Topics in Science Research
Project Leader: Bruno Serfass
Members: Perry Francois-Edwards
Jose Martinez
Kadeem Palacios
Matthew Constantino
Calorimetry
Our overall project objective was to study how we use calorimetry to detect the
energy that a dark matter particle would deposit inside our calorimeter. We used ordinary
particles from a radioactive source to demonstrate this measurement. The existence of
dark matter can be proven by looking at objects such as stars or galaxies revolving
around certain areas. The content that we can detect in these areas have far too little mass
to create gravity that would make objects revolve around it. We can assume that these
areas have extra matter that provides the needed gravity: dark matter. It is “dark” because
it is matter that we cannot see or detect with the technology that we currently have. In
order to understand how to detect dark matter, we must understand calorimetry.
During the last two and one half weeks, we learned about heat capacity, heat
conductivity, and calorimetry. Heat capacity is the ratio of heat absorbed by a substance
to the substance’s increase in temperature. Heat conductivity is the rate at which thermal
(heat) energy that can flow through a substance at a higher or lower temperature.
Calorimetry is the measurement of the amount of heat absorbed in a chemical reaction,
change of state, or form of a solution. We conducted four experiments to understand the
concepts of heat capacity, heat conductivity, and calorimetry.
First Experiment
The first experiment we performed involved the concept of heat conductivity. The
purpose of this experiment is to test and find out which metal out of those available
would conduct heat most effectively. The following metals were used in this experiment:
Copper, Aluminum, Brass, and Lead. Each rod of metal conducts heat at a different rate.
We used a Bunsen burner as a steam boiler to heat the bottom of the rods at the same
time at the same rate. We tracked the temperature by hooking up thermometers on the top
of the rods and connected them to a laptop that makes a spreadsheet telling us the
difference in temperature. The copper’s temperature raised highest and fastest which
means that the heat moved to the top faster than all of the other metals. This shows that
the copper had the highest heat conductivity.
Second Experiment
The second experiment we did involved using the concept of heat capacity. Heat
capacity is the mass times the specific heat, which is defined as the amount of heat
needed to change 1 gram of a substance’s temperature by 1°C. The purpose of this
experiment is to test which of the five materials has the highest heat capacity. The five
substances, of the same volume, we tested on were lead, glass, zinc, brass and iron. The
way this experiment works is we heat up all test substances to 100°C. Then we release
the balls onto a sheet of paraffin. Whichever substance melts through first has the most
heat capacity. Each ball has a different mass and specific heat so therefore each have a
different heat capacity. When we dropped the balls on the paraffin, we noticed that iron
made it through the paraffin first. Zinc and brass made it halfway. The rest of the metals
barely melted any of the paraffin at all. From this, we drew the conclusion that iron had
the highest heat capacity out of those substances tested. One thing to note is that some
balls had high mass but low specific heats so they didn’t fall through and vice versa.
Third Experiment
In another experiment, we used a small-scale calorimeter. A calorimeter isolates
an object from emitting any heat to other non-measurable sources such as the air. The
object is submerged in isolated water as to allow the heat to be transferred there. The
temperature of the water is now measured as to see how much energy was transferred
from the object to the water.
The objective for this experiment was to find the energy that was transferred into
the brass based on the change in temperature of the water by using this formula:
q= mc(T2-T1)
 q is the energy that is being transferred
 m is the substance’s mass
 c is the specific heat which is the amount of heat needed to change the substance’s
temperature by 1 degree
 T2-T1 is the change in temperature
A calorimeter is shaped like a large can filled with water and layered with a type
of pottery material that keeps heat from being transferred from the water inside to any
outside source. The object we were trying to measure is a brass cylinder. The brass was
suspended on a string and submerged in the water inside the calorimeter, not touching the
inside walls of the calorimeter. We tried to measure and compare the temperature of the
brass and only the water the brass was touching. However this proved too difficult
considering the size of the brass compared to the area in which it was placed. The
thermometer for the water only had touched both the brass and the inside of the
calorimeter. Its not supposed to do that. Unfortunately there was no way we could
accurately do this and this experiment was deemed unsuccessful.
Fourth Experiment
The formula above can be rearranged to show what the change in temperature
depends on:
T2-T1= q/mc
When we tried to find the change in temperature involving a particle with very low
energy (10 keV), we found the change way too small to be accurately measured. Thus the
only way you can make the measurement more reasonable is to cool the substance down
to a very low temperature. When you lower the temperature, you lower the specific heat
(c). The specific heat is one of the dividers besides mass (m). If you lower the divider, the
quotient will be larger and can be more accurately measured.
In our fourth and final experiment, we used a huge fridge that uses liquid helium
and a mixture of He3 and He4 gas to lower the temperature of the calorimeter. The
absorber of the calorimeter (a germanium crystal) is connected to the fridge using copper
links, which as shown in the first experiment, has a high conductivity.
The objective of this experiment is to record the energy that is transferred into the
calorimeter by a particle when it collides with the germanium crystal.
The substance that we are trying to measure is a small particle instead of brass. A
radioactive source will shoot particles through the germanium crystal. The particles will
collide with the atoms in the crystal. When they collide, they leave energy in the form of
vibrations. Just like the water, the crystal absorbs the energy but his time as vibrations
instead of heat. We measure these vibrations or pulses or events just like the change in
temperature.
The events are recorded in under a second since these pulses appear very rapidly.
They go up and immediately go down because the entire area is being put at a very low
temperature by the helium bath. The vibrations are slowed down immediately after
occurring due to the low temperature.
We hope to use calorimetry to find the energy of a dark matter particle when it
hits a germanium crystal deep underground. It’s underground because it is mostly
isolated from all other particles that won’t interfere with the germanium crystal.