng ht no i gn st ht nhn mi chu lc y tnh in, rt mnh lm cho n c th lch hng bay vi gc lch ng k.

3. L THUYT TN X HT a TRN NGUYN T, CNG THC TN X (RUDPHO): T mu nguyn t nu trn Rudpho thit lp cng thc cho php tnhton c s ht b tn bi mt l kim loi mng.

Gi thit ht v ht nhn u l nhng in tch im v tng tc y l tng tc Culong. Cc electron c khi lng rt nh nn c th b qua tng tc ca chng. Bi ton cn li ch l tng tc ca hai vt v chnh l 2 in tch im mang in tch dng. Ngoi ra cn gi thit rng hy nhn nguyn t c coi l ng yn v bia ng yn.

Hy xt chm ht c ng nng T t xa bay v pha ht nhn. Khi khong cch t ht nhn n phng chuyn ng ca ht a, nu nh khng c lc tc dng gia chng c nh ngha bng khong cch nhn b, ng vai tr nh mt thng s va chm, c lin quan n gc tn x . L gc gia

phng ti ban u v phng b lch ca ht . V vy khi ht ti gn ht nhn lc y Culong tng ln rt nhanh v mt phn ng nng ca ht a chuyn thnh th nng Culong: U= k vi qui c th nng bng 0.

Theo c hc di tc dng ca lc y xuyn tm ht a s chuyn ng theo mt qu o Hypecbol m ht nhn l mt trong hai tiu im. Gc tn x q l gc hp bi hai ng tim cn ca nhnh Hypecbol (hnh 1-3). N lin h vi khong cch nhm b theo cng thc sau:

cotg= (1-1)

Khng th xc nhn trc tip cng thc trn bng thc nghim v khngc khong nhm b.

Trc ht ta nhn xt rng mt ht tin gn li ht nhn vi khong nhm b s b tn x theo gc xc nh nh trn. Nu khong nhm nh hn b, th gc s ln hn. Hay mt ht a bay theo phng no trong phm vi din tch hnh trn b2 bao quanh mt ht nhn, chc chn s tn x vi gc ln hn .

Din tch s=b2 gi l tit din ca tng tc.

Xt tm kim loi c b dy d, cha n nguyn t trong mt n v th tch (mt din tch) s l nd v mt chm ht ti l kim loi c in tch A s bao quanh ndA ht nhn. Tit din tng tc tng cng s bng sndA. T suy ra h s t l u ca cc ht ti b tn x vi gc ln hn c nh ngha:

u = n.d..b2 .

Rt b t (1-1)

u = .n.d. cotg2 (2-1)

( Gi thuyt l kim loi mng tit din tng tc ca cc ht nhn khng che khut ln nhau).

c th tin hnh th nghim nhm xc nh kt qu tnh ton sa ht a tn x. Ta hy xt t l ht dU tn x trong gc gia q + dq.

Ly vi phn (2-1).

=.n.d..(3-1)

Khi nhng ht a tn x gia gc +d, s phi i qua mt i cu c b rng r.d. (hnh 1-4)

(Vi r bn knh hnh cu), bn knh ca i cu l r.sin, do din tch ds ca mn m s ht a tn x trong khong gc q v q+dq s i qua l:

ds = 2.r2sin.d = 42sincosd.

Hnh 1 - 4

Nu gi N0 l ton b s ht a i qua l vng trong qu trnh tin hnh th nghim th s ht a tn x theo hng q trong khong gc dq l N0dU. Vy s ht N(q)p vo mt n v din tch ca mn vi gc tn x q s l:

hay:

N()=(4-1)

Cng thc (4-1) gi l cng thc tn x Rupho. i lng N(q) s o c t th nghim.

Hoc l i lng:

N(). sin4 = const.

Kt qu ca th nghim hon ton ph hp vi tnh ton l thuyt ca Ruphov l thuyt v ht nhn c khng nh.

Mu hnh tinh nguyn t, kch thc ht nhn.

1. MU HNH TINH NGUYN T:Ta c th hnh dung tng qut v mu nguyn t Rupho nh sau: Nguyn t gm mt ht nhn chim mt th tch cc nh chnh gia, ti tp trung in tch dng v gn nh ton b khi lng ca nguyn t. Xung quanh ht nhn c cc electron chuyn ng, tng in tch m ca cc electron bng tng cc in tch dng ca ht nhn. Nu s electron ca nguyn t l Z th in tch dng ca ht nhn l +Ze.

S Z chnh l nguyn t s ca cc nguyn t. Nh vy c th ni rng s sp xp th t ca cc nguyn t ho hc trong h thng tun hon Mendeleep thc cht l do s electron ca mi nguyn t qui nh.

Ngoi ra ngi ta cng cho rng cc electron quay quanh ht nhn trn nhng qu o Elip, ging nh chuyn ng ca cc hnh tinh quanh mt tri trong thi dng h. V th mu nguyn t ca Ruopho cn c gi l mu hnh tinh nguyn t. S khc bit duy nht gia hai h thng ch l lc tng tc. Vi nguyn t l lc ht tnh in cn vi thi dng h l lc hp dn.

2. KCH THC HT NHN. phn trn ta ch rng bn knh ca ht nhn rt nh so vi bn knh nguyn t, nh hn hng ngn ln, v chnh kt qu th nghim cng xc nhn iu ny. Bi v trong th nghim ca Rupho, khi m s ht tn x trong gc(), tc l cc ht c khong cch nhm b rt nh (nh hn gi tr gii hn).

(T: ng nng)

Th kt qu sai lch rt nhiu so vi l thuyt. T suy ra khong cch ri vi ht nhn, nh lut v tng tc tnh in khng cn ng na, m thay vo l mt tng tc mi, c bit ch tn ti trong phm vi ht nhn. Nh vy gi tr b0 c coi l kch thc ht nhn. N c gi tr trong khong10-13 - 10-14m. Tc l nh hn t 1013 - 1014 mt ngn n mt vn ln so vinguyn t.

Tuy nhin t mu nguyn t Ruppho cng ny sinh mt s mu thun khng th gii thch ni.

Trc ht theo in ng lc hc mt ht nhn chuyn ng c gia tc (electron chuyn ng quay) s bc x lin tc sng in t vi tn s bng tn s quay quanh ht nhn. Nh vy ph ca nguyn t phi l ph lin tc, nhng thc nghim li xc nhn ph nguyn t l ph vch.

Th hai l: Khi electron bc x in t lin tc th nng lng ca n cng gim lin tc, dn n kt qu l qu o ca cc electron b thu hp dn theo ng xoy c cui cng ri vo ht nhn v nguyn t b ph hu. Nhng thc t li cho thy cc nguyn t li tn ti bn vng.

Nhng mu thun trn i hi phi xy dng l thuyt mi c c s gii thch cc tn ti trn. Phng php quan trng nghin cu cu trc nguyn t l nghin cu quang ph do cc nguyn t pht ra.

Quy lut quang ph nguyn t Hydr

Cui th k 19, khi nghin cu quang ph, ngi ta thy cc bc sng trong ph nguyn t hp thnh nhng dy vch quang ph xc nh c gi l dy quang ph.

Banme(Balmer) l ngi u tin thit lp c cng thc kinh nghim c th xc nh chnh xc tt c cc bc sng thuc vng nh sng nhn thy ca ph nguyn t Hydro. V vy dy ny c gi l dy Banme. Vch c bc sng di nht v r nht l c bc sng 6564 (k hiu l H), vch tip theo: 4863,4 (k hiu H). Bc sng cng gim cc vch cng st gn nhau, v cng sng cng yu dn, cho ti vch khng phn bit r c na m ch l mt di m. Cng thc tnh bc sng ca dy Banme l:

.n = 3,4,5, (3-1)

R l hng s gi l hng s Ritbe (Ridberd), c gi tr R=1,096776.107 m-1.

Vch H ng vi n=3; H ng vi n=4; H ng vi n=5 vch gii hn ng vi n=.

Ngoi dy Banme ngi ta cn tm thy dy ph, thuc nhng vng ngoi nh sng nhn thy. Vi mi dy u c cng thc tng t nh cng thc dy Banme.

Trong vng t ngoi l dy Laiman (Lyman) vi cc bc sng.

n=2,3,4 (3 -2)

Trong vng hng ngoi c dy Pasen (Paschen) theo cng thc

n=4,5,6 (3 - 3)

Trong vng hng noi xa c dy Braket(Brackett) v Phun(Pfund) theo cng thc:

n=5,6,7, (3 - 4)

n=6,7,8, (3 - 5)

Tt c cc cng thc trn c vit di dng cng thc Banme tng qut:

nk>n1 . (3 - 6)

Gi nguyn n1 thay i nk ta tm c bc sng ca cc vch trong cng dy, cn nu thay i n1 v nk ta c cc bc sng ca mi dy khc nhau.

S tn ti mt quy lut trt t ng ch nh vy trong quang ph nguyn t Hydro, cng nh trong cc ion tng t l nhng bng chng khng nh phi c mt l thuyt nht nh v cu trc nguyn t.

Thuyt Bo (Borh)

Da trn nhng thnh cng ca l thuyt Plng (Plack) v Anhstanh (Einstein), nh vt l ngi an Mch N.Bo ra mt l thuyt mi v cu trc nguyn t, nhm khc phc nhng mu thun m mu hnh tinh nguyn t ca Rupho khng gii quyt c.

Thuyt Bo c pht biu bng 2 nh vi ngha l tha nhn chng nh nhng tin trong ton hc:

1. nh I: (nh v trng thi dng ca nguyn t)Nguyn t ch tn ti trong nhng trng thi dng c nng lng xc nh v gin on hp thnh mt chui cc gi tr E1, E2, ,En. Trong trng thi dng, cc electron khng bc x nng lng v ch chuyn ng trn nhng qu o trn gi l qu o lng t, c bn knh tho mn iu kin sau y (gi l iu kin lng t ho ca Bo) v mme ng lng.

L= mvr = n (4 - 1)

Trong l hng s Plng rt gn: = Js v n l nhng s nguyn: n=1,2,3,

2. nh lut II: (nh v c ch hp th v c ch bc x ca nguyn t).Nguyn t ch hp th hay pht x nng lng di dng bc x in t, khi n chuyn t trng tha dngny sang trng thi dng khc (tc l ng vi s chuyn ca cc electron t qu o dng ny sang trng thi dng khc). Tn s v ca bc x in t m nguyn t hp th hoc pht x c xc nh bng biu thc:

. (4 - 2)

Vi E1,Ek l nng lng ng vi trng thi u v cui. Ta c: E1 - Ek>0 : qu trnh pht xE1 - Ek n1 (Enk>En1)

(5-10)

Cng thc trn xc nh bc sng ca ph pht x ca nguyn t Hydro c dng ging nh cng thc Banme tng qut.

V hng s Ritbec

m-1 (5-11)

Cc s nguyn trong cng thc Banme, biu din s th t ca cc trng thi dng ca nguyn t.

2. CC ION TNG T HYDRO:Bi ton nguyn t Hydro, hon ton c th p dng cho cc ion tng t nh : He+, Li++; Be+++; v.v Vi ht nhn mng in tch +Ze, iu ny dn n kt qu bn knh qu o ca cc electron s nh hn Z ln v n chu lc ht t pha ht nhn tng ln Z ln. V ta c:

(5-12)

(5-13)

(5-14)

3. CHUYN NG CA HT NHN:Trong bi ton trn, ta gi thit ht nhn ng yn. Nhng thc t khi lng ca ht nhn khng phi l ln v cng, nn n vn chuyn ng cng electron quanh khi tm chung ca h. iu ny dn n s hiu chnh ca khi lng ca electron. Nh vy nng lng v hng s Ricbe cng thay i i cht.

4. NH GI THUYT BO:Thuyt Bo vi hai tin mang n nhng yu t mi m cha tng c trong vt l hc c in l quan nim lng t v nng lng ca nguyn t.

Trc ht dng l thuyt Bo gii quyt c bi ton nguyn t Hydro, dng thuyt Bo gii thch c tnh quy lut quang ph hydro, v tnh ton chnh xc cc bc sng ca cc vch quang ph.

Tuy nhin bn cnh nhng thnh cng Bo cng bc l nhng thiu st ln v nhng hn ch ng k l:

V cng , b rng v cu trc tinh th ca cc vch quang ph, th l thuyt Bo hon ton khng gii quyt c. V thiu st c bn nht ca thuyt Bo l s thiu nht qun ca bn thn l thuyt. Trong khi a ra cc tin c tnh c o, cch mng th Bo vn tha nhn c hc c in v vn p dng cc nh lut ca in hc c in. Cc qui tc tng t c gn cho cc hnh mu c in khng theo mt lin h lgc no. tt c nhng yu t dn n ch b tc ca Bo. Sau ny c b sung thm thuyt Smphe (Somerfeld). Nhng cui cng vn khng trnh khi tht bi v khng gii quyt trit vn cu trc nguyn t. V chnh s b tc ny dn n s ra i ca c hc lng t, l nn tng ca mt l thuyt hon ton mi, c kh nng gii quyt ng n, v chnh xc mi hin tng, mi qui lut ca th gii vi m xy ra bn trong nguyn t v ht nhn.

Tuy n ch c gi tr lch s tm thi, v ch tn ti trong khong thi gian 10 nm. Thuyt Bo vi nhng thnh cng c o, vn xng ng c coi l chic cu ni khng th thiu c ca hai giai on pht trin ca vt l hc. N nh du s chuyn tip t vt l hc c in sang vt l hc hin i.

Chng II: C s hc lng t, Nguyn t hydr theo thuyt

lng t.

Lng tnh sng ht ca ht vi m. Gi thuyt Dbri (De Broglie)1. LNG TNH SNG HT CA CC HT VI M:Trong quang hc ta nghin cu r bn cht ca nh sng l bn cht sng ht. Nhng hin tng giao thoa, nhiu x th hin bn cht sng ca sng in t. Cn hiu ng quang in v tn x congtn (compton), li th hin bn cht ht ca nh sng - ht photon. Tnh cht hai mt ca nh sng c Anhxtanhdieenx t bng cng thc:

E=h.v (1-1)

P (1-2)

Trong E l nng lng v p l xung lng c trng cho tnh cht ht. Cn v l tn s, l bc sng c trng cho tnh cht sng.

Nm 1924 nh vt l ngi Php -Bri a ra gi thuyt to bo nhm pht trin vn rn i vi cc ht vi m. ng t cu hi ti sao nh sng c tnh cht ht th mi vt ni chung li khgn th c tnh cht sng? T ng pht trin l thuyt ca mnh v sng vt cht.

2. GI THUYT _BRI:-bri nu mt gi thuyt nh sau: chuyn ng ca mt ht t do vi xung lng p=mv v nng lng (ng nng) E c biu din bi mt sng phng lan truyn theo phng chuyn ng ca ht vi bc sng l v vi tn s n biu din qua cc h thc sau y:

(1-3)

Mc d c hnh thc ging nhau gia cng thc -Bri v ca Anhstanh. Nhng s khc nhau v ni dung l: vi photon, chuyn ng trong chn khng vi vn tc lan truyn e ca sng in t, tc l gia tn s n v bc sng l ca nh sng c mi lin h: . Cn i vi sng - Bri th khng c h thc . Bi v sng -Bri khng phi l sng in t.

khng nh tnh ng n ca gi thuyt -Bri, ta cn phi chng minh s tn ti ca sng -Bri. Ni cch khc phi tin hnh th nghim xc nhn sng -Bri l c thc. Mun vy chng ta hy tnh bc sng -Bri i vi electron.

Gi s chm ht electron chuyn ng t do vi nng lng E thu c sau khi cho chng tng tc qua mt in trng c hiu in th V, t trng thi ngh ban u.

Bc sng -Bri l :

(1-4)

(mv = ; E=q.V=e.V) A0.Nh vy bc sng ca electron ng vi chuyn ng t do ca mtelectron sau khi c tng tc bi mt hiu in th c 150V, s ng bng 1A0, tc l cng bc vi bc sng tia X.

Th nghim nhiu sng -BriHin tng nhiu x l hin tng th hin trc tip bn cht sng ca nh sng. Do vy nu chng ta tao ra c hnh nh nhiu x ca chm electron th l s chng minh r rt nht s tn ti tnh cht sng ca ht electron.

Vo nm 1927, hai nh vt l vitSon v Gicm (avisson-Germer), tin hnh th nghim nhiu x chm ca chm electron. Da vo hin tng nhiu x ca chm tia X bng cch dng mt cch t nhiu x c khong cch gia cc khe cng bc vi bc sng tia X (~A0). Ngi ta chn mng tinh th thin nhin lm cch t nhiu x, v n p ng c cc yu cu nu trn. Trong th nghim nhiu x tia X, ngi ta chiu chm tia X song song vo mng tinh th v tin hnh quan st chm tia nhiu x thao hng phn x ca chm tia ti trn b mt mng tinh th.

Khi iu kin thu c cc i nhiu x theo hng quan st c gi l iu kin Vunph-Brc (wulf-Bragg), s nh bi cng thc:

2dsin=n.

Vi d l khong cch gia hai mt phng cha cc nt mng gi l hng s mng tinh th, l gc hp bi chm tia ti vi b mt mng tinh th gi l gc trt.

Chnh th nghim nhiu x chm tia X, va c m t trn ta c th p dng pht hin tnh cht sng ca chm electron, da trn c s l bc sng ca chm electron gn bng vi bc sng ca tia X, nh tnh ton phn trn.

S th nghim c m t hnh 2-2

Chm electron pht ra t mt Catt nng nhit cao ri c tng tc bi mt hiu in th V vn, sau khi qua mt khe hp to thnh chm song song c chiu vo mng tinh th Ni.

V ngi ta nghin cu cng chm electron phn x nh ng m electron.

Tt c cc dng c trn t trong bung chn khng. Ging nh i vi tia X chm electron ti b mt mng tinh th di gc trt , xuyn qua 3 hoc 4 lp nguyn t v b chch hng (nhiu x) ti khe cch t. Trong c hng phn x cng gc c la chn l hng quan st. Nu chm electron phn x c tnh cht sng th cng ca chm s t gi tr cc i khi h thc Vunph-Brc c tho mn.

Kt qu vi electron ta c:

2.d.sin = n. (2-1)

Trong V l th tng tc tnh bng Vn, cn d tnh bng Angstron. Vi tinh th km : d=2,15A0 v chn gc =150. Ta c:

(2-2)

Cng chm electron phn x t th nghim cho thy n t nhng gi tr cc i lin tip ng vi cc gi tr ca cch u nhau, chng t mi cc i ca cng ng vi mt bc nhiu x khc nhau.

n=1 V=121V cc i bc 1 n=2 V=484V cc i bc 2 n=3 V=1089V cc i bc 3Nh vy th nghim xc nhn r tnh cht sng ca cc electron.

Sau ny ngi ta cn xc nhn khng ch electron m cn c nhng ht vi m khc nh proton, ntron v.v cng c tnh cht sng.

Tnh cht sng ca electron c ng dng vo ngnh khoa hc k thut mi l ngnh quang hc in t.

Vn cui cng t ra l l gi thuyt -Bri liu c p dng cho bt k ht vt cht no hay khng?

Theo gi thuyt -Bri:

Do vi nhng ht thng thng m khi lng rt ln so vi khi lng electron th bc sng c gi tr v cng nh, nh ti mc m khng cn ngha din t tnh sng na. Nh vy khi nim v lng tnh sng ht ca gi thuyt -Bri ch th hin cc ht vi m m thi.

Nguyn l bt nh Haixenbec (Heisenberg)Trong c hc c in, lun lun xc nh c cc i lng c trng cho trng thi ca mt h nh v tr, vn tc, xung lng, nng lng,v.v v mt l thuyt php o ng thi cc i lng ni trn bao gi cng c th t c chnh xc tu , min l cc dng c o cho php lm vic . S d nh vyl v cc php o khng nh hng g n h , trong khi ta bit rng php o bao gi cng cn n mt nng lng dng truyn t thng tin ly t h c o.

i vi cc vt th v m phn nng lng ny rt nh, hon ton khng nh hng g n h . Nhng khi chuyn sang h vi m, phn nng lng ny tr thnh ng k v n cng bc vi ln nng lng ca h phi o do vy n c th lm thay i trng thi ca h. iu ny dn n kt qu l c nhng i

lng vt l c trng cho trng thi ca h khng th ng thi xc nh mt cch chnh xc, n khng phi do mc chnh xc b hn ch ca cc dng c o m nguyn nhn thuc v bn cht ca i tng cn o.

Nm 1925, nh vt l Haixenbec pht biu mt nguyn l lm nn tng cho nhng quy lut ca th gii qui m. Nguyn l ny c gi l nguyn l bt nh Haixenbec. Ni dung ca n nh sau:

Khng th xc nh ng thi chnh xc to v xung lng ca mt ht (vi m). Nu to x c xc nh vi chnh xc x v thnh phn xung lng px=m.vx. c xc nh chnh xcpx th tch c gi tr cng

bc t nht bng hng s Plng:.

Ta s minh ho nguyn l bt nh bng th d sau:

Xt mt chm electron nhiu x qua mt khe hp (hnh 2-4), trn mn t pha sau khe ta thu c hnh nh nhiu x gm mt cc i trung tm c cng gn 80% s electron v nhng cc i ph thuc c cng nh.

Ta khng bit chc chn tng electron i qua khe v tr no, hay ni cch khc c bt nh v to vo bc kch thc ca khe, tc l x=d. Khi qua khe chm electron c xung lng khng i theo hng Oy. Nhng sau khi qua khe chm electron chuyn ng theo nhng hng khc nhau, tc l xut hin thnh phn trn trc . Gi s xt electron no ri vo im M, ng vi cc tiu th nht cua nhiu x v ti y thnh phn xung lng theo Ox l: px=p.sin. v ta c th coi bt nh v thnh phn xung lng px ng bng pox.

(3-2)

Theo quang hc ta c: M l cc tiu th nht nn

Suy ra: dp.sinq=h.

Vy:. (3-3)

Nu k thm mt s electron bn ngoi khong MN th: . Do vy m ta c:

V to x c chn tu nn ta c biu thc tng t:

H thc bt nh Haixenbec c ngha rt ln v v cng su sc, n phn nh bn cht ca i tng vi m v gn vi tnh cht sng ca cc ht. Chng ta khng th xc nh chnh xc tuyt i v tr ca cc ht v chuyn ng ca ht c tnh cht sng. Trong khi cc ht thng thng, bn cht sng khng c th hin do vy m ta xc nh c chnh xc to v xung lng ca ht. H thc bt nh cho thy khi xung lng c xc nh chnh xc bao nhiu th php o to cng km chnh xc by nhiu.

Nguyn l bt nh c xem nh l tiu chun nh gi phn bit ranh gii gia c hc c in v c hc lng t.

Hm sng ca ht vi m. on nhn thng k ca hm sng.Tnh cht sng ca ht vi mc khng nh, v vy chng ta cn m t sng ca ht vi m bng mt hm sng. Mc d bn cht ca sng -Bri ny cha c lm sng t, nhng hon ton c th biu din n mt cch hnh thc ging nh mi qua strnh sng bit trong c hc.

1. HM SNG CA HT T DO:Theo gi thuyt -Bri sng ng vi ht t do l sng phng. Trong c hc mt s sng phng lan truyn theo phng x vi vn tc v c biu din:

(4-1)

Du (-) ng vi sng truyn theo chiu dng trc Ox. Thay gi tr v v v=.v ta c:

(4-2)

Nu biu din di dng hm phc:

(4-3)

Trong phn thc din t sng thc truyn theo trc Ox.

(4-4)

By gi hy p dng mt cch hnh thc biu thc sng trn cho sng - Bri, vi cc lu sau y:

Thay cho y l mt i lng vt l c th ta dng k hiu hm sng l , n khng phi l i lng o c thng hng m l mt hm ton hc dng phc. Ngoi ra cn thay cc c trng ca sng (v,l) bng cc c trng ca ht (E,p) theo cng thc -Bri ta c:

(4-5)

(4-6)

Ly du (-) c l ring ca c hc lng t: gi l hng s Plng rt gn.

M rng cho ht chuyn ng t do theo phng thc trong khng gian ta c biu thc tng qut:

l:

(4-7)

Hoc vit di dng thnh hai phn ring, ph thuc thi gian v khng gian

(4-8)

2. HM SNG CA HT CHUYN NG TRONG TRNG LC:Trong trng hp tng qut, ht chuyn ng di tc dng ca trng lc m ph bin l trng lc th, sng -Bri tng ng khng cn l sng phng na, dng ca hm sng tr nn phc tp hn nhiu. Tuy nhin nu ch gii hn trng lc dng (th nng U khng ph thuc thi gian) th biu thcca hm sng phn ph thuc thi gian vn gi nguyn dng . V hmsng by gi c biu din di dng:

(4-9)

Dng tng minh ca hm sng s ph thuc vo trng lc c th trong ht chuyn ng. tm n chng ta phi gii phng trnh trong c hc lng t l phng trnh Sring. Nghim ca phng trnh ny chnh l hm sng m ta cn tm.

3. NGHA CA HM SNG DIN T SNG -BRI. ON NHN H THNG HM SNG.Sng -Bri khng phi l sng vt cht thng thng v ta khng th tm thy s lan truyn trong khng gian ca mt i lng vt l thc no gn vi sng. Vy ta s hiu ngha ca sng ny l g?

Vo nm, 1928, nh vt l hc Boc (Born) gii thch: hm sng c on nhn theo quan im thng k. hiu c on nhn ny, ta s tr li hnh nh nhiu x quen thuc ca chm electron thu c trn mn hunh quang hay trn mt knh nh. Hnh nh ny khng th gii thch c bng s chng cht ca sng ti mi imhoc cng pha, hoc khc pha dn n s tng cng hoc trit tiu cng sng nh i vi nh sng v rng ta ni sng -Bri khng h gn vi dao ng thc ca mt i lng vt l no, v mi electron khi ri vo im no l mt thc th nguyn vn. Do ch c th gii thch hin tng ny th hin s phn b ca cc electron, ti cc thi im khc nhau trn mn, s phn b ny tun theo quy lut ca sng: cc i nhiu x ng vi nhng im ti s electron ri vo nhiu nht, cn cc tiu nhiu x ng vi nhng im s electron ri vo t nht. Nu din t theo quan im thng k th c th ni: Kh nng electron ri vo im c cc i nhiu x hay xc sut tm thy electron ti l ln nht, ngc li kh nng electron ri vo im c cc tiu nhiu x hay xc sut tm thy electron ti l t nht. Nh vy c th ni thc cht ca hnh nh nhiu x din t tnh cht sng ca electron l hnh nh phn b xc sut tm thy electron ti im ny hay im khc trong khng gian.

Mt khc nu lp lun theo tnh Logc hnh thc ging nh nh sng, cng sng t l vi bnh phng bin sng (quan im sng) hoc t l vi s photon i ti (quan im ht), ta cng c th nhn nh rng s electron ri vo mi im ca mn s t l vi bnh phng bin sng -Bri ti im . Dn n cch on nhn cui cng nh sau: , din t xc sut tm thy ht trong mt n v th tch bao quanh im c to (x,y,z). V xc sut c tnh cng c nn mt h qu hin nhin l kh nng tm thy ht trong ton b khng gian phi l mt iu chc chn dn n iu kin sau y gi l iu kin chun ho ca hm sng.

(=100%) (4-10)

Cn ch hai im sau:

-V hm sng ni chung c th l hm phc m xc sut l mt s thc, nn bt buc phi bnh phng mdun hm sng . Trong l hm lin hip phc ca m bo kt qu l mt s thc. Nh vy bn cht ca hmth cha c ngha c th.

-ng l phi biu din xc sut tm thy ht theonhng v thnh phn ph thuc thi gian ca hmc dng nn kt qu tr thnh:

(4-11)

Ni cch khc, phn b xc sut tm thy ht khng ph thuc thi gian (trong trng lc dng).

Tm li, bn cht sng -Bri c xc nh, n khng phi l sng vt cht m l gn vi phn b xc sut tm thy ht ti mi v tr trong khng gian, quy lut phn b ny hon ton tun theo quy lut sng. Cng v vy khng bao gi ta c php ng nht electron hay mt ht vi m no vi sng v lun lun ht vn tn ti nguyn vn. Trpng th nghim v s nhiu x ca chm electron nu ta cho tng electron i qua mt, th kt qu cui cng vn cho ta hnh nh ging nh cho mt chm electron i qua. V vy ch c th gii thch tnh cht sng qua phn b xc sut tm thy ht trong khng gian, v c gi l on nhn thng k.

Phng trnh Sring (Schrodinger)Nh ni phn trn tnh cht sng ca ht vi m c m t bng mt hm sng, m mun tm hm sng ny ta phi gii mt phng trnh vi phn m hmchnh l nghim ca n. Phng trnh do Srig thit lp v n c vai tr v cng quan trng trong c hc lng t, ging nh phng trnh ca Niutn trong c hc c in, hay phng trnh Mcxoen trong in hc.

Ta hy thit lp phng trnh xut pht t hm sng ca sng -Bri vi chuyn ng ca ht t do, sau khi qut ho thu c phng trnh vi phn c bn m ta t c th gii tm hm sng cho nhng trng hp bt k.

1. PHNG TRNH SRING DNG PH THUC THI GIAN.Hm sng -Bri c dng:

(5-1)

tm phng trnh vi phn tho mn hm sng ta ln lt ly o hm ca theo thi gian:

(5-2)

V o hm theo cc to (x,y,z).

Tng t:

(5-3)

(5-4)(5-5)

Cng (5-3), (5-4), (5-5) v theo v ta c:

++= (5-6)

Vi trng hp ht chuyn ng trong trng lc th, ta c nng lng ton phn:

E = T + U =

Vi U l hm ca to v thi gian, nhn 2 v vi ta c:

(5-7)

T (5-2) (5-5) ta thy:

(5-8)

V: (5-9)

Thay vo (5-7) ta c:

+U. (5-10)

l phng trnh Sring dng tng qut.

2. PHNG TRNH SRING DNG DNG:Khi th nng U khng ph thuc thi gian hm sng dng:

(5-11)

Thay vo phng trnh Sring ta c:

Hoc bin i thnh:

(5-12)

(5-13)

l phng trnh Sring dng dng, thng c p dng rng ri trong nhiu bi ton c hc lng t cho php ta tm c cc thnh phn ca hm sng ch ph thuc vo cc ta khng gian . Trng hp c bit khi vn dng cho ht chuyn ng t do th phng trnh (5-13) cn c dng n gin hn:

(5-14)

Vi E l ng nng ca ht.

*Nhn xt:

-Phng trnh Sring suy t hm sng ca ht t do nhng li p dng c cho mi trng hp k c khi ht chu tc dng ca trng lc bt k U(x,y,z) hoc trng lc dng U(x,y,z). Tuy nhin khng c cch chng minh s suy din l ng, m ch c th tha nhn nh mt tin , sau xem xt kt qu tm c bng l thuyt c ph hp vi thc nghim hay khng. V vy phng trnh Sring cng c coi l mt tin .

-iu kin vn dng phng trnh Sring l nng lng ca ht l phi tng i tnh. Tc l ch xt khi v MY, tc l khi lng ca nguyn t m ln hn khi lng ca nguyn t con. Nng lng trong phn r xut hin di dng ng nng ca cc ht sinh ra trong phn r, ging nh khi phn r .

Q = DY + De

V khi lng ca electron nh hn khi lng ca ht nhn hng ngn ln nn ng nng git li ca ht nhn con c th b qua v Q De, ging nh phn r ph nng lng thu c trong phn r phi l ph gin on th nhng khi o nng lng trong phn r ngi ta li thu c mi gi tr ca nng lng tc l nng lng trong phn r ng l ph lin tc.

gii thch mu thun gia l thuyt v thc nghim trong phn r , nm 1930 Paoli a ra mt gi thuyt v s tn ti ca mt ht mi trong qu trnh phn r , v mi ti nm 1956, gi thuyt ny mi c xc nhn bng thc nghim. Ht c tn l ntrin. Ht ntrin c tnh cht l:

Khng mang in (trung ho v in) C khi lng ngh bng 0, v vy n lun chuyn ng vi vn tc nh sng. C Spin bn nguyn (S = 1/2 )

Vi cc tnh cht trn s tham gia ca ht ntrin vo qu trnh phn r b, s khng lm thay i in tch v s nuclon, nhng li dn ti s m bo cho nh lut bo ton nng lng v xung lng c tho mn.

Ni chung nng lng phn r Q c phn phi cho ng nng ca c hai ht: ntrin v electron, v th electron pht ra khng phi l n nng m c mi gi tr nng lng lin tc v ch khi nng lng (xung lng) ca ntrino bng 0 th ta mi c Q = De = Dmax, ng vi mt s electron c nng lng ln nht.

i vi nh lut bo ton xung lng v c thm vect xung lng ca ht ntrin, nn tng 3 vect bng khng, th electron bc x v ht nhn con, khng chuyn ng ngc chiu nhau, y l c s tm ht th ba. Trong thc t vic tm ntrin l v cng kh khn, bi v ntrin gn nh khng c tng tc vi vt cht, v c th xuyn qua mi vt.

Cui cng s c mt ca ntrin cng tha mn nh lut bo ton Spin. Nu ht nhn m c Spin nguyn th Spin ton phn ca ba ht l ht nhn con, ht ntrin, electron, cng phi c gi tr nguyn, v iu c hon ton tho mn v ht nhn con c Spin nguyn cn electron c pin bn nguyn.

S phn r + c vit l:

(5-11)

Phn r + l ht nhn pht ra ht pzitron, mang in tch dng v v mt nng lng phn r + s tho mn khi khi lng tnh ca ht nhn m ln hn khi lng tnh ca ht nhn con v ca pzitron, v vy nh lut bo ton nng lng l:

Hoc:

MX - Zme = [MY - (Z-1)me ] + me +

MX = MY + 2me +(5-12)

Trong MX, MY l khi lng ca nguyn t m v con, me l khi lng ca pzitron, Q l nng lng gii phng trong phn r, xut hin di dng ng nng ca 3 ht: pozitron, ntrino v ht nhn con. Vy iu kin phn r b+ l:

MX > MY + 2me

Ging nh phn ra -, ph nng lng ca phn r + l tng i n gin v pzitron c sinh ra s khng bn v b phn hu bi mt electron, to thnh 2 photon bay ngc chiu nhau, mi photon c nng lng c 0,51MeV. Vy s phn r + lun c c trng bi s xut hin hin tng hu cp.

Ngoi hai loi phn r k trn cn mt kiu phn r khc na l s bt electron. Trong phn r ny mt electron qu o ca nguyn t b ht nhn bt v kt hp vi proton ca ht nhn bin n thnh mt ntron, ging nh trong phn r . Hin nhin mt trong nhng electron thuc lp v trong cng ca nguyn t s d dng b b hn v v electron ny thuc lp K nn thng gi l s bt K. Qu trnh bt K v phn r + xy ra ging nhau ch mt proton bin thnh mt ntron, khc nhau ch trong bt K mt electron b hp th, cn trong phn r + mt pozitron c pht ra.

Quy tc bin i ca s bt electron nh sau:

nh lut bo ton nng lng c th vit:

(5-13)

hay:

me+(MX - Zme )= [MY - (Z-1)me ] +

MX = MY +(5-14)

Qu trnh bt electron, khng th hin bng mt ht mang in bc x. Nhng c th nhn bit cn c vo s thay i tnh cht ho hc ca cc nguyn t phn r hoc bng cch quan st cc tia X phng x. Khi phn r xy ra.

Cc h thc c bn lin quan n phn r b c m t nh sau:

- : + : Bt e: Hp th ntrin:

Tm li: Nu p dng quy tc tng qut l s pht x mt ht th tng ng vi s phn hp th mt phn ht v ngc li, th ta c th thy c 4 qu trnh phn r l tng ng.

3. PHNG X (GAMMA)Qu trnh phng x l qu trnh m ht nhn trng thi kch thch khi tr v trng thi c bn s pht ra bc x. Qu trnh c din t nh sau:

nh lut bo ton nng lng l:

Ec - Eth = hv +D

Ec, Eth l mc nng lng cao nht v thp ca ht nhn phng x, hv l nng lng ca photon pht x cn D l ng nng git li ca ht nhn phng x.

V xung lng c lin h:

ng nng git li ca ht nhn phng x l:

Tia phng x ca mt ht nhn kch thch c xem nh du hiu trc tip nhn bit tnh khng bn ca ht nhn. Vic phn tch cc nng lng tia cho php thit lp c s mc nng lng ca ht nhn, l ngha c bn nht nghin cu cu trc ht nhn, xy dng l thuyt v ht nhn nguyn t.

Tc ng ca tia phng x i vi mi trng. n v phng x.

Chng ta bit rng tt c cc tia phng x u gy ra nhng thay i trong c th sng, chng c th hu dit t bo, lm ion ho mi trng vt cht v gy ra nhng t bin trong cc t chc sng tc l lm bin i di truyn.Mt trong nhng c im c bn ca cc tia phng x l chng c tnh tch t. tc l vi cc tia phng x c cng yu th rogn mt thi gian di n s c tc dng ging nh cc tia phng x c cng mnh.

o tc ng ca cc tia phng x i vi mi trng vt cht, ngi ta dng nhiu n v khc nhau l:

a) Rnghen (R) l liu lng phng x ca tia Gamma () c th lm ion ho mi trng v to mt n v tnh in in tch trong khng kh iu kin tiu chun.

1R=2,57976.10-4 c/kg

Cn phn bit gia cc n v liu lng phng x vi n v hot phng x m chng ta ni trong hn phng x. n v hot phng x phn nh tnh c lp khch quan ca ngun phng x cn n v liu lng phng x th ph thuc ch quan vo i tng vt cht m n tc ng.

b) n v o nng lng ca bc x truyn cho mi kilogam vt cht m n i qua c gi la gray (Gy). n v ny c s dng ph bin trong vic o lng tc ng ca tia phng x ln c th ngi.

1Gy = 1 Jun/kg

c) n v o liu lng hp th bc x ca sinh vt l Sievert (Sv). i vi con ngi, bc x hp th c ngun gc t nhin v ngun gc nhn to, u gy ra nhng tc ng nh nhau trong trng hp cc lng bc x c hp th mt ln v ng u trn ton c h th 1Gy tng ng 1Sv, i vi cc bc x v .

Hiu qu sinh l ca lng phng x ng u trn c th ngi l: T 0 - 250mgy: khng nh hng n con ngi.250 - 1000mgy: gim nh s bch cu.

1000 - 2500mgy: gy nn ma, thay i cc thnh phn mu - iu tr c

t 2500 - 5000mgy: nh hng nghim trng sc kho. Trn 2500mgy: gy t vong.

Cc phng php v dng c ghi nhn bc x ht nhnPhng php pht hin bc x ht nhn da trn hiu ng xy ra khi cc ht phng x mang in i qua cc mi trng vt cht khc nhau, n thng gy ra s kchd thch v ion ho cc phn t ca mi trng vt cht, l phng php c dng ph bin nht. Phng php ny cng c dng pht hin nhng ht khng mang in v nhng ht ny khi i qua mi trng vt cht s va chm v truyn nng lng cho nhwnxg ht mang in, v cc h mang in va chm li gy ra hin tng ion ho trn ng i ca cng. Dng c pht hin bc x ht nhn ny gi l ng m. N c phn bit theo loi vt cht m cc ht bc x i qua v theo cch quan st, ghi nhn hin tng ion ho xy ra trn ng i ca ht bc x.

Cc ng m dng cht kh hot ng theo nguyn tc ghi nhn cc xung in to bi s ion ha. Ngoi ng m kh ngi ta cn s dng cc ng m dng cht lng hoc cht rn, pht hin hin tng phng x.

1. NG M KH:ng ny c cu to gm mt ng kn c mt in cc dc theo trc ca ng, cch in vi v ng v c t mt hiu in th dng V so vi v ng. Trong ng c rt ht khng kh v cho vo hn hp cht kh p sut thp )c vi CmHg).

Ca s ca ng thng lm bng nhm, n d dng cho ht , i qua. Khi mt ht mang in i vo ng m, cc phn t kh b ht vo cc dng trung tm to thnh dng in trn in tr ngoi R. Nhng xung in ny c phn tch v m nh mt b phn in t thch hp. Tu theo gi tr ca in

th V m dng in thu c khc nhau, tu theo dng in khc nhau m cch thc hot ng ca cc ng m cng khc

nhau.

2.NG M NHP NHY:

Hnh 5-1

Nguyn tc hot ng ca ng m ny khc hn so vi cc loi ng m kh ni trn. Cu to ca mt ng m nhp nhy l: Phn u l tinh th NaI, CsIc c tnh pht x nh sng nhp nhy khi c tia X hoc tia i qua.

nh sng ny chiu vo ng nhn quang, gm qiang cattd trong sut t pha trc v pha sau l mt dy cc tm nhy sng gi l int, gia tng cp int duy r hiu in th c 100V. Khi nh sng p vo Catt. mt electron b t do hiu ng quang in, electron ny p vo int u tin va chm v lm bt ra mt electron mi. Nhng electron ny ti imt th hai v gii phng thm nhiu electron mi na. qu trnh tip tc ti int cui cng, lc li ra ca ng nhn quang c dng xung in rt mnh. Nh vy ng m nhp nhy l loi ng m t l c th dng o nng lng ca photon. N c dng kh ph bin trong thc nghim ht nhn v c u im l c hiu sut m cao.

3. NG M NHP NHY:

Hnh 5-2

L loi ng m mi c cp n sau ny, khi cht bn dn c ph bin u nhng nm 60 th k 20. Nguyn l hot ng ca n da trn c s hiu ng xy ra lp tip xc p - n, ca cht bn dn c tp cht, loi ng m ny c u im l phn gii nng lng cao vn tc m nhanh, tc xung in ln, nng lng to cp ion n, gn nh v c bn cao, ngun nng lng tiu th thp.

Chng VI: Bin i nhn to ca ht nhn

Phn ng ht nhn. Tit din hiu dng ca phn ng ht nhn1. PHN NG HT NHN:Hin tng phng x l hin tng t pht xy ra bn trong ht nhn khng chu nh hng ca mi trng bn ngoi. Cc cht phng x t nhin thng l nhng ng v ht nhn nng tp trng ch yu 4 h phng x m chng ta xt trc y. Nhng ngy nay cc cht phng x t nhin gn nh cn kit, nm ng dng ca chng th c vai tr rt ln trong i sng k thut. V vy cn to ra cc cht phng x mi c nhiu ng dng hu ch cho con ngi v phng php to ra cc ht nhn phng x mi l phng php bin i nhn to ht nhn, thng qua cc phn ng ht nhn. thc hin mt phn ng ht nhn ngi ta thng dng mt ht n c nng lng ln bn ph cc ht nhn bia v c kh nng xy ra kt qu l:

Ht n ch i rt gn ht nhn bia v b tn x n hi, m khng gy ra phn ng ht nhn, nh trng hp th nghim Ruopho.

Ht n xuyn vo bn trong ht nhn v ht nhn bt gi ht n ny, tr thnh mt ht nhn mi. ht nhn mi ny thng l khng bn v ngay sau t phn r cho ra mt ht nhn mi km heo mt ht n nh bay ra. V khi mt phn ng ht nhn c thc hin.

Phn ng ht nhn c biu din nh sau:

a: ht n.

X: ht nhn bia. Y: ht nhn con.b: l ht nh bay ra sau phn ng.

(1-1)

Phn ng u tin do con ngi to ra l phn ng do Rupho thc hin nm 1919. Khi ng chn ht a lm n bn ph ht nhn Nit v phn ng c vit l:

Ht nh bay ra chnh l ht proton.

(1-2)

Phn ng ht nhn trn tho mn nh lut bo ton in tch, bo ton s nuclon, v bo ton khi lng.

n nm 1932, cc phn ng ht nhn u c thc hin bi cc ht a hoc tia g t cc ngun phng x t nhin. Sau khi c my gia tc ht, ngi ta dng cc ht c gia tc lm n. V d dng chm ht proton c nng lng 500KeV bn ph ht nhn Li theo phn ng:

(1-3)

Hoc dng chm ht a bn ph ht nhn Al.

(1-4)

Ht nhn khng bn v phn r thnh ng v bn vi chu k bn r 2,6 pht.

(1-5)

Cc ht nhn mi sinha sau phn ng khng bn v phn r t pht theo nh lut phng x l mt c im ca nhiu phn ng ht nhn. Hin tng gi l phng x nhn to. Nh vy phn ng ht nhn l bin php ch yu thu c cc ng v phng x nhn to.

Cc phn ng ht nhn cn c k hiu vn tt nh sau: X(a,b)Y. (1-6)

2. TIT DIN HIU DNG CA PHN NG HT NHN:Chng ta ni n phn ng ht nhn, by gi chng ta s xt xem cc kh nng xy ra mt phn ng ht nhn . Chng ta bit rng khng phi c c mt ht n ti ht nhn bia l c phn ng ht nhn xy ra, m kh nng xy ra mt hn ng ht nhn ch c mt xc sut no m thi.

Ta hy tng tng mi ht nhn X trong cc ht nhn bia c gn vi mt tit din s gi l tit din hiu dng theo hng vung gc vi phng ti ca ht an. Bia c xem nh l rt mng sao cho khng c mt ht nhn no b che lp bi cc ht nhn khc, v nu ht n lt vo tit din s ny th chc chn phn ng ht nhn xy ra. ngc li nu ht n khng i qua bt k mt tit din hiu dng s no th khng c phn ng ht nhn xy ra.

Gi s c n1 ht nhn p vo bia trong ch c ns ht i qua cc tit din hiu dng tc l to ra ns phn ng ht nhn. Vy xc sut P tm mt phn ng ht nhn c th xy ra bng t s: , tc l: .

Xc sut ny cng bng t s ca tit din hiu dng ton phn i vi tt c cc ht nhn bia v din tch ton phn ca bia: Nu din tch ca bia l A, b dy ca bia lad d v s ht nhn bia trn n v th tch l N th tit din hiu dng ton phn l s.N.A.d v xc sut P phn ng bng:

Vy xc sut ca phn ng th t l vi tit din hiu dng. Tit din hiu dng c gi tr thay i tu theo phn ng. Ngoi ra n cn ph thuc c vo nng lng ca ht n ti. n v dng o tit din hiu dng gi l bara.

1 bara = 10-24cm2 = 10-28 m2.

1 bara = 10cm = 10m.

Php o tit din hiu dng bng thc nghim c mt gi tr rt quan trng v gi tr o c s cho ta bit xc sut ca phn ng xy ra. Trong cc th nghim, khi cho ht a n nng p vo bia, ngi ta o bng cch xc nh s ht b bay ra hay l s ht nhn sn phm Y c to thnh, t tm .

Cc nh lut bo ton trong phn ng ht nhn. Nng lng ca phn ng ht nhn1. CC NH LUT BO TON TRONG PHN NG HT NHN:Phn ng ht nhn l mt qu trnh vt l nn cng phi tun theo cc nh lut bo ton ging nh cc hin tng vt l khc. Nhng nh lut bo ton ch yu nht m phn ng ht nhn phi tha mn:

1.1 _nh lut bo ton in tch: in tch ca cc ht tham gia phn ng phic bo ton c ngha l s proton trong phn ng phi gi nguyn.

1.2 _nh lut bo ton xung lng: Vect xung lng ton phn s gi khng i trong phn ng, k c xung lng ca ht photon (tia ). Khi c ht ny xut hin trong phn ng.

1.3 _nh lut bo ton mmen xung lng bao gm c mmen Spin ca ht nhn.

1.4 _nh lut bo ton nng - khi lng : Nng lng ton phn phi khng i trc v sau p. Chng ta s xem xt k nh lut ny v n c vai tr rt quan trng.

2. NNG LNG CA PHN NG HT NHN:

Xt phn ng ht nhn X(a,b)Y. Ta gi s rng ht nhn X lc u l ng yn cn ng nng ca ht khc l DY, Da, Db.

Khi nghin cu cc phn ng ht nhn ta c nh lut bo ton nng - khi lng l:

Trong : WX, Wa l ni nng ca ht X v a.

WY, Wb l ni nng ca ht Y v b

Thng th tng ni nng trc phn ng Wt khc tng ni nng sau phn ng Ws. Do tng ng nng trc phn ng Dt cng khc tng ng nng sau phn ng Ds. Hiu s:

Q = Wt - Ws = Dt - Ds (2-2)

Gi l hiu ng nng lng ca phn ng ht nhn.

Nh vy nng lng ta ra trong phn ng ht nhn c th tnh trc tip t cc khi lng ca cc ht tham gia phn ng.

Ta c:

Q = [(ma + mX) - (mb + mY)]c2 (2-3)

C th xy ra cc trng hp sau:

Q > 0: phn ng c gi l phn ng ta nng lng; trong khi lng d chuyn thnh ng nng ca cc ht bay ra.

Q < 0: phn ng gi l thu nng lng c th xem phn ng nh l mt phn ca s va chm khng n hi trong mt phn fng nng ca ht n chuyn thnh khi lng.

Q = 0: c ng nng v khi lng tnh ca ht trc v sau phn ng c gi nguyn ta c th coi y l va chm n hi.

V d: Xt phn ng:

. (2-4)

Q = 0,01864.931 = 17,35MeV

Q>0: phn ng ny ta nng lng.

Ta hy xt s phn r ca mt ht ng yn khng b kch thch. y cng c th xem nh mt trng hp c bit ca phn ng ht nhn vi Dt = 0; Ds > 0. Nh vy Q>0, c ngha l mt ht ch c th t phn r nu hiu ng nng lng ca qu trnh y l dng. Ni cch khc tng khi lng ca ht nhn sinh ra phi b hn khi lng ca ht nhn ban u:

3. NH LUT BO TON XUNG LNG:Gi s ht nhn X lc u ng yn nh lut bo ton xung lng c vit l:

(2-5)

Gi l gc gia cc vn tc ca ht n a v ht bn ra b. Ta c:

Gia xung v ng nng c biu thc:

P2 = 2mD. Do vy ta c:

Hnh 5-3

(2-6).

Ntron.1. LCH S DN N HT NTRON:D on v thnh phn cu to ht nhn gm c ht proton mang in tch dng v mt ht na khng mang in c nh vt l hc ngi Nga Ivanhenc nu ra t nhng nm 1930. V mi ti nm 1932, ngi ta mi xc nhn c s tn ti ca ht ny thng qua vic nghin cu cc phn ng ht nhn nhn to.

Lc u hai nh vt l ngi c l Bz v Bchc (Botho - Becker), pht hin thy khi dng chn ht bn ph cc ht nhn Brili th thy xut hin mt tia khng nhn thy c kh nng m xuyn cc mnh m lc u tng l tia cng (tia c nng lng ln) theo phn ng:

(3-1)

Nhng sau Iren v Gilio Quiri lp li th nghim trn v thy tia phng x ny c th lm bt ra nhng proton c nng lng c 6MeV v tm bay ti 26cm trong khng kh, khi cho tia ny i qua lp paraphin. Hin tng ny lc u c gii thch bng hiu ng Conpton. Nhng da vo nh lut bo ton nng lng d dng nhn ra c, phn ng ny khng tho mn nh lut bo ton nng lng.

Cng nm 1932 Chartrich a ra d on l trong phn ng trn d sinh ra mt ht khng mang in, v c khi lng gn bng vi khi lng ca proton v nh t tn cho n l ht ntron(k hiu ). V vy phng trnh phn ng trn c vit li nh sau:

(3-2)

Theo nh lut bo ton nng-khi lng, phn ng trn cho thy ntron c gii phng ra vi nng lng c 6MeV v sau va chm vi proton cha trong paraphin, truyn ton b nng lng ca n cho proton: Gi thuyt hon ton ph hp vi kt qu thc nghim.

S pht hin ra ntron lm hon thin v l thuyt thnh phn cu to ht nhn. Vai tr ca ntron cng tng ng nh proton bn trong ht nhn vi ngha l mt thnh phn ca ht nhn: ht nuclon.

2. SN SINH RA NTRON:Ngy nay c nhiu phng php thu c ntron. Phng php n gin nht l dng ngun Ra-Be di dng hn hp. Cc ht a phng x t Radi vachm vi Be ca hn hp to thnh phn ng v cc ntron vimt di nng lng rng s c pht ra.

Mt phn ng quang ht nhan cng c th cho ta ntron. Th d phn ng:. phn ng c th xy ra, nng lng ca phton ti phi ln hn 1,76MeV ; c th s dng cc tia pht x t cc cht phng x t nhin hoc nhn to phn ng ny.

Ntron cng c th c to ra t cc phn ng phn ph cc ht nhn bia khc nhau bng cc ht n mang in nh p,d c tng tc nh cc my gia tc mnh. Cc phn ng nh vy c bit c li khi dng l ngun ntron v ntron to thnh trong trng hp ny l n nng. Mt phn ng in hnh l dng ht ton tng tc bn ph vo bia Triti:

(3-3)

y l phn ng c dng trong cc my pht ntron hin i.Phn ng ny thuc loi to nng lng vi Q=17,6MeV.

Mt cch thu ntron c nng lng rt cao cn n gin hn l thc hin m va chm trc din gia proton c nng lng cc ln v mt ntron n c trong mt ht nhn bia. Chng hn khi cho proton c nng lng 2MeV p vo mt bia, cc ntron c cng nng lng bt ra theo pha trc v proton truyn nng lng v xung lng ca n cho proton.

V ngun cung cp tt nht cho ntron c mt rt ln l l phn ng ht nhn hot ng theo nguyn l ca hin tng phn hch.

3. PHT HIN RA NTRONNtron l ht khng mang in nn vic pht hin ra n phi s dng phng php gin tip, l phi t ntron phi to ra ht mang in, cc hn mang in ny s c pht hin ra d dng hn. V l nguyn tc hot ng ca ng m ntron. ng m ntron. ng m t l l ng m cha y hn hp hi Bo, hoc l hp cht rn ca Bo. Khi ntron i vo ng mny, trong ng m sinh ra phn ng v s ion ho do ht a gy rach ghi nhn.

Va chm gia ht ntron v mt ht nh mang in, nh l proton, cng c th lm c s cho vic pht hin ra ntron.

Cc phng php khc pht hin ntron l da vo s phng x ca phn ng bt bc x ntron. Th d ntron b ht nhn bt theo phn ng.

Phng x nhn to Poditrn. ng dng ca ng v phng x

Ht nhn ng v sau phn r -.

(3-4)

Hot phng x - c th pht hin v o c, nu tit din bt (), b dy kim loi, thi gian v hng s phn r du bit th c th tnh c dng ntron.

4. VAI TR CA NTRON.Trc khi tm thy ntron, th trong cc phn ng ht nhn, ngi ta ch dngcc ht n mang in nh , , ,Nhc im chnh ca cc ht n ny l chng chu lc cn Culng khi tin dn ti cc ht nhn bia do hn ch kh nng xuyn su vo bn trong ht nhn, dn ti lm gim tit din hiu dng ca phn ng ht nhn.

Vi ht ntron th nhc im trn c khc phc bi v ht ntron khng mang in nn khng chu lc cn Culng v d dng xuyn su vo trong ht nhn. S bt ntron c th xy ra khi mt ntron c nng lng tu va chm vi mt ht nhn. Chnh v vy, sau khi pht hin ra ht ntron th hng lot cc phn ng ht nhn c thc hin v t lm xut hin v s cc ng v phng x mi, m ra mt hng nghin cu thc nghim gii thch l thuyt v cu trc ht nhn. Ngy nay c mt ngnh vt l ntron ring bit.

Cc phn ng do ntron gy ra rt a dng. V d:

Phn ng bt bc x: Ntron bn vo ht nhn bia v b bt, ht nhn to thnh trng thi kch thch phng x .

Ht ng v phn r -.

(3-5)

(3-6)

Phn ng phn hch: l loi phn ng c bit, dng ntron bn vo ht nhn Urani 235 ta thu c cc ntron th cp vi s lng nhiu hn gp hai, ba ln phn ng ny cung cp cho ta mt ngun nng lng khng l m con ngi c th s dng vo mc ch ho bnh. Chng ta s xem xt loi phn ng ny chng sau.

Nh chng ta bit, hu ht cc ht nhn ca cc ng v c sinh ra trong phn ng ht nhn l nhng ng v phng x. V chng c gi l cc ng v phng x nhn to, mc ch l phn bit cc cht phng x t nhin.

Nhng ng v phng x nhn to ch yu l phn r v , rt t khi phn r . Ngoi ra trong cc ht nhn ng v phng x nhn to chng ta cn gp mt loi phn r c bit m t khi thy trong phn r t nhin l phn r +. Ht nhn ng v pht ra ht pzitron mang in tch dng v sau ny ta c bit n l phn ht ca ht electron. Cc ht pzitron c Anecsn pht hin vo nm 1932 trong tia v r, chng c to thnh do qu trnh sinh cp: mt photon phn r thnh cp electron - pzitron.

Phn ng ht nhn to ra pzitron do Gili Quiri thc hin u tin vo nm 1934.

(4-1)

ng v khng bn v phng x b+, vi chu k ban r T = 2,5 pht.

(4-2)

Cc phn ng by ntron cng l ngun cung cp cc ng v phng x nhn to, nhng ng v ny thng phng x -.

Phn ng quang ht nhn l loi phn ng trong hp th tia dn n s phn r ca ht nhn hp th v cc ht nhn sn phm v cng l nhng ng v phng x nhn to.

My gia tc ht

l ng v phng x -.

(4-3)

(4-4)

Ngy nay nh cc phn ng ht nhn m ngi ta to ra v s cc ng v phng x mi, con s cc ng v phng x ln ti hng ngn nguyn t ng v. Cc ng v phng x cng c tnh cht ho hc ging nh cc nguyn t bn. V vy nu ta pha trn mt lng nh cht ng v phng x vi cc nguyn t bn ca cng mt nguyn t. Th thng qua s theo di hot phng x chng ta tm c cc qu trnh xy ra bn trong c th sng, hoc s vn chuyn cht trong cy xanh, phng php ny gi l phng php nguyn t nh du.

Ngy nay cc ng v phng x nhn to c s dng rng ri trong nhiu lnh vc y hc, sinh hc, nng nghip, thc phm, a cht,v.v

Chng ta bit rng d thc hin c phn ng ht nhn ta cn c nhng ht n c nng lng ln. Ngun phng x t nhin tuy pht ra nhng ht n, nhng cha p ng c yu cu ca phn ng ht nhn. V vy vic nghin cu v ch to cc my gia tc ht l nhm gii quyt cc yu cu trn.

Cc ht mang in l nhng ht c gia tc tt nht n c th l electron, proton, ton hoc nhng ion dng. Cc my gia tc ht gm c hai loi my gia tc chnh l: My gia tc thng v my gia tc trn.

1. MY GIA TC THNG:My gia tc thng hot ng theo nguyn tc gia tc tnh in, trong in th tng tc ch s dng mt ln.

2. MY GIA TC TRN:Loi my ny khc vi my gia tc thng l sau mi vng trn ht mang in li c tng tc mt ln, v mi ln tng tc cc ht c nhn thm nng lng, nh vy ht quay c bao nhiu vng th in th tng tc li s dng c by nhiu ln. Vn k thut c bn y l phi m bo v duy tr s ng b gia chu k quay ca ht vi s i chiu ph hp ca in th tng tc. Ta bit cng thc ca lc t (lc Lorenx). Tac dng ln ht mang in tch dng q l:

(5-1)

Suy ra: (5-2) Qung ng i c ca ht in tch q l:

Nh vy thi gian t l i lng khng i: Chu k quay s l:

(5-3)

Tn s l:

(5-4)

(5-5)

Khi vn tc chuyn ng ca ht cn nh, hiu i ng tng i tnh cha xut hin, th chu k ca ngun ph hp vi chu k quay ca ht. Nhng khi vn tc ln s xut hin ng tng i tnh, lc ny chu k quay ca ht khng ph hp vi chu khi quya ca in trng na. V vy khng th gia tc ht vi vn tc qu ln trong cc my gia tc thng thng.

Chng VII: Nng lng ht nhn

Hin tng phn hch1. HIN TNG PHN HCH.Trong cc phn ng ht nhn, chng ta s xt xem mt loi phn ng ht nhn c bit, l phn ng phn hch ca cc ht nhn cc nng.

Hin tng ny do hai nh bc hc ngi c l Han v Sraxman (Hahn - Strassman) pht hin nm 1939, khi bn ntron vo ht nhn nng, ht nhn ny b v thnh hai mnh c khi lng gn bng nhau.

Qu trnh phn hch c gii thch theo m hnh git cht lng ca mu ht nhn l: Trong ht nhn, lc y Culng gia cc prton c khuynh hng ph v kch thc ca ht nhn, ngc li lc cng b mt ca cc nuclon pha ngoi li c khuynh hng gi nguyn dng hnh cu ca ht nhn. Nu ht nhn nhn m nng lng kch thch th hnh dng ca n bt u thay i, t hnh cu chuyn sang hnh elipxot. Nu mt cng lc ngoi ln gi c cc nuclon li vi nhau th giot ht nhn ch dao ng ri sau tr v trng thi ban u ca n. Nhng nu nng lng kch thch ln, lm cho ht nhn dao ng mnh th n chuyn dn thnh hnh s 8 ri sau v thnh hai mnh.

Hin tng ny xy ra khi mt ntron c nng lng thp b bt bi ht nhn nng: ng v Urani 235. Ht nhn trng thi kch thch vi nng lng c 6,8 MeV. Ht nhn ny v thnh hai mnh (c lc ti 3 hoc 4 mnh). Cc mnh v eeuf d tha ntron nn khng bn, m phng x tip cc ntron th cp. sau cc mnh v li tip tc bin cc ntron thnh cc proton, r thnh ng v bn hn, kt qu l cc mnh v thng pht ra cac tia phng x b- v g.

Ta xt mt v d sau: V d 1:

Cc mnh phn hch tip tc phn r nh sau:

(1-1)

V d 2:

(1-3)

(1-2)

Cc nhnh phn hch tip tc phn r nh sau:

(1-4)

(1-5)

(1-6)

Chng ta bit rng qu trnh phn hch to ra mt nng lng rt lm v pht ra mt s ntron th cp. Chnh iu ny l c s thc hin phn ng dy chuyn phn hch ht nhn.

V l thuyt cc ntron th cp ny tip tc gy ra phn hch v li gii phng tip ntron. Nh vy qu trnh xy ra cho ti no khng cn nguyn t Uran na. Nhng trong thc t, phn ng phn hch khng hon ton xy ra nh vy m n cn ph thuc vo cc yu t sau:

Khng phi mi ntron i vo khi Uran u gy ra phn ng ht nhn m ch c cc ntron b ht nhn 235U bt c mi gy ra phn ng phn hch.

Khng phi mi ntron c sinh ra u c th s dng vo phn ng phn hch c, bi v mt s thot ra khi khi Uran.

Trong khi Uran cn c cc ng v tuy bt c cc mtron, nhng hon ton khng gy ra phn ng phn hch (V d: 236U). V nhng l do trn m phn ng phn hch ht nhn ch c thc hin vi nhng iu kin nht nh.

2. IU KIN XY RA PHN NG PHN HCH:Chng ta gi n l s ntron trung bnh c sinh ra trong mt phn ng phn hch. S ntron trung bnh ny lm gim nng lng ca chng, mt s b238U hp th m khng gy ra phn ng phn hch, mt s b cc tp cht hp th v mt s khc i ra ngoi khi khi Uran, do vy cng khng gy ra phn ng phn hch ht nhn.

Chng ta gi s rng ch c p ntron c lm chm li, tc l c np ntron chm. Trong s np ntron chm ny th khng phi u c 235U hp th. Chng ta gi thuyt rng ch c k ntron chm b 235U hp th m thi, vy k c gi l h s s dng ntron chm. V ta c npk ntron c kh nng gy ra phn ng tip theo. Nhng chng ta li cng thy rng vn c nhng ntron nhanh b 235U hp th v gy ra phn ng phn hch. V ta coi cc trng hpny tng ng vi h s (=1,03-1,1). Vy ta c tch s:

f = .n.p.k (2-7)

Tch s trn c gi l h s nhn ntron. V vy .n.p.k >1 th s ntron lm phn hch ht nhn tng ln. Vy th mun duy tr c phn ng phn hch ht nhn tc l duy tr c phn ng dy chuyn th iu kin cn l.

L phn ng ht nhn

Phn ng phn hch dy chuyn t duy r u tin do fecmi thc hin nm 1942 ti thnh ph Chicago (M) trong mt l phn ng ht nhn dng Urani thin nhin lm nguyn liu v graphit l cht lm chm ntron.

Mc d c nhiu kiu l phn ng khc nhau nhng ni chung chng u phi tun theo mt nguyn tc c bn nh ca l phn ng ht nhn dng Urani thin nhin.

Trc tin, iu kin phn ng dy chuyn c duy tr i hi sau khi ht nhn Urani b phn hch th t nht phi c mt ntron lm phn hch mt ht nhn na. Ta bit tit din hiu dng ca phn ng phn hch ca ht nhn 235U s tng khi s ntron chm tng. Trong khi cc ntron th cp l cc ntron nhanh. V th vn l phi lm chm li cc ntron th c, v trong l phn ng ht nhn ngi ta dng mt cht lm chm thch hp nhng khng hp th ntron. V ngi ta sp xp cc thanh nhin liu xen k cc thanh nhin liu Urani gia cc cht lm chm . Nhng cht cha nhiu nguyn t Hydr tc l cha nhiu proton s lm gim ng nng ca ntron kh cao, nhng n cng bt cc ntron vi xc sut ln. Do vy cc cht lm chm thch hp l: D2O, grapht, be v mt s cht hu c.

gim bt t l ntron b tp cht hp th, ngi ta phi tinh ch nhin liu gim tp cht n mc sti thiu. chng s tht thot cc ntron ngi ta cn lm mt lp phn x ntron bao quanh l phn ng. Nu l phn ng c kch thc b cng lm cho nhiu ntron thot ra ngoi hn so vi l c kch thc ln.

Khi khc phc c cc nguyn nhn lm tht thot ntron duy tr phn ng phn hch dy chuyn. Nu mt phn ng phn hch to ra t hn mt phn ng phn hch khc, tc l phn ng dt chuyn khng c duy tr, ngc lain nu mt phn ng phn hch li gy ra nhiu hn mt phn ng phn hch khc th l trng thi hot ng mnh, trng thi ny nng lng gii phng qu ln v c kh nng dn n v n nh mt qu bom nguyn t.

cho l phn ng hot ng bnh thng ngi ta phi s dng cc thanh iu khin bng Cadimi (Cd), t xen k gia cc thanh nhin liu Urani. Thanh Cd c kh nng bt ntron rt cao, do tu theo v tr ca nhng thanh ny a ln cao hay cm xung su m c th tng hoc gim tc phn ng dy chuyn, dn n thay i cng sut l.

Tuy nhin vic iu khin hot ng ca l phn ng bng c hc s khng th thc hin kp nu c phn hch sn sinh ra nhiu ntron th cp v tc cc phn ng ny xy ra rt nhanh. khc phc iu ny, ngi ta phi tnh n vic cc ntron c sinh ra ch sau mt vi phn r - ca cc mnh v, v vy mt ntron tr c th gy ra phn ng phn hch sau thi gian 10s, do iu kin duy tr phn ng phn hch l phi tnh n t s ntron tr mi c th iu khin c phn ng v mt thi gian.

Hin nay c cc cch phn loi l phn ng ht nhn nh sau:

Theo nhin liu: l nhin liu thin nhin hay nhin liu nhn t.

Theo cht lm chm ntron: bng nc, bng grapht, hay cc cht khc.

Theo cch phn b ca nhin liu trong cht lm chm: ng nht hoc khngng nht.

Theo nng lng ca ntron lm chm: l chm, nhanh hay trung bnh.

Theo cht trao i nhit: nc, hi hay kim loi lng.

Theo cng dng: cho nng lng, cho ngun ntron, cho snr xut cc dng v,

Trn th gii hin nay rt nhiu nc s dng in nguyn t, m l phn ng ht nhn chnh l b phn quan trng nht, nc ta l phn ng ht nhn lt vi cng sut 5000KW, ch phc v cho cng tc nghin cu khoa hc v iu ch mt s ng v phng x dng trong y hc.

Cc nh my in nguyn t treen th gii hng nm khng ngng tng ln. Cng vi vic pht trin nhiu nh my in nguyn t: ngi ta cn a vo sn xut th nghim cc nh my in nguyn t s dng l phn ng ntron nhanh.

Tuy nhin vo nm 1986 s c nh my in nguyn t Trecnobn (Ucraina) buc ngi ta xem xt li mt cch nghim tc rt nhiu vn quan trng ca in nguyn t nh: Kim sot qu trnh phn ng phn hch, t ng ho cao v tin cy rt cao trong qu trnh iu khin, yu cu nghim ngt v vic chp hnh cc quy trnh vn hnh k thut, v s phi hp quc t khi xy ra s c.

Phn ng nhit ht nhnPhn ng nhit ht nhn hay cn gi l phn ng nhit hch l phn ng tng hp hai ht nhn m thnh ht nhn nng hn. Sau y l mt s th d.

(3-1)

(3-2)

(3-3)

Thc nghim cho thy cc phn ng trn u l phn ng to nng lng. V trong mi phn ng trn tng khi lng ca cc ht v phi nh hn tng khi lng ca cc ht v tri. Nng lng ca phn ng to ra rt ln, ln gp hng chc ln phn ng ho hc thng thng v ln hn c nng lng ca phn ng phn hch.

phn ng nhit hch c th xy ra th cc ht nhn tham gia phn ng phi c vn tc rt ln. Ni cch khac nhit ca phn ng rt cao.

V lc y Culng ngn cn cc ht nhn tin li gn nhau, nn mun tng hp hai ht nhn ta phi lm cho chng c nng lng ln thng lc y ny. Ni cch khc cc ht nhn phi c nng lng ln vt ra hng ro th nng tng tc gia chng. Chiu cao ca hng ro th ny rt ln, ngay c ht nhn tch in t nh ng v ca Hydr th cng vo c: 350 - 500 KeV.

Do hiu ng ng ngm, mt ht nhn c nng lng nh hn chiu cao hng ro th nng cng c th chui qua hng ro th xm nhp vo ht nhn kia nhng xc sut xn nhp gim i rt nhanh khi nng lng gim. Mun duy tr phn ng phi lm sao cho cc ht nhn lun lun c nng lng ln, c th thc hin iu bng cch tng nhit . Nu nung nng n mt triu th ng nng trung bnh ca ton xp x bng 130eV, khi xc sut tng hp ht nhn vn cn rt nh. Tuy nhin ng nng l ng nng trung bnh, nn xc sut tng hp ht nhn thc t cao hn. Nh vy khi tng nhit ti mt gi tr no , th c th duy tr c phn ng tng hp ht nhn.

Cc phn ng nhit hch c thc hin u tin trn mt t l cc phn ng khng diu khin c v dng vo mc ch chin tranh, l Bom Hydr (Bom H). Trong Bom H ngi ta t mt hn hp ton - Triti vo lng qu bom, gia hn hp l qu bom nguyn t (bom A). Khi s dng bom H ngi ta cho n bom A lm cho hn hp ton - Triti t ti hng triu , vi nhit ny phn ng nhit hch xy ra. Nng lng ca phn ng nhit hch ta ra l rt ln, v vy bom h c sc cng ph rt ln.

Sau chin tranh th gii th II, nhiu phng th nghim trn th gii i vo nghin cu phn ng nhit hch c iu khin. Mc d cho ti nay, con ngi vn cha thnh cng trong hng nghin cu ny, nhng ngi ta vn hy vng rng cc phn ng nhit hch s mang li mt ngun nng lng mi c thni hu nh v hn. V trong nc sng ngi, ao h, i dng c cha 0,015% l nc nng m t c th iu ch c ton, cn Triti c th iu ch t .

Kh khn trong nghin cu phn ng nhit hch c iu khin l cch to ra nhit cao. Bi v nhit cao (hng trm triu ) th vt cht no cng bin thnh hi v ion ho thnh mi trng cc ht mang in - gi l mi rng Platxma, ch khng phi l mi trng kh thng thng. V tt nhin cng khng vt liu no lm bnh cha Platxma c c v mi vt u bin thnh hi.

Con ng gii quyt kh khn trn l dng t trng cc mnh gi Platxma trong gii hn nht nh, ng thi cho cc xung in phng qua Platxma nung nng chng. Ngay nay ngi ta t c Platxma nhit cao c triu , ngng ch duy tr trong thi gian cc ngn. V vy m kt qu ny cha c ngha thc tin.

Trong lng mt tri v cc ngi sao c nhit rt cao do vy cc phn ng nhit hch c thc hin. Phn ng ny l ngun nng lng v i ca cc thin th. Ngi ta cho rng mt tri v cc v sao to thnh t khi Hydr v mt s nguyn t khc nhng ch yu l Hydr. Lc u do lc hp dn tc ng ln khi vt cht ni trn, n b nn li lm cho khi vt cht b nng ln v to thnh mi trng Platxma nng. Trong mi trng ny phn ng nhit hch to thnh ht nhn nng v c m t nh sau:

u tin proton kt hp vi nhau to thnh ton, ton li kt hp vi proton to thnh ng v Heli: . Sau hai ng v Heli kt hp vi nhau to thnh ht nhn Heli v proton. Ngi ta gi chui phn ng l chu trnh Hydr.

Chu trnh Hydr ch c th xy ra giai on u tin ca qu trnh hnh thnh mt tri v cc ngi sao v lc nhit cn thp, khong 10 triu , nhit cao hn khi trong cc ngi sao c s lng ng k Heli th c th to thnh nhng phn ng ht nhn ca nhng ht nng hn.

Sau y chng ta hy xt mt lot phn ng nhit hch thng xy ra trong lng mt tri v cc ngi sao:

bc x

bc x bc x

Kt qu ca qu trnh trn l s tng hp ca 4 proton thnh ht nhn v chng ta li thu c nh lc u. Ta gi tp hp cc phn ng l chu trnh Cacbon - Nit 9hay cn gi l chu trnh Betho), v c s tham giaca Cacbon v Nit. Php tnh ton v mt nng lng chng t chu trnh trn c th xy ra nhit vi chc triu v to ra nhit lng c 26,8 MeV.

Chng VIII: Ht c bn

M u cc loi tng tc c bnI. KHI NIM HT C BN.Danh t ht c bn c dng ch nhng ht rt nh cu to nn vt cht ni chung. C th ni ht c bn u tin chnh l ht electron m Tmxn khm ph nm 1897. Ngy nay s ht c bn tng ln rt nhiu, ti hng chc ht ( l khng k n cc ht cng hng khc). V vy m kh nh ngha c ht c bn theo ng ngha c bn ca n. R rng l tn gi ht c bn mang nhiu tnh cht quy c v bn thn mi ht c th c cu trc ni ti phc tp m chng ta cha bit. Ngoi ra phn ln cc ht c bn u c th phn r thnh cc ht c bn khc, thm ch c th theo nhiu cch khc nhau, tc l tng tc gia chng rt phong ph v gn lin vi cc quy lut vt l mi.

Trong nhng nm nm mi th k 20 ngi ta ch da vo cc tia v tr nghin cu cc ht c bn v l ngun nng lng duy nht c th s dng c. Tia v tr chnh l nhng chm ht c bn (ch yu l proton), c nng lng c t eV, t khong khng v tr bay vo tri t. Khi i vo lp kh quyn ca tri t n tng tc vi cc ht nhn ca cc nguyn t lp kh quyn cao v gy ra cc phn ng to thnh cc ht c bn mi. Tuy nhin ngun ht t v tr l rt t i, v vy hiu qu do cc tia v tr gy ra la rt b.

Sau khi ngi ta xy dng c cc my gia tc khng l, mi cung cp y cc chm ht c nng lng cc ln, v n sc, lc con ngi mi lin tip khm ph ra hng lot cc ht c bn mi. Ngoi ra cc my gia tc ht, ngy nay cn c cc phng tin k thut hin i hn dng nghin cu cc ht c bn, in hnh l cc bung bt ln cha y Hydr lng cho pho chp nh ghi nhn c cc qu trnh tng tc phc tp din ra gia cc ht c bn.

C th kt lun l vt l ht c bn chnh l vt l nng lng cao, n cho php i su vo th gii bn trong ht nhn. L thuyt v ht c bn vn ang c pht trin mnh m vn cn nhiu gi thuyt cha c khng nh, chng ta hy vng trong tng lai khng xa th gii vi m s c khm ph y .

II. CC LOI TNG TC C BN:Chng ta bit rng trong t nhin ch tn ti 4 loi tng tc:

1. Tng tc u tin l tng tc hp dn: l tng tc yu nht nhng li ph bin nht. Lc hp dn bao trm trong mi lnh vc v c biu din bng nh lut vn vt hp dn. Lc t l nghch vi bnh phng khong cch.

2. Tng tc th hai l tng tc in t: c din t bng nh lut Culng (Coulomb), Ampe (Ampere) v Bi-Xava (Biot-Savart) cng l lc t l nghch vi bnh phng khong cch. Lc in v lc t thc cht l hai lc biu hin ca cng mt hin tng thng nht. Lc in t chi phi tnh cht ca electron trong nguyn t v phn t. Lc in t cng c tnh ph bin v l tng tc c hiu bit mt cch y nht.

3. Tng tc th ba l tng tc gia cc nuclon trong ht nhn v n c tn l tng tc mnh: tng tc ny c bn knh tc dng rt ngn vo bc fecmi (10-15m), do khng c nh hng g i vi cu trc v electron ca nguyn t. Tng tc mnh khng ch cc qu trnh phn r , phn hch, nhit hch v tn x nuclon trn ht nhn nng lng cao. Cho ti ngy nay ngi ta cha bit dc nhiu lm v cng cha c biu thc ton hc c th ca lc tng tc ny.

4. Tng tc th t l tng tc yu: N l mt loi lc chi phi trong ht nhn m in hnh l gy ra s phn r - ca ht nhn. Tuy nhin n phn bit vi tng tac mnh tc phn r chm.

S hiu bit v cc loi tng tc trn rt cn thit cho vic m t hin tng ca cc ht c bn.

Ta c th nh gi tng quan v bc ln ca 4 loi tng tc k trn bng bng so snh sau y:

Tng tcMnhin tYuHp dn

ln110-1210-1210-40

Ht v phn htChng ta bit kt qu ca vic gii phng trnh Sring trong c hc lng t. Mt phng trnh c bn khc cng c vai tr tng t nh phng trnh Srding nhng c kt hp c hiu ng tng i tnh l phng trnh irc. Vic gii phng trnh ny dn n kt qu tm thy gi tr Spin ca electron v c mmen t ring ca electron. Nhng n khng dng li m trong phng trnh ca mnh irc s dng cng thc nng lng tng i tnh p dng cho electron.

(2-1)

Vi m0 v p l khi lng ngh v xung lng ca electron khc vi vt l hc c in, y chng ta tha nhn c gi tr m ca nng lng. Electron l ht t do nn khng c s lng t ho nng lng. Cc eletron th hin mi gi tr nng lng, tu theo gi trj ca xung lng. gii thch gi tr m, irc a gi thuyt rng chn khng c quan nim gm cc electron chim y trng thi c nng lng m do c khi lng qun tnh m v v th nhng electron o khng th quan st hoc c pht hin c. Mt electron thc tn ti trng thi nng lng dng khng th vt qua khong cm chuyn xung trng thi nng lng m bi l tt c cc trng thi ny u b electron o chim ch.

Nhng nu v l do no mt electron o nhn c mt nng lng ln n s chuyn ln vng nng lng dng, ti y n xut hin nh mt electron thc c khi lng qun tnh dng. ng thi trong min nng lng m xut hin mt l trng, chn khng b ht i mt khi lng m s tng ng vi s xut hin mt khi lng dng v l trng c coi l mt ht c khi lng dng. Ht ny ging ht electron ch khc du v in tch, irc t tn cho ht ny l pzitron v coi n nh mt phn ht caelectron. Nh vy t mt photon c nng lng 2m0c2 to thnh mt cp electron - pzitron hay l cp - phn ht.

Qu trnh ngc li xy ra khi mt electron t min c nng lng dng chuyn xung mt l trng trong min c nng lng m. Kt qu l mt electron thc bin mt ng thi vi mt l trng v khi electron chim ch cn b trng, n li tr thnh mt electron o. Ni cch khc, mt cp electron - pzitron ng thi bin mt, hin tng ny gi l s hy cp.

V nguyn tc mt photon c th nhng nng lng ca n to thnh cp electron - pzitron. Tt nhin photon phi c nng lng nh nht l 2m0c2. Nhng thc t mt photon d c nng lng ln i bao nhiu chng na cng khng th to cp trong mt chn khng hon ton nu khng c t trng ngoi. Ni chung qu trnh sinh cp thng xy ra trong mt in trng mnh gn ht nhn hn l rong ht nhn. l i hi ca cc nh lut bo ton nng lng v xung lng phi ng thi tho mn. Tng t trong qu trnh ngc li s hy cp phi km theo nng lng sinh ra di dng photon, nhng cng khng th ch cho mt photon m phi l hai photon chuyn ng ngc chiu nhau.

Sau ny khi ngi ta tm thy cc ht c bn khc th ng thi cng tm thy tt c cc phn ht ca chng, ngoi tr mt vi trng hp c bit phn ht trng nhau nh ht photon, ht Mezon 0. Ni chung gia ht v phn ht u c th xy ra hin tng hy cp v sinh cp.

Phn loi cc ht c bn v cc c trng ca chngI. PHN LOI:C th phn chia cc ht c bn thnh 4 loi cn c vo khi lng ca chng nh sau:1-1_Photon: l lng t ca rng in t c khi lng ngh bng khng. 1-2_Lepton hay ht nh: gm electron, muyn, v ntrin. C hai loi htntrin: Ntrin thuc v electron v Ntrin thuc v muyn.

1-3 _Mezn hay ht trung bnh: c khi lng ln hn electron nhng b hn nuclon. C hai loi ht gm mzn v mzn K - cn gi l pin v Kan.

1-4 _Barin hay ht nng: gm cc nuclon (proton v ntron) v cc Hypern, Lamda, Xicma, Kxi, Omega

Ngi ta cng c th tp hp cc ht c bn theo tng tc m chng phn r nh sau:

Cc ht bn: c 9 ht khng phn r theo bt k tng tc no, l:

v photon . Tt c cc ht c bn cn li khng bn v phn r theo cc tng tc yu, in t hoc mnh. Cc ht phn r theo tng tc yu l muyn mzn ntron, phn ntron v cc hypern.

Cc ht phn r theo tng tc in t: gm Meznv cc hypern.Thi gian sng ca cc qu trnh ny vo cs

Cc ht phn r theo tng tc mnh: Trong tng tc ny ht c coi nh tn ti trong mt trng thi lin kt trc khi phn r thnh cc ht c bn khc. Thi gian sng l cc ngn vo c . Trng thi lin kt c gi l ht

cng hng mc d thc cht khng phi l mt ht c th quan st c. Mun xc nhn s tn ti ca n ch c th da vo s phn b nng lng ca cc sn phm phn r.Ni chung s phn loi cc ht c bn ngoi yu t v khi lng, v thi gian sng, v v tng tc nh trn ngi ta cn c th da vo nhng c im quan trng khc ca cc ht c bn.

2. CC C TRNG C BN:Chng ta ch cp y nhng c trng c bn nht ca cc ht c bn l:

2-1.Khi lng: Theo thuyt tng i th nng lng v khi lng l hai c trng trng nhau v gia khi lng v nng lng c mi lin h . Nng lng v khi lng ph thuc vo trng thi chuyn ng ca ht . Nhng khi lng ngh ca mt ht l c trng ni ti ca n. V vy khi ni n mt ht c bn, trc ht phi ngh n khi lng ngh ca n.

2-2.in tch: in tch ca tt c cc ht, khng k du u l bi ca ddieenj tch nguyn t. V vy ngi ta thng biu din in tch ca mt ht bng mt s nguyn dng hoc m. V d in tch ca electron l -1, ca photon bng +1. Khi ta phi hiu rng cn nhn s nguyn biu din in tch vi in tch nguyn t .

2-3.Kch thc: Cho n nay ta cha r kch thc ca proton, ntron v cc ht c bn khc. Nhng chc chn rng kch thc ca chng khng th ln hn kch thc ht nhn. V vy ngi ta chn di c lm di dc trng cho th gii cc ht c bn v gi di l fecmi.

Thi gian c rng trong th gii cc ht c bn vo c

2-4.Spin: Spin l i lng khng c mt trong th gii v m m ch c mt trong th gii vi m, ni mt cch n gin l ta c th coi Spin l i lng m t s t quay ca ht xung quanh mt trc. Ly n v l hng s Plng th Spin ca mt ht c biu din bng mt s nguyn hay bn nguyn. V d: Spin ca electron, proton v ntron u bng , cn Spin ca photon bng 1.

2-5.Cc c trng khc:

-Mmen t: Mmen t c sinh ra khi c dng in chy trong mch kn nhng trong th gii cc ht c bn th c nhng ht khng mang in nhng vn c mmen t khc khng, chng hn nh ntron.

-Ngoi in tch cc ht c bn cn c nhng c trng khc cng c gi l tch l tch Lepton v Barion tch. ng thi cc ht c Spin ng v (khc Spin m ta ni trn) s l. Tt c nhng c trng ny l nhng khi nim rt mi v khng c trong th gii v m.

Cc nh lut bo ton

Cc tng tc ca ht c bn tun theo nhiu quy tc lng t th hin qua cc nh lut bo ton. Nhng nh lut u tin quen thuc nht l nh lut bo ton nng lng, xung lng v momen xung lng (k c Spin), cc nh lut ny vn ng trong lnh vc nng lng cao nht v khng gian nh nht ca ht nhn. in tch cng l i lng c bo ton trong mi tng tc. Tnh bn tuyt i ca proton dn n s bo ton Barin.

Cc c trng lng t khc cn li ch c bo ton trong mt s qu trnh m khng c bo ton trong mt s qu trnh khc. V d: tnh chn l khng c bo ton trong tng tc yu. Spin ng v I ch c bo ton trong tng tc mnh, cn hnh chiu Iz v s l S th li thay i trong tng tc yu. S d cc thnh phn ca mt b a tuyn ng vi I xc nh c khi lng khc nhau l ng vi iu kin tng tc, in t khng bo ton Spin ng v.

Chng ta cng nhn thy c nhng i lng vt l khng bo ton trong bt c tng tc no. V du: mmen t ca cc hat.

Ngi ta cn a ra mt vi quy tc chn lc c th m t cch thc m mt nh lut bo ton khng p dng. V d: s l S khng c bo ton trong tng tc yu, nhng n khng bao gi thay i qu mt n v trong tng tc, t dn ti quy tc chn lc cho tng tc yu. V vy htkhng phn rac thnh nuclon v mezn m li phn r theo kiu thc, mi ln k tip s l li bin i 1 n v.

Cc nh lut bo ton c thng k trong bng sau y:

Vi nt v quy lut i xng ht QuarkTrong bi hc trc chng ta ni n vic sp xp cc ht c bn theo khi lng ca chng. l cch sp xp rt th s, n khng mang li cho ta nhng thng tin g quan trng. Trong nhng nm 50 th k 20, s cc ht c bn c tm thy ln ti vi trm ht. Do vic xp loi chng cn phi c phn tch mt cch t m hn.

Trong nhng cch sp xp mi, ngi ta ch yu quan tm n xp loi cc ht Hadrn, v photon v Lepton ch chim mt s rt t trong cc ht c bn.

Nhng hadrn l cc ht tham gia tng tc mnh nn khi xp theo cc ht hadrn, ngi ta da vo tnh cht i xng ca tng tc mnh. T s phn tch cc tnh cht i xng hai nh vt l thuyt l Niman v Ghen man lm vic c lp vi nhau v cng cng b nm 1961. Ni dng ca gi thuyt l tng tc gia cc hadrn c chung tnh cht i xng ca mt nhm ton hc gi l nhm SU(3)

Da vo gi thuyt , cc ht c bn c th chia ra thnh mt s h. S ht trong cc h khng ging nha. C h ch gm mt ht, c h gm ba ht, tm ht, mi ht.

Sau khi phn thnh h, ngi ta xp cc ht c bn pht hin ra vo cc h ni trn, d nhin cc ht trong cng h phi tha mn nhng tnh cht c trng ca h .

Khi lm cng vic ny ngi ta nhn thy rng trong h 10 ht ch tm thy 9 ht tha mn nhng tnh cht cn thit ca h . Nh vy l cn thiu 1 ht na mi lp y 10 ht. Ngi ta t tn trc cho ht cn thiu l Omga tr . i vi h 3 ht l h rt c bn th li cha thy ht c bn no tha mn nhng tnh cht c trng ca h , ngha l h 3 ht l h cn trng hon ton.

u nm 1964 mt my gia tc mnh Bruckven cho cc proton nng lng ln bn vo bung bt Hydr v ngi ta chp c trn mt trm nghn bc nh. Sau khi phn tch cc bc nh ngi ta tn thy ht trong mt bc nh. l s kin cc k quan trng, n chng t gi thuyt ca Ghenman c c s v ngi ta coi l thnh tu c bn nht ca vt l ht c bn.

Tuy nhin cho ti ngy nay ton b h 3 ht vn cn l iu b n. cng nm 1964 Ghenman li a ra cch on nhn rt c o v h 3 ht ny. Theo Ghenman th trng thi b 3 ht di dng t do. Ghenman t tn cho 3 ht ny l 3 ht Quark. Tnh cht c o ca gi thuyt Ghenman l ch cc ht quark mang in tch ca mi ht khng phi l bi ca in tch nguyn t m li l mt phn s. Ghenman cho rng trong 3 ht quark ch c mt ht mang in tch l (l in tch nguyn t).

ng thi Ghenman cho rng h 3 ht ny c v tr rt c bit,khc vi cc h khc: 3 quark l 3 ht siu c bn, 3 quark v 3 phn quark s cu to thnh tt c tt c cc ht trong h khc. V d: proton c cu to t hai quark in tchv mt quark c in tch cn ntron c cu t hai quark in tch:v

Tn gi quark l do Ghenman ly t mt cun tiu thuyt ni ting ca Gioix, nh vn ni ting Ailen k v mt gic m huyn o. trong cun tiu thuyt c mt bi ht m u bng t Baquark c ngha l ba iu v vn bng cch t tn quark cho ht gi nh, Ghenman mun nhn mnh nhng tnh cht bt thng, tnh cht k d ca nhng ht .

Sau ny quark cso tn l u (up), d (down) v S (Strange) v 3 phn quark:

L thuyt quark ra i lm cho cc nh vt l rt ch bi v l thuyt c th gii thch cc tnh cht ca cc hadrn mt cch n ging ng thi cng c th gii thch mt s d kin thc nghim.

Tuy nhin l thuyt quark khng dng li gi thuyt ca Ghenman. Cui nm 1974 c hai nhm cc nh vt l thc hin cng tm ra hai ht mi. Mt nhm t tn cho ht mnh tm ra l J. Cn nhm kia t tn cho ht ca h l y. Nhng chang bao lu sau khi hai nhm cng b cc ht J, y th ngi ta nhn ra rng hai ht l mt, v sau ny ngi ta quen gi l y.

Ht l ht c nhng tnh cht ht sc t bit: Dng l thuyt ba quark: u, d, S khng th gii thch c tnh cht ca n. V vy ngi ta cho rng gii thch c bn cht ca ht , cn phi t thm mt ht quark na gi l quark C (charm).

n nm 1977 ngi ta li tm ra mt ht na mi v nng hn ht . Ht ny tm gi tn l e (ipxilon). gii thch bn cht ca ht e ngi ta li thy rng cn phi c mt thm mt ht quark mi gi l quark b (bottom). Nhng v bn ht quark trc c nhm lai thnh hai cp theo cc tnh cht ca chng, cp u, d cp S, c. V vy cc nh vt l l thuyt cho rng tnd ti quark th nm b to thnh mt cp. Ht quark th su c t tn l (top).

Chng ta ni rng ht c bn l nhng ht khng c cu trc. Nhng vi s ra i ca l thuyt quark th cac hadron khng th coi l cc ht c bn. V vy ngayf nay nhiu ngi ngh rng ch c su ht Lepton, su ht quark v mt vi ht trung gian trong qu trnh tng tc yu nh photon, ht Wmi l cc ht c bn theo ng ngha ca n. Tt c cc ht cn li m ta vn quen gi l ht c bn thc ra chng c cu to t cc Lepton, quarkHin nhin kin trn y cng l mt gi thuyt mi. Bi v ngi ta tn nhiu cng sc tm kim quark khp ni. Trong tia v tr trong nc bin sng h, trong cc mu thin thch ri xung tri t, trong cc my gia tc ht v.vNhng cho n nay vn cha tm thy quark.