Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory

Figure 3: 60Fe/ Fe concentration in ocean crust

sample vs. age of sample in millions of years.

References -- Figure 1: http://astronomyonline.org/Stars/HighMassEvolution.asp Figure 2: Jose, Iliadis. Nuclear Astrophysics: the unfinished quest for the origin of the

elements. Figure 3: Knie, et al. 60Fe Anomaly in a Deep-Sea Manganese Crust and Implications for a

Nearby Supernova Source.

AMS RESULTS:

Sample   Concentration

Blank Sample:  

MSU:  

AMS Test:  

VERA Fe-2:  

VERA Fe-3:  

VERA Fe-4:  

3

2 1

Part 2: Activity Measurement & Outlook The second measurement that must be done is the Activity of the sample.

The decay scheme for 60Fe is illustrated in the figure on the right. For our

measurement, we are pursuing the direct decay measurement with the

VERA samples. This decay, from the excited state to the ground state in 60Co will either be by Internal Conversion (~98% of the time) or by Gamma

Ray emission (~2% of the time). With our VERA sample, we will be able to

measure the gamma rays produced using two HPGe Planar Detectors.

These three spectra are the

energy deposited (y axis)

vs. the position in the

detectors (x axis). The 1st

and 2nd are of the VERA

sample, “Fe-2.” The 2nd

has a shield in front of the

detector, blocking out

most of the 60Ni

contaminant. The 3rd

spectra, with the shield is

the “MSU” sample. Right

is the concentrations of

each sample. These were

as expected.

Part 1: Accelerator Mass Spectrometry (AMS) The AMS facility at Notre Dame uses of the FN tandem accelerator and the Browne-Buechner Spectrograph (see

diagram). After the magnet, there are two detectors: a Parallel Grid Avalanche Counter to detect the position of

the beam and an Ionization Chamber which detects the energy loss of the beam. Both detectors are filled with

isobutene. Filling the gap between the magnet poles with Nitrogen allows us to separate stable isobars,

specifically 60Ni and 60Fe.

Figure 2: Layers of burning sequences in a massive,

before (left) and during (right) a SN explosion. Note

60Fe position before explosion; it is located in a layer

that will be expelled.

Figure 1: Life cycle of a Massive Star.

We therefore see evidence of

60Fe in 3 key places:

1. Galactic gamma-ray activity

from 60Fe’s decay from 60Co to

stable 60Ni.   2. Enrichment of its stable

daughter product, 60Ni, in

meteorites formed during the

early Solar System.

3. Ferromanganese ocean crust

samples, suggesting a

supernova about 3 million

years ago that deposited its

ejecta on the Earth.

The half life of 60Fe, which is in

dispute, can serve as important

constraints for early Solar

System and stellar evolution

models.

Motivation

The long lived radioisotope 60Fe is only

produced in AGB stars and in Core-

collapse Supernovae. It is found in the

carbon shell burning region of a massive

star, which is expelled from the star

during the supernova explosion.

    60Fe Samples Two separate sets of samples were used. The first set was produced at Michigan

State University (MSU) and the second set is from the Paul Scherrer Institute

(PSI) beam dump.

The MSU set was made in 2009. This set included two samples: “AMS Test” and

“MSU Sample”.

The PSI beam dump set consisted of 3 samples, all part of a dilution series,

called “Fe-2”, “Fe-3”, and “Fe-4”.  

How to find Half life of long lived radioisotopes

For isotopes with long half lives, we count the number of atoms of interest (   )

and measure the activity of the sample (   ) once. Then from the following

equation, we can calculate the half life:

    and the decay constant,    and   is the half life of the sample..

Measurement of the Half Life of the long lived radioisotope 60Fe

1 University of Notre Dame, Notre Dame, Indiana. 2 Michigan State University, Michigan. 3 Argonne National Laboratory, Illinois. 4 Vienna Environmental Research

Laboratory, Austria. 5 Hebrew University of Jerusalem, Israel. 6 The Australian National University, Australia. 7 Joint Institute of Astrophysics.

K. Ostdiek1,6, S. Austin2,7, W. Bauder1,7, M. Bowers1,7, P. Collon1,7, J. Green3, W. Kutschera4, W. Lu1,7, M. Paul5, D. Robertson1,7, A. Wallner6

This research is funded by a grant though NSF, #Phy1068192.

Left: Two planar HPGE Detectors surrounded by a

lead castle, and attached to an automatic LN2 filling

system.

Below: VERA Sample evaporated and dripped onto

Mylar sheet.

Right: Spectrum of the

VERA Sample, run for 48

hours (Purple). Blue =

Background run. Note the

peak from the 60mCo decay

at 58.6 keV. The other peak

around 63.5 keV is a

background peak.

Measurement & Analysis Ongoing!