Neutron Interactions Part II - uthgsbsmedphys.org Neutron Lecture 02 200… · Neutron Interactions...

MPMP--6407: Radiation Biology Fall 20056407: Radiation Biology Fall 2005Rebecca M Howell Ph DRebecca M Howell Ph D

Neutron Interactions Part II

Rebecca M. Howell, Ph.D.Radiation Physics

[email protected]

mailto:[email protected]

Clarification from neutron lecture 1• Elastic denotes a reaction in which incident

projectile scatters off target nucleus with total KE being conserved (final nucleus is the same as bombarded nucleus).

• Non-elastic is a general term referring to nuclear reaction that are not elastic (i.e. KE is not conserved).

• Inelastic refers to specific type of non-elastic reaction in which KE not conserved, but final nucleus is the same as bombarded nucleus.

ICRU Report 63

November 2007 November 2007 Rebecca M. Howell, Ph.D.Rebecca M. Howell, Ph.D.

Why do we as Medical Physicists care about neutrons?

• Neutrons in Radiation Therapy• Neutron Therapy

• Fast Neutron Therapy• Boron Neutron Capture Therapy

• Contamination Neutrons in X-Ray Therapy• Contamination Neutrons in Proton Therapy

• Neutron Shielding• Neutron Dose


Neutrons in Radiotherapy

• Fast Neutron Therapy Beams• Boron Neutron Capture Therapy• History and Current Facilities• Treatment sites


Fast Neutrons Methods of Production

• Neutrons can be produced in a cyclotron by accelerating deuterons or protons and impinging them on a beryllium target.

• Protons or deuterons must be accelerated to ≥50 MeV to produce neutron beams with penetration comparable to megavoltage x- rays.


Fast Neutrons Methods of Production

• Accelerating deuterons to ≥50MeV• Requires very large

cyclotron, too large for hospital.

• Accelerating protons to ≥50MeV• Much smaller cyclotron

b/c proton has ½ the mass of deuteron.


P+

n

Fast Neutrons from Deuteron Bombardment of Be

• Stripping Process –• Proton is stripped from the deuteron.• Recoil neutron retains some of the incident kinetic energy

of the accelerated deuteron. • For each neutron produced, one atom of Be is converted

to B.

Be94 B10

5 n

+ γ


Fast Neutron Spectra from Deuteron Bombardment of Be

• Neutron spectra consists of a single peak, with a modal value of about 40% of the energy of the incident deuterons.

Fig 24.2a

Hall fig 24.2a


Fast Neutrons from Proton Bombardment of Be

• Knock-out Process • Protons impinge target of beryllium, where they knock-

out neutrons.• For each neutron “knocked-out”, one atom of Be is

converted to B.

Be94 nP+ B9

5

+ γ


Fast Neutron Spectra from Proton Bombardment of Be

• The neutron spectra spans a wide range of energies.• Necessary to filter (polyethylene) out the low energy

neutrons to achieve acceptable dd-distribution.

Fig 24.2b

Hall fig 24.2b Based on our

knowledge of neutron interactions why would polyethylene be a good choice for removing the low energy component from the neutron beam?


Isodose Distribution

• Neutron beam (produced from 50-MeV protons or deuterons) has comparable depth dose distribution/isodose to 6MV photon beam.

Bewley, Fig 4.3

Note: differences incearse for low isodose lines


Long Treatment Distances

• Neutron beam treatment distances are 100 to 140 cm due to large collimator• Collimator materials:

• Hydrogenous material to absorb neutrons• Pb or other high Z material to absorb γ-ray component


Clinical Experience with Fast Neutrons

• First experience at Lawrence Berkeley Laboratory• Hammersmith Hospital in London

3 Neutron Therapy Facilities in the US• Northern Illinois University Institute for Neutron

Therapy at Fermilab

• University of Washington Medical Center

• Gershenson Radiation Oncology Center at Harper University Hospital, Detroit


Modern Neutron Therapy Facilities

University of Washington Medical Center

• Cyclotron accelerates protons (50.5MeV)

• Rotating gantry

• MLC equipped

Gershenson Radiation Oncology Center

• Superconducting cyclotron accelerates deuterons• physical size is much

smaller than a room- temperature cyclotron would be.

• Rotating Gantry• MLC equipped


Fast Neutron Therapy

Considerations:• Who should be treated with neutrons?

• Subgroups of patients that may benefit from neutrons.• Slower growing tumors.

• Cancers w/ good response to neutron Therapy:• adenoidcystic carcinoma (cancer of parotid glands)• locally advanced prostate cancer • locally advanced head and neck tumors • inoperable sarcomas • cancer of the salivary glands

Generalizations about L-Q Model Early verses Late Responding Tissue

Early Responding Tissue• Dose response curve has

a marked initial slope that dose not bend until higher doses. • α/β is large ≈

10Gy

Late Responding TissueDose response curve bends at lower doses (appears more curvy)

α/β is small ≈ 2Gy Hall fig 22.6

Late Responding• Curvier• Bends at lower

doses• Lower α/β

Early Responding• Straighter at low doses dose then bends at high doses.

• Higher α/β


Neutrons for Radiation TherapyA few references……………• Fast neutron radiotherapy for locally advanced prostate cancer. Final report of

Radiation Therapy Oncology Group randomized clinical trial. (American Journal of Clinical Oncology. 1993 Apr; 16(2):164-7)

• Fast neutron irradiation of metastatic cervical adenopathy: The results of a randomized RTOG study. (International Journal of Radiation Oncology Biology Physics, Vol. 9, pp. 1267-1270)

• Neutron versus photon irradiation for unresectable salivary gland tumors: Final report of an RTOG-MRC randomized clinical trial. (International Journal of Radiation Oncology Biology Physics, Vol. 27, pp. 235-240)

• Fast neutron radiotherapy for soft tissue and cartilaginous sarcomas at high risk for local recurrence. (International Journal of Radiation Oncology Biology Physics, Vol. 50, No. 2, pp. 449–456)

• Photon versus fast neutron external beam radiotherapy in the treatment of locally advanced prostate cancer: results of a randomized prospective trial. (International Journal of Radiation Oncology Biology Physics, Vol. 28, pp. 47-54)


Boron-Neutron Capture Therapy• The idea:

• Preferentially deliver Boron containing drug to the tumor.

• Then deliver thermal (0.025eV) neutrons, which interact with the boron to produce alpha particles.

• Recall 10B has large thermal cross section: σ = 3837 barns

• the 10B absorbs the thermal energy neutron and ejects an energetic short-range alpha particle (1.47MeV) and lithium ion (0.84MeV) which deposit most of their energy within the cell containing the original 10B atom.


Why Boron???Several nuclides have high thermal neutron σ, but 10B is the best choice for several reasons:1. it is non-radioactive and readily available, comprising

approximately 20% of naturally occurring boron;2. Emitted particles (α

and 7Li) have high LET

Combined path lengths are approximately one cell diameter; i.e., about 12 microns, theoretically limiting the radiation effect to those tumor cells that have taken up a sufficient amount of 10B, and simultaneously sparing normal cells

3. Chemistry of boron is well understood and allows it to be readily incorporated into a multitude of different chemical structures.


Boron-Neutron Capture Therapy

• Beam Energy Selection• Limited penetration of thermal neutrons.

• Thermal neutrons rapidly attenuated by tissue.• HVL only about 1.5cm.• Not possible to treat depths greater than a few cm.

• Can use epithermal neutrons (1eV-10keV), which are theramlized by tissue (via collisions w/ H).

• Peak in dose occurs at 2 to 3cm;• Avoid high surface doses, but still poorly penetrating!


Figure taken from MIT BNCT site: http://web.mit.edu/nrl/www/bnct/info/description/description.html

Boron-10 Neutron Interaction

• An epithermal beam rapidly loses energy by elastic scattering in tissue thermal neutrons

• The thermal neutrons are captured by the 10B atoms which become 11B atoms in the excited state for a very short time (~ 10-12 s).

• The 11B atoms then splits into alpha particles, 7Li recoil nuclei and in 94% of the reactions, gamma rays.


BNCT Neutron Source at MIT/Harvard

• The MIT/Harvard group makes use of a fission converter based epithermal neutron beam at the MITR-II Research Reactor.• filtered by aluminum, Teflon, cadmium, and Lead. • provides a broad spectrum epithermal beam with low

incident gamma and fast neutron contamination while maintaining an incident neutron flux of ~5 x 109 neutroncm-2sec-1.

• permits irradiations for clinical trials to be conducted in 1 - 4 fractions in 10 minutes or less


Treatment Sites for BNCT

• Clinical Trials for:• Glioblastoma Multiform (GBM)

• Sweet and colleagues first demonstrated that certain boron compounds would concentrate in human brain tumor relative to normal brain tissue.1

• Melanoma

1(Sweet, W.H., Javid, M., "The possible Use of Neutron-capturing Isotopes such as boron-10 in the treatment of neoplasms," I. Intracranial Tumors, J. Neurosurg., 9:200-209, (1952) )


Production of Secondary Neutrons


Great Reference for Nuclear Data

T2.lanl.gov


Production of Neutrons

(γ,n) Reactions


Secondary Neutrons Radiation Therapy

• X-Ray Therapy• Neutrons can be produced via (γ-n) reactions

primarily with high atomic number materials within the treatment head.

• Proton Therapy• Neutrons can be produced via (p,n) reactions,

not limited to high Z materials.• At the high energies other reactions are also

possible……………..


Particle Production Cross Sections ENDF/B-VII Incident-Gamma Data

Note: Magnitude of the cross sections 0.1- 0.6 barns

(γ,n) cross section

High energy 18MV x-ray treatment beam has max energy of 18MeV and an average energy of 6MeV. Secondary neutron Production is possible in high Z components of linac head. No neutrons for 6MV x-ray beam all photons below threshold

Threshold energy for (γ,n)


(γ-n) Reaction Cross-Sections Elements in Tissue (C,O,N)

0.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Energy (MeV)

γ-n

Rea

ctio

n C

ross

Sec

tion

(bar

ns)

C-12

O-16

N-14

Note:

•Threshold energies are much higher compared to high Z

•The magnitude of the reaction x- sections are an order of magnitude lower than for high Z (0.005 – 0.02).

•These data are from the T-2 Nuclear Information Service.


Transport of Secondary Neutrons through the Linac Head

• The distribution of neutrons from (γ,n) reactions is approximately isotropic and resembles a fission spectrum.

• The neutron energy decreases as a consequence of their transport through the components of the treatment head (primary collimators, flattening filter, secondary jaws, MLC, etc).

• The primary mechanisms of energy loss are inelastic scattering and (n,2n) reactions.


Photoneutron Spectra Effect of Collimators and room shielding

• Photoneutron spectrum for 15MeV electrons striking W target (designated 15MeV W PN bare)• Spectrum with 10 cm of W

shielding surrounding W target.

• Spectrum with 10 cm of W shielding surrounding W target inside a concrete room

• A 252Cf fission spectrum shown for comparison

NCRP-79 Fig 25


Secondary Neutron Spectra Measured for Varian 18MV Linac

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

3.5E+04

4.0E+04

1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Energy (MeV)

Flue

nce

per u

nit L

ethe

rgy

per M

U

(ncm

-2u-1

MU

-1)

Emory Closed Jaws Closed MLC

MDA Closed Jaws Closed MLC


Production of Neutrons

(p,n) Reactions


Particle Production Cross Sections ENDF/B-VII Incident-Proton Data

Note: High Z material (e.g. Pb-207):

Magnitude of the (p,n) cross sections are higher than (γ,n) and continue to increase with increasing energy.The proton beam energies can be as high as 250MeV, well above the threshold.


Particle Production Cross Sections ENDF/B-VII Incident-Proton Data

Note low Z material (e.g. C-12): Magnitude of the (p,n) cross sections are much lower than in high Z materialsenergy thresholds for (p,n) in low Z are higher compared to high ZEnergy threshold similar to (γ,n)


Transport of Secondary Neutrons

• Strongly dependent on absorbing material and incident neutron energy.

• Example: 207Pb • The next 15 slides of the presentation are

provided as an example of the data that are available for a given isotope, given time constraints, these can not be covered in detail.


T2.lanl.gov• What Data are

provided in this file?

• Let’s consider an example:

• For 207Pb, the PDF file has 179 pages of data.

View PDF files for various elements/

isotopes


Principal Cross Sections Low Energy (Log-Log Plot)


Principal Cross Sections High Energy (Linear Plot)


Inelastic Cross Sections are provided on Separate Plots


Inelastic Cross Sections• What is (n,n*1), (n,n*2), etc.• There is a discrete energy band gap between

energy levels in the nucleus.• *1 refers to promoting a neutron into the first excited

state.• *2 refers to promoting a neutron into the second excited

state.• (n,x) – Anything above 20th excited level (not n,γ)

• How much energy are we talking?• http://www.nndc.bnl.gov/nudat2/


NuDat 2.4Select Levels and Gamma Search

http://www.nndc.bnl.gov/nudat2/


Enter Isotope of Interest

Search


Nuclear Level and Gamma Search

1st excited State2nd excited State3rd excited State


Threshold Reactions


Angular Distributions (provided for all elastic and inelastic Scattering)

• Angular Distribution of Elastic Scatter (0-30MeV)

• Angular Distribution of inelastic (n,n*1)Scatter (0-30MeV)


Shielding Considerations for Secondary Neutrons

forHigh Energy X-Ray Beams


Shielding for Photoneutrons

• High beams (>10MV) are contaminated with neutrons.• Produced by high energy x-rays and e-s incident

on various materials (target, flattening filter, collimators, etc.).

• Many more neutrons in x-ray beam than in e- beam.

• X-section for (e,n) reactions smaller than x-section for (γ,n) by factor of 10.

• In electron mode beam current is about 1000X less than in x-ray mode due to inefficiency of Brems. Production.


Shielding for Photoneutrons• Neutron contamination increases rapidly with

energy from 10 to 20 MV, then remains approx. constant above 20MV (recall that there are very few linacs with max energies greater than 25MeV).

• Neutron contamination at cax for 16-25MV x-ray beam is approx. 0.5% of x-ray dose, and falls off to about 0.1% outside the field.• Higher for IMRT more beam on time to

achieve same photon dose.


Particle Production Cross Sections ENDF/B-VII Incident-Gamma Data

Note: Magnitude of the cross sections 0.1- 0.6 barns

(γ,n) cross section

Neutron contamination increases rapidly with energy from 10 to 20 MV, then remains approx. constant above 20MV (recall that there are very few linacs with max energies greater than 25MeV).

Threshold energy for (γ,n)


Shielding for Photoneutrons• Concrete barriers designed for x-ray shielding are

sufficient for photoneutrons.

• Door must be protected against neutrons that diffuse into the maze and reach the door.• Required door shielding can be minimized with a good

maze.• Maze > 5m desirable.

• This length is chosen because the TVL for the photoneutrons entering the maze is approximately 5m (MKcGinley, pg 71)


Example of Door in High Energy Vault shielded for Neutrons

Note: Figure (5.5) is taken from Shielding Techniques 2nd ed. by Patton McGinley

Note: the average energy of the neutrons at the Maze entrance is approximately 100keV (NCRP, 1984)

Note: there are many ways to design a door, in some cases, the lead is placed before the polyethylene, and in some cases it is sandwiched between two layers of lead, this is just one example of a door design.


Door Design Photoneutron Shielding

• After multiple scattering interactions in the polyethylene (high H content) the neutrons are thermalized.• Thermal neutrons can undergo neutron capture releasing high

energy γ-rays (n,γ) γ-rays energies can exceed 8MeV, and have an average energy of 3.6MeV.

• How do we eliminate these high energy γ-rays? Add 5% Boron to the polyethylene.• Boron absorbs (high thermal absorption cross section) the low

energy neutrons before they have a chance to undergo (n,γ) reactions.

• But the reaction also results in a 0.48MeV γ.

• Lead is placed after the boronated polyethylene, where it attenuates the photons produced in the boron (0.48MeV) and any capture gamma rays generated in the maze by neutron capture in the concrete walls, ceiling, and

McGinley, 2002


Boron Interaction with Thermal Neutrons

• Materials with B are effective absorbers of thermal neutrons because of the high thermal neutron cross section• The thermal neutrons are captured by the 10B atoms which become

11B atoms in the excited state for a very short time (~ 10-12 s). • The 11B atoms then fissions producing α-particles, 7Li recoil nuclei,

and in 94% of the reactions, gamma rays (0.48MeV).


Door Design for Neutron Shielding Details

1. Boronated polyethylene:The polyethylene (high H content) slows (moderates) the fast and intermediate energy neutrons to thermal energies.The 5% Boron absorbs the low energy neutrons (high cross section for thermal neutron absorption).

2. Lead absorbs the 0.48MeV photon that results from the (n,α) and capture gammas ( from maze ceiling, and floor).

Polyethylene 5% Boron

Steel Casing

Lead

Maz

e


Activation of Materials in Linac components

Reaction Mode of Decay T1/2

Photon E (MeV)

27Al(n,γ)28Al β− 2.3 min 1.78063Cu(n,γ)62Cu β+ 9.7 min 0.51155Mn(n,γ)56Mn β− 2.6 hr 0.84763Cu(n,γ)64Cu β+/β− 12.7 hr 1.34665Cu(n,γ)64Cu β+/β− 12.7 hr 1.346186W(n,γ)187W β− 23.9 hr 0.479/0.68658Ni(n,γ)57Ni β+ 36.0 hr 1.378/1.920

Reproduced from Table 4.4, McGinley


Activation Material in Air• Air is made radioactive by medical accelerators

operated above 10MeV primarily by:

• Each reaction produces a positron emitter with a relatively short half-life.• Patients/personnel can be exposed to 0.511 MeV

annihilation photons.

ReactionHalf-life

(sec)Threshold Energy

(MeV)14N(γ,n)13N 600 10.516O(γ,n)15N 122 15.7


Activation Material in Air• Maximum permissible concentration in air (MPCa )

based on a 40-hr work week and typical treatment vault (air volume).

Isotope Organ MPCa (Bqm-3)

DI (nSvs-1)

13NSkin 1.5x106 41.7

Whole Body 8.5x106 6.95

15OSkin 7.4x105 41.7

Whole Body 8.5x106 6.95Reproduced from Table 7-5, McGinley


Activation Material in Air• McGinley at al (1984) calculated annual total

dose equivalent to radiation therapists skin• Conservative Calculation Assumptions:

• 40 patients per day• 5 days per week• 4Gy/fx• Daily treatment time = 120-s• Therapist stay time of 600s per patient

• Far below the Maximum Permissible Skin dose (0.5Sv).

• Air activation presents minimal hazard.


Neutron Dose

Two main Categories of “Neutron Dosimetry”

• Clinical Neutron Beam Dosimetry• Dose from neutron beams used for patient

treatment.• Protection Dosimetry for unwanted neutron

dose (low neutron doses)


Clinical Neutron Dosimetry

• Dose Calculations based on Bragg-Gray• AAPM Report 7 – Protocol for Neutron Beam

Dosimetry• ICRU Report 26 – Clinical Neutron Beam

Dosimetry


Neutron and γ-ray Dose Determined Separately

• Neutron fields are always accompanied by gamma rays contamination• Source: interactions with the target, the primary

shielding, collimating system, the biological object or phantom being irradiated, and from the surroundings.

• Photon component increases markedly with increasing field size and depth in phantom/patient.

• AAPM report 7 recommends that neutron and γ- ray components of Absorbed dose are determined separately.


Neutron and γ-ray Dose Determined Separately

• Two instruments, with different relative neutron sensitivities, are used for the evaluation of the component radiations.

1. Chamber with approximately equal neutron and photon sensitivity

• TE ionization chambers with TE gas2. Second instrument is relatively insensitive to

neutrons (measure photon component). • Mg-Ar chamber


TE Ion Chamber


Dose Specification• AAPM report 7 recommends specification of

absorbed dose for clinical applications in terms of the TOTAL DOSE.

• Why?• Uncertainties

• Uncertainty in Neutron Calibration ~ 5-8.5%• Uncertainty in Gamma Calibration ~ 2.5%

• Small photon component compared to neutron component

• Total dose (neutron plus gamma) specified with the relative contribution of the photon dose component, expressed as a percentage of the total dose, DT(percent DG) e.g. 10Gy(2%G).


Protection Quantities for Neutrons


Quantities used in Radiation Protection

Quantities used in Radiological Protection• There are two types of quantities used in

radiological protection:1. Protection Quantities - defined by the

International Commission on Radiation Protection (ICRP).

2. Operational Quantities - defined International Commission on Radiation Units and Measurements (ICRU).


ICRP Protection Quantities

• The (ICRP) defines limiting or protection quantities as dosimetric quantities specified in the human body.

• Recommended dose limits are expressed in terms of protection quantities.

• These quantities are not directly measurable but may be related by calculation to the radiation field in which the exposure occurs.


ICRU Operational Quantities• Operational quantities were designed by the ICRU

in response to ICRP recommendations on radiological protection.

• Used to demonstrate compliance with dose limits.

• Operational quantities provide a reasonable estimate of the protection quantities and serve as calibration quantities for dosimeters used in monitoring.


Physical QuantitiesFluence, Kerma, Absorbed

Dose

Operational Quantities•Ambient Dose Equivalent•Personal Dose Equivalent

Protection Quantities•Equivalent Dose•Effective Dose

Measurements and Conversion Coefficients Calculations and Conversion

Coefficients

Calibration

Instrument Response

Conservative Approximation


Protection Quantities


ICRP Protection Quantities• Absorbed Dose, DT , is the

mean absorbed dose in a specified tissue or organ of the human body, T,

• Equivalent Dose, HT , is the absorbed dose averaged over the tissue or organ, T, irradiated in a radiation field consisting of several different radiations with different values of WR ,

• Effective Dose, E, is the sum of the weighted equivalent doses in all the tissues and organs of the body,

• where, mT is the tissue or organ mass, DT is the absorbed dose in the mass element dm.

• where, DT,R is the average absorbed dose from radiation, R, in tissue T.

• where, HT is the equivalent dose in the tissue or organ T and WT is the weighting factor for the tissue.

∑ ⋅= TT HWE

∑= RTRT DwH ,

∫=TmT

T Ddmm

D 1


ICRP Protection QuantitiesICRP-60 Tissue Weighting Factors

Tissue or Organ Tissue Weighting Factor, WT

Gonads 0.2Bone marrow (red) 0.12

Colon 0.12Lung 0.12

Stomach 0.12Bladder 0.05Breast 0.05Liver 0.05

Esophagus 0.05Thyroid 0.05

Skin 0.01Bone Surface 0.01

Remainder 0.05

Note: In the case in which a single one of the remainder organs receives an equivalent dose in excess of the highest dose in any of the 12 organs for which a weighting factor is specified:

• a weighting factor of 0.025 should be applied to that tissue and

• a weighting factor of 0.025 applied to the average dose in the rest of the remainder organs.


Radiation Weighting Factors


Operational Quantities


ICRU Operational Quantities Dose Equivalent

• The Dose Equivalent, H as defined by the ICRU is the product of Q and D at a point in tissue:

• where D is the absorbed dose• Q is the quality factor at this point

• The SI unit for H is the Sievert (Sv).

QDH =


ICRU Operational Quantities Dose Equivalent

• The quality factor depends on the unrestricted linear energy transfer, L, for charged particles in water, specified in ICRP publication 60.

• For photons and electrons the quality factor is unity. For neutrons, the quality factor is strongly energy dependent (ICRU Report 66).

( )∫−= dLDLQDQ L1


Determining Dose Equivalent• Dose equivalent is essentially unmeasurable.

• But, as shown in the previous diagram, it can be determined by calculation or by a combination of calculations and measurements.

• Quantities needed to determine dose equivalent are: • absorbed dose and the quality factor or• fluence and fluence-to-dose equivalent conversion

coefficients.


References• Eric J. Hall. Radiobiology for the Radiologist 5th Ed. (2000)• Frank H. Attix. Introduction to Radiological Physics and Radiation Dosimetry.

(1986)• Patton H. McGinley. Shielding Techniques for Radiation Oncology Facilities 2nd

ed.• D.K. Bewley. The Physics and Radiobiology of Fast Neutron Beams (1989)• AAPM Report 7 Protocol for Neutron Beam Dosimetry• ICRU 45 Clinical Neutron Dosimetry• NCRP 79 Neutron Contamination from Medical Electron Accelerators• NCRP 151 Structural Shielding Design and Evaluation for Megavoltage X- and

Gamma-Ray Radiotherapy Facilities (2005)• ICRP74/ICRU57 (Jointly published by both ICRU and ICRP) Conversion

Coefficients for use in Radiological Protection against External Radiation• ICRP 60 Recommendations of the International Commission on Radiological

Protection• ICRU 66 Determination of Operational Dose Equivalent Quantities for Neutrons• http://web.mit.edu/nrl/www/bnct/info/description/description.html• T2.lanl.gov• http://www.nndc.bnl.gov/nudat2

http://web.mit.edu/nrl/www/bnct/info/description/description.html

Neutron Interactions Part II - uthgsbsmedphys.org Neutron Lecture 02 200… · Neutron Interactions...

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