3.3 Results and Discussion
The TOF spectra obtained by both methods, NRTA (dotted lines) and the selfindication method (solid lines), around the 4.9 eV resonance of
197 Au are shown in
Fig. 3.2. Neutron absorption resulting from the 4.9 eV resonance of
197
Au can be
observed as a dip and a lack of peak for the NRTA and the self-indication method,
respectively. Here the net area ratio R, which is defined as the ratio of resonance
absorption to the number of incident neutrons, is defined by
R ¼
X I max
i¼I min
C out, i À C in, i
ð
Þ =
X I max
i¼I min
C out, i ,
ð3:1Þ
where C i is the net counting rate of the i
th channel in the TOF measurement and the
subscripts “in” and “out” mean “with” and “without” sample. Background events
were estimated by TOF measurement without an indicator and subtracted from the
foreground TOF spectrum. The 4.9 eV resonance peak ranges from the I min
th to
I max
th channel. The net area ratios for the NRTA and the self-indication method can
be expressed as follows:
R NRTA ¼
Z E max
E min
1 À exp
À À nσ tot E
ð Þ
È
É
dE=
Z E max
E min
dE
ð3:2Þ
4.9 eV resonance
m
Fig. 3.2 Comparison of TOF spectra obtained by transmission method and self-indication method
for 4.9 eV resonance of
197
Au
24
J. Hori et al.