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Cosmic Alchemy: How Are We Made ?. Prof. Paddy Regan FInstP Department of Physics University of Surrey Guildford, GU2 7XH [email protected] Medieval alchemist…trying to turn base metals into gold… Mistake…to try and use ‘chemistry’…needed nuclear physics. the neutron. the nucleus.

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Cosmic alchemy how are we made

Cosmic Alchemy: How Are We Made ?

Prof. Paddy Regan FInstP

Department of Physics

University of Surrey

Guildford, GU2 7XH

[email protected]


Cosmic alchemy how are we made

Medieval alchemist…trying to turn base metals into gold…

Mistake…to try and use ‘chemistry’…needed nuclear physics


Cosmic alchemy how are we made

the neutron

the nucleus

radioactivity

Marie Curie (see later)

Nobel Physics 1903

Nobel Chemistry 1911

the electron

Ernest Rutherford

Nobel Chemistry 1909

Founder of Nuclear Physics

For element X write

AXN

Z

J J Thomson

Nobel Physics 1906

Atoms comprise nuclei andelectrons - known since 1910

Nuclei comprise protons andneutrons - known since 1932

Z = number of protons

N= number of neutrons

A = N+Z = mass number

neutral atom has Z electrons

m(nucleon)  2000  m(electron)


Cosmic alchemy how are we made

Atoms (‘indivisible’) …… ~10-10 m, electrons (and their

orbital structure) determine chemistry of the elements, e.g., NaCl

Nuclei…..~10-14m across, protons determine the

chemical element (Z); neutron number (N) determines

the mass, (A = N+Z). > 99.9 % of the mass of the atom

is in the nucleus.

Nucleons (protons and neutrons ~10-15m) have a

substructure, three quarks in each nucleon

(‘ups’ and ‘downs’)…but they don’t exists on their

own.


Cosmic alchemy how are we made

Mendeleyev


Cosmic alchemy how are we made

Moseley’s Law….evidence for

Atomic numbers….

‘Characteristic’ X-rays…with a

chemical (Z) dependence


Cosmic alchemy how are we made

Z=43

Tc

Z=61

Pm

Z=84

Po

Elemental composition of the Solar Nebula


Cosmic alchemy how are we made

Figure Wiescher, Regan &

Aprahamian, Physics World

Feb. 2002, page 33-38

Slow-neutron capture process

allows formation of elements

from A~56 to A=209 (Bi)...

terminates at 209Bi...why?


Cosmic alchemy how are we made

X-rays come from

atomic ‘vacancies’

i.e. holes in the

electron shells

around the atom.

Quantum mechanics

means that the

electron orbits are

fixed in energy….

X-rays come from an

electron ‘dropping’

from one energy level

to a lower one


Cosmic alchemy how are we made

X-rays come from

atomic ‘vacancies’

i.e. holes in the

electron shells

around the atom.

Quantum mechanics

means that the

electron orbits are

fixed in energy….

X-rays come from an

electron ‘dropping’

from one energy level

to a lower one


Cosmic alchemy how are we made

X-rays come from

atomic ‘vacancies’

i.e. holes in the

electron shells

around the atom.

Quantum mechanics

means that the

electron orbits are

fixed in energy….

X-rays come from an

electron ‘dropping’

from one energy level

to a lower one

X-ray

emitted


Spectral maps of the galaxy

Spectral Maps of the Galaxy

Ref http://adc.gsfc.nasa.gov/mw/mmw_images.html


Cosmic alchemy how are we made

Radioactive 26Al around the Galaxy….

Diehl et al., Astron. Astrophys 97, 181 (1993)

Full-sky Comptel map of 1.8 MeV gamma rays in 26Mg following 26Al b-decay. Nuclear reactions are taking place continually around the galaxy.


Chart of the nuclei

Chart of the Nuclei

6

5

4

Z = No. of Protons

3

2

11B

12C

13C

10B

9Be

1

0

6Li

7Li

6

7

8

9

11Be

12Be

8He

3He

4He

9Li

7B

13B

14B

15B

15C

16C

17C

10C

8Li

14C

9C

6Be

12B

9B

7Be

10Be

11C

6He

8B

5Li

10Li

11Li

14Be

1H

2D

3T

n

0

1

2

3

4

5

N = No. of Neutrons


Chart of the nuclei1

Chart of the Nuclei

The Landscape

~300 stable

~ 7000 unstable … radioactive.


What makes a nucleus stable

What makes a nucleus ‘stable’?

  • There is an ongoing interplay and competition between coulomb repulsion and strong nuclear force interactions

  • The result is that only certain combinations of Z and N give rise to stable configurations (about 300 in total).

  • Other non-stable types can ‘radioactively decay’ (about 7,000 predicted).


Cosmic alchemy how are we made

Radiation in our Environment

We are all constantly subject to irradiation mainly from natural sources.

There are three main sources of such radiation.

  • a) Primordial-around since the creation of the Earth ( 4.5 x 109years)

    • 235,8U ( and daughters including 210Po), 232Th or 40K (+ 87Rb, 138La and others....)

  • b) Cosmogenic – from interaction of Cosmic rays with Earth and atmosphere.

    • 14C, 7Be formed from cosmic ray interactions. Cosmic rays are mostly protons.

  • c) Produced or enhanced by human activity.

    • Medical or dental X-rays;

    • 137Cs (product from nuclear fission, 239Pu,

    • 241Am, 239Pu from weapons fallout


Cosmic alchemy how are we made

From NRPB-Average Radiation Dose in UK

NRPB is now HPA-RPD


Cosmic alchemy how are we made

Radioactive species in the body

Average amount by weight

Activity

Isotope

U-Uranium 90μg 1.1Bq

Th-Thorium 30 μg 0.11Bq

40K 17mg 4.4 kBq

Ra 31pg 1.1Bq

14C 22ng 3.7kBq

3H-tritium 0.06pg 23Bq

Po-Polonium 0.2pg 37Bq

Some variation- for example smokers have 4-5 times more Po.


Cosmic alchemy how are we made

Z=43

Tc

Z=61

Pm

Z=84

Po

Elemental composition of the Solar Nebula


Cosmic alchemy how are we made

How it all starts….Hydrogen (Z=1) to Helium (Z=2)

The Proton-Proton Chain


Cosmic alchemy how are we made

Nuclear Fusion creates energy up to A~56 (Z=26 = Iron)

If the star is hot enough, nuclear fusion will fuel the star

and create elements up to A~56


Cosmic alchemy how are we made

Figure Wiescher, Regan &

Aprahamian, Physics World

Feb. 2002, page 33-38

Slow-neutron capture process

allows formation of elements

from A~56 to A=209 (Bi)...

terminates at 209Bi...why?


Once you have 4 he what next

Once you have 4He what next?

  • 4He + H→5Li not energetically allowed…neither is 4He+4He →8Be…we’re stuck with A=1,2,3 and 4….

  • BUT!!! 4He can fuse with 2 other 4He (8Be) stuck together for a short time (~10-16sec) to make 12C…complicated but understood.

  • Once we have made 12C (Z=6) nuclei can fuse together and gain energy (if the star is hot and massive enough) to make all elements up to Z=26 (Iron=Fe).


Cosmic alchemy how are we made

DB ~1.5 MeV per A


Once you have 56 fe what next

Once you have 56Fe what next?

  • Top of the binding energy per nucleon curve reached at A~56…fusion above this costs energy…bad news for the star - supernova

  • BUT elements from 27-92 exist in nature – how are these made ?

  • Neutron Capture – neutrons have no charge – no electrostatic repulsion.


Cosmic alchemy how are we made

Figure Wiescher, Regan &

Aprahamian, Physics World

Feb. 2002, page 33-38

Slow-neutron capture process

allows formation of elements

from A~56 to A=209 (Bi)...

terminates at 209Bi...why?


Cosmic alchemy how are we made

Slow-neutron capture process

allows formation of elements

from A~56 to A=209 (Bi)...

terminates at 209Bi...why?

Figure Wiescher, Regan &

Aprahamian, Physics World

Feb. 2002, page 33-38

Neutron capture…

no electrostatic barrier

to nuclear fusion….

all you need are enough

Neutrons…


Cosmic alchemy how are we made

Beta –radioactive decay, (consequence of E=mc2)

2 types: (i) Beta- plus proton changes to a neutron (Z ->Z-1)

(ii) Beta – minus neutron changes to a proton (Z -> Z+1)


Cosmic alchemy how are we made

Nuclear reactions in

Red giant stars create

‘spare’ neutrons

Stellar neutron sources in the

middle of Red Giant stars

(e.g., Betelguese)

13C+4He→17O*→16O + n

22Ne+4He →26Mg*→25Mg + n


So how do you make gold

So, how do you make Gold ?

  • Gold has 79 protons (i.e. Z=79)

  • Start with Z=78 protons (i.e. Platinum)

  • Specifically 196Pt ( Pt = Z=78, N=196-78=118)

  • Reaction is 196Pt + neutron to make 197Pt

  • 197Pt is radioactive and ‘beta-decays’ to make 197Au (i.e., normal ‘stable’ gold).


Cosmic alchemy how are we made

S-process makes 209Bi from 208Pb+n → 209Pb (T1/2=3.2hr) → 209Bi

Neutron capture on stable 209Bi →210Bi (T1/2 =5 days) → 210Po.

210Po → a + 206Pb (stable nucleus, as is 207Pb and 208Pb)

Polonium-210 ‘terminates’ the period table at Bi (via the s-process)


Cosmic alchemy how are we made

The Natural Decay Chain for 238U

Qa(210Pb) = 5.41 MeV

Ea = 5.30 MeV

E(206Pb) = 0.11 MeV

T1/2 = 138 days.

‘Radium’

‘218At

=Radium B’

210Po

=Radium ‘F’

Radon

=‘Emanation’

C’

‘218Po

=Radium A’

E

C

D

C’’

BUT: Evidently, heavier (radioactive) elements like Th (Z=90) ; U (Z=92) exist ?

How are they made?


Cosmic alchemy how are we made

= 214Pb

= 214Bi


Cosmic alchemy how are we made

SN1987a before and after !!


Cosmic alchemy how are we made

A=N+Z = fixed


Cosmic alchemy how are we made

Mass Parabolas and Radioactive Decays

A = constant

For a give fixed A (isobar), we have

different combinations of Z and N.

e.g., A=Z+N=137 can be from

Z=56, N=81 →137Ba81 ; or

Z=55, N=82 → 137Cs82 (see later)…


Example of a mass parabola

Example of a mass parabola

125Ba : Z=56; N=69

125In : Z=49

p →

n + b+ + n

n →

p + b- + n

A=N+Z=125

125Cs : Z=55; N=70

125Sn : Z=50;

Mass energy

(mc2)

125Xe : Z=54; N=71

125Sb : Z=51;

125I : Z=53; N=72

125Te : Z=52; N=73

STABLE ISOBAR FOR A=125


Cosmic alchemy how are we made

Figure Wiescher, Regan &

Aprahamian, Physics World

Feb. 2002, page 33-38

Slow-neutron capture process

allows formation of elements

from A~56 to A=209 (Bi)...

terminates at 209Bi...why?


Summary

Summary

What’s made where and how.

  • Hydrogen to Helium (in the sun, p-p chain CNO cycles).

  • Helium to Carbon, triple-alpha process, special fusion.

  • Carbon to iron: nuclear fusion reactions, if hot enough.

  • Above 56Fe,

    • (a) up to Z=92, 238U, supernova, rapid neutron captures...also spits out material for future neutron capture in 2nd / 3rd generation star

    • (b) can get up to 209Bi (210Po end-point) by slow neutron capture


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