accelerator mass spectrometry; from dating the ice man …nsl/lectures/junior_seminar/junio...
TRANSCRIPT
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