Hefei, Anhui, , P.R. CHINA b Institute of Management, University of Science and Technology of China, Beijing,

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This artile was downloaded by: [China Siene & Tehnology University] On: 27 November 214, At: 1:27 Publisher: Taylor & Franis Informa Ltd Registered in England and Wales Registered Number: 172954

1 This artile was downloaded by: [China Siene & Tehnology University] On: 27 November 214, At: 1:27 Publisher: Taylor & Franis Informa Ltd Registered in England and Wales Registered Number: Registered offie: Mortimer House, Mortimer Street, London W1T 3JH, UK Journal of Nulear Siene and Tehnology Publiation details, inluding instrutions for authors and subsription information: Measurement of Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel Bangjiao YE a, Rongdian HAN a, Zhongmin WANG a, Yangmei FAN a, Xiaoqi YU a, Huaijiang DU a & Zhenxi XIAO b a Department of Modern Physis, University of Siene and Tehnology of China, Hefei, Anhui, 2327, P.R. CHINA b Institute of Management, University of Siene and Tehnology of China, Beijing, 188, P.R. CHINA Published online: 15 Mar 212. To ite this artile: Bangjiao YE, Rongdian HAN, Zhongmin WANG, Yangmei FAN, Xiaoqi YU, Huaijiang DU & Zhenxi XIAO (1998) Measurement of Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel, Journal of Nulear Siene and Tehnology, 35:1, 1-5, DOI: 1.18/ To link to this artile: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Franis makes every effort to ensure the auray of all the information (the Content ) ontained in the publiations on our platform. However, Taylor & Franis, our agents, and our liensors make no representations or warranties whatsoever as to the auray, ompleteness, or suitability for any purpose of the Content. Any opinions and views expressed in this publiation are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Franis. The auray of the Content should not be relied upon and should be independently verified with primary soures of information. Taylor and Franis shall not be liable for any losses, ations, laims, proeedings, demands, osts, expenses, damages, and other liabilities whatsoever or howsoever aused arising diretly or indiretly in onnetion with, in relation to or arising out of the use of the Content. This artile may be used for researh, teahing, and private study purposes. Any substantial or systemati reprodution, redistribution, reselling, loan, sub-liensing, systemati supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of aess and use an be found at

2 Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 35, No. 1, p. 1-5 (January 1998) Measurement of Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel Bangjiao YE*>+, Rongdian HAN*, Zhongmin WANG*, Yangmei FAN*, Xiaoqi YU*, Huaijiang DU* and Zhenxi XIAO** * Department of Modern Physis, University of Siene and Tehnology of China **Institute of Management, University of Siene and Tehnology of China (Reeived February 3, 1997) The double-differential ross setions (DDX) of a-partile emission from the reation of 14.6 MeV neutrons with elemental nikel have been measured using a multitelesope system. The ross setions at sixteen reation angles from 25' to 164.5' have been obtained. The angle-integrated spetrum and the angular distribution of a-partile emission have been dedued from the DDX. The total a-partile emission ross setion was 12 & 8 mb. The present result was ompared with the evaluation of ENDF/B-VI and other measurements. KEYWORDS: MEV range 1-1, neutrons, neutron reations, double-differential ross setions, natural nikel, multitelesope system, nikel, alpha partiles, angular distribution I. Introdution Cross setion data for the reations of neutrons with strutural materials to produe a-partiles are very important for the evaluation of radiation damage and nulear heating in fission and fusion reators. The (n, za) reation leads to a buildup of helium gas, residual radioativities, and the prodution of reoils from the lattie. It also indues nulear transmutation, whih an affet the strutural strength of the materials. Theoretial understanding of the reation is limited by the signifiant unertainties in suh quantities as the level density parameters, the pre-equilibrium proess modeling, and the a-luster preformation probabilities. At neutron energies around 14 MeV, several reation hannels open. Consequently, the (n, za) reation ross setion is the sum of (n, a), (n, na), (n, an), and possibly (n, 2a) reation ross setions. Two methods are used to measure the helium prodution data. One method is the helium-aumulation with whih only the helium-prodution ross setion an be given. Another method is the diret detetion of a-partiles to obtain the double differential a-partile prodution ross setion. With the latter one an obtain the angular distributions as well as the a- prodution ross setions. However, there are two problems in DDX measurements of low ounting rates and high bakgrounds. The latter are due to y-rays oming from t,he (n, n'y), (n, 2n) and (n, y) reations and the bakgrounds are higher than the (n, za) reation ounts by a fator of lo3 to lo6 for an unshielded detetor. Over the past 2 years, some new detetion sys- * Hefei, Anhui 2327, P.R.CHINA. **Bezj'ing 188, P.R.CHINA. ' Corresponding author, Tel (), Fax. $ , bjye@lx4.mphy.ust.edu.n tems have been developed to detet a-partiles, for example, the harged partile time-of-flight (TOF) spetrometer at Ohio University(3), the magneti quadrupole spetrometer at Lawrene Livermore National Laboratory(4), the multitelesope systems at Vienna Univer- ~ity(~) and University of Siene and Tehnology of China (USTC)@), and the wide range harged partile spetrometers at Tohoku University") and Los Alamos National Laboratory@). The energy spetra and angular distributions of emitted a-partiles have been studied for some strutural materials with these detetion systems. Sine 1986 the researhers of USTC have built a multitelesope system similar to that of Vienna Uni~ersity(~). The energy loss (AE) signal, the pulse-shape disrimination (PSD) signal and the energy (E) signal are gathered and their ombinations are used to identify protons, a- partiles and y-rays. A thik target tehnique(g) has been employed to inrease the event rates and derease statistial errors. In this way it beame possible to measure the high energy parts of the spetra with muh better auray than with a thin target method, and also the results are muh less sensitive to the bakgrounds. Some (n, zp) reations have been studied by using this system(1 )-(12) This paper reports a measurement of DDX of a-partile emission from the natni(n, za) reation at a neutron energy of 14.6 MeV using the USTC system. 11. Experimental System and Proedure The USTC multitelesope system onsists of a twolayer ring-shaped energy loss detetor and a entral CsI(T1) energy detetor as shown in Fig. 1. The outer layer of the energy loss detetor onsists of 32 separate proportional ounter, whih are used to obtain the energy loss signals (A&) of harged partiles. The inner layer onsists of 16 separate proportional ounters, and their signals (A&) serve as one of the triple-oinidene 1

2 B. YE et al. Fig. 1 The USTC multitelesope system: (a) top view and (b) side view signals. A target foil was laid on one-half of the target holder (overed with a.

3 2 B. YE et al. Fig. 1 The USTC multitelesope system: (a) top view and (b) side view signals. A target foil was laid on one-half of the target holder (overed with a.3mm lead foil) and a lead foil for bakground-measurement was plaed on the other half of the target holder. Lead has very small ross setions of the (n, a) reation (<lmb). The two sets of outer 16 ounters for both foils were used for simultaneous measurement of the foreground and bakground, respetively. The top- and ground-plates of detetor system were overed with a 1-mm thik tungsten foil to stop all harged partiles produed in the plates. A CsI(T1) rystal, lmm in height and 25.4mm in diameter, was used as an energy detetor. A 2-m long Fe bar was used to shield the CsI(T1) detetor from neutrons. The distane between the neutron soure (T-Ti +-A & Csl TI) target) and the CsI(T1) was 4mm. The angular aeptane funtion of eah outer ounter was alulated by using a Monte-Carlo method (lo6 events) aording to geometri relation(13). Eah of the outer proportional ounters, in onjuntion with the entral CsI(T1) rystal, ats as a normal ounter telesope that allows measurement of partile energy and identifiation of partiles. The telesopes orrespond to reation angles of 25', 32.8', 43.9', 55.', 67.2', 77.1, 88.3", 98.3", 18.6", 117.9', 128.', 136.6', 144.3', 151.9", 157.8" and 164.5'. The proportional ounters were operated with a gas mixture of 95%Ar+5%C2 at a gas pressure of.1 MPa and at a voltage of -62V. An elemental nikel target with a.5 mm thikness and a 4 x 288mm2 area was used. The target thikness is seleted to be thik enough to stop the maximum energy a-partiles from the reation. Figure 2 is a simplified eletronis blok diagram. The eletronis system onsists of two parts: the eletroni signal readout iruits and the CAMAC data olletion system. For eah (n, za) reation event, five signals, AE, E, PSD, TIME and ADDR, are reorded sequentially on a disk in an on-line omputer. A harged partile produed by a neutron-indued reation at the target foil must traverse one of the outer proportional ounters and produes both analog and digital (ADDRess readout) signals. The digital signal is fed to an address logi and transformed into five-bit address that identifies the ative ounting wire. The analog pulse is amplified, and fed into a linear gate. At last, all 32 analog signals are ombined into one and fed into ADC. The CsI(T1) sintillator is used to produe both E and PSD signals. The PSD signal is fed into a slow oinidene (SC) iruit and the SC iruit produes an SC signal that ats as a strobing signal to open all ADC gates. The TIME signal was made by the time differene between the signals from one of the outer layer ounters and the CsI(T1) detetor. CAMAC Controller NIM Crate CAMAC Crate ComDuter +. **amplify, ADC * 'DE 32-outer - summing, signals linear gate, *E 16-inner addr. readout * TIME signals : oinidene, * PSD oder, deoder, CSI(T1) peak-keeper,et. ADDR. Signals Trigger On-line Computer Fig. 2 Blok diagram of the eletronis system JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

4 Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel 3 A new intelligent CAMAC rate ontroller was designed to ontrol the ADC iruits and ommuniate with the on-line omputer. Data are reorded in a buffer region of the CAMAC rate ontroller. When the buffer region is full or the olletion of data is ompleted, the data are read out and stored in a disk by the host omputer. Neutrons of 14.6MeV were produed by a 15-kV Cokroft-Walton aelerator at USTC. The target was irradiated for about 12 h at a neutron soure strength of 3 x lo9 nls. The neutron flux was determined by using the assoiated a-partile method. During the entire experiment, one bakground telesope was equipped with a weak 241Am a-soure to monitor the energy alibration of the CsI(T1) rystal. The energy resolution of the telesope is 8.% for the MeV a-partiles from the 241Am a-soure. The stability of the entire measuring system was heked ontinually by monitoring ount rates of the important signals. The target foil was rotated by 18' at the midpoint of the experiment to redue asymmetry effets between the two different halves of the reation hamber Data Analysis and Results Data analysis was performed aording to the following proesses. First the PSD spetra and the AE spetra were used to disriminate partiles. The PSD spetra show a good separation among protons, a-partiles and y-rays, as shown in Fig. 3. The two-dimensional spetra for ombinations of two of AE, PSD and E signals were used for further disrimination of partiles. Figures 4(a) to () show three two-dimensional spetra for AE-E, E-PSD and AE-PSD, respetively. From the AE-E spetrum we see that AE ahieves good separation in the low energy region, while PSD shows good identifiation in the high energy region as shown in the E-PSD spetrum. Combining the two advantages we 16 I I *' an identify partiles learly as seen in the AE-PSD spetrum. Then the hane oinidene ounts were eliminated by using the TIME spetrum as shown in Fig. 5. Bakground ounts were rejeted by subtrating the bakground spetrum from the foreground spetrum hannel by hannel as shown in Fig. 6. After these proesses the thik target a-partile emission spetra N(E, ) were obtained for the 16 reation angles. 224 = m W a 64 1 = u m g 128 w = 192 u 16 m e w a E (Channel) (a) AE-E spetrum PSD (Channel) (b) E-PSD spetrum ounts I I PSD Fig. 3 PSD spetrum for the natni(n, za) reation PSD (Channel) () AE-PSD spetrum Fig. 4 Two-dimensional AE-E, E-PSD and AE-PSP spetrums VOL. 35, NO. 1, JANUARY 1998

5 4 B. YE et al. Fig. 5 8oo L... % -. I L-...L Time (Channel) Time spetrum of the natni(n, za) reation Bakground Energy (Channel) Fig. 6 Foreground, bakground and net energy spetra for the natni(n, za) reation at 25' In order to obtain the double-differential a-partile emission ross setions, N(E, ) must be unfolded. This was done by numerially differentiating the quantity N(E, O)(dE/dz) with respet to d9), where (&/dz) is the speifi energy loss for a-partiles of energy &(I4). First the energy spetrum N(E, ) was multiplied by the (&/dz)(ei), where ~j is the energy of hannel i, and the resulting spetrum was differentiated by alulating giving the equivalent thin target spetrum. At last, the double-differential a-partile emission ross setions were obtained for the 16 reation angles as the following: d2a - AT'(&, 8) -- d&dq AaAR@,Snq ' (3) where AT'(&, 8) is the ounts in the energy region of E to E + AE and at the reation angle 8, ASZ the solid angle of the CsI(T1) detetor to the target, Qn the total neutron fluene, S the target area for eah telesope, n the number of atoms in a unit volume and q is the detetion effiieny. Figure 7 shows the double-differential ross setions at the reation angle 88.3". The data errors onsist of statistial errors of la and systemati errors. The total systemati error is 6.2%, whih onsists of the errors of the neutron flux 3.3%, the target height 2%, the solid angle of the entral detetor 3%' the de/dx value 2%, and the data redution proedure 2%' and other possible unertainties 3%. The angular distributions an be desribed well by a series of the Legendre polynomials up to 1 = 2 (4) The angle-integrated a-partile emission ross setions were derived from the least-squares fit of the Legendre polynomials up to 1 = 2 to the experimental d2u/d&dq values. Figure 8 shows the angle-integrated ross setions in omparison with the experimental results by Grimes et u1.(4) and Baba et az.('), and the ENDF/B- Fig E a v 4 b 1 m Alpha-partile energy (MeV) Double-differential ross setion of the natni(n, za) reation at 88.3' and at a neutron energy of 14.6 MeV Alpha-partile energy (MeV) Fig. 8 Angle-integrated a-partile ross setions of the nat Ni(n, za) reation JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel 5 t 1 11-13 MeV I 3 6 9 12 15 18 Reation angle (Deg.) Fig.

6 Alpha-Partiles Emitted from Interation of 14.6 MeV Neutrons with Elemental Nikel 5 t MeV I Reation angle (Deg.) Fig. 9 Angular distribution of a-partile emission from the nat Ni(n, za) reation VI evaluation. In the low energy region the present results are slightly higher than those of Grimes and Baba, but agree with their values within the quoted errors in the high energy region. The ENDF/B-VI evaluation is in good agreement with the present result in the low-energy region but slightly lower in the high-energy region. The experimental angular distributions of the a- partiles are shown in Fig. 9. In order to show the hange of the angular distribution with the a-partile energy, angular distributions are shown for three a-partile energy regions of 4-7MeV, 7-11MeV and 11-15MeV. They show a slight forward-bakward asymmetry in the higher energy region and the equilibrium emission is dominant. The total a-partile emission ross setion is obtained as 12 f 8mb. Figure 1 shows the total a-partile emission ross setion of natni in omparison with the experimental results by Graham et az.(15), Kneff et az.(16), Grimes et az.(*) and Baba et uz.(~), and the evaluations by ENDF/B-VI(17), JENDL-3(18) and CENDL-2(lg). The present result is in agreement with the results of Grimes et al. and Kneff et az. within the range of error. IV. Summary We have measured the double-differential natni(n, za) reation ross setion at a neutron energy of 14.6 MeV for 16 reation angles using a multitelesope system. Partiles have been identified by using two-dimensional AE-E E-PSD and AE-PSD spetra. A thik target tehnique was used to inrease event rates and derease statistial errors. The result is in good agreement with other experiment a1 results. ACKNOWLEDGMENT The authors would like to express appreiation to Prof. M. Baba for providing his experimental data whih have 1 Resentwork- A Graham x Knff o Grimes - Baba -IENDL3 - B-6..._- CENDLZ Neutron Energy (MeV) Fig. 1 Total natni(n, za) reation ross setions been used in this paper. We also aknowledge Dr. S. Chiba for his ritial review of this paper. This work was supported in part by the General Company of Nulear Industry of China and the Young Funds of USTC. We thank the Atomi Energy Soiety of Japan for the generous support given in publishing this paper. -REFERENCES- ( 1 ) Haight, R. C., et al.: Pro. Int. Conf. on Nulear Data for Siene and Tehnology, Gatlinburg, p. 275 (1994). ( 2 ) Takao, Y., et al.: JAERI-Conf 96-8, 165 (1996). ( 3 ) Saraf, S. K., et al.: Nul. Si. Eng., 17, 365 (1991). ( 4 ) Grimes, S. M., et al.: Phys. Rev. C, 17, 58 (1978). (5) Traxler, G., et al.: Nul. Instrum. Methods, 217, 121 (1983). ( 6 ) Ye, B. J., et al.: Commun. Nul. Data Prog., 1, 19 (1993). (7) Baba, M., et al.: Pro. Int. Conf. on Nulear Data for Siene and Tehnology, Gatlinburg, p. 941 (1994). (8) Sterbenz, S. M., et al.: ibid., p ( 9 ) Fisher, R., et al.: Phys. Rev., C 37, 578 (1988). (1) Ye, B. J., et al.: Nul. Si. Eng., 117, 67 (1994). (11) Ye, B. J., et al.: Nul. Si. Eng., 122, 136 (1996). (12) Ye, B. J., et al.: Nul. Phys. A, 612, 213 (1997). (13) Lin, G., et al.: J. China Univ. Si. Tehnol. 25, 25 (1995). (14) Ziegler, J. F.: "Helium Stopping Powers and Ranges in All Elemental Matter", Pergamon Press, New York, (1997). (15) Graham, S. L., et al.: Nul. Si. Eng., 95, 6 (1987). (16) Kneff, D. W., et al.: Nul. Si. Eng., 92, 491 (1986). (17) Evaluated Nulear Data File (ENDF/B-VI) Summary Doumentation, BNL-NCS17541, (1991). (18) Shibata, K., et al.: Japanese Evaluated Nulear Data Library, Version-3 (JENDL-3), JAERI-1319, (199). (19) Zhou, D., Zhang, J., Liu, T.: Chinese Evaluated Nulear Data Library (CENDL-2), Final Rep. for IAEA Contrat Nr. 5962/Rl/RB. VOL. 35, NO. 1, JANUARY 1998

SHIELDING MATERIALS FOR HIGH-ENERGY NEUTRONS

SHIELDING MATERIALS FOR HIGH-ENERGY NEUTRONS SHELDNG MATERALS FOR HGH-ENERGY NEUTRONS Hsiao-Hua Hsu Health Physis Measurements Group Los Alamos National Laboratory Los Alamos, New Mexio, 87545 USA Abstrat We used the Monte Carlo transport ode Los