Fluorescence yields from N2
and dry air excited by electrons
Motohiko Nagano
Fukui University of Technology
M.Nagano, K.Kobayakawa, N.Sakaki and K.Ando ;
to be submitted to Astroparticle Physics (2002)
Fluorescence from Nitrogen
N ２＋
Data from
Bunner (1964) : weighted averages of
three experiments with an accuracy of not
better than ±30%.
Kakimoto et al (1996) : 1.4MeV-1000MeV
are mainly used in UHECR experiments.
Chamber
Top view
H7195PX selected for low noise
photomultiplier tube
A window of 2.5cm
diameter is used to
detect photons.
filter
shutter
collimator
scintillator
Source
collimator
lead brick
Electron beam
90Sr
（28.8y）
β
99.98%
β
2.28MeV
3.3MBq
90Y
average 0.85MeV
（64.1h）
0.02%
1.75MeV
90Zr
Filter
337.7nm
391.9nm
400.9nm
380.9nm
356.3nm
314.7nm
Block diagram of data
acquisition
AMP
H1161PX
H7195PX
RPN
-090
Discri
ADC
RPN
-110
Scaler
Photons
Coin
Fan In/Out
LeCroy
622
LeCroy
429A
Scaler
ADC
RPC-022
gate
TDC
start
H7195PX
H7195PX
H1161PX
H7195PX
Electrons
H7416
ADC
ADC
Scaler
Scaler
Scaler
Scaler
200nsec
RPC-061
stop
ADC
150nsec
100nsec
Scaler
delay
Delay
180nsec
160nsec
LeCroy
429A
Scaler
LINUX
LeCroy
2551
ADC and TDC data
e
Electron
delay
stop

t

TDC
180nsec
Photon
start
180nsec
backgrounds
stop
start
TDC data
Systematic errors
Item
Errors
Quantum efficiency of PMT
10 %
Collection efficiency of PMT
Transmission coefficient of filter
10 %
5%
Contamination from lines at the tail of
filter transmission
Total
5%
15.8 %
Fluorescence decay time
1


1

1


1
 radiation  int_quenching  collision  o
kMT 1
c 
4 nn p
kMT 1
p' 
4 nn  o

1
c
o  c
p’=reference pressure
4 o 
Mn  Mo
1

f n nn  f o no

p'
2M o
kM nT 
 1 
1  D
 p 
 
T
   o p'   o
1
1
for air




Life time vs Pressure (Nitrogen)
 o  (26.4  14.7) nsec
p '  (3.7  2.2) hPa
 nn  (6.1  1.2) 10 19 m 2
1
 o p'
1
o
Nitrogen
Life time vs Pressure (Air)
4 o
1

p'
kM nT

 f n nn  f o no M n  M o

2M o





 dE   Ei ( p) 
Yi  


dx
h


 
i 
Ei ( p) 
E
0
i
E
0
i
p
1
p'
dE
: Energy loss (g cm-2)
dx

: Density
h i : Photon energy
: Fluorescence efficiency in the absence of collisional quenching
(Fluorescence efficiency is defined by the radiated energy
divided by the energy loss of the electron in a unit length)
1
p
1
p'
: fraction of available energy kept after collisional losses
p’ is the reference pressure
Photon Yields per electron
N
Y
I  a     f  QE  CE
Y : Photon yields per unit length (m)
N : Total number of signal counts
a : Length of the fluorescence portion
 : Solid angle of the PMT
:
Quartz window transmission
f : Filter transmission
efficiency of the PMT
QE Quantum
:
CE :Collection efficiency of the PMT
Nitrogen
Yi  Ci
p
p
1
p 'i
1
dE o
Ci 
Ei
RN 2 T (h i ) d x
Fitting is not good with one
parameter p’.
open squares : Kakimoto et al. (1996)
Nitrogen
E0
Comparison of fluorescent efficiencies at 800 hPa
Air
Mixtures of
N2 : 78.8 %
O2 : 21.2 %
open squares : Kakimoto et al.
Air
E０
Comparison of fluorescence efficiencies at 800 hPa.
Two lines analysis
Yobs
1
 obs
C1 p
C2 p
 Y1  Y2 

p
p
1
1
p'1
p '2
Y1
1
Y2
1
(
) (
)
Y1  Y2  1 Y1  Y2  2
1
p
1
 

 1  o1 p'1  o1
1
p
1
 

 2  o2 p ' 2  o2
Assumptions:
p’ and τ0 values are the same for the transitions
from an upper level to lower levels of different
vibrational states.
For example:
p’ and τ0 are the same for 2P(0,0), 2P(0, 1), 2P(0,2), ...
p’ and τ0 are the same for 2P(1,0), 2P(1, 1), 2P(1,2), ...
M.N.Hirsh et al. Phys. Rev. A1 (1970) 1615
Measurement of the fluorescence efficiency
for the 391.4 nm band from N2 and air
excited by 0.65 - 1.6 MeV electrons.
(under the pressure range 0.05 - 10 hPa)
N2
E o (1.46 MeV)  (6.0  1.9) 10 3
p’=1.43 hPa
Air
E o (1.46 MeV)  (4.75  1.5) 10 3
p’=1.25 hPa
N2 391nm
•
391.4 nm
389.4 + 394.3 nm
Air 391nm
391.4nm 1N(0,0)
389.4+394.3 nm
2P(3,6) 2P(2,5)
316nm
311.7 nm 2P(3,2)
313.6 nm 2P(2,1)
315.9 nm 2P(1,0)
356nm
353.7 nm 2P(1,2)
357.7 nm 2P(0,1)
337nm
333.9 nm 2P(1,1)
337.1 nm 2P(0,0)
400nm
399.8 nm 2P(1,4)
405.9 nm 2P(0,3)
Air
380nm
375.6 nm 2P(1,3)
380.5 nm 2P(0,2)
Photon yields between 300 and 406nm
Photon attenuation with distance
Conclusions
• We have measured photon yields from N2 gas and dry air excited by
electrons of average energy of 0.85MeV.
• From the pressure dependences of photon yields and life times,
fluorescence efficiencies for 12 lines in the absence of collisional
quenching are determined.
• Photon yields are determined as a function of the gas density and the
temperature for 12 lines.
• Total photon yields between 300nm - 406 nm are 17% larger than the
summary by Bunner at 1000 hPa and at 20oC.
• Those are 14% larger than those used by the HiRes group. Taking into
account the wave length dependence of Rayleigh scattering and HiRes
filter, the number of photons expected to be observed are estimated as a
function of distance between the shower trajectory and the observational
site. It is possible that HiRes energy is overestimated by about 10%.
• Reference pressures are quite different from those in Bunner. We need the
detailed evaluation, taking into account the density and temperature
dependence of each band and other factors which depend on wave length.