PHOTONUCLEAR REACTION ON MOLYBDENUM ISOTOPES

2015 KPS fall Meeting 2015. 10. 22.

Han Dong Yoon

Faculty of Physics MSU Skobeltsyn Institute of Nuclear Physics

B.S. Ishkhanov, I.M. Kapitonov, A.A. Kuznetsov, V.N. Orlin, Han Dong Yoon, 2014, published in Yadernaya Fizika, 2014, Vol. 77, No. 11, pp. 1427–1435DOI : 10.1134/S106377881410007X

2

Outline

• Introduction

• Description of experiments

• Experimental calculation

• Theoretical Calculation

• Results

• Analysis

• Summary

3

Introduction

0

Nuclear Resonance Fluorescence ≈ 10 МэВ

Bn,p 10MeV

GDRσ

Eγ100MeV

Schematic cross-section of photonuclear reaction

γ GDR

92Mo

2n10-19с

γ

10-9 - 10-17s

10-9 - 10-17s

90Mo

90Nb

ε /β+

T1/2 = 5.56 h

p n

Diagram example of GDR flow : reaction 92Mo(γ,2n)90Moγ

γ

4

Description of experiment

e-

Electron accelerator

Converter

Target of study

Irradiated target

HPGe Detector

Bremsstrahlung photons

Transportto detector

• Electron accelerator RTM-70 pulsed racetrack microtron

• Bremsstrahlung converter tungsten with 2.5mm thick

• Target of study : natural mixture of molybdenum 100Mo(9.82%), 98Mo(24.39%), 97Mo(9.60%), 96Mo(16.67%), 95Mo(15.84% ), 94Mo(9.15%), 92Mo(14.53%).

• Detector : Canberra GC3019 HPGe - efficiency : 30% - energy resolution : 0.9 keV at 122 keV , 1.9 keV at 1.33 MeV

Endpoint of Bremsstrahlung photons 67.7 MeV 29.1 MeV 19.5 MeV

Duration of irradiation 4h 25m 1h 03m 1h

Duration of measurement 138h 39m 196h 39m 18h 34m

Parameters of 3 experiments

5

Theoretical Calculation

Isotope yield of photonuclear reaction on the natural mixture of Mo

𝑌 (𝐸𝑚)=𝑛∫𝐸 h𝑡 𝑟

𝐸𝑚

𝜎 (𝐸 )𝑊 (𝐸 ,𝐸𝑚)𝑑𝐸n - number of irradiated nuclei of the isotope under study;σ(E) - reaction cross section, which depends on the energy E;Ethr - reaction threshold; Em – endpoint of photon energy;W(E,Em) - bremsstrahlung photon spectrum, its endpoint is E m;

*in this calculation reconstructed by GEANT4;

Calculated cross-sections on the basis of combined photonucleon-reaction model

6

Results – 67.7MeV

Reaction Final-state nucleus (JP)

T1/2 (decay type of final-state

nucleus)

Threshold(MeV)

67.7MeV

Experimental yield (error)

Theoreticalyield

100Mo(γ,n) 99Mo (1/2+) 67h (β-) 8.29 100 (6) 100

100Mo(γ,pn) 98mNb (5+) 51min (β-) 18.10 0.31 (0.03)98Mo(γ,p) 97Nb (9/2+) 72min (β-) 9.79 6.6 (0.1) 7.897Mo(γ,p)

98Mo(γ,pn)96Nb (6+) 2.4h (β-) 9.23

17.87 11 (1) 7.72.4 10.1

96Mo(γ,p)97Mo(γ,pn)

95Nb (9/2+) 35d (β-) 9.316.72 5.1 (0.4)

10.6 (0.5)

10.0 (γ,p)

15.096Mo(γ,p)

97Mo(γ,pn)95mNb (1/2-) 3.6d (IT + β-) 9.53

16.95 5.5 (0.3) 5.0 (γ,pn)

94Mo(γ,pn)94Mo(γ,pn)

92Nb (7+)92Nb (2+)

3.5 x 107yr (ε)10.2d (ε)

17.3217.45 2.60 (0.02) 3.0

92Mo(γ,n) 91Mo (9/2+) 15.5min (ε) 12.68 34 (5) 65.092Mo(γ,2n) 90Mo (0+) 5.6h (ε) 22.78 5.1 (0.4) 2.792Mo(γ,pn) 90Nb (8+) 14.6h (ε) 19.51 14 (5) 3.5

92Mo(γ,p2n)92Mo(γ,3n)→89Nb

89Nb (9/2+) 2.0h (ε) 29.59 1.9 (0.2)0.9

92Mo(γ,p2n)92Mo(γ,3n)→89mNb

89mNb (1/2+-) 66min (ε) 29.62 1.8 (0.3)

92Mo(γ,4n) 88Mo (0+) 8min (ε) 46.39 0.04 (0.01) 0.005

7

Results – 29.1 and 19.5MeV

Reaction Final-state nucleus (JP)

T1/2 (decay type of

final-state nucleus)

Eth

(MeV)

29.1MeV 19.5MeV

ExperimentalYield* (error)

TheoreticalYield*

Experimentalyield* (error)

TheoreticalYield*

100Mo(γ,n) 99Mo (1/2+) 67h (β-) 8.29 100 (6) 100 100 (5) 100

98Mo(γ,p) 97Nb (9/2+) 72min (β-) 9.79 2.8 (0.1) 4.9 0.33 (0.05) 0.60

97Mo(γ,p)98Mo(γ,pn)

96Nb (6+) 2.4h (β-) 9.2317.87 4.0 (0.3) 5.2

0.7 5.9 0.65 (0.06) 1.1

96Mo(γ,p)97Mo(γ,pn)

95Nb (9/2+) 35d (β-) 9.316.72

4.2 (0.1)

6.8(γ,p)

9.1 0.69 (0.03) 1.196Mo(γ,p)

97Mo(γ,pn)95mNb (1/2-) 3.6d (IT + β-) 9.53

16.952.3

(γ,pn)

92Mo(γ,n) 91Mo (9/2+) 15.5min (ε) 12.68 49.0 (4.0) 65

92Mo(γ,2n) 90Mo (0+) 5.6h (ε) 22.78 0.52(0.03) 0.43

92Mo(γ,pn) 90Nb (8+) 14.6h (ε) 19.51 0.76 (0.35) 0.63

*Both experimental and theoretical yield were normalized to the yield of reaction 100Mo(γ,n)99Mo, which was set to 100

8

Analysis of the results

N=501g9/2

2p1/2

1g7/2

2d5/2

2d3/2

3s1/2

1h11/2

N=82

1f5/2

2p3/2

1f7/2

1g9/2

2p1/2

1f5/2

2p3/2

1f7/2

2d5/2

1g7/2

2d3/2

3s1/2

1h11/2

92Mo

93Mo

Shell diagram of molybdenum isotopes Nucleon separation Energy

• As mass number A decreases, Bn increases → En decreases → probability of penetration decreases → Yn decreases → Yn decreases

• Large difference of Bn between 93Mo and 92Mo → Discrepancy between experimental and theoretical calculation of the yield

82 86 90 94 98 102 106 110 114 1180

2

4

6

8

10

12

14

16

18

Bn

Bp

40 44 48 52 56 60 64 68 72 76 n p

9

Summary• Photonuclear reaction experiments were conducted

with Bremsstrahlung photon with three different endpoints: 19.5, 29.1 and 67.7 MeV.

• The theoretical calculations were performed on the basis of combined photonucleon-reaction model.

• The comparison of two result shows that the theoretical model satisfactory describes the yield of photonuclear reaction.

• Steep decrease of Bn for 92Mo results in discrepancy between experimental and theoretical calculations.

• This effect can be interpreted on the basis of the shell structure of molybdenum isotopes.

10

Thank you for attention!