Transcript Studies of Muon-Induced Radioactivity at NuMI David Boehnlein Fermi National Accelerator Laboratory (on behalf of the JASMIN Collaboration) NuFact09 – July 24, 2009

Studies of Muon-Induced
Radioactivity at NuMI
David Boehnlein
Fermi National Accelerator Laboratory
(on behalf of the JASMIN Collaboration)
NuFact09 – July 24, 2009
The JASMIN Collaboration
•
D. J. Boehnlein, A. F. Leveling, N. V. Mokhov*, K. Vaziri
•
Y. Iwamoto, Y. Kasugai, N. Matsuda, H. Nakashima*, Y. Sakamoto*
•
M. Hagiwara, Hiroshi Iwase, N. Kinoshita, H. Matsumura, T. Sanami, A. Toyoda
•
Fermi National Accelerator Laboratory
•
Japan Atomic Energy Agency
•
High Energy Accelerator Research Organization (KEK)
•
Kyoto University Research Reactor Institute
•
Kyushu University
•
Pohang Accelerator Laboratory
•
Shimizu Corporation
•
Tohoku University
•
Aurora, Illinois
•
H. Yashima
•
H. Arakawa, N. Shigyo
•
H. S. Lee
•
K. Oishi
•
T. Nakamura
•
Noriaki Nakao
* Co-Spokesperson
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The JASMIN Experiment
• JASMIN – Japanese & American Study of
Muon Interactions and Neutron Detection
(Fermilab T972)
• A study of shielding and radiation physics
effects at high-energy accelerators
• Studies to date have focused on the antiproton production target (AP0) and NuMI.
• We present here status of work in progress to
study activation at the NuMI muon alcoves.
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Experimental Goals of JASMIN
• Benchmarking of Monte Carlo codes
• Radiation safety
• Study of muon interactions
• Material activation
• Shielding
• Muon detection & measurement
• Improved characterization of NuMI muon
monitors.
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Motivation
• Why is a neutrino experimenter talking to a
group of accelerator physicists about radiation
physics?
• This workshop is considering machines that
could produce unprecedented muon intensities.
• If such machines are to be built, one must
consider the radiological issues, including the
potential for radioactivation due to muons.
• Monte Carlo codes used for simulations
should accurately account for it.
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Source of electron, photon and neutron
Photo nuclear reaction
A


n
e-
A
e+
Bremsstrahlung
Electro-magnetic cascade
Bremsstrahlung
Pair production
Radiations around intense muon beam (T.Sanami)
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Neutrinos at the Main Injector
• The NuMI beamline focuses a νμ beam toward
Soudan, Minnesota.
• Since the neutrinos come from 2-body pion decay, the
world’s most intense neutrino beam is also the world’s
most intense muon beam.
• Arrays of ionization chambers in downstream alcoves
monitor muons co-produced with the neutrinos.
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NuMI Muon Monitoring Alcoves
Decay pipe
muons
Absorber
Alcove-0
Alcove-1
Alcove-2
Alcove-3
Alcove-4
0m
13.7 m
33.5 m
67.1 m
• Schematic layout of the muon alcoves at NuMI
• Note that Alcove 1 is in the Absorber Hall.
• See L. Loiacono’s talk at this workshop for a
discussion of the muon monitors.
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Estimated Muon Fields
Alcov Charged Particle
Beam Size
e
Fluence
1
6.5 x 105cm-210190 cm
12ppp
2
0.9 x 105cm-210250 cm
12ppp
5cm-2103
0.35
x
10
190
cm
• Predicted data from Kopp et al. [NIM A 568 (2006)503]
12ppp
• Assumes Low-Energy Beam.
• Beam size is FWHM.
• Neutrons < 1% in downstream alcoves.
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Procedure I
• Copper and Aluminum
disks were placed in
alcoves 1 -4.
• Disks are 8 cm diameter
x 1 cm thick.
• Beam exposure was
22.8 hours.
• NuMI beam put 6.26 x
1017 p.o.t.
• Additional samples were
placed to measure
neutron activation.
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Procedure II
• JASMIN operates parasitically with
NuMI.
• Samples are placed and retrieved during
natural beam-down periods.
• Isotopic signatures are measured on
High-Purity Ge counters at HighIntensity Lab.
• Operations so far have occured in
November 2007 and November 2008.
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Radionuclides observed in Samples
• This table
summarizes the
radionclides
observed in the
exposed copper
samples.
•
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54Mn, 57Co, 60Co
have substantial halflives (beyond a
reasonable cooldown period for
accelerator
maintenance).
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Preliminary Results
• Attenuation of muons,
as shown by yield ratios
normalized to Alcove 2.
• Yield ratios vs. distance
(top)
• Yield ratios vs. nucleons
emitted from target
nucleus (bottom)
• Note Aluminum results
are included (24Na).
• Figures courtesy of H.
Matsumura
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Preliminary Results II
• The narrow line is a fit to
an empirical formula for
photospallation
(Rudstam et al. Phys Rev
126, 5 (1962) 1852).
• The lower plot histogram
is a MARS15
calculation.
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Mass yields (atom-1 proton-1)
• Alcove 1 shows evidence
of neutron activation.
10-32
Alcove-1
-33
10
10-34
10-35
10-36
10-37
20
30
40
50
60
Product mass number
10-33
Mass yields (atom-1 proton-1)
• Activation Products on
copper samples by mass
number.
Alcove-2
Experimental
M ARS15
10-34
10-35
10-36
10-37
10-38
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40
45
50
55
60
65
Product mass number
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Summary
• JASMIN has measured radionuclides
produced in Aluminum and copper in the
muon alcoves
• It’s not clear how much of the activity is
produced by muons and how much by
muon-produced neutrons (for radiation
safety, does it matter?)
• MARS15 simulations give good
predictions of dose rates and activation.
• Studies will continue in Fall 2009.
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Backup Slides . . .
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ACNET Readout for Exposure
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10-6
10-9
10-10
10
-11
10-12
10
-13
10-14
Muon flux (GeV-1 cm-2 proton -1)
-2
10-8
-1
-1
Muon flux (GeV cm proton )
10
Alcove-1
Alcove-2
Alcove-3
Alcove-4
-7
8
x 10 -8
6
4
2
0
0
2
4
6
8
10
Energy (GeV)
10-15 -1
10
100
101
Energy (GeV)
102
FIG. Calculated muon spectra in units of number of
muons per GeV, per cm2, and per primary proton in
Alcove-1, Alcove-2, Alcove-3, and Alcove-4.
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100 cm
Samples for Neutron Studies
AA-06
AA-07
AA-08
AA-09
AA-10
AA-11
AA-12
AA-13
AA-14
AA-15
AA-16
AA-17
Distance
each 10 cm
60 cm
Beam Size:
3 ft. diameter
Decay Pipe:
6 ft. diameter
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Activation Yields vs Charge
• Alcove 1
• Fitted to
Rudstam’s
empirical
formula.
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0711NuMI Alcove-1
nat
Fraction of isobaric yields
• Plot of
nuclides vs
change in
nuclear
charge.
101
Na-24
Cu
100
C△
C+
▽
10-1
10-2
I
□
10-3
5
4
Neutron deficient
3
2
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0
Z-Zp
-1
-2
-3
-4
-5
Neutron rich
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Theoretical calculation
Target (Graphite)
120 GeV -256kW typical
Decay pipe (670m long – 2m diam.)
MARS code
Simulate interaction and transport of 120 GeV proton and secondary
particles
Fermilab rock
Ca : O : C : Mg : H =
0.09 : 0.56 : 0.17 :
0.08 : 0.10
ρ=2.85 g/cm3
Absorber hall and muon alcoves
Radiations around intense muon beam (T.Sanami)
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