ACCELERATOR MASS SPECTROMETRY;

from dating the ice man and tracing

oceans to the stars

Philippe Collon,

University of Notre Dame

What is Accelerator Mass spectrometry (AMS)

The determination of the concentration of a given radionuclide in a

sample can be done in 2 ways:

a) measure the radiation emitted during the decay

b) count the number of atoms themselves

In many cases where concentrations and/or small or

long t1/2 this becomes impractical

1mg carbon = 6 x 107 at 14C ~1 decay/hour

In a Mass Spectrometer a sample material is converted to an ion

beam that is then magnetically (and electrostatically) analysed

MS separates ions by their mass only

Goal of AMS

However in many cases a high background (molecular, isobaric, …)

makes it impossible to separate the ions of interest.

The use of an accelerator in AMS makes it possible to go to much

higher energies (several MeV vs. keV) and the measurement of

a range of properties that do not depend on ionic charge.

- Range

- Stopping power

- TOF

An unambiguous (A, Z) identification would solve this problem

(A, Z)

The high sensitivity of the method makes it possible to measure

down to several counts per hour from a beam of the order of

microamperes (1.6 mA = 1 x 1013 ions).

MS vs. AMS

E

E

Mass spect romet ry

Acce le ra tor mass spect romet ry

Tandem acce lera to r

St r ipper

Negat ive ion sourceElect ros ta t ic ana lyser

Detector setup

Cyc lo t ron

Pos i t i ve ion source

Low-energyanalys ingmagnet

Low-energyana lys ingmagnet

High-energyana lys ing

magnet

Low-energyana lys ingmagnet

ion source

ion detec tor

Typical AMS setup

From carbon dating the Ice Man:

To nuclear Astrophysics:

The measurement of the cross-section of the

suspected main production channel of 44Ti: 40Ca(a, g)44Ti

The detection of the decay of 44Ti by Compton gamma-ray obs.

A clear indicator for ongoing 44Ti nucleosynthesis

14C age = 5300 years

North

(Austria)

South(Italy)

Aug. 1989, G. Patzelt

The Iceman Oetzi discovered in an Alpine Glacier

Some applications of AMS

AMS can be used in many different fields and adapted to different

isotopes.

The following slides will illustrate:

- the application to environmental studies

- AMS technique developed for 2 different isotopes

AMS is however also applied to:

- Nuclear physics

(t1/2 measurements, cross-section,…)

- Nuclear astrophysics

- Archeology

(14C,10B,…)

Why is there a need for isotope Why is there a need for isotope

tracers in sciences?tracers in sciences?

Natural resources

on Earth are limited

Human activities are

no longer negligible

Therefore a better understanding of environmental

systems is necessary

The environment is not a controlled laboratory but

an extremely complex dynamical system

Special tools are needed to trace the main environmental

transport processes and to determine their dynamics:

ISOTOPES

Cosmogenic radionuclides as tracers

Atlantic conveyor belt circulation

Concept of the Conveyor belt

The application of 39Ar dating to groundwater is limited by the fact that

underground production in granitic rock 39K(n,p)39Ar can be substantial.

Properties of 39Ar

• Mainly produced through cosmic ray induced spallation on

argon in the atmosphere 40Ar(n, 2n)39Ar Q= -9.87 MeV

• Anthropogenic production is estimated to be below 5% [Loosli

1983]

• Subsurface production can be significant in rocks with high

uranium content 39K(n,p)39Ar

t1/2 = 269 years39Ar/Ar = 8.1 x 10-16

Activity of 1 l water

1 l ocean sea water contains ~ 6500 39Ar atoms (In ocean water: Ar solubility

0.4 cm3 STP/l)

Activity(t=0) =5.3x10-7 Bq or ~17 decays per year.

How can 39Ar be counted?

Low Level Counting

Possible on large samples (~1000 l), done by H.H. Loosli in Bern

Laser

The extremely low concentration makes this a very difficult isotope for laser techniques

AMS (with small vol. samples)

several difficulties (M/M, low concentration, …)

AMS for 39Ar

5 Main difficulties

The 39Ar/Ar = 8.1x10-16 ratio

Isobar separation between 39K and 39Ar (M/M = 1.55x10-5)

A tandem (as used in traditional AMS lab) cannot be used for noble gasses

Source efficiency

Overall transmission

Principle of the gas filled magnet

In the gas filled magnetic region, the discreet charge states coalesce around a

trajectory defined by the mean charge state of the ion in the gas

Br mv / q-

Gas filled magnet setup

Scatter ing chamber

Beam

Enge Spl i t Pole spect rograph

PPAC + ionisat ion chamber

Ni t rogen (10 tor r )

39K

39Ar

ATLAS layout

Split-Pole Enge Spectrograph

Experimental setup I

Initial beam tuning

As it is not possible to tune on 39Ar8+ it was decided to use as pilot beam : 78Kr16+ from the ECR source

Beam energy

78Kr16+ Energy: 464 MeV resulting in a 39Ar8+ beam with 232 MeV

Total transmission ~20% (without stripping)

Later detector set-up

Pp = 113.6 MeV

Booster = 348.8 MeV

ATLAS = 464 MeV

Cath: - 430 V

Anode: + 575 V

Grid: + 300

Div: +240V / -365V

N2 = 12.1 Torr

PPAC = 3 torr (Isob)

IC = 21 torr (Isob)

Beam:

Detect:

Using a quartz liner in the plasma chamber

How to sample ocean water?

R/V Nathaniel B. Palmer

Nathaniel B.Palmer cruise 0106

Water sampling rosette

Ocean water samples

Results from May 2002 AMS run

Sample CPS/emA 39Ar/Ar “age”

n-act 2.69x10-3 5.80x10-14

natAr 3.57x10-5 7.70x10-16

SAVE 294/5000 1.67x10-5 3.59x10-16 44% mod.

SAVE 294/850 2.43x10-5 5.23x10-16 65% mod.

Watson creek 2.02x10-6 4.35x10-17 5.4%

SAVE 95/4717 1.21x10-5 2.61x10-16 32% mod.

natAr 3.96x10-5 8.53x10-16

n-act 2.79x10-3 6.01x10-14

3.76 x10-5 8.1 x 10-16

University of Notre Dame

- ~8000 Undergraduate students

- ~ 2200 Graduate students

70 years of electrostatic accelerators at ND

Initial budget: 900$

Cost overrun: 450$

Max voltage: 2MV

Further accelerators

NSL Facilities & Layout

Browne-Buechner

Spectrograph

JN Accelerator

~1MV

KN Single ended Accelerator

~3-4MV

200kV Inplanter

ISIS

FN Tandem

Accelerator

~11MV

AMS for nucl. astrophysics at Notre Dame

The passage of time....before and after

Experimental Layout and AMS Facility

Detection System

PPAC

PPAC and Ionisation Chamber (IC) for

position and energy determination

Both containing Isobutane gas

Thin Mylar windows, low energy loss

TOF can aid in particle identification

MANTIS- ND AMS system

6.2x10-6 Torr 58Ni

14+

13+

5x10-5 Torr N258Ni

8x10-4 Torr N258Ni

14+

13+

0.49 Torr

Isobar separation in the GFM

0.99 Torr

58Fe

1.5 Torr

58Ni

2.0 Torr2.5 Torr3.0 Torr3.5 Torr

dt ~ 20 min

Bspec = 0.620 Tesla

Entrance foil: Mylar

vzfq

zfmqmvB

)(

)(//r

58Fe

58Ni

Position (Channel number)

58Ni

58Fe

Beam tuned to 80MeV 58Ni11+

Fe/Ni Mixed cathode (200:1)

injected

MANTIS @ 2.9 Torr N2 , B =

0.484T

En

ergy

Lo

ss (

Ch

an

nel

nu

mb

er)

Position (Channel number)

58Ni

58Fe

Beam tuned to 80MeV 58Ni11+

Fe/Ni Mixed cathode (200:1)

injected

MANTIS @ 2.9 Torr N2 , B =

0.484T

En

ergy

Lo

ss (

Ch

an

nel

nu

mb

er)

First AMS measurement

Short-lived radionuclides in meteorites

An important result concerning the formation of the solar system is the discovery of several short-lived nuclides (with half-lives varying from ~105 to ~108 years) in meteorites (10Be, 26Al, 36Cl, 41Ca, 60Fe, 53Mn…..)

There are 2 generally accepted possible models for the production of short-lived radionuclides at the formation of Calcium-Aluminium-rich inclusions (CAIs).

They either originated from the ejecta of a nearby supernova

They originated in the in-situ irradiation of nebular dust by energetic particles (mostly, p, a, 3He: X-wind irradiation model

0.0E+00

5.0E-16

1.0E-15

1.5E-15

2.0E-15

2.5E-15

3.0E-15

3.5E-15

0 2 4 6 8 10 12 14

age [Myr]

60

Fe

/Fe

_m

ea

su

red

K. Knie et al., Phys. Rev. Lett. 93(2004)171103

Provides a model for the formation of both CAIs and Chondrules in primitive solar nebula

60Fe/Fe

The importance of 60Fe as a direct observable of stellar

nucleosynthesis

Supernovae

Cassiopea A, x ray images of a supernovae remnant

Credit: NASA/CXC/MIT/UMass

Amherst/M.D.Stage et al.

Broadband x-rays from iron (from Chandra)

ESA’s INTEGRAL satellite

n pn p

e-

e-

60Fe

60Co*

60Ni*

60Ni

deacy

deacy

= 1.5 My

= 5.3y

g 59 keV (2%)

g 1.173 MeV (99.9%)

g 1.332 MeV (99.9%)

0+

5+

2+

0+

4+

2+

60Fe

60Co

60Ni

SATELLITE

Produced in stars

In order to link observations to our models we have to know this decay half-life precisely. The present accepted value of 1.5

My has been questioned by a new measurement of 2.5 My (Munich AMS group)

In addition to x-ray observation we can use isotopic specific

information by measuring the gamma decay lines

Notre Dame involvement in the measurement of the

production of 60Fe

Production of a 60Fe sample

using the superconducting

cyclotron of the National

Superconducting cyclotron

Laboratory

The sample produced will be used at Notre Dame for the half-life

determination using Accelerator Mass Spectrometry (AMS) and gamma

activity measurement.

Predicted distribution of 60Fe radioactivity along the galactic plane. The GRASP

(Gamma-Ray Astronomy with Spectroscopy and Positioning) project that we are part

of, will aim at mapping sources of 60Fe in the galactic plane

Improve our knowledge of 60Fe galactic distribution:

Improve our knowledge of the 60Fe half-life:

Accelerator mass spectroscopy with long-lived radioactive

isotopes 60Fe – The origin of Mankind

The oldest “walking”

human ancestor

Australopithecus afarensis

Dr. Collon

Dr. Wiescher

Nearby supernovae explosion may have influenced certain processes

on Earth

The is evidence that a nearby supernova explosion injected material into

the solar system

Deposition in geological

formations

(ferromaganese crusts)

Supernovae

Injection into the

solar system

0.0E+00

5.0E-16

1.0E-15

1.5E-15

2.0E-15

2.5E-15

3.0E-15

3.5E-15

0 2 4 6 8 10 12 14

age [Myr]

60

Fe

/Fe

_m

ea

su

red

Detection of 60Fe signal in

ferromaganese crusts using

AMS

Knie et al 2003

Simulation to Detection

40Ca 40K

40Ca

40K

Detector Positioning (cm)

Cou

nts

40Ca 40K

Detector Positioning (cm)

En

ergy (

MeV

)

40Ca 40K

Only 1 unit of Z separation

SNO+ Motivation

12 m diameteracrylic vessel

Support structure for 9500 PMTs,concentrators

Urylon liner

Vectransupportropes

Control room

Norite rock

2090 m to surface

105 m to upperatmosphere

1011 m to Sun1020 m to Galactic centre

With thanks to Kara Keeter

1700 tonneslight water

5300 tonneslight water

1000 tonnesheavy water

Preparation and Samples

Sample #1

Starting material = 5g

Cathode material ~ 100 g

Yarn sample #2

Starting material = 5.28g

Cathode material ~ 100 g

Acrylic sample #1

Starting sample = 6.46g

Cathode material = unknown

With thanks to Jaret Hise

Sample Running – Proof of Principle

Sample Normalized 40K Sample Description

Ultra Pure Cu 1.0Ultra Pure Goodfellow Cu,

Cleaned with DCM, ETHO, H2O, H2O2/H2SO4, H2O, 4M HNO3, H2O

Ultra Pure Cu 1.3Ultra Pure Goodfellow Cu,

Cleaned with DCM, ETHO, H2O, H2O2/H2SO4, H2O, 4M HNO3, H2O

2nd Ultra Pure Cu 1.7Ultra Pure Goodfellow Cu,

Cleaned with DCM, ETHO, H2O, H2O2/H2SO4, H2O

NSL Cu Cathode 4.8 Standard Cu cathode used at NSL, Oxygen free Cu

Vectron Yarn #2 160Ashed Vectron Yarn, ~g range.

Residue mixed with 3ml DI water and 1ml evaporated in ultra pure Cu cathode

Ashed Yarn #1 793 Yarn Ashed and residue compacted into ultra pure Cu cathode

Leached Acrylic 2.4Leached Acrylic material, ~g range.

Residue mixed with 3ml DI water and 1ml evaporated in ultra pure Cu cathode

NSL DI H2O 1.23ml DI water put through similar procedures & 1ml evaporated in ultra pure

Cu cathode

All measurements at present are only relative to reduced background

Running Measurements

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

100,000,000N

SL

Cat

ho

de

Tre

ated

1 (

Pu

re C

u c

ath

od

e)

Tre

ated

3 (

Pu

re C

u c

ath

od

e)

Tre

ated

5 (

Dif

f P

ure

Cu

cat

ho

de)

Tre

ated

7 (

DI

wat

er)

Tre

ated

6 (

Acr

yli

c)

Treated 2 (Yarn Ash)

Treated 4 (Vectron)

Cts

/s/

A(6

5C

u)

Sample Runs