Nuclear Physics Research At Surrey

…from pure to applied and everything in between..

What is (nuclear physics) research ?

• Pure fundamental, knowledge-driven inquisitive search for understanding….

• To help obtain a basic, fundamental understanding of how things work.

• Part of the basic cultural fabric of society, research for research sake, beauty in nature, parallels to the arts.

• Usefulness….generation of income, to enhance the quality of life,

(i.e., why bother at all ?)

Some areas….

• Pure, fundamental nuclear physics research:

– Exotic nuclei, some very ‘big science questions’

– What are the limits of nature ?

– Underlying nuclear theory

– Some surprises (e.g., nuclear halos)

– How were the chemical elements created ?

– Trapping (and releasing) nuclear energy.

Some more areas?

• (Some) applications of fundamental nuclear physics research:

– Environmental / nuclear waste monitoring.• Gamma-ray spectrometry..let’s play ‘find the

uranium’

– Instrumentation development, new detectors,

– Surrey ion-beam centre (PIXE, PIGE)• Looking at diseases (arthritis with nuclear probes)

– Looking inside stuff….

A recent survey of General Public in UK asked:

“The nuclei of atoms make up 99.99% of all matter. So what are they made of?• Electrons• Quarks• Photons• Neutrinos• DNA”

Only 2% knew correct answer!!

A recent survey of General Public in UK asked:

“The nuclei of atoms make up 99.99% of all matter. So what are they made of?• Electrons• Quarks• Photons• Neutrinos• DNA”

Only 2% knew correct answer!!

Is it surprising that the general public does not know this?

Should we be worried?

Does is matter???

Is it surprising that the general public does not know this?

Should we be worried?

Does is matter???

ANSWER:

Quarks.

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.

Chart of the Nuclei

1H 2D

3He 4He

6Li 7Li

n

9Be

3T

6He

5Li

6Be 7Be8Li 9Li

10Be10Li 11Li

8He

11Be 12Be

10B 11B9B

14Be

12B 13B 14B 15B8B7B

12C 13C 14C 15C 16C 17C11C10C9C

Z =

No.

of

Pro

tons

0

1

2

3

4

5

6

N = No. of Neutrons

0 1 2 3 4 5 6 7 8 9

October

2002 issue

W.Catford

et al.,

October

2002 issue

W.Catford

et al.,

Signal for existence of tetraneutron in 14Be breakup reaction at GANIL

‘Nuclei = combinations of protons (Z) and neutrons (N).

Chart of the Nuclides = a ‘2-D’ periodic table……

<300 of the (Z,N) combinations are stable and make up’everyday’ atoms.

~7,000 other combinations are unstable nuclei.

Most energetically stable nuclei in the middle, More exotic, unstable nuclei at the edges….

Z=43Tc Z=61

Pm Z=84Po

Elemental composition of the Solar Nebula

218Po

…formation of ‘exotic’ radioactive nuclei (in nature)…new elements created e.g., Pa, Actinium, Radium, Radon, Polonium etc.

‘218Po =Radium A’

‘218At =Radium B’

C

D

E

210Po=Radium ‘F’ Radon

=‘Emanation’

‘Radium’

C’

C’’

The Natural Decay Chain for 238U

Aside: information here is used extensively in environmental monitoring; + radioactive dating – age of the earth ~109 yrs…evidence for evolution....

For a ‘typical’ nucleus,

Nuclear Volume A (= number of protons and neutrons)

Since for a sphere, V = 4R3/3

Thus nuclear radius, R A1/3 R = (1.2 x10-15m) A1/3

Rutherford Scattering experiments showed this relation to

hold for all nuclei studied….so what’s new to learn….

Then…1985 – the strange case of ‘Lithium -11’ (note stable lithium isotopes are Lithium-6 and Lithium-7)

The probability of a beam of ‘neutron-rich’ lithium-11 isotopes colliding on carbon target was much larger than expected.

Lithium beam

targetdetector

Two Surrey nuclear ‘former PhD’ students

Nuclear ‘halos’ and Borromean Nuclei….Nuclear ‘halos’ and Borromean Nuclei…. Nuclear ‘halos’ and Borromean Nuclei….Nuclear ‘halos’ and Borromean Nuclei….

J.S. Al-Khalili & J.A. Tostevin, Phys. Rev. Lett. 76 (1996) 3903

Halo nuclei are examples of ‘Borromean’ systems,only bound with three Interactions…remove any oneand the other two fall apart….

The neutron dripline in light nuclei

tetra-neutron?

proton dripline

Borromeanhalo states

N=84n

4n

How Far Can We Go ?

• What are the ‘nuclear limits’ ?

• What is the heaviest element ?

• How are the heavier elements formed ?

What about ‘inside’ the nucleus(i.e. nuclear ‘structure’) ?

• Can we see ‘inside’ the nucleus ?

• What does it tell us?

Nuclear Excited States – Nuclear Spectroscopy.Nuclei can exist in either the ground state or an excited stateEach nucleus is different….but groups of structural patterns do appear….

• Nuclear states labelled by spin and parity quantum numbers and energy. • Excited states (usually) decay by gamma rays (non-visible, high energy light).• Measuring gamma rays gives the energy differences between quantum states.

gamma ray decay

Evidence for nuclear shell structure…..energy of 1st excited state in even-even nuclei….E(2+).

What do we expect ?

large gaps in single-particle structure of nuclei…MAGIC NUMBERS = ENERGY GAPS

(SOME) BIG NUCLEAR PHYSICS’ QUESTIONS TO BE ADDRESSED

• Does the ordering of nuclear quantum states change ?•How robust are the magic numbers?•What are the limits of nuclear existence?

K-electrons

L-electrons

T1/2 = 10.4 s205Au126

202Pt

N=82N=126

• A (big!) problem, can’t reproduce the observed elemental abundances.

• We can ‘fix’ the result by changing the shell structure (i.e. changing

the magic numbers)….but is this scientifically valid ? N=126N=82

• Need to look at N=82 and 126 ‘exotic’ nuclei in detail….

Turning Lead into Gold and Platinum….

Super Heavy Elements?

• Rutherford worked with decays from Thorium and Uranium the heaviest element (Z=90 & 92) known at the time.

• He inferred their presence and other elements in their decay chains by characteristic alpha decay sequences….

Darmstadtium

Roentgenium Copernicium

Selection of science news websites, between 6 and 10 April 2010:

Yu. Ts. Oganessian et al.

Predictions for the heaviest elements….

Robust theoretical predictions of nuclear quantum shell structurein the heaviest (indeed, so far unknown) elements

….these drive future experimental investigations

Nuclear isomers: energy traps

[Phil Walker and George Dracoulis, Nature 399 (1999) 35]

excited state half-lives ranging from nanoseconds to years

(‘Big’) Physics Questions from the STFC Nuclear Physics Advisory Panel

What is the Nature of Nuclear Matter?• What are the limits of nuclear existence?• How do simple patterns emerge in complex nuclei?• Can nuclei be described in terms of our understanding of the

underlying fundamental interactions?• What is the equation-of-state of nuclear matter?• How does the ordering of quantum states change in extremely

unstable nuclei?• Are there new forms of structure and symmetry at the limits of

nuclear existence? What are the Origins of the Elements?• How, and where, were the heavy elements synthesised?• What are the key reaction processes that drive explosive

astrophysical events such as supernovae, and X-ray bursts?• What is the equation-of-state of compact matter in neutron stars?• What are the nuclear processes, and main astrophysical sites, that

produce the γ-ray emitting radionuclides observed in our galaxy?• How do nuclear reactions influence the evolution of massive stars,

and how do they contribute to observed elemental abundances?

SN1987a before and after !!

Q210Pb) = 5.41 MeVE = 5.30 MeV E(206Pb) = 0.11 MeVT1/2 = 138 days.

‘218Po =Radium A’

‘218At =Radium B’

C

D

E

210Po=Radium ‘F’ Radon

=‘Emanation’

‘Radium’

C’

C’’

The Natural Decay Chain for 238U

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

= 214Pb

= 214Bi

Movie

Surrey Ion Beam Centre 3 MV Tandetron

Ion beam induced charge (IBIC) irradiation study in synthetic single crystal diamond using 2.6 MeV protons

abstract

D

E

CC

E [

%]

90

100

F

CC

E [

%]

25

100

A

B

C

(a) (b)

500 μm

Silver paint

Co

nta

ct

ed

ge

CCE [%]40 60 80 100

Counts [x103]

0

20

40

60

+150 V (holes) -100 V (electrons)

abstract

D

E

CC

E [

%]

90

100

F

CC

E [

%]

25

100

A

B

C

(a) (b)

500 μm

Silver paint

Co

nta

ct

ed

ge

(b)

110

25

(54)x10150.050.04F

(1.00.4)x10150.180.08E

( 51)x10140.60.14D

(1.001)x10142.60.3C

(1.101)x10132.40.3B

(1.101)x10122.60.3A

Dose

[cm-2]

Area

[10-3 cm2]

Label

A. Lohstroh, P. J. Sellin, S. Gkoumas, J. M. Parkin, P. Veeramani, G. Prekas, M. C. Veale, and J. Morse,

phys. stat. sol. (a) 2008, 205(9); p.2211-2215

Synovial Joints

Sections from human femoral head, showing typical scan

areas Bone scan 1 Bone scan 2 Trabecular

bone

Proton beam scanned across the

sample in 2D grid

van Donkelaar et al., J. Anat.(2007) 210, pp186–194,

PIGE• 19F(p,p'γ )19F; γ-rays of 110 and 197 keV

• 23Na(p,p'γ)23Na & 23Na(p,α'γ)20Ne; γ-rays: 440, 1634, 1636 keV

• 35Cl(p,p'γ)35Cl and 37Cl(p,γ)38Ar; γ-rays of 1220 and 1640 keV

• The peaks typically a result of nuclear excitation by inelastic scattering, with transitions to the ground state except for the 1634 keV peak of Na, which feeds transitions to the ground state.

• 3 MeV proton beam was focused to ~ 100 µm x 6 µm spot size and a beam current of ~0.5 µA

PIXE/PIGE Set-upSi (Li) PIXE detectorShielding large volume

HPGe detector for PIGE

Basic Science is important –applications may take a long time to surface

Radiation therapy has improved markedly in the UK. It would be improved further if we built some hadron therapy machines

Can use PET scans to check where energy deposited

We also do this….(see poster by Leena Al-Sulaiti)

“Some people won’t even believe me when I tell themI’m a nuclear physicist. I think that it’s partly because I’m a woman and partly because I look younger than my age. Occasionally I can’t be bothered and say that I am a trapeze artist. They don’t believe that, either.”

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