2-1 Nuclear Forensics Summer School Production and prevalence of radioisotopes Terms and definition overview Production of isotopes §Formation of elements.

2-1

Nuclear Forensics Summer SchoolProduction and prevalence of radioisotopes

• Terms and definition overview• Production of isotopes

§ Formation of elements§ Historic overview§ Production of radioelements

• Utilization of isotopes§ Sources§ Medical§ Nuclear Power

• Relate production and prevalence of radionuclides to nuclear forensics

2-2

Terms and definitions• Nuclear Forensics (From AAAS)

§ The technical means by which nuclear materials, whether intercepted intact or retrieved from post-explosion debris, are characterized (as to composition, physical condition, age, provenance, history) and interpreted (as to provenance, industrial history, and implications for nuclear device design)

• Radiochemistry§ Chemistry of the radioactive isotopes and elements§ Utilization of nuclear properties in evaluating and understanding chemistry§ Intersection of chart of the nuclides and periodic table

• Atom§ Z and N in nucleus (10-14 m)§ Electron interaction with nucleus basis of chemical properties (10-10 m)

à Electrons can be excited* Higher energy orbitals* Ionization

Ø Binding energy of electron effects ionization§ Isotopes

à Same Z different N§ Isobar

à Same A (sum of Z and N)§ Isotone

à Same N, different Z§ Isomer

à Nuclide in excited state à 99mTc

Chemical SymbolAZ N

2-3

1. decay (occurs among the heavier elements)

2. decay

3. Positron emission

4. Electron capture

5. Spontaneous fission

Types of Decay

EnergyRnRa 4222286

22688

EnergyXeI 13154

13153

EnergyNeNa 2210

2211

EnergyMgAl 2612

2613

EnergynRuXeCf 10

10844

14054

25298 4

2-4

X-rays

• Electron from a lower level is removed§ electrons of the higher levels can come to occupy

resulting vacancy§ energy is returned to the external medium as

electromagnetic radiation• radiation called an X-ray

§ discovered by Roentgen in 1895§ In studying x-rays radiation emitted by uranium

ores Becquerel et. al. (P. and M. Curie) discovered radioactivity in 1896

2-5

X-rays• Removal of K shell electrons

§ Electrons coming from the higher levels will emit photons while falling to this K shellà series of rays (frequency n

or wavelength l) are noted as Ka, Kb, Kg

à If the removed electrons are from the L shell, noted as La, Lb, Lg

• In 1913 Moseley studied these frequencies n, showing that:

• where Z is the atomic number and, A and Z0 are constants depending on the observed transition.

• K series, Z0 = 1, L series, Z0 = 7.4.

L L

K L

K

O

N

M

L

K

)( oZZA

2-6

Fundamentals of x-rays

• X-rays§ X-ray wavelengths from 1E-5 angstrom to

100 angstromà De-acceleration of high energy electronsà Electron transitions from inner orbitals

* Bombardment of metal with high energy electrons

* Secondary x-ray fluorescence by primary x-rays

* Radioactive sources* Synchrotron sources

2-7

Natural Element Production• Nuclear Astrophysics

§ fundamental information on the properties of nuclei and their reactions to the

§ perceived properties of astrological objects§ processes that occur in space

• universe is composed of a large variety of massive objects § distributed in an enormous volume§ Most of the volume is very empty (< 1x10-18 kg/m3) and cold (~ 3 K)§ Massive objects very dense § (sun's core ~ 2x105 kg/m3) and very hot (sun's core~16x106 K)

• At temperatures and densities § light elements are ionized and have high enough thermal velocities to

induce a nuclear reaction§ heavier elements were created by a variety of nuclear processes in

massive stellar systems• systems must explode to disperse the heavy elements

§ distribution of isotopes here on earth • underlying information on the elemental abundances • nuclear processes to produce the primordial elements

2-8

2-9

2-10

Origin of elements

• Initial H and He• Others formed from nuclear reactions

§ H and He still most abundant

2-11

Abundances

• general logarithmic decline in the elemental abundance with atomic number § a large dip at beryllium (Z=4) § peaks at carbon and oxygen (Z=6-8), iron (Z ~ 26) and the

platinum (Z=78) to lead (Z=82) region§ a strong odd-even staggering

• all the even Z elements with Z>6 are more abundant than their odd atomic number neighbors§ nuclear stability § nearly all radioactive decay will have taken place since

production § the stable remains and extremely long lived§ isotopic abundances

à strong staggering and gapsà lightest nuclei mass numbers multiple of 4 have highest

abundances

2-12

Abundances• earth predominantly

§ oxygen, silicon, aluminum, iron and calciumà more than 90% of the earth’s crust

• the solar system is mostly hydrogen§ some helium§ Based on mass of sun

• Geophysical and geochemical material processing

2-13

Origin of elements

• Timeline§ 10-43 s after the Big Bang,

à Planck timeà temperature of 1032 K (kBT ~ 1019 GeV)

* k BT(eV) = 8.6 x 10-5 T(K) à volume that was ~10-31 of its current volume. [

§ Matter existed in plasma of quarks and gluons§ particles were present and in statistical equilibrium

à particle had a production rate equal to the rate at which it was destroyed

à As Universe expanded it cooled and some species fell out of statistical equilibrium

§ 10-6s (T~1013 K)à photons from the black body radiation could not sustain the

production of the massive particles à hadronic matter condensed into a gas of nucleons and mesons

* Universe consisted of nucleons, mesons, neutrinos (and antineutrinos), photons, electrons (and positrons) The ratio of baryons to photons was ~ 10-9.

2-14

Timeline

• 10-2s (T~1011 K)§ T(K)=1.5E10t1/2, t in seconds

• density of the Universe dropped to ~ 4 x 106 kg/m3 • neutrons and protons interconvert by the weak interactions

§ neglect free neutron decayà Life time too long (10.6 m)

§ neutron-proton ratio, n/p, was determined by a• Boltzmann factor, i.e.,• n/p = exp (-mc2/kT)

§ T=1012K, n/p ~ 1, T=1011 K n/p ~ 0.86, etc.§ T = 1011K, no complex nuclei were formed

• 1 second§ T= 1010K § pair production since kT < 1.02 MeV § neutron/proton ratio was ~ 17/83.

• 225 seconds§ neutron/proton ratio was ~ 13/87, § T ~ 109K

density was ~ 2 x104kg/m3

§ first nucleosynthetic reactions occurred.

2-15

Origin of Elements• Gravitational coalescence of H and He into clouds• Increase in temperature to fusion• Proton reaction

§ 1H + n → 2H + g§ 2H + 1H → 3He§ 2H + n → 3H§ 3H + 1H → 4He + g§ 3He + n → 4He + g § 3H + 2H → 4He + n§ 2H + 2H → 4He + g § 4He + 3H → 7Li + g§ 3He+3He → 7Be + g

à 7Be short livedà Nucleosynthesis lasted 30 minutes

• Chemistry began in 106 years at 2000K• Further nucleosynthesis in stars

§ No EC process in stars

2-16

Stellar Nucleosynthesis• He burning

§ 4He + 4He ↔ 8Be + γ - 91.78 keV à Too short lived

§ 3 4He → 12C + γ + 7.367 MeV§ 12C + 4He →16O§ 16O + 4He →20Ne

• CNO cycle§ 12C + 1H →13N + g§ 13N →13C + e+ + νe § 13C + 1H →14N + γ § 14N + 1H →15O + γ § 15O →15N + e+ + νe § 15N + 1H →12C + 4He § Net result is conversion of 4

protons to alpha particleà 4 1H → 4He +2 e++ 2 νe +3 γ

2-17

Origin of elementsNeutron Capture and proton

emission§ 14N + n →14C +1H;

14N(n,1H)14C• Alpha Cluster

§ Based on behavior of particles composed of alphas

Neutron Capture; S-process§ A>60§ 68Zn(n, γ) 69Zn§ 69Zn → 69Ga + b- + n§ mean times of neutron

capture reactions § reaction =ln2/rate =

ln2/Nn<v>.§ Nn ~ 1011/m3, = 0.1 b at

En ~ 50 keV, then ~ 105 years

§ Up to Bi§ Neutrons from (a,n) on

light nuclei

2-18

2-19

Nucleosynthesis

• R process§ nuclei are bombarded with a large neutron flux § form highly unstable neutron rich nuclei § rapidly decay to form stable neutron rich nuclei

• P process§ Photonuclear process, and also couple with positron decay§ 190Pt, 168Yb

2-20

2-21

2-22

2-23

Origin of elements

• Binding energy§ Difference between

energy of nucleus and nucleonsà Related to mass

excess

* Dm=mnucleons-mnucleus

* Ebind=Dmc2

Ø Related to nuclear models

2-24

Origin of elements• How is Au formed from

Ir?§ Start with 193Ir and

base on s processà 193Ir + n->194Ir + b-->194Pt

à 194Pt + 3n ->197Pt + b- ->197Au* Relies upon

nuclear process

2-25

Periodic property of element

• Common properties of elements§ Mendeleyev

• Modern period table develop § Actinides added in

1940s by Seaborg§ s, p, d, f blocks

2-26

History of Radiation• 1896 Discovery of radioactivity

§ Becquerel used K2UO2(SO4)2• H2O exposed to sunlight and placed on photographic plates wrapped in black paper

§ Plates revealed an image of the uranium crystals when developed

• 1898 Isolation of radium and polonium§ Marie and Pierre Curie isolated from U ore

• 1899 Radiation into alpha, beta, and gamma components, based on penetration of objects and ability to cause ionization§ Ernest Rutherford identified alpha

• 1909 Alpha particle shown to be He nucleus§ Charge to mass determined by Rutherford

• 1911 Nuclear atom model§ Plum pudding by Rutherford

• 1912 Development of cloud chamber by Wilson• 1913 Planetary atomic model (Bohr Model)• 1914 Nuclear charge determined from X rays

§ Determined by Moseley in Rutherford’s laboratory

2-27

History• 1919 Artificial transmutation by

nuclear reactions§ Rutherford bombarded 14N with

alpha particle to make 17O• 1919 Development of mass

spectrometer• 1928 Theory of alpha radioactivity

§ Tunneling description by Gamow• 1930 Neutrino hypothesis

§ Fermi, mass less particle with ½ spin, explains beta decay

• 1932 First cyclotron§ Lawrence at UC Berkeley

2-28

History• 1932 Discovery of neutron

§ Chadwick used scattering data to calculate mass, Rutherford knew A was about twice Z. Lead to proton-neutron nuclear model

• 1934 Discovery of artificial radioactivity§ Jean Frédéric Joliot & Irène

Curie showed alphas on Al formed P

• 1938 Discovery of nuclear fission§ From reaction of U with

neutrons, Hahn and Meitner• 1942 First controlled fission reactor • 1945 First fission bomb tested• 1947 Development of radiocarbon

dating

SiP

PnAlHe

3014

3015

3015

10

2713

42

2-29

Radioelements

2-30

Technetium• Confirmed in a December 1936 experiment

at the University of Palermo§ Carlo Perrier and Emilio Segrè.§ Lawrence mailed molybdenum foil

that had been part of the deflector in the cyclotron

§ Succeeded in isolating the isotopes 95,97Tc

§ Named after Greek word τεχνητός, meaning artificialà University of Palermo officials

wanted them to name their discovery "panormium", after the Latin name for Palermo, Panormus

§ Segre and Seaborg isolate 99mTc

2-31

Promethium

• Promethium was first produced and characterized at ORNL in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell 

• Separation and analysis of the fission products of uranium fuel irradiated in the Graphite Reactor

• Announced discovery in 1947• In 1963, ion-exchange methods were used at

ORNL to prepare about 10 grams of Pm from used nuclear fuel

2-32

Np synthesis

• Neptunium was the first synthetic transuranium element of the actinide series discovered§ isotope 239Np was produced by McMillan and Abelson in

1940 at Berkeley, California§ bombarding uranium with cyclotron-produced neutrons

à 238U(n,g)239U, beta decay of 239U to 239Np (t1/2=2.36 days)§ Chemical properties unclear at time of discovery

à Actinide elements not in current locationà In group with W

• Chemical studies showed similar properties to U• First evidence of 5f shell• Macroscopic amounts

§ 237Npà 238U(n,2n)237U

* Beta decay of 237Uà 10 microgram

2-33

Pu synthesis• Plutonium was the second transuranium element of the actinide

series to be discovered§ The isotope 238Pu was produced in 1940 by Seaborg,

McMillan, Kennedy, and Wahl § deuteron bombardment of U in the 60-inch cyclotron at

Berkeley, Californiaà 238U(2H, 2n)238Np

* Beta decay of 238Np to 238Pu§ Oxidation of produced Pu showed chemically different

• 239Pu produced in 1941§ Uranyl nitrate in paraffin block behind Be target

bombarded with deuterium § Separation with fluorides and extraction with diethylether§ Eventually showed isotope undergoes slow neutron fission

2-34

Am and Cm discovery• Problems with identification due to chemical

differences with lower actinides§ Trivalent oxidation state

• 239Pu(4He,n)242Cm§ Chemical separation from Pu§ Identification of 238Pu daughter from alpha

decay• Am from 239Pu in reactor

§ Also formed 242Cm• Difficulties in separating Am from Cm and

from lanthanide fission products

2-35

Bk and Cf discovery

• Required Am and Cm as targets§ Needed to produce theses isotopes in sufficient

quantities à Milligrams

§ Am from neutron reaction with Pu§ Cm from neutron reaction with Am

• 241Am(4He,2n)243Bk§ Cation exchange separation

• 242Cm(4He,n)245Cf§ Anion exchange

2-36

Cf data

• Dowex 50 resin at 87 °C, elute with ammonium citrate

2-37

Einsteinium and Fermium

• Debris from Mike test§ 1st thermonuclear test

• New isotopes of Pu§ 244 and 246

à Successive neutron capture of 238U § Correlation of log yield versus atomic mass

• Evidence for production of transcalifornium isotopes§ Heavy U isotopes followed by beta decay

• Ion exchange used to demonstrate new isotopes

2-38

2-39

Md, No, and Lr discovery

• 1st atom-at-a-time chemistry§ 253Es(4H,n)256Md

• Required high degree of chemical separation• Use catcher foil

§ Recoil of product onto foil§ Dissolved Au foil, then ion exchange

• No controversy§ Expected to have trivalent chemistry§ 1st attempt could not be reproduced

à Showed divalent oxidation state§ 246Cm(12C,4n)254No

à Alpha decay from 254Noà Identification of 250Fm daughter using ion exchange

• For Lr 249, 250, 251Cf bombarded with 10,11B• New isotope with 8.6 MeV, 6 second half life

§ Identified at 258Lr

2-40

Applications• Sources

§ Well loggingà Neutron or gamma

source for determining soil properties

§ Irradiation sourceà 137 Cs, 60Co

• Medical§ 99mTc, 19 F, external sources

• Nuclear Power§ Enrichment§ Fission products§ Actinides

2-41

U enrichment• Utilizes gas phase UF6

§ Gaseous diffusionà lighter molecules have a higher velocity at same

energy

* Ek=1/2 mv2

à For 235UF6 and 238UF6

• 235UF6 impacts barrier more often

0043.1311

314

235

238

238

235

2238238

2235235

m

m

v

v

vmvm

2-42

Gas centrifuge

• Centrifuge pushed heavier 238UF6 against wall with center having more 235UF6

§ Heavier gas collected near top• Enriched UF6 converted into UO2

§ UF6(g) + 2H2OUO2F2 + 4HF• Ammonium hydroxide is added to the

uranyl fluoride solution to precipitate ammonium diuranate§ 2UO2F2 + 6NH4OH (NH4)2U2O7

+ NH4F + 3 H2O• Calcined in air to produce U3O8 and

heated with hydrogen to make UO2

Final Product

2-43

Fission• Nucleus absorbs energy

§ Excites and deforms § Configuration “transition state”

or “saddle point” • Nuclear Coulomb energy decreases

during deformation§ nuclear surface energy increases

• At saddle point,the rate of change of the Coulomb energy is equal to the rate of change of the nuclear surface energy

• If the nucleus deforms beyond this point it is committed to fission§ neck between fragments

disappears§ nucleus divides into two

fragments at the “scission point.”à two highly charged,

deformed fragments in contact

• large Coulomb repulsion accelerates fragments to 90% final kinetic energy within 10-20 s.

• Particles form more spherical shapes§ converting potential energy to

emission of “prompt” neutrons then gamma

2-44

Fission• Competes with evaporation of nucleons and small nucleon

clusters in region of high atomic numbers• When enough energy is supplied by the bombarding particle

for the Coulomb barrier to be surmounted

§ as opposed to spontaneous fission, where tunneling through barrier occurs

• Nuclides with odd number of neutrons fissioned by thermal neutrons with large cross sections

§ follow 1/v law at low energies, sharp resonances at high energies

• Usually asymmetric mass split

§ MH/ML1.4

§ due to shell effects, magic numbers

2-45

Fission• Primary fission products always on neutron-excess side

of stability§ high-Z elements that undergo fission have much

larger neutron-proton ratios than the stable nuclides in fission product region

§ primary product decays by series of successive - processes to its stable isobar

• Probability of primary product having atomic number Z:

• Emission of several neutrons per fission crucial for maintaining chain reaction

• “Delayed neutron” emissions important in control of nuclear reactors

c

ZZexp

c

1)Z(P

2p

2-46

Spontaneous Fission

• Rare decay mode discovered in 1940§ Observed in light actinides § increases in importance

with increasing atomic number until it is a stability limiting decay modeà Z ≥ 98à Half-lives changed by

a factor 1029

* Uranium to Fermium

§ Decay to barrier penetration

2-47

Fission Products• Fission yield curve varies with fissile isotope• 2 peak areas for U and Pu thermal neutron induced fission• Variation in light fragment peak• Influence of neutron energy observed 235U fission yield

2-48

Fission Fragments

• Fission product distribution can change with isotope

2-49

Questions

• What is nuclear forensics?• What decay modes are related to production of

radionuclides?• Why do the radioelements have no stable

isotopes?• What are the techniques that are relevant to

both element discovery and nuclear forensics?• Which applications of radionuclides are

relevant to nuclear forensics?• Why does the fission yield charge with fissile

isotope?