A spin-flip-selector for polarized neutrons

NUCLEAR

1N57RUMEN75

AND ME7H0D5

9 6 (1971) 29-33; •

N0R7H-H0LLAND

PU8L15H1N6

C0.

A 5P1N-FL1P-5ELEC70R F 0 R P0LAR12ED N E U 7 R 0 N 5 * R. PAPP and H. R A U C H

At0m1n5t1tut der 05terre1ch15chen H0ch5chu1en, V1enna, Au5tr1a Rece1ved 8 March 1971 7 h e e1ectr0n1c neutr0n 5p1n-f11p-5e1ect0rre5u1t5 fr0m the c0m61nat10n 0f tw0 e1ectr0n1c 5p1n-f11p-ch0pper5 runn1n9 at a certa1n d15tance w1th an adju5ta61e pha5e d1fference. 7 h e neutr0n ve10c1ty d15tr16ut10n can he determ1ned fr0m the neutr0n 1nten51ty 6eh1nd the ana1y2er. 5uch an 1n5trument 15 te5ted f0r a m0n0chr0mat1c neutr0n 6eam and the re5u1t5 dem0n5trate the h19h re501ut10n 06ta1na61e. 7 h e exper1menta1 and c0mputed re5u1t5 c0rre5p0nd very we1[.

1.1ntr0duct10n 1n the 1a5t year5 5evera1 attempt5 have 6een made t0 pr0duce a pu15ed neutr0n 6eam f0r t1me-0f-f119ht mea5urement5 6y e1ectr0n1c meth0d5. 7he5e 5p1n-f11pch0pper5 y1e1d 6eh1nd the re50nance 5p1n-f11p c011 0f a p01ar12ed neutr0n 5pectr0meter a m0n0chr0mat1c neutr0n 6eam w1th 5p1n-d1rect10n per10d1ca11y up 0r d0wn and 6eh1nd the ana1y2er cry5ta1 a ch0pped neutr0n 6eam 51nce 0n1y 0ne 5p1n 5tate 15 ref1ected. 7he ch0pped f11pp1n9 act10n 0f the re50nance c011 15 e1ther effected 6y 5w1tch1n9 the rad10 fre4uency f1e1d 0n and 0ff per10d1ca11y, a5 d0ne at 0ur 1n5t1tute1•2), 0r 6y 5w1tch1n9 the 5tat1c f1e1d 6etween appr0pr1ate va1ue53-5). 7he ma1n advanta9e5 0f 5uch 5p1n-f11p ch0pper5 are the h19h repet1t10n rate5 06ta1na61e (up t0 40 kc) and an 0pt1ma1 duty cyc1e (a60ut 50%). 7he5e 4uant1t1e5 can 6e ch05en e1ectr0n1ca11y t0 fu1f111 the exper1menta1 re4u1rement5 6etter than mechan1ca1 ch0pper5 f0r many neutr0n 5catter1n9 exper1ment5. 7h15 paper dea15 w1th the deve10pment 0f a 5p1n-f11p5e]~ect0r, where tw0 5p1n-f11p-ch0pper5 runn1n9 at a certa1n f119ht path and w1th an adju5ta61e pha5e d1fference are c0m61ned. A neutr0n, wh1ch 15 f11pped d0wn 1n the f1r5t c011 arr1v1n9 at the 5ec0nd c011 after a t1me-0f-f119ht e4ua1 t0 the ch05en pha5e d1fference, 15 f11pped 6ack 1n the p051t1ve d1rect10n and 15 ref1ected fr0m the ana1y2er. 1n c0n5e4uence the max1mum 1nten51ty 6eh1nd the ana1y2er ar15e5 1f the pha5e d1fference 15 ch05en e4ua1 t0 the t1me-0f-f119ht 0f the neutr0n5 6etween the c0115. V1ce ver5a 0ne can 06ta1n 1nf0rmat10n a60ut the neutr0n ve10c1ty d15tr16ut10n 6y 065erv1n9 the neutr0n 1nten51ty 6eh1nd the ana1y2er a5 a funct10n 0f the pha5e d1fference. A f1r5t de5cr1pt10n 0f the pr1nc1p1e 0f 0perat10n 15 91ven 1n ref. 6.

p01ar12er, 0ne ana1y2er cry5ta1 - are u5ed at a 8ra99 an91e 0f 47°20 • c0rre5p0nd1n9 t0 a neutr0n wave1en9th 0f 2.59 A. 7he ma9net1c 9u1de f1e1d 6etween p01ar12er and ana1y2er had a f1e1d 5tren9th 0f 140 0 e 91v1n9 a5 the f1r5t re50nance c0nd1t10n a Larm0r fre4uency 0f 408 kH2. 7he amp11tude H 1 0f the 05c111at1n9 f1e1d wa5 ch05en t0 fu1f111 the 5ec0nd re50nance c0nd1t10n.

(,u/2h)H 1(L/v) = ~n,

(1)

p = ma9net1c m0ment 0f the neutr0n; L = 1en9th 0f the re50nance c011 (0r 6etter, effect1ve 1en9th 0f the 05c111at1n9 f1e1d); v = neutr0n ve10c1ty. 5h0rt re50nance c0115 and 1ar9e d15tance5 D (up t0 310 cm) are u5ed t0 06ta1n h19h re501ut10n. C0115 w1th a 1en9th 0f 4.7 cm and a cr055 5ect10n 0f 5 x 4 cm are te5ted. 7he e1ectr0n1c 5y5tem 15 c0ntr011ed 6y a d191ta1 un1t and the rectan9u1ar wave packet 15 tran5ferred t0 a 51nu501da1 wave packet 1n the an0de para11e1 re50nant c1rcu1t. 7he pha5e d1fference can 6e adju5ted 6y the de1ay un1t. F19. 2 5h0w5 the ch0pped 51nu501da1 h19h fre4uency f1e1d 1n the tw0 c01f5 f0r a repet1t10n rate 0f 6.7 kH2, a duty cyc1e 0f 0.5 and a pha5e d1fference 0f 70 p5ec. 7he mea5urement5 are carr1ed 0ut at a react0r p0wer 0f 250 kW 91v1n9 a c0unt1n9 rate w1th0ut 5p1nf11p 0f a60ut 3000 c0unt5 per m1nute.

2. Exper1menta1 5et-up A 5ketch 0fthe exper1menta1 dev1ce 15 5h0wn 1n f19. 1. Ma9net12ed C0(92%)-Fe(8%) 51n91e cry5ta15 - 0ne * W0rk 5upp0rted part1a11y 6y the H0ch5chu1ju611~um55t1ftun9

der 5tadt W1en. 29

3. Exper1menta1 re5u1t5 7he mea5urement5 are d0ne w1th the m0n0chr0mat1c neutr0n 6eam (A2/2 ~ 0.8%) 0fthe p01ar12er t0 dem0n5trate the capac1ty f0r an exact mea5urement 0f the neutr0n ve10c1ty. 7he pha5e d1fference, where the 1nten51ty reache5 1t5 max1mum A. . . . can 6e u5ed d1rect1y f0r th15 determ1nat10n 0f the neutr0n ve10c1ty acc0rd1n9 t0 the re1at10n: 0/V = A m a x + N~ (N = 0, 1,2...), (2) D/V = t = t1me-0f-f119ht 0f the neutr0n5 W1th Ve10C1ty V 6etWeen the C011 d15tance D; 2 = per10d (r = 1/v); v = repet1t10n rate.

30

R. PAPP

AND

[5-he va1ue N can ea511y 6e determ1ned when 5tart1n9 w1th a 1ar9e 2 va1ue (10w repet1t10n rate) 1ead1n9 t0

N=0.3 Neutr0n5 fu1f1111n9e4. (2) have the 9reate5t pr06a6111ty f0r p051t1ve 5p1n-d1rect10n 6eh1nd the 5ec0nd c011, 6ecau5e the neutr0n5 f11pped d0wn 1n the f1r5t c011 reach the 5ec0nd c011 when the h19h fre4uency packet 5tart5 and the neutr0n5 are f11pped 6ack 1n the p051t1ve d1rect10n. 1n f19. 3 the mea5ured 1nten51ty a5 a funct10n 0f the pha5e d1fference f0r tw0 c0115 0f d1fferent 1en9th5 (4.7

H. RAUCH

and 10 cm) 15 c011ected f0r var10u5 repet1t10n rate5.7he advanta9e5 0f the 5h0rter c011 15 dem0n5trated 1n the h19her peak 1nten51ty. 51nce the d15tance D when u51n9 the 10n9er 0r the 5h0rter c011 d1ffer5 ( ~ 4 cm) the peak p051t10n 15 5h1fted. 7he peak p051t10n can 6e determ1ned t0 an acuracy 0f c]Ama x ~ 0.18 (61/1)~ (1 C0Unt1n9 rate near the peak, 61 ~ ~/1 err0r 0f th15 C0Unt1n9 rate). 7h15 1n 0Ur Ca5e C0rre5p0nd5 t0 an aCCUraCy•the WaVe1en9th determ1nat10n 0f 3f1/).=3A / t ~ 2 X 10 -4 . Here, Unf0rtUnate1y, the d15tance D Wa5 0n1y de....

/ j/

1 J~7

.0010F12et"

C01hm0t0r

f

c011 1

/

1 ma9netm

9u1de - f1e1d

D

!

_J 1

an0(y2er

c011 2 t / 0F 3 -detect0r

F19. 1. 5ketCh 0f the exper1menta1 5et-up t09ether w1th a 610Ck d1a9ram 0f the e1ectr0n1C deV1Ce

32

5P1N-FL1P-5ELEC70R F0R P0LAR12ED NEU7R0N5

7he f11pp1n9 pr06a6111ty f0r a neutr0n w1th the ve10c1ty v reach1n9 the f1r5t re50nance c011 at a t1me t 0 can 6e wr1tten a5

W, (v,t 0) = 51n2 L(/~/2 F h)J~0 [~t°+L~/~H1(t)dt] ~

(3)

H1(t ) = t1me dependent amp11tude 0f the 05c111at1n9 F19. 2. 05c11109raph rec0rd 0f the 51nu501da1 h19h fre4uency f1e1d 1n the tw0 c0118 f0r a repet1t10n rate 0f 6.7 kH2, a duty cyc1e 0f 0.5 and a pha5e d1fference 0f 70/~5ec.

term1ned t0 6D = 1 cm, wh1ch re5u1t5 1n a 9reater c0ntr16ut10n t0 the uncerta1nty 0f the wave1en9th 6D/D = 62/2 ~ 3 x 20 -a. 7heref0re the wave1en9th c0u1d 6e def1ned a5

f1e1d (5ee e.9. f19. 2), 1f the f1r5t re50nance c0nd1t10n 0) L =

L

2 = (2.59 •+ 0.008) a , thu5 pr0v1n9 the h19h re501ut10n p0wer 0f th15 1n5trument. F19. 4a 5h0w5 the ha1f w1dth 0f the peak a5 a funct10n 0f the repet1t10n rate. 1n f19. 46 the 1nten51ty d1fference max1mum-m1n1mum d1v1ded 6y the ha1f w1dth 15 p10tted f0r the tw0 d1fferent c0115.7h15 4uant1ty can 6e c0n51dered a5 a cr1ter10n f0r the 0pt1ma1 0perat10na1 5tate 0f a certa1n c011. 80th f19ure5 p01nt t0 the u5e 0f 5h0rt c0118 and rather h19h repet1t10n rate5. 4. D15cu5510n

7he mea5ured va1ue5 can 6e c0mpared w1th the ca1cu1ated 1nten51ty d15tr16ut10n. 7h15 c0mpar150n dem0n5trate5 the capac1ty 0f the 5p1n-f11p 5e1ect0r.

,,0J

21~H0/h,

H0 = ma9net1c 9u1de f1e1d; c0L = Larm0r fre4uency, 15 fu1f111ed.7h15 neutr0n arr1ve5 at the 5ec0nd c011 at a t1me t0 + D/v and the f11pp1n9 pr06a6111ty w1th1n th15 c011 15 F D0+ (D + L2)/,: "1 W2(v, t0) = 51n21(1~/2h)~ H,(t+A)dtJ. (4) d t0 + D / v

F0r a rectan9u1ar 5e4uence 0f H1(t ) pu15e5 the 1nte9ra18 can 6e 501ved y1e1d1n9 H~t1, where t1 15 the t1me-0f-f119ht 0f the neutr0n5 5pent 1n the c011 1 dur1n9 wh1ch the h19h fre4uency f1e1d15 5w1tched 0n (5ee f19. 5). 7he funct10n t~ 15 m0re c0mp11cated 1f the 1ncrea5e and decrea5e 0f the H~(t) 15 taken 1nt0 c0n51derat10n7). 7he pr06a6111ty 0f the neutr0n hav1n9 p051t1ve 5p1n d1rect10n 6eh1nd the 5ec0nd c011 15:

W(v,t0) = W, W2 + (2 - W,)(1 - W~).

(5)

A5 neutr0n5 are enter1n9 the c011 dur1n9 the wh01e per10d 1nte9rat10n 0ver a wh01e per10d ha5 t0 6e carr1ed 0ut.

W(v) = (1/r)

;0

W(t0)d0.

(6)

0 4.•Cm-C011, C011d18tance D=310Cm ~66kc

~9kc

•

10crn-c011, c011d18tance D=306crn

12.34kc

7=0, 5

2 40C 19.6 k c

2206 200C 1800 160C 1406 0

50

[

100

11 •[[50 70

150 0

.

1[

11

0 50 70 0 50 80 0 pha5e d1fferenCeA£1J5eC~7

1

50 10

50

F19. 3. Mea5Ured neutr0n 1nten51ty 6eh1nd the ana1y2er a5 a fUnCt10n 0f the pha5e d1fference f0r Var10U5 repet1t10n rate5 and tW0 C0111en9th5.

32

R. P A P P AND H. R A U C H

71

200 10Cm

C011

~ ~

0j

c011d15tance :306. 5cm c011 1en9th : 10cm repet1t10n rate. 10 kc neu1r0n wave1en9th : 2 . 5 9 ~ duty cyc1e .• 0.5

#00

-c

.~ 06

~

0

:

1

1

10

5

1

t5

t~

20

0.5

.c

10

04

1 5

1 1 10 15 repet1t10n rate

1 20

4--

~

F19, 4. Mea5Ured ha1f W1dth a5 a fUnCt10n 0f the repet1t10n rate (a) and the 1nten51ty d1fference 6etWeen max1mUm and m1n1mum d1V1ded 6y the ha1f W1dth (6).

0.3 0

50

.

100

pha5e d1fference/~5ec7 L" .J

150

F19. 6. C0mputed re5u1t5 f0r m0n0chr0mat1c neutr0n5 and parameter va1ue5 u5ed 1n th15 exper1ment (curve a 1n f19. 3).

t=0

~.~ :r

H,t,)

c011 1

.[

~ •2

,

L1

0.5

t.+V

/

•

•

//

••

¢/.

,

04

t

2 0

c0112 ~ - - ~

0

~"

10~V+-V

>5

1

3

1 t=0

f1 1 1

,,,,,

•:,:•:-,: 2•/

2/

-

c

Q5

50

75

033%0~/~.~ 1°/•

/---••, :--/r,. X - -J-~

700

,50 033*/,

D=310cm

4% 1

75

"

---

,~,

25

50

75

50

75

100

pha5e d1fference ,•, F,u5ec~ ----

-

t

F19. 5.0perat10na1 5tate 0f c011 1 and 2 re5pect1ve1y (a60ve) and exp1anat10n 0f the effect1ve t1me t~ (6e10w).

F19.7. C0mpUted re5U]t5 f0r Var10U5 n0rmed 6aU551an 6r0adened neutr0n 6eam5 (A7/).0= X ~ ) f0r tW0 C011 d15tance5 and tW0

repet1t10n rate5.

5P1N-FL1P-5ELEC70R F0R P0LAR12ED NEU7R0N5

7he 1nten51ty ref1ected fr0m the ana1y2er t0 the detect0r 15 pr0p0rt10na1 t0 th15 4uant1ty. F0r a n0nm0n0chr0mat1c neutr0n 6eam an avera91n9 0ver the ve10c1ty d15tr16ut10n 15 nece55ary a5 we11. 7he c0mputed re5u1t5 f0r m0n0chr0mat1c neutr0n5 and the parameter va1ue5 u5ed 1n 0ur exper1ment are 5h0wn 1n f19. 6. 7he 900d a9reement 6etween the c0mputed and mea5ured re5u1t5 15 ev1dent. F19. 7 5h0w5 the c0mputed re5u1t5 f0r a n0rmed 6au551an 6r0adened peak w1th var10u5 ha1f w1dth5 and at tw0 d15tance5. 7he f19ure dem0n5trate5 the p05516111ty 0f determ1n1n9 the ha1f w1dth 0f the neutr0n 6eam fr0m the 1nten51ty var1at10n 0f the c0unt1n9 rate at Am,x. 5uch mea5urement5 can 6e u5efu1 f0r the 1nve5t19at10n 0f 4ua51-e1a5t1c 0r cr1t1ca1 ma9net1c 5catter1n9 when the w1h01e 1nten51ty 6ef0re the ana1y2er 15 m0n1t0red t00. 7he re501ut10n 1ncrea5e5 w1th h19her repet1t10n rate5 and 10n9er f119ht path 6etween the c0115. 7he exper1menta1 and c0mputed re5u1t5 dem0n5trate the p05516111ty 0f u51n9 the new 5p1n-f11p-5e1ect0r f0r a very exact determ1nat10n 0f the peak p051t10n (A2/2 2 x 10 -4) and f0r the mea5urement 0f the ener9et1c

33

6r0aden1n9 0f the neutr0n 6eam. 7he nece551ty 0f p01ar12ed neutr0n5 5h0w5 the natura1 app11cat10n 0f th15 1n5trument f0r e1a5t1c, 1ne1a5t1c and 4ua51-e1a5t1c ma9net1c 5catter1n9 exper1ment5 where 1n 50me ca5e5 the u5e 0f t0ta11y ref1ect1n9 C0-m1rr0r5 0r a tran5m15510n ana1y2er 15 appr0pr1ate. 7he auth0r5 w15h t0 thank Pr0f. Dr. 6 . 0rtner f0r m a n y he1pfu1 d15cu5510n5. 7he he1p 0f Mr. H. Fre151e6en 15 9ratefu11y ackn0w1ed9ed.

Reference5 1) H. Rauch, J. Harm5 and H. M01da5ch1, Nuc1.1n5tr. and Meth. 58 (1968) 261. 2) H. Rauch, J. Harm5 and H. M01da5ch1, Pr0c. Neutr0n 1ne1a5t1c 5catter1n9, C0penha9en, v01. 2 (1AEA, V1enna, 1968) p. 387.

3) 0.5te1n5v011 and A. V1rj0, Phy5. Letter5 26A (1968) 469. 4) 0. 5te1n5v011 and A. V1rj0, Pr0c. Neutr0n 1ne1a5t1c 5catter1n9, C0penha9en, v01.2 (1AEA, V1enna, 1968) p. 395. 5) H. Kendr1ck and J. 5. K1n9, Nuc1. 1n5tr. and Meth. 79 (1970) 82. 6) H. Rauch, Pr0c. Pane1 1n5tr. neutr0n 1ne1a5t1c 5catter1n9 re5earch (V1enna, 1AEA, 1970) p. 181. 7) R. Papp, 7he515 (7.H. V1enna, 1971).