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Neutron sources

ByMahmopud samahin

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NEUTRON SOURCES

Neutron emission  Excited energy > B.E(n)

Nuclear reactor Spontaneous fissionA. Spontaneous fission

• Transuranic heavy nuclide

• Thick container Fast neutron ; gamma ray.

• Most spontaneous fission by Californium-252

• Alpha emission rate is about 32 times spontaneous fission.

• Neutron yield=0.116n/s per Bq(compined ) ( 2.23 Mn/s per microgram ;unit

mass basis)

Much more limited

possible choices

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• sources involve very small active materialMade in very small size

• 3.8 average neotron + 9.7 average gamma photons/fission

•

>85% prompt gamma ray in first nanosecond

1.3 MeV

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B. Radioisotope(α,n) source:

*Alpha decay (from convenient nuclides)Self-contained

neutron source

Be9

Max neutron yield

Q -value=5.71Mev

1/10000

react with

beryllium -9

*Inimate mixture of alpha particle

emitter and berylium

*Homogeneously

*Small relative

concetration

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Alpha emitter Actinide elements (89-103) Stable

alloyMBe13 

Without any

intermediateenergy loss

Ra226

Ac227

and

*long chain of daughter products

*contribute a large alpha-ray

background

Ra-Be

Ac-Be

More elaborate handling

procedures because biological

hazard of alpha –radiation.

The remaining

radioisotopes

Simpler

alpha decays

Gamma-

background is

much lower

•availabilaty

•Cost

•Half-life

Physical size of sources : no longer negligible ( but hlaf  –life short as possible )

Specific activity of emitter is high

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Ra /Be226

The most widley used•About 16 g of material1 Ci

•Few cm’s in dimension10^7n/s

To increase the neutron yield without

increasing the physical size ,alpha emitter withhigher specific activites must be subistituted

Sourcesincorporating

Am+241

Pn238

•Widley used

•High neutron yield

Cm244 •

Represent near idealcompromise between

activity and source life-time

•Not always widely available

•Peaks andvalleys

Carbon-12

excaitedsates

•Washes out of continuousenergy distribution

Small sourcespectrum same (α,n)

reactionLarger sources secondery prosses

(scattering,(n,2n) reactions in (Be) ,(n, fission)

plutonium ,actinide

(introduce some dependence on source size)

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Because large activity of 

actinideSafely

materials

Tow stanless

cylenders

( expantion space

helium gas)

Small

amounts of 

contaminant

Alpha alpha

activity

Origonalradioisotopes

Decay of precursor

(other plotunium)

Am + β 241

Pu241

Alpha- decay

Significant

(βhalf-life=13.2 y) 

Neutron yield

increase with

time

Growth

rate 2% /y

Q-value 

Small lower n-yield

Li(α,n) usefull

Q=-2.79 

7

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c. Photoneutron sources

Absorpation of gamma

Free neutron

emissiom

Only two target nuclie(practical significent)

Neutron energy

Monoenergetic

gammaMonoenergetic

neutrons

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D. Reaction from accelerated

charged particles