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Page 1
Cross-sections of Neutron Threshold Reactions studied
by activation methodAnne Larédo
Supervisor: Dr. Vladimír Wagner
Nuclear Physics Institute, Academy of Sciences of Czech RepublicÉcole des Mines de Nantes (France)
Page 2
Plan
Introduction
Uppsala experiment
Spectrum analysis
Cross section measurements
Incertainty calculation
Correction calculation
Page 3
Introduction
Threshold reactions on Au, Al, Bi, In, Ta, Ni, Zn, Y, I
Up to now almost no experimental cross-section data for high energy neutron reaction (E>20MeV)
The Uppsala experiment enable new cross-section measurements for high energy neutrons (62 to 93 MeV).
My work consists in analysing the gamma spectrum resulting from the experiment to obtain experimental cross-sections.
Page 4
Uppsala experiment (1/2)
Took place in February 2010 in Uppsala, Sweden
Neutron source : • quasi-monoenergetic• based on reaction 7Li(p,n)7Be• energy range 11-175 MeV
Proton beam energies : 62, 70, 80, and 93 MeV
Page 5
Uppsala experiment (2/2)
Threshold reactions on Au, Al, Bi, In, Ta, Ni, Zn, Y, I
Al Au Bi Co In Ta
Experimental disposition
Page 6
Spectrum analysis(1/5)
Gamma spectrum peak analysis using DEIMOS32 software
Page 7
Spectrum analysis(2/5)
Gamma spectrum for different neutron energy and different time
MeV File Treal [s]62 S6RBiP21 3787
S6RBiP22 7224S6RBiP23 37749
65 S62BiP11 4207S62BiP12 37288S62BiP13 85038
70 S70BiP21 3869S70BiP22 7214S70BiP23 24597
80 S80BiP21 3654S80BiP22 7246S80BiP23 21830
93 S93BiP21 3410S93BiP22 23916
Page 8
Spectrum analysis(3/5)
Possible reactions and isotopes producted by these reaction enable to know what we are looking for.
Page 9
Spectrum analysis(4/5)
Determination of present isotopes using the result tables from DEIMOS32 compare to data base (decay data search) on gamma radiations.
..\ANALYSIS\Bi analysis - 4.xlsx
energy609.341661.331663.686670.542791.292802.949820.181824.982847.027880.860897.180899.119910.444911.707912.831918.113983.846
Page 10
Spectrum analysis(5/5)
10 isotopes found from (n,2n) to (n,9n) reactions
Isotope1 201Bi2 202Bi3 203Bi4 204Bi5 205Bi6 206Bi7 207Bi8 208Bi9 201Pb
10 203Pb
Page 11
Cross-section measurement(1/4)
Determination of Nyield
)()(
)(
11
1
)(
)( 0
irrreal tirr
t
t
foillive
real
areaP
aabspyield e
t
e
e
mt
t
CCoiEI
BECSN
Peak area Self-absorption correction
Beam correction
Dead time correction Decay during cooling and measurement
γline intensity
Detector efficiency
Correction for coincidences
Square-emitter correction
Weight normalization
Decay during irradiation
Page 12
Cross-section measurement(2/4)
First approximation of Nyield
)()(
)(
11)(
0
irrreal tirr
t
t
live
real
P
pyield e
t
e
e
t
t
EI
SN
))).(ln()).(ln())².(ln()ln(.exp()( 43 EeEdEcEbaEP
• Detector efficiency determination
080924654,0
127329,2
834704,20
083642,89
19554,144
e
d
c
b
a
Page 13
Cross-section measurement(3/4)
)()(
)(
11)(
0
irrreal tirr
t
t
live
real
P
pyield e
t
e
e
t
t
EI
SN
Peak area Sp : given by DEIMOS for each peak
γline intensity Iγ : from decay data search
treal : data from experiment
tlive : data from experiment
Decay constant λ :
T1/2 : data from libreries as decay data search
t0 = Beam end – start of measurement
tirr : time of irradiation
2/1
)2ln(
T
Page 14
Cross-section measurement(4/4)
Afoiln
yield
NmN
ASN
..
..
Nyield : previously calculate
Nn : number of neutrons in peak (per cm²)For experiment condition and energies
MeV Nn
65 2,9820E+0970 5,3165E+0980 6,3691E+0993 7,6936E+09
Foil mass mfoil (given data from experiment)
Foil size S : (2,5)² cm² = 6,25 cm²
Relative mass A : 208,98 [g.mol-1]
Avogadro’s number NA = 6,022.1023
Page 15
Incertainty determination(1/4)
i
NN i
averageyield _
First approximation :
Nyield_average : mean of Nyield for a same neutron energy
Ni : Nyield for a neutron energy
Precise analysis :
n
i i
n
i i
i
averageyield
N
N
N
N
12
12
_ 1
Page 16
Incertainty determination(2/4)
With :
ideimosi NaerrN .
aerrdeimos : incertainty on the peak area from the software Deimos32
n
i i
averageyield
N
N
12
_1
1
Then :
Page 17
Incertainty determination(3/4)
Next step :
)1(1
2
2_
2
nn
N
NN
X
n
i i
iaverageyield
If:
2_
2 .yincertaint1 XNX averageyieldElse :
averageyieldNX _2 yincertaint1
..\ANALYSIS\Bi analysis - 4.xlsx
Page 18
Incertainty determination(4/4)
Last step :
combinaison of the relative uncertainty (from the Deimos data) with the uncertainty from intensity, neutron spectra, detector uncertainty :
ΔNyield_average : Deimos uncertainty 10% : Beam intensity uncertainty 10% : neutron spectra uncertainty 3 % : detector efficiency uncertainty
Finally:
2222_. etectoreutroneamaverageield DNBN
..\Results - Cross-section graphs\XS Bi vysledne srovnani.xls
Page 19
Results (1/7)
Bi207 : The results for this isotope are for
now out range. Current work : using
spectrum from after and before irradiation
to soustract the gammas which are not from
the irradiation we are interrested in but
from previous one.
Page 20
Results (2/7)
Bi206 : very small incertainty
Page 21
Results (3/7)
Bi205 :
Page 22
Results (4/7)
Bi204 :
Page 23
Results (5/7)
Bi203 :
Page 24
Results (6/7)
Bi202 :
Page 25
Results (7/7)
Bi201 :
Page 26
Correction calculation
COI : correction for coincidences between severals gamma rays of an isotope.
..\COI\COI calculation.xlsx
Ba : Beam correction
..\beamcorr-Upps2010.xls
CS-A : Self absorption correction
..\Self-absorption\Self-absorption correction
.xlsx
Background correction..\ANALYSIS\Bi analysis - 4.xlsx
Dabs e
DC
.1
.
Page 27
Conclusion
Now the first result for the cross section are calculated.
We compared experimental datas to theorical model.
Most importants correction have been added
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