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