Transcript Charterhouse2-gelletly-elements

Charterhouse – November 2009
1. Introduction
2. The abundances of the elements
3. Some simple nuclear physics
- Geiger and Marsden
- Rutherford and Nuclear Reactions
- Chadwick and the neutron
- The need for accelerators
- Why radioactive decay?
4. Where do they come from?
- Big Bang
- Star formation
- Main Sequence Stars
- Explosive Events
5. Searching for Superheavy Elements
- Element 112 and beyond.
Charterhouse – November 2009
Chemical elements in the body
Chemical Element
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
Potassium
Sulphur
Sodium
Magnesium
Composition by
Weight
65
18
10
3
1.5
1.0
0.35
0.25
0.15
0.05
Cu,Zn,Se,Mo,F,Cl,I,Mn,Co,Fe
Li,Sr,Al,Si,Pb,V,As,Br
0.70
trace levels
The abundances of the elements in the Solar System
Note:- Logarithmic scale
The Abundances of the
Elements for A = 70 - 210
Note the double peaks at
N = 46/50, 76/82, 116/126
They are due to production
by the two separate
processes –
the slow ( s ) and rapid ( r )
neutron capture processes
Relative Abundance of elements in Earth’s upper crust
The Beginnings of Nuclear Physics
Before and After Geiger and Marsden
J.J.Thomson
E.Rutherford
H.Geiger and E.Marsden
Manchester University
Proc.Roy.Soc A82 (1909)
The Atom
u u
d
proton
u d
d
neutron
u
e
d
e
proton
}
nucleus
neutron
electron

u - up quark
d - down quark
e - electron
-e neutrino
First Controlled Nuclear Reaction
Rutherford’s last major piece of work at Manchester
A follow up to some work of E.Marsden in Rutherford’s lab.
- Alpha particles passing through H gas seemed to produce
long range particles.
Source of α - particles
ZnS Screen
Thin metal plate
First Controlled Nuclear Reaction
Source of α - particles
ZnS Screen
Thin metal plate
 With CO2 or O2 in the chamber no.of scintillations on ZnS screen fell with stopping
power of the gas but if N2 was introduced no. of scintillations with brilliance of
H-scintillation (proton) went up.
Conclusion he had observed the first controlled nuclear reaction or transmutation
14N
+ 4He
17O
+p
The Radioactive Decay Law
1902 – Rutherford and
Soddy deduced from
careful observations
that the rate of
disintegration of a
radioactive substance
followed an exponential. Frederic Soddy
(1877-1956)
dN/dT = -λN or
N = N0 exp(-λt)
1903 – They suggested that Radium was a
disintegration product and since it was
always present in Uranium minerals it
had to come from Uranium decay. It was
not long before the whole natural decay
chains from U and Th to Lead (Pb) were
unravelled.
a

p
b
g
p
n
f2
f1
n
g
b

n
The need for Accelerators
Incident particle
• When close together two nucleons attract each other strongly
and so nuclei interact strongly
• As a result studying reactions is fine
but two positively charged particles repel one another
• In order to make them interact we must give them enough energy,
we must accelerate them.
Chadwick’s Experiments
Radiation
Cloud Chamber
Radiation
The Elements of Nuclear Structure
1932 – Discovery of Neutron
1932 – Heisenberg immediately interpreted the nucleus
as consisting of protons plus neutrons and isotopes
have a natural explanation in terms of having the same
no. of protons and different nos. of Neutrons.
e.g 1H – 1 proton
nucleus of Hydrogen
2H – 1 proton + 1 neutron
nucleus of deuterium
3H – 1 proton + 2 neutrons nucleus of tritium
1932 – Explanation of Beta Decay [Pauli]
1932 – Discovery of positron by C.D.Anderson,
which had been predicted by P.A.M.Dirac
Super Heavies
Fewer than 300 nuclei
Proton Drip Line
Neutron Drip Line
Another View of the Nuclear Landscape
E = mc2
So the valley represents
the nuclei with the lowest
total energy.
The nuclei up on the sides of
the valley are unstable and will
decay successively until they
reach the bottom and hence
stability.
Neutron masses plotted versus N and Z
For the light nuclei
Our raw materials for nuclear
Physics are the atomic nuclei at
the bottom of the valley-there are
283 stable or long-lived isotopes
we can find in the Earth’s crust or
atmosphere
Super Heavies
Fewer than 300 nuclei
Proton Drip Line
Neutron Drip Line
Where were the elements made?
In essence only H and He were made in the Big Bang
in the ratio H : He = 75: 25 by mass
 All other elements
were either made in
stars or in the
laboratory.
Core temp. ~ 1.5 x 107 K
H burning
heats core
Gravity
Stars form in collapsing clouds of gas and dust
The proton-proton chain
1H
+ 1H = 2H + e+ +
(A)
1H
+ 1H = 2H + e+ +
1H + 2H = 3He + g
(B)
(C)
+ 2H = 3He + g
3He + 3He = 4He + 1H + 1H + 
(D)
(E)
1H
Thus the sequence of reactions turns 4 protons into an alpha particle.
1H
+ 1H + 1H + 1H
4He
+ 2e+ + 2e + 3g
Since the alpha particle is particularly tightly bound this process of
turning 4 protons into an alpha releases about 26 MeV of energy.
It is this energy which heats the stellar interior,allows it to withstand
the gravitational pressure and causes it to shine!
After the Main Sequence
1.Once a star’s hydrogen is used up its future life
is dictated by its mass
2.During the H-burning phase the star has been creating
He in the core by turning four protons into a He nucleus
plus electrons and neutrinos.
3.Once H burning stops in the centre the star contracts
and some of the potential energy is turned into heat.
If the core temperature rises far enough then He burning
can begin.
1010
years
Red Giant
(3000ºK
Red)
H burning
The Earth
will be
engulfed!!
a+a+a 12C +a 16O
Core temp now 108 K
If Etoile
the star is massive
eight times more
massive than the Sun
supergéante
H He
C
O
Ne Na Mg
Al Si P S
SUPERNOVA
Gravitación
Fe
C. THIBAULT (CSNSM)
White Dwarf
H, N, O
¡¡only!!
(Hubble)
Fluorescence
Helix Planetary Nebula in the constellation of Aquarius
Death of a Red Giant:
SUPERNOVA – SN1987A
October 1987
1056 Joules of energy
This happened 170000 years ago in the nearest galaxy
The End of Fusion Reactions in Stars
A = 56
Binding Energy per nucleon as a
function of Nuclear Mass(A)
[Remember E = mc2]
•When two nuclei fuse together energy is released up to mass A = 56
Beyond A = 56 energy is required to make two nuclei fuse.
•As a result we get the burning of successively more massive nuclei
in stars.First H, then He, then C,N,O etc.
•In massive stars we eventually end up with different materials burning
in layers with the heaviest nuclei burning in the centre where the
temperature is highest.
•When the heaviest(A = 56) fuel runs out the star explodes-Supernova
Principe de
nucléosynthèse
Principle
of laNucleosynthesis
protons
63
65
28 Ni
58 59 60 61 62
64
27 Co
26 Fe
59
29 Cu
54 55 56 57 58
35
30
40
neutrons
Il y a compétition
Competition
between twoentre
processes
••Capture
Captureof
d’un
neutron
a neutron
••b Radioactivité
Radioactivityb–
n  p + e-+
C. THIBAULT (CSNSM)
Part of the Slow Neutron Capture Pathway
In Red Giant Stars neutrons are produced in the 13C( 4He,n) 16O or
22Ne(4He,n)25Mg reactions.
The flux is relatively low.As a result there is time for beta decay before
a second neutron is captured.
The boxes here indicate a stable nuclear species with a particular Z & N.
Successive neutron captures increase N. This stops when the nucleus
created is unstable and beta decays before capture.
The pathways for the s- and r-processes
S-process:Neutron flux is low so beta decay occurs before a second
neutron is captured.We slowly zigzag up in mass.
R-process:Neutron flux is enormous and many neutrons are captured
before we get beta decays back to stability.
The Abundances of the
Elements for A = 70 - 210
Note the double peaks at
N = 46/50, 76/82, 116/126
They are due to production
by the two separate
processes
S – process
&
R-process.
Earth:
~1890 Kelvin: ~20-40 Myears
radioactivity
1905 Rutherford => billions
of years
[age: 4.55 billion years
(radioactive dating)]
Radioactivity  40% of heating of
Earth
Heaven:
26Al
all-sky map:
T1/2=0.74 My
Eγ =1.8 MeV
 continuous
nucleosynthesis
picture by COMTEL
The Elements beyond Uranium (Z = 92)
We do not find them on Earth because they are all short-lived compared with the
age of the Earth [ ~ 5 x 109 years ]. So even if they have been produced in stars we
would no longer be able to find them.
However we have been able to make another 15-20 elements in the laboratory
The basic route is via Nuclear reactions with the first attempts being in the 1930s
following the discovery of the neutron.
Neutron-Induced Reactions.
In the years following its discovery Rutherford’s prediction that such a particle would
readily interact with nuclei was amply fulfilled.
The importance of the neutron capture reaction was highlighted by the work of
E.Fermi and his collaborators. They produced many new radioactive species in this
way.
They realised it should be possible to make new, heavier elements this way. For
example
238U
+n
239U
239U
239Np
+γ
+ e- + 
This reaction and subsequent decay does occur but it was masked by the many other
activities following fission.
 Hahn and Strassmann (1939) finally reported that among them their were isotopes
of Ba, La and Ce. They did not take this to its logical conclusion.
Transuranic elements
 1940 – McMillan and Abelson identify 23993Np
β
238
239
92U + n
β
239
92U
239
93Np
23.5 m
α
235
94Pu
2.4 x 104 y
2.3 d
92U
 1940 – 1960 further elements discovered in neutron capture
239
94Pu
4n
243
94Pu
β
243
95Am
n
244
95Am
β
244
96Cm
This needs high neutron flux = Nuclear weapons debris
 Further elements have been discovered in Heavy Ion Collisions
249
11 B
Cf
+
98
5
256
103Lr
+ 4n
Transuranic elements
 Pu (94), Am (95), Cm (96), Bk (97), Cf(98)
all discovered at University of California,Berkeley under Seaborg
 Es (99), Fm (100), Md (101), No(102), Lr (103)
again discovered at Berkeley now under Ghiorso
Rf (104), Db(105), Sg(106), Bh(107)
Joint Institute for Nuclear Research, Dubna,Russia – Flerov
Hs (108), Mt(109), Ds (110), Rg (111), Cn(112)
at GSI under Armbruster, Munzenberg and Hoffman
Copernicium
Elements 113-118
still unconfirmed but Dubna under Oganessian
Super Heavies
Fewer than 300 nuclei
Proton Drip Line
Neutron Drip Line
Shell Correction Energies Eshell in the Region of Superheavy
Elements
P. Möller et al.
Elements 107-112
first synthesised
and identified at GSI;
New names:
107 – Bh
108 – Hs
109 – Mt
110 – Ds
111 – Rg
region of spherically
shell stabilised nuclei
(“island of stability”)
208Pb
region of deformed shell
stabilised nuclei around
Z=108 and N=162
Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04
SHIP- Recoil Mass separator at GSI, Darmstadt.
Recoilling nuclei from the target are separated from the
beam particles and from each other by mass as they
pass through the crossed electric and magnetic fields
of the spectrometer. The reactions of interest are where the
two nuclei fuse gently and so there is little internal
energy. As a result only 1 neutron
pops out leaving the heavy
super-heavy nucleus in
the final detector.
Final detector
Needed to keep the target cool
Synthesis and Identification of SHE at SHIP
n
70Zn
208Pb
277112
277112
273110
269Hs
265Sg
kinematic separation
in flight
known
257No
253Fm
8.34 MeV
15.0 s
Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04
261Rf
8.52 MeV
4.7 s
CN
11.45 MeV
280 s
11.08 MeV
110  s
9.23 MeV
19.7 s
4.60 MeV (escape)
7.4 s
identification
by a-a correlations
to known nuclides
SHE Synthesis
– Present Status
FLNR
GSI
RIKEN
low cross-sections
( ≈ 35 fb)
high cross-sections
(0.5 – 5 pb)
D.Ackermann
Dieter-Ackermann_GSI/University_of_Mainz_-_IReS-Symposium-2004
Creeping up on the Superheavies
at GSI
region of spherically
shell stabilised nuclei
(“island of stability”)
The Limits of Nuclear Existence
• Challenge: To create elements 112-116 and beyond.
• Two routes:Cold and hot fusion
•
• Question:Will n-rich projectiles
allow us to approach closer to
the anticipated centre of the
predicted Superheavy nuclei.
• There is some evidence that extra
neutrons enhance fusion below the
barrier.The figure shows studies
at Oak Ridge with 2 x 104 pps
J.F.Liang et al.,PRL91(2003)152701 where it is clear that there is a large
enhancement below the barrier.
• RNBs may allow us to approach the spherical N=184 shell.
But might the LHC discover yet more particles?
Well, actually, our best theories say there may be more
To discover: Supersymmetric Particles!
The p-p chain;the reactions which power the Sun
Overall - 4p  4He + 2e- +2 + 26.7 MeV
The CNO-Cycle:
In stars where we already have
C,N and O we can get hydrogen
burning
4p
a + 2e- + 2 +26.4 MeV
The C,N and O nuclei act as
catalysts for the burning process
Hans Bethe-1938
Life Cycle of Stars and Nucleosynthesis
1. Formation from large clouds of gas and dust.
2. Centre of cloud is heated as it collapses under gravity
3. When it reaches high enough temperature then nuclear reactions
can start.
4p 4He + 2e + 2ν + 26.7 MeV
4. This raises temperature further and star eventually reaches
equilibrium under heating internally and gravitational collapse.
5. The process of making heavier nuclei occurs in the next stage.
After the Main Sequence
1.Once a star’s hydrogen is used up its future life is dictated by its mass.
2.During the H-Burning phase the star has been creating He in the core
by turning 4 protons into a He nucleus plus electrons and neutrinos.
Once the H burning stops in the centre the star contracts and some
of the potential energy is turned into heat. If the core temperature
rises far enough then He-burning can begin. Coulomb(electrostatic)
barrier is 4 times higher for two He nuclei compared with protons.
3.Now we face again the problem of there being no stable A = 5 or 8
nuclei.
4.It turns out that we can bypass these bottlenecks but it depends
critically on the properties of the properties of individual levels in
Be and C nuclei.
The Creation of 12C and 16O
• H and 4He were made in the Big Bang.Heavier nuclei were
not produced because there are no stable A = 5 or 8 nuclei.
There are no chains of light nuclei to hurdle the gaps.
• How then can we make 12C and 16O?
• Firstly 8Be from the fusion of
two alphas lives for 2.6 x 10-16 s
cf. scattering time 3 x 10-21 s.
They stick together for a
significant time.
• At equilibrium we get a concentration
of 1 in 109 for 8Be atoms in 4He.
• Salpeter pointed out that this meant that C must be produced
in a two step process.
• Hoyle showed that the second step
must be resonant.He predicted that
since Be and C both have 0+
s-wave fusion must lead to a
0+ state in 12C close to the Gamow
peak at  3 x 108K.
• Experiment shows such a state at
7654 keV with  = 5 x 10-17s
The 7654 keV state
has a/g  1000
A rare set of
circumstances indeed!
The Destiny of the Stars…
White
Dwarf
Main
Sequence
AÑOS
Density/
109
109
Brown
Dwarf
Red
Giant
Massive Stars
Supernova
Algún
109
segundo
100 kg
C. THIBAULT (CSNSM)
Spectrum of Cassiopeia
We see here the remnants of a
supernova in Cassiopeia.This
radio telescope picture is taken
with theVery Large Array in
New Mexico.
From the measured rate of
expansion it is thought to have
occurred about 320 years ago.
It is 10,000 ly away.
With optical telescopes almost
nothing is seen.
The inset at the bottom shows a small part
of the gamma ray spectrum with a clear
peak at 1157 keV,the energy of a gamma
ray in the decay of 44Ti.
Abundance Predictions
Synthesis and Identification of SHE at SHIP
n
70Zn
208Pb
277112
277112
273110
269Hs
265Sg
kinematic separation
in flight
known
257No
253Fm
8.34 MeV
15.0 s
Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04
261Rf
8.52 MeV
4.7 s
CN
11.45 MeV
280 s
11.08 MeV
110  s
9.23 MeV
19.7 s
4.60 MeV (escape)
7.4 s
identification
by a-a correlations
to known nuclides
SHE Synthesis – Status September 2004
FLNR
GSI
RIKEN
Ds
282
Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04