nuclear spectroscopy: from natural radioactivity to studies of exotic isotopes. prof. paddy regan...

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Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics University of Surrey, Guildford, & Radioactivity Group, National Physical Laboratory, Teddington [email protected]

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Page 1: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes.

Prof. Paddy Regan Chair of Radionuclide Metrology,

Department of PhysicsUniversity of Surrey, Guildford,

& Radioactivity Group,

National Physical Laboratory, Teddington

[email protected]

Page 2: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Outline of talk

• Elements, Isotopes and Isotones

• Alpha, beta and gamma decay

• Primordial radionuclides…..why so long ?

• Internal structures, gamma rays and shells.

• How big is the nuclear chart ?

• What could this tell us about nucleosynthesis?

Page 3: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 4: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Darmstadtium

Roentgenium Copernicium

Page 5: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

•ATOMS ~ 10-10 m

•NUCLEI ~ 10-14

m•NUCLEONS-10-15 m

•QUARKS ~?

The Microscopic World…

Page 6: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 7: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

7

Mass Spectrograph (Francis Aston 1919)

Atoms of a given element are ionized.

The charged ions go into a velocity selector which has orthogonal electric (E) and magneticfields (B) set to exert equal and opposite forces on ions of a particular velocity → (v/B) = cont.

The magnet then separates the ions accordingto mass since the bending radius isr = (A/Q) x (v/B) Q = charge of ion & A is the mass of the isotope

Nuclear Isotopes

0.4% 2.3 11.6 11.5 57.0 17.3

Results for natural terrestrial krypton

Not all atoms of the same chemical element have the same mass (A)Frederick Soddy (1911) gave the name isotopes.(iso = same ; topos = place).

Krypton, Z=36

N = 42 44 46 47 48 50

Page 8: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Nuclear chartNuclear chart

Page 9: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

9

= binding energy

MeV eV

(nuclear + atomic)

Atomic Masses and Nuclear Binding Energies

M(Z,A) = mass of neutral atom of element Z and isotope A

M(Z,A) m ( 11H ) + Nmn -

Bnuclear

The binding energy is theenergy needed to take a nucleus of Z protons and N neutrons apart into A separate nucleons

ener

gy

Mass of Z protons+ Z electrons + Nneutrons (N=A-Z)

Mass of neutral atom

Page 10: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Radioactivity…..

The science of decay…

Page 11: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

11

ISOBARS have different combinations of protons (Z) and neutrons (N) but same total nucleon number, A → A = N + Z.

(Beta) decays occur along ISOBARIC CHAINS to reach the most energetically favoured Z,N combination. This is the ‘stable’ isobar.

This (usually) gives the stable element for this isobaric chain. A=125, stable isobar is 125Te (Z=52, N=73); Even-A usually have 2 long-lived.

incr

easi

ng b

indin

g e

nerg

y =

sm

alle

r m

ass

A=125, odd-A even-Z, odd-Nor odd-Z, even N

A=128, even-A even-Z, even-Nor odd-Z, odd- N

increasing Z → increasing Z →

125Sn,Z=50, N=75

125Xe,Z=54, N=71

Page 12: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

decay: 2 types:

1) Neutron-rich nuclei (fission frags)n → p + - +

Neutron-deficient nuclei (18F PET)p → n + + +

137Cs82

137Ba81

137Xe83

A=137 Mass Parabola

Mass

(ato

mic

mass

unit

s)

Nucleus can be left in an excitedconfiguration. Excess energyreleased by Gamma-ray emission.

Page 13: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

‘signature’

1461 keV

gamma

Some (odd-odd) nuclei can decay by competing types of beta decay (a)p → n + + ; (b) n → p + + ; (c) p + e- → n+ v ).

Decay rate depends on energy released (Q value) and CONSERVATION OF ANGULAR MOMENTUM.

Big change in angular momentum and small Q →long half-life.

14

61

Note, the number of 40K decays would then be equal to the number of 1461 keV gamma rays emitted, divided by the ‘branching ratio’ which is 0.1067 in this case.

Page 14: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Nuclei can also decay by emission..

ejection of a 4He nucleus….

Depends (again) on binding energies & masses

Before…

232Th, Z = 90 N = 142

After…

228Ra, Z = 88 N =140

4He, Z=2 N=2

Page 15: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Radioactive decays occur as a result ofconservation of mass/energy E=mc2

M(232Th) = 232.038055 u = mass / energy before alpha decay. M(4He) = 4.002603 u + M(228Ra) = 228.031070 u = mass after.

1 u = 1 atomic mass unit = 931.5 MeV/c2

mc2 = M(232Th) – [ M(228Ra) + M(4He)])c2

mc2=0.004382 uc2 = 4.08 MeV

4.08 MeV of ‘binding energy’ from 232Th is released in its decay to 228Ra by the emission of a 4He nucleus ( particle).

Due to conservation of linear momentum, this energy is split between the energy of the emitted alpha particle (4.01 MeV) and the recoil energy of the residual 228Ra nucleus (0.07 MeV).

Page 16: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Geiger-Nuttall rule links Q values to explain long lifetimes of 232Th, 238U compared to other ‘heavy’ nuclei.

‘Classic’ evidence for quantum mechanical ‘tunnelling’ effect through a barrier.

Page 17: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Alpha decay can also leave daughter in excited states which can then decay by (characteristic) gamma emission.

Page 18: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

•Radiation occurs in nature…the earth is ‘bathed’ in radiation from a variety of sources.

•Humans have evolved with these levels of radiation in the environment.

Naturally Occurring Radioactive Materials

These include Uranium-238, which has radioactive half-life of 4.47 billion years.

238U decays via a series of alpha and beta decays (some of which also emit gamma rays). These create radionuclides including:

• Radium-226• Radon-222• Polonium-210

Page 19: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

•Radiation occurs in nature…the earth is ‘bathed’ in radiation from a variety of sources.

•Humans have evolved with these levels of radiation in the environment.

Naturally Occurring Radioactive Materials

These include Uranium-238, which has radioactive half-life of 4.47 billion years.

238U decays via a series of alpha and beta decays (some of which also emit gamma rays). These create radionuclides including:

• Radium-226• Radon-222• Polonium-210

(all of which are emitters).

Other NORM includes 40K (in bones!)

Page 20: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Bateman equations, for ‘secular

equilibrium’, The activity (decays per

second) of cascade nuclide equals the

activity of the ‘parent’.

Page 21: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

How do you measure the gammas?

i.e.,

How do you see inside the nucleus?

Page 22: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Little ones…single hyper-pure germanium detector, CNRP labs, U. of Surrey

Page 23: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Bigger ones…the RISING array at GSI-Darmstadt, Germany,105 Germanium detectors (see later)…

Page 24: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

How do you know how much radioactive material is present?

Activity (A) = number of decays per second

The activity (A) is also equal to the number of (radioactive) nuclei present (N), multiplied bythe characteristic decay probability per secondfor that particular nuclear species ().

A = N

is related to the half-life of the radioactive species by = 0.693 / T1/2

One signature that a radioactive decay has taken place is the emission of gamma raysfrom excited states in the daughter nuclei.

If we can measure these, we can obtain an accurate measure of the activities of the different radionuclides present in a sample.

Page 25: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Not all the gamma rays observed have to originate from the same radionuclide.

Different radionuclides are identified by their characteristic gamma-ray energies.

226Ra

228Ac

40K

Page 26: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Making a Radiological Map of Qatar

• Arabic Gulf state,• Oil Rich (oil industry all around)• To host World Cup (2022)

Page 27: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 28: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 29: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 30: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 31: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 32: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

662 keV

Page 33: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Characteristic gamma signatures can be used

to measure emissions of radionuclides from‘man-made sources’ such as Fukushima,Chernobyl, nuclear weapons tests…etc.

– Nuclear Fission fragments:• 137Cs (T1/2 = 30 years)

• 131I (T1/2 = 8 days)

– Neutron-capture on fission products in reactors• 134Cs (T1/2 = 2 years)

Page 34: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 35: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics
Page 36: Nuclear Spectroscopy: From Natural Radioactivity to Studies of Exotic Isotopes. Prof. Paddy Regan Chair of Radionuclide Metrology, Department of Physics

Summary

• Radionuclides (e.g. 235U, 238U, 232Th, 40K) are everywhere.

• Radioactive decays arise from energy conservation and other (quantum) conservation laws.

• Characteristic gamma ray energies tell us structural info.