High Power Laser Science and Engineering, (2017), Vol. 5, e16, 5 pages.
© The Author(s) 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2017.15
A new method on diagnostics of muons produced by a
short pulse laser
Feng Zhang, Boyuan Li, Lianqiang Shan, Bo Zhang, Wei Hong, and Yuqiu Gu
Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, CAEP, Mianyang 621900, China
(Received 16 November 2016; revised 14 April 2017; accepted 5 May 2017)
Abstract
Muons produced by a short pulse laser can serve as a new type of muon source having potential advantages of high
intensity, small source emittance, short pulse duration and low cost. To validate it in experiments, a suitable muon
diagnostics system is needed since high muon flux generated by a short pulse laser shot is always accompanied by high
radiation background, which is quite different from cases in general muon researches. A detection system is proposed
to distinguish muon signals from radiation background by measuring the muon lifetime. It is based on the scintillator
detector with water and lead shields, in which water is used to adjust energies of muons stopped in the scintillator
and lead to against radiation background. A Geant4 simulation on the performance of the detection system shows that
efficiency up to 52% could be arrived for low-energy muons around 200 MeV and this efficiency decreases to 14%
for high-energy muons above 1000 MeV. The simulation also shows that the muon lifetime can be derived properly by
measuring attenuation of the scintilla light of electrons from muon decays inside the scintillator detector.
Keywords: diagnostics; Geant4 simulation; muon source; short pulse laser
1. Introduction
A muon
[1, 2]
is one of the elementary particles in fundamen-
tal physics which belongs to the second generation of lep-
tons. It has a spin of 1/2 and a mass of 105.7 MeV/c
2
inter-
mediate between the proton and the electron. Since the dis-
covery in the cosmic rays research in 1936, muon was a pop-
ular research object in particle physics and applied physics.
Due to its larger mass compared to that of electron, a muon
does not produce significant synchrotron radiation, conse-
quently negligible bremsstrahlung which is at an advantage
of muon collider and related neutrino physics
[3, 4]
. Polarized
muon source can also be applied as a suitable probe in
many disciplines such as material science, biomedical, su-
perconductor physics and so on
[5]
. Benefitting from its high
penetrability, a muon can go through more than hundreds
of g/cm
2
which is much longer than X-ray radiography
[6]
.
Therefore, muon radiography can be applied on imaging of
dense object such as nuclear materials
[7–9]
.
In general, the muon is produced as a secondary cosmic
ray from the π and K meson decays by the interactions of the
primary cosmic ray protons with nuclei (N, O atoms) in the
air
[2]
. The intensity of cosmic muon flux is 1 cm
−2
· min
−1
with a mean energy at 4 GeV. Hence, cosmic ray muon
Correspondence to: Y. Gu, Academy of Engineering Physics, Mianyang
621900, China. Email: yqgu@caep.ac.cn
source has low intensity, high energy, and a very long
stopping range. Muons can also be produced by accelerators
through the decay of mesons which are produced in nuclear
interaction between accelerated protons and nuclear targets.
The accelerator muon source has high intensity and a con-
trollable stopping range for the energy covering from eV to
hundreds of MeV. However, high budget makes it impossible
to be applied commonly in laboratories except finite facilities
in the world
[10–13]
.
Another possible source of a muon with both signs is the
Bethe–Heitler lepton pair production process
[1, 14–16]
γ + A → A
0
+ µ
+
µ
−
, (1)
in high-energy photon interactions with high Z materials.
Although the muon pair production in this process is sup-
pressed relative to the electron–positron pair production
by a factor of (m
e
/m
µ
)
2
≈ 10
−4
, a muon source can
still be realized this way
[17, 18]
. In fact, along with the
development of petawatt laser in the last decade, electrons
have been produced and accelerated to several GeV which
have exceeded the threshold of muon generation by the laser
wakefield acceleration method
[19–22]
. The typical electron
flux is at the magnitude of tens of pC corresponding to ∼10
8
electrons in a bunch, and would produce 1 × 10
2
muon pairs
with pair energy centered around 1 GeV as expected by Titov
1
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