240,242Pu(n,f) measurement @ n_TOF

A. Tsinganis (CERN/NTUA), E. Berthoumieux (CEA Saclay),M. Calviani (CERN), V. Vlachoudis (CERN)

n_TOF Annual Collaboration MeetingLisbon, December 13-15, 2011

Outline PART I Samples & detector

Samples The Micromegas chamber Mounting the samples Mounting the chamber in the EAR

PART II Data and analysis

Data Preliminary analysis

Part III Simulations

Technique Results End goals

Conclusions / To do

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Introduction An (n,f) measurement on 240,242Pu… …using a Micromegas detector (FIMG – FIssion MicromeGas)

Proposal CERN-INTC-2010-042 / INTC-P-280 (21/05/2010) http://cdsweb.cern.ch/record/1266869/files/INTC-P-280.pdf

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

PART I :Samples & detector

Samples Eight (8) samples (4 x 240Pu, 4 x 242Pu) received from IRMM (Geel)

3 cm diameter Chemical form: PuO2 (plutonium oxide) 0.25 mm aluminium backing (5cm diameter)

Mass ~ 3.5 mg (Pu-240, 99.89%) ~ 3.0 mg (Pu-242, 99.97%) Surface density 0.10-0.13 mg/cm2

Total mass is lower than included in proposal

Activity 27.3 MBq (Pu-240) 1.2 MBq (Pu-242)

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

The Micromegas chamber

Designed to hold up to 10 samplesand microbulk Micromegas detectors …although with some difficulty BNC connections for signals and HV Aluminium chamber Kapton windows

Gas 88% Ar 10% CF4

2% iso-C4H10 (isobutane) 1 bar

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Mounting the samples Mounting carried out in ISOLDE lab under strict RP supervision Samples placed in appropriate holders for mounting

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Mounting the samples and detectors Detectors mounted similarly on the internal frame Finally, the setup looks like this

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Mounting the samples A 235U sample (for reference) and an empty frame also mounted

Samples and connection arranged as shown

EMPTY Pu-240 Pu-242U-235

BEAM

10 9 8 7 6 5 4 3 2 1Vd1 = 400V

Vd2 = 400V

CAEN multi-channel HV supply

Conventional HV supply

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Mounting the detector in the EAR FIMG chamber placed downstream of the TAC

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Mounting the detector in the EAR 16-channel preamplifier

Constructed at INFN-Bari, based on FIC electronics Electronic protection in place to prevent channel breakage (quite effective, short of 100%) A second module is available (we have 2 broken channels)

Shielding of pre-amp necessary to reduce γ-flash oscillations Also HV filters replaced with better shielded ones (provided by E. Griesmeyer)

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

PART II :Data & analysis

Data Sample signals

Baseline oscillation after γ-flash (down to a few MeV)

Obvious difference in α-activity

Pu-242 Pu-240

FFα

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Baseline oscillations - grounding EAR-1 grounding

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Data Data acquisition in parallel with C6D6 (Ni-58, U-236) and TAC

(U-236) measurements Removed for U-238 TAC measurement

Total protons: ~ 5 x 1018 (beginning of July – mid-September) Still short of proposed 8.0 x 1018

Furthermore, the proposal was based on higher mass and assuming fission collimator setup

Size of data is considerable Lengthy retrieval, ROOT-file creation and processing times! Quota issues on lxplus

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis The high α-activity of the 240Pu samples makes the pulse

recognition routine unworkable in its present form Routine to be adapted to tackle the problem

The preliminary analysis has thus focused on the 235U reference sample (high counting rate) and 242Pu

The analysis routine for the Diamond detector data (developed by Carlos & Christina) has been used to create the DST files

Retrieval of data very slow due to size of files ROOT files have been created for only a limited part of acquired data

(10% of 2011 statistics)240,242Pu(n,f) measurement @ n_TOF

n_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis Artefacts due to γ-flash oscillations

U-235

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis Artefacts due to γ-flash oscillations

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis Artefacts due to γ-flash oscillations

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis Amplitude spectrum – alpha/FF separation

U-235

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Preliminary analysis U-235 resonances 1-10eV

Compared with ENDF VII

Preliminary analysis Pu-242 at threshold

Compared with ENDF VII

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

~10% of 2011 statistics

PART II :Simulations

Simulations FLUKA simulations

Attempt to reproduce signals from α-particles and fission fragments α-particles and fission fragments studied separately Initial position sampled randomly within the sample volume Particles emitted isotropically within 2π solid angle

Alpha-particles Energy: 5.2MeV

Fission fragments Mass and energy systematics from G.D.Adeev et al., Preprint INR 861/93

1993240,242Pu(n,f) measurement @ n_TOF

n_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations Simplified geometry created in FLUKA

Simulation of samples and active detector volume Energy deposition along z-axis is scored event-by-event

From energy deposition to charge (~26eV / electron-ion pair)

Sample

Gas

dE/dz

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations Electron drift velocity calculated for given gas mixture and drift

voltage …using GARFIELD

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations Simplified geometry created in FLUKA

Simulation of samples and active detector volume Energy deposition along z-axis is scored event-by-event

From energy deposition to charge (~26eV / electron-ion pair) Electron drift velocity calculated for given gas mixture and drift voltage

…using GARFIELD …we can thus calculate the current reaching the readout electrode This signal is passed through a CR-RC circuit to obtain the final pulse

Typical amplifiers use a CR-(RC)4 circuit to achieve a quasi-gaussian pulse shape

Sample

Gas

dE/dz

V

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations: data reconstruction A large time window is selected in which we randomly add:

White noise

α-particle and fission fragment pulses …at appropriate rates

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations: data reconstruction Total (mixed) signal:

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations: data reconstruction Each component is known…

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Simulations: data reconstruction …we can therefore apply the pulse recognition routine used for the

experimental data and attempt to reconstruct an amplitude spectrum

Amplitude

Coun

ts

Amplitude cut

Fission fragments

α-particles

Noise

The quality of the α – FF separation can then be estimated

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

Conclusions To do:

Fix analysis routine to address: γ-flash oscillation α-activity in 240Pu

Carry on with data processing and analysis (obviously) Finalise simulations

Create realistic signals for different count rates Pulse recognition routine Study α – FF separation

Compare with experimental amplitude spectrum Study pile-up probability Detector efficiency Once simulations are in place, the same technique can be used for the fission tagging

measurements FIMG chamber with Pu samples presently stored by RP in view of the 2012 run

Accumulate as much statistics as possible within 2012 planning Actions during winter shutdown

Address grounding issues in EAR-1 (general action) Investigate shielding improvement of pre-amp box 240,242Pu(n,f) measurement @ n_TOF

n_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.

The end

240,242Pu(n,f) measurement @ n_TOFn_TOF Annual Collaboration Meeting – Lisbon, December 13-15, 2011 | A.T.