Conceptual Physics

What are Self Powered Neutron Detectors?

2025-04-13T14:42:00.005+05:30

Self Powered Neutron Detectors (SPNDs) are used as in-core Neutron Fluence Detectors in Nuclear Power Plants. These detectors don't use external power to collect the charge generated in the neutron interaction with sensitive material of the detector. hence these detectors are called as Self Powered Neutron Detector

BORON TRI-FLUORIDE (10BF3) NEUTRON DETECTOR

2025-04-13T13:43:00.015+05:30

The field of Radiation Detectors with their applications has grown rapidly in the recent past. Though the gas filled radiation detectors are earliest type of nuclear radiation detectors, their application persists due to their versatile characteristics like inexpensiveness, simple in design and fabrication, easy to operate, long operation life etc.

These detectors are still being used in real time applications like monitoring delayed Neutron activity in Pressurized Heavy Water Nuclear Reactors for failed fuel detection, nuclear waste assay monitoring systems, special nuclear material detection systems.

This article reviews the physics behind the BF3 gas filled thermal neutron detectors and their characteristics.

INTRODUCTION

Boron-10, an isotope of Boron has got a reaction cross-section of about 3840 barns for thermal neutrons. The abundance of B-10 is only about 19%. Elemental 10B in powder form can be used as sensitive medium directly by coating onto cathodes of detectors, but the limitation is that they have low sensitivity & poor pulse height characteristics. Hence, the idea of using 10B in gas form has emerged. Boron-Tri- Fluoride 10BF3 gas is widely used for radiation sensors for the purpose of thermal neutron detection.

PRINCIPLE OF OPERATION

The basic configuration of any gas filled detector with assumption of cylindrical geometry is as shown in following Fig.

The concept in operation of any gas filled detector is collection of charge generated due to dissipation of energy of incoming radiation particle in the gas gap between the electrodes.

The modes of operation of gas filled detectors have been classified into three major regions derived from the plot of applied voltage vs output pulse height (shown in below Fig).

They are

i) Ionization region ii) Proportional region and iii) Geiger Mueller region.

10BF3 gas filled detectors are operated in the proportional region and hence are classified as proportional counters.

Proportional region is the applied voltage region of the detector during which the output variation will be proportional to the incident radiation flux. These detectors usually operate in pulse mode unlike ionization chambers as number of incident events information is required.

To produce enough charge, good amount of charge is required which couldn’t be generated in primary ionization. Hence, high potential is applied to these detectors which could amplify the amount of charge generated. This process is called as gas multiplication.

“Gas multiplying means multiplying charge carriers created due to primary ionization of gas by incident radiation in the gas. The charge carriers i.e. electrons drift towards the anode at positive potential. The electrons gain momentum and get accelerated to high energies which can transfer to other atoms resulting in emission of further electrons called secondary electrons.

The multiplication occurs more near the regions of anode wire as there is very high electric field intensity in the vicinity. The phenomenon of multiplication of charge in gas under influence of external high voltage is called as gas multiplication(M). Gas multiplication depends on pressure, voltage and mass of charge carriers.
According to Diethron, the expression for ‘M’ is

where

‘M’ is gas multiplication factor;

‘V’ Is applied voltage;

‘a’ is anode radius;

‘b’ is cathode radius and

‘P’ is gas pressure

K = E/P ; where ‘E’ is electric field and ‘P’ is pressure inside the detector

The high voltage region, in which this gas multiplication is linear and the collected charge is proportional to initial ionization i.e. number of original ion pairs created by incident radiation, is called as proportional region.

10BF3 counters are operated in this region and are hence called as 10BF3 gas filled proportional counters.

When a thermal neutron impinges on to the detector filled with 10BF3 gas, the probability of nuclear reaction is high and may result in an event which happens by following reaction:

The gas acts both as sensitive medium and ionizing medium. The reaction products “Li⁺⁺” & “He⁺⁺” are ionized and hence possess charge and share the energy resulting in ionization by electrostatic interaction.

DESIGN

ANODE

For a cylindrical shaped detector, the electric field at a radial distance ‘r’ measured from the axis is given by

Where, V is the positive potential applied to central wire(anode) of radius ‘a’ and ‘b’ is radius of outer cylinder kept at ground potential. It is evident that the lesser the radius of anode wire, the more the intensity of electric field due to potential on anode. Hence, Tungsten wire with diameter of few microns usually 1mil or 2 mil wire is used as anode to generate strong electric field for same applied voltage.

Materials

Aluminum is a desirable material due to its low absorption crossection for thermal neutrons.

But all commercial aluminum was found to have high background count when exposed to high neutron flux due to induced radioactivity in the impurities.

Copper has got good strength but has high absorption cross-section for neutrons.

Both Aluminum and Copper are not suitable for high vacuum degassing process.

Hence, Stainless steel of grade 304L is generally used for body of the detectors.

For electrical isolation of electrodes, High pure ceramic to metal seals are used.

PERFORMANCE

The quality of the ¹⁰BF₃ detector could be estimated by using pulse height analyser. Typical output pulse height distribution from a ¹⁰BF₃ counter for thermal neutrons is as shown in Fig-3. Here, pulse heights are expressed in units of the energy deposited in the counter.

The full width at half maxima (FWHM) of the peak will determine the resolution and thus quality of collection of charge in the detector.

The pulse height(Vo) at the detector output is given by

Where, Q is secondary charge created near anode due to avalanche formation; ‘n’ is no. of primary ion pairs created by ionization of gas by Li and He; Cf is feedback capacitance of charge sensitive amplifier.

CHARACTERISTICS

HV Plateau curve

The curve is derived by recording the variation of average counts observed in a preset time with high voltage applied to anode. A sample curve is shown in Fig-4.

Plateau length (Operating voltage range) is the range of high voltage over which counter can be operated in proportional mode. The gas multiplication almost remains constant over this range of operation. The region is selected in such a way that the difference of count rate is less. In other words, slope shall be minimum.

Plateau slope per volt is given by

Good slope indicates that the pulse height distribution is good.

OPERATING VOLTAGE

This is the voltage which is selected based on the sensitivity required and stability of high voltage power supply. This shall be noted that the count rate at lower end of plateau region will be low as compared to count rate at high end of plateau. Hence deciding operating voltage will also decide sensitivity of detector.

SENSITIVITY(S)

S = counts per second at operating voltage/ incident neutron flux

Theoretical expression for sensitivity is

where ‘N’ is number of converter nuclei per unit volume;
V is sensitive volume of detector

EFFICIENCY

The efficiency of the detector along radial direction is given by

ξ = 1-exp^(-N^σ^t)

‘N’ is number of converter nuclei per unit volume;
σ is neutron absorption crossection
‘t’ is gas gap thickness

EFFECT OF PRESSURE AND TEMPERATURE ON PERFORMANCE OF ¹⁰BF₃ DETECTORS

The pulse height distribution (PHD) in the detector gets affected by temperature. Broadening of the PHD is observed with increase in pressure, however with increase in efficiency of detection. The PHD width decreases with decrease in temperature. Thus to obtain good efficiency a high pressure detector could be used maintaining low temperature.

CONCLUSION

Literature pertaining to BF3 counters was reviewed and insight is given to the basic principle of operation, design parameters and the functional characteristics. This article would help readers to understand the physics behind the operation of 10BF3 counters and understand the functionality.

REFERENCES

[1] G F Knoll, Radiation Detection & Measurement, John Wiley & Sons

[2] I.L. Fowler and P.R.Tunnicliffe, Boron Trifluoride Proportional Counters; The review of Scientific Instruments; Volume-21, Number 8

[3] I.L. Fowler, Very large Boron Trifluoride Proportional Counters; The review of Scientific Instruments; Volume-34, Number 7, July 1963

[4] Shraddha S.Desai, Mala N. Rao; Effect of Temperature on performance of Boron Trifluoride Neutron Proportional Counters; Radiation Measurements, 144(2021)106593

[5] SS Kapoor, V S Ramamurthy, Nuclear radiation Detectors, New Age International Publishers

General Science - 4

2024-02-17T21:46:00.002+05:30

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201) The Refractive index of Diamond is 2.41

202) Density of diamond is 3.51gm/cm³

203) Density of graphite is 2.25gm/cm³

204) Third form of carbon is discovered in 1996 by “HW.KROTO”; “Resmasy”. C60.

205) Distance between two layers in graphite is 3.35A^o

206) C-C bond length is 1.42 A⁰ in graphite.

207) C-C bond length is 1.52 A^oin diamond.

208) Radioactivity was discovered by Henry Bequerel in 1896.

209)To avoid overturning of a vehicle moving on a curved road , the height of center of gravity of vehicle must be nearer to the ground.

210)When a spin bowler throws a cricket ball towards the batsman , the center of mass of ball follows a parabolic path.

211) Newton’s laws of motion apply only to centre of mass.

212) A body is heated uniformly keeping it on a smooth surface . the position of center of mass wrt that body does not change in position.

213)Two balls are thrown simultaneously in air the acceleration of centre of mass of those two balls in air is equal to ‘g’.

214)If two particles initially at rest approach each other due to mutual force, they two meet at center of mass of system.

215) The center of mass of Earth and moon describes elliptical path.

216)When a person walks on a rough road , the frictional force exerted by the road on him is along his direction of motion.

217) Less mileage is obtained per litre of fuel by a car making frequent stops. Here st each time of starting it has to overcome static friction.

218) Small brake and large brake both are equally effective in stopping a cycle as friction doesn’t depend on area of contact.

219)Coefficient of friction can be greater than 1.

220)When a person walks on a rough surface reaction of force applied by a man on surface keeps him moving.

General Science - 3

2024-02-16T19:54:00.004+05:30

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151) Shearing strain = 2 x longitudinal strain

152) Bulk strain = 3 x Longitudinal strain

153) Annealing : means slow cooling after heating . Annealing reduces elastic property of the body.

154) If temp increases generally the elastic property of body decreases.

155) In case of rubber , the modulus of elasticity increases with increase in temperature.

156) Elasticity of a perfectly rigid body is infinite.

157) For liquids and gases young’s modulus (Y) and rigidty modulus(ƞ) do not exist.

158) Gases are least elastic as they are most compressible.

159) Poisson’s ratio lies between -1 and 0.5. but in actual practise it lies between 0 and 0.5.

160) For most of solids ‘σ’ lies between 0.2 and 0.4.

161) ‘σ’ for rubber is nearly 0.5

162) For incompressible liquids Bulk modulus is infinite and poisson’s ratio is 0.5

163)The pressure inside a bubble or liquid drop is greater than the outside pressure. This excess pressure is inversely proportional to radius of bubble.

164)Pressure inside a smaller bubble is greater than the pressure inside a larger bubble or drop.

165)A sphere has minimum surface area for given volume.

166)When a bigger drop splits into smaller drops energy is absorbed.

167) When a smaller drops merge to form a larger drop , energy is absorbed.

168) A water proofing agent changes angle of contact from an acute to obtuse value.

169) Meniscus of mercury in capillary is convex.

170) When a soap bubble is charged it expands.

171) Viscocity of liquids increases with increase of pressure.

172)Venturimeter is the device to measure rate of flow of liquid through a pipe.

173) In winter as temperature falls , viscocity of lubricants increases so machine parts will be jammed during winter.

174) Principle behind working of Gas burner is Bernouli’s principle.

175) A rifle bullet is cylindrical so that it doesn’t experience any dynamic lift.

176) Rain drops falling from high clouds reach the earth with uniform velocity but different for different sizes.

177) The coefficient of Viscocity is highest for water.

178) Good lubricant should have high viscocity.

179) Clouds float In atmosphere because of their low viscocity.

180) Equation of continuity is law of conservation of mass.

181) Invar steel—64% steel; 36% nickel.

182) Coefficient of linear expansion of rubber is negative .

183) A bimetallic strip consists of copper and steel strips.

184) Water has ananalous expansion due to formation of more no. of hydrogen bonds.

185) ”Diatometer “ is used to study the anamolous expansion of water.

186) Soft rubber also exhibits anamolous expansion.

187) At 0 ^oC, the coefficient of expansion of water is zero.

188) Water has minimum volume and maximum density at 4^o C or 277 K

189) If an air bubble raises from bottom to surface of a lake then its volume increases

190) The gas thermometers are more sensitive than liquid thermometers because gases expand more than liquids.

191) Triple point of water is 0.01 ^oC

192) Triple point of CO₂ is 216.65 K at 3.8mm of Hg

193) Triple point of Iodine is 387 K at 90mm of Hg.

194) Ice at 0^o C produces more cooling than water at 0 ^oC.

195) At boiling point specific heat of water is infinite.

196) Entropy during change of phase may increases or decrease.

197) Specific heat of gas in isothermal process is Infinity.

198) A block of ice can radiate energy.

199) The waves produced during earth quakes are infrasonics.

200) Sound travels in rocks in the form of both longitudinal and transverse elastic waves.

General Science - 2

2024-02-01T21:27:00.006+05:30

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101) Electron microscope is designed by “knoll” and “Ruska”.

102) The Refractive index of Diamond is 2.41

103) Density of diamond is 3.51gm/cm³

104) Density of graphite is 2.25gm/cm³

105) Third form of carbon C-60 is discovered in 1996 by “HW.KROTO”; “Resmasy”.

106) Distance between two layers in graphite is ----3.35A^o

107) C-C bond length ------1.42A in graphite.

108) C-C bond length -------1.52A^oin diamond.

109) Radioactivity was discovered by Henry Becquerel in 1896.

110) To avoid overturning of a vehicle moving on a curved road, the height of center of gravity of vehicle must be nearer to the ground.

111)When a spin bowler throws a cricket ball towards the batsman , the center of mass of ball follows a parabolic path.

112) Newton’s laws of motion apply only to centre of mass.

113) A body is heated uniformly keeping it on a smooth surface . the position of centre of mass wrt that body doesn't change in position.

114)Two balls are thrown simultaneously in air the acceleration of centre of mass of those two balls in air is equal to ‘g’.

115)If two particles initially at rest approach each other due to mutual force, they two meet at centre of mass of system.

116) The center of mass of Earth and moon describes elliptical path.

117)When a person walks on a rough road , the frictional force exerted by the road on him is along his direction of motion.

118)Less mileage is obtained per liter of fuel by a car making frequent stops because each time of starting it has to overcome static friction.

119)Small brake and large brake both are equally effective in stopping a cycle as friction doesn’t depend on area of contact.

120)Coefficient of friction can be greater than 1.

121)When a person walks on a rough surface reaction of force applied by a man on surface keeps him moving.

122) Helium has the lowest critical temp -268 ^oC of all known gases.

123) Helium has no triple point.

124) Boiling point of Helium is 4.2 Kelvin.

125) No white Dwarf star can have mass larger than 1.4 times mass of sun.

126) Work done by Contripetal force is zero.

127) Centripetal force and centrifugal reaction from action – reaction pair. But centripetal force and centrifugal force doesn’t form action –reaction pair.

128) Centrifugal force is a pseudo force.

129) Centripetal force & Centrifugal reaction are Real forces.

130) Mass of earth is 6x10²⁴ kg

131) Mean density of earth is about 5500kg/m³

132) Mean radius of earth is about 6400km.

133) Acceleration due to gravity depends on density of planet.

134) ’g ‘ is maximum on Jupiter.

135) ‘g’ is minimum on mercury.

136) Orbital velocity for a surface satellite is about 8 km/sec.

137) The orbit in which a geostationary satellite moves is called Parking orbit.

138) Relative velocity of parking satellite wrt earth is zero.

139) Time period of revolution of parking satellite 24hrs.

140) Orbital linear velocity is about 3kms^-1.

141) A satellite cannot be coast in a stable orbit in a plane not passing through the earth’s centre.

142) Communication satellites are placed in Parking orbits.

143) Time period of revolution of a satellite around planet is independent of mass of satellite.

144) Time period of a surface satellite of earth is 84.6 min or 1.4 hrs

145) If a rocket is launched in the equatorial plane from west to east , advantage is upto 0.47 kms^-1 in launching speed.

146) Negative total energy of satellite indicates that energy must be supplied to remove the satellite from the orbit against gravitational attraction.

147) Apparent weight of a body in satellite is zero.

148) If 1 kg of sugar is weighed using a spring balance at poles and the equator more quantity is obtained at equator.

149) For geostationary satellite the time period is equal to rotation of earth about its axis.

150)The first artifiacial satellite launched by India is Aryabhatta in 1975, April 19.

General Science - 1

2024-01-29T22:38:00.006+05:30

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51. Velocity of sound is high at 30 degree centigrade in moist air.

52. The distance between Earth and sun would be minimum on January 3.

53. ‘Uranus’ and ‘Venus’ have sunrise in West

54. In Tiruvananthapuram sunrays never fall perpendicularly.

55. Sun is seen in Arctic and , Antarctic even at mid night.

56. Dol drums belt will be at equatorial plane of earth.

57. Calcium carbonate is the substance transforming into pearls

58. ’Periscope’ is used to view objects at greater heights.

59)If we use a red flower from a blue glass, it would appear as Black.

60) If we add impurity to solvent the boiling point increases.

61) When we separate butter from milk the density of milk decreases.

62) The air bubble inside the water acts as a Convex lens.

63) “Toricelli” has invented Barometer.

64) The heat of steam inside pressure cooker depends on volume of pressure cooker.

65) If temperature of water is raised from 0^oC to 10^oC the density of water first rises up to 4^oC and then decreases.

66) Common salt gets wet in Rainy season due to presence of impurities such as Magnesium chloride.

67) Element "Tin" has highest number of stable isotopes. It has 10 stable isotopes.

68) lightining conductors are made of copper.

69) Ignition process in diesel engines is due to compression.

70) The hydraulic breaks in automobile vehicles works on pascal principle

71)Spring balance works on Hookes law.

72) Efficiency of electric engine is high.

73) silicon is most abundant metal in ores.

74) Gobar gas consists of mainly methane.

75) Bromine is the metal existing in liquid form at room temperature.

76) Red Phosphorous is used in matchsticks manufacturing.

77) Dry ice can be used as good refrigerant

78) Metal used in storage battery is lead

79) Sodium is stored in Kerosene

80) Methane is called as Marsh gas

81) Graphite is used as Lubricant.

82) Silicon carbide is known as Carborondom.

83) Teflon material is pasted on non stick wares.

84) In allotropic forms of Carbon, Diamond is hardest and Graphite is soft.

85) Lead is the metal responsible for pollution of air in cities.

86) Sulphar is added to original rubber in process of Vulcanization.

87) Cellulose is the chemical name of Rayon.

88) Powder method is used for viping off fire due to petrol.

89) Parsec is the biggest unit of distance.

90)Density of water is 13.6 times the density of mercury.

91)Hydrometer works on Archimedes principle.

92)It is easy to swim in sea than lake because density of sea water is high according to

Archimedes principle.

93) Embedding shock absorbers to vehicles depends on conservation of momentum principle.

94)Due to viscocity of air clouds float in air.

95)To clean oily utensils we use hot water because it reduces the viscocity of water and this

can clean utensils easily.

96) When wind flows , a paper on table lifts due to Beernouli’s principle.

97)As temp increases viscocity of liquids decreases and that of gases increases.

98)when we sleep on land we exerts less pressure on land.

99)when we are running we exerts greater pressure on land.

100)One gets blood from nose at higher mountain ranges because pressure at higher altitudes is less than that of sea level.

Electric & Magnetic Fields - Direction

2023-09-03T09:35:00.001+05:30

MOTION IN A STRAIGHT LINE - FORMULAE

2023-09-01T19:54:00.001+05:30

KINETIC THEORY FORMULAE

2023-09-01T19:42:00.003+05:30

CIRCULAR MOTION FORMULAE

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COMPARISON OF ELECTRIC FIELD AND MAGNETIC FIELD

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ELECTRIC FIELD	MAGNETIC FIELD
Source is “ Charge”	Source is current
Obeys inverse square law	Obeys inverse square law
Obeys principle of superposition	Obeys principle of superposition
It is independent of angle	It is dependent on angle
Electric field lines don’t form close loops	Magnetic field lines form closed loops
Electric field changes kinetic energy of particle	Magnetic field doesn’t change kinetic energy of particle.
A particle experiences electric field whether it is at rest or in motion	A particle experiences magnetic field only in motion and a charge at rest doesn’t experience the magnetic field.

USES OF ISOTOPES

2023-08-29T06:33:00.001+05:30

Purpose	Isotope Name
IN MEDICINE
For testing blood	Chromium-51
For testing blood circulation	Na-24
For testing brain tumor	Hg-203
Thyroid problem	I-131
Treatment of Cancer	Co-60
For blood disorders	Au-189
For skin diseases	P-31
IN ARCHAEOLOGY
Carbon Dating	C-14
Determining age of meteorites	K-40
Determining age of earth	Pb isotopes
IN AGRICULTURE
For protecting potato crop from earth worm	Co-60
For artificial rains	AgI
For fertilizers	P-32

Types of Nuclei - Isotopes, Isobars, Isotones, Mirror Nuclei, Isoelectronic Species, Isodiaphers

2023-08-28T19:32:00.004+05:30

Characteristics of different types of Nuclei is as follows:

Isotopes

Same Atomic Number(Z)
Same number of electrons
Same number of Protons
Different Mass Numbers
Different number of Neutrons
Same chemical properties
Different Physical Properties
Belong to same element

eg: ₁H¹ , ₁H² , ₁H³

Isobars

Different Atomic Number(Z)
Different number of electrons
Different number of Protons
Same Mass Number
Different number of Neutrons
Different chemical properties
Different Physical Properties
Belong to different elements

eg: ₆C¹⁴ , ₇N¹⁴, ₈O¹⁴

Isotones

Different Atomic Number(Z)
Different number of electrons
Different number of Protons
Different Mass Number
Same number of Neutrons
Different Chemical Properties
Different Physical Properties
Belong to different elements

eg: ₁₆S³⁶ , ₁₇Cl³⁷

Mirror Nuclei

Different Atomic Number(Z)
Different number of electrons
Different number of Protons
Same Mass Number
Different number of Neutrons
Neutrons and Protons are interchanged

Isoelectronic Species

Species having equal number of electrons.

Isodiaphers

Nuclides having the same difference between Protons & Neutrons

Different Atomic Number(Z)
Different number of electrons
Different number of Protons(P)
Different Mass Number(A)
Different number of Neutrons(N)
Same (P-N)

eg: ₉₂U²³⁸₉₀Th²³⁴

Comparison between "Series" & "Parallel" Combination of Inductors

2023-08-28T18:52:00.003+05:30

Let L1 & L2 are inductance of two Inductors. Ls is series inductance and Lp is parallel inductance for the two Inductors. M is "Mutual inductance".

SERIES COMBINATION	PARALLEL COMBINATION
L_s = L₁ +L₂ If both coils are placed close to each other, L_s = L₁ +L₂± 2M	L_p = L₁L₂/L₁ +L₂ If both coils are placed close to each other, L_s = L₁L₂ – M²

If ‘n’ coils of equal inductance ‘L’ are put in series, then L_s = nL	If ‘n’ coils of equal inductance ‘L’ are put in series, then L_p = L/n

L_s/L_p = n²	L_p/L_s =1/ n²

Voltage ‘V’ is divided	Voltage ‘V’ is not divided

2023-08-27T13:12:00.008+05:30

What is Parity?

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What is Parity?

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What is Parity?

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What is Parity?

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What is Parity?

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What is Parity?

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What is Parity?

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Chemical Resistance and Physical Properties of Various Plastics

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PHYSICS DICTIONARY

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Viscosity

It is the property of a fluid which opposes the relative motion between its layers. Viscosity is known as fluid friction.

Visible Spectrum

Molecular spectrum obtained in visible or ultraviolet region.

Vitrification

During firing of a ceramic body, the formation of a liquid phase that upon cooling, becomes a glass bonding matrix.

VME

VME stands for Versa Module Europa. It was jointly introduced in 1981 by Mostek, Motorola, Phillips, and Thompson. The original motivation of VME development and standardization was to introduce modular approach to highly intense computing tasks. However it was quickly adopted by researchers in other fields as well, so much that it now probably stands as the most used system in research laboratories. Due to its flexibility and expandability, it has received its fair share of popularity in industrial environments as well. The original VME standard is now referred to as VME32 as it could handle up to 32 bits of data. The new standard is called VME64 and has the capability of 64 bit data transfers.

VME Logic

VME is a TTL based system. That is, its internal functioning follows TTL logic. However modules accepting and producing other logic signals can be integrated into the system.

Volt

It is the unit used to measure electric potential difference between two points. One volt is electric potential difference between two points when one joule of work is done in carrying one coulomb of positive charge from one point to another.

Voltage

It represents electric potential energy per unit charge. It is measurement of the energy contained within an electric field, or an electric circuit, at a given point.

Volume Strain

It is the change in volume per unit original volume or it is the fractional change in volume.

Vulcanization

Non reversible chemical reaction involving sulphur or other suitable agent where in crosslink’s are formed between molecular chains in rubber materials. The rubber’s modulus of elasticity and strength are enhanced.

VVER

Acronym for Voda Vodyanoi Energitechesky reactor (water cooled water moderated energy reactor)

PHYSICS DICTIONARY

2023-05-28T13:36:00.004+05:30

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Translucency

It is the property of the substance transmitting light only diffusively; objects viewed through a translucent medium are not clearly distinguishable.

Transmission Electron Microscopy

The image seen with TEM is formed by electron beam that passes through specimen. Details of internal microstructure features are accessible to observation; contrasts in the image are produced by differences in beam scattering or diffraction produced between various elements of microstructure or defect. Since solid materials are highly absorptive to electron beams, a specimen to be examined must be prepared in the form of very thin foil; this ensures transmission through specimen of an appreciable fraction of incident beam. The transmitted beam is projected onto a fluorescent screen or a photographic film so that the image may be viewed. Magnifications approaching 10⁶ times are possible with TEM, which is frequently utilized in study of dislocations.

Transmission

It is property of a substance to permit the passage of light, with some or none of the incident light being absorbed in process.

Transmitting Power

The ratio of amount of radiations transmitted by a body in a certain time to amount of radiations incident on it in the same time is called transmitting power.

Transverse Wave Motion

Type of wave motion in which particles of medium vibrate at right angles to direction of propagation of wave.

Triple Point

The temperature and pressure combination for a substance at which liquid vapor curve, fusion curve and sublimation curve coincide. It is the combination at which substance coexists in solid, liquid and vapor phases.

Triton

Nucleus of Hydrogen-3 (₁H³ ) atom, consists of one proton and two neutrons bound together with a total binding energy of 8.48 Mev. The H-3 atom, a radioactive isotope of hydrogen with a half life ty₂ of 12.32 yrs, is called as Tritium and consists of a nucleus and one electron.

Tropopause

The boundary between the troposphere and the stratosphere is called the "tropopause", located at an altitude of around 5 miles in the winter, to around 8 miles high in the summer, and as high as 11 or 12 miles in the deep tropics.

Troposphere

The troposphere is the lowest major atmospheric layer, extending from the Earth's surface up to the bottom of the stratosphere. The troposphere is where all of Earth's weather occurs. It contains approximately 80% of the total mass of the atmosphere. The troposphere is characterized by decreasing temperature with height (at an average rate of 3.5 ^oF per thousand feet, or

6.5 ^oC per kilometer).

Trough

The trough of a wave is the point at which particle has maximum amount of negative or downward displacement from the rest position.

Tuning Fork

Arrangement of U–shaped rod attached to metal stem, used as a source of standard frequency. It is made of an alloy of Nickel and steel.

Tunnel Diode

A tunnel diode is a P-N junction where both P-and N-type regions are degenerately doped. As a result, the Fermi level in the N-type material is above the minimum of the conduction band and the Fermi level in the P-type material is below the maximum of the valence band. The doping concentrations are so high that the width of the space-charge region at the junction is extremely thin, and usually measures less than 10nm. The diode exhibits negative resistance characteristics.

Twin Boundaries

A twin boundary is a special type of grain boundary across which there is a specific mirror lattice symmetry; that is atoms on one side of boundary are located in mirror image positions of atoms on the other side. The region of material between these boundaries is approximately termed as a twin.

Twin Paradox (Relativity)

It is well known hypothetical concept in relativity under time dilation. As per this concept, one of two twins remains at rest and other moves in space ship moving with nearly velocity of light for some duration and come back. Applying theory of relativity, age of twin in space shuttle appears to be high. This leads to paradox.

Type-I Superconductor

Superconductor which exhibits complete Meissner effect for magnetic fields up to a limit is called critical magnetic field.

Type-II Superconductor

This type is discovered by Schubikov. Superconductor which exhibits Meissner effect till a particular magnetic field range, beyond which admits magnetic flux but retains zero resistance till a particular field value (critical field II) beyond which settles to normal state.