Nuclear Structure and Reactions - Jefferson Lab• “We propose for the new radio-isotopes formed...

Brad Sherrill Chief Scientist Facility for Rare Isotope Beams

10-12 June 2013

Nuclear Structure and Reactions

§ One of HUGS goals is to introduce students to “topics of interest in nuclear physics”. My lectures will attempt to describe what is interesting in the study of nuclei.

§ Lecture 1: Search for the limits of nuclear binding and production of new isotopes

§ Lecture 2: Attempts to model atomic nuclei I § Lecture 3: Attempts to model atomic nuclei II § Lecture 4: Nuclear Reactions § Lecture 5: The origin of atoms – Nuclear Astrophysics I § Lecture 6: The origin of atoms – Nuclear Astrophysics II

Outline of my six lectures

It is important for you to ask questions.

Sherrill HUGS Lecture 1 , Slide 2

Nuclear Landscape

•  Chart of the nuclides

•  Black squares are the 263 stable isotopes found in nature (> 1 Gy)

•  Dark green closed area is the region of isotopes observed so far.

•  The limits are not known.


§ Let’s define “possible” as lasting long enough to make an atom that could react chemically (10-6 s; probably 10-16 is valid)

§ Neutron drip line

§ Proton drip line

§ Heaviest elements – The claim for up to atomic number 118 has been made at Dubna (Oganessian et al.)

How many isotopes are possible?

22C 20C 13C

p

12C

n

Mass model


Open Questions: § How many elements can exist? We are up to element 118 and

counting. § Are there long-lived superheavy elements, with half lives of

greater than 1 year? § Where are the atoms of the various elements formed in

nature? § What makes atomic nuclei stable? We know Strong and

Electroweak forces are involved, but don’t understand how in detail. The inability to answer this question is reflected in our inability to answer the first three questions.

Open Questions in the Search for the Limits


History of Element Discovery

Democritus – idea of atoms

India Babylonia Egypt China

Copper Age

1700+ Rise of modern chemistry – Dalton’s Atomic Theory

Source: Mathematica + Wikipedia


The history of element discovery 1200-2010

Time of the Alchemists

Chemistry Dalton’s Atomic Theory Cavendish, Priestly, Scheele, …

Mendeleev’s Periodic Table

Particle Accelerators Reactors

Future?


Result: Periodic Table of the Elements http://www.sciencegeek.net

Sherrill HUGS Lecture 1

We don’t know the limit. Some estimates are that we have discovered only half of the elements, but we don’t know.

Superheavy: Only stable due to many-body effects

, Slide 8

48Ca-ions

rotating entrancewindow

gas-filledchamber

detectorstation

recoils

position sensitivestrip detectors

TOF-detectors

“veto” detectors

22.50

SH recoil

side detectors

Recently named elements 114, 116; claims for 113,115,117,118 Synthesis of the heaviest elements


Y Oganessian et al In new element searches fusion happens only 1 in 1018

Z=113

169

, Slide 9

48Ca+237Np

§ Alpha (α)-decay – emission of a Helium nucleus • Why not two protons and two neutrons?

§ Beta (β)-decay – weak decay of proton (neutron) to a positron and electron neutrino

§ Electron capture – atomic electron is captured, anti-electron neutrino emitted

§ Gamma (γ)-decay – nucleus de-excites by emission of a photon § Internal conversion – energy from nuclear transition is carried away by

an atomic electron (very important for transitions in heavier nuclei) § Cluster Decay – for example 14C § Spontaneous fission – for example 252Cf decays by breaking into

roughly equal mass pieces § Proton decay – emission of a hydrogen nucleus, p § Neutron decay – emission of a neutron (observation still controversial)

Radioactive Decay


Superheavy Elements


115/287

10.59

3 ms2

113/283

10.12

0. s1

111/279

10.37

0.17 s

109/2 57

10.33

9.7 ms

107/2 17

105/2671.2 h

α

α

α

α

α

109/276

9.71

0.72 s

107/272

9.02

9.8 s

113/284

10.00

0.48 s

115/288

10.46

87 ms

105/2681.2 d

111/280

9.75

3 6. s

104/268

α

α

α

α

α 243Am 242Pu, 245Cm

226Ra

Sg/266 0.2 s

Hs/270 10 s

9.06

α 237Np

244Pu, 248Cm 249Cf

34 nuclides

48Ca +

249Bk T1/2= 320d ORNL High Flux Reactor

164

104/270

105/270

107/274

109/278

111/282

113/286

115/290

117/294

103/266 102/266

107/273

109/277

105/269

111/281

113/285

115/289

117/293

104/269

48Ca +249Bk

2009-2012

RiKEN (Japan) 209Bi +70Zn

§ Summary §  Figure adapted

from Y. Ogannessian

§ Dubna, RIKEN, GSI, LBL, …

, Slide 11

Collaboration: FLNR (Dubna), ORNL (Oak-Ridge), LLNL (Livermore), IAR (Dmitrovgrad) Vanderbilt University

Today’s Extremes of Z and A Discovery of Element 117

Phys. Rev. Lett. 104, 142502 (2010) Phys. Rev. Lett. 108, 022502 (2012)

Bk from HFIR

Dubna accelerator

Hot cell target prep

249Bk +48Ca 330 days


The Challenge of Even Higher Atomic Numbers

780254526

E def

(MeV

)

r (fm)

z (fm

)

bubble

band

normal

`2M. Bender et al., to be published

P. Pyykkö: Phys. Chem. Chem. Phys. 13, 161-168 (2011) “Half of chemistry is undiscovered. Other view– above Z=122 all chemistry is the same due to relativistic effects For stability of Z>120 see also Jachimowicz, Kowal, Skalski, PRC 83 (2011)


Half-lives of Superheavy Elements

Log

T (s

ec.)

α

150 160 170 180 190140

5

15

10

20

0

-5

-10 116

118

112

114

110

108

108

Neutron number

α - decay

DeformedShell

SphericalShell

Symbols: exp. values Lines calc. Sobiczewski & Smolanczuk


1 year

Element 118 48Ca + 249Cf

Discovery of Isotopes § Fredrick Soddy – Credited with discovery of isotopes

• Extremely talented chemist who began his career at McGill as a lecturer in 1900

• Rutherford came to McGill at the same time. Rutherford needed the help of a Chemist to try to understand radioactivity.

• Rutherford won 1908 Nobel prize "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances” (identified α and β radioactivity)

§ Isotopes •  In 1910 Soddy found that the mass of lead from thorium decay

differed from lead from uranium decay • He realized that atoms of a given elements must come in different

forms that he called isotopes (Greek for “at the same place”) JJ Thompson in 1913 showed the first direct evidence – Ne isotopes in cathode ray tube.

•  "Put colloquially, their atoms have identical outsides but different insides.” – Soddy Nobel Prize Lecture

• Won Nobel Prize in 1921 for discovery of isotopes


McGill

First Synthesis of Radioactive Isotopes

• The first artificial isotopes were produced by F Joliot and I Curie (Nature, 10 Feb 1934 ) by bombarding B, Al, Mg with alpha particles from Po

• “We propose for the new radio-isotopes formed by the transmutation of boron, magnesium and aluminum, the names radionitrogen, radiosilicon, radiophosphorus”

• For this discovery, Curie and Joliot won the Nobel Prize in chemistry in 1935


New isotope discoveries per year

Radio- activity

Mass spectroscopy

First accelerators

Projectile fragmentation

WWII

Fusion evaporation Spallation

Reactors

Thoennessen and Sherrill, Nature 473 (2011) 25


§ You can find out at the website www.nndc.bnl.gov - National Nuclear Data Center

Where Are We Now?


Value of Isotopes


§ Some examples of the cost of isotopes • May 27 value of Au-197 C$1438/ounce • H-3, tritium, isotope of hydrogen $1.1 M/ounce

§ Normal Calcium (Calcium-40 $.32 per ounce)

§ Expensive Calcium (.2% Calcium-48 $7M per ounce)

§ Among most expensive: Berkelium-249 $644M/ounce

20 protons

28 neutrons

20 protons

20 neutrons

, Slide 19

Goal of Current Isotope Research


20 protons

40 neutrons

§ Normal Calcium (Calcium-40 $.32 per ounce – 4 x1023 atoms)

§ Goal at FRIB: Calcium-60 ($10,000 for 1000 atoms)

20 protons

20 neutrons

Isotope Production Scheme •  Cartoon of the isotope production process – projectile fragmentation or

fission (Coulomb breakup, transfer, …)

•  To produce a key nucleus like 122Zr the production cross section (from

136Xe) is estimated to be 2x10-18 b (2 attobarns, 2x10-46 m2 ) •  Nevertheless with a 136Xe beam of 8x1013 ion/s (400 kW at 200 MeV/u) a

few atoms per week can be made and studied (>80% collection efficiency) •  For comparison: Element 117 production cross section was 1.3 (+1.5 -0.6)

pb (1.3x10-12 b) (Oganessian, Yu. Ts. et al PRL 104 (2010) 142502) •  Few x10-46 m2 is on the order of 100 MeV neutrino-electron elastic

scattering cross sections

projectile target


Production and Identification of Isotopes Sometimes looking for 1 event from 1018 beam particles

Example: 40Mg Production 120 pnA 48Ca 140 MeV/u Goal was to produce 40Mg


First observation of 40Mg

T. Baumann et al. , Nature 449, 1022 (2007)

€

ρ =m⋅ vB⋅ q

tof =distv

→mq

ΔE (inmaterial)∝ Z 2

v 2


LISE++ Simulation Code

The code operates under Windows and provides a highly user-friendly interface. See me at this school for a tutorial session It can be downloaded from the following internet address:

O. Tarasov, D. Bazin et al. http://www.nscl.msu.edu/lise


§ The probability of production of a fragment is related to its production cross section:

§ For production cross sections of 1 mb and 9Be target thickness of 1 g/

cm2 the production probability (and fragment rate) is high:

§ Beam of 1014/s beam would yield 7x109 /s § Note: Key is σ – cross section , τ – target thickness, N0 – beam

intensity

Production Probability

dN(τ )dτ

=NaσAt

→ P = N(τ )N0

= 1− e−τ NaσAt

#

$%%

&

'((

τ target thickness (g/cm2) Na Avagodro’s number At target mass number σ production cross section

€

P =N(τ)N0

= 1− e−1⋅6.022×1023 ⋅1×10-27

9⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ = 7 ×10

−5


€

σ = π rt + rb( )2 ≈ 600 mb

Cross Section for Production Beam Target

rt rb 18O 17N 16C 15B

14Be 13Li 12Li 11Li

One nucleon removal Around 50 mb (light nuclei) P ≈ 5% 2n removal 5 mb P = .5% And so on Rule of thumb .1 x for each neutron removed

Actual: 16O +12C interaction cross section: 1000 mb (measured at 970 MeV/u) Note: Above around 300 MeV/u the interaction length is shorter than the electronic stopping range of the 16O so most beam particles can interact


§  Fragmentation (FRIB, RIBLL Lanzhou, NSCL, GSI, RIKEN, GANIL) o  Projectile fragmentation of high energy (>50 MeV/A) heavy ions o  Target fragmentation of a target with high energy protons or light HIs. In

the heavy ion reaction mechanism community this would include intermediate mass fragments.

§  Spallation (ISOLDE, TRIUMF-ISAC, EURISOL, SPES, …) o  Name comes from spalling or cracking-off of target pieces. o  One of the major ISOLDE mechanisms, e.g. 11Li made from spallation of

Uranium. §  Fission (HRIBF, ARIEL, ISAC, JYFL, BRIF,…)

o  There is a variety of ways to induce fission (photons, protons, neutrons (thermal, low, high energy)

o  The fissioning nuclei can be the target (HRIBF, ISAC) or the beam (GSI, NSCL, RIKEN, FAIR, FRIB).

§  Coulomb Breakup (GSI) o  At beam velocities of 1 GeV/n the equivalent photon flux as an ion passes

a target is so high the GDR excitation cross section is many barns.

Production Mechanisms – High Energy (more in lecture 4)


Spallation From Wikimedia Commons: http://en.wikipedia.org/wiki/File:Spallation.gif


Method of discovery of the isotopes


§ Funded by DOE Office of Science – 2020 completion

§ Key Feature is 400kW beam power (5 x1013 238U/s)

§ Separation of isotopes in-flight • Fast development

time for any isotope • Suited for all

elements and short half-lives

Major US Project – Facility for Rare Isotope Beams, FRIB


Isotope Separation On-Line ISOL

§ Highest power ISOL facility - >50 kW § Programs in nuclei, astrophysics, symmetry tests,

condensed matter, medical isotopes

Major Canadian Facility – TRIUMF ISAC and ARIEL


100 µA, 500 MeV, p

projectile

target 5 mA, 25 MeV, electrons

Rare Isotope Production Methods


Worldwide Growth of Rare Isotope Beam Facilities


How many isotopes might exist?

§  Estimated Possible: Erler, Birge, Kortelainen, Nazarewicz, Olsen, Stoitsov, Nature 486, 509–512 (28 June 2012) , based on a study of EDF models

§  “Known” defined as isotopes with at least one excited state known (1900 isotopes from NNDC database)

§  Represents what is possible now


The Number of Isotopes Available for Study at FRIB (next generation facilities)

§  Estimated Possible: Erler, Birge, Kortelainen, Nazarewicz, Olsen, Stoitsov, Nature 486, 509–512 (28 June 2012) , based on a study of EDF models

§  “Known” defined as isotopes with at least one excited state known (1900 isotopes from NNDC database)

§  For Z<90 FRIB is predicted to make > 80% of all possible isotopes


Uncertainty in Estimates Estimated Possible: Erler, et al. to be published


Open Questions: § How many elements can exist? We are up to element 118 and

counting. § Are there long-lived superheavy elements, with half lives of

greater than 1 year? § Where are the atoms of the various elements formed in

nature? § What makes atomic nuclei stable? We know Strong and

Electroweak forces are involved, but don’t understand how in detail. The inability to answer this question is reflected in our inability to answer the first three questions.

Open Questions in the Search for the Limits


§ History of nuclear physics - E. Segre, From X-Rays to Quarks, W.A. Freeman & Co, San Francisco, 1980

§ Heavy element searches - Heaviest nuclei from Ca-48-induced reactions, Yu. Oganessian, J. Phys. G 34(2007) R165-R242.

§ Isotope searches - http://www.nscl.msu.edu/~thoennes/isotopes/ § Rare isotope science – Geesaman, Gelbke, Janssens, Sherrill, Annu.

Rev. Nucl. Part. Sci. 2006. 56:53–92 § Rare isotope production – Geissel, Munzenberg, Riisager, Ann Rev.

Nuclear and Part. Science Vol. 45 (1995) 163-203.

References


Nuclear Structure and Reactions - Jefferson Lab• “We propose for the new radio-isotopes formed...

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