Fission dynamics in the proton induced fission of actinide nuclei...
Transcript of Fission dynamics in the proton induced fission of actinide nuclei...
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E.M. Kozulin
Flerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia
Fission dynamics in the proton induced fission of actinide nuclei
at intermediate energies
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13, 20, 40, 55+ 242Pu → 243Am
13,20,40,55
20, 40, 55
+ 232Th → 233Pa
+ 238U → 239Np
MeV
Elab
The aim of the present work has been investigation more completely the proton induced reactions p + 232Th, 238U, 242Pu using the complex correlation measurements of the fission fragment mass and total kinetic energy distributions and of the double differential neutron and γ-rayspectra;
to investigate of super asymmetric fission mode connected with influence of the nuclear shells N=50 and Z=28(78Ni fission mode)
P
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small angular momentum transferred to the compound system;
the possibility to reach very low excitation energy of the compound system;
in contrast to heavy ion induced fission, there is no quasi-fission and inelastic processes in these reactions.
Fission reactions induced by light particles such as protons, neutrons etc. are interesting due to:
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Target
232Th, 238U,242Pu
F1
F2
solid angle – 0.3 sr
angular resolution – 0.30
TOF-startdetector
BeamP
position sensitivestop detector
x, y, TOF
mass resolution – 2 a.m.u
TOF-startdetector
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The measurements were carried out at the Accelerator Laboratory, University of Jyväskylä (Finland), using the setup that included:
the two-armed time-of-flight reaction products spectrometer CORSET built with the use of microchannel plates (MCP);
8 detector time-of-flight neutron spectrometer DEMON;
High Efficiency Neutron DEtection System (HENDES) facility to measure neutron multiplicity;
12 BaF2 detectors of γ-rays
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CORSETthe two-armed time-of-flight reaction productspectrometer CORSET composed of microchannelplates•Time resolution δt 120-150 ps•Mass resolution δΜ/Μ 2 amu•Angular resolution δΘ, δϕ ±0.3°•Solid angle of each arm 360 msr•Range of measured angles:
in the reaction plane Θ from 20°to 160° ±20°out of plane ϕ ±7°
DEMON8 detector time-of-flight neutron spectrometerDEMON using scintillation modules•Time resolution δt 1.5 ns•Neutron energy resolution - 4% at 3 MeV•Intrinsic efficiency 50% at 3 MeV
HENDESTime resolution δt 120-150 psIntrinsic effeciency 34% to 22% at 1-10 MeVPosition resolution ±5cm
BaF2 detectors12 detectors scintillation γ-quanta multiplicityspectrometer
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120140160180200220
T
KE
, MeV
242Pu(p,f)238U(p,f)
232Th(p,f)
01234
Yie
ld, %
140150160170180
,
MeV
60 80 100 120 140 1600
50100150200
σ2 T
KE, M
eV2
mass, u80 100 120 140 160
mass, u60 80 100 120 140 160
mass, u
AHy140 AHy140 AHy140
From top to bottom: two dimensional mass-TKE matrices, mass distribution of fission fragments, average TKE and square variance of TKE as a function of fission fragment mass for proton-induced fission of 232Th, 238U, 242Pu
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220 240 26080
100
120
140
160
243Pu233Th
132Sn
AH
AL
Mea
n m
ass o
f fis
sion
frag
men
t gro
up
Mass number of fissioning nucleus
239U
– our experiments
J.P.Unik et al., in Proc. Symp. Physics and Chemistry of Fission, Vol.2, IAEA, Vienna, 1974, 20.
The experimental mass distributions are similar for all studied reactions. The most probable mass of the heavy fission fragment for all target nuclei studied is close to the AH=140 (asymmetric mode S2). The origin of this mode could be attributed to the deformed neutron-shell closure N≈88 in the heavy fragments.
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120
140
160
180
200
220
TKE,
MeV
Ep=55 MeVEp=40 MeVEp=20 MeV
Ep=13 MeVp +232Th →233Pa
012345
Yie
ld, %
130
140
150
160
170
, M
eV
60 80 100 120 140 1600
50
100
150
σ2 TK
E, M
eV2
mass, u
80 100 120 140 160
mass, u
60 80 100 120 140 160
mass, u
60 80 100 120 140 160 180
mass, u
From top to bottom: two dimensional mass-TKE matrices, mass distribution of fission fragments, average TKE and square variance of TKE as a function of fission fragment mass at the proton energies 13, 20, 40 and 55 MeV
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60 80 100 120 140 16010-4
10-3
10-2
10-1
100
0
1
2
3
4
5
6
Yie
ld, %
Mass, amu
Yie
ld, %
Ep=13 MeV Ep=20 MeV Ep=40 MeV Ep=55 MeV
232Th(p,f)
The mass distribution in linear and logarithmic scale for the proton-
induced fission of 232Th at the proton energies 13, 20, 40 and 55 MeV
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70 80 90 100 110 12010-5
10-4
10-3
10-2
10-1
100
101
242Pu(p,f) Ep=13MeV 242Pu(p,f) Ep=20MeV 242Pu(p,f) Ep=55MeV 242mAm(nth,f)
Lohengrin data
mass, u
Yie
ld, %
A=78
Y=0.089% for the 242Pu(p,f) Ep=55 MeV
Y=0.035% for the 242Pu(p,f) Ep=13 MeV
Y=0.016% for the 242Am(nth, f)
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60 80 100 120 140 160 18010-410-310-210-1100101
242Pu(p,f)NCN/ZCN=1.56
mass, u
Yie
ld, %
60 80 100 120 140 160 18010-410-310-210-1100
238U(p,f)NCN/ZCN=1.57
Yie
ld, %
60 80 100 120 140 160 18010-410-310-210-1100101
232Th(p,f)NCN/ZCN=1.56
Ep: 13 MeV 20 MeV 40 MeV 55 MeVY
ield
, %
A=78
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Ion beams:
DEMON
CORSET
Gamma
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10-410-310-210-1
10-410-310-210-1
10-410-310-210-1
10-410-310-210-1
10-410-310-210-1
10-410-310-210-1
2 4 6 8 10 12 1410-4
10-310-210-1
2 4 6 8 10 12 14
Θ=14.50
φ= 00
p(13MeV)+232Th
Θ=29.50
φ= 00
Θ=44.50
φ= 00
Θ=59.70
φ= 00
Θ=89.20
φ= 00
Θ=119.20
φ= 00
Θ=164.00
φ= 00 Θ=-14.50
φ= 00
Θ=-29.50
φ= 00
Θ=-44.50
φ= 00
Θ=-59.70
φ= 00Θ=-89.20
φ= 00
Θ=-119.20
φ= 00
d2N
/dEd
Ω, M
eV-1st
r-1
E, MeV
Θ=-164.00
φ= 00
E, MeV
10-510-310-1
10-510-310-1
10-510-310-1
10-510-310-1
10-510-310-1
10-510-310-1
0 10 20 30 4010-5
10-310-1
0 10 20 30 40
Θ=14.50
φ= 00
p(40MeV)+232ThΘ=29.50
φ= 00
Θ=44.50
φ= 00Θ=59.70
φ= 00
Θ=89.20
φ= 00Θ=119.20
φ= 00
Θ=164.00
φ= 00Θ=-14.50
φ= 00
Θ=-59.70
φ= 00
Θ=-29.50
φ= 00
Θ=-89.20
φ= 00
Θ=-44.50
φ= 00
Θ=-119.20
φ= 00
En, MeV
d2N
/dE
dΩ, M
eV-1st
r-1Θ=-164.00
φ= 00
En, MeV
Double differential experimental neutron spectra (black points) and their decomposition (in assumption of three sources model) for proton-induced fission of
232Th at two proton energies Ep = 13 and 40 MeV
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In our experiments on the proton induced fission we extractedpre-equilibrium neutrons, and after we applied standardprocedure (three source model) on deducing neutronmultiplicities: pre-fission, and two post-fission multiplicitiesfrom both fragments.
After having received the number of pre-equilibrium neutrons, we corrected our mass distributions.
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poststpre2 2n,i nn n nn n n
stpre 2 stpre post 3/ 2 posti 1n n i i
M EM Ed M exp expdE d 4 (T ) T 2( T ) T=
< >< > ε ⎧ ⎫ ⎧ ⎫ε ε= − + −⎨ ⎬ ⎨ ⎬Ω π π⎩ ⎭ ⎩ ⎭
∑
n n n CN(FF) CN(FF) CN(FF) CN(FF) CN(FF)E 2 E E / A cos E / Aε = − Φ +
ΩΘ=110
φΘ=1080
φ
Θ=1080
φΘ=110
φ
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Average preequilibrium , average statistical prescission and postsscission neutron multiplicities as well as average γ-ray multiplicity , average energy emitted by γ-rays and average energy per one gamma quantum as a function of mass and total kinetic energy (TKE) of fission fragments were measured in proton induced reactions.
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70 80 90 100 110 120 130 140 150 160 1700,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
70 80 90 100 110 120 130 140 150 160 1700,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0p + 242Pu -> 243Am
mass [amu]
Ep=55MeVEp=20MeV
mass [amu]
p+ 238U -> 239Np
Ep=13MeV
Ep=55MeVEp=20MeV
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– Ep = 20 MeV
– Ep = 55 MeV
70 80 90 100 110 120 130 140 150 160 1700123456789
70 80 90 100 110 120 130 140 150 160 1700123456789
[ M
eV ]
Ep=55 MeV Ep=20 MeV
Ep=55 MeV Ep=20 MeV
p+238U->239Np
mass [amu]
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70 80 90 100 110 120 130 140 150 160 1700123456789
70 80 90 100 110 120 130 140 150 160 1700123456789
p + 242Pu -> 243Am
p+ 238U -> 239Np
Ep=55 MeV Ep=20 MeV
Ep=13 MeV
Ep=55 MeV Ep=20 MeV
mass [amu]
70 80 90 100 110 120 130 140 150 160 1700123456789
70 80 90 100 110 120 130 140 150 160 1700123456789
[ M
eV ]
p + 242Pu -> 243Am
p+ 238U -> 239Np
[ M
eV ]
Ep=55 MeV Ep=20 MeV
Ep=13 MeV
Ep=55 MeV Ep=20 MeV
mass [amu]
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80 90 100 110 120 130 140 150 160 1700
1
2
3
4
5
6
7
8
9
80 90 100 110 120 130 140 150 160 1701,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
p+242Pu->243Am
Ep = 13 MeV Ep = 20 MeV Ep = 55 MeV
mass [ amu ]
Ep = 13 MeV Ep = 20 MeV Ep = 55 MeV
70 80 90 100 110 120 130 140 150 160 1700
1
2
3
4
5
6
7
8
9
70 80 90 100 110 120 130 140 150 160 1701,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
Ep = 20 MeV Ep = 55 MeV
mass [ amu ]
p+238U->239Np
Ep = 20 MeV Ep = 55 MeV
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With help of average gamma-ray multiplicity we mayobserve the influence of shell effects (that isimportant, because our aim is to investigate the yield of doubly-magic 78Ni nucleus), the mean spinof the fragments.
With help of average neutron multiplicity we may obtainthe excitation of fragments, the level densityparameter.
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90 100 110 120 130 140 150 160 170
0,6
0,8
1,0
1,2
1,4
1,6
1,890 100 110 120 130 140 150 160 170
0
1
2
3
4
5
6
7
8
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
[ M
eV ]
mass [ amu ]
, and as a function
of single fragment mass. is taken from the paper
Budtz-Jørgensen and H.-H. Knitter, Nucl. Phys. A490 (1988).
252Cf
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70 80 90 100 110 120 130 140 150 160 1700123456789
70 80 90 100 110 120 130 140 150 160 1700123456789
p + 242Pu -> 243Am
p+ 238U -> 239Np
Ep=55 MeV Ep=20 MeV
Ep=13 MeV
Ep=55 MeV Ep=20 MeV
mass [amu]
80 90 100 110 120 130 140 150 160 1700,8
0,9
1,0
1,1
1,2
1,3
1,4
70 80 90 100 110 120 130 140 150 160 1700,8
0,9
1,0
1,1
1,2
1,3
1,4
mass [ amu ]
p+242Pu->243Am
[ M
eV ]
Ep = 55 MeV Ep = 20 MeV Ep = 13 MeV
p+238U->239Np
[ M
eV ]
Ep = 55 MeV Ep = 20 MeV
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70 80 90 100 110 120 130 140 150 160 170
0,75
1,00
1,25
1,50
1,75
2,00
2,25
2,50
70 80 90 100 110 120 130 140 150 160 170
0,75
1,00
1,25
1,50
1,75
2,00
2,25
2,50
mass [amu]
Ep=55MeVEp=20MeV
[M
eV]
mass [amu]
p + 242Pu -> 243Am p + 238U -> 239Np
Ep=13MeV
Ep=55MeVEp=20MeV
[M
eV]
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We observed the large enhancement of fission fragment yield for super asymmetric mode at AL < 80 in the proton-induced fission of 242Pu, 238U and 232Th at Ep= 55 MeV. Obtained results allow us to plan future experiments on the investigation of neutron-rich exotic nuclei with proton number around 28.
For the first time it has been obtained data on neutron and γ-rays emission in the coincidence with fission fragments for the reactions 232Th(p,f), 244Pu(p, f).The multiplicities and average energies of neutrons and γ-rays also confirm the suggestion about closed-shell structure of fission fragments with AL
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E.M.Kozulin, A.A.Bogachev, M.G.Itkis, J.Kliman, G.N.Kniajeva, L.Krupa, A.Yu.Chizhov
Flerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia
J.Äystö, W.A.Rubchenya, W.H.Trzaska, V.Lyapin, M. Sillanpää, S. Yamaletdinov, M. Mutterer
Department of Physics, University of Jyväskylä, Finland
E.VardaciINFN – Sezione di Napoli, Italy
A.M.StefaniniINFN - Laboratori Naziolali di Legnaro, Italy
S.V.KhlebnikovKhlopin Radium Institute, St. Petersburg, Russia
O. DorvauxInstitut de Recherches Subatomiques, CNRS-IN2P3, Strasbourg, France
F. HanappeUniversite Libre de Bruxelles, Belgium
Spokesperson: E. Kozulin