Physics 736. Experimental Methods in Nuclear-, Particle-, and Astrophysics

Transcription

1 Physics 736 Experimental Methods in Nuclear-, Particle-, and Astrophysics - Passage of Particles & Radiation Through Matter - Karsten Heeger heeger@wisc.edu

2 Class Schedule & Course Website Course website

3 Review of Last Lecture Calorimeter Principle - what are the relevant quantities? - how is the T rise determined? - how is the relaxation time determined?

4 Review of Last Lecture Calorimeter Principle - what are the relevant quantities? - how is the T rise determined? - how is the relaxation time determined?

5 Interaction of Charged Particles characteristic features energy loss deflection of particles from incident direction classes of particles e +,e - heavy particles: μ, π, p, α primary processes inelastic collisions elastic scattering

6 Cherenkov Counters

7 Review of Last Lecture What is stopping power? S(E) = de dx

8 Stopping Power Bethe-Bloch At low β -de/dx 1/β 2 decreases rapidly as β increases. reaches a min at βγ 3 (a particle at the energy loss min is called mip). typically de/dx depends only on β (given a particle and medium)

9 Stopping Power Bethe-Bloch for particles below minimum ionizing energies de/dx lor l03 Energy ['lev] ro5 low momentum region where -de/dx 1/β 2 and the relativistic rise depend on m so can be used for particle identification (PID)

10 Bremsstrahlung

11 Collision vs Radiation Loss collision loss radiation loss de dx Z A 1 β 2 [ln(energy)] de dx EZ2

12 Collision vs Radiation Loss? ql o a x l0' tt UJ o Bremsstrohlung loss :.:.:.:.:.:.;.:.;.;. lo3 Energy [Mev] critical energy (de dx ) rad = ( de dx ) coll E c 800 MeV Z +1.2

13 Collision vs Radiation Loss stopping power for muons in copper? ql o a x l0' tt UJ o Bremsstrohlung loss :.:.:.:.:.:.;.:.;.;. lo3 Energy [Mev]

14 Critical Energies Trblc 2.2. Critical cneryb of ronc matcrials Matcrirl Pb AI Fe Cu Air (STP) Lucitc Polyrtyrcnc NrI Anthrtcme Hp Critical cncrgy tmcu 9.5t lv2 tm r09 t7.1 rqt 92

15 Radiation Length radiation length - mean distance over which a high-energy electron loses all but 1/e of its energy by bremsstrahlung - 7/9 of the mean free path for pair production by a high-energy photon L rad = 716.4A Z(Z +1)ln(287/ Z) g/cm 2

16 Range and Absorption of Electrons straggling range for electrons < range number-distance curves for electrons absorption of beta electrons gtcmz I = I 0 e µx

17 Radiation Energy Loss high-energy limit E = E 0 e x L rad exponential energy loss radiation length L rad = 716.4A Z(Z +1)ln(287/ Z) de dt E 0 radiation energy loss is independent of material type t = distance in Lrad

18 Exercise Question (2 min group exercise) You want to measure a particle s mass. Which physical processes are most useful and why? ionization (energy deposited) Cherenkov Bremsstrahlung Compton scattering Discuss pros and cons for 2min and then let s discuss it

19 Multiple Coulomb Scattering Rutherford Experiment

20 Multiple Coulomb Scattering data and approximation J o 0 o 0O3 o a r 3 o o O02 g 2 o E 00r o '- o d Goussion \l t'l T\I Gaussian small-angle approximation single, large-angle Coulomb scattering tail 0 Scott?rirB ongle [dcarcs]

21 Multiple Coulomb Scattering Backscattering of low-energy electrons 0.3 Absorber backscattering coeff r 0.3 o.2 0l AU A9 Fig. 2.16, Backscattering of electrons duc to large angle multiple scatterings 0 I 0l t r [ucv] r energy [ucv] Fig Some measured electron backscattering coefficients for various materials. The elcclrons are pcrpcndicularly incident on the surface of the sample (from Tobata ct d )

22 Energy Loss & Energy Straggling Central Limit Theorem sum of N random variables all following the same statistical distribution approaches that of a Gaussian-distributed variable in the limit N random variable = δe = energy loss in single atomic collision total E loss = sum of many independent δe, all commonly distributed for sufficient number of collisions N the total will be of Gaussian form

23 Energy Loss Distribution - Thin Absorbers Pulse herghi, orbrirory unrts = o v o o a o - VOvilOv lheory --- Symon lhaory + Erperim nlol points o a E C o U e o : o c o I! o e 5 a probobte Meon energy energy loss loss (! 8,o r0n3040 EnergYtoss I xev]

24 Radiation Protection & Doses

25 Radiation Doses - equivalent dose Radiation Weighing Factor to normalize measure of biological effect trl 3.2. Radiation weighting factors [3.2] Hiation type and energy Radiation weighting factor, w* tlcons, all cnergies Ectrons and muons, all energiest lbtrons < t0kcv 5 l0kev to lookev t0 > 100 kev to 2 McV 20 >2MeV to 20MeV l0 >20 MeV 5 hotons, other than recoil protons, energy>2mev 5 o-grrticles, fission fragmcnts, heavy nuclei 20 'Ercluding Auger electrons emitted from nuctei bound to DNA 1 Sv of alphas has same effect as 1 Sv of gamma rays

26 Radiation Doses - effective dose Tissue Weighing Factor Trblc 3.3. Tissue wcighting factors [3.21 Tissuc or organ Gonads Bone marrow Colon Lung Stomach Bladdcr Breast Livcr Oesophagus Thyroid Skin Bone surfacc Rcmainder Tissue weighting factor, ry t o.t t

27 Radiation Doses fl Estimatcs of cffective doses from some common sources Average dose per person (msv/yr) World population [3.3] usa t3.41 Germany [3.5] kural sources Overall Comic rays Tcrrcstial bhalcd radon Environmental sources Nwlcar powcr Beggage chcck at airport Subsonic airplane flight at 8000m Medicol exposures Diagnosis (c.9. t chest x-ray) Occupational I 0.@ o 0. I t.6? nsv/trip 2 psv/hr mSv/x-ray 0.r r.5

28 Radiation Dose and Risks Tcble 3,7. Risk of radiation-induced cancer [3.41 Radiation exposure Excess fatal cancers (per td persons cxposed) Single, brief exposure to 0. I Sv 790 Continuous lifetime exposure to I msv/yr 560 Continuous exposure to 0,0t Sv/yr from age le until age

29 Radiation Dose and Risks Irblc 3.t. Comparison of risk from radiation with risk from other occupations.normal tife expectancy is rrlen as 73 years. (from [3.6]) Occuparion 010 Sv (typical dose of radiation workcr in rescarch lab after 47 yrs, i.e. from age 18 until 65) C-5 Sv (typical dose of worker in nuclear power plant after 47 yrs) a3j Sv Tndc Scrvice industries Tnnsportation and public utilities Off-thc-job accidcnts C.onstruction Iiaing and quarrying Averagc loss of lifc expectancy (months) 0.4 I 5 I t r0 It

30 Radiation Shielding What materials would you use for shielding the following radiation types? gamma rays electrons positrons heavy charged particles neutrons

31 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

32 Pair Production Cross-Section τ pair 4Z 2 αr 2 e [ 7 9 ln(...)... ] pair production cross-section higher for high-z materials λ pair 9 7 L rad

33 Radiation Length radiation length - mean distance over which a high-energy electron loses all but 1/e of its energy by bremsstrahlung - 7/9 of the mean free path for pair production by a high-energy photon L rad = 716.4A Z(Z +1)ln(287/ Z) g/cm 2

34 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

35 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

36 Collision vs Radiation Loss collision loss radiation loss de dx Z A 1 β 2 [ln(energy)] de dx EZ2

37 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

38 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

39 Stopping Power Bethe-Bloch - # = 2 n N^ r! ^, " p + il^ (ry^) -' P with density and shell corrections G de dx higher de/dx for denser materials typically de/dx depends only on β (given a particle and medium)

40 Stopping Power Bethe-Bloch For a given particle (z) and target (I,N,Z,A), the energy loss depends only on the velocity of the particle! higher de/dx for denser materials

41 Radiation Shielding Table Shielding materials for various radiations Radiation Gamma-rays Electrons Positrons Charged particles Neutrons Shielding High-Z material, e.g. Pb Low-Z materials, e.g., polystyrene or lucitc. High-Z material should be avoided because of bremsstrahlung production, For intense electron sources, a double layer shield consisting of an inner layer of low-z matcrial followed by a layer of Pb (or some other high-z material) to absorb bremsstrahlung should bc used. Thc inner layer should, of coursc, be sufficiently thick lo stop the electrons while the outer layer should provide sufficient attenuation of bremsstrahlung. High-Z material. Since the stopping of positrons is always accompanied by annihilation radiation, the shield should be designed for absorbing this radiation. A double layer design, here, is usually not n cessary. High density materials in order to maximizn de/dx Hydrogenous material such as water or paraffin. As for electrons, this shielding should also be followed by a layer of Pb or other high-z material in ordcr to absorb y's from neutron capture reactions.

42 Interaction of Neutrons Neutron Moderators neutron cross-section neutron energy distribution after several elastic scatterings 6 (t,4,.9 u c, o o Hro '-"--i_-_pn'f3!_ pnotons \- \ 6 p lcrl t t0- lo-r Energy [Mev] tol original monoenergetic neutron - average lethargy change is constant - greatest delta E from early collisions

43 Shielding in Accelerator Labs shielding personnel from experiment s radioactivity

44 Shielding in Low-Background Experiments shielding the experiment from environmental radioactivity

45 Shielding in Low-Background Experiments shielding the experiment from environmental radioactivity low-background lead that is less radioactive due to missing cosmic activation (2000 yrs at bottom of sea)

46 Karsten Heeger, Univ. of Wisconsin NUSS, July 13, 2009

47 Karsten Heeger, Univ. of Wisconsin NUSS, July 13, 2009