Half Life of Water

EXPERIMENT: Physics of the Atom

AIM: To investigate investigate if the half-life of water dripping from a !rette is constant"

T#E$R%: #alf-life &t'( is the time re)!ired for a )!antity to fall to half its val!e as meas!red at the the egi eginni nning ng of the the time time peri period od"" In physi physics cs** it is typi typical cally ly !sed !sed to desc descri rie e a prope propert rty y of radioactive decay* therefore radioactive half-life for a given radioisotope is a meas!re of the tendency of the n!cle!s to decay or disintegrate and s!ch is ased p!rely !pon that proaility" The half-life is independent of physical state &solid* li)!id or gas(* temperat!re* press!re* the chemical compo!nd in which the n!cle!s find itself and any other o!tside infl!ences" It is also independent of the chemistry of the atomic s!rface" The only thing that has an impact on the half-life of an o+ect is direct n!clear interaction with the particle from o!tside" E,ample: a high energy energy collisio collision n in an acceler accelerato ator" r" #alf-li #alf-life fe can e !sed !sed for estimati estimating ng the age of a dead dead organism" The amo!nt of caron-. in the atmosphere has not changed in tho!sands of years" Even tho!gh it decays deca ys into nitrogen* new caron-. is always eing formed when cosmic rays hit atoms high in the atmosphere" Plants asor caron dio,ide from the atmosphere and animals eat  plants" This means all living things have radioactive caron-. in them" /hen an organism* e"g" a tree* dies it stops ta0ing in caron dio,ide" The amo!nt of caron-. in the wood decreases with time as it decays into nitrogen with a half-life of ao!t 1233 years" 4y comparing how m!ch caron-. there is in the dead organism with the amo!nt in a living one* the age of the dead organism can e estimated"

APPARAT56: APPARAT56: 4!rette 4!re tte /ater  6topwatch 4ea0er 

7ARIA48E6: 9ontrolled: The speed at which the water flows* the amo!nt of water !sed for the two sets of readings* environmental conditions" E"g" wind* Manip!lated; 7ol!me of water  Responding: The time ta0en for every five cm< of water to decrease"

MET#$=: " The apparat!s was set !p as shown in the diagram with the !rette filled aove the 3cm< mar0" >" The tap was ad+!sted so that it is dripping )!ic0ly" <" /hen the water reached the 3cm< mar0" ." The time t was recorded at every 1cm< decrease in vol!me witho!t stopping the stopwatch" 1" The remaining vol!me of water 7 was recorded and the corresponding time noted on the stopwatch !ntil the vol!me remaining falls to 3cm<" ?" The method was repeated a second time witho!t ad+!sting the the flow of water or the tap"

4!rette

Resort 6tand

Tap &vertical: tap on( &#ori@ontal: tap off(

4ea0er  /ater dripping into  ea0er 

RE658T6: TA48E 6#$/IN T#E BIR6T REA=IN B$R T#E T$ATA8 TIME TACEN B$R /ATER  T$ =E9REA6E E7ER% 1 9M< IN 7$85ME 7ol!mecm<

Timesec

13"3

3"33

.1"3

<"&D(

.3"3

2"&D(

<1"3

>"&3(

<3"3

?"&<(

>1"3

>"&(

>3"3

>1"&D(

1"3

<"&3(

3"3


TA48E 6#$/IN T#E 6E9$N= REA=IN6 B$R T#E T$ATA8 TIME TACEN B$R  /ATER T$ =E9REA6E E7ER% 1 9M< IN 7$85ME 7ol!mecm<

Time

13"3

3"3

.1"3

<"&(

.3"3

2"&(

<1"3

>"&3(

<3"3

?"&1(

>1"3

>"&(

>3"3

>?"&3(

1"3

<"&<(

3"3

<2"&(

9A8958ATI$N6: Birst raph #alf-life from 13 F >-3 F>"3

#alf-life from .3 F >1"D-2"D FD"3

#alf-life from <3 F <"3-?"< F."2

6econd raph #alf-life from 13 F >"3 - 3"3 F>"3

#alf-life from .3 F >?"3 - 2"1 FD"1

#alf-life from <3 F <"< - ?"1 F."D

PRE9A5TI$N6: " The ottom of the menisc!s war read" >" The co!ntdown method was !sed to red!ce reaction time error"

<" B!ll attention was paid to the water levels at all time" ." "B!ll !nderstanding of how to operate the stopwatch was ac)!ired efore cond!cting the e,periment" 1" The water in the !rette was filled aove the @ero mar0 and thr stopwatch was started as the water flowing reached the 3 mar0 to otain a more acc!rate starting time" ?" The e,periment was carried o!t twice to ens!re that the readings were acc!rate" 2" 4efore cond!cting the e,periment* all apparat!s was chec0ed for systematic errors"

6$5R9E6 $B ERR$R6: " The !rette was not 33G vertically straight which wo!ld have ca!se a slight inacc!rate in readings >" Reaction time error wo!ld still e involved altho!gh the co!ntdown method was !sed" <" As the water level in the !rette decreased* the speed at which the water flowed decreased" ." It was hard to lap the times eca!se of the small lap !tton on the stop watch !sed on the  phone"

=I69566I$N: The res!lts of this e,periment is random meaning that it wo!ld vary every time the e,periment is cond!cted* therefore if another classmate is to cond!ct the same e,periment* they wo!ld not otain the res!lts as seen in the tales"" Radioactive decay* also 0nown as n!clear  decay or radioactivity* is the process y which a n!cle!s of an !nstale atom loses energy y emitting particles of ioni@ing radiation" Radioactive decay is a random process at the level of  single atoms* in that* according to )!ant!m theory* it is impossile to predict when a partic!lar  atom will decay" #owever !nderstand and characteri@e the decay of radion!clides on the asis of  statistical analysis" $nly y loo0ing at a large n!mer of atoms of a given isotope of a given element and co!nting the decay events over time can we )!antify the decay rate" This is what the term half-life is !sed to state* ased on the statistics* when half of a given )!antity of a s!stance will have !ndergone radioactive decay" After calc!lating the time ta0en for the vol!me to fall to half for several different val!es of vol!me* the res!lt shows that the half-life was not constant" The val!es were >"3* D"3 and ."2 from the first graph and >"3* D"1 and ."D in the second graph"  This e,periment was an en+oyale e,periment and a s!ccessf!l one" #owever* improvement co!ld have een made" These improvements incl!de:

" >" <" ."

5se an easier stop watch with a igger lap !tton 5se a straighter resort stand" Ta0e practice in carrying o!t the e,periment efore act!ally doing the e,periment" Ens!re that the speed at which the water was flowing is easy to 0eep a time record

9$N9856I$N: /ithin the limits of e,perimental error* the half-life dripping from a !rette was fo!nd not to e constant"