M. A. Darzi

High Altitude Research LaboratoryAstrophysical Sciences Division

Bhabha Atomic Research CentreGulmarg Kashmir.

High Altitude Research Laboratory (HARL),

Gulmarg.

Station Coordinates:

Latitude : 34.07oN

Longitude ( :74.42o E

Altitude: h : 2743 m.a.s.l

Cut-off rigidity Rc:11.4 GV

LFGNM HOUSING

COSMIC RAYS(A radiation of very high penetrating power enters our atmosphere from above’)

•1912 - Victor Hess reaches 5350 m altitude in a balloon and shows conclusively that the rate of charged particles increases significantly with height:

•There is an extraterrestrial source of radiation !

•Cosmic Rays were named by Millikan (1925)

•1930 – Pierre Auger discovers particle showers.

•1936 - Hess gets Nobel Prize for discovery of cosmic rays.

•Cosmic ray Composition

•Protons ~87%

•He ~12%

•1% heavier nuclei: C, O, Fe and other ionized nuclei synthesized in stars

•2% electrons, -rays, neutrinos

History

Primary Cosmic Ray Spectrum

Neutron Monitor Galactic and solar cosmic ray particles entering the earth's atmosphere with

energy above 0.5 GeV undergo nuclear interactions, producing secondaries whose effect is extended down to the sea level.

However in these secondaries, neutrons form a majority of component at the ground level and have an energy spectrum dominating towards lower energies covering a wide range from 0.01 eV to 10 GeV with evaporation peak at around 1 MeV and a knock on peak at around 100 MeV.

Neutron monitors with their reliability and basic simplicity offer a means of studying the longer-term temporal variations while their sensitivity and high counting rates make possible the observation of short term intensity changes as well.

Therefore neutron monitors play a key role as a research tool in the field of space physics, solar-terrestrial relations, and space weather applications.

Solar modulation refers to the influence the Sun exerts upon the intensity of galactic cosmic rays. As solar activity rises (top panel), the count rate recorded by a neutron monitor decreases (bottom panel).

CONVENTIONAL NEUTRON MONITORS AND LFGNM

NM64 SECTION

GNM SECTION

IGY SECTION

Paraffin Moderator

Counter Dia = 3.8 CmsActive Length= 90Cms

No lead used in GNM

28cm

7.5cm

LFGNM Section

Counters IGY NM64 LFGNM

Active length (cm) 87 191 87

Diameter (cm) 3.8 14.8 3.8

Pressure (mbar) 600 270 600

Moderator

Material paraffin polyethylene Paraffin

Average thickness (cm) 3.2 2.0 8

Producer

Material lead lead No

Average depth (g cm-2) 153 156 -

Reflector

Material paraffin polyethylene paraffin

Average thickness (cm) 28 7.5 28

Characteristics of neutron monitors

BF3 Detector

• Actually the signal is amplified somewhat in the

strong electric field very near the wire

• Electrons ionize the gas, producing a cascade

• For appropriate potentials, the amplification is

proportional

Fill Gas Pressurre: 45 cmHg

B10 enrichment: 96%

Active dia: 3.8 cms Active length: 90 cms

Anode wire: Tunguston 25m Thick

Cathode material : Brass (1mm thick)

 

ANODE

CATHODE

1n0 + 10B5 7Li3 (0.84 MeV)+ 42 (1.47 MeV) + (0.48MeV)

• About 94% of the reactions leave the 7Li3 in an excited state, releasing 2.31

MeV of kinetic energy.

1n0 + 10B5 7Li3 (1.02 MeV)+ 42 (1.77 MeV )

• About 6% go directly to the ground state, releasing 2.79 MeV

• This can produce about 2x105 free electrons

• Most of the kinetic energy appears in the alpha particle

• The alpha particle can hit the wall of the detector and not deposit all of its

energy

Neutron Detection Reaction in BF3 counter

LEAD-FREE GULMARG NEUTRON MOINITOR (LFGNM)

PRE AM P& AM P

DISC

SCALER SCALER SCALER

PRE AM P& AM P

PRE AM P& AM P

DISC DISC

M em ory and P C in te rface

Paraffin 3BF Counters

• The modified detector is housed below a 70o slant roof at the High Altitude Research Laboratory – Gulmarg.

• Detector: standard 21 BF3 neutron counters.

• Upper paraffin thickness ~ 8 Cm

• Lower paraffin thickness ~ 28 Cm

• 3 – Channels of 7 counters each.

• Efficiency ~ 3 %

• Count rate ~ 36000 per Hour

• Pressure coefficient = -0.84 / millibar

• A digital Barometer is used to obtain 3 minute readings of the atmospheric pressure.

Optimum Moderator Thickness

Spectrum

0

20

40

60

80

100

120

140

160

180

200

220

0 32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 512 544 576 608 640 672 704 736 768 800 832 864 896 928 960 992 1024

Channel No.

Discriminator

• Computers and logic are simpler if the analog signals

are converted to digital signals

• The simplest conversion device is the discriminator,

which produces an output signal each time the input

exceeds a specified threshold

DAQ OF LFGNM (Lead-free Gulmarg Neutron Monitor)

Modulation effects recorded with Lead-free Gulmarg Neutron Monitor

• Short term modulation effects

(Forbush Decrease of 29th October 2003 event)

• Long term Modulation effects September 2007 to

September 2008

(during the quiet sun period of 23rd solar cycle)

Forbush decrease recorded with Lead-free Gulmarg Neutron Monitor

The Gulmarg, Athens and Tibet Neutron Monitors detected a large Forbush decrease on 29th October 2003

Long term modulation recorded by LFGNM

from 1/9/2007 to 31/8/2008

Large-scale profile matching of LFGNM and ESOIR for September 2007 to August 2008

Large-scale 27 days moving average profile matching of LFGNM and ESOIR for September 2007 to August 2008

Anti-correlation of LFGNM count rate and Solar Wind Velocity for the quiet sun period of September 2007 to

August 2008

Conclusion LFGNM responds to solar modulation effects as any other

conventional neutron monitor.

The response during quiet sun periods is overwhelmingly large compared to conventional neutron monitors and indicates that the modulation signatures can very well and effectively be studied with the help of lead-free neutron monitors.

The decrease observed during solar quiet times indicates that solar wind velocity plays a dominant role in modulating the cosmic ray flux.

The ground based lead-free neutron monitors can effectively reflect the variations that can occur in the interplanetary medium. Therefore making such monitors important tools in studying solar modulation of cosmic rays.

Thank You

High energy cosmic rays are rare. Observing them at high time resolution requires a large detector.• Ground based instruments remain the state-of-the-art method for studying these elusive particles. • Neutron monitors on the surface record the byproducts of nuclear interactions of high energy primary cosmic rays with Earth's atmosphere.

H A R L GULMARG

LEAD-FREE GULMARG NEUTRON MOINITOR (LFGNM)

they play a key role as a research tool in the field of space physics, solar-terrestrial relations, and space weather applications.