Download [3] Nuclear Principles in Engineering By Tatjana Jevremovic - IFIN-HH

CHESTIONARUL Nr. 1 *
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Marie Curie Initial Training Networks (ITN)
Call: FP7-PEOPLE-2007-1-1-ITN
(DITANET)
Perioada de derulare:
01.06.2009 – 31.05.2012
Physics, Multidisciplinary
Ariile tematice SCIE în care se încadrează
colaborarea ‡:
Instituţiile participante din străinătate / Coordonator
University of Liverpool, Department of Physics
Denumire
The Cockcroft Institute (S.18)
Instituția coordonatoare.
4, Keckwick Lane
Adresa
Daresbury
Warrington WA4 4AD
United Kingdom
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*
Welsch
Prenume
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2
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Carsten
2
CERN
Swiss
Nume
Lefevre
Prenume
Thibaut
Chestionarul a fost elaborat în cadrul proiectului ”Evaluarea potenţialului românesc de cercetare în domeniul
fizicii şi elaborarea strategiei naţionale de cooperare internaţională” (ESFRO, Contract ANCS-IFA nr. 2S/31.08.2009)
în scopul evaluării participării României la mari colaborări internaţionale în domeniul fizicii.
†
O colaborare internaţională în domeniul fizicii se consideră MARE dacă are un program ştiinţific de anvergură
(abordează probleme fundamentale ale cunoaşterii), utilizează mari infrastructuri experimentale, cuprinde un
număr mare de participanţi (cel puţin 5 ţări şi 10 instituţii) şi care implică costuri ridicate (peste 1MEuro). Marile
colaborări internaţionale în domeniul fizicii includ proiectele aferente marilor infrastructuri, reţelelor și
organizaţiilor internaţionale de cercetare. Participarea instituţiei la colaborare poate fi finalizată sau în desfășurare
și implică o perioadă de minimum 3 ani. Informaţiile solicitate se referă la perioada 2001-2010. Se va completa
câte un chestionar pentru fiecare colaborare mare la care participă instituţia. Pentru colaborări internaţionale de
mai mică anvergură vă rugăm completaţi Chestionarul nr. 2.
‡
Ariile tematice SCIE sunt prezentate în Anexa transmisă odată cu chestionarul; vă rugăm selectaţi una sau mai
multe arii tematice, după caz.
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France, Germany, Sweden, Spain
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Str. Atomistilor no.407, P.O.BOX MG-6, Bucharest - Magurele, ROMANIA
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Prezentarea succintă (1 pagină) a programului ştiinţific al colaborării internaţionale (în ansamblul ei),
obiective generale şi specifice, activități importante (vă rugăm includeţi referinţe, pagină web etc).
DITANET
DIagnostic Techniques for future particle Accelerators of a new European NETwork
(http://www.ditanet.uni-hd.de)
Dezvoltarea noilor acceleratoare de particule cu caracteristici ale fasciculelor fara precedent
conduce la nevoia de programe intensive de cercetare-dezvoltare in tehnicile de diagnosticare.
Operarea cu succes a acestor masini va fi posibila numai cu o instrumentatie specifica adecvata.
Scopul acestui program de pregatire de tip Marie Curie este acela de a dezvolta dincolo de limite
tehnici de diagnosticare pentru acceleratoarele viitorului si de a instrui studenti si cercetatori tineri in
cadrul unei retele europene formate din mai multe centre de cercetare importante, universitati renumite
si parteneri din industrie.
DITANET acopera dezvoltarea metodelor avansate de diagnosticare a fasciculelor pentru un
spectru larg de acceleratoare existente sau din viitor, atat pentru ioni cat si pentru electroni. Cercetarile
propuse pentru metodele de profilare si de masurare a curentului si a pozitiei sunt in mod evident
deasupra tehnologiei actuale si vor marca noile standarde ale viitorului.
Prezentare succintă (1 pagină) a obiectivelor concrete ale participării instituţiei la colaborare, cu încadrare
în programul ştiinţific al colaborării internaţionale mari (în ansamblul ei).
DITANET
DIagnostic Techniques for future particle Accelerators of a new European NETwork
(http://www.ditanet.uni-hd.de)
Programul de instruire din IFIN-HH include pregatirea stiintifica a candidatilor in fizica si inginerie
fizica, ca si pregatirea lor tehnica in CAD (proiectare computerizata) pentru insusirea tehnologiei de
realizare a circuitelor si a aparatelor electronice. Expertii locali, in colaborare stransa cu Institutul
Politehnic din Bucuresti, vor asigura introducerea completa in secretele uneltelor de simulare si a
pachetelor de programe existente. Ca parte a dezvoltarii carierelor lor personale, 2 absolventi cu cel mult
5 ani de activitate, avand masteratul, vor primi o instruire complementara in managementul proiectului,
managementul si finantarea proiectelor de cercetare, abilitatea de a comunica si de a redacta propuneri.
Deasemenea ei vor fi instruiti in drepturile proprietatii intelectuale, in valorificarea rezultatelor cercetarii
in industrie si in tehnica de conducere a unei afaceri.
Institutul National pentru Fizica si Inginerie Nucleara Horia Hulubei (IFIN-HH)
1. Dezvoltarea unui detector de tip “zero-time” pentru acceleratoarele de particule din viitor
Pentru oricare sistem ce include acceleratoare de particule este extrem de necesara cunoasterea detaliata a
geometriei fascicolului. Aceasta determinare ar trebui facuta in timp real si in fascicul direct utilizand asa-numitul
detector de tip “zero-time”. El poate fi utilizat pentru studiul compozitiei fasciculului si a pozitiei ionilor grei in
fascicul. Se pot face deasemenea pozitionarea si focalizarea fasciculului respectiv. Acest detector se poate
construi, de exemplu, in geometrie rectangulara. Figura urmatoare reprezinta schematic conceptul acestui tip de
detector.
BEAM
+V1

-V 2

Grid
B
E
RX
Chevron
Aluminized mylar
window
R1
Detection
plate
R2
Detectorul de tip “zero-time”
Electronii retroimprastiati de catre o folie din aluminiu sunt indepartati din fasciculul principal cu ajutorul unui
camp magnetic perpendicular pe campul electric aplicat detectorului. In acest mod ei vor fi detectati de catre un
sistem convenabil ales respectand imaginea suprafetei care i-a emis.
Planul implementat pentru intreaga perioada
Primul
Al doilea Al treilea
an
an
Simularea miscarii particulelor in campurile E si B combinate
an
X
Designul detectorului
X
Teste si masuratori
X
Cum se concretizeaza:
-
Raportarea rezultatelor simularilor (luna a 12-a)
Raportarea designului detectorului (luna a 24-a)
Raportarea rezultatelor masuratorilor (luna a 36-a)
2. Dezvoltarea electronicii dedicate detectorului de tip “zero-time”
Semnalele masuratorilor descrise in sectiunea precedenta vor fi amplificate de preamplificatoare sensibile la
sarcina si apoi analizate electronic. Va fi dezvoltat un sistem de extractie si analiza a datelor bazat pe circuite
electronice existente.
Sarcina principala este de a dezvolta schemele si circuitele imprimate in vederea extragerii si apoi a amplificarii si
corectarii semnalelor pentru a putea fi prelucrate de catre sistemele de achizitie.
Planul implementat pentru intreaga perioada
Studiul preamplificatorului
Proiectarea cartelei multistrat a preamplificatorului
Teste si masuratori (impreuna cu detectorul)
Primul
Al doilea Al treilea
an
an
an
X
X
X
Cum se concretizeaza:
-
Raportarea rezultatelor simularilor (luna a 18-a)
Raportarea designului preamplificatorului (luna a 24-a)
Raportarea rezultatelor masuratorilor (luna a 36-a)
Stadiul colaborării și activitățile desfășurate în cadrul programului de colaborare cu accent pe rezultatele
obținute (max. 2 pagini). Listele lucrărilor ISI publicate (article, proceedings paper, review), brevetelor,
echipamentelor, tehnologiilor, etc., strict legate de colaborare se pot anexa/ataşa separat.
REPORT 19th March 2010 – 5th October 2010
Abdul Haneefa Kummali
Research Assistant
IFIN-HH
(Joined IFIN-HH, Romania, between 19th March 2010 - 5th October 2010 as Early Stage Researcher under DITANET project
“Development of a Zero Time Detector for Future Particle Accelerators”)
Supervisor: Dr. Horia Petrașcu (IFIN-HH, Romania)
Design of Zero Time Detector
1.
Introduction:
Secondary electron emission from thin foil has been used for Zero-Time detector technique. Same as from the bibliography
[1 -3], here we are also employing the isochronous transport of secondary electron emission from thin foil when the beam hits
the foil under the influence of perpendicular magnetic and electric fields. Following figure shows the conceptual design of the
detector:
Figure 1. Electric and Magnetic axis
Figure 2.Schematic diagram of Secondary Electron Movement.
As it is shown in the figure above, an isochronous transport system for secondary electrons is required which requests the foil
to remain perpendicular to the fragment path and the detector to be placed in a location separated from the beam. Here we are
exploiting the maximum interaction phase in which the foil’s image is tilted (45-60, needs to be optimized) from the ion beam
[4].
2.
Explanation of Electron Transport in E/B Fields
Motion of a charged particle in the simultaneous presence of electric and magnetic fields has variety of manifestations
ranging from straight line motion to the cycloid and other complex motion. Both electric and magnetic fields impart
acceleration to the charged particle. But, there is a qualification for magnetic field as acceleration due to magnetic field relates
only to the change of direction of motion. Magnetic force being always normal to the velocity of the particle tends to move the
particle on a circular trajectory. On the other hand, electric force is along electric field and is capable to bring change in both
direction and magnitude depending upon the initial direction of velocity of the charged particle with respect to electric field. If
velocity and electric vectors are at an angle then the particle follows a parabolic path.
One of the important orientations of electric and magnetic fields is referred as “crossed fields”. We use the term “crossed
fields” to mean simultaneous presence of electric and magnetic fields at right angle. The behavior of charged particles such as
electrons under crossed fields has important significance in the study of electromagnetic measurements and applications.
Figure 3 . Planar view of applied electric and magnetic fields.
3.
Simulation using Galette and Geant4
3A. Galette – One Dimensional Simulation Tool
Simulation using Galette gives the one dimensional picture to fix the length and height of the trajectories. For different
values of combined magnetic and electric fields is shown in the following table. Different consideration in optimizing the
dimension of this detector is taken into account. Firstly we considered the maximum voltage that can be handled by the
detector. Special attention is given to make a compact design in order to handle and to put it into a vacuum chamber. This
consideration limited the choice of magnetic field (by reducing the value of B, the trajectory length is increased).
B
E
Ymax , cm
(Height of the trajectories, cm)
Xmax
(Gauss)
(Volt / cm)
(Length of trajectories, cm )
75
800
1.619
5.081
80
800
1.423
4.466
85
800
1.261
3.956
75
700
1.417
4.466
80
700
1.245
3.908
85
700
1.103
3.461
90
700
0.908
3.087
Figure 4. Sample date from the Galette simulation, for finding electron trajectory.
Above table gives the sample result for most suitable combinations of electric and magnetic field. From which, B = 80 Gauss,
E = 700 V/cm are more suitable for our purpose.
3B. Geant4 – Tool toolkit for the simulation of the passage of particles through matter
Geant4 is a toolkit for particle-matter simulation using modern object-oriented design principles [7]. It contains about a
million lines of C++ code. Geant4 has components to model the geometry, the materials involved, the fundamental particles of
interest, the generation of primary particles for new events, the tracking of particles through materials and external
electromagnetic fields, the physics processes governing particle interactions, the response of sensitive detector components, the
generation of event data, the storage of events and tracks, the visualization of the detector and particle trajectories, and the
capture for subsequent analysis of simulation data at different levels of detail and refinement [8,9].
Using Geant4, we succeeded to have a look for the concrete structure of proposed zero-time detector. We successfully
defined the equipotential electric and magnetic field using Geant4. But the complete parameters are not implemented yet in
Geant4.
4.
Design and Optimization of Detector size
As per the above equation we obtained a suitable electric filed and magnetic field to make the detector compact. A
possible approach to reduce the mean electron initial velocities – which hold for every thin-foil timing detector – is to use the
secondary electrons emitted backward from the foil rather than the forward electrons. The secondary electron emission exhibits
large energies spectra [5].
Mathematical calculations using above equations are verified by using Galette software. Finally optimized parameters are
the following:
Accelerating Voltage: 700 V/cm
Magnetic Field, B: 80 Gauss
MCP Diameter: 2.5 cm
Al/ Cu Foil Diameter: 1 cm
Electron Trajectory height = 1.24 cm
Electron Trajectory length = 3.906 cm
Distance between foil and MCP: 2.15 cm
Optimum X axis = 2.5 cm
Optimum Y axis = 8.15 cm
Optimum Z axis = 2.5 cm
Total voltage that must be applied should be 1750 Volt on a distance of 2.5 cm and the magnetic field strength from permanent
magnets should be 80 Gauss. To avoid the fringing effect of electric fields at edges, the distance between MCP to the detector
ends are kept between h/2 – h/3 value, where h = height of the detector. The top view of detector is shown here:
Figure 5. Top View of Detector
5.
Equipotential Lines and Electrical Connection
Equipotential lines are essential to keep the electric field constantly inside the detector. Total voltage of 1750 V is thus
divided into 7 parts. So in general there will be eight resistors in 3mm distance apart. Besides a complete equipotential, it is
better in practice to consider more lines at the secondary electron production area (Near the bottom area- Foil, MCP plane
area). Appropriate resistors must be used. SMD type resistors may be quite better in this compact design. Proposed
construction may include the following geometrical shape and concept. It is better to allocated space in the detector
construction to including a capacitor in parallel with each resistor for avoiding the destruction because a large possibility of
secondary electron production and great chance to halter the equipotential surface. Sample calculation how to find the values
for resistors are given here (not yet conformed), the height of the detector being defined as 2.5 cm divided with 8 resistors. The
distance between two resistors are noted as 3mm, so the voltage across each will be approx. 1750 V / 8 = 220 V.
Current value may be in between 20 μA – 50 μA. Let’s say it is 20 μA. Then value for resistor will be 11 MΩ. This value
for resistors is a common value for resistors. Appropriate value for capacitors in parallel with the resistors may be connected to
insure the long term stability of the detector.
6.
Common features of MCP
A microchannel plate (MCP) is a high gain, thin secondary-emission current amplifier which consists of parallel array of
millions of hollow semi-conducting glass cylinders (channels). Typically these channels have diameters in the range of
10-100 μm and length-to-diameter ratio between 40 and 100. They can be made circular, rectangular or virtually any
shape depending on the geometry of the instrument as desired (Figure 6). MCPs are processed commonly to have length-todiameter (L/D) ratio, α of 40:1, 60:1 or 80:1, which is a ruling factor for the gain.
Figure 6. Micro-Channel Plates cut in several formats. The zoomed picture shows microscopic view of
the channels (pores) of these plates. [Reference (7)]
Optical fiber drawing techniques are used to make desired MCP formats. The inner walls of the channels are
processed in a way to enhance the secondary emission characteristics by making the walls semi-conductive. A thin metallic
film is deposited on both input and output ends of the MCP in order to give parallel electrical contact to the channels. This
film acts as the electrodes thereby making each channel as an independent secondary electron multiplier. Originally
developed as an amplification element for image intensifiers, MCPs are also recognized as an extremely useful tool for
scientific applications including astronomy, mass spectrometry, etc. as they have direct sensitivity to charged particles, XRays and UV light. [6]
6A.Working Principle
The basic process that is taking place in the MCP is the secondary electron emission. When a particle like electron, ion,
UV photons or X-rays enters into a channel of the MCP, on hitting the wall, it loses its energy due to collision and a part
of this energy gets transferred to the electrons at the surface. On attaining sufficient energy the electrons can get knocked
out of the metal surface to form secondary emission current. Due to the presence of an electric field which is produced by
applying a voltage difference called as MCP bias voltage across the two ends of the MCP, the electrons are controlled to
accelerate in the forward direction. They travel with parabolic trajectories and again re-emit more secondary electrons on
hitting the wall inside the channel. This cascading process continues until the electrons reach the end of the channel,
generating several thousands of electrons producing high gains.
There are two separate currents running in the MCP, one due to the secondary electron emission and the other through the
walls of the MCP due to the applied bias voltage across it, named as strip current. It is the electrons forming this strip
current which replenish or fill the electron depleted regions of the channel walls created due to the secondary electron
emission. If the depleted regions would not be filled by the electrons from the strip current, it would prohibit the process
of secondary emission since there would not be any electron available at the surface of the wall to be knocked out.
Figure 7. a) Sketch showing the channels of MCP b) Sketch showing the working principle of the
MCPs. [Reference (4)]
6B. Proposed MCP Model (Open MCP Detectors)
As manufacturer of 25 mm proximity focused MCP image intensifiers, PROXITRONIC offers a broad variety of open detector
systems. When using these systems, a two-dimensional image of electrons, particles (neutral or charged), X-rays and UVradiation is possible. Open MCP detector systems are specially suitable for the energy range from 10 eV ... 1000 eV (approx.
120 nm ... 1 nm).
Figure 8. Open MCP
Features
a.
M C P with 25mm or 40mm diameter
b.
I n t e g r a t i o n in CF flange
c.
Single, double or triple MCP versions
d.
Different types of MCP plates
e.
Many camera and sensor types
f.
Coupling with fibre optical plates (1:1)
or adaption of field of view by taper:
g.
Screens with P43, P46, P47 and other
h.
Power supply for MCP operation
Figure 9. Camera with open MCP Detector system with transportation container
7.
Reference
[1] A. M. Zebelman et al., A TIME- ZERO DETECTOR UTILIZING ISOHORONOUS TRANSPORT OF SECONDARY
ELECTRONS, Nucl. Instr. and Meth. 141 (1977) 439.
[2] T. Odenweller et al., A GRIDLESS POSITION SENSITIVE TIME – ZERO DETECTOR FOR HEAVY IONS, Nucl.
Instr. and Meth. 198 (1982). 263-267.
[3] J. David Bowman et al., A NOVEL ZERO TIME DETECTOR FOR HEAVY ION SPECTROSCOPY, Nucl. Instr and
Meth. 148 (1978), 503-509.
[4] W. Lang et al., A FAST ZERO-TIME DETECTOR FOR TIME-OF-FLIGHT MEASUREMENTS WITH HEAVY IONS,
Nucl. Instr and Meth. 126 (1975), 535- 539.
[5] K. E. Pferdekamper and H. G. Clerc, Z. Physick A275 (1975), 223, and Z. Physick A280 (1977), 155.
[6] Wiza, Joseph Ladislas, Microchannel Plate Detectors, Nuclear Instruments and Methods, Vol. 162, p. 587 to 601.
[7] Geant4 webpage, http://wwwinfo.cern.ch/asd/geant4/geant4.html.
[8] S. Agostinelli et al. Geant4: A SIMULATION TOOLKIT, Nuclear Instruments and Methods in Physics Research Section
A: Accelerators, Spectrometers, Detectors and Associated Equipment, 506(3):250–303, 2003. (over 100 authors, incl. G.
Cooperman).
[9] J Allison et al. Geant4: DEVELOPMENT AND APPLICATIONS, IEEE Transactions on Nuclear Science, pages 270–
278, 2006. (73 authors, incl. G. Cooperman).
[10] Photonis. Burle Long-Life™ MCP selection guide, Photonis. [Online]
http://www.photonis.com/upload/industryscience/pdf/MCP/EP107.pdf.
8.
Summer School Program (CSSP- 2010)
Participated in the Carpathian Summer School of Physics 2010 Exotic Nuclei and Nuclear /Particle Astrophysics
(III) “From nuclei to stars” held at Sinaia, Romania from June 20 – July 3, 2010,hosted by IFIN-HH, Romania. The first
week of the event has a ‘school’ character defined by a series of courses on the relevant topics of Astrophysics and Nuclear
Physics, which is really exciting. The second week has a conference format focused on current research of different groups
including FAIR, Cyclotron Institute Texas A&M, GANIL, and institutes like IFIN-HH, Bucharest, Berkeley Research Institute
and many others. Interaction and active discussions throughout the program helped me to make contact with Eminent
Professors from different institutes.
REPORT 28th April 2010 – 4th October 2010
Fairoja Cheenicode Kabeer
Research Assistant
IFIN-HH
(Joined IFIN-HH, Romania, between 28th April 2010 - 4th October 2010 as Early Stage Researcher under DITANET project
“Development of a Zero Time Detector for Future Particle Accelerators”)
Supervisor: Dr. Dorin Dudu (IFIN-HH, Romania)
Mentor: Dr. Hermann Schubert (IFIN-HH, Romania)
1. Introduction:
Secondary electron emission from thin foil has long been used for Zero-Time detector technique.
Same as from the literature [1 -3], here also we are employing the isochronous transport of secondary
electron emission from thin foil when the beam hits the foil under the influence of perpendicular
Magnetic and Electric Fields. Following figure shows the concept of the detector.
As it is shown in the above figure, an isochronous transport system for secondary electrons is
required which follows the foil to remain perpendicular to the fragment path and the detector to be
placed in a location shielded from the beam. To maximize the interaction of the beam with the foil, the
foil is tilted (45-60, needs to be optimized) towards the direction of the ion beam [4].
2. Explanation of Electron Transport in E/B Fields
Charged particle in the simultaneous presence of electric and magnetic perform complex motion.
Electric fields impart acceleration to the charged particle where the magnetic field leads only to the
change of direction of motion. Magnetic force being always normal to the velocity of the particle forces
this to move in a circular trajectory. On the other hand the electric field is capable to bring change in
both direction and velocity depending upon the direction the charged particle with respect to electric
field. If velocity and electric vector are at an angle, then the particle follows a parabolic path.
One of the important orientations of electric and magnetic fields is referred as “crossed fields”. We
use the term “crossed Fields” to mean simultaneous presence of electric and magnetic fields at right
angle. The behavior of charged particles such as electrons under crossed fields has important
significance in the study of electromagnetic measurement and application (determination of specific
charge of electron, cyclotron etc.).
The equation of motion describing the electron trajectories in orthogonal Electric and Magnetic fields
are verified here. Let the charged particle be subjected to mag.field (B) acting along X direction and
electric field (E) acting along the Z direction. If the charge is at rest at the initial point, it will be
accelerated along Z axis because of E . Acceleration is given by
a = q E/ m ………………………..………….(1)
As soon as the charge acquires velocity , it begins to experience mag. Force FB
FB = q (E + v x B )
……………………………(2)
Electrical force experience by the charge
FE = qE k^ ………………………………………...(3)
Resultant Lorentz Force acting on the charge
F = FB + FE
= q E ḱ + q (B z. j – B y. k^)
= qB z. j + ( qE – qB y. ) k^………………………(4)
According to Newton’s law force experienced;
F = m d2 r/ dt2 = m¨r ……………………………….(5)
F = m y¨j^ + mz¨k^ ……………………………… (6)
Comparing the Equation (4) and (6)
my¨ = qBz. …………………………………………...(7)
mz¨ = qE – qBy.
………..……………………………… (8)
We have the following equations,
y¨ = dVy / dt, y . = Vy ;
z¨ = dVz / dt , z. = Vz
qB/ m = w ;
qE/m = (qB /m) (E/B) = w (E/B)
Applying these equations in the (7) and (8).
dVy / dt = wVz ………………………………………....(9)
dVz / dt = E/Bw – wVy……………………………..….(10)
From equation (10)
wVy = E/B w – dVy / dt
Vy = E/B – (1/w) dVz/dt ………………………… (11)
Applying equation (11) in (9),
d 2 Vz / dt2 = - w2 Vz ………………………………….(12)
From simple harmonic equations, the solution for the above gives,
Vy= E /B – A cos (wt +ɸ)
From initial conditions, A = E/B and ɸ = 0.
By integrating the equations for Vy and Vz over time internal (t),
Then equations becomes,
y (t) = (Ez / Bx w) [ wt – sinwt ] ……………………… (13)
z (t) = (Ez / Bx w) [ 1- coswt] …………………………(14)
x (t) = 0.
………………………………………….....(15)
While considering the initial velocity term of the ejecting electron from foil as u and Uy and Uz in y and z
directions, final equations becomes [2].
y (t) = (Ez / Bx w) [ wt – sinwt ] + (Uz/w) [ 1- cos(wt)] + (Uy/w) sin(wt) + yo
z (t) = (Ez / Bx w) [ 1- coswt] + Uy/w) [ 1- cos(wt)] + (Uz/w) sin(wt)
From the above equations (13) and (14) we can calculate the trajectories of secondary electrons emitted
from the foil. In this project, we need to optimize the size of detector according to E, B, MCP-size and
finally looking to the compactness.
3. Design and Optimization of Detector size
With the equations above we obtained suitable electric and magnetic fields to make the detector
compact. A possible approach to reduce the mean electron initial velocities – which hold for every thinfoil timing detector – is to use the secondary electrons emitted backward from the foil rather than the
forward electrons. The secondary electron spectra exhibit a large forward- backward anisotropy at high
electron energies, whereas nearly no anisotropy appears at low energies [5].
Mathematical calculations using the equations above are verified by using Galette software. The
optimized parameters are the following:
Accelerating Voltage : 700 V/cm
Magnetic Field, B : 80 Gauss
MCP Diameter: 2.5 cm
Al/ Cu Foil Diameter: 1 cm
Electron Trajectory height = 1.24 cm
Electron Trajectory length = 3.906 cm
Distance between foil and MCP : 2.15 cm
Optimum X axis = 2.5 cm
Optimum Y axis = 8.15 cm
Optimum Z axis = 2.5 cm
Total Voltage that must be applied should be 1750 for a distance of 2.5 cm and Magnetic field strength
from Permanent magnets should be 80 Gauss. To avoid the fringing effect of electric fields at edges, the
distance between MCP to the detector ends are kept has h/2;
here h = height of the detector. Top view of detector is shown here,
Reference:
[1] : A.M Zebelman et al., Nucl. Instr, and Meth. 141 (1977) 439. “ A TIME- ZERO DETECTOR UTILIZING
ISOHORONOUS TRANSPORT OF SECONDARY ELECTRONS”
[2]: T. Odenweller, et al., Nucl. Instr and Meth 198 (1982). 263-267 “ A GRIDLESS POSITION SENSITIVE
TIME – ZERO DETECTOR FOR HEAVY IONS”.
[3]: J. David Bowman, et al., Nucl. Instr and Meth 148 (1978) 503- 509. “ A NOVEL ZERO TIME DETECTOR
FOR HEAVY ION SPECTROSCOPY”.
[4]: W. Lang et al., Nucl. Instr and Meth 126 (1975) 535- 539. “ A FAST ZERO-TIME DETECTOR FOR TIMEOF-FLIGHT MEASUREMENTS WITH HEAVY IONS”
[5]: K.E Pferdekamper and H.GClerc, Z.Physick A275 (1975) 223, and Z. Physick A 280 (1977) 155.
POSITRON GUN
Introduction
A positron gun consists of two basic parts


The positron source
The acceleration section (electron gun)
A) The positron source
Positron can be obtained from the + decay of radio active isotope. 22Na is a favorite source for the
positron studies because the energy spectrum of beta positrons is peaked at 178 keV, end point energy
is 545 keV, half-life is 2.6 years, relatively high positron yield of 90.4% and 1.28 MeV gamma ray emitted
immediately after the positron[1].
The decay reaction is:
22Na22Ne
+e .
2.602 a
22Na
+ (90.4 %)
3.7 ps EC (9.5 %)
+ (0.1%)
 (1.274 MeV)
22Ne
Decay scheme of the radioactive isotope 22Na.
Another main source for the positron is 13N, a radio active isotope of Nitrogen which is produced
by the deuteron bombardment of natural carbon foil [2].
The reaction can be written as:
12C
(d,n) 13N () 13C
13N
decays by emitting positron to 13C. 13N has a half life of 9.965 minutes and the nuclear spin is
(1/2)-. The energy difference between the ground state of 13N and 13C is 2.22 MeV. Hence the maximum
available positron energy is 1.2 MeV [3].
Energetic positrons entering a solid which are not backscattered at high energies and are
undergoing inelastic collisions to lose energy very rapidly. If implanted into a metal (moderator) with
energy greater than a few keV positron will reach thermal equilibrium with its surroundings.
The mechanisms occur on the surface of moderator are:



Fall into the surface well, where they are eventually annihilated
Pick up an electron and leave as positronium
Leave as free positrons into the vacuum with an energy determined by the positron work
function Ф+
The choice of moderator material (W, MgO, we sound, etc..) is depends on the geometry of
moderation and extraction. The moderator efficiency έ is defined as the number of essentially
monoenergetic positrons delivered to a target per unit time divided by the total activity of the primary
positron source. With the help of an optoelectronic system we can separate and can control the speed
of positron beam. An appropriate detector system is used to observe and characterize positron beams
[1].
B) The acceleration section
In principle the acceleration of positrons is similar to electron-acceleration, but with opposite electrical
polarity. Therefore, an electron gun can be used by only changing the electrical polarity after the
electron beam tests.
The Electron Gun
An electron gun is a device that produces a beam of accelerated electrons.
The main parts of an electron gun are:


Filament: The filament consists of a piece of wire, commonly made of a refractory material such
as tungsten, which is heated by electric current.
Accelerating Region: The accelerating region consists of two electrodes known as the cathode
and the anode.
Design and Construction
An electron gun with large apertures geometry (the planned positron source has dimensions of
2-8mm) dedicated for energy analysis (moderated positron separation) was designed.
Picture 1: Scheme of the electron gun.
In order to minimize the influence of ambient magnetic fields we use this 1-3 kV accelerator
structure. The electrical scheme can be seen below:
V2
TRANSFORMER AUTO
TRANSFORMER ISOLATED
T1
1
220V/50Hz
T2
0-1kV
0-1kV
V3
f1
5
1
4
8
UA
f2
1
T3
g
a1 a2
H
V
tinta
5
UA
-HV
M1
METER UA
TRANSFORMER ISOLATED
4
M2
METER UA
8
R4
1k
V1
R5
470k
300k
0-30kV/30mA
P1
2M
300k
R1
1M
P2
R2
1M
P3
R3
1k
GND
10V/1kHz
GND
Picture 2: Schematic Diagram of the electron gun.
R6
1M
Picture 3: Experimental Setup at Department of Applied Physics, IFIN-HH.
Picture 4: Electron gun used for the Experiment
Picture 5: The image produced on the phosphorus screen by the beam.
Experiments and Results
Preliminary measurements are done by thermal emission of electrons from a light bulb filament,
with voltages and currents as seen below:
U = 4-15V
I = 0.2-110μA
A calculated efficiency of extraction as given below;
Sbeam / Sw = Ibeam/Ik ~5-8%
The focusing of the beam is done by adjusting the distance and alignment of the electrodes and
their voltage values. The Image of the focused beam is shown on the properly aligned phosphorus
screen. (picture 5)
The following table is the experimental record with a collimator having Ф = 6mm
UF
UW
UK
UA1
UA2
UH
UV
IK
Icol
Ifoc
OBS.
40
3215
3214
2187
242
377
167
2000
37
45
L=L0 + 300mm, η=2-4%/58%
40
3215
3196
2187
107
335
161
~0
0,5
0,2
Cut-off = 19V
40
3269
3263
2312
107
348
148
500
10
15
L=L0 + 300mm
50
3269
3263
2312
107
348
148
2000
15
100
L=L0 + 300mm, η=5-6%/58%
40
3002
3002
2325
1520
110
271
5400
View from L0 , estimated energy
separation power <100eV
40
4000
4000
2800
2230
110
465
3000
This experiment was carried out to test the ability of the beam optic to produce similar beams (intensity
and area of cross) at variable focus distances.
The electron beam intensity was obtained in the range of 0.1-12μA in a cross section of 1-5mm2.
Conclusions
The experimental model was developed for simulating a positron gun and to obtain the
experimental data needed to produce a mono-energetic positron beam with variable energies.
The positron emitting surface will be in the order of cm2. High yield of positron occurs at very low
intensities (1-100nA). The chosen beam optics will lead to a nearly paraxial beam with a small cross
section (some mm2).
The unconventional structure of the electron gun having an aperture of approximately 4mm gives the
possibility of mounting the positron source and the W-moderator assembly inside the gun.
The further development is the creation of a mono-energetic positron sources in line with the Cyclotron
Accelerator producing positrons in vivo via nuclear reactions, moderating them and then using the
electron gun for extraction of the thermalized positrons.
References
[1] Positron Beams and their application By Paul Coleman
[2] 12C(d, n)13N Total Cross Section from 1.2 to 4.5 MeV By R.J.Jaszczak*, R.L. Macklin, and J. H. Gibbons
Phys. Rev. 181, 1428–1430 (1969)
[3] Nuclear Principles in Engineering By Tatjana Jevremovic
Summer School Program
I participated the Carpathian Summer School of physics 2010, Sinaia, June 20th – July 3rd 2010,
“Exotic Nuclei & Nuclear/Particle Astrophysics (III) – From Nuclei to Stars” organized by Horia Hulubei
National Institute of Physics and Nuclear Engineering (IFIN-HH), Romania, Cyclotron Institute, Texas
A&M University (TAMU), USA and the Abdus Salam International Centre for Theoretical Physics (ICTP),
Italy.
The first week of School concentrated on the relevant of Astrophysics and Nuclear Physics, which
are really exciting and the second week has a conference format focused on current research of
different groups including FAIR, Cyclotron Institute, Texas A&M, GAINL, IFIN-HH, Bucharest, Romania,
Berkeley Research Institute and many other international collaborations.
The main Topics Discussed are:










Exotic Nuclei
Experiments with rare isotope beams
Double beta decay
Issues in nuclear astrophysics
Nucleosynthesis
Neutrino properties and new neutrino experiments
The sun and solar neutrinos
Supernova neutrinos
Cosmic rays and neutrinos
Dark matter.
In this way the conference covers areas in Nuclear Physics, Neutrino Physics, Astroparticle Physics
and Cosmology, with nuclei being the central object connects all items in the program.
Manifestări ştiinţifice internaţionale organizate în ţară în cadrul cooperării
Click here to enter text.
Proiectele interne/internaţionale prin care s-a realizat cooperarea şi valorile finanţării interne (RO) şi respectiv
externe.
Finantarea acestui program FP7 este facuta exclusiv cu fonduri straine.
BUGET (€)
INSTITUTULUI NATIONAL DE CERCETARE DEZVOLTARE PENTRU FIZICA SI ENGINERIE NUCLEARA "HORIA
HULUBEI" (IFIN-HH), alocat de catre DITANET
Monthly
living and
mobility
allowance
(A)
Year
1
Year
2
Year
3
Year
4
Total
Travel
allowance
(B
Career
exploratory
allowance
(C)
Contribution
to the
participation
expenses of
eligible
researchers
(D)
Contribution
to the
organisation
of
international
conferences,
workshops
and
events (F)
0
Management
activities
(including
audit
certification)
(G)
Contribution
to
overheads
(H)
9,600
Contribution
to the
research/
training/
transfer of
knowledge
programme
expenses
(E)
9,600
32,336.89
2,000
4,000
48,505.33
2,000
48,505.33
0.00
5,753.68
63,290.57
0
14,400
14,400
0
0.00
7,930.53
87,235.86
2,000
0
14,400
14,400
0
0.00
7,930.53
87,235.86
16,168.45
0
0
4,800
4,800
0
0.00
2,576.84
28,345.29
145,516.00
6,000
4,000
43,200
43,200
0
0.00
24,191.58
266,107.58
TOTAL
266,107.58
60%
159,664.55
- 50% Cat E
12,960.00
Transfer
146,704.55
to IFIN-HH
Contribuţii in-kind la colaborare (conform MoU)
Contribuţii in-cash la colaborare (conform MoU)
Total
Cofinanţarea activităţii în ţară (pe categorii de cheltuieli: manoperă, deplasări, dotări, cheltuieli cu terţi,
indirecte, etc)
Click here to enter text.
Unităţi industriale/economice care au participat şi contribuţia adusă
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Alte aspecte considerate relevante (max. 1 pagină)
Din cauza imposibilitatii de a se inscrie in timp util la doctorat in Romania, ambii participanti au decis sa se retraga
din proiect in data de 05.10.2010, respectiv 04.10.2010, pentru a se putea inscrie si urma un program de pregatire
doctorala in alte tari din Europa.