nuclear spectrometry and scope of instrumentation in nuclear field

8/6/2019 Nuclear Spectrometry and Scope of Instrumentation in Nuclear Field

1/20

Submitted to :- Presented by:-

Mr. Manish Sharma Prerit Tiwari

Nuclear Spectroscopy and Scope of

Instrumentation in Nuclear field


2/20

Nuclear SpectroscopyContent :-

What is Nuclear Spectroscopy .

Block diagram.

Radiation dosages.

Scintillation Counter. Preamplifier.

The Photo peak.

Other Effects.

The Detector

The Scintillator

HighVoltage Power Supply

Multichannel analyzers (MCAs).

Advantages & disadvantages. Scope of Instrumentation in Nuclear field


3/20

Nuclear Spectroscopy:-

y Definition:-

y Nuclear spectroscopy is a powerful tool in the arsenal of scientistsand forensic investigators because it allows detailed study of thestructure of matter based upon the reactions that take place inexcited atomic nuclei.

y Nuclear spectroscopy is a widely used technique to determine thecomposition of substances because it is more sensitive than otherspectroscopic methods and can detect the trace presence ofelements in an unknown substance that may only be present on theorder of parts per billion.


4/20

Nuclear Spectroscopyy The instrumentation and experimental methods in this lab are

reminiscent of those used throughout particle physics andmedicine. These techniques are also important in radiation safetyand in the uses of radioactivity for dating in archaeology and otherfields. In this experiment, you will measure the energies of

gamma rays emitted in the process of nuclear decays.Measurements of this nature have been used to determine theinternal structure of nuclei, much as optical spectroscopy wasused to determine atomic structure.

y Since the energies corresponding to nuclear excitations are so

large, one can easily detect a single nuclear decay. You willcalibrate the detection system using radioactive sources withgamma rays of known energy and then you will measure theenergies of the gamma rays of an unknown source.


5/20

Block diagram :-


6/20

Radiation dosages.

y Beginning with the definitions of the curie and the rad, determine the absorbed dose (in millirads)for your entire body for one afternoon spent 1 meter from a radioactive sample with a sourceactivity (# decays/sec) of 1 microcurie of137Cs (E=0.663MeV). To do this you will need to make arough estimate of the size of your body (cross sectional area and thickness). You will also need toestimate the fraction of incident gamma ray energy that is absorbed by a given thickness of tissue.This can be done using the relation

y (1)

y where is the fraction of gamma rays that penetrate (i.e., are not absorbed by) a thickness x, mm isthe mass absorption coefficient, and r is the density of the absorbing medium (e.g.,your body orlead shielding). Assume that mm and r for your body are the same as that of water (see enclosedgraph of mm). How does the answer change if you are 2 m away?

y Here is some useful information about units of radiation:

y 1 Gray (Gy) = 100 rad = 1 J/kg (a unit of absorbed dose; Grays are now preferred)(2)

y

1 Curie (Ci) = 3.7 x 1010

decays/sec (a unit of source activity)y 1 Becquerel = 1 decay /sec (a unit of source activity)

y Now suppose that you are 2 meters away and that in addition the source is surrounded by 4centimeters of lead (see enclosed graph for mm of lead). Estimate your total exposure for oneafternoon in lab. Compare


7/20

Scintillation Counter.

y The scintillator you will use consists of a sodium iodide crystal attachedto a photomultiplier tube. Small quantities of thallium (0.1% to 1%)have been introduced into the crystal structure as a photosensitiveimpurity. Incident gamma rays produce a high-energy electron in thecrystal, generally through the photoelectric effect. This high-energy

electron travels th

rough

th

e crystal, producing an ionization trackconsisting of a huge number of electrons in the conduction band of thematerial. Since each one has an energy of only about 10 eV, while theprimary high energy electron may have an energy of 1 MeV, there may

be 105 or so of these secondary electrons, which then interact with theThallium impurity atoms, raising them to an excited state.When theseexcited atoms return to their ground state, they emit visible or near-visible light (luminescence). The function of the scintillator crystal is toconvert the incident gamma ray photon to a much larger number ofvisible photons.


8/20

reamplifier.

y The preamplifier receives the signal from the PMT andintegrates over the entire electron pulse, which may changethe length, squareness and polarity of the pulse. The outputof the preamplifier is a pulse withheight proportional to thetotal energy deposited in the scintillator. This is the signalpassed onto the multichannel analyzer card in your computer,which further amplifies the pulse signal. Ideally the pulseheight should also be proportional to the energy of the

incident gamma ray. However, if the initial conversion eventinvolves energy loss mechanisms, such as Compton scatteringor pair production, this is not always the case.


9/20

Multichannel analyzers (MCAs).

y Your computer has a board which functions as aspectrometer: an analyzer that produces a histogram of thenumber of photons measured by the PMT as a function ofphoton energy. Such devices are called multichannelanalyzers (MCAs). The MCA outputs a spectrum of emittedgamma rays. You may use an internal amplifier to furtheramplify the preamplified PMT signal. The MCA also allowsthe user to perform a variety of software functions that

determine how the spectrum is accumulated, and to furtheranalyze the resulting spectrum.


10/20

The Photo peak.


11/20

The Photo peak

y If a mono energetic source of gamma rays (e.g. 137Cs) isplaced near a scintillation detector, ideally, the spectrumconsists of a single photo peak caused by the photoelectriceffect in the NaI crystal as in Figure 2. However, otherprocesses take place by which the gamma ray energy isabsorbed, thus altering the spectrum shape.


12/20

Other Effectsy Any photons scattered into the crystal by shielding material,

tabletops, holders, etc, will possess less than the full energy of theoriginal gamma ray and this process will give rise to a broaddistribution of pulses in the Compton plateau. However, the

kinematics of the problem together with a varying angularscattering probability tends to produce a bump on the low energypart of the spectrum, called the backscatter peak. (Fig. 4) Even ifthe holders are removed and the detector is moved far from thetabletop, this peak, although smaller, still occurs from

backscattering within the source itself and also from gamma raysthat pass right through the scintillation crystal and are scattered

back into the crystal from the photomultiplier tube.


13/20

Advantages and Disadvantages

Advantages:-

y Very precise instrument.

y Detection rate very good.

y It can be interfaced with Lab View.Disadvantages

Very High Cost.

Setup is very Expensive.

Need regular check.


14/20

Other Effects


15/20

The Detector

y The detector is the \thermos bottle" like structure shown inFig.. The cap" of the bottle contains the scintillate, and theradiation enters through the top of the cap. The body of thethermos contains the photomultiplier tube. The thermos

bottle sits on top of a cylinder called the detector outputstage.


16/20

The Scintillate

y When an energetic electron appears in the scintillator, eitherby entering the scintillator as a beta ray or being produced inthe scintillator by a gamma ray, a number of 3 eV photons areproduced. The number of these 3 eV photons is proportionalto the initial energy of the electron. The NaI(Tl) scintillator isa crystal of sodium iodide that has been doped withThalium(Tl). This crystal is transparent to 3 eV photons.


17/20

High Voltage Power Supply

y Generates high voltage which goes to the detector outputstage and then to the electron multiplier. Output voltage isdetermined by a multi-turn potentiometer and there is adigital readout of the voltage in kV.When turning this powersupply on and to be sure that the potentiometer is fullyCCW.


18/20

Scope of Instrumentation in Nuclear

field

y With extensive training and experience, our field servicetechnicians have the depth and breadth of industryknowledge and pharmaceutical experience to deliverconsistent and high quality service on a wide variety ofanalytical instrumentation.


19/20

Scope of Instrumentation in Nuclear

fieldy Instrument design scope

y project management

y cable list

y loop and circuit diagram

y sequence diagram

y

data sheets and instrument sizingy panel design

y control room layouts

y instrument installation drawings - hook ups

y instrument location and cable tray layout

y instrument air distribution layouts

y MTOy procurement

y documentation

y site supervision


20/20

Thank you

nuclear spectrometry and scope of instrumentation in nuclear field

Documents