neotron sources

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Neutron sources

ByMahmopud samahin



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 (2.65 y)

• Alpha emission rate is about 32 times spontaneous fission.

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

mass basis)



• Very small size

• 3.8 average neotron /fission

• 9.7 average gamma photons 1.3 MeV

•>85% prompt gamma ray in first nanosecond



B. Radioisotope(α,n) source:

*Alpha decay (from convenient nuclides) Self-containedneutron source

Be

9 Q -value=5.71Mev

Max neutron yield

Using thick target :

Most alpha particles

are stopped

1/10000react with

beryllium*Inimate mixture of

alpha particle

emitter and berylium*Homogeneously

*Small relative

concetration



Alpha emitter Actinide elements (89-103) Stable

alloyMBe13

Without any

intermediateenergy loss

Ra226

Ac227

and

*long chain of daughter products

*contribute alarge alpha-ray

background

Ra-Be

Ac-Be

More elaborate handling

procedures because biological

hazard of alpha –radiation.

The remaining

radioisotopes

Alpha-

backgroun

d 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



Ra /Be226

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 ,alphaemitter with higher specific activites

must be subistituted

Sources

incorporating

Am+241

Pn238 •Widley used

•High neutron yield

Cm244 •Represent near

ideal compromise

between activity andsource life-time

•Not always widely

available

Small variations

depend on alpha

energies

Small sourcespectrum same (α,n)

reaction

Larger sources secondery prosses

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

plotounium ,actinidde

(introduce some dependence on source size)



Because large activity of

actinideSafely

materials

Tow stanless

cylenders

( expantion space

helium gas)

Alpha

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



c. Photoneutron sources

Absorpation of gamma

Free neutron

emissiom

Only two target nuclie(practical significent)

Neutron energy



D. Reaction from accelerated

charged particles

neotron sources

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