Lunchtime S.I.E.S.T.A.

James Butterworth

Finding Atomic NucleiOffenders with James the Nuclear Detective

“It’s element.. element...

elementary my dear Watson!”

Setting the Scene

CERNLHC CMS

ATLAS

ALICE

LHCb

ISOLDE

How ISOLDE works – The Primary Target

Primary Target

1.4 GeV Protons Exotic Nuclei – Reaction Products

1.4 Gev protons impinge on primary target

Reactions occur Exotic nuclei are liberated

Reactions:• Fission• Fragmentation• Spallation

How ISOLDE works – The Ion Source

Ion Source

Ion source ionises atom by knocking out one or more electrons

Ion is now in charge state +q

Types of ion source:• Surface• Laser• Plasma

How ISOLDE works – The Separator Z = Number of

protons A = Number of

protons + number of neutrons

Separates ions according to their A/q ratio So only ions of the mass we’re interested in get through

How ISOLDE works – REX

Cooler and Buncher

Electron Beam Ion Source Linear Accelerator

Electrostatic AcceleratingElements

Ions are trapped, cooled and bunched

Ions are ionised further by EBIS

Ions are accelerated along linear accelerator to experimental station

How ISOLDE works – Miniball

SecondaryTargetγ

γ

Miniball Detector

Miniball Detector

What can we learn from these gamma rays?

Nothing – we’re just doing it for fun...

Nuclear structure – a fundamental part of the fabric of the universe

Nuclear astrophysics – how the elements were created Applications – MRI, nuclear power etc.

So why do we need a detective?

Blue Z = 38 (Sr), A = 78, q = +1 Green Z = 37 (Rb), A = 78, q = +1

Problem: We get contamination from nuclei with different Z but the same A: isobars

These are our atomic nuclei offenders

Separator

The scale of the problem

The Solution – The Detector

SecondaryTargetγ

γ

Miniball Detector

Miniball Detector

The YorkBragg

Detector

The York Bragg Detector

Gas detector Consist of six flared modules The modules sit after the secondary target position and

surround the ongoing beamline

How does a Bragg Detector work?

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)

How does a Bragg Detector work?

Where are we now?Simulations

Construction

The future... The York Bragg Detector will be set up and used routinely at Miniball, for

nuclear physics experiments A package of simulations will be available for the users of the detector

Thank you - Any questions?

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