• • •

Nuclear Forensics Summer School Production 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

2-1

• • •

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)



Electrons can be excited

*

Higher energy orbitals

*

Ionization



Binding energy of electron effects ionization Isotopes



Same Z different N Isobar



Same A (sum of Z and N) Isotone



Same N, different Z Isomer



Nuclide in excited state



99m Tc

A Z Chemical Symbol N 2-2

Types of Decay

1.



decay (occurs among the heavier elements)

226

Ra

88  222

Rn

86  2 4 

2.



decay

131

I

53  131

Xe

54      

Energy



Energy

3. Positron emission

22 11

Na

 22 10

Ne

     

Energy

4. Electron capture

26 13

Al

    26 12

Mg

  

Energy

5. Spontaneous fission

252 98

Cf

 140 54

Xe

 108 44

Ru

 4 0 1

n



Energy

2-3

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

2-4

• • • •

X-rays

Removal of K shell electrons



Electrons coming from the higher levels will emit photons while falling to this K shell



series of rays (frequency



or wavelength

l

) are noted as K



, K



, K

g 

If the removed electrons are from the L shell, noted as L



, L



, L

g

In 1913 Moseley studied these frequencies



, showing that:

L g L  K  L  K   

A

(

Z



Z

)

o

where Z is the atomic number and, A and Z 0 are constants depending on the observed transition. K series, Z 0 = 1, L series, Z 0 = 7.4. O N M L K

2-5

Fundamentals of x-rays

•

X-rays



X-ray wavelengths from 1E-5 angstrom to 100 angstrom



De-acceleration of high energy electrons



Electron transitions from inner orbitals

*

Bombardment of metal with high energy electrons

*

Secondary x-ray fluorescence by primary x-rays

*

Radioactive sources

*

Synchrotron sources

2-6

• • • • • •

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 Massive objects very dense (sun's core ~ 2x10 5 -18 kg/m3) and cold (~ 3 K) kg/m3) and very hot (sun's core~16x10 6 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

2-7

2-8

2-9

Origin of elements

• •

Initial H and He Others formed from nuclear reactions



H and He still most abundant

2-10

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

 

strong staggering and gaps lightest nuclei mass numbers multiple of 4 have highest abundances

2-11

• • •

Abundances

earth predominantly



oxygen, silicon, aluminum, iron and calcium



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

2-12

Origin of elements

•

Timeline



10 43



s after the Big Bang, Planck time



temperature of 10

*

32 K (kBT ~ 10 k BT(eV) = 8.6 x 10-5 T(K) 19

  

GeV)



volume that was ~10 -31 of its current volume. [ Matter existed in plasma of quarks and gluons particles were present and in statistical equilibrium



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



As Universe expanded it cooled and some species fell out of statistical equilibrium 10 6 s (T~10 13



K) photons from the black body radiation could not sustain the production of the massive particles



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.

2-13

Timeline

• • • • • • •

10 -2 s (T~10 11



K) T(K)=1.5E10t

1/2 , t in seconds density of the Universe dropped to ~ 4 x 10 6 kg/m 3 neutrons and protons interconvert by the weak interactions



neglect free neutron decay



Life time too long (10.6 m)



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



mc 2 /kT)

 

T=10 12 K, n/p ~ 1, T=10 11 K n/p ~ 0.86, etc.

T = 10 11 K, no complex nuclei were formed 1 second



T= 10 10 K



pair production since kT < 1.02 MeV



neutron/proton ratio was ~ 17/83.

225 seconds



neutron/proton ratio was ~ 13/87,

 

T ~ 10 9 K density was ~ 2 x10 4 kg/m 3 first nucleosynthetic reactions occurred.

2-14

• • • • •

Origin of Elements

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

 1 H + n → 2 H + g  2 H + 1 H → 3 He        3 3 2 H + n → 3 H H + 1 H → 4 He + g He + n → 4 He + g 3 2 H + H + 2 2 H → H → 4 He + 3 H → 3

He+

3

He

→ 4 He + n 4 He + g 7 Li + g 7

Be

+ g  

7 Be short lived Nucleosynthesis lasted 30 minutes Chemistry began in 10 6 years at 2000K Further nucleosynthesis in stars



No EC process in stars

2-15

• •

Stellar Nucleosynthesis

He burning



4 He



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

  

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



12 C + 1 H → 13 N +

g   

13 13 N → 13 C + e + + νe C + 1 H → 14 N + γ 14 N + 1 H → 15 O + γ

  

15 O → 15 N + e + 15 N + 1 H → 12 C + 4 He Net result is conversion of 4 protons to alpha particle



+ νe 4 1 H → 4 He +2 e + + 2 νe +3 γ

2-16

emission



14 N + n → 14

Origin of elements

Neutron Capture and proton C + 1 H; 14 N(n, 1 H) 14 C

•

Alpha Cluster

 

Based on behavior of particles composed of alphas Neutron Capture; S-process A>60

 

68 Zn(n, γ) 69 Zn 69 Zn → 69 Ga +

      

mean times of neutron capture reactions



reaction =ln2/rate = ln2/Nn<



v>.

Nn ~ 10 11 /m3,



= 0.1 b at En ~ 50 keV, then



~ 10 5 years

 

Up to Bi Neutrons from (



,n) on light nuclei

2-17

2-18

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

 190 Pt, 168 Yb 2-19

2-20

2-21

2-22

Origin of elements

•

Binding energy



Difference between energy of nucleus and nucleons



Related to mass excess

* * 

m=m nucleons m nucleus E bind =



mc 2



Related to nuclear models

2-23

Origin of elements

•

How is Au formed from Ir?



Start with 193 Ir and base on s process



193 Ir + n-> 194 Ir +



-> 194 Pt



194 Pt + 3n -> 197 Pt +



-> 197 Au

*

Relies upon nuclear process

2-24

Periodic property of element

• •

Common properties of elements



Mendeleyev Modern period table develop



Actinides added in 1940s by Seaborg



s, p, d, f blocks

2-25

• • • • • • • •

History of Radiation

1896 Discovery of radioactivity



Becquerel used K 2 UO 2 (SO 4 ) 2 • H plates wrapped in black paper 2 O exposed to sunlight and placed on photographic



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

2-26

• • • • •

History

1919 Artificial transmutation by nuclear reactions



Rutherford bombarded 14 alpha particle to make 17 O N with 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

2-27

• • • • • •

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

4 2 He  27 13 Al  1 0 n  30 15 P 30 15 P     30 14 Si 2-28

Radioelements

2-29

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 95,97 Tc Named after Greek word τεχνητός, meaning artificial



University of Palermo officials wanted them to name their discovery "

panormium

", after the Latin name for Palermo,

Panormus

Segre and Seaborg isolate 99m Tc

2-30

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

2-31

Np synthesis

• • • •

Neptunium was the first synthetic transuranium element of the actinide series discovered



isotope 239 Np was produced by McMillan and Abelson in 1940 at Berkeley, California

 

bombarding uranium with cyclotron-produced neutrons



238 U(n,

g

) 239 U, beta decay of 239 U to 239 Np (t 1/2 Chemical properties unclear at time of discovery



Actinide elements not in current location =2.36 days)



In group with W Chemical studies showed similar properties to U First evidence of 5f shell Macroscopic amounts



237 Np



238 U(n,2n) 237 U

 *

Beta decay of 237 U 10 microgram

2-32

• •

Pu synthesis

Plutonium was the second transuranium element of the actinide series to be discovered



The isotope 238 Pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl



deuteron bombardment of U in the 60-inch cyclotron at Berkeley, California



238 U( 2 H, 2n) 238 Np

 *

Beta decay of 238 Np to 238 Pu Oxidation of produced Pu showed chemically different 239 Pu 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

2-33

• • • •

Am and Cm discovery

Problems with identification due to chemical differences with lower actinides



Trivalent oxidation state 239 Pu( 4 He,n) 242 Cm

 

Chemical separation from Pu Identification of decay 238 Pu daughter from alpha Am from 239 Pu in reactor



Also formed 242 Cm Difficulties in separating Am from Cm and from lanthanide fission products

2-34

Bk and Cf discovery

• • •

Required Am and Cm as targets



Needed to produce theses isotopes in sufficient quantities



Milligrams

  

Am from neutron reaction with Pu Cm from neutron reaction with Am 241 Am( 4 He,2n) 243 Bk Cation exchange separation 242 Cm( 4 He,n) 245 Cf



Anion exchange

2-35

Cf data

•

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

2-36

Einsteinium and Fermium

• • • •

Debris from Mike test



1 st thermonuclear test New isotopes of Pu



244 and 246



Successive neutron capture of 238 U



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

2-37

2-38

Md, No, and Lr discovery

• • • • • •

1 st



atom-at-a-time chemistry 253 Es( 4 H,n) 256 Md Required high degree of chemical separation Use catcher foil



Recoil of product onto foil



No controversy



Expected to have trivalent chemistry

 

Dissolved Au foil, then ion exchange 1 st



attempt could not be reproduced 246 Showed divalent oxidation state Cm( 12 C,4n) 254 No

 

Alpha decay from 254 No Identification of 250 Fm daughter using ion exchange For Lr 249, 250, 251 Cf bombarded with 10,11 B New isotope with 8.6 MeV, 6 second half life



Identified at 258 Lr

2-39

Applications

• • •

Sources



Well logging

 

Neutron or gamma source for determining soil properties Irradiation source



137 Cs, 60 Co Medical



99m Tc, 19 F, external sources Nuclear Power



Enrichment

 

Fission products Actinides

2-40

• •

U enrichment

Utilizes gas phase UF 6



Gaseous diffusion



lighter molecules have a higher velocity at same energy 235 UF 6

 *

E k =1/2 mv 2 For 235 UF 6 and 238 UF 6 impacts barrier more often

m

2 235

v

235 

m

2 238

v

238

v

235

v

238 

m m

238 235  314 311  1 .

0043 2-41

Gas centrifuge

• • • •

Centrifuge pushed heavier 235



UF 6 238 UF 6 against wall with center having more Heavier gas collected near top Enriched UF 6



UF 6 converted into UO (g) + 2H 2 O



UO 2 F 2 2 + 4HF Ammonium hydroxide is added to the uranyl fluoride solution to precipitate ammonium diuranate



2UO 2 F 2 + 6NH 4 OH



(NH 4 ) 2 U 2 O 7 + NH 4 F + 3 H 2 O Calcined in air to produce U 3 O 8 and heated with hydrogen to make UO 2 Final Product

2-42

• • • • • •

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.”



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

2-43

• • • •

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

 

M H /M L



1.4

due to shell effects, magic numbers

2-44

• • • •

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:

 Z  P ( Z )  1 c  exp     c Z p  2   

Emission of several neutrons per fission crucial for maintaining chain reaction “Delayed neutron” emissions important in control of nuclear reactors

2-45

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 mode



Z ≥ 98



Half-lives changed by a factor 10

*

29 Uranium to Fermium



Decay to barrier penetration

2-46

• • • •

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

235 U fission yield 2-47

•

Fission product distribution can change with isotope

Fission Fragments

2-48

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?

2-49