Deterination of Neutron Bea Diaeter in 3 rd Horizontal Channel of Dalat Nulear Reator Nguyen S 1*, Dang L 1 and Ho HT 1 Dalat University, 01 Phu Dong Thien Vuong, Dalat, Vietna Nulear Researh Institute, 01 Nguyen Tu Lu, Dalat, Vietna Researh rtile Reeived date: 18/04/017 epted date: 03/05/017 Published date: 09/05/017 *For Correspondene Nguyen S, Dalat University, 01 Phu Dong Thien Vuong, Dalat, Vietna, Tel: (+84) 977363840. E-ail: sonna@dlu.edu.vn BSTRCT Neutron bea diaeter (NBD) is a very iportant paraeter in experiental nulear in the nulear researh reator. urate deterination of the NBD is the best ethod, whih akes an optial saple size orretly, to redue data analysis errors. To identify the NBD, we an use soe ethods: siulation by Monte-Carlo ethod, neutron iaging, and neutron ativation analysis. In this report, we deterined NBD of the 3rd horizontal hannel of Dalat nulear reator that ativated Gold foil. The results showed this ethod to be ore quikly and orret results, and experiental aterial ould reuse for another experient. Keywords: Neutron ativation analysis, Neutron bea diaeter, The 3rd horizontal hannel of Dalat nulear reator, Neutron iaging. INTRODUCTION Neutrons have played an iportant role in the haraterization, developent, testing and appliation of aterials over the past 70 years. Deterination of NBD in nulear researh reator (NRR) is neessary that build shielding syste, saple sharp, saple position. The orret NBD would redue the experiental result errors and hoose better nulear aterial shielding. Norally, three ethods deterined the NBD as the following: - Neutron iaging (neutron radiography); - Siulation; - tivation. The traditional experiental ethod deterined the NBD of the neutron hannel in the nulear reator was the neutron radiography (NR). The first suessful experients in neutron radiography were arried out in 1935 after the disovery of the neutron, by Kallann and Kuhn using a sall neutron reator [1,]. Thanks to this ethod, the NBD ould find the shape of neutron bea by a photo of the fil but it was unlearly. The sharpness of the neutron bea depended on the quality of fil, ativated tiing. So it was the ain restrition of the ethod. For siulation ethod, in the priniple, we ould alulate and siulate filtered neutron, and the NBD at any neutron paths of hannel of nulear reator [3,4]. However, oparison between the alulated and experiental results is ore differential results. Therefore, the ethod was to be prepared before to do the real experient, so it ould not replae epirial ethods. Typially, in the horizontal hannel of nulear reator, onstrution of the neutron bea guide onfigured out, and still adjusts aordingly that ust real experient. Reently, after setup guiding and fousing neutron beas, the experiental ethod often used to ativate Gold foil was deterined. Norally, the foil ativated by two ways as the following [5,6] : RRJPP Volue 5 Issue pril - June, 017 4
- Using ativated very sall gold foils, whih put surrounding the neutron bea position. fter gold foils were ativated, easured delay gaa fro sall foil we ould find the NBD; - Using ativated ore gold strings, whih arranged a grid. fter finishing ativation, ut the gold strings, easured delay gaa fro sall gold frations we ould find the NBD. However, the liits of two ways of this ethod were to be easured delay gaa several ties, easily istaken position of gold foils. The error of diaeter neutron depends on the size of the gold fration strongly. In this paper, we ativated foils whih are the sae aterial (this researh used gold foils, 197 u) and sae ativation position in the way of outoe neutron. This experient was set up in the 3 rd horizontal hannel of DNR. One gold foil is saller diaeter than the NBD and another is larger diaeter than the NBD. Thus, in this ethod, the sall foil would ativate whole its, and large foil would not ativate whole its. Dalat nulear reator (DNR) is a NRR, whih based on TRIG ark II design. It has 4 th horizontal irradiation hannels and theral neutron flux (n. -.s -1 ): + Tangential bea port No. 3: 1.4 10 6 (n, gaa) + Radial bea port No. 4: 1.8 10 7 (PGN, NDT ) + Radial bea ports No. : 1. 10 7 (PGN) + Radial bea ports No. 1: not used (Figure 1). Figure 1. The struture of horizontal hannels of DNR. The tangential bea port No. 3 (the 3rd horizontal) of the DRN was designed to transport neutrons to the theral neutron, where the instruent using the gaa-gaa oinidene spetroeter was installed. The previous researhes, NBD of the 3rd neutron hannels of DNR deterined neutron radiography. In the Figure, the NBD sharpness was not learly, the border was blurred, so the value of NBD was false. RRJPP Volue 5 Issue pril - June, 017 5
Figure. The sharpness of the neutron bea of 3rd hannel by neutron radiography. THEORETICL In the neutron ativation analysis, the inidene neutron flux oe to saple was deterined as the following funtion [7] : Net / t φth = S D C I θ ε σ N 0 γ where Net is the net area of the photoeletri peak; t is the ounting tie on seond (s); is the ass ato; S = 1 e λt is d the saturation fator; t is the irradiation tie (s); D = e λt λ is the fator deay tie; t d is the deay tie (s); 1 e t C = is the fator ounting ties; is the weight of the ativated saple (gra); I 0 is gaa intensity (gaa branh ratio, %); θ is abundane isotope; ε γ is effiieny of spetroeter at photoeletri gaa peak energy; σ is theral ross setion (barn); N is vogadro onstant nuber, N 6.0 10 3 ol -1 ). In the nulear reation, 197 u foil ativated neutron, foring 198 u, then deays inus beta, and 198 Hg prodution. 198 Hg would de-exite to gaa rays eitting. In this experient, gaa ray was seleted 411.8 kev interesting (beause 411.8 kev gaa ray has nearly 100% branh ratio). Figure 3 showed deay shee of 198 u [8]. λt (1) 197 79 u n + 1 0 198 79 + u.69d β 0.985%.5 ps 1087.7 kev ( + ) β 98.995% γ (1087.7 kev) γ (675.9 kev) β 0.05% 3.16 ps 411.8 kev ( + ) γ (411.8 kev ) 198 80 Hg 0 (0 + ) Figure 3. 198 u diagra shee. Beause the filtered neutron was sae aterials whole plaes, and neutron flux was sae value on the sae horizontal ross setions, so in the horizontal distane of NBD that has sae neutron flux values. Figure 4a desribed relative neutron flux values depended on NBD. RRJPP Volue 5 Issue pril - June, 017 6
φ 0 d/ d Figure 4a: The relative neutron flux depended on NBD. EXPERIMENT ND DISCUSSION Experiental Desription The experient established on the 3rd hannel of DNR. Figure 4b showed the 3rd hannel of DNR struture onfiguration. Output H O 15 80 Neutron bea 1500 Pb Si Paraffin-B 3150 H O ir Conrete Input H O Pup Figure 4b. The strutural onfiguration of 3rd hannel of DNR. The 3rd horizontal hannel syste onsists of the steel hollow ylinder whih has 03 outside diaeter, and 3150 length. Inside the ylinder, a silion rystal ylinder was to be filtered neutron, whih was neutron theralization; water was ontrolled neutron flux (open and lose neutron bea); paraffin-b, lithiu, adiu was neutron olliator; onrete, lead was shielding. The saple was ativated a sae plae where was 4 distane fro the end of the neutron olliator to outside and diretly opposite. fter the saple was ativated opletely and deayed, used the gaa HPGe detetor spetroeter, whih was 1.9 kev FWHM solution, 70% relative effiieny (133 kev), and the ount rate bakground was less 10 ps. Two ativated gold foils were produed by Russia, 197 u, 99.99% enrihent, 0.05 thikness. The sall foil is 1/4 inh (0.635 ) diaeter, and 0.0078 gras, another foil are 1 inh (.540 ) diaeter, and 0.651 gras, respetively. Two ativated gold foils were plaed onentri, right angle and sae position of neutron bea on the 3 rd horizontal hannel of DNR. Figure 5 showed the relative of NBD and foils. RRJPP Volue 5 Issue pril - June, 017 7
Figure 5. The relative of NBD and foils desription. (a) For the gold foil saller diaeter than NBD. (b) For the gold foil larger diaeter than NBD. RESULTS ND DISCUSSIONS Calulation the irradiation tie (t) was orretly so that it redued neutron sattering on foil. The foil was irradiated, delayed, and easured the gaa spetru with the appropriate tie, respetively. In the gaa spetru, as disset above, we only interested 411.8 kev gaa ray. To iniize errors in the ethod, we olleted the ount of 411.8 kev peak ore than 15,000 ounts, so the statistial error of 411.8 kev peak was <1%. The neutron flux followed forula (1) for two different gold foils were shown on the Table 1. Table 1. Soe inforation of gold foils and soe paraeter results in forula (1). Gold foil t (s) t d (s) t (s) S D C S D C Cps (411.8 kev) φ 10 5 (n/ /s) Diaeter (6.35 ) 3565 9575 4573.54 0.0106 0.9719 0.9355 0.0096 0.3471 1.6567 Diaeter (5.40 ) 160 57530 3838.16 0.0048 0.846 0.9943 0.0040 6.7319 1.833 In the results, the sall foil diaeter was ativated for whole saple, so the value of φ th alulated by forula (1) to orret, other hand, the large foil diaeter was not ativated, so φ th alulated by forula (1) to less neutron flux orretly. The less neutron flux alulated depended to the overweight that the weight foil was not ativated. By alulating and reduing the overweight, we have orret weight of saple that was ativated, and after that, we alulated auray the NBD. Return on the forula (1), theoretially, if the saple diaeter is not larger (saller until equal) than NBD then the forula (1) take aurate the neutron flux, and always give the real neutron flux (the neutron flux was onstant). On the otherwise, the forula (1) gave wrong neutron flux. For the sae aterial foils, the neutron flux was alulated by forula (1) to depend on Net / t, where is ass saple, whih was a funtion of radius of saple as the following: S D C = π r d ρ () Where r, d, and ρ is radius, thikness, and density of saple, respetively. Now, interesting the large foil, iaging the large foil devised two onentri irle parts whih one (inner irle) has 1 ass, and the diaeter of inner irle was equal the NBD, and the other (annular) has ass whih was overweight ass, so the ass of large foil was =1 +. In this researh, =1 + =0.4651 (g). Figure 6 showed iaging saple division. The inner irle The annular Figure 6. The divided saple two parts iaging. Fro forula (1), we have: Net / t X X φ = = = S D C I θ ε σ N ( + ) Net / t where X = S D C I θ ε σ N 0 γ 1 RRJPP Volue 5 Issue pril - June, 017 0 γ (3) 8
X If φ was obviously aurate neutron flux, then φ was ust equal φ =, where 1 was above value analysis. Divided X forula (3) by X 1 φ = : φ 1+ 1 1 = = φ X 1+ (4) 1 syste of equation for 1 and as the following: f 1.833 1 = = f 1.6567 + 1+ = 0.4651 (g) 1 The value of φ was also the neutron flux that olleted by sall foil, φ s. In this experiental result, for Table 1, φ s =1.6567 10 5 n/ /s, and φ=1.833 10 5 n/ /s. pplying for forula (5), the values of 1=- =0.3603 (g). Using the forula (), we have the final result of the inner irle diaeter was d=1.968, whih was also aurate NBD. The NBD error was deterined by onventional errors with 3 paraeter errors were: the theral neutron ross setion gold error, the effiieny detetor error of 411.8 kev peak, and the statistial ount error. ( σ) ( ε) ( N) ( ) ( ) ( ) d = + + = 1% + 3% + 1% = 3.3% So, when reduing the overweight of gold foil, whih was not ativated by this alulated ethod, the aurate NBD was d=1.968 ± 3.3 % (). CONCLUSION Thanks to the neutron ativation analysis, NBD of the 3rd horizontal hannel of DNR was identified. The ethod was siplified and exatly to deterine the neutron bea diaeter. This ethod was overae liitations of other previously experiental ways whih was the sae ativation ethod. The other benefit of this ethod was the gold foil ould use again or ore than one. The reused ativated gold was very siplified alulation, so the ethod reused experiental aterial. The errors in this ethod were redued until as best as possible by the ounting tie, the irradiation tie, and the deay tie adjustent. CKNOWLEDGEMENTS The authors would like to thank the leader of Dalat Nulear Researh Institute has supported and help in this researh. REFERENCES 1. Kallan H. Researh. 1947.. IE. Database of propt gaa rays fro slow neutron apture for eleental analysis, the IE in ustria. 007. 3. Nasientoa F, et al. Optiization of filtered neutron beas for the alibration of superheated droplet detetors at the RPI superheated droplet detetors at the RPI, Nulear Instruents and Methods in Physis Researh. 007;580:8-85. 4. Iván L and László K. Monte Carlo Partile Transport Methods: Neutron and Photon Calulations. 000. 5. Musa Y, et al. Deterination of radial and axial neutron flux distribution in irradiation hannel of NIRR-1 using foil ativation tehnique. nnals of Nulear Energy. 01;50:50-55. 6. Sogbadji RBM, et al. Deterination of Neutron Fluxes and Spetru Shaping Fators in Irradiation Sites of Ghana s Miniature Neutron Soure Reator (nsr) by tivation Method after Copensation of Loss of Exess Reativty. World Journal of Nulear Siene and Tehnology. 011;1:50-56. 7. IE. Use of researh reators for neutron ativation analysis. IE-TECDOC-115, IE, Vienna. 001. 8. Bé MM, et al. Table of Radionulides. Édité par le BIPM, Frane. 010. (5) RRJPP Volue 5 Issue pril - June, 017 9