Characteristics of the direct and scattered components of electron-photon shower optical radiation for distances R  500 m from the shower core to a detector, allowing for the Cerenkov and fluorescent mechanism of photon generation are presented. The results of calculations are employed to clarify the techniques for determination of the shower parameters detected by both installations registering fluorescent light and those recording Cerenkov light

Chuykova, T. A.

Galkin, V. I.

Ivanenko, I. P.

Roganova, T. M.

English

NASA Technical Reports Server

211 HE 4.4-19
LATERAL-ANGULARAND TEMPORAL CHARACTERISTICS OF EAS
OPTICAL RADIATION
Chuykova T.A., Galkin V.I., Ivanenko I.P., Roganova T.M.
Institute of Nuclear Physics, Moscow State University,
Moscow 119899, USSR
The paper presents characteristlcsof the direct and
scattered components of electron-photon shower optical ra-
diation for distances R_5OOm from the shower core to a
detector, allowing for the Cerenkov and fluorescent mecha-
nism of photon generation. The results of calculations can
be employed to clarify the techniques for determination of
the shower parameters detected by bothlnstallatlonsregis-
terlng fluorescent light and thoserecordlng Cerenkov light.
1.Introductlon. Optical radiation has beenused for many
years t0 investigate the lateral EAS development/1,2/.Each
new more accurateand/or detailed consideration of the op-
tical component leads, as a rule, to decreasing uncertain-
ties in the determination of shower parameters and some-
times allows finding new characteristics of the shower op-
tlcal image, which are more sensitive t_ the nuclear inter-
action parameters at superhlgh energy or to the shape of
the primary cosmic ray spectrum than thoseused earller/3/.
One of these improved considerations has been reported
in /4,5/ where "contamination" of the fluorescent component
of EAS optical radiation by scattered Cerenkov light has
been examined, and both lateral-angular and temporal charac-
teristics of the shower optical image has been presented.
The author of /4,5/ devldes the Cerenkov light _eglstered.by a detector into three components, direct(non scattered)
light, scattered light, and fluorescent llght, thus assum-
ing that fluorescent photons, unlike to Cerenkov ones,
would not scatter in the atmosphere(i.e, the fluorescent
light being always only direct). When considering the scat-
tered component, the author confines himself to a single
scattering_ _s a model of longitudinal development of EAS
with Eo=I017 IO18eV the author have used a cascade curve
of a showe_induced deep in the atmosphere by a gamma-ray
" of Eo=2.10"eV, with the hope that this simplification
would not considerablydistort the relative contributions
of various optical radiation components. The papers /4,5/
furthermore have not presented the temporal characteristics
" of a direct Cerenkov component. Since the results obtained
using the above noted approximations, on one hand, are only
preliminary and, on theother hand, seem to be important
. and interesting, we attempted to consider this group of
phenomena with the help of simulating program of a diffe-
rent type.
2. The preSent paper approach. A separate consideration of
the Cerenkov and fluorescent components undoubtedly gives
an additional information of their relatlvecontributlons,
however most of modern installations are incapable of dis-
https://ntrs.nasa.gov/search.jsp?R=19850027712 2020-03-20T17:05:46+00:00Z
212 _E 4.4-19
tinguishing the nature of photons arriving atoadetec_or.
We performed calculations for a _O00-8000A wavelength-
band. Since large distances(R_._5OOm)from the core to a '
detector are considered at which the characteristic temporal
scale of a pulse is _I00 ns, the time of flUorescent ph@ton
reemission can be neglected in thefirst approximation.Thus,
in the situation of interest for us the differences between
the two components reduce to their _lar characterlstlcs
whichpractically do not affect the simulation algorithmic
aspect. So, a unified source of photons is used composed of
Cerenkov and fluorescent sourceswith approprzateangular
characteristics andintensitles,and the photon transfer from
this source to a detector is considered as usually introduc-
ing the photon t_me:dela_:
- "c_o 7,where Ho=7.5km (I)
is the exponential atmosphere depth; q_=2.9.10-4 is the di-
verslty from a unity of an atmosphere refrection index at
sea level;_=(%)_To)beingthe shower generation point;Zo= _e6;P4p,e_) i the point under consideration;_=C_@, the sphe-
rical coordinate system is bound to a detector.
As far as a large core distances region is concerned a
simple shower model-that of a movingpoint-isval$d, i.e.
we neglect the electron lateral distribution and take into
account their angular distributions only. The direct optical
radiation component is calculated on average. U@e:Ismade of
a model of the angular distributlon/6/,_9 ..... :#here _
is calculated using momen_s_also present in V6/. The cas-
cade curve approximation used is _6._ = g_ 4U_ S" _c_) C2)
where e=E_(s)/#_ _o=EoD[_/9 _ _ =81 MeV, D(s) and q(s) are
the known cascade functions from /7/. ......
Forthe Cerenkov component E is the threshold energy of
Cerenkov light, and for the fluorescent component E=O. A
charged particle is assumed to produce 5photons over a me-
ter of path due to the fluorescent mechanism. The scattered
component was Monte-Carlo simulated. Over each segment of
the shower trajeCtory, approximately O.1 m.U. long, 6x13
photons(6 cells over the azimuth and 13 cells over the polar
angle) were radiated and followed till their arrival at a
_etector, till their absorption by the Earth'S surface,till
their leaving the atmosphere or till their departurefroma
detector td a distance larger than some value, Whenarrlving
at a detector, a photon was given a weight faztor proportin-
nal to the overall light amount radiated by the shower elec-
trons over a fixed trajectory segmen%and to the weight of
angular cell from which centre of mass the photon has been
radiated. The dlfferential crosssection_ofscatteredlight ,
waS, as in /4,5/, proportional to (1+cos=3O, where S is the
scattering polar angle. The data on the scattering length
(molesular Rayleigh and aerosol) were taken from /8/.- The
detector comprised 200 temporal bins each of 10 ns and one
integral bin for delays _ 2000 ns. The angle 1_ste_ was
derided into 120 bins (12 equal-size bins over the az_th
anglex10 equal-size bins over the polar angle) covering
213 nE 4.4-19
different solid angles(.04 ster to .08 ster). ThOugh the
program canslmulate inclined showers, the present paper
reports on the results for the vertical electron-photon
showers with Eo=1017eV for distances R=.5, 2.0, 8.0 km from
detector. Pot a better comparison with the results of /4,5/
we considered production depth 119 g/cm2(H=16.1 km) that
yields tm=896 g/cm and the same distance Hobs-Hm=1.2 km, as
in /4,5/. For each R _ne aata on scattered light were obtain-
ed by averaging over 10 showers. ,,
3.Simulation results. The lateral-angular distribution of
the light In _ig.1(the solid curves are for the present cal-
culation, the dash-dot Ones - /4,5/- the sum of direct Ceren-
kov and fluorescent _hotqns, the dashed curves are for scat-
tered Cerenkov llght/4,5/). All the data are divided by de-
tector sol_d angles; The data /4,5/ are furthermore multipli-
ed by 5-I0P to allow for the differences in primary energies.
The present paper data were selected from the blnsfacing
the shower core. Unlike to the data /4,5/, our curves for
scattered light do not reveal such an abrupt rise with ze-
nith angle, though an increaseof scattered light in the
overall flux is noticeable even at R=.5 km that is eXplained
by a decreasing contribution of the Cerenkov mechanism. At
R=8 km, the two sets of data are the most similar, though
some differences in lutensity are observed which can be ex-
plained by the diversity between the cascade curves and so-
lid angles of detectors in /4,5/ and present paper.
Pig.2 shows the data on PWHM_ of scattered light puls-
es. PWH_ of the scattered componen_,aCcordlng to our cal-
culation, is noticeably broarder than that of!thedirect
one(multlple scattering really matters) and increases with
R, though slower than _ of the direct component. In the
present _a_er _ increases with zenith angle similar to
that in /4/. Pig.3 shows t_plcal pulses for the direct and
scattered components(Integrated over all bins facing the
shower core).
. References
I. Jelly J. Cerenkov radiation, Moscow, 1960.
2. Nesterova N.M., Chudakov A.E., 1962, JETP, 42, vyp6,1622.
• 3. Galkin V.I., Nakarov V.V., 1983, 18th ICRC, v.b, 236
4. Protheroe R.J., 1982, J. Phys. G., v.8, L165.
5. Protheroe R.J., 1983, Proc. 18th ICRC, v.6, 240.
6. Belyaev A.A. etal. Electron,photon showers in cosmic
- rays at superhigh energies, 1980, Moscow.
7. Belenky S.Z. Avalanche processes in cosmic rays, 1984,
Moscow •
8. Martynov A.Ya. Course of applied astrophysics, _964,e
MOSCOW.
214
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Lateral-angular and temporal characteristics of EAS optical radiation

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