Ionisation of H 2 O by Proton and Atomic Hydrogen Impact at velocities ~ the Bragg peak Sam Eden Institut de Physique Nucléaire de Lyon [email protected].

Ionisation of HIonisation of H22O by Proton and O by Proton and

Atomic Hydrogen Impact at velocities Atomic Hydrogen Impact at velocities ~ the Bragg peak~ the Bragg peak

Sam EdenSam EdenInstitut de Physique Nucléaire de LyonInstitut de Physique Nucléaire de Lyon

[email protected]@ipnl.in2p3.fr

The IPM GroupThe IPM Group

Particle - Matter Particle - Matter Interactions Interactions Group members:Group members:

Bernadette FarizonBernadette Farizon

Michel FarizonMichel Farizon

Sam EdenSam Eden

Bruno CoupierBruno Coupier

Jean TabetJean Tabet

http://lyoinfo.in2p3.fr/ipmhttp://lyoinfo.in2p3.fr/ipm

Helium impact upon ionic hydrogen Helium impact upon ionic hydrogen clusters Hclusters H33

++(H(H22))nn

Proton collisions with gas phase Proton collisions with gas phase molecules (Hmolecules (H22O, He, uracil, DNA bases)O, He, uracil, DNA bases)

Atomic hydrogen collisions with gas Atomic hydrogen collisions with gas phase molecules (Hphase molecules (H22O, He)O, He)

Proton impact upon biomolecule - water Proton impact upon biomolecule - water clustersclusters

CollaborationsCollaborationsTilmann MTilmann MäärkrkPaul Scheier Paul Scheier Institut für Ionenphysik, Innsbruck, AustriaInstitut für Ionenphysik, Innsbruck, Austria

Saïd OuaskitSaïd OuaskitFaculté Ben M’sik, Casablanca, MoroccoFaculté Ben M’sik, Casablanca, Morocco

Marie-Christine BacchusMarie-Christine Bacchus LASIM, UCBL, Lyon, FranceLASIM, UCBL, Lyon, France

Alain Bordenave-MontesquieuAlain Bordenave-MontesquieuPatrick Moretto-CapellePatrick Moretto-CapelleIRSAMC, Toulouse, FranceIRSAMC, Toulouse, France

Nelson Velho de Castro FariaNelson Velho de Castro FariaGinette JalbertGinette JalbertDepartamento de Física Nuclear, Instituto de Física, Departamento de Física Nuclear, Instituto de Física, Universidade Federal do Rio de Janiero, BrazilUniversidade Federal do Rio de Janiero, Brazil

IntroductionIntroduction

Proton impact upon gas phase HProton impact upon gas phase H22OO

Neutral hydrogen atom impact upon Neutral hydrogen atom impact upon gas phase Hgas phase H22OO

An experiment to observe collisions An experiment to observe collisions between protons and biomolecule – between protons and biomolecule – water clusterswater clusters

Why study water?Why study water?

Incident rays can damage living tissue through direct (or Incident rays can damage living tissue through direct (or primaryprimary) particle-biomolecule interactions…) particle-biomolecule interactions…

… … And through interactions with And through interactions with secondarysecondary species species

These secondary fragments and electrons create the These secondary fragments and electrons create the track patternstrack patterns along the path of the energetic particle along the path of the energetic particle

The water content of a living cell is ~ The water content of a living cell is ~ 70%70% by weight by weight

We will need absolute cross sections for gas phase HWe will need absolute cross sections for gas phase H22O O

to interpret the proton – biomolecular cluster collision to interpret the proton – biomolecular cluster collision resultsresults

At these energies, KE transfer is mainly to bound electrons At these energies, KE transfer is mainly to bound electrons in the absorbing medium (in the absorbing medium (excitationexcitation, , ionisationionisation))

Coincides with the Coincides with the Bragg peakBragg peak (~ 100 keV / amu) (~ 100 keV / amu)

Proton therapyProton therapy: incident protons of velocity ~ the Bragg : incident protons of velocity ~ the Bragg peak dramatically degrade the reparability of DNApeak dramatically degrade the reparability of DNA

The energy regimeThe energy regime(20–150 keV)(20–150 keV)

Charge transfer eventsCharge transfer events

Changes in the charge state of the projectile areChanges in the charge state of the projectile are

understood to play a critical role in the occurrence understood to play a critical role in the occurrence

of the Bragg peak in irradiated mediaof the Bragg peak in irradiated media

seesee M. Biaggi M. Biaggi et al.et al., Nucl. Instr. Methods Phys. Res. B , Nucl. Instr. Methods Phys. Res. B 159159, 89 (1999), 89 (1999)

The experimental systemThe experimental system

Cross sections which are differential in Cross sections which are differential in terms of terms of

direct ionisation direct ionisation

electron captureelectron capture

Proton impact upon Proton impact upon gas phase Hgas phase H22OO

The experimental systemThe experimental system

Each product ion can be associated with a single incident Each product ion can be associated with a single incident protonproton

The charge state of the detected projectile determines the The charge state of the detected projectile determines the ionisation process:ionisation process:

Event by event analysisEvent by event analysis

HH++ →→ direct ionisation direct ionisation (emission of at least one (emission of at least one ee--))

HH → single electron capture → single electron capture

HH-- → double electron capture→ double electron captureLarge samples (typically > 10Large samples (typically > 104 events) events)

→ → precise cross sections for all but the rarest eventsprecise cross sections for all but the rarest events

The system can be configured to detect either positive or The system can be configured to detect either positive or negative ions negative ions

Processes in which two or more product ions are formed in Processes in which two or more product ions are formed in a single collision event can be identifieda single collision event can be identified

Experimental (continued…)Experimental (continued…)

Absolute cross sectionsAbsolute cross sections

→→ Calibration using previous cross sections for cation Calibration using previous cross sections for cation

production and electron emission by Hproduction and electron emission by H22O upon HO upon H++ impact impact

M.E. Rudd M.E. Rudd et alet al., Phys. Rev. A ., Phys. Rev. A 3131, 492 (1985), 492 (1985)

The experimental systemThe experimental system

Cross sectionsCross sections

Comparisons with proton Comparisons with proton impact ionisationimpact ionisation

Hydrogen impact upon Hydrogen impact upon gas phase Hgas phase H22OO

The experimental systemThe experimental system

H

Neutralising gas (Ar)

target ionisationtarget ionisationσσ00 00 → → 0101 : H + (H: H + (H22OO++)* + e)* + e--

projectile + target ionisationprojectile + target ionisation oror electron loss + target ionisationelectron loss + target ionisationσσ00 00 → → 1111 : H: H++ + (H + (H22OO++)* + 2e)* + 2e--

electron loss with target excitationelectron loss with target excitationσσ00 00 → → 1010 : H: H++ + (H + (H22O)* + eO)* + e--

σσi i i i → → f ff f

initial charge of projectile (0)initial charge of projectile (0)

initial charge of target (0)initial charge of target (0) final charge of projectile (0 or +1)final charge of projectile (0 or +1)

final charge of target (0 or +1)final charge of target (0 or +1)

Event by event analysisEvent by event analysis

The first neutral hydrogen impact experiment The first neutral hydrogen impact experiment

to separates these processes to separates these processes

σσi f i f

initial charge of projectile (0)initial charge of projectile (0) final charge of projectile (0 or +1)final charge of projectile (0 or +1)

σσ+ + σσ-- target cation productiontarget cation production total electron (or anion) productiontotal electron (or anion) production

R. Dagnac R. Dagnac et alet al., J. Phys. B ., J. Phys. B 33, 1239 (1970), 1239 (1970)

L.H. Toburen L.H. Toburen et alet al., Phys. Rev. ., Phys. Rev. 171171, 114 (1968), 114 (1968)

M.A. Bolorizadeh and M.E. Rudd, Phys. Rev. A M.A. Bolorizadeh and M.E. Rudd, Phys. Rev. A 3333, 893 (1986), 893 (1986)

Previously measuredPreviously measured

M.E. Rudd M.E. Rudd et alet al., Phys. Rev. A ., Phys. Rev. A 3131, 492 (1985), 492 (1985)

U. Werner U. Werner et alet al., Phys. Rev. Lett. ., Phys. Rev. Lett. 7474, 1962 (1995), 1962 (1995)

→→ calibration carried out by comparison with previous Hcalibration carried out by comparison with previous H++ impact cross sectionsimpact cross sections

Absolute cross sectionsAbsolute cross sections

Each H impact measurement is accompanied by an HEach H impact measurement is accompanied by an H++ result with the same target conditionsresult with the same target conditions

Current work:Current work:An experiment to observe collisions between An experiment to observe collisions between

protons and biomolecular clustersprotons and biomolecular clusters

Mixed clusters composed of one DNA Mixed clusters composed of one DNA base (or uracil) and base (or uracil) and nn H H22O moleculesO molecules

Fragmentation mechanisms and Fragmentation mechanisms and reactions within a cluster will be studied reactions within a cluster will be studied as a function of as a function of nn

Comparisons with gas phase results Comparisons with gas phase results (H(H22O, uracil, and the DNA bases - O, uracil, and the DNA bases - currently being measured)currently being measured)

Key information to quantify the direct Key information to quantify the direct and indirect effects of ionising radiationand indirect effects of ionising radiation

1. Condensation under vacuum of vaporised

biomolecules and water in the presence of

electrons (≤ 100 eV)

2. Acceleration of ions and ionic clusters (up

to 30 keV)

3. Energy and mass selection → monochromatic beam of ionic

clusters comprising one biomolecule and n water molecules

4. Ionic cluster beam crossed with a monochromatic beam of protons (20 - 150 keV)

5. Event by event

coincidence analysis of projectiles and target products

post-collision→ analogous

to present experiment

The experimental The experimental systemsystem

AcknowledgementsAcknowledgements

Our collaboratorsOur collaborators

The technical staff at IPNLThe technical staff at IPNL

And the financial support ofAnd the financial support of

The French research council CNRSThe French research council CNRS

The French and Austrian Governments through The French and Austrian Governments through the PICS and Amadee programmesthe PICS and Amadee programmes

The French The French Ministère de la RechercheMinistère de la Recherche