The games in order are Half-Life, Half-Life 2, Episode 1, then Episode 2. There are expansions for the original Half-Life (like Blue-Shift and Opposing Force), but those aren't technically canon. There is also Portal, which seems to take place between HL and HL2. Compare deals for a Half-Life 2 key from our verified stores! We currently have 30 key offers across 9 stores. Pick the best deal from our list of trusted & legitimate stores we verify and check daily. All 30 deals are backed by legitimate store guarantees, so there is nothing to worry about for you. Check our 30 cheap deals, buy from quality stores and start gaming within minutes!
Skills to Develop
- To define half-life.
- To determine the amount of radioactive substance remaining after a given number of half-lives.
Whether or not a given isotope is radioactive is a characteristic of that particular isotope. Some isotopes are stable indefinitely, while others are radioactive and decay through a characteristic form of emission. As time passes, less and less of the radioactive isotope will be present, and the level of radioactivity decreases. An interesting and useful aspect of radioactive decay is the half-life. The half-life of a radioactive isotope is the amount of time it takes for one-half of the radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by conditions and is independent of the initial amount of that isotope.
Consider the following example. Suppose we have 100.0 g of 3H (tritium, a radioactive isotope of hydrogen). It has a half-life of 12.3 y. After 12.3 y, half of the sample will have decayed to 3He by emitting a beta particle, so that only 50.0 g of the original 3H remains. After another 12.3 y—making a total of 24.6 y—another half of the remaining 3H will have decayed, leaving 25.0 g of 3H. After another 12.3 y—now a total of 36.9 y—another half of the remaining 3H will have decayed, leaving 12.5 g of 3H. This sequence of events is illustrated in Figure (PageIndex{1}).
We can determine the amount of a radioactive isotope remaining after a given number half-lives by using the following expression:
[mathrm{amount: remaining=initial: amounttimes left ( dfrac{1}{2} right )^n} label{Eq1}]
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where n is the number of half-lives. This expression works even if the number of half-lives is not a whole number.
Example (PageIndex{1}): Fluorine-20
The half-life of 20F is 11.0 s. If a sample initially contains 5.00 g of 20F, how much 20F remains after 44.0 s?
SOLUTION
If we compare the time that has passed to the isotope’s half-life, we note that 44.0 s is exactly 4 half-lives, so we can use Equation ref{E1} with (n = 4). Substituting and solving results in the following:
[ begin{align*} mathrm{amount: remaining} &=5.00: g times left(dfrac{1}{2}right)^4 [4pt] &=5.00: g times dfrac{1}{16} [4pt] &=0.313: g end{align*}]
Less than one-third of a gram of 20F remains.
Exercise (PageIndex{1}): Titanium-44
The half-life of 44Ti is 60.0 y. A sample initially contains 0.600 g of 44Ti. How much 44Ti remains after 180.0 y?
0.075 g.
Half-lives of isotopes range from fractions of a microsecond to billions of years. Table (PageIndex{1}) lists the half-lives of some isotopes.
| Isotope | Half-Life |
|---|---|
| 3H | 12.3 y |
| 14C | 5,730 y |
| 40K | 1.26 × 109 y |
| 51Cr | 27.70 d |
| 90Sr | 29.1 y |
| 131I | 8.04 d |
| 222Rn | 3.823 d |
| 235U | 7.04 × 108 y |
| 238U | 4.47 × 109 y |
| 241Am | 432.7 y |
| 248Bk | 23.7 h |
| 260Sg | 4 ms |
Example (PageIndex{2}): Iodine-125
The isotope (ce{I})-125 is used in certain laboratory procedures and has a half-life of 59.4 days. If the initial activity of a sample of (ce{I})-125 is (32,000 : text{counts per minute (cpm)}), how much activity will be present in 178.2 days?
Solution
We begin by determining how many half-lives are represented by 178.2 days:
[dfrac{178.2 : text{days}}{59.4 : text{days/half-life}} = 3 : text{half-lives} nonumber]
Then we simply count activity:
[begin{align} text{initial activity} : left( t_0 right) &= 32,000 : text{cpm} nonumber text{after one half-life} : &= 16,000 : text{cpm} nonumber text{after two half-lives} : &= 8,000 : text{cpm} nonumber text{after three half-lives} &= 4,000 : text{cpm} nonumber end{align} nonumber]
Be sure to keep in mind that the initial count is at time zero (left( t_0 right)) and we subtract from that count at the first half-life. The second half-life has an activity of half the previous count (not the initial count).
Equation (ref{Eq1}) can be used to calculate the amount of radioactivity remaining after a given time:
[N_t = N_0 times left( 0.5 right)^text{number of half-lives} nonumber]
where (N_t =) activity at time (t) and (N_0 =) initial activity at time (t = 0).
If we have an initial activity of (42,000 : text{cpm}), what will the activity be after four half-lives?
[begin{align} N_t &= N_0 left( 0.5 right)^4 nonumber &= left( 42,000 right) left( 0.5 right) left( 0.5 right) left( 0.5 right) left( 0.5 right) nonumber &= 2625 : text{cpm} nonumber end{align} nonumber]
Typical radioactive decay curve.
The graph above illustrates a typical decay curve for (ce{I}-125). The activity decreases by one-half during each succeeding half-life.
Looking Closer: Half-Lives of Radioactive Elements
Many people think that the half-life of a radioactive element represents the amount of time an element is radioactive. In fact, it is the time required for half—not all—of the element to decay radioactively. Occasionally, however, the daughter element is also radioactive, so its radioactivity must also be considered.
The expected working life of an ionization-type smoke detector (described in the opening essay) is about 10 years. In that time, americium-241, which has a half-life of about 432 y, loses less than 4% of its radioactivity. A half-life of 432 y may seem long to us, but it is not very long as half-lives go. Uranium-238, the most common isotope of uranium, has a half-life of about 4.5 × 109 y, while thorium-232 has a half-life of 14 × 109 y.
On the other hand, some nuclei have extremely short half-lives, presenting challenges to the scientists who study them. The longest-lived isotope of lawrencium, 262Lr, has a half-life of 3.6 h, while the shortest-lived isotope of lawrencium, 252Lr, has a half-life of 0.36 s. As of this writing, the largest atom ever detected has atomic number 118, mass number 293, and a half-life of 120 ns. Can you imagine how quickly an experiment must be done to determine the properties of elements that exist for so short a time?
Key Takeaways
- Natural radioactive processes are characterized by a half-life, the time it takes for half of the material to decay radioactively.
- The amount of material left over after a certain number of half-lives can be easily calculated.
Concept Review Exercises
- Define half-life.
- Describe a way to determine the amount of radioactive isotope remaining after a given number of half-lives.
Answers
- Half-life is the amount of time needed for half of a radioactive material to decay.
- take half of the initial amount for each half-life of time elapsed
EXERCISES
1. Do all isotopes have a half-life? Explain.
2. Which is more radioactive—an isotope with a long half-life or an isotope with a short half-life?
3. What percent of a sample remains after one half-life? Three half-lives?
4. The half-life of polonium-218 is 3.0 min. How much of a 0.540 mg sample would remain after 9.0 minutes have passed?
5. The half-life of protactinium-234 is 6.69 hours. If a 0.812 mg sample of Pa-234 decays for 40.14 hours, what mass of the isotope remains?
6. The half life of Carbon-14 is 5730 years. Determine the time it takes for 100. mg of carbon-14 to decay to 6.25 mg.
7. How long does it take for 1.00 g of 103Pd to decay to 0.125 g if its half-life is 17.0 d?
8. A radioisotope decays from 55.9 g to 6.99 g over a period of 72.5 hours. What is the half-life of the isotope?
9. It took 75 y for 10.0 g of a radioactive isotope to decay to 1.25 g. What is the half-life of this isotope?
ANSWERS
1. Only radioactive isotopes have half-lives.
2. An isotope with a shorter half-life decay more rapidly is more radioactive
3. 1 half-life: 50%; 3 half-lives: 12.5%
4. 9.0 min = 3 half-lives (make 3 arrows): 0.540 mg --> 0.270 mg --> 0.135 mg --> 0.0675 mg
5. 0.0127 mg
6. 22,920 years
7. 51.0 d
8. It takes three half-lives to go from 55.9 g to 6.99 g in a total time of 72.5 hours. 72.5hr÷3=24.2hr. One half-life is 24.2 hours.
9. 25 y
Half Life 2 The Orange Box MULTi18-ElAmigos Free Download skidrow codex PC Game direct link. Half Life 2 The Orange Box MULTi18-ElAmigos was published on Friday, 12 March 2021 12:35:26 PM
About The Game
1998. HALF-LIFE sends a shock through the game industry with its combination of pounding action and continuous, immersive storytelling. Valves debut title wins more than 50 game-of-the-year awards on its way to being named Best PC Game Ever by PC Gamer, and launches a franchise with more than eight million retail units sold worldwide.
NOW. By taking the suspense, challenge and visceral charge of the original, and adding startling new realism and responsiveness, Half-Life 2 opens the door to a world where the players presence affects everything around him, from the physical environment to the behaviors even the emotions of both friends and enemies.
The player again picks up the crowbar of research scientist Gordon Freeman, who finds himself on an alien-infested Earth being picked to the bone, its resources depleted, its populace dwindling. Freeman is thrust into the unenviable role of rescuing the world from the wrong he unleashed back at Black Mesa. And a lot of people he cares about are counting on him.
The intense, real-time gameplay of Half-Life 2 is made possible only by Source®, Valves new proprietary engine technology. Source provides major enhancements in:
- Characters: Advanced facial animation system delivers the most sophisticated in-game characters ever seen. With 40 distinct facial muscles, human characters convey the full array of human emotion, and respond to the player with fluidity and intelligence.
- Physics: From pebbles to water to 2-ton trucks respond as expected, as they obey the laws of mass, friction, gravity, and buoyancy.
- Graphics: Sources shader-based renderer, like the one used at Pixar to create movies such as Toy Story® and Monsters, Inc.®, creates the most beautiful and realistic environments ever seen in a video game.
- AI: Neither friends nor enemies charge blindly into the fray. They can assess threats, navigate tricky terrain, and fashion weapons from whatever is at hand.
Game Title: Half-Life 2 THE ORANGE BOX
Store Page:https://store.steampowered.com/sub/469/
Genres: Action
Developers: Valve
Publisher: Valve
Release date: 10 Oct, 2007
Half Life 2 The Orange Box MULTi18-ElAmigos
SIZE: 5.85 GB
Compilation of five games:
Half-Life 2
Half-Life 2: Episode One
Half-Life 2: Episode Two
Portal
Team Fortress 2
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