cac pp ghi do

Hc phn 1.5 Cc ph-ng php ghi o bc x

Phase2Int d:\hoang's document\hieplq\cacphuong phap ghi do 1.5.doc Printed: 28/11/2005

Phn 1

Kin thc c bn

Hc phn 1.5

Cc ph-ng php ghi do bc x

tm tt kim sot cc nguy him bc xa ni lm vic v trong mi trng ni

chung th cn phi ghi v o c lng bc x ion ho c th c mt .

V chng ta khng th ghi bc x ion ho bng bt k mt gic quan no ca

chng ta nn chng ta phi xem kh nng bc x ny tng tc vi cc cht

khc nhau bng cch ghi v o n. Hc trnh ny tho lun v cc tng tc

khc nhau ny v a ra cc nguyn tc vt l chnh c s dng ghi o

bc x ion ho. N cng tho lun mt vi h thng ghi o thng s dng

ni lm vic.

Trc khi hc hc trnh ny th iu quan trng l bn phi c v hiu

nhng thng tin trong bn hc trnh trc. c bit, bn cn phi hiu r

thng tin trong hc trnh 1.4 tng tc ca bc x vi vt cht.

Mt s hiu bit v cch lm vic ca cc loi detector khc nhau cng s

gip bn trong s la chn mt detecor v phng php s dng n. V vy,

hc trnh ny cung cp cho bn cc thng tin nn cn thit hiu c hc

trnh sau, hc trnh 2.4 s dng thit b kim tra bc x. Do iu quan

trng l bn cn hiu cc thng tin trong hc trnh ny trc khi tip tc vi

kho hc ny.

C mt hot ng thc hnh gn lin vi hc trnh ny. Bn s tm cc thng

tin thch hp trong v bi tp ca bn. Nh rng hot ng thc hnh ny

phi c hon thnh trc khi bn c th nhn ton b chng ch ca kho

hc ny. Do bn nn sp xp thi gian ph hp vi ngi hng dn bn

lm cng vic thc hnh ny.



Phn b thi gian

c chng bn s cn s dng tm n mi ting hon thnh hc trnh

ny trc khi bt u cng vic thc hnh. Thi gian c chng ny ch dng

hng dn bn. ng lo nu bn cn thi gian nhiu hn hiu hc

trnh ny.

Cc ti liu

Bn s cn c cc ti liu vit ghi li nhng iu cn ghi nh v tr li

cc cu hi v thc hnh cc cng vic trong hc trnh ny.



Cc mc tiu cn hc

Khi bn hon thnh hc trnh ny bn s c th lm cc cng vic sau:

1) M t c su phng php c bn ghi o bc x.

2) Bit c trng thi nguyn tc hot ng c bn ca cc dtector cha

kh.

3) Lit k c ba loi detector cha kh chnh v m t c hot ng

ca chng.

4) Gii thch c cc thut ng phn gii thi gian, thi gian phc hi v

thi gian cht trong s lin h vi cc detector cha kh.

5) Thit lp c mt detector Geiger-Muller v o c cc c tnh hot

ng ca n.

6) Bit c trng thi nguyn tc hot ng c bn ca cc detector dn

in trng thi rn.

7) Bit c trng thi nguyn tc hot ng c bn ca cc detector

nhp nhy.

8) M t c chc nng ca mt ng nhn quang in.

9) Bit c trng thi nguyn tc hot ng c bn ca cc detector ghi

o notron.

10) Bit c trng thi cc u im v nhc im ca mi loi detector

ghi o bc x.

11) La chn c cc loi detector tiu biu ph hp nht ghi o cc

loi bc x khc nhau.

12) Lm khp c cc thnh phn ca mt h thng m in hnh vi

cc chc nng ca chng.



By gi bn hy sn sng bt u cng vic.

1. Cc c ch -c s dng ghi o bc x.

V bc x ion ho khng th nhn thy bi cc gic quan ca con ngi,

chng ta da vo s ghi o cc thay i c to ra bi bc x khi n tng

tc vi cc vt cht. Cc detector bc x hot ng bng cch ghi o mt

thay i trong mi trng hp th m n b gy ra bi s truyn nng lng

t bc x ion ho ti mi trng ny. C mt vi nh hng gy ra bi bc

x ion ho m cho php chng ta ghi o bc x v iu ny c a ra nh

sau:

S ion ho;

S nhp nhy;

Nhit pht quang;

Cc c ch ho hc;

S t nng; v

cc c ch sinh hc.

1.1 S ion ha

S ion ho c gy ra trc tip bi bc x alpha, beta v gin tip bi cc

tia-X, gamma, notron. Cc cp ion m c to ra c th c thu nhn v

s cp ion c thu nhn c th lin quan ti lng bc x gy ra s ion

ho. Nhiu thit b kim tra bc x s dng s ion ho nh mt k thut ghi

o.

1.2 S nhp nhy

S nhp nhy l qu trnh to ra nh sng sau khi cc electron chuyn ng

t cc qu o c mc nng lng cao xung cc mc nng lng thp trong

mt cht hp th. Cc electron c dch chuyn ln cc qu o c mc

nng lng cao hn bi qu trnh kch thch. (Nh li t hc trnh 1.4 s

tng tc ca bc x vi vt cht l s kch thch xy ra khi nng lng t



s bc x ion ho lm cho cc electron tm thi dch chuyn ln cc mc

nng lng cao hn). nh sng c gii phng c th b bin i thnh mt

tn hiu in. Kch thc ca mt tn hiu in ph thuc s electron dch

chuyn n cc qu o c mc nng lng cao hn v do c th gn

lin ti lng bc x gy ra s nhp nhy. S nhp nhy l k thut ghi o

rt quan trng kim tra bc x v cc detector m s dng k thut ny

c gi l cc cc detector nhp nhy.

1.3 Nhit pht quang.

Khi cc electron trong cc cht nht nh hp th nng lng th chng s

dch chuyn n cc mc nng lng cao hn hoc cc vng cm. Chng

c gi li trong cc vng ny cho n khi cc cht ny c t nng n

mt nhit nht nh. Nng lng t nng ny gii phng cc electron v

cc cht ny pht ra nh sng khi cc electron ny dch chuyn v mc ban

u ca chng. nh sng ny b bin i thnh mt tn hiu in ci m c

th gn lin ti lng bc x ti. Cc cht nhit pht quang c s dng

kim tra cc liu lng c nhn ( tc l liu i vi tng ngi) v iu ny

s c tho lun thm na trong hc trnh 2.5 php o liu c nhn.

1.4 Cc c ch ho hc

Bc x ion ho c th gy ra cc thay i ho hc. Hiu ng ny c tin

hnh trong s dng phim nh i vi php o liu c nhn, cc tia-X trong y

t v k thut chp X-quang. Trong mt vi trng hp, bc x ion ho tng

theo tc m cc phn ng ho hc xy ra v k thut ny c th c s

dng o cc liu lng cao trong sut s chiu x ca dng c y t.

1.5 S t nng

Bc x ion ho c th tng theo nhit ca mi trng hp th v o cn

thn s tng ny c th a ra mt php o liu lng bc x. K thut ny

(c gi l php o nhit lng) l khng thch hp i vi thit b o

thng thng trong bo v an ton bc x v cc liu lng cao i hi thm

ch cn phi nng nhit nh ln cao. Tuy nhin n s dng nh mt



chun s cp chun thit b (xem hc trnh 2.4 s dng cc thit b kim

tra bc x).

1.6 Cc c ch sinh hc

Cc liu cao ca bc x c th gy ra cc thay i sinh hc trong cc t bo

sng. iu ny s c tho lun thm na trong hc trnh 1.6 cc hiu ng

sinh hc ca bc x ion ho. Cc thay i sinh hc ch c s dng

nh gi liu lng trong cc tnh hung cui cng con ngi na tin

na ng s c ri ro b thu nhn mt liu lng cao.

1.7 Tm tt cc c ch ghi o.

Bng 1 tm tt cc c ch m c th c s dng ghi bc x ion ho.

Bng 1 Tm tt cc c ch c s dng cho s ghi nhn bc x

C ch S dng chnh Loi thit b Detector

S ion ho Cc thit b kim tra bc x.

1. Bung ion

2. ng m t l

3.ng m Geiger-Mller

4. Trng thi rn

1. Cha kh

2. Cha kh

3. Cha kh

4. bn dn

S nhp nhy Cc thit b kim tra bc x.

ng m nhp nhy Tinh th hoc lng

Nhit pht quang Liu c nhn Liu k nhit pht quang(TLD)

Tinh th

Ho hc Liu c nhn Phim nh Nh tng nh

S t nng Chun s cp v chun thit b

My o nhit lung Rn hoc lng

Sinh hc Cc tnh hung ri ro

M sinh hc M sinh hc



T kim tra 1

By gi xem bn hiu bi nh th no bng cch tr li cc cu hi sau

trong v bi tp ca bn.

1. Ti sao chng ta cn phi kim tra bc x ion ho?

2. Cc detector ghi o bc x hot ng nh th no?

3. a) Lit k su c ch ca s ghi o bc x.

b) C ch ghi o no trong cc c ch l quan trng i vi cc thit b

kim tra bc x?

c) C ch no trong cc c ch l quan trng nht cho s kim tra liu

c nhn?

By gi kim tra cc cu tr li ca bn vi cc cu tr li mu trong v bi

tp ca bn.

2. Cc detector da trn s ion ho.

Nh c cp, nhiu thit b kim tra bc x s dng s ion ho nh l

c ch ghi o v hai loi detector m thng c s dng nhiu nht l cc

detector cha kh v cc detector dn in trng thi rn.

2.1 Cc detector cha kh.

Cc detector cha kh bao gm mt bung cha kh (thng l khng kh) v

hai tm in th c gi l cc in cc. in cc dng c gi l

anode v thng nm trung tm ca bung o. N c cch in vi lp

v bc bn ngoi. Lp v bc bn ngoi ca bung ny thng l in cc

m hoc cathode. Hnh 1 ch ra mt s n gin ca mt detector cha

kh.



Hnh 1 Mt detector cha kh n gin

2.1.1 Cch chng lm vic

Bc x ti tng tc vi cc vch ca bung hoc cc ht kh v to thnh

cc cp ion. Khi mt in th c p gia cc in cc th cc ion dng b

ht v pha cathode tch in m v cc electron b ht v pha anode tch

in dng. Mt in tch c tch lu trn anode s gy ra mt bin i

in th trong mch. S bin i in th ny c xem nh l mt xung v

s c mt ca xung ny sinh ra mt dng chy trong mch ngoi. Bng cch

ghi o hoc l xung hoc l dng in ny th chng ta c th ghi nhn s c

mt ca bc x ion ho.

Kch thc ca xung ph thuc s electron c thu nhn bi anode v iu

ny c th ph thuc va lng bc x ion ho trong bung cng nh loi

bc x v nng lng ca n.

Gas-filled chamber



Thm vo , kch thc ca xung cng l mt hm ca in th c p

vo gia anode v cathode. Hnh 2 ch ra cch thay i kch thc xung

(hoc ln) khi in th p vo c tng ln.

Hnh 2 S thay i cao ca xung theo in th i vi mt detector cha

kh

Khi bn xem t hnh 2 th s thay i ln ca xung theo in th biu din

mt s vng c xc nh r rt. Nhng vng ny c gi l cc vng: ti

hp, bung ion, t l, Geiger- Muller v phng in lin tc.

2.1.1.1 Vng ti hp Khi in th trong bung l kh thp th lc tc dng ln cc ion (m ht

chng ti cc in cc) cng l kh thp. Trong trng hp ny, c hai qu

trnh cnh tranh i vi cc ion. Mt trong hai qu trnh ny l s tp hp ion

v hai l s ti hp ion. iu ny c ngh a l sau khi mt ion c to thnh

th n c th ti hp tr li trung ho trc khi n c th c thu nhn v

cc in cc. V vy xung ny mch ngoi ph thuc vo kt qu gia hai

qu trnh ny.

Khi in th qua cc in cc c tng ln th cc ion ti in cc nhiu

hn v kch thc ca xung tng ln (xem hnh 2). Tuy nhin, s ti hp ca

cc ion vn l ng k v vy vng ny c gi l vng ti hp. Cc



detector cha kh thng khng c hot ng trong vng ny v s ti hp

ca cc ion lm cho n rt kh o c lng bc x ti.

2.1.1.2 Vng bung ion Khi in th l ln th hu ht cc ion c pht ra u i ti in cc v

cc ion b mt do s ti hp l khng ng k. Trong vng ny gn nh tt

c cc ion s c thu nhn v kch thc ca xung khng tng na theo

in th c p vo. Thay vo , cc mc ngoi tin ti mt trng thi n

nh c gi l vng bung ion (xem hnh 2).

Dng chy trong mch ngoi cng tin ti mt gi tr cc i c gi l

dng bo ho. Dng bo ho ny t l vi lng bc x trong bung v nu

lng bc x c tng ln th dng bo ho cng c tng ln.

2.1.1.3 Vng t l. Khi th c tng nhanh trong vng bung ion th kch thc xung bt u

li tng. Chng ta c th gii thch ti sao kch thc xung tng nu chng ta

kho st nhng g ang xy ra i vi cc ion. Khi in th p vo c tng

ln th cc ion khng ch nhn thm nng lng i ti cc in cc m

cn nhn thm nng lng c gia tc nhanh hn. S gia tc ny

sinh ra nhiu cp ion hn, chng c to ra qua s ion ho th cp ca cc

ht trong cht kh. Qu trnh ny c gi l s nhn kh v dn n Cc

ion c thu nhn nhiu hn v do thu c mt xung rng hn.

Hnh 3 ch mt electrn n l s c gia tc thng n anode v s to ra

mt thc cc ion.



Hnh 3 S nhn kh trong vng t l

S tng s cc ion c thu nhn l mt hm ca in th t vo. Tuy

nhin, kch thc xung tng m c to ra cng t l vi s cc ion ban u

c to ra trong cht kh. V l do ny nn vng ny ca mt detector cha

kh iu ny xy ra c gi l vng t l.

2.1.1.4 Vng Geiger-Muller Nu in th vn c tng thm na th s nhn kh l ln n mc m mt

ht ion ho n l to ra nhiu cc thc ion dc theo chiu di ca ande,

dn n kch thc xung l rt rng. Vng iu ny xy ra c gi l

vng Geiger-Muller (GM) v trong vng ny th kch thc ca xung l nh

nhau khi khng k ti lng nng lng ban u b lng ng. Thay v l ,

kch thc xung ny c iu chnh bng mch ngoi nhiu hn so vi

bng bung cha kh v ln ca xung ch c nng ln rt nh khi in

th c tng ln (xem hnh 2).

2.1.1.5 Vng phng in lin tc Nu in th c tng ln vt xa hn so vi trng thi n nh ca vng

Geiger-Muller th in th l cao ion ho trc tip cc phn t kh v

mt tn hiu rng c pht ra ngay c khi trng bc x b dch chuyn.

Vng ny c gi l vng phng in lin tc v khi kt qu c c

th s khng ng, cc detector ghi bc x s khng c hot ng trong

vng ny.



Cc detector ghi bc x phi khng c hot ng trong vng phng

in lin tc.

T kim tra 2

by gi xem bn hiu bi nh th no bng cch tr li cc cu hi sau

trong v bi tp ca bn:

1. C ch ghi o c bn no m tt c cc detector cha kh u ph

thuc?

2. in vo ch trng mt t hay mt cm t thch hp:

Cc detector cha kh bao gm mt bung cha kh c mt ____ V

hai bn in th c gi l __________. in cc dng c gi l

_______ v in cc m c gi l __________. Bc x ti tng tc

vi cc vch ca bung ny hoc cc ht kh v to ra ____ _______.

Khi mt in th c p vo gia cc in cc _________ _____ b

ht thng n in cc tch in m, v _________ b ht thng n

in cc tch in dng. Mt in tch c to ra, gy ra s bin i

in th trong mch. S bin i ny trong in th c xem nh mt

__________, V iu ny sinh ra mt dng in trong mch ngoi.

Bng cch ghi o hoc l s thay i th hoc dng ny th chng ta

c th ghi nhn c cc bc x ion ho c mt trong bung.

3. Hon thnh bng sau bng cch in y nm vng ca mt

detector cha kh. Sau lm khp cc vng khc vi cc m t ca

chng.

!



Vng S m t

1. R____________ a) L vng m in th c p vo l ln gy ra s s gia tc ca cc ion.

2. I___ C________ b) L vng m hu ht cc ion s c thu nhn v dng in tin ti mt gi tr khng i c gi l dng bo ho.

3. P____________ c) L vng m nhiu ion khng ti cc in cc.

4. G____-M______ d) L vng m in th l ln ion ho trc tip cc phn t kh.

5. C_______ D_________ e) L vng m kch thc ca xung l nh nhau khi khng ch ti lng nng lng b gi li.

4. Vng no ca cc vng ny c s dng ghi o bc x ion ho?

by gi hy kim tra cc cu tr li ca bn vi cc cu tr li mu trong v

bi tp ca bn.

2.1.2 Phn gii thi gian, thi gian cht v thi gian phc hi.

Trc khi kho st hot ng ca cc loi detecor cha kh khc nhau th

iu quan trng l phi hiu cc khi nim: thi gian cht, thi gian phc hi

v phn gii thi gian. iu ny cn phi hiu bi v nu phn gii thi gian

ca mt detector l qu di cc tc m cao th cc xung t detector c

th c m rng ra v vy trong thi gian rt gn nhau s c nhiu thng tin

b mt. iu ny c ngha l tng cc s m khi c th b nh gi sai.

Phn gii thi gian ca mt detector c nh ngh a l lng thi gian nh

nht m phi phn bit c hai s kin chng c ghi li nh hai qu

trnh tch ri nhau. Phn gii thi gian ph thuc vo cc tham s sau:

Thi gian cht ca detector ny (tc l di thi gian i vi tn hiu

hoc xung c tch lu ln ghi nhn c n); v

Thi gian phc hi (tc l di thi gian m detector khi phc t mt

s kin ion ho v tr li trng thi ban u ca n).



Hnh 4 biu din cch t hp thi gian cht v thi gian phc hi trong mt

detector Geiger-Muller a ra phn gii thi gian.

Hnh 4 Phn gii thi gian i vi mt ng G-M

Phn gii thi gian ca detector ny ph thuc vo cc tng tc g m

chng xy ra trong detector. Tuy nhin, ton b phn gii thi gian ca mt

thit b hon chnh cng s ph thuc vo thi gian cht gn lin vi cc b

phn in t ca mt h m.

Trong thc hnh, cc thut ng thi gian cht v phn gii thi gian c s

dng hon i cho nhau. Bt c thut ng no c s dng th gi tr c

trch dn l cn phi o kh nng ca thit b phn bit hai s kin ring

bit m xy ra rt gn nhau trong cng mt khong thi gian. Cc thit b k

thut ca cc nh sn xut thng s dng thut ng thi gian cht m

t cch phi hp h thng dm ca detector ny.

2.1.3 cc loi detector cha kh

Trong phn sau chng ta s tm hiu ba loi detector cha kh c s dng

trong cc thit b kim tra bc x. Ba loi l nh sau:

Bung ionho;

ng m t l; v

Pulse Voltage

Dead Time Recovery Time

Resolving Time



ng m Geiger-Muller.

2.1.3.1 Cc bung ion ho

Cc bung ion ho (thng c gi ph bin hn l cc bung ion) c

thit k hot ng dng bo ho trong vng bung ion c biu din

trong hnh 2. Dng in trung bnh li ra c o v t l vi lng bc x ti

m bung ny c chiu x. v li ra l khng ph thuc vo in th

nn khng cn c mt ngun in th n nh cao. Tuy nhin, iu quan

trng l in th n nh bo m rng dng bo ho c duy tr.

ngn cn bung ion t s hot ng trong vng t l th in th c p

vo c gii hn thp hn so vi yu cu t ra gy ra s ion ho th

cp ca cc phn t kh. Nu mt ngun in th 25V c s dng th nng

lng c tng thm do s gia tc mt electron gia cc in cc khng

th ln hn 25 eV. Nng lng ny l khng gy ra s ion ho thm

na.

Cc dng c to trong cc bung ion l rt nh, tiu biu l c bc 10-12 A

v v vy phi c khuch i i vi cc kt qu o. Do cc thit b m

kt hp cc detector bung ion th yu cu mch trng thi rn kh phc tp

khuch i cc dng mt chiu v cng nh ny.

Thit k cc bung ion v chn la kh vo ph thuc vo ng dng ring

ca tng thit b. i vi cc thit b kim tra bc x c th mang theo th

bung ny thng cha y khng kh v c cu to t cc cht c s

nguyn t thp. Nu thit b c s dng o bc x alpha hoc beta th

bung ny phi c cc lp vch mng hoc mt ca s rt mng. Ch bng

cch loi detector ny mi c th c s dng phn bit gia cc loi

bc x bng cch t mt tm chn trn ca s mng ngn cn cc ht

alpha hoc beta t trong bung.

Mt thit b kim tra bc x beta/gamma c th mang theo cha mt

detector bung ion c ch trong hnh 5. Ch s trt tm kim loi m

c kt hp trong thit k thit b ny. Do s trt tm kim loi ny trn u

ca s ca bung ion nn bn c th phn bit gia bc x beta v gamma.



Mt trc Mt sau

Hnh 5

S kt hp mt thit b kim tra bc x beta gamma tiu biu vi mt detector bung ion

Lu rng cc bung ion cng c th c kt hp vi cc thit b khc

phn bit gia cc nng lng khc nhau ca bc x ti. Qu trnh ny c

gi l quang ph hc.

2.1.3.2 Cc ng m t l

Mt ng m t l hot ng trong vng t l c ch trong hnh 2. Do nh

hng ca s nhn kh c th tng s electron c to thnh gn 1 04. iu

ny c ngha l i vi mi electron c to ra bi mt s kin s ion ban

u th c th c thm 10 nghn electron c to ra. Do mi s kin ion

ho c th phn bit c v m c.

Li ra t mt b m t l l mt chui cc xung m c m bi mt mch

m. ni chung, thi gian phn gii thng rt ngn i vi cc b m ny

(nh hn mt micro giy) v vy cc tc xung ln c th m c. Tuy

nhin, bin ca mi xung l rt nh (c bc minivolt) v s khuych i

trc l cn phi c trc khi cc xung ny c th c m. C mt im

na hy nhn hnh 2. Bn s nhn thy rng dc ca th trong vng t

Ca s mng

Mt tr-t kim loi



l l kh dc. iu ny c ngh a l mt thay i nh ca in th c p

vo s c mt nh hng ti ln xung. Do iu quan trng l ngun

cao th n nh c s dng iu ny s m bo rng bt k s thay i

li ra no th cng gn lin vi s thay i bc x ti hn l mt thay i ca

in th c p vo.

Nh c ch ra phn trc, kch thc xung tng t l vi nng lng

c gi li bi bc x. V vy, cc ng m t l c th c s dng vi

mt mch phn bit cao ca xung phn bit gia cc loi bc x trn

c s kh nng ion ho ca chng. V d, nu thit b ny c chiu x c

hai loi bc x alpha v beta vi cng mt mc nng lng th bc x alpha

s to ra nhiu s cp ion hn vi cng di qung dng v vy ln

xung ny s rng hn. Nu s dng cc mch ngoi khc nhau th cc ng

m t l cng c th c s dng phn bit gia cc mc nng lng

khc nhau ca bc x ti (tc l thc hin quang ph hc).

Cc ng m t l dng kh thng c s dng m cc mu (xem

hnh 6). Bung m c mt ca s rt mng cho php cc bc x alpha

v beta i vo trong bung. Thut ng dng kh c s dng bi v phi c

mt dng kh lin tc trong bung thay th cho kh m b khuch tn ra

ngoi qua ca s mng. Loi kh c s dng thng l hn hp ca mt

kh tr vi mt hydrocarbon. V d, thng th kh P-10 l thng xuyn c

s dng. Kh ny cha 90% argon v 10% methane.

Hnh 6 B m t l dng kh



2.1.3.3 Cc b m Geiger-Muller (G-M)

Cc b m Geiger-Muller hot ng trong vng Geiger-Muller (G-M) c

ch ra trong hnh 2 v s dng mt cht kh nh P-10 c s dng trong

cc b m t l. ln ca xung li ra khng ph thuc nng lng ca ht

ion ho. iu ny c ngha l n khng th phn bit bng in t gia bc

x alpha v beta. M c th cng khng o hoc phn bit gia cc mc

nng lng ca bc x ti.

Trong vng Geiger-Muller th mt s phng in xy ra dc dy anode. S

phng in ny phi b dp tt ngn cn s duy tr ca bn thn n v

ngn cn s to nhiu xung. S dng mt kh thch hp nh cc kh hu

c (v d ethyl alcohol) hoc cc halogen (v d chlorine, bromine) thm vo

trong bnh kh th n s gip ch cho s dp tt ny. Cc kh hu c trn

c s dng trong sut qu trnh dp tt, do cc ng c dp tt bng

hu c c mt gii hn thi gian sng hu ch khong 109 tng s m. Cc

halogen c u im l c khng s dng trong qu trnh dp tt v vy cc

ng cha kh halogen c thi gian sng di hn v gip ch hn trong cc

trng thi tc m cao.

Cc b m Geiger-Myller c th to cc hnh dng v kch thc khc

nhau. i vi phn ln cc ng dng th b m l mt hnh tr v c gi

l ng m GM (xem hnh 7).

Hnh 7

Mt thit b kim tra bc x c mt ng Geiger-Muller

ng m GM vi ca s mng



Mt ng m G-M nh c th nhy o cc sut liu thp trong khi mt

bung ion ho vi nhy tng t s cn phi c kch thc rng hn. Nu

b m c s dng o bc x alpha v beta th n phi c mt ca s

mng ngn cn bc x vo trong ng.

Mt b m G-M thng m cc xung vi cng cch thc nh ca b m

t l. Tuy nhin, n c th c thay i o dng trung bnh khi c lm

bi bung ion ho. Mt u im ca cc b m G-M l xung li ra c

vi volt, v vy tn hiu khng cn phi khuych i trc v mch c th

c bo qun n gin. iu ny c nha l cc b m Geiger-Muller l

rt bn v do chng thng c s dng ni lm vic kim tra bc

x gamma.

Nu cc detector G-M c s dng nh cc dng c o liu hoc sut liu

th chng phi c mt s p ng tng t vi m ca c th ngi trn mt

di nng lng rng. Khi cc ng m G-M p ng nng lng thp hn

khong 200 keV th chng thng c bao bc trong vt liu lc thch hp

bo m rng nng lng p ng ny l c th tuyn tnh. iu ny

c gi l s b tr nng lng.

Mt trong nhng nhc im ca mt b m G-M la phn gii thi gian ca

chng di. Thi gian phn gii ny thng c 100 n 300 microsecond (ms)

Bng 2

Tm tt cc detector cha kh

Detector Loi bc x

Hiu sut Ch gii

Bung ion Alpha Cao (c ca s mng v n nh)

s dng m v quang ph hc.

Beta trung bnh (c ca s mng v n nh)

S dng trong cc thit b kim tra bc x c th mang theo.

Gamma



ng m t l Alpha Cao (vi ca s mng v n nh)

s dng m v o ph.

Beta trung bnh (vi ca s mng v n nh)

S dng cho qu trnh m tt c cc mc nng lng.

C th s dng i vi quang ph hc vi nng lng



2.1.4 Tm tt cc detector cha kh.

Nhiu thit b kim tra bc x c th mang theo s dng cc detector cha kh. Bng 2 tm tt cc thuc tnh v c trng ca chng. Nh rng iu quan trng phi kho st dy ca ca s m bc x i qua vo trong detector nu bn ang hy vng ghi bc x alpha hoc beta.

Hot ng thc hnh

Hot ng c trng ca mt detector Geiger-Muller.

y l mt cng vic thc hnh m bn s hc cch thit lp mt ng G -

M n s hot ng ng v a ra cc kt qu thch hp. Cc chi tit ca

cng vic c tm trong v bi tp ca bn. Lin h vi ngi hng dn

bn sp xp thi gian thch hp hon thnh hot ng thc hnh ny.

T kim tra 3



1. a) Hy lm khp cc thut ng sau vi cc m t chng.

Thut ng S miu t

1. Phn gii thi gian a) L lng thi gian nh nht m phi phn bit hai s kin ring bit chng c ghi li nh hai qu trnh ring.

2. Thi gian cht b) di thi gian detector thu c t mt s kin ion ho v tr v trng thi ban u ca n.

3. Thi gian phc hi c) di thi gian m tn hiu hoc xung c tch lu ln n c ghi nhn.

b) Ti sao phn gii thi gian ca mt detector cha kh li l vn

quan trng cn c kho st?

2. Hai loi no ca cc detector cha kh cn phi c s khuch i

dng?



3. a) Loi detector cha kh no cn phi c mt ngun in cao th n

nh?

b) Ti sao loi ny li cn nh vy?

4. Loi detector cha kh no c th c s dung vi mt mch phn bit

ln xung phn bit gia cc loi bc x ion ho?

5. Cc loi no ca cc detector cn phi c ca s mng phn bit

gia cc loi bc x khc nhau?

6. a) Loi detector no thng c s dng ghi o bc x gamma

ni lm vic?

b) Ti sao loi ny li nh vy?

7. a) Gii thch thut ng chng chp xung gn lin vi cc b m

Geiger-Muller.

b) Ti sao kh nng xy ra chng chp xung l iu quan trng cn

kho st ?

By gi kim tra cc cu tr li ca bn vi cc cu tr li mu trong v bi

tp ca bn.

2.2 Cc detector dn in trng thi rn.

Tnh dn in m ch kh nng ca mt cht i vi vic dn mt dng in

v cc cht m c dn tt (v d cc kim loi) th chng c gi l cc

cht dn in. Cc cht m c tnh dn in km ( v du g) th chng c

gi l cc cht cch in. Mt cht bn dn l mt cht c cc thuc tnh

trong khong gia hai cht trn, v mc d c mt s vt cht c thuc tinh

bn dn th cc cht ny hu ht thng c s dng bo v an ton

bc x chng l cc tinh th rn ca silicon and germanium.

Cc detector dn in trng thi rn ng nh tn ch ra bi v chng

cha cc cht rn tinh th bn dn. Khi bc x ion ho tng tc vi cc

cht rn ny th ton b tnh dn in ca cht c tng ln. Nu s tng

ny l sau c o th n c th lin quan ti lng bc x ti.



2.2.1 Cch chng lm vic

hiu cch lm vic ca cc detector dn in trng thi rn chng ta cn

phi kho st s tng tc ca bc x ion ho vi cc cht bn dn trn mt

qui m rt nh. Khi bn c th nh li phn 1.1 cu trc ca vt cht, cc

electron ch c th tn ti trong cc mc nng lng xc nh. Trong cc

cht rn, cc mc nng lng ny c kho st nh cc vng nng

lng. Cc vng nng lng ny c phn bit bi cc vng c gi l

cc vng cm, v vng nng lng cao nht m cc electron thng tn ti

c gi l vng ho tr.

Bc x ion ho c th truyn nng lng cho mt electron trong mt cht

rn tinh th bn dn chuyn n t mc nng lng thng thng ca n

(trong vng ho tr) qua cc mc cm thng thng (trong vng cm) v ln

mt trng thi nng lng cao hn (c gi l vng dn). Khi n ri khi

vng ho tr th n s sinh ra khong trng (hoc l trng) trong vng ho tr

(xem hnh 8).

Hnh 8

S to thnh mt cp Electron-l trng do s bc x ion ho

S a mt electron ln vng dn c gi l s ion ho v kt qu l mt

cp electron- l trng c to thnh, cp kt qu ny c th c so snh

vi cp ion trong mt detector cha kh. Ging nh cch cc ion m v

dng dch chuyn gia cc in cc trong mt detector cha kh, cp ion

ny s dch chuyn trong mt detector trng thi rn khi p vo gia hai in

Vng ho tr

Vng dn

Vng cm

Bc x ti

= in T

=L trng



cc mt in th. S dch chuyn dch ny dn n mt xung trong mch

ngoi c th c o.

Lu rng trong thc t, cht c tch in dng khng th dch chuyn

trong mt tinh th rn. Cc s vic thc t g cc l trng c lp y bi

cc electron ln cn m chng dch chuyn qua v to ra mt l trng khc

sau . Trong cch thc ny th xut hin s dch chun cc l trng.

Cc detector dn in trng thi rn bao gm cc cht bn dn m dn

in ca chng c tng ln. Ni chung, dn in c nng ln bng

cch a thm cc tp cht tr thnh cht bn dn. Qu trnh ny c

gi l s kch thch v cc tp cht c a vo cung cp thm hoc l

cc electron hoc l cc l trng. Nu tp cht cung cp thm cc electron

ti vng ho tr (v d trong trng hp kch thch thm asen hoc

phosphorus) th cc electron lin kt lng lo c th dch chuyn ln vng

dn ch vi mt lng nh nng lng s b gi li trong vt cht. Trong cch

thc ny, c ch dn in ch yu l s dch chuyn ca cc in tch m v

vt cht c gi l cht bn dn loi n. Nu tp cht cung cp thm l

trng ti vng ho tr (v d trong trng hp kch thch thm boron hoc

gallium), th c ch dn in ch yu l s dch chuyn cc l trng tch in

dng v vt cht c gi l cht bn dn loi p.

Cc detector bn dn trng thi rn thc t bao gm c vt liu loi p v n

lin kt vi nhau. Mt in th c p vo lp tip gip ca hai loi bn dn

cc l trng v cc electron dch chuyn khi lp tip gip. Vng xung

quanh lp tip gip l cc l trng v electron t do v n c gi l lp

ngho. Lp ngho ny l mt phn ca vt cht m n s ghi o bt k mt

bc x ti no (xem hnh 9).



Hnh 9 Cu trc c bn ca mt detector dn in trng thi rn

Khi bc x ion ho i qua vng ngho th n to thnh cc cp electron-l

trng. cc cp electron-l trng ny dch chuyn v mt pha to ra mt xung

trong mch ngoi. Sau xung ny c th o c. Bng cch ny th lp

ngho to thnh th tch nhy ca detector trng thi rn v n tng

ng vi mt bung trong mt detector cha kh.

2.2.2 Cc loi detector

C rt nhiu loi khc nhau ca cc detector dn in trng thi rn c th

s dng ghi o bc x ion ho. Cc loi ca cc detetor dn in trng

thi rn c kho st trong hc trnh ny l:

Cc diode tip gip khuych tn;

Cc detector hng ro mt;

Detector cy ghp ion;

Detector c cha lithium; v

Detector germanium siu tinh khit;

+ + + +

- - - -

in t L trng

V

Vng ngho

Loaij p type

Loi-n type

- +



2.2.2.1 Cc diode tip gip khuych tn.

Trong cc diode tip gip khuych tn tp cht loi p c cho php

khuych tn hoc truyn lan vo trong cht loi n. iu ny to ra mt vng

ngho ngay di b mt tinh th (ph bin thng khong 1mm di b mt

tinh th) nh c ch trong hnh 10. Lp b mt tng ng mt lp cht

hoc ca s m bc x phi i qua trc khi vo trong th tch nhy.

Hnh 10 Cu trc c bn ca mt diode tip gip khuch tn

Ca s ny c th l mt nhc im trong quang ph hc ht tch in bi

v mt vi ht c nng lng thp hn khng th ghi nhn c. trnh

nhc im ny th cc diode tip gip khuych tn phi c thay th trong

nhiu ng dng quang ph hc ca cc ht tch in bng cc detector hng

ro mt (xem phn 2 2.2.2). Tuy nhin, cc diode tip gip khuych tn

(c lm hoc l silicon hoc l germanium) vn c s dng ghi nhn

ht tch in v chng bn hn so vi cc detector hng ro mt.

Mt cng vic thc hnh khc s dng cc diode tip gip khuych tn

silicon c khm ph gn y. Cc diode ny (thng c xem nh

cc photodiode PIN silicon) c th c kt hp trong cc liu k in t

(xem hnh 11) o lng bc x gamma c thu nhn bi

mt ngi trn mt khong thi gian (tc l o liu lng gamma c

nhn ).

n-type material

depletion layer

1 mm p type material

Incident radiation

+ V -

window



Hnh 11

S kt hp mt liu k in t vi mt potodiode PIN silicon Lu rng cc liu k in t cng c ch to cng vi cc detector G -M.

u im chnh ca vic s dng mt detector trng thi rn l trng lng

ca thit b nh hn.

2.2.2.2 Cc detector hng ro mt

Cc detector hng ro mt c mt lp vt liu loi p rt mng c kt ta

trn vt cht loi n (xem hnh 12). Hn na bc x ti cn phi i qua lp

ny d ti th tch nhy nhng do b dy lp ny ca detector hng ro mt

th cc ht tch in c th d dng c ghi nhn.

Hnh 12 Cu trc c bn ca mt detector hng ro mt

n type layer

Depletion layer Very thin p type layer

Incident radiation

- V +



Cng nh kh nng ghi o cc ht tch in th cc detector hng ro mt

cng c kh nng phn bit tt cc nng lng khc nhau ca bc x ti

(tc l chng c phn gii nng lng rt tt). V d, cc detector hng ro

mt c th phn bit ba ht alpha gn nhau t Am-241 vi cc nng lng

5.486, 5.443 v 5.389 MeV.

Mt trong nhng vn chnh ca cc detector hng ro mt l b mt

tinh th phi gi sch v khng b nhim du hoc cc vt liu khc. Chng

cng rt nhy vi nh sng bi v nh sng cc proton c th i n th tch

nhy v to ra cc cp electron-l trng.

2.2.2.3 Cc detector cy ghp ion.

Mt phng php khc ca s a vo cc tp cht b mt ca mt cht

bn dn l chiu x ln b mt ny mt chm cc ion c to ra bng

mt my gia tc. V d, mt tinh th silicon c chiu x n cc ion boron

th s c mt lp vt cht loi p c to ra gn b mt ca thit b. Phng

php kch thch ny gi l s cy ghp ion v n sinh ra mt tinh th bn

vng hn rt nhiu v n gn nh t b nh hng bi cc iu kin mi

trng. Trong thc t, cc detector loi ny l rt bn v chng c th c

ch to cng vi cc ca s mng ghi o alpha v beta.

Cc detector cy ghp ion c rt nhiu ng dng bao gm phn tch ph

alpha, ghi o beta nng lng thp v cc ion nng.

2.2.2.4 Cc detector ko theo lithium

cc detector hng ro mt v cy ghp ion rt tt cho vic phn tch ph ca

cc ht tch in nhng do cc tp cht vn gn lin vi cc tinh th bn dn

nn chng khng c mt th tch nhy ln phn tch ph photon (tc l

tia gamma v tia-X). chng li cc nh hng do cc tp cht ny gy ra

th cc cht bn dn c th thm lithium to ra mt th tch nhy ln hn.

Vng gia cc vt cht loi p v loi n th c gi l vng ko theo lithium

hoc vng thc v kch thc ca vng thc ny xc nh th tch nhy ca

detector (xem hnh 13).



Lu rng, mc d thm lithium cho mt cht bn dn c kho st

cung cp mt th tch nhy ln hn nhiu nhng trong cc iu kin thc t

th kch thc ca ton b detector thc t l rt nh. iu ny c ngh a l

mt u im ca detector dn in trng thi rn l cc kch thc ca

detector c th nh hn rt nhiu so vi cc detector cha kh.

Hnh 13 Cu trc c bn ca mt detector ko theo lithium

Khi lithium c thm vo mt tinh th germanium th detector ny c gi

l mt detector germanium c cha lithium (hoc detector Ge(Li) ).

nhit phng cc nguyn t lithium s tip tc dch chuyn qua s bin i

t nhin tinh th germanium ca vng ring, v vy iu quan trng l mt

detector Ge(Li) lun lun c duy tr nhit rt thp (s dng nit lng),

thm ch c khi khng s dng. Cc detector germanium c cha lithium l

cc detector c kh nng ghi o bc x gamma v c phn gii nng lng

rt tt.

Cc detector silicon c cha lithium (hoc Si(Li), nh l s m ch tn

ca chng th chng bao gm mt tinh th silicon cha lithium. Cc detector

Si(Li) ny l rt ging cc detector Ge(Li) nhng c mt u im l chng

c th c bo qun nhit phng m khng gy h hng cho tinh th.

Chng c th hot ng c nhit phng nhng hiu sut ca chng

s c ci thin hn nu chng c lm lnh bng nitrogen lng trc khi

s dng. Silicon c s ngun t rt thp so vi germanium v vy n t kh

p type region

n type

Intrinsic region

+ V -

n type region



nng tng tc vi cc bc x gamma. Do cc detector silicon c cha

lithium khng c kh nng ghi o bc x gamma nh cc detector Ge(Li).

Tuy nhin, chng to ra cc detector tt cho rt nhiu tia gamma nng lng

thp (nh hn khong 150 keV), cc tia-X v cc ht beta.

2.2.2.5 Cc detector germanium siu tinh khit.

Gecmanium tinh khit c hiu sut ghi cao i vi s ghi o ca bc x

gamma. V vy nu cc tp cht trong mt tinh th germanium c duy tr

thp th c th thu c cc vng ngho (cc th tch nhy) m chng c th

so snh c vi cc vng ngho ca mt detector Ge(Li). Detector loi ny

c gi l detector germanium siu tinh khit (hoc HPGe ) (xem hnh

14).

Hnh 14 S sp t mt detector gecmanium siu tinh khit (HPGe)

Nh detector Ge(Li) th detector HPGe hot ng y nh mt detector gamma

hiu sut cao cng vi phn gii nng nng lng tt. Tng t, c hai

detector u yu cu lm mt bng nit lng c hiu sut hot ng cao

nhng mt u im ca ca detector HPGe l c th bo qun c nhit

phng khi khng s dng.

Liquid Nitrogen Dewar

HPGe detector



2.2.3 Tm tt cc detector dn in trng thi rn.

Bng 2 tm tt cc thuc tnh ca cc detector dn in trng thi rn khc

nhau.

Bng 2

Tm tt cc detector dn in trng thi rn

Detector S dng chnh

Cc u im Cc nhc im

Diode tip gip khuych tn

Ghi o ht tch in

Bn hn so vi hng ro mt

Khng ghi o cc ht nng lng thp

Silicon PIN Photodiode

Ghi o photon trng lng nh

Hng ro mt Phn tch ph alpha v beta

C kh nng ghi o cc ht tch in

Phn gii nng lng rt tt

B mt phi c gi sch

Rt nhy vi nh sng

Cy ghp ion Phn tch ph alpha v kim tra beta nng

lng thp

t kh nng b nh hng bi cc diu kin mi trng

Rt bn

Ge(Li) Phn tch ph gamma

C kh nng ghi o bc x gamma

Phn gii nng lng rt tt.

Phi gi nhit nit lng mi thi gian.

Si(Li) Phn tch ph beta, gamma

v tia-X

s dng tt cho cc tia gamma nng lng thp (< 150 keV), tia-X v cc ht beta

C th hot ng nhit phng

t kh nng tng tc vi bc x gamma hn cc detector Ge(Li).

nn c lm lnh vi nit lng trong sut qu trnh hot ng.

(HPGe) Phn tch ph gamma

C kh nng ghi o cc bc x gamma.

Phn gii nng lng tt.

C th bo qun nhit phng khi khng s dng.

nn c lm lnh vi nit lng trong sut qu trnh hot ng.



2.3 So snh gia cc detector trng thi rn so vi cc detector cha kh.

Cc detector trng thi rn c mt s u im hn cc detector cha kh v

cc iu ny l nh sau:

Cc detector dn in trng thi rn l nh hn rt nhiu.

Chng c phn gii nng lng tt hn i vi tt c cc loi bc x.

Chng c hiu sut ghi cao hn i vi bc x gamma.

Th tch nhy ca detector ny c th c la chn thch hp vi tng

ng dng c th.

Cc nhc im chnh ca cc detector trng thi rn.

Chng c th cn c lm lnh n nhit nit lng khi hot ng.

Kh nng di chuyn ca chng km hn so vi cc detector cha kh.

T kim tra 4



1. in vo cc trng bng mt t thch hp:

a) Mt cht m c dn in km c gi l mt ____________.

b) Mt cht m c dn in bnh thng gi l mt ____________.

c) Mt cht m c dn in tt gi l mt ____________.

2. Tn ca hai cht bn dn thng c s dng trong cc detector dn

in trng thi rn.

3. a) S kchthch l g?

b) Ti sao cc cht bn dn phi b kch thch?

4. Cch thc g ca cc detector bn dn ging nh cc detector cha

kh?

5. Gii thch thut ng phn gii nng lng.



6. Loi no ca detector dn in trng thi rn s ghi o tt nht i vi

cc loi bc x sau?

a) Cc ht alpha.

b) Cc ht beta.

c) Gamma nng lng thp v cc tia-X.

d) Cc tia gamma nng lng cao v trung bnh.

7. Cc u im g ca detector dn in trng thi rn l hn so vi cc

detector cha kh?

By gi hy kim tra cc cu tr li vi cc cu tr li mu trong v bi tp

ca bn.

3. Cc detector da vo s nhp nhy.

3.1 Cch chng lm vic

Cc detector nhp nhy da trn mt vi cht thc t (c gi l cc

phosphor) chng s pht nh sng nhn thy khi cc electron thay i mc

nng lng. Nu bn nh hc trnh 1.4 s tng tc ca bc x vi vt

cht th bc x ion ho c th truyn cho cc electron nng lng dch

chuyn ln mt lp v c mc nng lng cao hn. Trong mt cht

phosphor th cc electron ny khng duy tr mc nng lng cao trong mt

khong thi gian di. Thay v th, chng tr li mc ban u ca chng v

khi chng lm nh vy th chng pht x cc photon di dng nh sng

nhn thy (xem hnh 15)



Hnh 15 Qu trnh to s nhp nhy

Do s nh sng ca cc photon c pht x v cng ca nh sng

ny t l vi nng lng ca bc x ti. V vy, cc detector nhp nhy c

th c s dng khng ch ghi o bc x m cn phn bit cc mc

nng lng ngoi (tc l chng c th c s dng cho cc mc ch o

ph ).

3.2 Cc kiu ca detector nhp nhy.

Cc cht phosphor m c th c s dng trong cc detector bc x phi

c cc thuc tnh nht nh, nh cc iu sau:

Chng phi bin i mt phn ln nng lng hp th thnh nng

lng nh sng.

Thi gian gia s kch thch ca electron v s pht x nh sng

photon phi ngn.

Chng phi cho php cc photon nh sng c to ra i qua lp vt

cht.

nh sng c pht ra cn phi c bin i d dng v hiu sut to

nn mt tn hiu in.

Mt s a dng ca cc cht ph hp cc tiu chun ny v iu ny lm

thnh nn tng ca cc detector nhp nhy. Cc loi detector nhp nhy

c tho lun trong hc trnh ny l cc loi sau:

Cc detector sulphide km;

Cc detector natri iodide;

Lower energy shell

Higher energy shell

Incident radiation

Electron goes up to higher energy level

Electron returns to lower energy level with visible light released



Cc cht nhp nhy hu c do; v

Cc cht nhp nhy hu c lng.

Mt vi cht phosphor ny c th c cc lng nh tp cht (c gi l cc

cht hot ho) chng c thm vo kim sot cch m cc electron

dch chuyn v cc mc nng lng thp hn. iu ny bo m rng cc

photon ny c pht x s l cc photon nh sng nhn thy.

3.2.1 Cc detector sulphide km.

Cc detector sulphide km(ZnS) thng c cc nguyn t bc c thm

vo nh l cc cht hot ho. Cc detector loi ny c gi l cc

detector ZnS(Ag), chng c kh nng ghi o bc x ion ho. Tuy nhin,

v vt cht loi ny khng cho php cc photon nh sng nhn thy i qua n

mt cch d dng nn n ch c th c s dng cc lp mng (xem hnh

16). Mc d iu ny c ngha l cc detector ny gip ch cho s ghi o cc

ht alpha v cc ion nng nhng nhc im chnh l lp mng ny c th

d dng b m thng bi cc vt nhn.

Hnh 16 Mt detector sulphide km

Thin film Zinc Sulphide detector



3.2.2 Cc detector Natri iodide.

Cc detector natri iode cng vi s cng thm cc nguyn t thallium NaI(Tl)

th chng c rt nhiu kh nng ghi o bc x gamma, thm ch cn nhiu

hn so vi cc detector dn in trng thi rn. Tuy nhin, tinh th ny s

hp th hi m t khng kh v lm h hng rt nhanh. Do n c t

trong mt bnh kn khng kh. Bnh ny thng c lm bng nhm (xem

hnh 17) v c th c mt ca s rt mng.

Hnh 17 Mt detector natri iodide xch tay c s dng o tia gamma

Cc tinh th NaI(Tl) c th to cc b dy khc nhau. Mt tinh th mng c

dy 3mm th c rt nhiu kh nng ghi o bc x gamma vi nng lng

ln ti khong 150 keV. Mt tinh th dy hn l cn cho s duy tr kh nng

ghi o cao hn i vi cc gamma nng lng cao hn. Mt detector Na I(Tl)

s dng d hn trong cng vic mi trng so vi mt detector dn in

trng thi rn bi v n khng cn phi lm lnh. N cng c nhiu kh nng

o tt hn, c bit cc mc nng lng cao hn. Tuy nhin, phn gii

nng lng ca n l km khi c so snh vi mt detector trng thi rn.

Hnh 18 ch mt detector natri it tiu biu gn lin vi mt mch o ph

gamma.

Sodium iodide detector



Hnh 18 Mt detector natri iodide tiu biu o ph gamma

3.2.3 Cc cht nhp nhy hu c do

Cc cht nhp nhy hu c do th r v c th c ch to trong mt s

a dng ca cc hnh dng v kch thc khc nhau. Chng thng c s

dng trong s lin kt vi cc detector ZnS(Ag) kim tra bc x alpha v

beta.

3.2.4 Cc cht nhp nhy hu c lng

Cc cht nhp nhy hu c lng c s dng ring kim tra bc x

alpha v beta, c bit l bc x beta nng lng thp nh carbon -14 v

tritium. s dng mt cht nhp nhy lng cho php cht nhim bn m mnh

quan tm c trn trc tip vi cht nhp nhy v c th dn n hiu sut

ghi rt cao.

3.3 Tm tt ca cc detector nhp nhy.

Bng 3 tm tt cc thuc tnh ca cc detector nhp nhy khc nhau.

Bng 3

Tm tt ca cc detector nhp nhy

Detector S dng chnh Cc u im Cc nhc im

Sunphide km Ghi o ht alpha v cc ion nng

C kh nng ghi cc ht alpha v cc ion nng

Ca s mng c th d dng b m thng bi cc vt nhn.

Natri iodide Ghi o v phn Nhiu kh nng ghi Phn gii nng

Sodium Iodide detector



tch ph gamma o gamma hn so vi cc detector dn in trng thi rn.

Khng cn lm mt

lng km hn so vi cc detector dn in trng thi rn.

Hu c do Kim tra bc x alpha v beta

R

C th to ra kch thc v hnh dng khc nhau.

Hu c lng Kim tra bc x alpha v beta

nng lng thp

Hiu sut ghi o cao khi gy nhim bn l hn cht nhim bn c trn vi cht nhp nhy.

3.4 Cc ng nhn quang in

Cc ng nhn quang in (hoc PM) l cn thit trong cc mch nhp

nhy bin i cc photon nh sng t cht nhp nhy sng thnh cc

xung in. Mc d, ni ng ra th cc ng PM thc s l nt phn ca h

thng in l ng hn so vi c ch ghi o nhng chng c bao gm c

trong phn ny bi v chng s dng ring vi cc detector nhp nhy v ni

chung khng nm trong cc mch m.

3.4.1 Cch lm vic ca chng.

Trc tin, bc x ti tng tc vi phosphor to mt nh sng photon.

Sau nh sng photon ny p vo b mt c ph bng mt cht nhp

nhy sng c gi l mt photocathode. Nng lng t nh sng photon

ny b hp th bi mt electron trong cht nhp nhy sng v electron ny

nhn thm nng lng di khi photocathode. Electron c pht ra

to thnh di dng c bn ca tn hiu in nhng trong cc iu kin thc

hnh th tn hiu ny phi c khuych i bng mt dy cc dynode. Mi

dynode v c bn l mt anode m gii phng khong bn electron i vi

rt nhiu electron c n thu nhn.



Hnh 19 S sp xp mt detetor nhp nhy kt hp vi mt ng nhn quang

in H thng dynode cn phi c mt ngun in cao th rt n nh n hot

ng kin nh. Hnh 19 ch ra cch nng lng c truyn t s kin nhp

nhy ban u ti mch in ngoi.

T kim tra 5



1. in vo trng mt t hay mt cm t thch hp.

Cc detector nhp nhy thc t da trn mt vi cht (c gi l

_______) m chng s pht ra nh sng nhn thy khi cc electron

thay i_______ _____. Khi bc x ion ho tng tc vi cc electron

trong vt cht loi ny th chng c truyn nng lng dch

chuyn n mt _______ v nng lng. Cc electron ny khng duy

tr y lu. Thay v th, chng quay tr li mc ban u ca chng,

khi chng lm nh vy th chng pht x_______ ______.

2. Cc detector nhp nhy c th c s dng cho cc mc ch o ph

c khng? Gii thch cu tr li ca bn.

3. Loi no ca cht nhp nhy bn s s dng ghi o cc ht alpha

v cc ion nng?



4. Loi no ca cht nhp nhy s c s dng ghi o bc x alpha tt

nht?

5. Loi no ca cht nhp nhy s c s dng ghi o tritium tt

nht?

6. a) a ra hai u im ca vic s dng detector Natri iodide so vi

mt detector germanium.

b) Nhc im ch yu ca cc detector Natri iodide l g?

7. Ti sao cc ng nhn quang in cn cho cc h thng ghi o nhp

nhy?

by gi hy kim tra cc cu tr li ca bn vi cc cu tr li mu trong v

bi tp ca bn.

4. Cc u d ntron

4.1 Cch chng lm vic.

Cc notron l cc ht khng tch in v v vy khng gy ra s ion ho trc

tip. Tuy nhin, khi chng tng tc vi vt cht chng to ra cc ht ion

ho th cp v s ghi o ca cc ht ny cho php chng ta ghi nhn cc

notron.

Phn ln cc tng tc thng c s dng trong cc detector notron l:

Tng tc vi boron-10, m to ra bc x alpha;

Tng tc vi helium-3, m to ra mt photon.

S tn x n hi bi ht nhn hydrogen.

Hai tng tc u tin l hu nh c kh nng xy ra vi cc notron c nng

lng ti 0,5eV. Cc notron ny cui ca di notron trung gian v trong di

notron nhit (0,025eV). S tn x n hi c th c s dng nhn biit

cc notron nhanh.



4.2 Cc loi detector notron

C mt vi tham s cn c tnh ton khi thit k mt detector notron thch

hp.

Cht lm chm phi c s dng lm chm cc notron nhanh (m

khng hp th chng) chng s tng tc vi vt cht ca detector.

Vt cht detector ny phi c mt tit din tip xc ln (tc l mt xc

sut cao) xut hin phn ng c trng v vy cc detector c th

c xy dng l khng qu rng.

Cc ht tch in nng to thnh trong sut s tng tc vi vt liu ghi

o phi b dng li ht trong th tch lm vic ca detector.

Bn loi detector notron m thch hp vi tiu chun ny l nh sau:

Cc b m t l boron trifluoride

Cc b m t l helium

Cc b m t l kh git li

Cc detector bt

4.2.1 Cc b m boron trifluoride

Cc b m t l boron trifluoride bao gm mt b m t l cha kh

c bm y kh c boron-10 c lm giu thnh kh boron triflouride

(BF3). Kh ny cung cp ton b kh cho detector cng nh bia i vi cc

notron nhit ti. Phn ng ht nhn m xy ra trong detector c ch ra bi

phng trnh 1:

10B + n 7Li + 1

Phn ng ny thng c vit nh sau 10B(n, )7Li.

Ht nhn lithium v cc ht alpha c hai u c nng lng gy ra s

ion ho th cp trong cht kh, v cc s kin ion ho th cp ny c th

c ghi nhn. Lu rng, mt vi tng tc notron to ra mt tia gamma

nng lng 0,48 MeV. Do , mt mch phn bit thch hp l cn thit

phn bit gia cc notron ti v cc tia gamma to thnh.



Cc b m t l boron trifluoride cng c th c s dng ghi o cc

notron trung gian v nhanh (ln ti 10 MeV). Tuy nhin,trong trng hp ny

th detector phi c bao xung quanh bng mt cht lm chm nh

polyethelen lm chm cc notron trc khi b bt (xem hnh 20). Cc tm

lc cadmium c s dng cung cp mt nng lng hng ng ging

nhau.

Hnh 20

Mt b m trifluoride boron

Cng nh vic ghi nhn tt i vi notron nhit, trung gian v notron nhanh

th cc b m t l boron trlouride c th c s dng cho cc mc ch

o ph notron.

4.2.2 Cc b m t l helium

Cc b m t l helium c nhiu chi tit tng t nh cc b m t l

boron trluoride. C ch ghi o ch yu i hi phi bt gi notron nhit,

nhng nu mt cht lm chm c s dng th cc b m t l hilium c

th c s dng ghi o cc notron trung gian v nhanh.

Nh tn gi th cc b m t l hilium s dng helium cho c bia v

trong bnh kh. Phn ng quan trng ny ch ra trong phng trnh 2:

Cadmium loaded polyethylene

sphere

Proportional counter filled with Boron-10 enriched BF3 gas



3He + n 3H + p [2]

Phng trnh ny thng vit nh sau 3He(n,p)3H.

Trong phn ng ny th mt nhn tritium v proton c to thnh v cc ht

tch in ny to ra t s ion ho th cp.

Mt khc, cc b m t l helium c th c s dng cho cc mc ch o

ph notron.

4.2.3 B m t l kh git li.

Cc b m t l kh git li s dng s tn x n hi vi ht nhn

hydrogen nh mt k thut ghi o chng.Trong cc b m ny th cc

notron vi nng lng ln hn khong 500 keV c ghi o s dng mt b

t l cha mt kh giu hydrogen nh methan. Mt notron nhanh s va chm

vi mt ht nhn hydrogen (m l mt proton n l) truyn cho n nng

lng. Sau ht nhn ny s tip tc qu trnh ion ho th cp.

Trong mt vi b m kh git li cc nguyn t hydrogen c th c cung

cp bng cch s dng vt liu nh polyethylene trong cc bc vch ca b

m. B m c bao quanh trong mt mng mng cadmium m dng hp

th notron nhit.

4.2.4 Cc detector bt

Cc detector bt cha cc git cht lng cc nh l lng trong mt gel ging

nh vt cht. Cc notron ti truyn nng lng cho cc git cht lng ny

lm cho chng si ngay lp tc v bin i thnh mt bt. Nhng bt ny c

th nh thy bng mt v c th dm c (xem hnh 21).



Hnh 21 Cc detector bt trc (tri) v sau (phi) chiu x notron

Thc t liu lng notron t l vi t trng ca cc bt, v iu ny c gi

c nh trong vt cht n khi liu k c xc lp li.

Cc my o liu bt ch yu c s dng i vi php o liu c nhn. Tuy

nhin, chng cng c th c s dng kim tra mi trng.

4.3 Tm tt cc detector notron.

Bng 4 tm tt cc thuc tnh ca cc detector noron khc nhau.

Bng 4

Tm tt cc detector notron

Detector S dng chnh Ch gii

B m t l boron trluoride

Ghi o cc notron nhit

C th c s dng ghi o cc notron c nng lng ti 10 MeV vi cht lm chmthch hp.

o ph notron

Cc tia gamma c th c to ra v mt mch phn bit l cn thit.

B m t l helium Ghi o cc notron nhit

C th c s dng ghi o

Cc tia gamma c th c to ra v mt mch phn bit l cn



cc notron c nng lng ti 10 MeV vi cht lm chm thch hp.

o ph notron

thit.

B m t l kh git li

Gho o cc notron nhanh

(< 500 keV)

Detector bt o liu c nhn

Kim tra mi trng

T kim tra 6



1. Ti sao khng th ghi o c cc notron bng cch s dng cc

detector hc cc phn trc?

2. a) S thay i g l cn thit i vi cc b m t l cho php

chng ghi o cc notron?

b) Ti sao mt vt liu nh polyethylene thng c s dng bao

xung quanh ng detector?

3. Loi no ca cc notron m hu nh phi tng tc vi boron hoc

helium?

4. Loi no ca cc notron m hu nh b cc va chm n hi vi ht

nhn hydrogen?

5. Loi detector notron no c th c s dng i vi php o liu c

nhn?

By gi hy kim tra cc cu tr li ca bn vi cc cu tr li mu trong v bi tp ca bn.

5. Cc thnh phn in t

Cho n y ca hc trnh ny chng ta kho st cc loi detector khc

nhau. Mt khi nng lng bc x ion ho bin i thnh tn hiu in th cc



thnh phn in phi c b xung thm thnh h ghi o cung cp mt

kt qu c c ngha.

Cc tn hiu in c to ra bi cc detector c hai loi l dng mt chiu

(nh trong bung ion) v xung. Nu tn hiu c o l mt dng mt chiu

th dng trung bnh qua nhiu s tng tc c ghi li v mch ny c

ni rng n ang hot ng ch dng. Nu tn hiu c o do mt s

thay i hoc s gim in th th cc tng tc ring c ghi li v kch

thc ca xung ph thuc vo s cc electron c thu nhn. iu ny c

gi l ch xung.

Dng mt chiu li ra c o bi mt my khuych i dng mt chiu

trong khi xung li ra c o bng mt mch m. Hnh 22 ch ra cc thnh

phn ca mt mch m ni chung.

Hnh 22 Mt mch m ni chung

Trong phn ny chng ta s tm hiu vn tt cc chc nng ca mt my

khuych i dng mt chiu v cc thnh phn cu to khc ca mt mch

m. Nh rng trong mt trng thit b tt c cc thnh phn thng gn

High Voltage Supply

Detector

Scaler

Pre-amp Amplifier Discriminator Rate meter

MCA



lin vi thit b, m c th gii hn kh nng ca thit b. Mt thit b thc

nghim c th c nhiu thnh phn lin kt vi nhau.

5.1 Ngun in

Mt ngun in th mt chiu n nh l cn thit cung cp th nng hot

ng cho detector. Trng cc thit b ph thuc vo cc b c qui cung

cp in th. Mc ca cao th v mc n nh yu cu ph thuc vo loi

detector. Ngun in thng c gi l ngun HV (cao th).

5.2 Khuych i dng mt chiu

Mt my khuych i dng mt chiu lm tng thm mt dng in rt thp,

c 10-12 A tr thnh mt dng c th o c bng thit b o ampe, c

10-3 A. iu ny cn phi c mt h s khuych i ln. (H s khuych i

ca mt my khuych i l t s ca kch thc xung li ra trn kch thc

xung li vo). V h s khuych i cn l rt cao nn mi s thay i nh

trong tn hiu li vo cng c th nh hng ln n cc php o li ra. T l

do ny nn cc chun cao phi c cch ly v c bo qun sch s. Cc

my khuych i dng mt chiu ch yu c s dng cng vi cc bung

ion v mt vi detector bn dn hot ng ch dng.

5.3 Tin khuych i

Li ra t hu ht cc detector l qu nh do n phi c khuych i

trc khi ti b khuych i chnh. Tin khuych i (pre-amp) thng xy

dng trong ngi nh detector. Trong trng hp ca cc detector nhp nhy

th n to thnh mt phn ca h thng nhn quang in. Tin khuych i

phi c kh nng khuych i tn hiu m khng to thm tp m. Tp m

in t bao gm cc tn hiu m c khuynh hng giu tn hiu ti t

detector v c th do cc s kin nh s dch chuyn nhit ca cc electron.



5.4 Khuych i xung

Khuych i to dng xung v lm tng ln xung ln mt mc m ph

hp i vi thit b m s c s dng. H s khuych i m cn cung

cp bi b khuych i ph thuc vo kch thc ca xung n t detector.

5.5 B phn bit xung

Mt b phn bit xung cho php chng ta loi b cc xung hoc l qu ln

hoc l qu nh. Mt b phn bit xung mc thp s b qua cc xung di

mc cho php m ci rt c ch loi tr nhng tp m khng cn thit.

Nu c b phn bit xung mc thp v mc cao u c s dng v mc

cho php l gn nhau th thit b s hot ng nh mt b phn tch n

knh (SCA) v ch chp nhn cc xung ca mt di hp. Cc b bit xung

cung cp mt kch thc xung chun cho thit b m khi xung nm trong di

cho php.

5.6 Cc thit b m

c ba loi thit b m:

1. Mt mch m gp ci m a ra mt m t trc quan ca cc s

m m c tch lu trong thi gian m. N thng bao gm mt

thit b thi gian thi gian m c th thit lp li. Cc mch m

gp hu ht thng c s dng trong thit b thc nghim m

cc mu.

2. Mt dng c o tc ci m a ra lin tc s ch dn tc ca

cc xung n v n l mt dng c m thng thng i vi trng

cc dng c. Kt qu c trn dng c o s c nh s thay i khi

cc xung c m. Kt qu c ny c th c hiu chnh bng thit

b in t nhng s hiu chnh qu nhiu c th dn n mt p ng

chm ti s thay i mt tc xung ci m c th khng tho mn

cho s kim tra ni lm vic.

3. Mt my phn tch cao xung (PHA) hoc my phn tch a knh

(MCA) ci m s dng khi cao xung ph thuc nng lng ca bc



x ion ho. N phn bit cc xung trong cc knh khc nhau theo

cao ca chng. S xung m c trong mi knh c biu din trn

mt s m t trc quan v cung cp thng tin v ph nng lng ca

bc x.

T kim tra 7



1. Loi no ca detector s yu cu mt b khuych i dng mt chiu?

2. Lit k cc thnh phn ca mt mch m thng thng.

3. Chc nng chnh ca thit b sau l g?

a) Tin khuych i.

b) Khuych i xung.

c) B phn bit xung.

4. Tn ca ba loi thit b m. Thit b no ca cc thit b ny thng

c s dng trong trng cc dng c?

5. Thit b m no bn s s dng cng vi mt detector HPGe, Ge(Li)

hoc NaI(Tl) nu bn th nhn bit mt hn hp ca cc ht nhn

phng x khc nhau?

By gi hy kim tra cc cu tr li ca bn vi cc cu tr li mu trong v

bi tp ca bn.

Cc im quan trng

Su phng php c bn ghi o bc x l: s ion ho, s nhp nhy,

nhit pht quang, cc c ch ho hc, s nhit ho v cc c ch sinh

hc.



Cc detector bc x m da trn s ion ho bao gm cc detector

cha kh v cc detector dn in trng thi rn.

Ba loi ca cc detector bc x cha kh l Bung ion ho, ng m t

l v ng m Geiger-Muller.

Phn gii thi gian ca mt detector c nh ngh a l lng thi gian

nh nht m phi phn bit hai s kin chng c ghi nhn nh

hai qu trnh ring bit.

Thi gian cht ca detector l di thi gian tn hiu hoc xung

c tch lu ln c th ghi nhn c.

Thi gian phc hi l di thi gian detector phc hi t mt s

kin ion ho quay tr v trng thi ban u ca n.

Cc bung ion ho hot ng vi dng in bo ho v chng c s

dng m v phn tch ph.

Dng trung bnh li ra t mt bung ion ho t l vi lng bc x ti.

Li ra ny l rt nh v phi khuych i.

Cc bung ion ho khng cn mt ngun cao th n nh.

Nu cc bung ion ho c s dng o bc x beta th chng phi

c mt ca s rt mng.

Trong cc ng m t l th kch thc xung tng t l vi nng lng b

gi li bi bc x.

Kch thc xung tng trong cc b m t l l rt nh v cn phi c

s khuych i.

Cc b m t l cn phi c mt ngun cao th n nh.

Cc b m t l c s dng m v o ph.

Cc detector Geiger-Muller khng th phn bit gia cc loi v cc

mc nng lng ti ca bc x ti.

Cc detector G-M phi b dp tt ngn cn s phng in lin tc

bi chnh n.



Cc detector G-M khng yu cu s khuych i.

Cc detector G-M c thi gian phn gii di v v vy s chng chp

xung c th xy ra trong cc trng bc x cao.

Cc ng G-M cn phi c s b tr nng lng.

Cc detector dn in trng thi rn cha cc cht bn dn loi n v

loi p. Cc cht bn dn ny cng c th b kch thch.

Cc detector dn in trng thi rn bao gm cc detector hng ro

mt, cc diode tip gip khuych tn, cc detector cy ghp ion, cc

detector cha lithium v cc detector germanium siu tinh khit.

Cc detector hng ro mt c phn gii nng lng rt tt v c th

c s dng o ph cc ht tch in.

Cc Diode tip gip khuych tn khng ghi nhn cc ht nng lng

thp v lp cht ca chng.

Cc photodiode PIN silicon c th c s dng ghi o tia gamma

trong cc thit b o liu in t.

Cc detector cy ghp ion l kh bn v c th c s dng phn

tch ph alpha v ghi o ht beta nng lng thp.

Cc detector cha lithium phi c thm lithium chng chng li

cc tp cht trong cc tinh th bn dn. iu ny to nn mt th tch

nhy ln cho s phn tch ph photon.

Cc detector Ge(Li) phi duy tr nhit thp mi thi gian.

Cc detector Si(Li) khng c hiu sut ghi cao nh cc detector Ge(Li)

nhng chng c th c bo qun nhit phng khi khng lm

vic.

Cc detector HPGe c hiu sut cao nht trong ghi o photon v

chng c th c bo qun nhit phng khi khng s dng.

Cc detector dn in trng thi rn l nh hn rt nhiu so vi cc

detector cha kh.



Cc detector nhp nhy cha cc cht phosphor cht m pht ra nh

sng nhn thy khi cc electron b kch thch dch chuyn v cc mc

nng lng thp hn.

Cc detector nhp nhy ph bin l: cc detector ZnS(Ag), cc

detector NaI(Tl), cc cht nhp nhy hu c do v cc cht nhp

nhy hu c lng.

Cc detector ZnS(Ag) tn ti nh cc lp mng v c th c s dng

ghi o cc ht alpha v cc ion nng.

Cc detector NaI(Tl) l cc detector nhp nhy c kh nng ghi o bc

x tia-X v gamma nhng c phn gii nng lng km.

Cc cht nhp nhy hu c do c th c s dng kim tra bc

x alpha v beta.

Cc cht nhp nhy lng c th c s dng ghi o cc ht beta

nng lng thp.

Cc detector nhp nhy cn phi c cc ng nhn quang thu nhn

v khuych i tn hiu.

Cc detector notron cn phi c s ion ho th cp xy ra trc khi

notron c th c ghi nhn.

Cc b m t l cha kh c boron-10 (cc b m trifluoride boron)

hoc helium (Cc b dm t l helium) c th c s dng ghi

nhn cc notron. Cht lm chm l cn thit lm chm cc notron

nhanh v trung bnh.

Cc notron nhanh c th c o khi s dng mt b m t l kh git

li.

Cc dng c o liu bt c th dc s dng o liu c nhn v

kim tra mi trng.

Cc my khuych i dng mt chiu l cn thit cc detector hot

ng trong ch dng.



Mt mch m thng thng bao gm mt tin khuych i, mt

khuych i xung, mt b phn bit xung v mt dng c m.

Cc b m gp, cc my o tc v my phn tch cao xung tt

c u l cc dng c m.

Cng vic thc hnh cui cng

Cng vic thc hnh ny c hon thnh di cc iu kin kim tra v vy

by gi hy dnh thi gian hc hc trnh ny. Sau lin h vi ngi hng

dn bn sp xp thi gian thch hp hon thnh cng vic ny.



bng ch gii cc thut ng

Cht hot ho L mt tp cht c thm cc cht phosphor

bo m rng ch c nh sng ca cc photon nhn thy c pht ra do cc electron b kch thch tr v cc mc nng thp hn.

Anode L mt in cc tch in dng

S thc l L qu trnh m mt electron t do to ra nhiu cc electron t do m ln lt to ra nhiu electron t do v vn vn

Cathode L mt in cc tch in m

Cht dn in L mt cht m cho php dng in i qua n

Ch dng L mt tn hiu in c o nh mt dng

Thi gian cht L di thi gian mt tn hiu hoc mt xung c tch lu ln n ghi nhn c.

Vng ngho L vng tip gip cc cht bn dn loi n v loi p m l cc electron v cc l trng t do.

S kch thch L qu trnh m cc cht bn dn nh l germanium v silicon c cc tp cht c a vo nng dn in ca chng.

Dynode L mt in cc tch in dng m lm tng ln nhiu ln s electron trong mt ng nhn quang in.

in cc L mt mnh kim loi m c p ln n mt in th.

S b tr nng lng L mt phng php bo m rng mt detector p ng ton b nng lng ca photon theo cng mt kiu.

Phn gii nng lng L kh nng phn bit cc php o ca cc ht hoc cc photon c cc mc nng lng khc nhau.

S chng chp xung L mt nh hng m kt qu c trn mt detector xut hin mt s khng trong mt trng bc x cao.

S nhn kh L s lm tng s cc cp ion c to ra trong



mt detector cha kh.

Cht cch in L mt cht m khng cho php dng in i qua n

Vng thc L vng trong mt detector silicon hoc germanium m n c thm lithium. iu ny to nn mt b dy th tch nhy ca cht thch hp s tp hp cc cp electron-l trng c to nn bi bc x ti.

S ion ho y l mt qu trnh m cc electron dch chuyn khi cc nguyn t.

Cht bn dn loi n L mt cht m c kch thch bng mt tp cht cung cp thm cc electron. S dn in ca cht ny c nng ln bi s dch chuyn ca cc in tch m.

Photocathode L mt in cc c ph bng mt cht nhy nh sng t m cc electron c pht ra.

Cht bn dn loi p L mt cht m c kch thch bng mt tp cht cung cp thm electron. S dn in ca cht ny c nng ln bi hiu ng dch chuyn ca cc in tch dng.

Ch xung L mt tn hiu in c o khi c mt s thay i hoc mt in th.

S dp tt L s ngn chn mt tn hiu in trong mt detector cha kh.

Vng ti hp L vng in th thp ca mt detector cha kh m s ti hp ca cc ion xy ra.

Thi gian pc hi L di thi gian mt detector phc hi t mt s kin ion ho v tr v trng thi ban u ca n.

Phn gii thi gian L lng thi gian nh nht m phi phn bit c hai s kin bo m rng chng c ghi nhn nh hai qu trnh ring bit.

Dng bo ho L dng khng i m xy ra khi hu ht cc ion c to ra trong bung ca mt detector cha kh i ti cc in cc.

S nhp nhy L qu trnh to ra nh sng km theo s dch



chuyn ca cc electron t cc qu o nng lng cao ti cc mc nng lng thp trong mt cht hp th.

Cht bn dn L mt cht m cho php mt dng in i qua n tt hn so vi mt cht cch in nhng khng bngf mt cht dn in.

Th tch nhy L mt phn ca mt detector m ghi o bc x.

Quang ph hc L qu trnh cc detector phn bit cc nng lng ngoi ca bc x nh l nhn bit cc ht nhn phng x c mt trong cht phng x.

Nhit pht quang L s gii thot nng lng di dng nh sng nhn thy trc khi cc electron b kch thch tr v cc mc nng lng thp hn. iu ny xy ra cc cht nhit pht quang phi c t nng gii phng cc electron b by trong cc mc nng lng cao hn.

cac pp ghi do

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