8/10/2019 Pi Mu Event

1/17

- EVENTStudy using Nuclear Emulsion

ABSTRACTTo find the range of Muon in Pi-Mu event

Sunil KumarSumit KumarSukhpreet Singh

8/10/2019 Pi Mu Event

2/17

8/10/2019 Pi Mu Event

3/17

About Nuclear Emulsion

Introduction Nuclear research emulsions were first developed in the1940s to meet the needs of physicists engaged in research on cosmic radiation. Nuclear emulsion is a versatileinstrument to detect the charged particle. It is not only capable of counting charged

particles, but also provides information regarding the mass, energies of particlesand their modes of collisions. It also allows studies of angular distribution of allout coming charged particles of the individual events in space with higher accuracyand in 4 geometry, although with rather limited statistics. The nuclear emulsionhas high stopping power. Its stopping power is approximately 1700 times the

stopping power of standard air. After development, the stacks of nuclear emulsionare kept under specific conditions. Thus photographed events can be preserved formany years.

Formation of Nuclear Emulsion The basic components are a gel, usually obtained from animal body tissues, andsilver halides, among which AgBr is the most common choice. The maindifferences of nuclear emulsions from products for more common photographic

applications are the quantity and size of AgBr crystals. Such emulsions are mostlyused as tracking devices with very high spatial precision and resolution; large-scale

batches have been produced with crystals smaller than 0.3 m, but it is also possible to produce emulsions with even smaller crystals (0.1 m and less) .Emulsion films are normally deposed on a transparent plastic support, coating oneor both sides. The emulsion basically consists of the following components

I. Silver Halides, mainly bromides with small admixture of iodineII. Gelatin and Glycerin

III. WaterIV. Nuclei of CNO group

The glycerin works as plasticizer for preventing nuclear emulsion stack from breaking. It may be pointed out that about 71% of interactions occur with heavyemulsion nuclei (AgBr), approximately 25% due to light emulsion nuclei, i.e.

8/10/2019 Pi Mu Event

4/17

Carbon, Nitrogen & Oxygen (CNO) and only 4% with hydrogen nuclei. Howeverthe cross-section of reactions with heavy , light and hydrogen nuclei depends on themass and energy of projectile. It is well known that the nuclei of nuclear emulsionhaving average atomic mass =73, mainly consist of CNO group with =14,

the AgBr group =94 and hydrogen =1.

Formation of the latent imageWhen a charged particle passes through nuclear emulsion with the AgBr crystalssuspended, it loses its energy by electromagnetic interactions. The energy lost bythe charged particle is transferred to the electrons of the atoms. As result of this,the later goes to an excited state. If the energy transferred to the electron is greaterthan the ionization potential of the atom, the electron is free to move from atom

and the atom is said to be ionized. It may be mentioned that the most importantmode of energy loss of a charged particle is the ionization and it depends on thecharge and velocity of the particle. The characteristics of the track depend on thenature and velocity of charged particle. Higher the velocity of the charged particle,rarer will be grain formed by it and vice versa. Sometimes it happens that theelectron receives energy, which is quite enough for further ionization and thussecondary tracks are observed projecting out of the primary track of the particle.These secondary tracks are termed as -rays. The number of -rays coming out

also depends upon the charge and velocity of the particle. As the particle traverses,the direction of its track also fluctuates along its length due to statisticalcombination of coulomb-scattering.

When a silver halide crystal absorbs light or ionizing radiation, it has the effect ofliberating mobile electrons and electron deficient bromine atoms. Transfer of anelectron from an adjacent bromine ion, which in turn creates an electrondeficiency, can overcome the electron deficiency of the bromine atom. In this way,a positive hole can move through the crystal lattice. This electron deficiency mayalso be known as a positive hole.

It is important for latent image formation that a significant proportion of electronsand positive holes are trapped separately, otherwise they could recombine andregenerate halide ions. The silver halide crystal contains free (interstitial) silverions, which can move through the lattice. When an interstitial silver ion encounters

8/10/2019 Pi Mu Event

5/17

a trapped electron, the charges are neutralized and an atom of metallic silver isformed. The single atom of silver is unstable but, while it exists, it increases theefficiency of the site as an electron trap. In this way a stable nucleus of four ormore atoms of silver can be built up. The site is then known as a latent image

centre, and that entire crystal may be reduced to metallic silver on development.

DevelopmentPhotographic development is the process by which the latent image contained in anemulsion is made visible by the reduction of silver ions in the silver halide crystalto metallic silver.

When developing nuclear emulsions, a developer is usually chosen which reduces

those crystals containing a latent image centre completely and leaves those notcontaining a centre unchanged. The development time used for processing materialshould be sufficient for those crystals with a latent image centre to be reducedcompletely, but not so long that unexposed crystals are developed. In practice, acertain number of crystals will be developed even though they do not contain alatent image centre. These grains, when developed, constitute what is known as fog or background.

Developing agents may be divided into two main groups, depending on the source

of silver ions for reduction. In practice, most developers give a combination of thetwo sorts of development.

The first group is known as physical developing agents. In physical development,silver ions are provided from the solution in the form of a soluble complex. Theseare deposited on the latent image centre and are reduced to metallic silver. This

produces spherical particles, the precise shape of which is affected by pH.

Chemical developing agents make up the second group and are more usually

chosen when processing nuclear emulsions. However, the choice between a physical developer and a chemical developer will largely depend on the grainstructure required in the processed image. In chemical development, silver ions are

provided from the silver halide crystal containing the latent image centre. Theaction of a chemical developer produces a mass of filaments bearing littleresemblance to the original crystal.

8/10/2019 Pi Mu Event

6/17

If silver halide solvents such as sulphite are present in a chemical developer, anopportunity exists for some physical development to occur. In this case, thefilaments in the processed plate will be shorter and thicker.

FixationThe purpose of fixation is to remove all the residual silver halide, leaving themetallic silver to form the image. If the silver halide was left in the emulsion, itwould slowly go brown and degrade the image. The fixing agents most widelyused are sodium or ammonium thiosulphate, which form thiosulphate complexeswith the silver halide. Silver thiosulphate is soluble in water and so may beremoved from the emulsion by washing.

Effects and CorrectionsThe three main effects that alter the position and slopes of microtracks in nuclearemulsions are Shrinkage, Linear Distortion & Parabolic Distortions which areshown in fig.

a) Shrinkage: grains are displacedvertically as a result of the thicknessreduction of the emulsion layer.Microtracks slopes are altered by a

constant multiplicative factor .

b) Linear distortion: a stress appliedon the surface, as would be forexample the friction caused by thedrying air flow, causes a constantviscous shear in the emulsionthickness. The plane in contact withthe support (bottom) is not displaced;the plane of the free surface (top) hasmaximum displacement. As a result,microtrack slopes are altered by anadditive constant.

c) Parabolic distortion: if a stressarises at the support surface (bottom),and no stress is applied externally,the stress field has to decrease frominside outwards. The simplestapproximation is a linear decrease ofthe stress, which produces a constantgradient of viscous shear

8/10/2019 Pi Mu Event

7/17

a) Shrinkage :The fixing stage stops the growth of filaments, and residual Ag and Br andother chemicals are then washed away, leaving only the gel with thedeveloped grains. The reduction in mass usually produces also a shrinkage

of the emulsion film (normally in the range 20% to 50%), which can becompensated if needed by the addition of glycerin.

b) Linear Distortions :After washing and drying, mechanical tensions on the plastic support or atthe surface may produce linear shifts in the position of grains. Such effectscan produce linear distortion, which is due to constant stress field on theemulsion medium.

c) Parabolic Distortion :During all the procedures, if a stress arises at the support surface (bottom),and no stress is applied externally, the stress field has to decrease frominside outwards. The simplest approximation is a linear decrease of thestress, which produces a constant gradient of viscous shear and parabolicdistortion altering the originally straight path of an ionizing particle.

Because of shrinkage and distortion, microtracks detected by human operators or

by automatic systems need to be corrected.

ScanningThe process of searching the position of the events caused by the collision of the

projectile and emulsion nuclei in nuclear emulsion is known as scanning of events.

There are two types of scanning:

i. Area scanningii. Line scanning

Area scanning is used in the present experiment. In case of area scanning, the fulldepth of the pellicle is examined by rolling the fine focus of the control Z of themicroscope. While observing the layers of nuclear emulsion one continuously goeson looking for the disintegrations present in the field of view and before shifting

8/10/2019 Pi Mu Event

8/17

the field more than one traverse must be made along the Z-motion. The field ofview is shifted along the X-motion of the microscope only when the whole X-stripof the pellicle is computed. On computing the X-strip one should switch on to thenext X-strip by giving the displacement in Y-direction equal to or less than one

field of view. Similarly, the whole area of the pellicle is scanned out.

Methods for measurement of track parametersThe commonly used observable properties of a track in emulsions are

I. RangeII. Ionization

III. Scattering

IV.

MultiplicityMeasurement of these quantities can provide information about the mass, chargeand energy of the particle forming track. In this particular experiment, we areconcerned with the range of in nuclear emulsion. So we will discuss only themethod for range measurement.

Measurement of RangeThe range of a charged particle is the average distance traversed by a particle inunprocessed emulsion before its kinetic energy reduces to zero. While computingactual value of the range we must take the shrinkage and other distortions intoaccount which the emulsion undergoes during its processing. These factors affectthe range of the particle.

As the track of the particle is usually not straight due to the various scattering, the projected track length is measured in the plane of emulsion and perpendicular to it.

The former is called the projected range I while the latter one is termed as thedip, Z. thus for measuring the range, the whole track is divided into n smallstraight segments. The value of I and Z for each segment are measured. Themeasured Z is then corrected for emulsion shrinkage. It may be pointed out thatin the case of unmounted pellicles both lateral and vertical shrinkage may take

place.

8/10/2019 Pi Mu Event

9/17

- Event

These secondary particles then undergo electromagnetic and nuclear interactions to

produce yet additional particles in a cascade process. Figure 1 indicates the generalidea. Of particular interest is the fate of the charged pions produced in the cascade.Some of these will interact via the strong force with air molecule nuclei but otherswill spontaneously decay (indicated by the arrow) via the weak force into a muon

plus a neutrino or antineutrino:

+ +

The muon does not interact with matter via the strong force but only through theweak and electromagnetic forces. It travels a relatively long instance while losingits kinetic energy and decays by the weak force into an electron plus a neutrino andantineutrino. We will detect the decays of some of the muons produced in thecascade. (Our detection efficiency for the neutrinos and antineutrinos is utterlynegligible.)

+ +

The event was first discovered and analyzed by C. F. Powell of Bristol in 1947, forwhich accomplishment he was awarded the Nobel Prize. In analyzing the event hediscovered the positive pi-meson which has a mass of approximately 272 electronmasses.

Notice the track of the pi-meson has increasing grain density and increasingscattering as one proceeds along the track toward the first decay process. This is anindication of the energy loss of the particle as it proceeds through the emulsion. Inthe first decay process the pi-meson decays into a mu-meson and a neutrino. Thereis no explicit experimental evidence for the existence of the neutrino here,however, it must be postulated in order to conserve momentum. Note the suddenchange in grain density at the point of decay; evidently a new charged particle, themu-meson, has been formed in the decay process since the grain density suddenly

8/10/2019 Pi Mu Event

10/17

Fig: Carried by History: Cesar Lattes, Nuclear Emulsions, and the Discovery of the Pi-meson,Physics in Perspective, ISSN 1422-6944, Volume 16 Number 1

becomes less. The mu-meson has a mass of approximately 210 electron masses. Notice the increasing grain density and increasing scattering of the track of the mu-meson; this is again evidence of the energy loss. At the end of the track of the -meson another decay process occurs with the resulting production of a positron.

Notice that the track of the positron is much lighter than the tracks of either of thetwo mesons which is an indication of the much smaller mass of the positron.

8/10/2019 Pi Mu Event

11/17

Characteristic Properties of Pions and Muonsa) Pions

Rest mass m = 139, 56995 MeV/c 2 Charge: q = 1.602 x 10 19 C

Mean life: = 2.6033 0.0005) x 10 8sSpin: s = 0Rest mass m 0 = (134.9764 0.0006) MeV/c2Mean life: 0 = (8.4 0.6) x 10 -17 sSpin: s = 0

b) MuonsRest mass: m = 105.658389 MeV/c 2 Charge: q = 1.602 x 10 19 C

Spin: s = Mean life: = (2.19703 0.00004) x 106 s

The decay processes of muons are a three-body decay, which means that thespectra of decay electrons are continuous in a similar way as the decay spectra ofelectrons in nuclear beta decay. The maximum transferable energy to the electronEe,max is approximately half the rest mass of the muon corresponding to 53MeV.The electron spectrum of muon decay at rest is shown in Fig.

Fig:- The continuum of energy of electron in decay

(Courtesy: Measurement of the Lifetime of Muons and Pions, Advanced LaboratoryExperiments, Universitt Siegen, Lecture Notes by Prof. Dr. I. Fleck)

8/10/2019 Pi Mu Event

12/17

It has been verified experimentally that the energy of the mu-meson in this event ischaracteristic, i.e. 4.1 MeV. When one finds an event like this in an emulsion It Isvery convenient because It makes possible the calibration of the emulsion as torange energy relationships. The average range of the mu-meson produced in this

reaction is 590 microns in the Ilford G-5 emulsion. The range energy relationshipwill vary somewhat for individual plates of the same type, however, 80 that theoccurrence of this event on a plate being scanned makes possible an internal range-energy calibration.

This event also gives a cross check on the spin of the pi-meson. From beta-raytheory, the spin of the neutrino is one-half and the spin of the mu-meson is alsoone-half. Then the spin of the pi-meson must be either 0 or 1. Independentexperimental evidence indicates that the spin of the pi-meson is actually 0.

8/10/2019 Pi Mu Event

13/17

Procedure 1. Calibrate the software (Scopeimage 9.0) to measure the range of muon

correctly (i.e. 1:100m).2. Locate the pi mu event in the given emulsion plate on the computer screen

with the help of the microscope.3. Use 10x lens for the better visibility of the event.4. Keep the event in the center of the field view of microscope.5. Now measure the range of muon.6. Find the projection of track in x-y plane (Lp ). Divide the whole range into

straight line segments and sum them.7. Now find the depth of the track (d ). Focus the microscope with the help of

the z-adjustment knob, 1 st at the start of the straight segment and then at theend. Find out z.

8. Now calculate the total length of the track.9. Now see the energy and momentum values from the calibration graph

corresponding to the range of muon, hence find mass of neutrino.

8/10/2019 Pi Mu Event

14/17

Experimental Data :

Record :Shrinkage factor of the emulsion plate = 2.5

Least count of the Z-scale = 2.34 m

Mass of = 139.567 MeV

Mass of = 105.559 Mev

Lp = Actual length of the muon track

Lp = Projection of muon track in xy -plane

d = Depth of the muon track in emulsion

Observation Table

Z1 Z2 d=Z d*2.34=d'(x10 -6m)

d''=d'*2.5(x10 -6m)

(d'') 2Lp

(x10 -6m)Lp'2

Lp(x10 -6m)

72 70 -2 -4.68 -11.70 1.37E-10 26 6.76E-10 28.51

70 72 2 4.68 11.70 1.37E-10 124 1.54E-08 124.55

72 74 2 4.68 11.70 1.37E-10 103 1.06E-08 103.66

74 74 0 0.00 0 0 62 3.84E-09 62.00

74 72 -2 -4.68 -11.70 1.37E-10 86 7.40E-09 86.79

72 74 2 4.68 11.70 1.37E-10 122 1.49E-08 122.56

74 70 -4 -9.36 -23.40 5.48E-10 96 9.22E-09 98.81

70 70 0 0.00 0 0 11 1.21E-10 11.00

70 70 0 0.00 0 0 25 6.25E-10 25.00

Lp

Lp

d

8/10/2019 Pi Mu Event

15/17

Calibration Graph

Calculations :Range of meson = 663m

For this range energy obtained from the Callibration graph, T = 6.5 MeV

From the energy conservation law

E = E + E

8/10/2019 Pi Mu Event

16/17

E = M - ( T + M )

E = 139.567 (6.5 + 105.659)

E = 27.408 Mev

For this range energy obtained from the Callibration graph, P = 66 Mev/c

P = -P

Mass of Neutrino

=

= (27.408) (65)

= 3473.8

= 58.3 MeV

8/10/2019 Pi Mu Event

17/17

References

1. Automatic microscopes for nuclear emulsion readout in high-

energy and particle physics, Current Microscopy Contributions to Advances inScience and Technology (A. Mndez-Vilas, Ed.), C. Bozza, T. Nakano, 20122. Measurement of the Lifetime of Muons and Pions, Advanced Laboratory

Experiments, Universitt Siegen, lecture notes by Prof. Dr. I. Fleck, 2009 3. Nuclei and Particles

Second Edition,1977Emlio SegreW. A. Benjamin, Inc.

4. Cosmic Ray Events Observed in Nuclear Emulsions Exposed at100,000 Feet, Zack Osborne, Philip Fitzpatrick & R. A. Howarb, Academy Of

Science, 1955