the york bragg detector – design and simulation james butterworth seminar at york 31/03/2010

The York Bragg Detector –Design and Simulation

James ButterworthSeminar at York

31/03/2010

Overview• Bragg Curve Spectroscopy• The York Bragg Detector

– Bragg Volume– PGAC

• Simulations– Simulation Path– SRIM/TRIM– Garfield– Matlab– Results

• Current state of the project and Future developments

1. BRAGG CURVE SPECTROSCOPY

• Bragg Curve Spectroscopy• The York Bragg Detector




Bragg Curve Spectrometry

Idea suggested in 1982 by Gruhn et. al.

“Conceptually BCS involves using the maximum data available from the Bragg curve of the stopping

heavy ion for purposes of identifying the particle and measuring its energy.”

Nuclear Instruments and Methods 196 (1982) 33-40

Typical Bragg Curves

0 5 10 15 20 250

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

Bragg Curves for the 35 Isobar

35-Ca

35-K

35-Ar

35-Cl

35-S

Target Depth (cm)

Ioni

satio

n (e

V/an

g/io

n)

From the Bragg Curve you can determine...

The range of the ion in the gas → AThe total area under the curve → EThe peak of the curve → Z

0 5 10 15 20 250

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1Bragg Curves for the 35 Isobar

35-Ca35-K35-Ar35-Cl

Target Depth (cm)

Ioni

satio

n (e

V/an

g/io

n)

How to analyse a Bragg Curve

0 5 10 15 20 250

0.010.020.030.040.050.060.070.080.09

0.1 Bragg Curves for the 35 Isobar

35-Ca35-K35-Ar35-Cl35-S

Target Depth (cm)

Ioni

satio

n (e

V/an

g/io

n)

1.07E+08 1.07E+08 1.08E+085.00E+07

5.50E+07

6.00E+07

6.50E+07

7.00E+07

7.50E+07

8.00E+07

8.50E+07

35-Ca

35-K

35-Ar35-Cl

35-S

E-ΔE Graph of the 35 Isobars

E (eV)

ΔE (

eV)

Taking the peak height gives ΔE.

Integrating the full curve gives E.

Can create an E- ΔE plot.

A Typical Bragg Curve Spectrometer

2. THE YORK BRAGG DETECTOR

Bragg Curve Spectroscopy• The York Bragg Detector




ISOLDE

Miniball

Contamination Issues

Isobaric contamination

A/q contamination

Contamination from radioactive decays in the beamline Isobar

q

A

The Munich Bragg Detector Situated at the end of the beam at

Miniball, REX-ISOLDE. An on axis Bragg detector for small

sampling of the beam. Designed and built at Technische

Universität München.

Main drawbacks:

1. On axis so Miniball target must be removed in order to obtain data.

2. Due to detector response time only takes small sample of the beam.

The York Bragg Detector Off axis. Allows concurrent monitoring of

the beam. Large acceptance. Forms an annulus around the

beamline. Highly sensitive and selective. Hope to achieve a Z resolution

of 1/40.

2.1 THE BRAGG VOLUME





Windows5.486MeV Alpha

Particle from 241Am

241MeV 78Sr Ion

Detector GasW = Mean energy needed to create an ion pair Projectile = 90Zr at 3.1 Mev/u, Gas pressure = 300 mbar

Frisch GridShielding Inefficiency g = spacing between grid wires

b α distance between grid & anoder = radius of the grid wires

0 5 10 15 20 25 30 35 40 450

0.02

0.04

0.06

0.08

0.1

0.12

0.14

b (mm)

Shie

ldin

g In

effici

ency

, σ

0.5 1 1.5 2 2.5 3 3.50

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Frisch Grid Wire Pitch, g (mm)

Shie

ldin

g In

efficie

ncy,

σ

EC = Electric field in the collection volumeED = Electric field in the drift volume

Z-resolution

Z resolution limited by:Charge state fluctuations around Bragg peakZ2/3 dependence of Bragg peak

Typical Z resolution = 1/40

-0.3182 -0.318 -0.3178 -0.3176 -0.3174 -0.3172

-0.045

-0.0445

-0.044

-0.0435

-0.043

-0.0425

-0.042

-0.0415

-0.041

-0.0405

78Sr78Rb

E

ΔE

1

-0.278-0.276-0.274-0.272 -0.27 -0.268-0.266-0.264

-0.039

-0.0385

-0.038

-0.0375

-0.037

-0.0365

-0.036

78Sr78Rb

E

ΔE

2

2.1 THE PGAC





The Grids

The Gas and Field PGAC gas same as Bragg gas at 1/10 pressure

The Mechanical Elements

3. SIMULATIONS

Bragg Curve Spectroscopy The York Bragg Detector




Simulation Path

SRIM/TRIM

Garfield

MatlabPreamplifierSimulation

Result

Data:Ions: 78Sr and 78Rb at 3.1 MeV/uDetector Gas: Propane at 100 mbar pressure

SRIM vs TRIM

TRIM Outputs – Text files containing data about the projectile, target layers, electromagnetic and nuclear energy loss, straggling etc.

SRIM Outputs – Single table containing data about energy loss, penetration depth and straggling.

Advantages of TRIM... Simulates individual events Allows multiple target layers Number of ions and random seed can be selected Deals with ionisation by ions and recoils

Introduction to Garfield Simulation program. Simulates

gaseous ionisation chambers. Uses the best available

approximations and techniques. Higher detail than Geant 4.

Garfield needs a description of the chamber and the gas as inputs.

Garfield then simulates the electron drift in the chamber, and the current induced on the chamber wires.

Garfield Inputs

Cell section Gas section Field section Drift section Signal section

The chamber is described in this section. Components are entered a 2D

planes or wires, infinite in the third dimension.

Complex structures can be simulated using arrays of wires.

The dimensions of each component and voltages on them are specified here.

The gas properties of the chamber are set here including... Pressure. Temperature. Ion mobility. Work function. Fano factor. SRIM file to be read in.

The field drift and signal sections contain various commands for calculating and plotting the field, drift lines and induced current.

Garfield Outputs

The Garfield/SRIM Interface

Garfield can interface with the SRIM quick range tables.

It makes use of the values for... Electromagnetic energy loss. Nuclear energy loss. Distance traversed by ions. Longitudinal straggling. Lateral straggling.For ions at a range of energies.Density of the gas is also read in. This replaces any value for density already read into Garfield.

The Garfield SRIM interface makes use of the fact...

nuclear andneticElectromag

electrons ofNumber dx

dE

The TRIMCAT Module

Reads in files from TRIM• D

ata read includes gas pressure, positions and thicknesses of layers and a table of ion energy against position(x, y, z) and EM energy loss.

Perform Numerical Differentiation• U

ses a lagrangian method to differentiate energy vs position to give the total ionisation dE/dx.

Calculate the splitting between EM and nuclear energy losses• U

se the differentiated values for total dE/dx and the values of EM dE/dx.

Generate electron clusters along the track• G

enerates clusters of electrons according to the ionisation distribution and drifts them using Monte-Carlo methods.

The Matlab Preamplifier Simulation

The Results (1): The SRIM Interface

-0.3182 -0.3181 -0.318 -0.3179 -0.3178 -0.3177 -0.3176 -0.3175 -0.3174 -0.3173

-0.045

-0.0445

-0.044

-0.0435

-0.043

-0.0425

-0.042

-0.0415

-0.041

-0.0405

78Sr78Rb

E

ΔE

-0.045 -0.0445 -0.044 -0.0435 -0.043 -0.0425 -0.042 -0.0415 -0.0410

5

10

15

20

25

30

78Sr78Rb78Sr Gauss78Rb Gauss

ΔE

Freq

uenc

y

The Results (2): The TRIMCAT Module

-0.278 -0.276 -0.274 -0.272 -0.27 -0.268 -0.266 -0.264

-0.039

-0.0385

-0.038

-0.0375

-0.037

-0.0365

-0.036

78Sr78Rb

E

ΔE

-0.278 -0.276 -0.274 -0.272 -0.27 -0.268 -0.266 -0.2640.136

0.137

0.138

0.139

0.14

0.141

0.142

0.143

78Sr78Rb

E

ΔE/E

0.137 0.1375 0.138 0.1385 0.139 0.1395 0.14 0.1405 0.141 0.1415 0.1420

2

4

6

8

10

12

14

16

18


ΔE/E

Freq

uenc

y

The Results (3): The effect of the PGAC

-0.278-0.276-0.274-0.272 -0.27 -0.268-0.266-0.264

-0.039

-0.0385

-0.038

-0.0375

-0.037

-0.0365

-0.036

78Sr78Rb

E

ΔE

-0.32 -0.318 -0.316 -0.314 -0.312 -0.31 -0.308

-0.044

-0.0435

-0.043

-0.0425

-0.042

-0.0415

-0.041

78Sr78Rb

E

ΔE

0.137 0.138 0.139 0.14 0.141 0.1420

2

4

6

8

10

12

14

16

18


ΔE/E

Freq

uenc

y

0.132 0.134 0.136 0.138 0.140

5

10

15

20

25


ΔE/E

Freq

uenc

y

4. CURRENT STATE OF THE PROJECT AND FUTURE DEVELOPMENTS



Simulations– Simulation Path– SRIM/TRIM– Garfield– Matlab– Results


The Engineering Designs PGAC complete. Mechanical design of Bragg

nearing completion at Daresbury Laboratory.

Designs ready in stages throughout this year.

Electrical design done by Bob Hyde in workshop at York.

Drawings courtesy of Jon Strachan, STFC Daresbury Laboratory, Cheshire.

The Prototype Prototype PGAC constructed at

York. Ready for testing with fission source at Manchester.

Prototype Bragg volume to be constructed over the coming months – needs to be outsourced.

Drawings courtesy of Jon Strachan, STFC Daresbury Laboratory, Cheshire.

The Simulations SRIM/TRIM Garfield Bragg Simulation Garfield PGAC Simulation Matlab Preamplifier Simulation Post Processing Software Geant 4 Efficiency simulation

ANYQUESTIONS?



Simulations– Simulation Path– SRIM/TRIM– Garfield– Matlab– Results

Current state of the project and Future developments

The Munich Comparison-100 -90 -80 -70 -60 -50 -40 -30 -20 -10

-6

-5

-4

-3

-2

-1

0

30Mg Sim17F SimMg ExpF ExpMg ScaleF scale

Preliminary!

the york bragg detector – design and simulation james butterworth seminar at york 31/03/2010

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