On the occasion of the June 3, 1982 intense gamma-ray solar flare a significant increase in counting rate due to solar neutrons was observed by the neutron monitors of Junsfraujoch and Lomnicky Stit located at middle latitudes and high altitudes. In spite of a larger detector employed and of the smaller solar zenith angle, the amplitude of the same event observed at Rome was much smaller and the statistical fluctuations of the salactic cosmic ray background higher than the ones registered at the two mountain stations, because of the greater atmospheric depth at which the Rome monitor is located. The effeciency for detecting a solar neutron event by a NM-64 monitor as a function of the Sun zenith angle, atmospheric depth and threshold rigidity of the station was studied

Iucci, N.

Parisi, M.

Signorini, C.

Storini, M.

Villoresi, G.

English

NASA Technical Reports Server

134
SH 1.4-3
SUGGESTIONS FOR IMPROVING THE EFFICIENCY OF GROUND-BASED
NEUTRON MONITORS FOR DETECTING SOLAR NEUTRONS
N.IUCCI, M.PARISI, C.SIGNORINI, MoSTORINI and G.VILLORESI
Istltuto dl Fislc_ dello Seazlo Interelanetar_o del CNR
DIPartlmento dl Fislca - Unlverslta' 'La Saelenza °
PJazzale Aldo Moro,2 - 00185 ROMA, ITALY
1o Introduction. On the occaslon of the June 3, 1982 intense
_mma-ra_ solar flare a significant increase in count_n_ rate
due to solar neutrons was observed b_ the neutron monitors of
Jun_frauJoch/J/ and Lomnlck_ Stit/2/ located at mlddle latl-
tudes and high altitudes. In selte of _ lar_er detector emel-
o_ed (12-NM64) and of the smaller solar zenlth an_le, the am-
elitude of the same event observed at Rome (see Figure 1) was
much sm_ller and the statLstlcal fluctuatlons of the _alactlc
cosmic ra_ background hi_her than the ones re_Istered at the
two mountaln _t_t_on_, because of the _reater atmosPherlc de-
Pth at which the Rome mor,ltor is located.
We will stud_ here the efflclenc_ for detect_n_ a solar neutr-
on event b_ a NM-64 monitor ms a functlon of the Sun zenith
an_le, _tmoseherlc d_th and threshold ri_id_t_ of the stati-
on; some suggestions for im_rovin_ remarkabl_ the detection
effic_enc_ will be _ven.
2. The eff_.clenc_ of a standard neutron mor,itor for the dete-
ction of solar neutron events. The increase _i(Xe) eroduced
b_ a solar neutron event in the neutron monitor countin_ rate
will deeend or, the amount of atmoseherlc matter _n the Sun's
direction, Xe=X/cos_, where X is the actual atmoseher_c de_th
_r, _/cm _ and_ the solar zenith an_le (see F_ure 2). The ob-
served relative amelltude is_I(X,O)/I(X,_ ,t), where the nuc-
leonlc intensit_ back._round I(X,_ ,t) is a funct_or, of atmos-
eher_c depth, threshold ri_id_t_ P_ and modulat_or, level at
the observatlon t_me t.
The standard error _ of the relative amel_tude is eroduced b_
the fluctuations in the cosmic ra_ background [S(X,P ,t) =
=_(X,_,t)/ VI(X,_ ,t) where _ _s in flrst _eeroximation the
mean detected multlpllcit_ ], therefore will deeend _Iso on
the s_ze and t_ee (IGY or IQSY) of monitor emelo_ed. In F_u-
re 3 we show the exeected chan_e of the relative _m_lltude
_J/I for a solar neutron event registered at the r_dit_ th-
reshold of Rome ( _= 6.3 GV ), as a function of X and _ .
For this comeutatlon we used the attenuation lengths A (X) of
the nucleonic component estlm_ted b_ BACHELET et _1./3/ for a
modulation level I( 1033,0,t )=0°9 I( 1033,0,Ma_ 1965 ). For
the se('ondar_ neutrons of the solar neutron event a tentative
attenuation length _= 110 _/c,_ was used.Th_s value of _was
derived from the June 3, 1982 solar neutron event (see F_ure
3).The expected chan_e of the relative amelitude for a chan_e
_X = (X"-X') '_natmospheric deeth _s a function of 8 is come-
1  
S  1. 4 - 3 
ESTI NS  IM I  T  Y  ND-BASED 
 I RS FO  TI G SO  S 
.I CI, . RISI, . I ORINI, . RINI a  . I RESI 
St1t t   .1C~ lla p l  I pl etar10   
I artl ento  l l  - nlverslta' -L  P1enza-
i ~ e l  oro,2 -  , ITA  
I. I t uctIon.  th  ~ .1on  t  J  ,  l t se 
Sa ma-ra~ l r   l~ f1cant ln se in ln~  
 to l r tr ns as r ed ~ th  tr n onitors  
~frau~och/jl  lck~ ti 1 ~   lddle I
e.  l~  1 es.  P1t   a ~  t tor pl-
~  (12-N 64) a  f t  . aller l r It  ~  th  a -
plit e f t  sa e nt s r ed t o e (s  ~ e ) as 
uc  d ler   stlcal lu atl ns   ~ tlc 
s lC ra':l aclt.!l.ir()I.md l~ r t  ·t  s ~lstered t t  
t  ountdln . a l n~, use  t  ~ r t ospherlc 
p   WhlCh  e onlt r  t d. 
e ll ~ re  lclenc~  tln~  l r utr-
 ent ~  -64 onltor a   ctl n f   it  
~  a ospherIc ~pth  old ~ 1t~   ti-
; u e . Ssestion.  l p ovin~ rkabl~  t ction 
iclenc~ ll  ~\ven. 
2. The Qff1c~en~~ of a .tandard neutron monitor for the dete-
• 
ction of solar neutron events. The 1ncrease AI( e) produced 
~  lar eutron ent i  t  utr n on1tor ntin~ t  
1ll ~pend Ofl t ' olJnt f ospherl~ atter l  t  un's 
ir ction, 9=X/co~, here  1. t  t al t ospherlc pth 
J n ~ 2  e t  lar rd th Sle  l~IJre ). he -
served relatlve ampll tlJde isAI (X,e) II (X 'PT ' t), where the rIIJC-
leonlc intensit~ back~round I(X,~ ,t) is a functlon of at os-
pheriC depth, threshold ri~ldlt~ PT and modulatlon level at  bservatlon tl e  
he st dard rror~ f t e r lative plItude i  pr duced ~ 
t  tuations l  t  1C ~ ck~round C~(X,P   
~":iii (X, FT ,t) I  I (X, F:,. , t) here iii 115 HI fl rst appro>dmation the 
ean etected lt1p 1cit~ J, t erefore ill epend al   
t e Slze a d ~pe (I  r I ) f onitor plo~ed. I  l~U­
re 3 e sho  t e pected an~e f t  r latl e a plitude 
AI/I f r a olar e t"i'On erlt ~istered t t  l~ldit~ t -
reshold of f~ome ( F+-::. 6.3 GV ), as a flJnction of X and & • 
or t l. computatIon e sed t e tt uation en~ths ~ ( ) f 
t e ucleofl1c ponent stl ated ~ CHELET t al./ 1 f r a 
odulatlon l el I( 0 3,0,t ) 0.9 I( 1033,0,Ma~ 965'. or 
t e se('ond~r~ eutrons f t e s lar eutron event a t tative 
attenudtion lerlsth A",= 110 ~/cm2. was IJsed. ThlS value of k""was 
derIved fr  t e June , 1982 solar eutron event (s e Fl~ure 
). he expected chan~e of t e relatlve a plitude f r a anse 
6  ::: ( " - ') "tn at osphey-ic epth as a f nctlon of 9 115 c p-
https://ntrs.nasa.gov/search.jsp?R=19850026451 2020-03-20T17:02:56+00:00Z
185
SH 1.4-3
uted bM
_I (X' :)e_ _i(x",e).. _ exP[ _X/(_..cos_)Ix,,I(X' I(X") e_.pr /.dX/ [ (X) .IA
Ir. Figure 3 the varlatLon of the inverse of the standard er-
ror of the relative amplitude is also Plotted. From this Plot
we n.a.Jestimate that the value of the signal to noise ratio
[&I/l]. _"_-'3 obtained for the June 3, 1982 ever'st registered
at Rome (e_ 20° ) beceme,_ 414 for the s_me NM-64 Placed at an
intermediate altltude r)f 750 __/(2,_.In Fieure 3 the comPutat-
ion,.,r(=latl.ve to _-O°ar( - also roPorted because the results
obtair,ed here for r:r= 6,3 GV c,_r,be aPPiLed to ar,u ri_iditu
threshold bu simP[u taPin_ It.to account the latitude effect
of the r,,Jcleor,_ccomponent.
3, Mod_ficatior,,_ of the star,d_rd r,eutror, monitor for imProvi-
r',_ _,he eff'tcLer, c,J of dete(:'tlr,._so]or r,e,Jtror,events, The re-
lative amplitude of the ever,t _TII for _ _iver, X,8, t mind PT
can be increased b:{ decr(._,sil,s_the back,_round cosmic ras_ int-
er',s.Lt,._I. This could be done _r, two different wa_s_ (a)- b,_
chan_irv't the er',er_u response of the standard neutron monitor
_owards lower el",er_._les al'ld (b)- b._ Ihod3f_ln_ the omhldlreCtl-
0138] ProPert_ of the standard rleutron monitor it, order to ha-
ve the maxzmun, ret, Ponse f(:)r Particles aPPrOat'hir, _4 the monitor
from t,h¢. _ Sub dlrectaon, A simple wa_ to increase the low ene-
r£4_ ret_f.onl;e {_r',d decreat_ _ the costal(." r6u baL'_._round is sugge-
sted b,_ the eher_ deF, endenoe of the number of r'leutror$s em:Lt-
ted b._ the nuclear disintegration in lead /4/ ; the number of
detected correlated neutrons (mi.Jltlpllct[t_3) will be also fun-
CtlOI, Of Lhe el,er_j_j of the collldln._ r,eutron /5/. It is exPe--
(3ted th_3t the secondaries Produc_)(_ b%_ solar neutrons of ener-
_ " 1GeV /6/ should influence malnl_J the lntensit_ 14 of the
channel of detected multiPlictt_J 1; for this channel the rel-
•ztive amplitude Of a SOldr neutron event _'al'_ be estinlated as:
AI 4 (X,l)) AI (X,_,)
-_ •K(X) where K(X) = I(X)/l 4 (X) ;
14 (X) I(X)
 4<x)= -- KV-RR- )/
The s_r,a] to r,olse ratio increases b_ a factor _(X). K_,
whluh zs _ 2 for a NM-&4 at sea leve]. In Figure 3 we show
the expected chanSe of the relative amplitude _I_/I4 and of its
I/_ for a solar neutror, ever,t re._stered b_ a NM-64 at 6.3
GV, as a fur,r'tior,of X and _ . The atter,uatior, ler,_th _4 (X)
of the detected multiPILCLt'._ _ WaS taker, from /7/; K(X) is
fo,,r,dto increase WLi,h altitude beca,,se X_(X) " _(X).
Wher, onl,_ the events w_th deLecLed multiPlicztu 1 are regist-
ered, it _s cor,venier,t to increase the Probabilitu of detect-
35 
 .  - 3 
ted ~ 
Al(X' ,s! / 6l(X II ,e) = 
I( ') / I(X") 
eHP( II XI ( A'l\. + cosS) J 
)(U 
HP [ f dXI A (X) J 
x' 
n 1Sur~   arl t on f  l erse f ~ Rndard 
r f  atlv~ plltude 1$ l.  plutted. f  lS pl t 
~ may imat~ t  l E' f  ls al  OIse tl  
(61/11. 6-'~  talned r ~ e ,  E'vent ~lstered 
t ("Jme -::1 ';.>0°  -c'snle'; ~  r  ScHlie -64 F'lacerj t  
l ~l'medlat,e c 1.t1.tIJde of  g/c.!n?   !~ure .3  COIlIPutat-
!  .... C'-'l  I.ve 1',0 e _0° arc" l  Of'urted <;e  sults 
obt,alr'll?d here fC:>r r!.r:::: 6.3 GV CcHI be aF,plLed to arl'" rl~ldltY 
,hrf:'.hnld ~ lmpL~ l-lng 1rlt,0 ("'C'olmt  t,ltlJ f.' f ct 
f  nucle-on1.C' C'ompo ent. 
,,~. c)r.h fl.C.!atltlrl'" f  ldd  n t n Illonl tor Ol' l prOVl-
ng the ~ f CL~nCY f -teC t!nA . ]ar ne-utron e-nt.. t  
lv - F,llt,udl" uf ht> -V~Hl  ATII. Ol' d Sl l ,&,t and  
 E' l Cl' ".,f?d ':l e-C~l'Pd'HII':.~ ~  sro  ::o~mlC cn.~ t-
~ns!t,y . hlS ould e on~ !n o lfferent ~.t a)- ~ 
nslrl~ he E'n~r.~ E'sponse f  <;tandard utron onltor 
t l'd~. ("Jwer ner'iHes nd b) - y modl f~lnS e nlr ldl rectl-
ond] p opert~ f he <;tandard n -utron onltor In r er o -
~ e- Xl m e-~pon~~ o  p rt C'les pp oa~hlnS e onitor 
rom h~ rl r~ctlon.  fulmple ~ o lncr d~e he ow e-
.~ .~r'onse ~n  rj~cre.~p the COqml~ rdY ~kground lS s Se-
t<:'d \~ he ~'rl~l'S~ }O'f.·rld~nC'~ f f.' rllJlllb~r f n l.Jtrons lt-
ed y e rllJC'l f.·ar lfulnte~rat!on HI ad 141  e ber f 
t~ctpd rrelated eutrons mu tlpllcit~) lll  lso un-
tl011 of f.' EHI~rch' f he C'oilldlns l~utron 15/. t lS -xpe--
C.!ted hat he econdar!e-s p oduc~rl l\y lar eutrons f ner-
g~ ~ 1GeV 161 fuhould lnf1.uenC'e malnl~ the- lntenslt~ ~of the 
a nel f etected u tlP1.icLt~ ; or lS C'hannel e el-
"Jtl  ',l!tudl" of  st)1. .. ~r E'utron e-nt ("'al'l I:le !  t 
6I",(X,S) AI(X,B) 
::1 • k'(X) wheT'e K(X) .:: I(X)/l", (X) ; 
I~ (X) I(X) 
er", ( X ) ::r 11 V 11 (X) .. ~ (X) [("'K(X) I m ( X ) J 
e .1.sna]  lO se NltlO HIl~rea.es ~  t r ih(X). V K(X), 
~h 1. z  r  -64   ~ l   1Sure    
the expected change of the re-Iat,lVf,' amF,lltude .o.IlI", and of ltS 
1/0'4 for a '..:;cIlal' neutl'on ever It reSJst~red b~ a N -64 at 6.3 
, ~.  WI("'tlCm    e- •  teI'II.Jat,l n .en~t,h k" X  
f  ~ l rj ultipl cLt,y j was ~n ro  1 /  ( ) lS 
found t  l r se wlt  Rltlt e becau<;e- ~~(X) ~ k( ). 
herl l", ,  ent. Wl t  f,'LecLf?d lp lCl.t~   Sl<;t -
~l'ed, 1 I', 1.fu ("urIV<-:lnll'rit  l -ase  pr bsblll t~  tect-
136
SH 1.4-3
zr1_ time locall,_ F,roduced neutrons; thzs could be obtazned b_
addlr',.,.1some BF3--cour_ters to the stsnderd _eometr_ wzthout In-
creaszn.q the anlount of lead; for instance, zf the detection
Probabzl_t_ zs Jr,creased b_ a "factor 2_ the sz_r,al to r,ozse
ratio F_I_/I4]._wzll zncrease b_ a factor 1.5-2.0.
Moreover the background cosmzc ra,..;intenszt_ can be lar_e]_
derreased, at lea_t at m_ddle l_t_tude,_, b_ shieldzn_ the mo-
r_ztor w_th an aPProPriate structure able to reduce the fluv
of c'o_,micra4 Partzc)es whzch aPProach the n.on,tor from the
Portlor_ of" the sk._ never scanned b_ the Sun. For znstar.ce at
42N _eo._raF,hzc latztude we m_ht shzeld the monztor from_20S
to 90N. I_ the background zntens,t,a zs reduced b_ a _actorN2
the s_r, al to nozse ratio _r,creases b._ a factor~l.4. Th_s ef-
fect can be zmProved remark.abl_ zf the monitor is mounted on
a _,l_tfor_, which rotates wzth the Sun; zn thzs case the shze-
ldzn_ structure ma_ also cover the lateral sides of the monz-
tot; a _osszble _eometr_ of thzs solar neutron telescope zs
._zven zn Fx_ure 5. Wzth this telescope the cosndc ra_ b_ck_r-
ound car. be r_duced b_ a factor 10. It, Figure & we show, for
a _ro_er |,etwork.of 9 near-e_uatorial solar neutron telescop-
es, located at mour,tain altztude, measurzn_ the zntenszt_ of
the detected m_.-_]tz_lic_t_1 and wzth _ncreased ( b,a a factor
2 ) _.robabzlzt,_ o'F detectzn_ the locall_ _roduced neutrons,
the cord,our--lir,es of (_I4/T 4),_4- A, 2A and 4A res_ectzvel_,
as _ function of tzme (dam and hour); the value of A ._iven zr,
Fz_ure 6 wa_._comF.uted for an event with observed relative am-
mlztude LSI/I -_0.5 Y. for F_ = 6.3GV, X = 1010 ._/cn_,8= 20_.
References.
/1/ H. DEBRUNNER et al._ iBth I.C.R. Conf. 4,75,1983.
/2/ G.E. KOCHAROV_ 8th E.C.R. S_m_. Tecno_rint, _.51,1983.
/3/ F. BACHEL[T et al.t Nuovo Czmento 35, 23,1965.
/4/ _. BERCOVITCH et al°_ Phys. Rev° 119, 412, 1760.
/5/ _.B. HUGHES and P.L, HARSD_N_J.Geo_h_s.Res.71,1435,1966.
/6/ E.L. CHUPP et al._ iBth I,C°R° Con_° 10,334,1983.
/7/ N. IUCCI et al._ Nuovo Cimento 6B,111,1971.
i!i /SUN
'_' 31000
ii- --IOIt | _"I01,3 , }'RAYS_, , ,_ , ,
ILOO 15 30 45 12OO 15 30 45 12,00
JUH_3,196! (tiT) Fz_ure 2
138 
SH 1.4 - 3 
InS the locall~ produced neutrons9 thlS could b~ obtained b~ 
addlnS Home B~-count~rs to th~ tandard Seometr~ wlthout In-
~reaSlnS the amount of lead; for in.t~nce, lf th~ detectlon 
probal:.llllt~ Ill> .ut(;,rt",,~sf~d b~ a fdetor 2, the 'Slgrlal to nOlse 
ratio r6I.., II", J.e;;i wlil InCreali>e b~ a fac·tor 1.5-2.0. 
Horeov~r the ha~k~ruund ~osmlC ra~ lntenli>lt~ can be larse]~ 
de~r~a'Sed, at lpa~t at mlddl~ ldtltud~., b~ shieldlns the mo-
rlltor wlth dn appropriate ll>tructure able to reduce the flux 
of cOll>mic ray partlcles Whl~h approach the monitor from the 
POT'tlClrl of the sk~ never scarlrled b~ the Sun. tor lnstance at 
42N geOtlraphl~ latltude we ml~ht shield the monltor from-20S 
to 90N. I f the backs rOIJnd I ntens 1 t\:l 1 S reduced b~ a facto r N 2 
the s1Snal to nOlse ratio Jncreall>es bl:l a factor-l.4. This ef--
fe~t can be 1mproved remarkabl~ 1f the monitor IS mounted on 
a pldtform which rotates With the Sun; ln thlS case the shle-
Idlng ~tructur~ mal:l also cover the lateral ll>ides of the mon1-
tor; a posslble seometr~ of thlS solar neutron telescope lS 
~1v~n 1n Fl.ure 5. With thIS telescope the cosmic ra~ backsr-
ound carl be T'aduced b~ a factor 10. Irl FislJre 6 we show, for 
a proper Iletwork of 9 near-eauatorial solar neutron telescop-
es, located at mountaln alt1tude, measurlns the lntensltl:l of 
the detected mu]tlpliclt~ 1 and wlth lncreased < b\:l a factor 
2 ) probablllt~ of d~tect1ng th~ localll:l produced neutrons, 
the CCHltuu r--1 i n~s clf <A 1'1 1 T 'I ) .6'.4" =' A, 2A arid 4A respect 1 ve 1 ~, 
as a fun~tlon of t1me <dal:l and hour); the value of A siven 1n 
F1sur~ 6 was computed for an event with observed relative am-
phtud€~ ~I/J .:: 0.5 7. for F'T =: 6.3GV, X =: 10 g/clT~' e =: 2<f'. 
References. 
III H. DEBRUNNER et al.: 18th I.C.R. Conf. 4,75,1983. 
121 G.E. KOCHAROV: 8th E.C.R. Sl:Imp. Tecnoprint, p.51,1983. 
131 F. BACHELtT et al.: Nuovo Clmento 35, 23,1965. 
141 M. BERCOVITCH et al.: Phl:ls. Rev. 119, 412, 1960. 
151 [.B. HUGHES and P.L. MARSDEN:J.Geophl:ls.Res.71,1435,1966. 
161 E.L. CHUPP et al.: 18th I.C.R. Conf. 10,334,1983. 
171 N. JUCCI et al.: Nuovo Cimento 6B,111,1971. 
... 
31500 ROM£ 121M-If >-Ii'! SUN 
.. i ~ .. 
i !:! 31000 = d 
/ 
.. 
• 
3050 
.. ~ .. ;:;- 10115 iii ~ §~ 101l3~ 
tloo 15 30 45 12.00 15 30 45 12.00 
JUN£3,1912 (UT) ~ Ulure 2 
~l!IIJre 1 
137
SH 1.4-3
F_sure 3: Chin_es of the ob-
..o
.-" served relative mmPlltude e-
..-'" nd of the inverse of its st-
.-" endard error,for m solar he-°
.o'" utron event registered b_ •
r',eutor,monitor located at
PT= a,3 OU vs, atmosPherlc
depth for dlfferent Sun zen-
ith an_les (total counts re-
iN _isteredt full l_nes; mult_-Pl_clt_ 1 counts rea_stered:
broken l_nes).
i
", 
" " 
0',' 
-10 i 
I 
" 
" 
" 
" o· 
" 20' 
25' 
137 
SH 1.4 - 3 
Fl!11Ure 3: Chan!!es of the ob-
serYed relatiye amplItude a-
nd of the inyerse of Its st-
andard error,for a solar ne-
utro  eyent r sistarad bw a 
neuton monitor located at 
PT= 6.3 GV ys. atmospherIc 
depth for dIfferent Sun zen-
Ith an!lles (total counts re-
sistered: full lInes; multl-
pllCltw 1 counts reslstered: 
bro~ er, llrHl's), 
Fl!1ure ,: S~etch of a posslble 
~olar neutron telescope for m-
lfirlle latltudes ("'400). 
JGO 
50 
1,/", 
, 
JUII[ 3,1912 (IUS-lise UT) 
, 
, 
, 
" JlS 
, 
E" 
I 
, 
, 
, 
, 
I: 
, 
',1,.110,11111 
, 
, 
, 
, 
, 
~ 
, 
A'\, 
, . 
"I _/tJ 
, .:!. 
J~ __ ~ __ ~~~~ __ ~ __ ~~~ 
100 100 100 1000 1100 1200 ./_ 
Fi~ure 4: The absolute a.pI1tu-
de 6. I of the Jurle 3, 1982 event 
for the Jun~frauJoch(J), Lo.ni-
ckw Stlt(LS), Ro.e(R) and Kiel 
(K) stations ys. at.ospheric d-
epth to SI.Jn Xe. The I are co.-
puted fro. the AlII bw applwin~ 
the latitude and altitude chan-
!les of I. 
... 
-~-
I:! ;:; 1Ii-. 
I:! 
• 
; 
I:! ;:; 1Ii- • 
<l 
I:! III 
'-
• =' 111 
... 
;:; 
~ 
s:l ;:; ;;-. 
Ii 


Suggestions for improving the efficiency of ground-based neutron monitors for detecting solar neutrons

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