Ultra Violet Radiations
Dr. Hira Jabeen
ANMC
Introduction
• UV is electromagnetic energy which is
invisible to human eye with
wavelengths btw 100nm & 400nm
• UV lies between visible light and Xrays in electromagnetic spectrum.
• UV spectrum divided into
– UVA (315~400nm)
– UVB (280~315nm)
– UVC (below 280nm)
• Ozone block UVC , so only UVA & small
amount of UVB received.
• UVA is closest to visible light and is the
longest (i.e., wavelength) and least
energetic, while UVC is the shortest and
most powerful, lying closest to x-rays on
the light spectrum.
Ultra violet generators
PRODUCTION OF UV RAYS
Ultra violet generators
• Various types of mercury vapour lamps
which employ either a high or a low
pressure tube across which a current is
passed.
1. High pressure mercury vapour burner.
2. Kromayer lamp
High Pressure/Air Cooled
Mercury Vapour Burner
Construction of lamp
Construction:
• U-shaped to act as a point source
• Burner quartz
– Allow UV to pass
– Withstand very high temp
– Low coefficient of expansion
• Inside a tube :
• Argon gas at low pressure
– reduce electric resistance
• Mercury
Cont..
• Electrode is sealed from both ends.
• Two metal caps at both ends  high
potential difference is applied to ionized
the argon gas
Ionization of Argon
• Highly stable
• Inert Gas
• For ionization 400 volts potential
difference is applied across the tubes for a
fraction of a second.
• For it auto transformer is used to stepup the mains voltage to 400 volts
Working
• Once argon ionized, normal mains voltage
btw the electrodes causes the neg and pos
particles to move through the burners, >electric current
• Two way migration of charged particles
causes collision btw moving ions and neutral
argon atoms
• So continuous generation of ionized particles
to sustain the current flow across tube
• This current flow can be seen as glow
discharge
• Heat is produced with passage of current
( Joule’s law)
• This heat then vaporizes the liquid
mercury in the tube
• This become ionized
Production of UV rays
1) Energy released by the re-combination
of electrons & positive mercury ions
2) Photons released when excited electrons
returns from their high energy
quantum shell to their normal shell
within the mercury atoms
• Other rays: IR ,visible, some portion of UV
• TIME :
– argon ionization, mercury vaporization, &
ionization takes some time
– A period of 5 min elapses btw starting a burner
and UV emission reaching its peak
• Turn off:
– Ions of argon recombine
– Mercury also
– Everything returns to neutral state
Tridymite Formation
• Heat formed in the burner causes some of
the quartz to change into another form of
silica called tridymite.
• Tridymite is opaque to UV and total
output of a lamp gradually falls as the
proportion of tridymite increases
Compensation for tridymite
• Variable resistance is introduced in the
burner circuit
• As resistance is reduced due to tridymite
formation, intensity of current is increased
to compensate for this (Ohm’s Law)
• Production of UV inc but less is
transmitted by quartz,
• Output is kept constant
Care of the UV tube
• To allow stabilizing resistance to be
reduced at appropriate times ( approx
every 100 hr) burning time is recorded or
on a meter incorporated in machine
• After 1000 hrs of burning so much
tridymite is formed that whole tube needs
to be changed
• Output further reduced if impurities etched
on quartz tube:
– Touching cold burner with fingers
– Leaving grease on tube
– Atmospheric dust settle on tubes
Cooling
• A considerable amount of IF is produced
by the high pressure burner
• Absorbed by human body converts to heat
• Lamp is air cooled so can be safely used
close to patient---50cm
• Burner is housed in parabolic reflector
• Position can be adjusted on a stand
Ozone formation
• The photochemical action of UV radiation
shorter than 250nm o atmospheric oxygen
is to form ozone (O3 )
• Ozone is a toxic gas
• Good ventilation
• Levels of ozone can be detected at
extremely low levels (0.1 ppm)
Kromayer/ Water Cooled
Lamp
Introduction
• Water cooled mercury vapor lamp
• Eliminates the danger of an IR burn
• Advantage:
– Can be used in contact with the tissues
– With a suitable applicator
– To irradiate inside a sinus or body cavity
Construction
• Same construction as High pressure
mercury vapor burner
• It is completely enclosed in a jacket of
circulating distilled water, to absorb IR
• Pump and cooling fan are incorporated in
lamp to cool the water
• After use, circulation of water is continued
for 5 min after the burner is switched off in
order to cool the lamp
• At front of lamp water circulates btw two
quartz windows which allow UV to emerge
• Treatment of sinus:
– Applicator of quartz fixed at window via
special attachment
– UV conveyed to tip by internal reflection
– Some dose is absorbed due to reflection so
longer dose given
Fluorescent tubes
• Mercury vapor lamp produce certain
amount of short UV rays
• Fluorescent tubes are used to produce
longer UV rays without the short wave
• Spectrum of tube depends upon phosphor
coating
• Each tube 120cm long
• Type of glass allow longer UV to pass
WORKING
• A low pressure arc set up inside the tube
btw its ends by process of ionization
similar to mercury vapor tube
• Shorter UV is produced but absorbed by
phosphor & re-emitted at longer
wavelength
• Depending on type of phosphor:
– Output may be part UVA & part UVB or totally
UVA
Theraktin tunnel
• Semi-cylindrical frame in which four
fluorescent tubes
• Each tube mounted in its own reflector in
such a way that an even irradiation of the
patient is produced, allowing treatment of
whole body in two halves
• Normally fluorescent tubes with spectrum
of 280-400nm used
PUVA Apparatus
• Irradiation with UVA only with special
fluorescent tubes, mounted vertically on
wall, or on four sides of a box totally
surround a pt.
• Two hrs after patient has taken a
photoactive drug such as psoralen: hence
the term PUVA (psoralen ultra violet A)
Thank you