Fission Product Yield Data for the Transmutation of Minor Actinide ...

where N C , N U are the modified and unmodified
mass distributions respectively, and s is the rms width
associated with the mass resolution (full width at
half maximum) given above.
These measurements involved the kinetic
energy, time of flight correlation method. The yields
of all fragments were measured simultaneously and
the systematic uncertainty due to the individual
measurements of the product nuclides in the radiochemical
method was avoided. Compared with the
radiochemical and mass spectrometric methods,
more nuclides were measured and the mass range
was wider. Since this study involved a two
dimensional (coincidence) measurement, and the
intensity of the source was low (3 × 10 5 fissions per
minute), the counting statistics were poor (only
~350 counts at the peak maximum) and the
statistical uncertainty was large. No uncertainty was
given by the authors in the paper, nor included in
the EXFOR entry. The main uncertainty was
statistical and assigned as 5% for the peak yields
(Y 0 ), whereas others were given as 5(Y 0 /Y) 1/2 %.
3.3.2.2. Thierens et al. [3.3.4]
The chain yields of 43 product nuclides were
determined by means of the catcher foil technique
and by g ray spectrometry using a Ge(Li) detector.
The intensity of the source was 1.2 × 10 6 fissions/min,
and the efficiency of the detector was calibrated to
within an uncertainty of about 5%. The uncertainty
from g peak area statistics was negligible. The chain
yield was derived from the measured CU yield by
adjusting the measured data using the charge distribution
formula, with c = 0.8:
1 È ( z-zp) pz ( ) = exp Í-
p c
ÎÍ
c
88
(3.3.2)
Gamma decay data were originally taken from
Nuclear Data Sheets, Nuclear Physics and other
literature published from 1972–1975. Most of these
data have been subsequently updated, and therefore
they were modified by using the newly recommended
data taken primarily from the CNDC evaluation and
Table of Isotopes [3.3.16]. Adjustment factors (b)
were based on the g ray measurement technique and
were calculated as follows:
(1) Yield was determined by one g ray, and b = I 0 /
I S, where I 0 is for the g ray intensity used by
the author, and I S is the new g ray intensity;
2
˘
˙
˚˙
(2) Yield was determined by multi g rays, and
, where W = Sw 1 I 0
b = Âw
i and
W i I
;
(3) Yield was determined by M product nuclides
and Nj g rays for j-th nuclide, ,
i
Si
-2
Wi = DI0i 1 1
I 0 ji
b = Â Â
where subscript i is for a g ray and j is for a
nuclide.
3.3.2.3. Blachot et al. [3.3.5]
Chain yields for 27 masses were measured by
using aluminium catcher foils for fission fragments.
The intensity of the source was 5 × 10 6 fissions/s and
the irradiation time was 1–17 d. Fission products
were first separated chemically into fractions
containing rare earth, alkali and alkaline earth
elements, ruthenium, zirconium and niobium.
Thereafter, the g rays of the individual nuclides
were measured with a Ge(Li) detector of energy
resolution 2.5 keV at 1.3 MeV. The sum of yields
under the heavy mass peak was normalized to a
total of 100%, giving a yield of 6.05 for the 140 Ba
monitor to which the other product yields were
normalized. To obtain the total chain yield for each
mass, the measured CU yield of a product was
adjusted for the independent yields of the nuclides
following the measured product in the mass chain,
using a charge distribution formula of the form of
Eq. (3.3.2).
As one of the two primary monitors, the yield
for 140 Ba (in fact, for the A = 140 mass chain) was
carefully evaluated in this work (see below), and a
value of 5.674 ± 0.098 was obtained. Then the data
were modified relative to this new monitor value.
The data at A = 99, 111, 117, 135, 137 and 149 were
discarded, as they were either too large (A = 149) or
too small (other A).
3.3.2.4. Nervik [3.3.6]
M N
j
The R values of 36 fission product nuclides
(A = 77–166) were measured by the radiochemical
method. Fission products were collected with an
aluminium catcher foil, chemically separated, and g
or b radiation was measured with a NaI detector or
b counter. The intensity of the 252 Cf source was 1 ×
10 6 /m, 2 × 10 7 /m or 7 × 10 7 /m. R values were
determined relative to the same nuclides measured
for 235 U thermal neutron fission and the 99 Mo yields
from 235 U thermal neutron fission and 252 Cf
spontaneous fission. Chain yields were calculated
using yield values of 6.14 for 99 Mo from 235 U
j
i
I
Sij