Indian Journal of Pure & Applied Physics Vol. 40, August 2002, pp.533-538

I

Measurement of (n,2n) reaction cross-sections on isotojles of zinc, germanium and scandium in neutron energy range --- - - - 13.82-14.7iMeV - -

I \ J _ .. M S Uddin, S K A Latif, M A l -Ialim, M N ]slam, R U Miah, N I Molla & M R Zaman*

Institute of Nuclear Science and Technology, AERE, GPO Box-3787, Dhaka- I 000, Bangladesh)

*Department of Applied Chemistry and Chemi cal Technology, Rajshahi University, Rajshahi -6205 , Bangladesh

Received 5 December 200 I; accepted 24 April 2002

The cross-secti ons for the reactions M Zn(II ,2n/" Zn, 76Ge(Il ,2n)75rn+gGe and ~5 S c(n ,2 1l )44rnSc were measured in the energy range 13.82- 14.7 1 MeV. The activat ion technique was used in combinati on with hi gh reso lution HPGe detector gamma-ray spectroscopy. Neutrons were produced via D-T reaction at J-25 neutron generator of the Institute of Nuclear Science and Technology, AERE, Dhaka, Bangladesh. The neut ron flu x at each energy was determined using monitor reacti on 27 AI(II ,a)24Na. The nuclear model calcul ations using the computer codes SI NCROS- II and EXIFON were undertaken to descri be the excitation fun ctio ns of the in ves ti gated reacti ons.

1 Introduction

One of the c haracte ri sti c features of our times is, the emergence o f nuc lear sc ience and the utili zati on of the results achieved in the fi e ld . The discovery of neutron by C hadw ick in 1932 and the in venti on of pa rti c le acce le rators the reafte r had gl ven an enormous impetu s to the development of nuc lear reacti on studies. Wherever radi oacti vity and nuc lear reacti ons are concerned , energetic ato m and transmutati on effects are at work. The study o f the reacti ons o f energetic atoms is of inte rest ma inly fo r two reasons: ( i) to identify new reac ti ons that are not common with the rmal ato ms and ( ii ) to acquire quantitative information on the reacti on c ross­section as a func ti on of energy and on the reac ti on threshold for new reacti ons.

Developing a mate ri a l suitable for the first wa ll and similar c ritical locati ons is one of the mos t di fficult problems of fusion. Present mate ri a ls fai l in the ir res istance to radi ation damage, c reep and other things to meet the life-time require ments of a fusion reactor by about an o rde r o f magnitude; ingeni ous considerati ons fo r frequent repl acement present cost penalties. T hu s, mate ri a ls development w ill be a criti ca l paci ng ite m in the future fusion programme l

.

Since 14 MeV neutrons do minate the neut ron fie ld around D-T pl asma, the accuracy of th e cross­secti on data at 14 M eV neutrons is important for the predicti on of reactor paramete rs such as trit ium

breeding, nuc lear heating, radi ati on damage, radi oacti ve was te estimati on, ca lcul ati on of the ac ti vation in mate ri a ls to be used in fu s ion reactors and so on.

Semiconduc tor e lec tro ni c co mponents are sometimes needed to be used in intense fast neut ron fi e lds for nuc lear measure ments . Radi oacti vit ies prod uced in semiconducto r mate ri a ls with neutron a re o f immense importance for nuc lear applicati ons. A parti cul ar semiconduc tor mate ri a l may consist of many stable isotopes. Fast neutrons, the refore, lead to the formati o n o f many radi oac tive products. There fore, an accurate know ledge of their fo rmati on, c ross-secti ons, is important fo r estimating the tota l induced acti vity .

The (n,xll ), (x ~2) and (n ,!) reac ti o ns can be used to enhance the neutron flu x through neut ron multiplicati on. Tn norma l D-T fu s io n reac tors , materia ls w ith high (/1 ,2n) cross-sec ti ons a re used as main or additi onal mate ri a ls in the first wa ll. They can lead to a signi ficant multipli cati on of the neutrons imping ing on the bl anket. These neut rons enh ance tritium breedin g. Because o f the Cou lomb barri e r, the emi ss ion o f neutrons is more like ly than that of c harged partic les . The cross-secti on data on (/1 ,2/1) react ions o f Ge-isotopes are of so me interes t fo r furth e r improvement of semi conductor techno logy and furt he r refinement o f the nuclear theory.

534 INDIAN J PURE & APPL PHYS , VOL 40, AUGUST 2002

Table I - Decay data of nuclear reaction products (Refs 9,16, 17)

ue/ear Reac ti on Isotopic Half-life of Q-value Decay Gamma-ray Gamma-ray abundance of the product (MeV) mode energy (keY) intensity Iy target (%) nue/ei (%)

"4Zn(II ,2I1t'Zn 48.90 38.50 m - I 1. 86 ~+ 5 11.00 185.00 7(,Ge(n, 211 ) 75m+gGe 7.70 82.80 m -9.43 ~- 264.80 12.00 4S SC(1I ,211 )44mSC 100.00 58.60 hr - I 1.60 ~+ 27 1.40 86.00

I 01 c~~.~~'---'-~~~~~...L...c~~

0.00 2.SOe+4 S.00e+4 7.SOe+4 1.00e+S

Deely Time (sec)

Fig. I - Composite decay curve for the radionuclides

("Zn and "4CU

As a result, there is an increasing demand fo r accurate nuc lear technology des ign and reliable assurance of nucl ear safety, which require neutron nuclear data wi th high accuracy . But, recent compilation on nuclear data requirements for reactor and semi conductor technology has shown that, cross-secti on values for fast neut rons particularly at 14 MeV neutron energies are not known with high accuracy . Moreover, cross-section values obtained in different laboratories in many cases differ too much wit h one another. So, re-in vest igati on of the in teracti on of fast neutrons with the potential materi als is now of prime importance. The authors chose to st udy (/1 ,2/1 ) reacti on on the (>-lZn, 7"Ge and 4SSC isotope in the neutron energy range 13 .82- 14.7 1 MeV. Nuclear model ca lcul ati ons with statis ti ca l codes SINCROS-II (Ref. 2) and EXTFON(Ref. 3) have been attempted. Zinc and scandium are most important constituents of the fusion structural

materials4. Germanium is an important semi­

conducting material. Some information has exi sted in Iiteratures.'4 but, there are large di screpancies among them. The present work reports some further new resu lts in cross-section data of the in vestiaated

. b

reactIOns .

Table 2 - Principal sources of uncertainty and their magnitudes

Source of uncertainty

Error in nux determi nation Neu tron flux variati on with time Stati stic of counting Efficiency of the detector Neutron absorpti on and scattering wi thin the sample Self absorption of gamma-ray in sample Irrad iati on geometry Sample weight Decay data Gamma-ray emission probability Error in peak area analysis

2 Experimental Details

Magni­tude (%) 1.0-3.0 0.5- 1.5 0.5-8.0 1.5-3.0 0.5 0.5 0.5- 1.5 ~ I

0.3-1.0 0.3- 1.0 0.5- 1.0

Cross-secti ons were measured by activati on and identificat ion of the rad ioactive prod ucts. The pertinent techniques have been app li ed . High purity samples of zinc ox ide, germani um metal and scandium ox ide of natural isotopic compos iti ons (from E MERK) in the form of powder were used. Five samples of zinc, five germanium samples and four scandium samples were prepared in the form of pellets by applying a pressure of 5 tons per cm" using a hydrauli c press. Each pell et weighed between 0.2250 and 0.7835 g and had the dimension of 1.2 cm diameter and - 0.2 cm thickness. The sa mples were packed separate ly in very th in polyeth ylene bags for non-destructi ve measurement. Aluminium (purity >99%) monitor fo il s of the same diameter as the samples were then attached at the front and back of each sample. The samples were placed in a rin g arou nd the sources at different

UDDIN et at.: REACTION CROSS-SECTION MEASUREMENT IN Zn, Ge & Sc 535

angles with respect to the direction of the deuteron beam.

300

250

200

Jj'

.s c 150 0 t; G)

(J) (/) 100 (/)

E u

50

0

-50 13

• Present work /:, Miah R U (1996) 'V Bychkov et a!. (1982) o Hand book on C.S. (1974) h---r~ (') Bormann et aJ. (1969)

EXJFON - SINCROS-II

14

Neutron Energy (MeV)

15

Fig. 2 - The excitation function of MZn(n,211)(,JZn reaction

Five zinc samples with AI-foils were irradiated

by neutrons at, 0°, 30°, 60°, 90° and 120° angle with respect to the deuteron beam direction in a ring­geometry arrangement over a period of 3 hr. Neutrons were produced at the 1-25 Neutron

. Generator of the Institute of Nuclear Science and Technology, AERE in Dhaka via JH(d ,n)4He

reaction with 110 keY deuterons of 200 IlA beam current. Five germanium and four scand ium samples were also irradiated separately by neutrons for I hr and 3 hr, respective ly . The angular positions for germani um samples were, 10°, 50°, 70°, 90°, 110° and fo r scand ium were 10°, 30°, 80°, 110° with respect to deute ron beam of I 10 keY energy and

100 IlA current.

The neutron energy, e ffec ti ve at each samp le was calcu lated from the kinematics of JH(d,1/ )4He process, taking into accou nt , the fin ite s ize of each capsule and the angle between the directi on of the deuteron beam and the capsu le. The effec ti ve

neutron flux density for each sample was determined via the monitor reaction 27AI(n,a)24Na

(T,n=15.02 hr, £1-1369 keY, /1-100%) using well­known formula; its cross-section was taken from the works of Vonach ' 5.

Jj'

.s c o

1400

1200

t; 1000 G)

(J)

OJ (/)

E u

800

600

13

• Present wor\(

/'; Miah R U (1996) Bychkov et al. (1982)

'V Gerhard Erdtman (1976)

o Okumura et al. (1967) - EXIFON

14

Neutron Energy (MeV)

15

Fig. 3 - The exci tat ion function of 7('Ge(Il ,21l)75m+gGe reaction

Radioactivity of each investigated product was determined via HPGe detector, low background gamma-ray spectroscopy. The gamma-ray spectra were accumulated and analyzed in Canberra S-IOO Multi Channel Analyzer (MCA), master board package based on personal computer. Count rates were subjected to usual correction for dead time loss, pi le-up loss and coincidence losses . The counts of 5 1 I keY gamma-ray energy were a lso corrected by subtracti ng background counts . In the case of the (" Zn(n,2nY~Zn reaction , a contribution of the I>IZn (n,p)'>lCu process was su btracted establi shing, composi te decay curve shown in Fig. I . From the corrected count rates, decay rates were obtained using the gamma-ray emi ssion intens ity and the efficiency of the detector. From the decay rates, the cross-sections were determined using we ll -known

536 INDIAN J PURE & APPL PHYS, VOL 40, AUGUST 2002

Table 3 - Measured cross-section of the investigated reactions.

Neutron Correspondi ng neutron emission energy (MeV) angle

6.1Zn(n,2n)f>JZn

00 14.7I±O. 11 121.01±11.57 100 14.70±O. 11 n.d

:10° 14.63±O. 11 I 00.49± 10.05

500 14.5I±O.09 n.d

600 14.4I±O.08 91.29±9.36

700 14.3 I±O.07 l1 .d

800 14.2 I±O.06 n.d

90° 14. 1O±O.04 96.53± I 0.62 1100 13.90±0.04 n.d

1200 13.82±O.06 86.49± 10.40 l1 .d = 110t determined

ac tivati on formula. Decay data of nuclear reaction products needed for the determination of cross­sections are shown in Table I .

The uncertainties in the cross-sections were determined by considering both the systematic and statistical e rrors. The princ ipal sources of uncertainty are shown in Table 2 . The total uncertain ty in each cross-section va lue was obtained by combining all the individual uncertainties in

quadrature .

In order to describe the measured cross-secti ons , nuc lear mode l ca lcu lati ons were performed in the neutron energy range 13-15 MeV using the computer codes SINCROS-II and EXfFON which are based on the stati stical mode l. eutron, proton and a lpha-parti c le e mi ss ions were taken into account from every compound nucleus and the necessary data for all nucle i were supplied . Instead of the excited state producti ons, the isomeri c state producti on cross-secti ons are directl y output. The isomer, of which the exc itation function is intended

to be oiven can be des ianated in the last row of the b' b

input data.

3 Resul t .. a nd Discussion

The measured cross-sections including errors at different e ne rgies in the range 13 .82- 14.71 MeV are gi ven in Table 3. T he quoted uncerta inty in the ~ross-sectio n values include, both systemat ic and statistica l e rrors. The deviation in the neut ron energy does not g ive an error. It describes the

Measured cross-sect ion (mb)

76Ge(n ,211) 75m+~Ge ~~Sc(n ,2n )44mSc

n.d I 64.70±1 3.75 1076.50±95. 16 n.d n.d 150.94±12.01 1068.71 ±90.34 n.d n.d n.d

1065.09±90.20 n.d l1.d 133.89± I 0.65 1055.16±89.29 l1.d

1053.24±89. 12 I 15.37±9.44 n.d l1 .d

energy spread due to the ang le of e mission of neutron, the finite s ize of the sample and deuteron energy loss in gas. The results of the investi gated reac tions are discussed in the subsequent sections.

6-JZn(Il,2n/3Zn Reactioll - On the measurement of cross-section for the reacti on 6-lZn(Il,2n)I"Zn, extreme ly fe w publi shed data a re avail ab le. More experiments are needed to g ive precision cross­secti on data of this reacti on. Measured data by the au thors and the literature data are shown in Fig. 2, as a function of neutron energy . The measured data a re lower than those of evaluated data of Bychkov e /

(/ 1.1, and the data repo rted in the handbook7 on

activation cross-sections , but , these data are re lati ve ly older. The data of experimental work by the authors are also lower than that of M iah ' and coverage in the middle of theoreti ca l calcul ati ons using statistical codes STNCROS-I1CRe f. 2) and EXTFON(Ref.3) . The present ex periment introduces some newer data points to the ex isting literature and theoretical calculations.

76Ge(n,211l5m+~ Ge React ion - Ex treme ly few publ ished ex peri men tal cross-sect ion data o r 7I>Ge(n ,2nr'm+~Ge reaction a rc avai lable and the re ex ist large discrepancies among them that demand more experiments to g ive reliable data . The measured data with lite rature arc "hown in Fig. ~, as a function of neutron energy . The results of the nuc lear model calculation llsing stat istica l code EXfFON are also shown in Fig. 1. All the measured va lues give the cumulative cross-sec ti on for the

UDDIN et ClI. : REACTION CROSS-SECTION MEASUREMENT IN Zn, Ge & Sc 537

formation of the ground-state. Since the metastable state could not be measured due to its short half-life of 48.9 sec, a correction for its contribution to the cumulative cross-section could not be estimated. The authors, therefore, calculated cross-sections for the independent formation of the two isomeric states and obtained the cumulative cross-section for 75Ge. The present data are lower than those of Miah5. Measured data by the authors are well supported by Okumura lll and Erdtman~. Measured data by the authors give 3-8 % lower values than the data evaluated by Bychkov et aL.h and - 4 % higher than those of theoretical calculation. There appears to be a good agreement between experimental results and theory.

• Present work 6 Miah R U (1996) 'V Wenrong et al. meas. (1989) , Wenrong et al. eva!. (1989) , Ikeda et al. (1988)

350 0 Hand book on C.S. (1974) 0 Perkin et 31.(1966)

300 o Arnold et 31. (1964)

- SINCROS-II

250 ,.., .0 E ..... c: 200 0 .. 0

, tHt!Frt~ G)

en (/) 150

/t (/)

0 l-

V

100 j 1 T 0 ' 0

50 1

t ~ .,. i'

J ~ 0 ,

13 14 15

Neutroo Energy (MeV)

rio 4 - The excitation function of 4s Sc(n,2n)44mSc reaction o·

45Sc(n,2n)44mSc Reaction - The results of this study along with the other literature data are shown as a function of neutron energy in Fig. 4. Although, activation cross-sections data of 45Sc(n,2n)44msc reaction are abundant in literature, the discrepancies of some reported cross-section data need further investigation. The measured data in the energy range 13.90-14.63 MeV are well supported with the data reported in the handbook7 on activation cross­sections and by Miah . The cross-section value of the present experiment at 14.70 MeV gives good agreement with Arnold & Royburn '4. The other literature values for this reaction show some discrepancies than the measured data. However, the increasing tendency of the present data with increasing energy is similar to the literature data. The results of the model calculation using SINCROS-ll are reproduced as a curve which is appreciably higher than the measured and all of literature data. The curve could possibly be fitted to experimental data by adjusting some input parameters.

References

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2 Nubuhiro Yamamuro, A 1I11c1ear cross-section calculatioll system with simplified illput-format version-II (SINCROS­II) , Report, JAERI -M 90-006, Japan Atomic Energy Research Institute, Tokaimura, Feb ( 1990).

3 Kalka H, A model Jor statistical multi-step reactions (code EXIFON) INDC (GDR)-0601L, Sept (1990) .

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5 Miah R U, Ph.D thesis, Dhaka University, Bangladesh, (1996).

6 Bychkov V M, Zolatarey K I, Pashchenko A B & Pl yaskin V I, Rept INDC (ccp)-1 83/L ( 1982).

7 Handbook 0 11 Iluclear activatioll cross-sectiolls , Technical report series no 156, IAEA, Vienna ( 1974).

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12 Ikeda Y, Komo C, Oishi K, Nakamura T, Miyade H, Kawade K, Yamamota Y & Kotoh T , Activatioll cross­section measurements Jor Jusion reactor struc/llral

538 INDIAN J PURE & APPL PHYS, VOL 40, AUGUST 2002

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13 Perkin J L, Private communication. Quoted in report BNL-325, Suppl 2, (1966).

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measurements, Technical report series 227, IAEA (1983 ) 59.

16 Health R L, Gamma-ray .Ipectrwn cataloRlIe. Ge and Si detector spectra, 4th Ed, Original work published in March (1974), Electronic version with updated nuclear data and decay schemes added in Sept (1998).

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