Problems
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8.7 The UVB molar absorptivity of provitamin D3 (7-dehydrocholesterol) is shown
in a figure of this chapter. If your epidermis had no other absorbing compounds
except provitamin D3 at a concentration of 20 μm/L, what depth would UVB light
of wavelength 280 nm reach before dropping in intensity by 90%?
8.8 Look up the typical binding energy of the carbon-carbon bond in an organic
molecule (usually given in kilocalories per mole.). Convert from kilocalories per
mole to electron-volt per molecule. Calculate the frequency of the photon which
will have sufficient energy to break this chemical bond. Calculate the wavelength
for this frequency, in nanometers. Look up where in the electromagnetic spectrum
this wavelength occurs, i.e. what is the name of this type of radiation? Look up the
full range, in nanometers, of this type of radiation. Are there named subcategories
for this type of radiation? If so, what are their names? Electric arc welders can get
burns on their face from this radiation. Why? Which frequencies in this radiation
range are likely to cause the most severe burns?
8.9 What makes infrared light more useful to investigate organic molecules than
ultraviolet light?
8.10 If the electron current in an X-ray tube is 50 mA, accelerated by a 12 kV
potential, how much heat might be generated in the tungsten target? What is the
highest frequency of X-ray produced?
8.11 Electrons, accelerated in a vacuum to 10 keV, hit a block of tungsten over an
area of 0.2 square centimeters. What is the shortest wavelength of X-rays produced?
If the electron current is 100 mA, estimate the maximum intensity the X-rays could
have just outside the tungsten?
8.12 What is shortest wavelength x-ray which can be emitted by an x-ray tube
that employs Bremsstrahlung production if the electrons are accelerated toward the
target anode by a 20 kV electric potential?
8.13 If a dentist’s X-ray machine uses 15 kV across its X-ray tube, what is the
minimum wavelength of X-rays from that machine.
8.14 Suppose x-rays of a certain wavelength drop in intensity through bone with an
absorption coefficient of 15/cm. How thick would the bone have to be to cause the
x-ray intensity to diminish to 1/10th of it original value?
8.15 An electron in an atom of oxygen in the water of your tissue is hit by an x-ray
photon of wavelength of 0.014 nanometers. If the electron was bound in the oxygen
by 46 eV, how much kinetic energy will the electron gain after being ejected?
8.16 X-rays of wavelength 1.4 Å are reflected from a series of parallel Bragg planes
in a crystal of DNA. If the reflected waves add coherently at an angle of incidence
and reflection of 25 ◦ , what is the minimum separation between the planes?
8.17 If a Computed Tomography (CT) procedure delivered 850 mrem into a
patient’s abdomen of mass 6.4 kg and density 0.94 gm/cm 3 , estimate the amount
323
8.7 The UVB molar absorptivity of provitamin D3 (7-dehydrocholesterol) is shown
in a figure of this chapter. If your epidermis had no other absorbing compounds
except provitamin D3 at a concentration of 20 μm/L, what depth would UVB light
of wavelength 280 nm reach before dropping in intensity by 90%?
8.8 Look up the typical binding energy of the carbon-carbon bond in an organic
molecule (usually given in kilocalories per mole.). Convert from kilocalories per
mole to electron-volt per molecule. Calculate the frequency of the photon which
will have sufficient energy to break this chemical bond. Calculate the wavelength
for this frequency, in nanometers. Look up where in the electromagnetic spectrum
this wavelength occurs, i.e. what is the name of this type of radiation? Look up the
full range, in nanometers, of this type of radiation. Are there named subcategories
for this type of radiation? If so, what are their names? Electric arc welders can get
burns on their face from this radiation. Why? Which frequencies in this radiation
range are likely to cause the most severe burns?
8.9 What makes infrared light more useful to investigate organic molecules than
ultraviolet light?
8.10 If the electron current in an X-ray tube is 50 mA, accelerated by a 12 kV
potential, how much heat might be generated in the tungsten target? What is the
highest frequency of X-ray produced?
8.11 Electrons, accelerated in a vacuum to 10 keV, hit a block of tungsten over an
area of 0.2 square centimeters. What is the shortest wavelength of X-rays produced?
If the electron current is 100 mA, estimate the maximum intensity the X-rays could
have just outside the tungsten?
8.12 What is shortest wavelength x-ray which can be emitted by an x-ray tube
that employs Bremsstrahlung production if the electrons are accelerated toward the
target anode by a 20 kV electric potential?
8.13 If a dentist’s X-ray machine uses 15 kV across its X-ray tube, what is the
minimum wavelength of X-rays from that machine.
8.14 Suppose x-rays of a certain wavelength drop in intensity through bone with an
absorption coefficient of 15/cm. How thick would the bone have to be to cause the
x-ray intensity to diminish to 1/10th of it original value?
8.15 An electron in an atom of oxygen in the water of your tissue is hit by an x-ray
photon of wavelength of 0.014 nanometers. If the electron was bound in the oxygen
by 46 eV, how much kinetic energy will the electron gain after being ejected?
8.16 X-rays of wavelength 1.4 Å are reflected from a series of parallel Bragg planes
in a crystal of DNA. If the reflected waves add coherently at an angle of incidence
and reflection of 25 ◦ , what is the minimum separation between the planes?
8.17 If a Computed Tomography (CT) procedure delivered 850 mrem into a
patient’s abdomen of mass 6.4 kg and density 0.94 gm/cm 3 , estimate the amount