Neutron Activation Cross Sections for Fusion

Adelle Hay

The University of York/Culham Centre for Fusion Energy

March 30, 2015

Adelle Hay (UoY/CCFE) Neutron activation cross sections March 30, 2015 1 / 17

Overview

1 Introduction

2 Validating Cross-section DataDifferential and Integral Data

3 Experimental Procedure and Activation AnalysisExperimental ProcedureAnalysis of ASP data

4 Current Work

Motivation for Determination of Cross-sections

Single D-T reaction releases a 14 MeV-neutron, which can activatefirst wall components.

Neutron activation cross sections must therefore be known to a highprecision to aid in the design of first wall components.

Inventory code (FISPACT) used to determine how long materials canbe left in the tokamak until they need replacing.

Results from FISPACT also help determine the safest way ofconducting maintenance.

Aim: To Validate Existing Cross-section Data

Ÿ2233 nuclidesŸStable and isomeric states (T ½ > 1s)

EAF-201066256 neutron induced reactions

5096 important reactions

2265 major reactions

1728 reactions with any experimental data

470 reactions with integral data

European Activation File (EAF): neutron cross sections

Cross sections

Validation: SACS

Validation: C/E

Decay data

Ÿ816 targets (H-1 to Fm-257)Ÿ86 reaction types

γ3 mins

stable

10.64 hours

0.3 μs

60.55 mins

Experimental and Theoretical Cross-Section Data

Validation of EASY-2007 using integral measurements UKAEA FUS 547 (2008)

C/E values

Differential and Integral Data

To validate cross-section data, require:

Integral results in several complementary neutron spectra.

Adequate experimental differential data.

Differential Data:

Cross-section measurements taken at a single, well-defined incidentneutron energy.

E.g. Neutron time-of-flight data.

Integral Data

Neutron energy spectrum with wide peaks, eg:

Experimental Procedure

ASP facility at AWE. Fusion Engineering and Design 87 (2012) 662666

Deuterons accelerated towards a tritiated target.

D-T fusion reaction releases 14 MeV-neutrons.

14 MeV-neutron beam irradiates a thin (0.5mm), cylindrical(diameter 5 - 12mm) foil of chosen material.

The foil is moved (remotely) from the irradiation site to the HPGedetector.

ASP facility at AWE.

Data from the ASP neutron generator is considered integral at theposition of the rabbit system.

Due to a broad neutron energy peak.

Beam is roughly the same diameter as the foil.

Foil further away = consider the data differential. Too much flux lostat this distance.

Reactions

Activation Analysis

time, t (s)

activity, A (Bq)

t = delay time (transfer time) t = measurement timed m

t = irradiation time0

A0 = Nφσ(

1 − e−λt0)

σ =A0

Nφ (1 − e−λt0)

A0 = activity at time t0

N= no. of atoms in sample

σ = neutron activation cross section

φ = neutron flux

λ = decay constant

Glenn F. Knoll, Radiation Detection and Measurment, John Wiley and Sons

Activation Analysis

time, t (s)

activity, A (Bq)

A0 = Nφσ(

1 − e−λt0)

σ =A0

Nφ (1 − e−λt0)

φ = neutron flux

λ = decay constant

Activation Analysis

time, t (s)

activity, A (Bq)

A0 = Nφσ(

1 − e−λt0)

σ =A0

Nφ (1 − e−λt0)

φ = neutron flux

λ = decay constant

Experimental Determination of Cross Section

time, t (s)

counts per live second, C

C (t) = C0exp

(− ln2

[t + td ]

C0 = count rate at time t0

= half life of radioactive daughter

Iγ = intensity of γ peak

ε = absolute efficiency of detector

M. R. Gilbert, L.W. Packer, and S. Lilley, Nuclear Data Sheets, Article DC8, 2013

time, t (s)

C (t) = C0exp

(− ln2

[t + td ]

time, t (s)

C (t) = C0exp

(− ln2

[t + td ]

Corrections to Data Analysis and Automated Processing

True coincidence summing effects.

Consderation of errors, and how to correctly carry these through the dataanalysis.

Making the equations used for calculating differential cross-sectionssuitable for integral data:

Variation of neutron energy with time.

Variation of flux with time.

Aim: to produce a robust, standard method of calculating cross-sectionsand associated error using integral data.

Gamma Spectroscopy at Culham

Characterisation of detectors recently available at Culham:

Well detector

Compton-suppressed BEGe detector

Co-axial HPGe detector

Acknowledgements

Supervisor: David JenkinsThe Nuclear Physics Group, The University of York

Supervisor: Steven LilleyThe Applied Radiation Physics Group, CCFEAndrew Simons, and the ASP team at AWE

Neutron Activation Cross Sections for Fusion

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