INSTITUT LAUE LANGEVIN - ILL · or 252Cf (spontaneous fission) àneeds shielding…-cadmium or gadolinium (but produce X-rays!)-boron, lithium (produce a-radiation! + Li à3H) àneeds

1T H E E U R O P E A N N E U T R O N S O U R C E

I N S T I T U T L A U E L A N G E V I N

Barbara BerkeAdrián González-Rodríguez

Free neutrons, fission and spallation

31/01/2017 NeutronFieldsForeverhttp://www.visitpennstate.org/events/strawberry-fields-forever-5407/

NEUTRON


The Neutron• History• Properties• InteractionsNeutron production• Fusion reactions• Fission reactions• Spallation sources Neutrons capture and decay• Where do neutrons go? Beta-decay & absorption• Absorption materials and cross section• Naturally occurring neutron capture in the universe

Overview

31/01/2017 NeutronFieldsForever

https://briankoberlein.com/2016/04/22/strange-case-decaying-neutrons/


Except for the pure H2

Neutrons are everywhere


http://www.thestargarden.co.uk/Images/Neutron-Stars-magnetic.jpg

http://pureenergycentre.com/wp-content/uploads/2013/10/Hydrogen_MCP_storage_cylinder-200-bar.jpg

http://clipart-library.com/city-cliparts.html

http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/northcarolina/

https://www.tes.com/lessons/frW9YPpnbB4IUg/nature


• 1908 Ernest Rutherford and Thomas Royds proved: a-radiation consists of He ions• 1911 Rutherford's model for the atom (mass and positive charge concentrated in a

very small nucleus)Gold foil experiment

History


kcmcgann.tripod.com/goldfoil.jpg


Disparity between atomic number and the mass of the atom• 1920 Rutherford suggested the existence of a neutrally

charged particle within the nucleus• 1930 Boethe and Becker – Li, Be, B + a reaction

à suspected artificial g-radiation• 1930 Joliot and Curie – worked more with Be + a reaction• 1931 Chadwick repeated the Be + a reaction• 1932 Chadwick published his paper about neutrons

• 1935 Nobel Prize in Physics "for the discovery of the neutron"

History


https://www.ill.eu/science-technology/the-neutron/the-neutron-in-history/

James Chadwick


“The Neutron is complicated enough to be interesting…

But is simple enough to be understandable.”

Geoffrey Greene



• Subatomic particle and a matter wavemean square radius: 0.8 × 10−15 m, or 0.8 fm

• No net charge, slight charge distribution (?)• Mass slightly larger than that of a proton

~1 atomic mass unit (1.0087 u); 1.675 × 10−27 kg, 939.6 MeV/c2

• Spin fermion (½)• Magnetic moment with a negative value

the orientation is opposite to the neutron’s spin

• Within the nucleus, bound together with protons through the nuclear force

Neutron


https://en.wikipedia.org/wiki/Neutron

∆𝐸 = ∆𝑚𝑐&𝑀 < 𝑍𝑚* + 𝑁𝑚-


• Free neutron is unstable (mean lifetime: 881.5 ± 1.5 s)• b- decay (Fermi, 1934): (exothermic)

• b+ decay: (endothermic)

• Electron capture: (endothermic)

Neutron


𝑋 → 𝑌 + 𝑒2 + �̅�5 + [𝛾]9:;<

9<

𝑛 → 𝑝 + 𝑒2 + �̅�5

𝑝 → 𝑛 + 𝑒: + 𝑣5

𝑝 + 𝑒2 → 𝑛 + 𝑣5

https://en.wikipedia.org/wiki/neutron


• Not directly

1.

• Mass of the protons and deuterons by mass spectrometry• Binding energy can be measured (g photon – 2.225 MeV) by high precision X-ray

diffraction

2. Using the b-decay• Momenta of the resulting proton and electron are measured

Mass of the neutron


𝑚- = 𝑚?-𝑚* + 𝐵?𝑝 + 𝑛 → 𝐷& + 𝛾

𝐵? = ∆𝑚 =∆𝐸𝑐&

http://www.clipartkid.com/balance-cliparts/


• 1948 Snell and Miller at Oak Ridge – radioactive decay of n was observed for the first time (> 21 min), detected decay protons

• 1950 Robson at Chalk River detection of electrons and protons in coincidence(~1100 sec)

Lifetime of the neutron


https://commons.wikimedia.org/wiki/File:Neutron_lifetime_value_from_PDG.svghttps://inspirehep.net/record/1351741/files/neutronLifetime.png

Lifetime of the neutron measuredat ILL in the last

decades


Small decay probability (3 particle decay, small Δm, weak interaction)Late development àresearch reactors were neededMethods:

Lifetime of the neutron


https://www.nist.gov/programs-projects/neutron-lifetime-measurement-using-cold-neutron-beam

Beam experiment(2 absolute measurement

cold neutrons)

« Bottle » experiment(2 relative measurement

ultra cold neutrons)

Jonathan MulhollandUniversity of Tennessee


• Not directly• Interactions with the atomic nuclei are used!

1. Neutron capture, then the compound nucleus emits more easily detectableradiation3He, 6Li, 10B, 233U, 235U, 239Pu

2. Elastic scattering (proton-recoil)Causing the nucleus to recoil à fast neutron detectors

NFF presentation on 07/03/2017

Detection



Interactions


Cold < 0.025 eVThermal ~ 0.025 eVEpithermal 0.025-0.4 eVCadmium 0.4-0.6 eVEpiCadmium 0.6-1 eVSlow 1-10 eVResonance 10-300 eVIntermediate 300eV- 1 MeVFast 1-20 MeVUltrafast > 20 MeV

What do we expect?• It should penetrate the matter easily

(no charge, no repulsion)• Interaction with the nuclei, but not

with the electon cloud• Sensitive to the magnetic properties

of the material• Spin-dependent interaction

Properties are energy-dependentOnly particle which shows all interactions: strong, electromagnetic, weak, gravitational

Neutron temperature or a free neutron’s kinetic energy:

https://en.wikipedia.org/wiki/Neutron_temperature


Classification of neutron reactions


Dr. David Hamilton; European Commission Institute for Transuranium Elements

Interaction with the matter:• Elastic scattering/ Diffraction• Inelastic scattering• Absorption/neutron capture• Neutron induced fission


Cross-section: the likelihood of particular interaction between an incident neutron and a target nucleus.standard unit: barn= 10-28 m2

Cross-section - s


http://xxpt.ynjgy.com/resource/data/20091107/U/NotreDame20090029/physics/nuclear-warfare/lecture-5.htm

The neutron cross-section depends on:• Target nucleus/isotopes• Type of the reaction (capture, fission, etc.)• Neutron energy (1/v)• Target energy (temperature of target

material)


Neutron-proton ratio


https://en.wikipedia.org/wiki/List_of_elements_by_stability_of_isotopeshttps://en.wikipedia.org/wiki/Beta-decay_stable_isobars

Half-life

Valleyof

stability


Energy gain/nucleon

Stability of the nuclei


https://en.wikipedia.org/wiki/Valley_of_stability

fusion

fission


Reactions


𝐵B;C + 𝐻𝑒 →&E

𝐶G;& + 𝐷 →;&

→ 𝐶G;I +p

→ 𝑁J;I +n𝑁J;E

∗Target nucleus

Bombarding particle

Transition nucleus

Product nucleus

Prompt particle

Short form: 10B(a,p)13C12C(d,n)13N

(f): fission(sf): spontaneous fission(n,f): neutron induced fission


• Alpha-induced reaction

• Photo-dissociation [g]

• Deuteron fusion

• Spontaneous fission

• Neutron-induced fission

• b-delayed n emission

• Spallation

Neutron production


http://chemistry.tutorvista.com/nuclear-chemistry/nuclear-fission.html


• 9Be(a,n)12C + 5.7 MeV (Chadwick!)a-radiation can be provided by 238Pu, 241Am, 210Po, 226Ra

• 11B(a,n)14N + 0.158 MeV• Continuous spectrum of neutrons

Alpha induced reactions


• 9Be(g,n)2a + 1.66 MeV• g-radiation can be provided by antimony (124Sb)

• Nearly monoenergetic neutrons

Photo-dissociationTypical startup

neutron sources!

𝑆𝑏;&E → 𝑇𝑒;&E + 𝛽2 + 𝛾

21T H E E U R O P E A N N E U T R O N S O U R C E31/01/2017 NeutronFieldsForever

• a-source (Am, Pu) mixed with Be in plastic to moderate the fast neutrons or 252Cf (spontaneous fission)

àneeds shielding…

- cadmium or gadolinium (but produce X-rays!)- boron, lithium (produce a-radiation! + Li à 3H)

àneeds shielding…

“There is no perfect crime in neutron science” – Ulli Köster

Portable neutron sources


• d(d,n)3He +3.3 MeV

• T(d,n)4He +17.6 MeV (3.5 + 14.1 MeV)

• Natural fusion in stars

(Deuteron) fusion


𝐷;& + 𝑇;I → 𝐻𝑒&E + 𝑛 http://hendrix2.uoregon.edu/~imamura/123cs/lecture-6/pp-bb.html

𝐶G;I + 𝐻𝑒&E → 𝑂Q;G + 𝑛

𝐷;& + 𝐷;& → 𝐻𝑒&I + 𝑛

Monoenergetic neutrons of high energy

Neutron generator


• 1934 (Rome) Enrico Fermi bombarding uranium with n –new elements were created with 93 and 94 p+

• 1934 Ida Noddack suggested that the nucleus breaks up• 1938 (Berlin) Otto Hahn, Fritz Strassmann and Lise

Meitner bombarded uranium with n, several products• 1938 Fermi received the Nobel Prize in Physics "for his

demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for hisrelated discovery of nuclear reactions brought about by slow neutrons »

• 1939 Hahn, Strassmann, Meitner, Otto Frisch understoodthat they were observing fission

Fission


https://en.wikipedia.org/wiki/Enrico_Fermi

Enrico Fermi


• 1939 Leó Szilárd and Eugene (Jenő) Wigner drafted the Einstein–Szilárd letter

à (1942-1946) Manhatten project• 1939 Frédéric Joliot and coworkers proves that it could be

used to make chain reactions• 1942 (Chicago) Fermi and coworkers built the first working

fission reactor• 1942 Meeting at the University of Chicago: the fission

bomb is theoretically possible (Edward (Ede) Tellersuggests the hydrogen bomb)

• 1945 Hahn received the Nobel Prize in Chemistry "for hisdiscovery of the fission of heavy atomic nuclei."

Fission


The Trinity test of the Manhattan Project

https://en.wikipedia.org/wiki/Manhattan_Project


• 252Cf(sf)134Te+115Pd+3n + 212 MeV (half-life: 2.638 years)

• 1940 Identified by Georgy Flyorov and Konstantin Petrzhak on Uranium

• Lightest natural nuclides (hypothetically):niobium-93 and molybdenum-94 - never been observed

• Thorium-232 is the lightest primordial nuclide that has left evidence of undergoing spontaneous fission in its minerals

• Superdeformed nucleus: strong force decays much faster than the Coulomb force, which becomes stronger when nucleons are greater than 2.5 femtometers apart

Spontaneous fission


https://en.wikipedia.org/wiki/Nuclear_fission


• 235U(n,f)134Te+99Zr +3n +185 MeV• 50 ways are possible, 300 isotopes of 35 elements• ~200 MeV energy gain + ~2.5 n (wide energy range)

Neutron-induced fission


http://www.mlz-garching.de/englisch/neutron-research/neutron-source.html

235U vs. 238U to fission or not to fission

Paired neutrons!

Chain reaction!


Energy-distribution

• kinetic energy of fission products: 160 MeV• kinetic energy of the neutrons: 5 MeV• energy of the g-rays: 5 MeV• energy of the secondary radioactive decay: 20 MeV• energy released at neutron capture: 10 MeV

Neutron-induced fission


prompt neutrons are too quick to control the chain reaction!!!


• Fission products (or fission product daughter after b-decay) may emit neutrons• Delayed (=not prompt) any time from a few milliseconds to a few minutes after the

fission event. • The half-life of b-decay is much longer than the nuclear level of emitter

à “b-delayed” à controllable reactors

• Plutonium has low % of delayed neutrons à reactor control would be challenging

B-delayed n emission


𝐵𝑟IBQJ → 𝐾𝑟∗IG

QJ + 𝛽2 𝐾𝑟∗IGQJ → 𝐾𝑟 +IG

QG 𝑛 + 1.3𝑀𝑒𝑉


To be continued afterthe coffee break

Spallation


http://coloring.raskraski.link/1646/Jimmy-Neutron.html


The Neutron• History• Properties• InteractionsNeutron production• Fusion reactions• Fission reactions• Spallation sources Neutrons capture and decay• Where do neutrons go? Beta-decay & absorption• Absorption materials and cross section• Naturally occurring neutron capture in the universe

Overview

https://briankoberlein.com/2016/04/22/strange-case-decaying-neutrons/

31T H E E U R O P E A N N E U T R O N S O U R C E21/04/2017

Spallation sources

http://pd.chem.ucl.ac.uk/pdnn/inst3/pulsed.htm


Spallation reaction

Spallation Reaction physics, Antonín Krása, Neutron sources for ADS


• Interaction with single nucleons.

• Particles produced mostly in the direction of the incident particle.

• Nucleus left in high excited stated.

The intra nuclear cascade

Spallation Reaction physics, Antonín Krása, Neutron sources for ADS


Deexcitation

• Time spam period: ~102;G

• Nucleus loses its energy by evaporation of particles.

• The particles are emitted isotropicaly.

• Neutrons gamma emission Beta decay.

• Fission also occurs as a competitive process (fission products undergo evaporation as well).


Spallation spectrum


Spallation spectrum𝑑&𝜎𝑑𝞨𝑑𝐸 = 𝐴; exp −

𝐸𝐸;

+b𝐴c exp −𝐸𝐸c

I

cd&

+ 𝐴5e𝑒𝑥𝑝 −𝐸 − 𝐸5e𝑊5e

&+ 𝐴c-5e𝑒𝑥𝑝 −

𝐸 − 𝐸c-5e𝑊c-5e

&

Evaporation Cascade Quasi-elastic Quasi-inelastic

Eel/inel≡ Average energy of the neutrons ejected after a single elastic collision.Wel/inel≡ Width of the Fermi motion of the struck nucleon.Ai,EiDepend on the target mass.


Spallation products

More than 900 isotopes were identified with a total cross section of 1.87 barns.


Naturally occurred spallation in the atmosphere• Cosmic rays are mostly 1 GeV p+ which are perfect for spallation.• Nitrogen is the most abundant element in our atmosphere

𝑁J;E + 𝑛C; → 𝐶G;E + 𝑝;;

• 14Cdecay: 𝐶G;E → 𝑁J;E + 𝑒2 + �̅�

𝑁 = 𝑁Cexp(−𝑡/𝜏)Radiocarbon dating!


Neutrons Decay• Freeneutronsareunstable:halflife~10min

• Radioactivedecay: 𝑛 → 𝑝: + 𝑒2 + �̅�5

• Radiativedecay:𝑛 → 𝑝: + 𝑒2 + �̅�5 + 𝛾

• Twobodydecays:𝑛 → 𝐻 + �̅�5

Internal Bremsstrahlung


• Beta neutron decay also happens to occur when neutrons are bound in a nucleus.

• Here the inverse process may also take place (positron emission): 𝑝: → 𝑛 + 𝑒: + 𝜈5

• By this process, unstable atoms obtain a more stable ratio of protons to neutrons.

Beta decay in the nuclei


• Most free neutron disappear through absorption when they collide with a nucleus.

• The neutron absorption cross section measures the probability of neutron capture.

• The absorption cross section of a material depends on the nature of the atoms within it, the energy of the incident neutrons and the T of the material (among others).

Absorption


Absorbing materialsAtom σA (barns) UsesH,D 0.33, 0.000519 Moderator

Li(6Li,7Li) 70.5 (940, 0.045) Source of T, Basification of moderators

B(10B) 76 (3835) Shielding, regulation of RPWCo 37.2 Medical radiotherapy, nuclear

reaction byproductRh 144.8Cd 2520 ShieldingIn 193.8

Sm 5922 Control rods, decay product atnuclear

Gd,155Gd,157Gd 49700 ShieldingU(235U) 7.57, (681) Nuclear Fuel

EronCem

al,MatteoBianchini


• Generally if E↑→ 𝜎< ↓ 𝜎qrs λ = uvwxyz{

u{

• Resonance effect:

Effect of the energy


Effect of the temperature

𝜎 = 𝜎C𝑇C𝑇

;/&

• 𝜎 ≡Microscopic cross section corrected for temperature. • 𝜎C ≡Microscopic cross section at reference temperature. • 𝑇C ≡ Reference temperature in K degrees. • 𝑇 ≡Temperature for which corrected value is being calculated.


Crosssection:geometricalinterpretation

n≡ number of particles per unit volume.𝑟 ≡ collision rate onto one target.N ≡number of targets per unit volume.

V= 𝜎𝑣𝑑𝑡

r𝑑𝑡 = 𝑛𝑉 = 𝑛𝜎𝑣𝑑𝑡r = 𝑛𝜎𝑣

𝞥 = 𝑛𝑣 → r =σ𝞥

Reaction rate per unit volume: R =N σ 𝞥Atomic radius ≈ 102;&cm → 𝜎 ≈ 102&Ecm&

𝜎<𝜖(0.33, 50000)


Naturallyoccurringneutroncapture:s/rprocesses

Neutron capture

EronCem

al, Matteo Bianchini


S-processes R-processes

Time scale Thousands of years Several seconds

Neutron Flux (per s per cm2) 105-1011 1022

Where Stars Supernovas

Beta decay Allowed Not allowed

Temperature Relatively low High

Products Stable isotopes and elements Unstable neutron rich decay

Starting material (seed) Iron Iron

s/rprocessescharacteristics


Source: 𝑁𝑒;C

&& + 𝐻𝑒&E → 𝑀𝑔;&

&B + 𝑛 → Weak component →Produces heavier elements than Fe up to Sr and Y

𝐶G;I + 𝐻𝑒&E → 𝑂Q;G + 𝑛 → Main component → Produces heavier

elements than Fe beyond Sr and Y, up to Pb

S processes


209Bi

210Bi Po

206Pb

209Pb

n

3n

End of s process

Net result: 4𝑛 → 𝐻5&

E + 2𝑒2 + 2𝑉�5 + 𝛾


Rprocess:

• Source: Compression of electrons generates a neutronization of matter.

• Beta decay is blocked due to the high electron density filling all available electron states until a Fermy energy which is higher than the energy of nuclear Beta decay.

• Afterwards, neutron capture is much faster than beta decay so the process goes along the neutron ‘’drip-line’’.


THEENDThanksforyourattention!

SpecialthankstoUlli Koester

Documents

INSTITUT LAUE LANGEVIN - ILL · or 252Cf (spontaneous fission) àneeds shielding…-cadmium or gadolinium (but produce X-rays!)-boron, lithium (produce a-radiation! + Li à3H) àneeds