-Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements
-
Upload
guenevere-adams -
Category
Documents
-
view
22 -
download
1
description
Transcript of -Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements
04/19/23 1
-Spectroscopy of Os-Isotopesß-Delayed Neutron Measurements
Irradiation position: Rabbit system #2
04/19/23 2
-ray detection with semi-conductors
-ray produces electrical charges in the semi-conductor. Total electric charge proportional to -ray energy.
Pulse heigth spectrum
++++
----
n-Ge p-Ge
-ray
200 400 600 800 10000
2000
4000
6000
8000
10000
12000
Cou
nts
KanäleEnergy (pulse heigth)
04/19/23 3
• (n,)-reaction produces 190mOs. 190mOs → 190gOs + • Low-level excited states correspond to rotational and vibrational excitation of the nucleus• Rotational energy as a function of total nuclear spin I:
))1((2
)(2
IIIErot
with I = 0, 2, 4,... (rigid rotator)
• Irradiation of natOs-sample: By (n,)-reactions production of 190mOs with T½ = 9.9 min• -Spektroscopy of irradiated sample after 2, 4, 6 ….20 min.
Determination of T½ for 190mOs and moment of inertia of the 190Os-nucleus for different I
-Spektroscopy of 190mOs
04/19/23 4
Decay scheme of 190mOs
))1((2
)(2
IIIErot
E(In+2 → In) = k [In+2(In+2+1)] – k [In(In+1)]
Measured Rigid Rotator ( = const.)
k
04/19/23 5
β-Delayed Neutrons
Fission of 235U:
Emission of 2.4 prompt Neutrons per fission event. Time scale: ca. 10-15 s
Prompt neutrons cannot be detected outside the reactor
Fission products:
Emission of a neutron if excitation energy of a daughter nucleus resulting from preceeding ß-decay is sufficiently high. Time scale: ß-decay half-life of precursor 87/89Br, 94Rb, 135Sb, 137I …… (T½= 2 - 56 s)
04/19/23 6
Properties of ß-Delayed Neutrons
0,0090,0270,009-----0,236
0,0180,0740,0134200,615
0,0680,2530,0726202,34
0,0440,1260,0654306,23
0,0630,1400,077560232
0,0070,0210,022250551
Yield for thermal fission [%]
233U 235U 239Pu
Energy
[keV]T1/2 [s]Gruppe
04/19/23 7
Sample
3He-Counting tube
Boron-carbide
Wood
Cadmium
PE
12 3He-Zählrohre:Efficiency………..18 %Background………4 cpm
DNAA: Delayed Neutron Activation Analysis • Cycle: 2 min. (100 kW) – 20 s cooling time – 1 min. Measuring time
• Detection of ß-delayed neutrons with 3He counting tubes via the reaction 3He(n,p)3H
• Irradiation and measurement of several U- and Th-samples with and without Cd-shield. Determination of the 235U- content in U-samples
Detection of ß-Delayed Neutrons
04/19/23 8
Spectrum obtained with 3He-counting tube
0 50 100 150 200 250 300100
101
102
103
104
105
106
107
Cou
nts/
Ch
ann
el
Channel
Delayed neutrons
-Back-ground
04/19/23 9
Calibration Curve for 235U
Without Cd shield
With Cd shield