N_TOF (neutron Time-of-flight @ CERN) n_TOF (neutron Time-of-flight @ CERN) Nicola Colonna Istituto Nazionale Fisica Nucleare, Sez. di Bari [email protected]

n_TOF(neutron Time-of-flight @ CERN)

Nicola ColonnaIstituto Nazionale Fisica Nucleare, Sez. di Bari

[email protected]

Nuclear Data for Science, Technology and … Society(Hans Blix, ND 2008)

Neutron cross-section measurementswith high accuracyat high resolution

in a wide energy range

for Nuclear Astrophysicsand for Nuclear Technology

• Motivations (15’)

• The n_TOF facility and experimental setups (10’)

• Results (15’)

• Status and perspectives (5’)

Outline

2Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

AstrophysicsNuclear Astrophysics(stellar nucleosynthesis)

Nuclear energy(fission products &Structural material)

Advanced nuclear reactors(actinides)

n_TOF in the Chart of Nuclides


Neutron studies for Nuclear Astrophysics

rs

0 50 100 150 200MASS NUMBER

10-2

10-1

100

101

102

103

104

105

106

107

108

109

1010

AB

UN

DA

NC

E

(Si =

106 )

FusionBB Neutron capture

Fe

Mass number

Abu

ndan

ce

sr

s-process (slow process):• Capture times long relative to decay time• Involves mostly stable isotopes• Nn = 108 n/cm3 , kT = 0.3 – 300 keV

r-process (rapid process):• Capture times short relative to decay times• Produces unstable isotopes (neutron-rich)• Nn = 1020-30 n/cm3

s-process

(Red Giants)

r-process

(Supernovae)

Radioactive beam facilities

The stellar nucleosynthesis

5

Neutron beams

Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

The s-process nucleosynthesis

56Fe 91.72

57Fe 2.2

58Fe 0.28

60Ni 26.223

59Co 100

59Fe 44.503 d

60Fe 1.5 106 a

60Co 5.272 a

61Co 1.65 h

61Ni 1.140

62Ni 3.634

63Ni 100 a

64Ni 0.926

58Co 70.86 d

62Cu 9.74 m

63Cu 69.17

64Cu 12.7 h

61Fe 6 m

Along the b-stability valleys-process nucleosynthesis proceeds through neutron captures and successive b-decay.

The abundance of elements in the Universe depends on thermodinamic conditions (temperture and neutron density) and on the neutron capture cross-sections.

s-process

capture rate: ln = Nn<s(n,g)·v>kT

s(n,g) is a key quantity

6

Neutron cross-sections are needed to:• refine models of stellar nucleosynthesis in the Universe;• obtain information on the stellar environment and evolution


The neutron capture cross-section

Bao et al. ADNDT 76 (2000)

7

For three classes of nuclei data are lacking or need substantial improvements:1. Nuclei with low cross-section, in particular neutron magic nuclei (s-process bottleneck)

• N=50 86Kr, 87Rb, 88Sr, 90Zr• N=82 138Ba, 139La, 140Ce

2. Isotopes unavailable in large amount, such as rare or expensive isotopes: • 186,187Os, 180W, etc…

3. Radioactive branching isotopes (“stellar thermometers”):• 79Se, 85Kr, 151Sm, 163Ho, 204Tl, 205Pb

Huge amount of data collected on many isotopes, mostly stable. Main features of s-process now well understood.

However, cross-section uncertainties in some cases remain high, in particular if compared with progresses in:

• observations of abundances (i.e. in meteorite grains)

• models of stellar evolution


Neutron studies for energy applications

The energy problem

9

Recently, renewed interest in nuclear energy due to:• continously increasing energy demand;• growing concern over production of greenhouse gases and related climate changes

More than 80 % of the energy consumed in the world comes from fossil fuels


CO2 and climate changes

10

,

Report of the Intergovernmental Panel on Climate Changes (IPCC), 2007

www.ipcc-wg1.unibe.ch/publications/wg1-ar4/wg1-ar4.html


The emission of CO2

11

To satisfy the world energy demand (in particular from developing countries), minimizing the impact on the climate, it is necessary a mix of energy sources which includes nuclear energy (Intergov. Panel on Climatic Change, IPCC-ONU, Valencia, 17 Nov. 2007).


Main problems of current nuclear reactors

12

97%238U

Fuel (LWR)

94%238U

Spent fuel

1% 235U

1% Pu and Minor Actinides

4% Fission products3% 235U

96%potentialfuel

Current reactors use only few percent of U resources.

Availability of U resources may become a problem in the medium term (100 y).

Closed cycle (recycling) would make U resources sufficient for thousands of years !!

Existing reactors have low burn-up efficiency and produce large amount of radioactive waste.


Figura Nucleosintesi (frecce che si muovono)

Foto FIC239Pu: 125 Kg/yr

237Np: 16 Kg/yr

241Am:11.6 Kg/yr 243Am: 4.8 Kg/yr

244, 245Cm 1.5 Kg/yr

LLFP

LLFP 76.2 Kg/yr

13

The nuclear waste problem

Quantities refer to yearly production in 1 GWe LW reactor


,

The actinides problem

14

Main problem in the nuclear waste are the transuranic actinides: Pu and MA (Np, Am, Cm,...)• 1.5% in mass but give the

biggest contribution to radiotoxicity and heat after 100 y

• problem persists for more than 105 y

• some isotopes are fissionable (proliferation and criticality concern).

At present, only solution to the high radiotoxicity nuclear waste is geological repositories


Geological repositories

15

With current reactors, it would be necessary to find a new geological repository like Yucca Mountain every 20 years.


Figura Nucleosintesi (frecce che si muovono)

Foto FIC

LLFP LLFP

The Th/U fuel cycle

16

232Th(n,g)233Th 233Pa 233Ub-, t1/2=22 m b-, t1/2=27 d


Recycling

New generation reactors

The revolutionary idea of Generation IV reactors is the recycling of the spent fuel (including minor actinides).

17

Other advantages of Generation IV (fast breeder) reactors:• improved safety, proliferation-resistence, lower costs and construction time• hydrogen production (to substitute fossile fuels in transport)

Other options now being considered:• Accelerator Driven Systems (nuclear waste incineration)• Use of the Th/U fuel cycle (currently being devoloped in India for energy production)


Once through

The development of Gen IV (fast breader) reactors requires accurate neutron data to minimize design uncertainty and optimize safety parameters.

Data needs for nuclear energy

18

Topic: Fission-2009-2.3.2: Improved nuclear data for advanced reactor systems. The combination of advanced simulation systems and more precise nuclear data will allow optimising the use of and need for experimental and demonstration facilities in the design and deployment of new reactors. A concerted effort including new nuclear data measurements, dedicated benchmarks (i.e. integral experiments) and improved evaluation and modelling is needed in order to achieve the required accuracies. The project shall aim to obtain high precision nuclear data for the major actinides present in advanced reactor fuels, to reduce uncertainties in new isotopes in closed cycles with waste minimisation and to better assess the uncertainties and correlations in their evaluation.

FP VII EURATOM

The overall list of requirements is rather long:• capture cross sections of 235,238U, 237Np, 238-242Pu, 241,242m,243Am, 244Cm• fission cross sections of 234U, 237Np, 238,240-242Pu, 241,242m,243Am, 242-246Cm

Data on a large number of isotopes are needed for design of advanced systems and for improving safety of current reactors.

• Nuclear fuel (U/Pu and Th/U cycles)Th, U, Pu, Np, Am, Cm (n,f), (n,) …

• Long-lived Fission Products99Tc, 103Rh, 135Xe, 135Cs, 149Sm (n,)

• Structural and cooling materialFe, Cr, Ni, Zr, Pb, Na, ... all

NEA/WPEC-26 (ISBN 978-92-64-99053-1)


Energy Range Current Accuracy (%)

Target Accuracy (%)

U238inel 0.5 ÷6.1 MeV 10 ÷ 20 2 ÷ 3

capt 2.04 ÷24.8 keV 3 ÷ 9 1.5 ÷ 2

Pu241 fiss 454. eV ÷1.35 MeV 8 ÷ 20 2 ÷ 5

Pu239 capt 2.04 ÷498 keV 7 ÷ 15 4 ÷ 7

Pu240 fiss 0.498 ÷1.35 MeV 6 1 ÷ 3

Pu242 fiss 0.498 ÷2.23 MeV 19 ÷ 21 3 ÷5

Pu238 fiss 0.183 ÷1.35 MeV 17 3 ÷5

Am242m fiss 67.4 keV ÷1.35 MeV 17 3 ÷4

Am241 fiss 2.23 ÷6.07 MeV 9 2

Am243 fiss 0.498 ÷6.07 MeV 12 3

Cm244 fiss 0.498 ÷1.35 MeV 50 5

Cm245 Fiss 67.4 ÷183 keV 47 7

Fe56 Inel 0.498 ÷2.23 MeV 16 ÷ 25 3 ÷ 6

Na23 inel 0.498 ÷1.35 MeV 28 4 ÷10

Pb206 inel 1.35 ÷2.23 MeV 14 3

Pb207 Inel 0.498 ÷1.35 MeV 11 3

Si28inel 1.35 ÷6.07 MeV 14 ÷ 50 3 ÷ 6

capt 6.07 ÷19.6 MeV 53 6

Target Accuracies for Gen IV Fast Reactors

Necessary to reduce uncertaintied to ~3-7 % for most Pu isotopes and Minor Actinides, in the energy range from a few keV to several MeV.

Source: Aliberti, Palmiotti, Salvatores, NEMEA-4 workshop, Prague 2007

The n_TOF facility at CERN

20

n_TOF is a spallation neutron source based on 20 GeV/c protons from the CERN PS on a Pb target (~360 neutrons per proton).

Experimental area at 200 m.


Technical details

22

pn• 80x80x80 cm3 Pb target surrounded by 5 cm water for

moderation (isolethargic flux) and cooling• 200 mt time-of-flight tunnel• several iron and concrete walls for shielding (from n, g, m,

etc…)• sweeping magnet for charged particle deflection• 2 collimators


The n_TOF facility

23

n_TOF is at present one of the most important facilities for neutron time-of-flight in the world (other TOF facilities are GELINA and LANSCE).

Other features of the neutron beam:

• high resolution in energy (DE/E = 10-4) …………….. study resonances

• large energy range (25 meV<En<1GeV) ………………. measure fission up to 1 GeV

• low repetition rate (< 0.8 Hz) ……………………………… no wrap-around

Main feature of n_TOF is the extremely high instantaneous neutron flux (105 n/cm2/pulse).

Unique facility for measurements of radioactive isotopes (maximize signal-to-background ratio):

• branch-point isotopes (Astrophysics)• actinides (nuclear technology)


The detectors for capture reactions

24

Two types of background (source of systematic errors):• g-rays from neutron scattered by the sample and captured in the setup (“neutron sensitivity”)• g-rays from environmental background, radioactivity of the sample, or competing reactions

(n,n)

(n,g)

A unique solution for all problems does not exist. At n_TOF, two different detectors built to minimize the two types of background.

Capture reactions are studied by detecting g-rays emitted in the de-excitation of the compound nucleus.

Neutron sensitivity big problem for isotopes with low capture cross-sections (Astrophysics)

Background from natural radioactivity big problem for actinides (applications)


Detectors with low neutron sensitivity

25

Apparatus used at ORELA in the past for capture measurements.

High neutron sensitivity, difficult to estimate and correct.

At n_TOF, neutron sensitivity enormously reduced, relative to the past.

Very small amount of material, and extensive use of carbon fiber.

Problem of this setup: low efficiency and selectivity


The calorimetric method

26

The Total Absorption Calorimeter (TAC) fundamental for neutron capture measurements of actinides

The calorimetric method allows to discriminate the background on the basis of total energy of detected g-rays.

bersaglio

Calorimetro (BaF2)

neutroni

In measurements of capture on actinides, the main problem is the g-ray background associated to the natural radioactivity of the sample, as well as to fission reactions.


The n_TOF TAC: • 4p array of 40 BaF2 scintillators (15 cm

thick)• High efficiency allows to reconstruct

the entire deexcitation cascade.

The n_TOF calorimeter

27

C12H20O4(6Li)2

NeutroniProblem with TAC: bad neutron sensitivity (detectors and heavy support structure)

At n_TOF, minimized neutron sensitivity with inner sphere of absorbing material, and capsules in carbon fibre with 10B.


La “Fission Ionization Chamber”• Standard detector, with fast gas and

electronics

The fission detectors

28

Parallel Plate Avalanche Counters (PPAC):• Fission fragments detected in coincidence• Very good rejection of a-background

neutroni

neutroni

The main problem in fission measurements is the background due to a-decay. At n_TOF, minimized by the very high instantanous neutron flux.


The Data Acquisition System


High instantaneous neutron flux several events for each neutron pulse + pile-up between signalsStandard DAQ methods are largely inadequate

n_TOF DAQ entirely based on Flash ADC• Up to 1 GSample/s (500 MHz bandwidth), 16 MB

buffer memory • Software Zero suppression• Commercially available in compact_PCI standard

(Acqiris)

Offline signal reconstruction for time and charge information

• Simple algorithm for a single signal• Fitting procedure for pile-up events

The Fission setup

30

Neutron beam

M. Calviani et al., Nucl. Instr. Meth. A 594, 220 (2008)

PPAC (coincidence method):235U, 238U ………..… reference (standad)232Th ………… Th/U fuel cycle233U, 234U …………… Th/U fuel cycle237Np …………..… Gen IV and ADS209Bi, natPb …………….. ADS

Fission chamber (single fragment) :235U, 238U ……..……… reference (standad)236U ……………… U/Pu fuel cycle232Th …………… Th/U fuel cycle233U, 234U ………… Th/U fuel cycle237Np …..……… Gen IV and ADS241,243Am …..………… Gen IV and ADS245Cm ……………… Gen IV and ADS


n_TOF phase 1 (2002-2004)Cattura151Sm204,206,207,208Pb, 209Bi24,25,26Mg90,91,92,94,96Zr, 93Zr186,187,188Os, 139La232Th, 233,234U237Np,240Pu,243Am

Fissione233,234,235,236U232Th, 209Bi237Np241,243Am, 245Cm

The n_TOF activity

31

– Misurements of capture reactions:

• 25 Isotopes (8 of which radioactive)• Often of double interest (Astrophysics and applications)• Several publication

– Measurements of fission cross-sections:• 11 isotopes (10 radioactive)• Mainly linked to Th/U cycle e transmutation• strong interest by International Nuclear Agencies• results are still being published

EC ContractsFP5: n-TOF-ND-ADS FP6: EUROTRANS FP7: ANDES

40 articles, 100 Conference Proceedings, 26 PhD thesis


The n_TOF Collaboration(80 Researchers from 30 European Institutes)

CERN

Technische Universitat Wien Austria

IRMM EC-Joint Research Center, Geel Belgium

IN2P3-Orsay, IN2P3-Strasbourg, CEA-Saclay France

FZK – Karlsruhe Germany

Univ. of Athens, Ioannina, Demokritos Greece

INFN Bari, Bologna, LNL, TriesteENEA – Bologna Italy

Univ. of Tokio Japan

ITN Lisbon Portugal

Charles Univ. (Prague), Univ. of Lodz Poland

IFIN Rumania

INR – Dubna, IPPE – Obninsk Russian Fed.

CIEMAT, Univ. of Valencia, Santiago de Compostela, University of Cataluna, Sevilla Spain

University of Basel Switzerland

Univ. of Manchester, Univ. of York UK

Notre Dame, Los Alamos, Oak Ridge USA

s-Process

The capture cross-section of 151Sm

150Sm 152Sm

151Eu 153Eu

152Gd 154Gd

The branching ratio for 151Sm depends on:• Termodynamical condition of the stellar

site (temperature, neutron density, etc…) • Cross-section of 151Sm(n,g)

151Sm used as stellar thermometer !!

151Sm is a branching point isotope (T1/2=90 y)

33

151Sm

152Eu 154Eu

153Sm


http://images.google.de/imgres?imgurl=www.br-online.de/wissen-bildung/thema/sonne/foto/redgiant.jpg&imgrefurl=http://www.br-online.de/wissen-bildung/thema/sonne/riesen.shtml&h=176&w=132&prev=/images?q=rote+riesen&svnum=10&hl=de&lr=&ie=UTF-8

http://images.google.de/imgres?imgurl=www.br-online.de/wissen-bildung/thema/sonne/foto/redgiant.jpg&imgrefurl=http://www.br-online.de/wissen-bildung/thema/sonne/riesen.shtml&h=176&w=132&prev=/images?q=rote+riesen&svnum=10&hl=de&lr=&ie=UTF-8

The n_TOF results on 151Sm

34

1000

1500

2000

2500

3000

3500

1970 1975 1980 1985 1990 1995 2000 2005Year

MAC

S [m

b] n_TOF

Models


n_TOF results confirmed model of Thermal Pulsing AGB stars

The capture cross-section of Pb/Bi

35

n_TOF

Past


Important implications on the origin of Solar System

The Zr saga


n_TOF

Past

New values for the neutron density in He burning shells of Red Giants

The Os trilogy


Age of the Universe from nuclear cosmocronometer: 14.9±2 Gyr

10 100 1000 10000 10000010-1

100

101

102

Re

spo

nse

(co

un

ts /

ns)

Neutron Energy / eV

n-TOF

232Th (0.0041 at/b)

208Pb

GELINA

232Th (0.0016 at/b)

208Pb

Very accurate data collected at n_TOF on neutron capture for 232Th:

• clear advantage over GELINA in the Resolved Resonance Region.

• important results also at high energy, (previous data off by 40 %).

The capture cross-section of 232Th


Important data for Th/U cycle !Fission cross-section on 233U measured for the first time from thermal to 50 MeV, with 5 % accuracy, and high resolution.

The fission cross-section of 233U

PRC referee report

The experiment and the data obtained are of high quality and clearly superior to earlier measurements. The result is of major importance for nuclear technology, in particular for the neutronics of nuclear reactors using the Th/U breeding cycle.….In conclusion the quality of the article and of the obtained data are exceptionally high. A publication in a journal on nuclear engineering would also be adequate, but personally I recommend the article for publication in Phys.Rev. C. Thus the results are more visible for the scientific community.


The cross-sections of 237Np

40

Previous data scattered all over.

Accuracy of n_TOF results better than 4% (up to 10 keV).

Solved large discrepancy in the Unresolved Resonance Region

237Np(n,g)

C. Guerrero et al., Phys. Rev. C, in preparation

C. Paradela et al., sub. to PRC

237Np(n,F)

D=50%

n_TOF results 6% higher than previous data and evaluations (all normalized to ONE measurements of 1983).

Very important result for design of future generation reactors (Np is the most abundant MA produced in current reactors)


The cross-sections of 240Pu

41

240Pu(n,g)

240Pu(n,F)

To be performed in 2011

First capture measurement in resolved resonance region.

Accuracy 6% (up to 10 keV).

Extracted nuclear properties (level spacing, average gamma widths, etc…).

C. Guerrero et al., Phys. Rev. C, in preparation

Ti(n,n)


The cross-sections of 241Am

42

241Am(n,g)

241Am(n,F)

To be performed in 2010

Large discrepancies in databases for several resonances.

Overall uncertainty too high for nuclear energy applications.


M. Calviani et al., Phys. Rev. C, in preparation

Cross-sections of 243Am

43

F. Belloni et al., Nucl. Sci. Eng., in preparation

243Am(n,F)

244Pu(3He,tf)

243Am(n,g)

E. Mendoza et al., Phys. Rev. C, in preparation

Ti resonance

Unique measurement (not easy to perform).

High-resolution and high-accuracy results up to a few keV (because of thick Ti capsule).

Improvements and new measurements are needed.

Clarified a long-standing discrepancy of more than 15 % !n_TOF data (3% accuracy) confirm current evaluations, against previous results (even of 2004 !!).


Cross-sections of 245Cm

44

245Cm(n,F)

M. Calviani et al., Phys. Rev. C

245Cm(n,g)

To be performed in the future

Very few measurements available on this isotope (difference up to a factor of 2, with evaluation in between). New data from n_TOF clarify that one of the two previous measurements is completely wrong.


n_TOF Phase 2

45

Some isotopes require a much higher flux (x100)

New Experimental Area at 20 m from spallation target.


The new spallation target

46

New pressure vessel

Moderator (4 cm)

Cooling water (1 cm)

Existing Pool

Existing retention vessel

PbØ = 60 cmL = 40 cmprotonis

It is now possible to use different moderators (to optimize neutron spectrum or minimize background)


Commissioning of the new target

47

Profilo

With borated water, background reduced by a factor 10 more !


The new experimental area

48

Area sperimentale

Dressing room

During shut-down, experimental area transformed in “Work Sector Type A” (for handling not certified radioactive samples).

Various modifications: sealed area, controlled ventilation, underpressure, fire-proof doors, fire detection systems, radioactivity monitor, etc…

Access: dressing room, hand/foot contamination monitor, decontamination area, etc…

Two possibilities to measure radioactive isotopes at CERN:• Encapsulated samples, with

ISO2919 certification;• Suitable experimental area

(hot lab).

In the past, we have used Ti/Al capsules, which however induce a large background.


The new facility


n_TOF changing roomThe n_TOF access tunnel

The escape lane

The experimental area

Next measurements

50

Esperiments approved by INTC:• n_TOF-10: Capture of 242Pu, 241Am and 245Cm with a TAC at n_TOF • n_TOF-12: New target commissioning and beam characterization : Borated water : Fluence,

Resolution Function, Background• n_TOF-13: The role of Fe and Ni for s-process nucleosynthesis in the early Universe and for innovative

nuclear technologies : 54,57,58Fe, 58,60,61,64Ni with C6D6 measurements• n_TOF-14: Angular distributions in the neutron-induced fission of actinides: Fission Measurements of

232Th, 235,238U with PPAC• n_TOF-16: Neutron capture cross section measurements of 238U, 241Am and 243Am (+197Au, natC, natPb,

Empty) with TAC+C6D6 at n_TOF

New proposals:• Measurement of fission cross-section of 240Pu, 242Pu and 245Cm with a MGAS or FIC0 detector• Experimental test of a fission tagging neutron capture measurement combining the n_TOF TAC with

a MGAS detector (233U)• The 33S(n,a) cross-section: implications for neutron capture therapy and Astrophysics• n_ToF dump as a facility for neutron detector testing


nTOF-10 Capture (TAC)233U 3.7242Pu 3.2245Cm 3.3

Total 10.2

nTOF-12 Beam characterization (10B-water)

Flux and spatial profile 0.8

Energy resolution 0.3

Background (neutrons and g) 0.2

Total 1.3

nTOF-13 Capture (C6D6)

54Fe 2.057Fe 2.058Fe 2.058Ni 2.060Ni 2.061Ni 2.064Ni 2.0

Total 14.

nTOF-14 Fission (angular distribution)

232Th+237Np+234U+235U+238U 15.

Total 15.

nTOF-16 Capture on actinides

TAC C6D6

238U 2.4 3.6241Am 3.1 0.4243Am 2.4 0.4Calibr. 0.7 1.

Total 14.

Total of protons needed for approved experiments (to date): 40x1018 (3 years)

Proton requests (in units of 1018)

• Almost 10 years of intense activity at n_TOF !!

• Measurements of capture (for Astrophysics and applications) and fission (mostly advanced nuclear technologies).

• With 3 years of data taking, produced 40 papers and more than 100 conference proceedings

• In 2008 upgrade of the spallation target, in 2009 upgrade of experimental area (WSTA).

• New measurement campaign started last year (commissioning, Fe/Ni), now in progress (Fe/ni, U, Am, fissione).

• Approved experiments at INTC cover next 3 year of proton beam, and more proposals coming.

Conclusions


WORK IN PROGRESS

Thank you

Real men measure neutrons

R. De SouzaIndiana University

1 MeV

Neutron spectrumin fast reactors(Gen IV e ADS)

Neutroncross-sections

(with threshold)

Fissile isotopes(without threshold)

Nuclear Physics of Gen IV reactors

The development of Gen IV fast reactors requires accurate neutron data (minimize design uncertainty and optimize safety parameters)

54

The innovation of Gen IV reactors consists in the possibility to produce energy by burning Pu and minor actinides Np, Am, Cm.

Most minor actinides present a fission threshold (~ 1 MeV).

To burn nuclear waste, it is necessary to use a fast neutron spectrum.


Gen IV fast breeder reactors (SFR, GFR and LFR) would fulfill a closed fuel cycle, thus:

• maximizing the use of U resources• minimizing waste

The age of the Universe: the nuclear way

• Cosmological way based on the Hubble time definition (“expansion age”)

• Astronomical waybased on observations of globular clusters

• Nuclear way based on abundances & decay properties of long-lived radioactive species

Traditional nuclear clocks are those based on:

• 235U/238U

• 232Th/238U

• 187Os/187Re

Documents

N_TOF (neutron Time-of-flight @ CERN) n_TOF (neutron Time-of-flight @ CERN) Nicola Colonna Istituto Nazionale Fisica Nucleare, Sez. di Bari [email protected]