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NSCL – Ongoing Activities and Future Perspectives. Premier national user facility for rare isotope research and education in nuclear science, astro-nuclear physics, accelerator physics, and societal applications

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nscl ongoing activities and future perspectives
NSCL – Ongoing Activities and Future Perspectives
  • Premier national user facility for rare isotope research and education in nuclear science, astro-nuclear physics, accelerator physics, and societal applications
  • 309 employees, incl. 59 undergraduate and 59 graduate students, 30 faculty – over 700 users
    • Largest campus-based nuclear physics laboratory in the U.S. – 10% of U.S. nuclear science Ph.D.s
    • Nuclear physics graduate program ranked #2 (behind MIT)as of Nov. 21, 2007
major research thrusts at nscl
Major Research Thrusts at NSCL
  • Production of nuclei with unusual ratios of protons to neutrons and the measurement of their properties – connection to mesoscopic science*
  • What are the limits of nuclear existence? What are the properties of nuclei with extreme ratios of protons and neutrons (neutron skins and halos)? Modification of shell structure, new doubly magic nuclei: 48Ni, 78Ni, 100Sn, 132Sn…
  • Exploration of the nuclear processes responsible for the chemical evolution of the universe through the ongoing synthesis of most elements in the cosmos – connection to astrophysics**
  • Where are most of the nuclei heavier than iron made? How do supernovae explode? Are Type 1a SN good standard candles?
  • Exploration of the isospin dependent properties of hot nuclear matter and how they affect supernovae and neutron star properties– connection to astrophysics**
  • What is the equation of state (EOS) of neutron-rich nuclear matter?
  • Exploration and tests of novel superconducting accelerator and beam transport concepts and the dynamics of high-intensity beams
  • One of the few universities that graduates accelerator physics/engineering PhDs
  • Alignment with 3 of the 5 key questions identified in the 2002 NSAC LRP: What is the structure of the nucleon? What is the structure of nucleonic matter? What are the properties of hot nuclear matter? What is the nuclear microphysics of the Universe? What will be the new Standard Model?
    • * Mesoscopic Theory Center at MSU
    • ** JINA (Joint Institute for Nuclear Astrophysics
atomic nuclei are made of protons and neutrons
Atomic Nuclei are Made of Protons and Neutrons

The number of protons, Z, determines the chemical element

The atomic weight is given by A = Z + N, where N is the number of neutrons

some unstable isotopes exist on earth
Some Unstable Isotopes Exist on Earth
  • Average life-times of unstable (“radioactive”) isotopes can range from less than a thousandth of a second to billions of years
    • Only long-lived isotopes can be found naturally on earth
    • Example: The isotope 14C (T1/2 = 5,730 y) is continually produced in the upper atmosphere by nuclear reactions induced by cosmic radiation: 14N+n  14C+p
example carbon dating
Example: Carbon Dating
  • Determination of the age of organic material from its 14C/12C content
    • 14C is embedded into living organisms with a known ratio of 14C/12C
    • When an organism dies, 14C decays – changing the 14C/12C ratio with time
  • Example: Isotope analysis determined when and where the “Ötzi” Alpine Iceman had lived: 5200150 years ago, south and within 50 km of the finding site…
unstable isotopes are important in science and technology
Unstable Isotopes are Importantin Science and Technology
  • Some radioactive isotopes (11C, 13N, 15O, 18F, …) provide major medical benefits through diagnosis or treatment of diseases
    • Many others have important applications in biological sciences, environmental sciences, archeology, national security and energy generation
positron emission tomography pet

Computer Tomography (CT)

Positron Emission Tomography (PET)

Fusion of PET & CT

4 mm resolution

Positron Emission Tomography (PET)

18F-labeled FDG (2-[18F] fluoro-2-deoxy-D-glucose) allows advanced diagnostics of cancer (Courtesy Kevin Berger, MD)

short lived rare isotopes have long decayed since earth was formed
Short-Lived (“Rare”) Isotopes… have long decayed since earth was formed
  • Thousands of rare isotopes are continually created in the cosmos
    • They have only a fleeting existence, but they play a crucial role in the still ongoing creation of the elements in the cosmos – as they did billions of years ago when the elements in our solar system were made
  • We are able to produce thousands of rare isotopes in the laboratory by smashing stable nuclei and explore their properties
production of rare isotopes at rest isol technique
Production of Rare Isotopes at Rest(ISOL Technique)

1. Bombard a thick target of heavy nuclei with energetic light particles, e.g. 1 GeV protons, to achieve random removal of protons and neutrons or fission

  • 2. Extract rare isotopes from the target material by diffusion or effusion; ionize and accelerate them to the desired energy
    • beams of high quality, but there are chemistry and lifetime limitations
production of rare isotopes in flight
Production of Rare Isotopes in Flight

1. Accelerate heavy ion beam to high energy and pass it through a thin target to achieve random removal of protons and neutrons in flight

hot participant zone

projectile fragment

projectile

target

2. Cooling by evaporation

Rare isotope beam

projectile fragment

scientific reach of heavy ion drivers
In-flight production allows chemistry-independent separation

Short beam development times

Negligible losses from decay (separation and transport in microseconds)

Fast beams have the furthest reach:

Use of thick targets provides large luminosity gains (typically by 103-104)

Avoid losses (> 10) incurred by gas-stopping and reacceleration

Enhanced efficiency by use of cocktail beams (ion-by-ion PID & tracking)

Nuclei very far from stability can be reached only with fast beams

Experiments with reaccelerated beams (e.g., transfer reactions) typically require beam intensities of 103-104 s-1 (production rates > 104 s-1) or more

Reaccelerated beams from in-flight production can reach many new states in nuclei closer to stability

Needed for fusion reactions

Scientific Reach of Heavy Ion Drivers

Measurements for the rarest nuclei provide the most important leverage to constrain theoretical models

*

* For simplicity, the transfer reaction limit in this graph assumes no losses from gas stopping, extraction, and reacceleration

rare isotope beam capabilities worldwide
Rare Isotope Beam Capabilities Worldwide

The research opportunities with intense beams of rare isotopes are now widely recognized, and major investments into advanced RIB capabilities

are being made world-wide: GANIL, GSI, RIKEN, TRIUMF, …

in flight production of rare isotopes at nscl

K500

Example: 86Kr → 78Ni

ion sources

coupling

line

86Kr14+,

12 MeV/u

K1200

A1900

focal plane

p/p = 5%

production

target

transmission

of 65% of the

produced 78Ni

stripping

foil

86Kr34+,

140 MeV/u

wedge

fragment yield after target

fragment yield after wedge

fragment yield at focal plane

In-Flight Production of Rare Isotopes at NSCL
rare isotope beams produced at nscl
Rare Isotope Beams Produced at NSCL

Research program requires large number of beam tunes and, hence, reliable and predictable operations (CCF availability > 90%)

Increasing science pressure to move towards heavier nuclei

More than 900 RIBs have been made – more than 600 RIBs have been used in experiments

evolution of shell structure
Evolution of Shell Structure
  • Provides an improved understanding of the nature of the effective interactions and operators used in nuclear structure models
    • Insight into tensor and 3-body forces in nuclei (e.g., Otsuka, et al.)
    • The continuum plays an important role in weakly bound nuclei(e.g., Nazarewicz, Zelevinsky, et al.)

Stable nuclei:N/Z ≈ 1 - 1.5

Sp,p ≈ 6-8 MeV

Neutron-rich nuclei:N/Z ≈ 2 - 2.5Sn << 1 MeV

continuum shell model oxygen isotopes
Continuum Shell Model (Oxygen Isotopes)

Experimental information is needed to pin down the interactions

sd space, HBUSD interaction,

single-nucleon reactions

A. Volya and V. Zelevinsky, Phys. Rev. C74 (2006) 064314;

Phys. Rev. Lett. 94 (2005) 052501; Phys. Rev. C67 (2003) 054322

discovery of 40 mg 42 43 al and 44 si in 2007

S800 Analysis Line

PID

Detector

Setup

Transport Beam Line

K500

Cyclotron

Timing Detectors

K1200 Cyclotron

A1900 Fragment Separator

Achromatic Degrader

Production Target

HFB-8

FRDM

Discovery of 40Mg, 42,43Al, and 44Si in 2007

Baumann et al., Phys. Rev. C75 (2007) 064613; Nature 449 (2007) 1022

Enhanced selectivity from two-stage separator:

1.5101748Ca nuclei (natW target, E/A = 141 MeV)

 three 40Mg nuclei

low energy beam ion trap lebit

Penning Trap Mass Spectrometry

< 1 eV

Cooling and

Bunching

PhD research ofAmanda Prinke

9.4 T Penning trap

Gas stopping

of fast ions

Degrader

100 MeV/u

Low Energy Beam Ion Trap (LEBIT)

stop fragments in helium-gas cell, extract, purify, and store in Penning trap

Since 2005: accurate masses for more than 30 isotopes of more than 10 elements:

33Si, 29, 34P,37,38Ca, 40-44S, 63-65Fe, 64-66Co, 63-64Ga, 64-66Ge, 66-68,80As, 68-70,81,81mSe, 70m,71Br

G. Bollen et al., PRL 96 (2006) 152501; P. Schury et al., PRC 75 (2007) 055801;

R. Ringle et al., PRC 75 (2007) 055503

T1/2= 123 ms

  • 44S:
  • MELEBIT = -9205(5)keV
  • 25-fold improvement over SPEG 2007:ME = -9100(130) keV
  • Disappearance of N = 28 magic number?
examples of precision mass measurements

G. Bollen et al.,

PRL 96 (2006) 152501

PhD thesis ofJosh Savory

Examples of Precision Mass Measurements

Stop high-energy fragments in helium-gas cell, extract, purify, and store in 9.4-Tesla Penning trap

  • 68Se:+-emitter
    • more important rp-process waiting point nucleus than previously thought
  • MELEBIT = -54189.3(5) keV
  • dm = 530 eV,dm/m=8·10-9
    • 35-fold improvement over CPT 2004: ME = -54 232(19) keV)

T1/2 = 440 ms

  • 38Ca: 0+ 0++-emitter
    • new candidate for the test of the conserved vector current (CVC) hypothesis
  • MELEBIT = -22058.53(28) keV
  • dm = 280 eV, dm/m=8·10-9
    • 17-fold improvement over AME 03: m = 5 keV

T1/2 = 35.5 s

nuclear spectroscopy with knockout reactions
Nuclear Spectroscopy with Knockout Reactions

Different P-distributions for individual states, tagged by g-rays: cross section is sensitive to wavefunction; shape identifies l of knocked-out nucleon

  • Breakdown of N=8 shell closure in 12Be: only 32% (0p)8 and 68% (0p)6-(1s,0d)2
occupation of single particle states
Occupation of Single-Particle States

Shell model: Deeply-bound states are fully occupied by nucleons. At and above the Fermi sea, configuration mixing leads to occupancies that gradually decrease to zero.

Correlation effects (short-range, soft-core, long-range and coupling to vibrational excitations): Beyond effective interactions employed in shell model and mean-field approaches. Occupancies will be modified.

Reduction factor with respect to the shell model:

Rs=C2Sexp/ C2Sth

RS

  • In stable nuclei, a reduction of Rs=0.6-0.7 has been established from (e,e’p) reactions
    • V. R. Pandharipande et al, Rev. Mod. Phys. 69, 981 (1997)
    • W. Dickhoff and C. Barbieri, Prog. Nucl. Part. Sci. 52, 377 (2004).
evidence for shell breaking near 56 ni
Evidence for Shell Breaking near 56Ni
  • The 57Cu-57Ni mirror pair is the heaviest T=1/2 system studied to date
    • The measured spin expectation value, <> = -0.78±0.031, is inconsistent with the assumption of an inert doubly-magic 56Ni core

Minamisono et al., Phys. Rev. Lett. 96 (2006) 102501

Determination of resonance frequency

-NMR

breaking of z n 50 core near 100 sn
Breaking of Z=N=50 Core Near 100Sn?

Coulex of neutron-deficient Sn isotopes

Nearly constant B(E2) values in 106-112 Sn are not expected from state of the art shell model calculations, but could be explained if g9/2 protons from within the Z = 50 shell contribute to the structure of low-lying states in this region.

Vaman et al., Phys. Rev. Lett. 99 (2007) 162501