Neutron cross-sections measurement at the facility at CERN Students’coffee – 26th meeting, Tuesday 28 October 2014, 864-1-D02-BE Auditorium Prevessin Massimo

Neutron cross-sections measurement at the

facility at CERN

Students’coffee – 26th meeting, Tuesday 28 October 2014, 864-1-D02-BE Auditorium Prevessin

Massimo Barbagallo, CERN/EN-STI and INFN

Outline

M. Barbagallo, Students’Coffee, 28 October 2014, Neutron cross-sections measurement at the n_TOF facility at CERN

• Motivations (Nuclear Astrophysics, Nuclear Technology, Nuclear Medicine, Nuclear Structure )

• The facility(ies) and the experimental program so far (extremely short review)

• Experimental Area 2

• Perspectives

• Conclusions

36 Institutions120 Researchers

High accuracy and precision measurements of neutron induced reaction cross-sections

(n,f), (n,cp), (n,)

n_TOF Collaboration


n_TOF measurements at a glance


AstrophysicsNuclear Astrophysics(stellar nucleosynthesis)Nuclear Astrophysics(stellar nucleosynthesis)

Nuclear energy(fission products &Structural material)

Nuclear energy(fission products &Structural material)

Advanced nuclear reactors(actinides)

Advanced nuclear reactors(actinides)

Nuclear Medicine(capture therapy)

Nuclear Medicine(capture therapy)

n_TOF facility (beam line 1+ EAR1)


PS 20 GeV

Linac50 MeV

Booster1.4 GeV

185 m flight path

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

Experimental area at 185 m.

n_TOF EAR1 features


Other features of the neutron beam:

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

• Wide energy range (25 meV<En<1 GeV) measure fission up to 1 GeV

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

Main feature: high instantaneous neutron flux

(105 n/cm2/pulse). very convenient for measurements

of radioactive isotopes, low cross sections, Isotope available in small quantity

Advantages of the PS proton beam: high energy, high peak current, low duty cycle.Advantages of the PS proton beam: high energy, high peak current, low duty cycle.

C. Guerrero et al., Eur. Phys. J. A (2012) 48:29

n_TOF facility (beam line 1+ EAR1)


Detection systems at n_TOF

C12H20O4(6Li)2

Neutron beam

Neutron beam(n

,)

C6D6

TAC

(n,f)

, (n,

cp)


FIC PPAC

MGAS

..and many others

n+197Au

M. Barbagallo et al., Eur. Phys. J. A (2013) 49:156

Road to a cross section..


The experimental program so far


Capture151Sm232Th204,206,207,208Pb, 209Bi24,25,26Mg90,91,92,94,96Zr, 93Zr186,187,188Os233,234U237Np,240Pu,243Am

Fission233,234,235,236,238U232Th209Bi237Np241,243Am, 245Cm

Capture25Mg88Sr58,60,62Ni,63Ni54,56,57Fe

,238U241Am

Fission240,242Pu

235U(n,/f)232Th, 234U237Np (FF ang.distr.)

(n,)33S,59Ni

Phase 1 (2001-2004)

Phase 2 (2009-2012)

236U

63Ni(n,)


63Ni (t1/2=100 y) represents the first branching point in the s-process, and determines the abundance of 63,65Cu

First high-resolution measurement of 63Ni(n,) in the astrophysical energy range.First high-resolution measurement of 63Ni(n,) in the astrophysical energy range.

62Ni sample (1g) irradiated in thermal reactor (1984 and 1992), leading to enrichment in 63Ni of ~13 % (131 mg)

In 2011 ~15.4 mg 63Cu in the sample (from 63Ni decay).

After chemical separation at PSI, 63Cu contamination <0.01 mg


197Au(n,) cross section is a standard at thermal energy and in the energy range 0.2-2.5 MeV

In order to possibly extend the standard also to the Resolved Resonance Region (few eV – few keV) it has been measured at n_TOF both with C6D6 and TAC.

C. Massimi et al., Phys. Rev. C 81, 044616 (2010)

197Au(n,)


T. Wright, Univ. of Manchester, PhD thesis

Overall (expected): 2-3% systematic uncertainty (depending on En)

238U sample (provided by JRC-IRMM)•6.125 (2) g •High purity (99.99%)•Rectangular: 53.90 x 30.30 mm

Used C6D6 and TAC to minimize systematic uncertainty related to detection effects

NEA request to measure 238U(n,) cross section with 2% accuracy from 100 eV to 25 keV

F. Mingrone, Univ. of Bologna, PhD thesis

Response from the community: measurements at n_TOF (x2), GELINA and LANSCEResponse from the community: measurements at n_TOF (x2), GELINA and LANSCE

238U(n,)

n_TOF history


Conceptby C.RubbiaCERN/ET/Int. Note 97-1919

97

2000

Commissioning

Constructionstarted19

99 New Targetinstalled20

08

2001

-200

4

Phase IMeasurement campaign

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

63Ni62Ni

Phase IIMeasurement campaign

2009

-201

2

Commissioning

200

9

2nd Exp. area

2014

Upgrades10B-water Class-A area20

10

Phase III

n_TOF history


n_TOF Experimental Area 2

20 mBeam line

Spallation target

Higher fluence, by a factor of 30, relative to EAR1.

The shorter flight path implies a factor of 10 smaller time-of-flight.

Global gain by a factor of 300 in the signal/background ratio for radioactive isotopes!

200 m Beam line

x30

Experimental Area 2 (EAR2) is placed (vertically) at 20m from spallation target.


n_TOF Experimental Area 2

EAR2

ne

utr

on

s

EAR1neutrons

• The new facility is presently undergoing the commissioning phase, particularly in terms of neutron flux and background.• First Physics experiment 240Pu(n,f) will start in few weeks.


Neutron flux@EAR2: measurement

Si

ne

utr

on

s

Transparent neutron monitor

• Array of four 3x3 cm2 silicon detectors (300 m thickness)

• 6LiF converter (420 g/cm2) 6LiFt

neutron energy (eV)

En

erg

y d

ep

osi

ted

(M

eV

)

detectors

converter

t


Neutron flux@n_TOF-EAR2

PRELIMINARY

x35

x20


EAR1

EAR2

Perspectives


7Be: the Phisycs case

Bing Bang Nucleosynthesis (BBN), together with Hubble expansion and Cosmic Microwave Background Radiation is one of the cornerstones for Bing Bang Theory.

BBN gives the sequence of nuclear reactions leading to the synthesis of light elements up to Na* in the early stage of Universe (0.01-1000 sec)

BBN successfully predicts the abundances of primordial elements such as 4He, D and 3He.

* R.H.Cyburt et al., Journal of Cosmology and Astroparticle Physics 11 (2008) 012

*

** A.Coc et al., The Astrophysical Journal, 744:158 (2012)

A serious discrepancy (factor 2-4) between the predicted abundance of 7Li and the value inferred by measurements (Spite et al, many others.)

Cosmological Lithium Problem (CLiP)



Approximately 95% of primordial 7Li is produced from the electron capture decay of 7Be (T1/2=53.2 d).

A higher destruction rate of 7Be can solve or at least partially explain the CLiP.

7Be is destroyed via (n,p) (~97%) and (n,) (~2.5%) reactions


7Be(n,p)7Be(n,)


7Be(n,) and 7Be(n,p) @n_TOF-EAR2


We plan to measure both 7Be(n,) and 7Be(n,p) reactions at n_TOF-EAR2.*

Taking advantage of the:• extremely high instantaneous neutron flux • state of art detectors and acquisition systems• high purity samples (PSI+ISOLDE)

First high accuracy measurement!**

(**in all the neutron energy range)

7Be(n,), 1 months measurement 7Be(n,p), <2 weeks measurement

*M. Barbagallo et al., CERN-INTC-2014-049/ INTC-P-417


Conclusions

• There is need of accurate new data on neutron cross-section both for astrophysics and advanced nuclear technology, as well as for nuclear medicine.

• Since 2001, n_TOF@CERN has provided an important contribution to the field, with an intense activity on capture and fission measurements.

• Several results of interest for stellar nucleosynthesis (Sm, Os, Zr, Ni, Fe, etc…).

• Important data on actinides, of interest for nuclear waste transmutation.

• To date, high resolution measurements performed in EAR1 in optimal conditions (borated water moderator, Class-A experimental area, etc…).

• A second new (and more intense flux) experimental area is now available. EAR2 will open new perspectives for frontier measurements on short-lived radionuclides.

• A rich experimental program is foreseen both in EAR1 and EAR2 for nuclear technologies, nuclear astrophysics and nuclear medicine.


Thanks for your kind attention!

…and come to visit n_TOF at any time!

Documents

Neutron cross-sections measurement at the facility at CERN Students’coffee – 26th meeting, Tuesday 28 October 2014, 864-1-D02-BE Auditorium Prevessin Massimo