Neutron Capture Cross Sections from 1 MeV to 2 MeV by Activation Measurements Korea Institutes of Geoscience and Mineral Resource G.D.Kim, T.K.Yang, Y.S.Kim, H.J.Woo, H.W.Choi, and W. Hong Korea Atomic Energy Research Institutes J.H.Chang

Introduction Activation method : Historically first means of measurement of NCCS in MeV range relatively simple to carry out completely selective for a given nuclide in a mixture of target isotopes Energies : 1 MeV to 2 MeV fusion reactor material research Material : 63 Cu and 186 W Mono-energetic fast neutrons source : 3 T(p,n) 3 He reaction. In KIGAM NCCS are being measured by activation method In KIGAM neutron facility Proton energy stability of the used accelerator : within 1keV Producible maximum neutron energy : 2.6 MeV

Target Analysis RBS ERD T : 4.6 x atoms/cm 2, Ti : 1.4 x atoms/cm 2 TiT target

Neutron Energy Spread  measured 2 =  resonance 2 +  tithick 2, : NES 1.3 % at 2.1 MeV NES 1.7 % at 1.67 MeV

Neutron Pulse Shape and Height Spectrum

KIGAM neutron facility detector sample beam Cooling system monitor Target chamber

D = N o  act (1-ee1-e R  d - t 1 - t 3 )( D   gamma counts per unit time, N o : areal density of sample  : neutron flux,  act : neutron captured cross section : decay constant of activated sample t 1 : neutron irradiation time t 2 : elapsed time from irradiation to measurement t 3 : measured time of gamma ray, R : transition probability  d : absolute gamma ray efficiency - t 2 ) Neutron Captured Cross Section

f(t) ;time dependence factor, subscript “ o ” refers to standard reaction D o = N o  o  o R o  o f o / o …… (1) D = N   R  f/  …… (2) (1)/(2)  = D o N  R  f o D N o  o R o  o f o oo =0.693/t ½,   /  = (ph o /t o )/(ph/t), t :neutron irradiation time  = D o N (ph) t o R  f t 1/2,0 D N o (ph) o t R o  o f o t 1/2 oo

Characteristics of Sample Purity(%)Weight(g)diameterThickness (cm) Density (g/cm 3 ) Molecular weight (g) Areal Density (10 22 ions/cm 2 ) Au Au Cu W Abundance : 63 Cu = 69.2 %of Cu, 186 W=28.6 % of W

Absolute Efficiency of HPGe detector speciesGamma energy [keV] Thickness [mm] Calculated efficiency Au or or Cu W By MCNP code and standard mixed source

Transition Probability transitionGamma energy [keV] Transition probility 198 Au- 198 Hg(  - ) Cu- 64 Ni(  + ) W- 187 Re(  - ) By Table of Isotopes

Gamma Spectrum of 198 Au 411 keV

Gamma Spectrum of 64 Cu 511 keV

Gamma Spectrum of 187 W and Background

Neutron energy(MeV)Irradiation time(hr) Elapsed time from irradiation to measurement (hr) Neutron fluxGamma counts (n,  )cross section (mb) Statis- tical Error (%) Au ,542,3795, Cu ,578,8931, Au ,793,8965, Cu ,720,6481, Au ,319,2124, Cu ,460,9251, Au ,444,7514, Cu ,014,7621, Measured Data Table

Neutron Captured Cross Sections of 63 Cu

Neutron Captured Cross Sections of 186 W

 t  ln IoIo I () NoNo I : neutron counts in sample – in I o : neutron counts in sample-out N o : areal density of sample In scattering correction factor D  t = (  /4) (DL/L 1 L 2 ) 2  n (0 o )  n (0 o )= (kR +1) 4 /4k 2 : diffraction theory based on a continuum model R = 1.33 A 1/ cm, D is diameter of detector L is distance from target to detector, L 1 is distance from target to sample L 2 is distance from detector to sample Total Cross Section

Total Cross Sections of Cu

Total Cross Sections of W

Results Neutron capture cross sections of 63 Cu and 186 W Total scattering cross section of Cu and W Geometric Efficiency of HP Ge detector