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1.&\multicolumn{2}{l}{What is the photon energy range corresponding to the UV radiation band?}\\[5pt]
2.&\multicolumn{2}{l}{The following set of count readings was made in a gradient-free
 $\gamma$-ray field, using
a suitable detector for repetitive time periods of one minute: 18.500; 18,410;
18,250; 18,760; 18,600; 18,220; 18,540; 18,270; 18,670; 18,540}\\
&(a)&What is the mean value of the number of counts?\\
&(b)&What is its standard deviation (S.D.)?\\
&(c)&What is the theoretical minimum S.D. of the mean?\\
&(d)&What is the actual S.D. of a single reading?\\
&(e)&What is the theoretical minimum S.D. of a single reading?\\[5pt]
3.&\multicolumn{2}{l}{A broad plane-parallel beam ofelectrons is perpendicularly incident upon a thin
foil which scatters the electrons through an average angle of $20\,^{\circ}$, stopping none
of them.}\\
&(a)&What is the ratio of the flux density of primary electrons just behind the
foil to that with the foil removed?\\
&(b)&What is the ratio of the number of electrons per cm$^2$ passing through a
plane just behind (and parallel to) the foil to that with the foil removed?\\[5pt]
4.&\multicolumn{2}{l}{The flux density decreases with increasing distance from a point source of rays
as the inverse square of the distance. The strength of the electric field surrounding
a point electric charge does likewise. At a point midway between two
identical charges the electric field is zero.}\\
&(a)&What is the flux density midway between two identical sources?\\
&(b)&What is the essential difference between the two cases?\\[5pt]
5.&\multicolumn{2}{l}{A point source of ${}^{60}_{\phantom{1}}\text{Co}$ gamma rays emits equal numbers of photons of $1.17$ and
$1.33$ MeV, giving a flux density of $5.7 \times 10^9$ photons/cm$^2$ sec at a specified
location. What is the energy flux density there, expressed in erg/cm$^2$ sec and
in J/m$^2$ min?}\\[5pt]
6.&\multicolumn{2}{l}{In problem $5$, what is the energy fluence of $1.17$-MeV photons during 24 hours,
in erg/cm$^2$ and J/m$^2$?}\\
7.&\multicolumn{2}{l}{A point source isotropically emitting $10^8$ fast neutrons per second falls out of
its shield onto a railroad platform $3$ m horizontally from the track. A train goes
by at 60 miles per hour. Ignoring scattering and attenuation, what is the fluence
of neutrons that would strike a passenger at the same height above the track
as the source?}\\[5pt]
8.&\multicolumn{2}{l}{An x-ray field at a point Pcontains $7.5 \times 10^8$ photons/m$^2$-sec-keV, uniformly
distributed from $10$ to $100$ keV.}\\
&(a)&What is the photon flux density at $P$?\\
&(b)&What would be the photon fluence in one hour?\\[5pt]
&(c)&What is the corresponding energy fluence, in J/m$^2$ and erg/cm$^2$?\\
9.&\multicolumn{2}{l}{Show that, for a spherical volume, Chilton's definition of fluence gives the same
value as the conventional definition in a uniform monoenergetic field. \emph{Hint}: The
mean chord length in any convex volume is $4V/S$, where $V$ is the volume and
$S$ is the surface area.}\\

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${}^{60}_{\phantom{5}18}\text{Co}$


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