# 30.5 Half-life and activity  (Page 7/16)

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A ${}^{\text{60}}\text{Co}$ source is labeled 4.00 mCi, but its present activity is found to be $1\text{.}\text{85}×{\text{10}}^{7}$ Bq. (a) What is the present activity in mCi? (b) How long ago did it actually have a 4.00-mCi activity?

(a) Calculate the activity $R$ in curies of 1.00 g of ${}^{\text{226}}\text{Ra}$ . (b) Discuss why your answer is not exactly 1.00 Ci, given that the curie was originally supposed to be exactly the activity of a gram of radium.

(a) 0.988 Ci

(b) The half-life of ${}^{\text{226}}\text{Ra}$ is now better known.

Show that the activity of the ${}^{\text{14}}\text{C}$ in 1.00 g of ${}^{\text{12}}\text{C}$ found in living tissue is 0.250 Bq.

Mantles for gas lanterns contain thorium, because it forms an oxide that can survive being heated to incandescence for long periods of time. Natural thorium is almost 100% ${}^{\text{232}}\text{Th}$ , with a half-life of $1\text{.}\text{405}×{\text{10}}^{\text{10}}\phantom{\rule{0.25em}{0ex}}\text{y}$ . If an average lantern mantle contains 300 mg of thorium, what is its activity?

$1.22×{\text{10}}^{3}\phantom{\rule{0.25em}{0ex}}\text{Bq}$

Cow’s milk produced near nuclear reactors can be tested for as little as 1.00 pCi of ${}^{\text{131}}\text{I}$ per liter, to check for possible reactor leakage. What mass of ${}^{\text{131}}\text{I}$ has this activity?

(a) Natural potassium contains ${}^{\text{40}}\text{K}$ , which has a half-life of $1\text{.}\text{277}×{\text{10}}^{9}$ y. What mass of ${}^{\text{40}}\text{K}$ in a person would have a decay rate of 4140 Bq? (b) What is the fraction of ${}^{\text{40}}\text{K}$ in natural potassium, given that the person has 140 g in his body? (These numbers are typical for a 70-kg adult.)

(a) 16.0 mg

(b) 0.0114%

There is more than one isotope of natural uranium. If a researcher isolates 1.00 mg of the relatively scarce ${}^{\text{235}}\text{U}$ and finds this mass to have an activity of 80.0 Bq, what is its half-life in years?

${}^{\text{50}}\text{V}$ has one of the longest known radioactive half-lives. In a difficult experiment, a researcher found that the activity of 1.00 kg of ${}^{\text{50}}\text{V}$ is 1.75 Bq. What is the half-life in years?

$1.48×{\text{10}}^{\text{17}}\phantom{\rule{0.25em}{0ex}}\text{y}$

You can sometimes find deep red crystal vases in antique stores, called uranium glass because their color was produced by doping the glass with uranium. Look up the natural isotopes of uranium and their half-lives, and calculate the activity of such a vase assuming it has 2.00 g of uranium in it. Neglect the activity of any daughter nuclides.

A tree falls in a forest. How many years must pass before the ${}^{\text{14}}\text{C}$ activity in 1.00 g of the tree’s carbon drops to 1.00 decay per hour?

$5.6×{\text{10}}^{4}\phantom{\rule{0.25em}{0ex}}y$

What fraction of the ${}^{\text{40}}\text{K}$ that was on Earth when it formed $4\text{.}5×{\text{10}}^{9}$ years ago is left today?

A 5000-Ci ${}^{\text{60}}\text{Co}$ source used for cancer therapy is considered too weak to be useful when its activity falls to 3500 Ci. How long after its manufacture does this happen?

2.71 y

Natural uranium is 0.7200% ${}^{\text{235}}\text{U}$ and 99.27% ${}^{\text{238}}\text{U}$ . What were the percentages of ${}^{\text{235}}\text{U}$ and ${}^{\text{238}}\text{U}$ in natural uranium when Earth formed $4\text{.}5×{\text{10}}^{9}$ years ago?

The ${\beta }^{-}$ particles emitted in the decay of ${}^{3}\text{H}$ (tritium) interact with matter to create light in a glow-in-the-dark exit sign. At the time of manufacture, such a sign contains 15.0 Ci of ${}^{3}\text{H}$ . (a) What is the mass of the tritium? (b) What is its activity 5.00 y after manufacture?

(a) 1.56 mg

(b) 11.3 Ci

World War II aircraft had instruments with glowing radium-painted dials (see [link] ). The activity of one such instrument was $1.0×{\text{10}}^{5}$ Bq when new. (a) What mass of ${}^{\text{226}}\text{Ra}$ was present? (b) After some years, the phosphors on the dials deteriorated chemically, but the radium did not escape. What is the activity of this instrument 57.0 years after it was made?

Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
how did you get the value of 2000N.What calculations are needed to arrive at it
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