Elastic Scattering of Neutrons from 6Li EUR 3454

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STIC SCATTERING OF NEUTRON!

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Joint Nuclear Research Center

Geel Establishment - Belgium

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entrai Bureau for Nuclear Measurements - CBNM

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EUR 3454.e

E L A S T I C S C A T T E R I N G O F N E U T R O N S F R O M 6L l

by H.-H. K N I T T E R and M. COPPOLA

European Atomic E n e r g y Community — EURATOM

Joint Nuclear Research Center — Geel Establishment (Belgium Central Bureau for Nuclear Measurements — CBNM

Brussels, April 1967 — 14 P a g e s — 4 Figures — F B 25

Angular distributions of neutrons elastically scattered from Li were measured in the energy region between 1.0 and 2.3 MeV using a fast neutron time-of-flight spectrometer. Flux attenuation and shape corrections were calculated and the final d a t a a r e presented in the form of coefficients of Legendre polynomial expansions.

EUR 3454.e

E L A S T I C S C A T T E R I N G O F N E U T R O N S F R O M 6L I

by H.-H. K N I T T E R and M. COPPOLA

European Atomic Energy Community — EURATOM

Joint Nuclear Research Center — Geel Establishment (Belgium Central Bureau for Nuclear Measurements — CBNM

Brussels, April 1967 — 14 Pages — 4 Figures — F B 25

Angular distributions of neutrons elastically scattered from Li were measured in the energy region between 1.0 and 2.3 MeV using a fast neutron time-of-flight spectrometer. Flux attenuation and shape corrections were calculated and the final d a t a a r e presented in the form of coefficients of Legendre polynomial expansions.

EUR 3454.e

E L A S T I C S C A T T E R I N G O F N E U T R O N S F R O M 6L I

by H.-H. K N I T T E R and M. COPPOLA

European Atomic Energy Community — EURATOM

Joint Nuclear Research Center — Geel Establishment (Belgium Central Bureau for Nuclear Measurements — CBNM

Brussels, April 1967 — 14 P a g e s — 4 Figures — F B 25

Angular distributions of neutrons elastically scattered from ^Li were measured in the energy region between 1.0 and 2.3 MeV using a fast neutron time-of-flight spectrometer. Flux attenuation and shape corrections were calculated and the final data are presented m the form of coefficients of Legendre polynomial expansions.

6-EUR 3454.e

EUROPEAN ATOMIC ENERGY COMMUNITY - EURATOM

ELASTIC SCATTERING OF NEUTRONS

FROM

6

Li

by

H.-H. KNITTER and M. COPPOLA

1967

Joint Nuclear Research Center

Geel Establishment - Belgium

SUMMARY

3

-Introduction

A systematic study of neutron elastic scattering from Li was

realized as a part of a program established to provide data

needed for reactor design. Some time-of-flight measurements

of neutron scattering from Li were previously accomplished

(1-5), hut the data are spread over a large range of

ener-gies up to 14 MeV and do not provide a consistent set of

ex-perimental results. R.O.Lane et al. (6) have measured neutron

differential cross sections of Li between 50 keV and 2.0 MeV

using BF.J counters. A complete survey of the neutron cross

sections of Li in the energy region 0.001 eV - 15 MeV

exis-ting up to July 1964 was made by E.D.Pendiebury (7). More

recently R.O.Lane et al. have measured polarization and

dif-f(

7-ferential cross sections for neutron scattering from Li and

Li between 0.2 and 2,0 MeV using the same technique as

be-fore.

In the energy region of the present measurements also the

reaction Uii(n,dn')a with a Q-value of -1.47 MeV is

energe-tically possible. However, sinoe these neutrons have much

longer flight times than the elastically scattered ones,

they contribute to a region far from the elastic peak in

the time spectra. In any case also at the highest primary

neutron energy no appreciable contribution was observed

from the Li(n,dn*)a reaction.

Experimental equipment

The measurements were performed at the 3 MeV Van de Graaf f

accelerator of CBNM using a fast neutron time-of-flight

spectrometer. The experimental equipment is the same used

for earlier measurements and was already described (9).

Neutrons were produced through the T(p,n)

He reaction in

occluded targets 1.0 and 0.6 mg/cm

thick. The scattering

samples were cylindrically shaped and enclosed in very

thin aluminium containers. The contribution to the

scatte-ring due to the containers was experimentally subtracted

using a dummy can. For best detection efficiency two

diffe-rent Li samples were used at diffediffe-rent energies.

_

k

-Sample I: Height 2,59 cm; 0 3,67 cm; Weight (

12,807 + 0,002)g

Sample II: Height 4,98 cm; 0 3,68 cm; Weight (24,666 + 0,005)g.

Both samples had an isotopie composition of 95,82$ Li and

4,18#

Li.

Due to the sample-to-detector collimation two different scin­

tillators were also used, in conjunction with the above des­

cribed samples.

Detector I: Stylbene crystal 1 3/4" 0 and 1" height

Detector II: NE 102 A plastic scintillator 4" 0 and 1" height.

In the case of Detector I the crystal was directly facing the

photocathode of a 56 AVP tube, while for Detector II a

light-pipe of plexiglass was inserted between scintillator and pho­

tocathode. The relative efficiencies of both deteotors were

obtained by comparison of the measured yield of neutrons scat­

tered from hydrogen at several angles with the known η-p dif­

ferential scattering cross sections (10). Proper beam attenu­

ation corrections in the hydrogenous sample were introduced.

Experimental results

Neutron scattering from Li was measured at several angles

between 20° and 150°, but for some of the angular distribu­

tions the maximum scattering angle was reduced to 145° be­

cause of geometry limitations.

Angular distributions of elastically scattered neutrons were

measured at incident neutron energies of 1.00, 1.10, 1.20,

1.33, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.09, 2.19

and 2.30 MeV, with energy spreads, due to target thickness

and finite geometry, of 62, 60, 59, 56, 54, 89, 87, 85, 83,

81, 78, 76, 75 and 74 keV respectively.

Por the absolute calibration of the cross sections, at each

primary energy the neutron scattering from a polyethylene

sample was measured at a certain angle. Absolute values of

the differential cross sections were then obtained by

COm-parison of the angular distribution results on Li with the

H(n,n)H differential cross section values.

Corrections for finite geometry, beam attenuation and mul­

5

-and the corrected differential cross section data were then

fitted with a legendre polynomial expansion of the form

7

$#(*) = > B

P

(cos*).

dfl

^ 0

The best fitting curves are presented in figs. 1, 2 and 3

with the corrected experimental points. The values of the

Β,- coefficients derived from the least squares fit proce­

dure are presented in table I, together with the computed

errors, which are only of statistical nature.

Overall errors on the absolute differential elastic croise

sections are estimated to be around 5$.

Integrated elastic scattering cross sections are presented

in table II and fig. 4. The agreement with the previous

results of R.O.Lane (6) is good.

The theoretical interpretation of our scattering data on

6 7

_{Li and Li is unde}

future publication.

6 7

_{Li and Li is under study and it will be the matter of a}

The authors wish to thank Dr. J.Spaepen, Director of CBNM,

for supporting these measurements. The cooperation of

6

-References

1) C.Wong et al. Nucí. Phys. ¿¿ (1962) 680

2) R.Batchelor and J.H.Towle Nucí. Phys. £7 (1963) 385

3) P.Merchez et al. Compt. Rend. 260 (1965) 3922

4) J.C.Hopkins LA-DC-7603 (1966)

5) P.Merchez et al. Paris Conf. CN-23/75 (1966)

6) R.O.Lane et al. Ann. Phys.

V¿

(1961) 135

7) E.D.Pendlebury AWRE 0-60/64 (1964)

8) R.O.Lane e t a l . Phys. Rev. J J 6 (1964) Β 1710

9) M.Coppola and H . - H . K n i t t e r EUR 2798.e (1966)

10) J.L.Gammel i n F a s t Neutron P h y s i c s P a r t I I ,

J.Wiley e Sons, New York and London (1963)

TABLE I

Values of the coefficients in the Legendre polynomial expansions in mb/sr

(MeV)

1 . 0 0 1 . 1 0 1 . 2 0 1 . 3 3 1 . 4 0 1 . 5 0 1 . 6 0 1 . 7 0 1 . 8 0 1 . 9 0 2 . 0 0 2 . 0 9 2 , 1 9 2 . 3 0

B

o

, 4 2 + 1 , 8 4 + 1 . 4 6 + 1 , 3 1 + 0 , 9 9 + 0

»99+p

, 1 7 + 0 7 4 + 0 8 6 + 0 , 7 0 + 0 , 6 1 + 0 . 3 8 + 0 , 5 6 + 0 2 0 + 0

, 3 1 . 4 0 . 5 0 . 2 7 , 5 1 , 7 3 , 9 3 . 3 7 . 6 5 , 4 7 , 5 7 , 7 6 , 7 7 , 6 9

B1

+ 5 9 . 8 9 + 2 + 6 6 . 8 2 + 3 + 5 6 . 0 9 + 3 + 4 7 . 8 3 + 0 + 4 8 . 5 6 + 1 + 3 9 . 7 5 + 2 + 4 7 . 0 9 + 2 + 4 7 . 9 1 + 0 + 4 5 . 7 5 + 1 + 4 8 . 3 9 + 1 + 5 2 . 8 3 + 1 + 6 0 . 5 7 + 2 + 5 7 , 3 6 + 1 + 6 2 . 3 8 + 2

. 3 6 . 1 2 . 1 6 , 7 2 . 2 1 . 1 7 , 6 4 , 9 8 , 5 5 , 1 4 27 , 3 3 , 9 4 , 1 7

B2

+ 2 7 + 19 +20 + 14 +20 + 18 + 12 + 14 + 10 + 1 3 . + 1 5 , + 2 6 + 2 7

+36

, 1 1 + 3 . 3 0 + 4 . 5 2 + 4 . 9 6 + 0 , 0 7 + 1 . 3 3 + 3 . 4 0 + 4 . 5 9 + 1 . 0 0 + 2 89 + 1 6 3 + 1 . 8 9 + 3 . 6 8 + 2 , 7 2 + 3

, 3 9 , 7 1 , 3 1 , 9 7 , 6 6 . 1 1 . 2 8 30 . 1 7 , 6 3 . 7 6 , 3 9 , 7 5 . 0 2

B3

+ 2 . 9 5 + 4 - 0 . 6 6 + 6 , - 8 . 0 2 + 5 , - 1 . 5 4 + 1 + 3 . 1 5 + 2 - 1 1 . 7 0 + 3 . + 1 . 9 4 + 5 - 5 . 3 0 + 1 - 4 . 0 7 + 2 + 1 . 8 8 + 2 , + 8 . 8 0 + 2 +17.80+4, + 1 2 0 1 + 3 +15.76+4

6 6 . 0 3 , 5 7 , 0 6 , 0 7 , 9 7 . 5 9 . 5 6 . 6 8 10 . 3 1 , 5 3 , 6 5 , 3 2

B4 +2 - 0 +3 +2 +4 +8 +6 +2 +2 + 1 - 4 +4 +2 +7

, 2 0 + 4 , 3 6 + 5 , 6 7 + 5 , 6 3 + 0 »84+1 , 6 2 + 3 , 9 8 + 4 . 4 7 + 1 . 5 2 + 2 , 3 0 + 1 , 5 7 + 2 , 5 3 + 3 , 2 0 + 1 , 9 2 + 3

. 1 9 . 1 1 , 0 2 . 8 8 , 7 5 . 6 4 , 5 9 , 3 2 , 2 6 , 4 4 , 6 7 , 8 7 , 8 9 . 9 1

B5

- 1 . 1 9 + 6 . - 3 . 5 6 + 8 - 7 . 8 0 + 7 - 0 . 7 6 + 1 - 1 . 0 5 + 2 - 1 2 . 6 4 + 4 + 5 . 4 7 + 5 - 3 . 3 2 + 2 - 4 . 4 2 + 3 - 1 . 5 2 + 3 + 5 . 9 1 + 2 +12.41+4 + 6 . 9 1 + 3 + 4 . 6 1 + 4

9 2 . 3 1 . 3 1 . 7 7 . 9 2 . 3 2 . 5 8 , 1 0 , 6 5 . 1 6 . 7 9 , 7 9 . 7 0 . 5 0

B6

- 0 - 4 + 0 , +0 - 0 +7 +0 - 0 - 0 - 0 +0 +6 +0 + 8

0 3 + 0 , 4 7 + 8 , 8 6 + 7 , 0 3 + 0 . 1 2 + 0 . 9 6 + 3 . 2 8 + 6 . 1 0 + 0 . 1 1 + 0 . 1 0 + 0 , 0 2 + 0 , 8 7 + 4 , 7 0 + 1 , 2 4 + 3

. 0 6 . 4 4 , 8 5 . 0 6 . 0 3 . 5 0 . 4 4 . 0 5 . 0 5 . 0 5 . 0 6 . 0 5 . 0 0 . 2 2

B7 - 0 - 7 - 8 - 0 - 0 - 1 - 0 - 0 +0 +0 - 0 +7 +0 +2

, 0 8 + 0 . 0 6 . 2 9 + 8 . 8 1 . 2 9 + 8 . 7 0 . 0 5 + 0 . 1 0 . 0 3 + 0 . 0 3 . 2 5 + 2 . 9 5 . 4 7 + 6 . 5 8 . 0 2 + 0 . 0 6 . 0 5 + 0 . 0 5 . 0 2 + 0 . 0 6 . 1 3 + 0 . 0 6 . 2 8 + 3 . 9 8 , 8 4 + 1 . 0 6 , 2 8 + 3 . 9 3

I

TABLE II

Integrated elastic cross sections

(MeV)» 1.00

= = = = = * = = = = = =

σ

β 1 !! 1023

(mb) ¡I

*

e l j{ 3 6

(mb) II

II

1.10

1040

36

1.20

= = = = = = =

985

34

1.33

958

33

1.40

: = = = = = = :

980

34

1.50

:== = = = = :

967

34

1.60

982

34

1.70

1.80

:= = = = = = | = = = = = = =

1027

36

990

35

1.90

: = = = = = ==

1064

37

2 . 0 0

= = = = = = :

1126

39

2 . 0 9

========

1198

42

2 . 1 9

= = = = = = =

1250

44

2 . 3 0

= = = = =

1321

46

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Fig. 3 Elastic scattering of neutrons from Li in the Lab system.

1.6

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•

present work

©

Lane et al. (6)

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