AGATA Demonstrator Test With a 252Cf Source: Neutron-

Gamma Discrimination

Menekşe ŞENYİĞİTMenekşe ŞENYİĞİT

Investigation the possibilities of discriminating neutrons and gamma rays are important !

Methods for neutron-gamma discrimination with tracking:

• The energy deposited in the first and second interaction points; • The difference in incoming direction of the gamma ray ;

• Selection based on the FM value

first secondandE E

E G

To check our methods, we consider an experiment with AGATA triple cluster , 252Cf source and BaF2 detector. BaF2 detector is used for timing. Test period is about 3-4 hours.

BaF2

Lead Shield

252Cf source60Co source

( cm3)

AGATA single cluster

Loss in gammas ~92-99%Loss in neutrons ~47-50%

Simulations1. Simulations Geant4 with

AGATA triple cluster

Cou

nts

Neutron Energy (MeV)

2. Simulated data: About 1 MeV -rays Neutrons emitted from 252Cf source

with 2.95 Ci (at LNL)

3. Tracking with MGT code

Gamma-ray energy spectrum after tracking (mgt)

EEγ (keV)γ (keV)

coun

tsco

unts

Neutrons emitted from 252Cf source with PHDEF Distance between lead shield and AGATA triple cluster is 60 cm

Number of events:35046000

Neutron multiplicity:4

Run time:3 hours

Tracking efficiency for gammas:0.97

EEγ (keV)γ (keV)

coun

tsco

unts

834 keV834 keVNo conditionsNo conditions

With conditionsWith conditions

Gamma-ray energy spectrum after tracking (mgt) * Neutrons emitted from 252Cf source with PHDEF and 1 MeV -rays

* Distance between lead shield and AGATA triple cluster is 60 cm

19854357θg – θc or Efirst or Esecond

or FM

11692646θg – θc or Efirst

145317 Efirst

10612543θg - θc

1 MeV gamma

bumppeak 834 keV

total834 keV, 72Ge834 keV, 72Ge

Time of Flight Spectra for 70 cm

TOF

Cou

nts

-rays

Neutrons

• In this experiment we would also like to use the TOF technique in order to know when a neutron is hitting detectors to check how succesful our methods are.

•One problem is that one don’t know the time resolution of the AGATA detectors.

•Without PSA, it may be around 10 ns but this may be reduced very much by the PSA.

•Time resolution is energy dependent.

Time ResolutionC

ount

s

Cou

nts

Cou

nts

TOF, Time resolution = 1 ns TOF, Time resolution = 3 ns TOF, Time resolution = 5 ns

Since we don’t know what the time resolution will be for AGATA detectors, we made TOF simulations by using different resolution values.

-rays Neutrons -rays

Neutrons-rays Neutrons

Cou

nts

TOF, Time resolution = 10 ns TOF, Time resolution = 15 nsC

ount

s

-rays Neutrons

-rays Neutrons

Conclusions

• We developed 3 methods for neutron-gamma discrimination by using tracking. We would like test these methods in a real test experiment where we shall use a 252Cf neutron source, one triple Agata detector and a BaF2 detector for timing.

• We made some simulation in order to check the effect of our methods.

• We checked the effect of different time resolution.

We are preparing a proposal for this test experiment which can be run just after the summer.