report on n-3he simulation using geant4

n-3He Simulation

Report on n-3He simulation using Geant4

Latiful Kabir

University of Kentucky

February 10, 2017

Latiful Kabir Report on n-3He simulation using Geant4 February 10, 2017 1 / 39

Outline

Outline

1 Geometry factors2 Simulation toolkit3 Geometry and materials4 Physics list5 Primary particles : Neutron beam profile6 Validation of the simulation7 Outcome from the simulation


Geometry factors

Geometry factors

Y hi = 〈Ei(1 + hPApcosθ)〉 (1)

Aim =

Y+i − Y−

i

Y+i + Y−

i(2)

Aim = PAp

〈Eicosθ〉〈Ei〉

(3)

Gi =〈Eicosθ〉〈Ei〉

(4)

Ap =1P

Aim

Gi(5)


Geometry factors

〈Ei〉 =N∑

k=1

Qki (6)

Gi =

∑Nk=1 Qk

i cosθki∑N

k=1 Qki

(7)

1

-1

0

Proton momentum direction Triton momentum direction Neutron momentum direction

n

t

p

Z

Y

X

ϴ


Simulation toolkit

Simulation toolkit : Geant4

Geometry Materials

Detector Construction

Simulated Event

Primary Particles

Information Extraction & Analysis

Visualization

Particles Physics Processes

Physics List

Initi

aliza

tion

Actio

n

Figure: A basic simulation process flow in Geant4


Geometry and materials


1

33.8

25.4

30.4

16

1.9

HV SignalBeam

z

y/x

Figure 0.1: Schematic of the wire layout in the n3He chamber, shown in cross section

through the chamber’s central axis. Each colored point represents one wire. During

operation the wires were aligned parallel to either the x (horizontal) or y (vertical)

beam-line axis to measure either PV or PC asymmetries. Linear dimensions are in

centimeters.

Figure: High voltge and signal wires inside the chamberLatiful Kabir Report on n-3He simulation using Geant4 February 10, 2017 6 / 39


Figure: A simplified geometry of the setup

Using,

ρ =gV

=PMRT

We get density of 3He, ρ = 5.796952× 10−5 gm/cm3


Physics List

Physics List

Neutron absorption reaction :

n +3 He→ p + t

This is an inelastic hadronic process.Process : G4NeutronInelasticProcessModel : G4ParticleHPInelastic (High Precision model)XS Data : G4ParticleHPInelasticData, uses ENDF/B-VII (repackaged in G4NDL)data

The energy loss of proton and triton through ionization.

p +3 He→ p +3 He+ + e−

t +3 He→ t +3 He+ + e−

The relevant class is G4hIonisation

Alternative way is to use reference physics list QGSP_BERT_HP which is a collectionof –Quark Gluon String (QGS) model, Precomputed (P) model used for de-excitation,Bertini-style cascade (BERT) and High Precision (HP) neutron model.


Primary particles : Neutron beam profile


Construction of the neutron beam profile was done in the following twosteps :

Neutron energy distribution : The monitor-1 (M1) signal wasused to generate the neutron energy profile at detector position.Neutron spatial profile : The beam scan data was used to getthe neutron’s position distribution on the xy plane at the front edgeof the detector.



14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5At M1 position

At detector position

Neutron time of flight [ms]

Inte

nsi

ty [

volt

]

Figure: Propagating unconvoluted M1 signal at detector position



14 16 18 20 22 24 26 28 300

20

40

60

80

100

120

140

160

Neutron time of flight [ms]

Wei

gh

t fo

r n

eutr

on

flu

x [

volt

/sec

]

Figure: Corrected unconvoluted M1 signal at detector position



2 3 4 5 6 7 80

500

1000

1500

2000

2500

[meV]n

Neutron energy E

eve

nts

)6

Nu

mb

er o

f n

eutr

on

s (p

er 1

0

Figure: Generated neutron energy distribution



Figure: Neutron spacial beam profile at upstream position from the beamscan data



Figure: Neutron position distribution on the XY plane from simulation aftercollimation (default collimation). Total 106 primary events considered.



Figure: Example of simulated capture events (2D view) inside the chamber.Yellow tracks are neutrons, blue tracks are protons and gray tracks are tritons.Also visible, few red tracks which are electrons, and green tracks which aregammas.


Validation of the simulation

Validation of the simulation

1. The conservation of energy2. The cross section comparison3. The energy dependence of cross section4. Comparison of stopping power with PSTAR and SRIM4. The energy range relationship comparison with PSTAR and SRIM6. The angular distribution of the outgoing particle’s momentum7. Comparison of yields with data8. Comparison with collimation scan data


The conservation of energy


10n +3

2 He→31 H +1

1 H

The theoretical Q-value for this reaction is already known from the resulting masschange.The masses of the reactants are10n = 1.008665 amu32He = 3.01603 amu31H = 3.0160511H = 1.007825 amuSo the resulting mass change is,∆m = 1.008665 + 3.01603 - 3.01605 - 1.007825 = 0.00082 amuSo, the Q-value = 0.00082 × 931.5 MeV = 763.83 keV

Ep = 573keV

Et = 191keV



100 200 300 400 500 600 700 8000

200

400

600

800

1000

310× p + t→He 3n +

Theoretical :Q-Value = 764 keV

= 573 keVpE = 191 keVtE

Initial KE [keV]

Nu

mb

er o

f ev

ents

Triton Proton

Figure: Initial kinetic energy of proton and triton in the simulation. Total 106

events considered.


Cross section comparison


To extract cross section value from this information, we note that thenumber of capture at position x inside the chamber is related to thecapture cross section as –

I(x) = I0e−NσxNσ (8)

where,N = density of nuclei in the volume (nuclei/cm3)σ = The capture cross section (barn, 1 barn =10−28m2)I0 = Initial beam intensityI(x) = Number of neutrons captured per unit length at distance xLinearizing the equation we can write,

lnI(x) = −Nσx + ln(I0Nσ) (9)

nV

=P

RT(10)



h2Entries 992579

/ ndf 2χ 43.45 / 49

Constant 0.00± 11.45

Slope 0.0002±0.1343 −

0 5 10 15 20 25 30 35

210

310

410

510 h2Entries 992579

/ ndf 2χ 43.45 / 49

Constant 0.00± 11.45

Slope 0.0002±0.1343 −

Distance along beam direction [cm]

Nu

mb

er o

f ca

ptu

res

= 10977 bσENDF = 10910 b (from slope)σGeant4

= 6 meVnET = 298 KP = 0.5 atm

Figure: Capture cross section from the simulation with pencil beam. Target isat room temperature. The cross section from the simulation is compared withENDF cross section value.


The energy dependence of cross section


For thermal neutrons there is a region called “1/v region" where the absorptioncross-section increases as the velocity (kinetic energy) of the neutron decreasesaccording to the 1/v law.

σa ∼1v∼ 1√

E(11)

0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.0098000

10000

12000

14000

16000

18000

20000

22000

24000

26000 Geant4 Simulation

ENDF

[b

arn

]σ

Cro

ss s

ecti

on

[eV]n

Neutron energy E

Figure: ENDF vs Geant4 cross section comparison for different thermalenergiesLatiful Kabir Report on n-3He simulation using Geant4 February 10, 2017 21 / 39


7− 6.5− 6− 5.5− 5− 4.5−9

9.2

9.4

9.6

9.8

10

10.2 / ndf 2χ 05 / 7− 9.785e

p0 0.01016± 6.75

p1 0.001838±0.4986 −

/ ndf 2χ 05 / 7− 9.785e

p0 0.01016± 6.75

p1 0.001838±0.4986 −

σlo

g

nlogE in meV]

n[E

in b

arn

]σ[

Figure: 1√E

depencence of crsoss section form simulation


The stopping power and ionization curve


– Compare stopping power from simulation with that from PSTAR andSRIM.– For PSTAR, the available medium is 4He.– For PSTAR no triton data is available.– However proton and triton stopping power in 3He can be estimatedfrom PSTAR proton data in 4He.To get triton data from PSTAR,[

dEp

dx

]E=E0

=

[dEt

dx

]E=3E0

(12)

Rt(E) = 3Rp(E3) (13)



0 100 200 300 400 500 6000

10

20

30

40

50

60

70

80

90

Proton Kinetic Energy [keV]

[ke

V/c

m]

dx

dE

- ..

Geant4 simulationHe4PSTAR data for

SRIM

Figure: Proton stopping power as a function of kinetic energy from theGeant4 simulation, PSTAR data and SRIM. The target is at room temperature(298K) and 0.47 atm pressure.



0 20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80

90

Triton Kinetic Energy [keV]

[ke

V/c

m]

dx

dE

-

.

.


SRIM

Figure: Triton stopping power as a function of kinetic energy from thesimulation, PSTAR data and SRIM. The target is at room temperature (298K)and 0.47 atm pressure.



6− 4− 2− 0 2 4 6 8 10 120

10

20

30

40

50

60

70

80

90

Distance from vertex [cm]

[ke

V/c

m]

dx

dE

-

Vertex

.

.


SRIM

Triton

Proton

Figure: Ionization curve from the simulation, PSTAR data and SRIM. Thetarget is at room temperature (298K) and 0.47 atm pressure.


The energy range relationship

The energy range relationship

6− 4− 2− 0 2 4 6 8 10 120

100

200

300

400

500

Distance from vertex [cm]

Kin

etic

En

erg

y [k

eV]

.

.


SRIM

Vertex

Triton

Proton

Figure: Comparison of proton and triton energy vs distance in 3He after thereaction from the simulation with PSTAR data and SRIM.


The angular distribution of tracks


1− 0.5− 0 0.5 10

2000

4000

6000

8000

10000

12000

θProton momentum direction cos

Nu

mb

er o

f ev

ents

(a) Distribution of proton momentumdirection cosθ

3− 2− 1− 0 1 2 30

2000

4000

6000

8000

10000

12000

[ rad]φProton momentum direction

Nu

mb

er o

f ev

ents

(b) Distribution of proton momentumdirection φ

Figure: Proton momentum angular distribution in the simulation. Total primaryevents considered 106.



1− 0.5− 0 0.5 10

2000

4000

6000

8000

10000

12000

Nu

mb

er o

f ev

ents

θTriton momentum direction cos

(a) Distribution of triton momentumdirection cosθ

3− 2− 1− 0 1 2 30

2000

4000

6000

8000

10000

12000

[rad]φTriton momentum direction

Nu

mb

er o

f ev

ents

(b) Distribution of triton momentumdirection φ

Figure: Triton momentum angular distribution in the simulation. Total primaryevents considered 106.


Comparison of yield

Comparison of yield

(a) Yield distribution from simulation (b) Yield distribution form typical n-3He data

Figure: Yield distribution in the ion chamber from simulation and typical n-3Herun data.


Comparison of yield

0 20 40 60 80 100 120 1400

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04 Simulation

He Data3n-

9 x Layer number + Wire number

No

rnal

ized

yie

ld

Figure: Yield distribution in the ion chamber from simulation and typical n-3Hedata


Comparison with beam scan data


(a) Yield distribution from data for col-limation scan : run# 37990

(b) Yield distribution from simulationfor collimation scan : run# 37990

Figure: Yield distribution in the ion chamber from simulation and data forcollimation scan : run# 37990



0 20 40 60 80 100 120 1400

0.02

0.04

0.06

0.08

0.1Simulation

He Data3n-


No

rmal

ized

yie

ld




0 20 40 60 80 100 120 1400

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Simulation

He Data3n-


No

rmal

ized

yie

ld




0 20 40 60 80 100 120 1400

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09Simulation

He Data3n-


No

rmal

ized

yie

ld



Outcome from the simulation


Layer number

Wir

e n

um

be

r

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1

2

3

4

5

6

7

8

9

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

Figure: The distribution of geometry factors for all the signal wiresLatiful Kabir Report on n-3He simulation using Geant4 February 10, 2017 38 / 39


0 20 40 60 80 100 120 1401−

0.5−

0

0.5

1


Geo

met

ry f

acto

r

Figure: The geometry factors with errors


report on n-3he simulation using geant4

Documents